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ADDITION OF ALKALINE MATERIALS TO BIOTRICKLING FILTER
OR BIO-FILTER MAKE-UP WATER
10
20
BACKGROUND
1. Field of Invention
Aspects and embodiments disclosed herein are directed to treatment of air
streams, and more particularly, to systems and methods for removing odor
causing
compounds from air streams.
Date Recue/Date Received 2022-03-02
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2. Discussion of Related Art
Sewage systems typically include conduits that collect and direct sewage and
other waste streams, such as industrial effluents, to a treatment facility.
Such systems
typically include various pumping facilities, such as lift stations, that
facilitate the
transfer of wastewater to such treatment facilities. During transit odorous
species are
often generated. Such odorous species may be objectionable when released or
discharged. Untreated sewage may generate multiple odor-causing compounds. One
of the most prevalent and most distinctive compounds formed is hydrogen
sulfide
to (HS). Other objectionable or odor-causing compounds from contaminated
air
streams may include compounds resulting from the volatilization of reduced
sulfur
compounds in a sewage or wastewater stream such as any one or more of carbon
disulfide, dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, methyl
mercaptans,
ethyl mercaptans, butyl mercaptans, allyl mercaptans, propyl mercaptans,
crotyl
.. mercaptans, benzyl mercaptans, thiophenol, sulfur dioxide, and carbon
oxysulfide.
SUMMARY
In accordance with an aspect of the present invention, there is provided a
biotrickling filter for the treatment of contaminated air. The biotrickling
filter
comprises a vessel, a contaminated air inlet in fluid communication with an
internal
volume of the vessel, a treated air outlet in fluid communication with the
internal
volume the vessel, a media bed disposed within the vessel and in fluid
communication
between the contaminated air inlet and the treated air outlet, and
biofiltering media
disposed in the media bed. The biofiltering media is configured to support
growth and
maintenance of a population of hydrogen sulfide oxidizing bacteria on the
biofiltering
media. A water introduction system is configured to introduce water from a
source of
water into the vessel, and an alkaline material introduction system is
configured to
introduce an alkaline material from a source of alkaline material into the
vessel.
In some embodiments, the biotrickling filter further comprises a manually
operated flow valve configured to regulate a rate of introduction of the water
and/or
alkaline material into the vessel.
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In some embodiments, the biotrickling filter further comprises an electronic
control system configured to automatically regulate a rate of introduction of
the water
and/or alkaline material into vessel. The biotrickling filter may further
comprise a pH
probe positioned downstream of the media bed and configured to measure a pH of
liquid having passed through the media bed and to provide an indication of the
pH to
the electronic control system. The biotrickling filter may further comprise a
sump.
The pH probe may be disposed in the sump.
In some embodiments, the electronic control system is configured to regulate
the rate of introduction of the alkaline material into the vessel responsive
to the
to indication of the pH. The electronic control system may be configured to
maintain the
pH between about 0 and about 4. The electronic control system may be
configured to
maintain the pH between about 1.6 and about 2.2.
In some embodiments, the alkaline material introduction system is configured
to introduce the alkaline material into the vessel with the water from the
source of
water.
In some embodiments, the vessel comprises a sump and the source of water is
the sump. The alkaline material introduction system may be configured to
introduce
the alkaline material into the sump.
In some embodiments, the source of water is a source of make-up water
external to the vessel.
In some embodiments, the alkaline material includes one or more of
magnesium hydroxide, potassium hydroxide, calcium hydroxide, sodium hydroxide,
potassium carbonate, and sodium carbonate.
In accordance with another aspect, there is provided a method of removing an
undesirable compound from contaminated air. The method comprises flowing the
contaminated air through a biotrickling filter including a media bed and a
population
of hydrogen sulfide oxidizing bacteria disposed on media in the media bed,
introducing water from a source of water into the biotrickling filter,
measuring one of
a pH of water within the biotrickling filter and a pH of water exiting the
biotrickling
filter, and maintaining the pH of the one of the water within the biotrickling
filter and
the water exiting the biotrickling filter within a predetermined range by
adding an
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alkaline material to the biotrickling filter and controlling an amount of the
alkaline
material added to the biotrickling filter per unit time.
In some embodiments, the method further comprises adjusting an amount of
water introduced to the biotrickling filter per unit of time.
In some embodiments, the method further comprises introducing the alkaline
material into the biotrickling filter at a fixed rate and adjusting an amount
of water
introduced to the biotrickling filter per unit of time.
In some embodiments, the method further comprises introducing the water
into the biotrickling filter at a fixed rate and adjusting an amount of the
alkaline
material introduced to the biotrickling filter per unit of time.
In some embodiments, the method further comprises controlling one of an
amount of water introduced to the biotrickling filter per unit of time and the
amount
of the alkaline material added to the biotrickling filter per unit time with a
manually
operated flow controller.
In some embodiments, the method further comprises controlling one of the
amount of water introduced to the biotrickling filter per unit of time and the
amount
of the alkali material added to the biotrickling filter per unit time with an
electronic
controller.
In some embodiments, the method further comprises controlling one of an
amount of water introduced to the biotrickling filter per unit of time and the
amount
of the alkali material added to the biotrickling filter per unit time with a
fuzzy logic-
based controller.
In some embodiments, the method further comprises measuring a p11 of water
having passed through the media bed, providing an indication of the pH to the
fuzzy
logic-based controller, and utilizing the pH as an input parameter in an
algorithm used
by the fuzzy logic-based controller to automatically control the one of the
amount of
water introduced to the biotrickling filter per unit of time and the amount of
the alkali
material added to the biotrickling filter per unit of time.
In some embodiments, the method further comprises selecting the
predetermined range to maintain the pH in the media bed within a range
conducive to
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maintenance of the population of hydrogen sulfide oxidizing bacteria in the
media
bed.
In accordance with another aspect, there is provided a method of reducing
water consumption of a biotrickling filter. The method comprises adding a pH
adjustment system to the biotrickling filter. The plI adjustment system is
configured
to introduce an alkaline material from a source of alkaline material into the
biotrickling filter, measure a pH of a liquid in the biotrickling filter, and
control a rate
of introduction of the alkaline material and a rate of introduction of water
into the
biotrickling filter to be sufficient to maintain the pH of the liquid within a
range
conducive to maintain a population of hydrogen sulfide oxidizing bacteria in a
media
bed of the biotrickling filter and to prevent clogging of the media bed.
In some embodiments, the method comprises controlling the rate of
introduction of the alkaline material and the rate of introduction of the
water with a
fuzzy logic controller utilizing the pH as an input parameter of a fuzzy logic
control
algorithm.
In some embodiments, reducing the water consumption of the hiotrickling
filter includes reducing the water consumption of the biotrickling filter by
at least
about 50%. Reducing the water consumption of biotrickling filter may include
reducing the water consumption of the biotrickling filter by at least about
99%.
In accordance with another aspect, there is provided a wastewater treatment
system. The wastewater treatment system comprises a basin including a
wastewater
inlet fluidly connected to a source of wastewater, a process gas outlet
configured to
output sulfur-containing process gas generated by the wastewater from the
basin, a
source of alkaline material, and a biotrickling filter. The biotrickling
filter comprises
a vessel, a contaminated air inlet providing fluid communication between an
internal
volume of the vessel and the process gas outlet, a treated air outlet in fluid
communication with the internal volume the vessel, a media bed disposed within
the
vessel and in fluid communication between the contaminated air inlet and the
treated
air outlet, and biofiltering media disposed in the media bed. The biofiltering
media is
configured to support growth and maintenance of a population of hydrogen
sulfide
oxidizing bacteria on the biofiltering media. A water introduction system is
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configured to introduce water from a source of water into the vessel, and an
alkaline
material introduction system is configured to introduce an alkaline material
from the
source of alkaline material into the vessel.
In some embodiments, the system further comprises a sensor configured to
measure a pH of a liquid within the vessel and to provide an indication of the
pH to a
controller configured to regulate a rate of introduction of the water and a
rate of
introduction of the alkaline material into the vessel.
In some embodiments, the controller is configured to regulate the rate of
introduction of the water and the rate of introduction of the alkaline
material into the
to vessel based on an output of a fuzzy logic algorithm utilizing the
indication of the pH
as an input parameter.
There is provided a method of removing hydrogen sulfide from contaminated
air, the method comprising: flowing the contaminated air through a
biotrickling filter
including a media bed and a population of hydrogen sulfide oxidizing bacteria
disposed on media in the media bed, the population of bacteria oxidizing
hydrogen
sulfide in the contaminated air into sulfuric acid; introducing water from a
source of
water into the biotrickling filter; measuring a pH of water having passed
through the
media bed; maintaining the pH of the water having passed through the media bed
within a predetermined range below 4 by: adding an alkaline material to the
biotrickling filter; and controlling an amount of one of the alkaline material
added to
the biotrickling filter per unit time and an amount of the water added to the
biotrickling filter per unit time utilizing a fuzzy logic algorithm performed
on a fuzzy
logic-based controller, the fuzzy logic algorithm using a difference between
the pH of
the water having passed through the media bed and a predetermined pH setpoint
which is an error value and a change in pH of the water having passed through
the
media bed per unit time which is an error-dot value as sole input parameters,
the fuzzy
logic algorithm having a total of five rules and a total of five fuzzy output
sets to
determine an output used to control the amount of the one of the alkaline
material
added to the biotrickling filter per unit time and the amount of the water
added to the
biotrickling filter per unit time; and providing sufficient water from the
source of
water to the media bed to rinse salts produced by reaction between the
alkaline
material and the sulfuric acid from the media bed to prevent clogging of the
media
bed.
Date Regue/Date Received 2022-08-31
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BRIEF DESCRIPTION OF DRAWINGS
The accompanying drawings are not intended to be drawn to scale. In the
drawings, each identical or nearly identical component that is illustrated in
various
figures is represented by a like numeral. For purposes of clarity, not every
component
may be labeled in every drawing. In the drawings:
FIG. 1 is a schematic diagram of a system generating an objectionable gaseous
species and a biofilter coupled to the system to remove the objectionable
gaseous
species from air from the system;
FIG. 2A is a schematic diagram of a biofilter for treating a contaminated air
to stream;
FIG. 2B is a schematic diagram of another biofilter for treating a
contaminated
air stream;
FIG. 3 is a block diagram of a computer system upon which embodiments of a
method for treating a contaminated air stream may be performed;
FIG. 4 is a block diagram of a memory system of the computer system of FIG.
3;
FIG. 5 is a chart relating error with a degree of membership in one or more
fuzzy input sets;
Date Recue/Date Received 2022-03-02
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FIG. 6 is a chart relating error-dot with a degree of membership in one or
more
fuzzy input sets;
FIG. 7 is a surface map of the output control value for all combinations of
error and error-dot for an embodiment of a biofilter as disclosed herein;
FIG. 8 is chart of data obtained during testing of an embodiment of a
biofilter
as disclosed herein;
FIG. 9 is another chart of data obtained during testing of an embodiment of a
biotilter as disclosed herein; and
FIG, 10 is another chart of data obtained during testing of an embodiment of a
biofilter as disclosed herein.
DETAILED DESCRIPTION
Aspects and embodiments disclosed herein are not limited to the details of
construction and the arrangement of components set forth in the following
description
or illustrated in the drawings. Aspects and embodiments disclosed herein are
capable
of being practiced or of being carried out in various ways. Also, the
phraseology and
terminology used herein is for the purpose of description and should not be
regarded
as limiting. The use of "including," "comprising." -having," "containing,"
"involving," and variations thereof herein is meant to encompass the items
listed
thereafter and equivalents thereof as well as additional items.
In wastewater treatment systems, various undesirable chemical species may be
generated, as discussed in the background section. Hydrogen sulfide (H2S) is
an
example of such a species. Hydrogen sulfide is generated in some wastewater
treatment systems and is considered an undesirable byproduct. Even small
concentrations of I I2S can negatively impact the air quality in the vicinity
of a
wastewater treatment plant or other components of a wastewater treatment
system.
It is generally desirable to remove hydrogen sulfide from air streams from
sewage systems, manhole headspaces, wastewater treatment systems, and/or other
systems in which hydrogen sulfide may be generated. Aspects and embodiments
disclosed herein include systems and methods for removing hydrogen sulfide
from
contaminated air streams. Aspects and embodiments disclosed herein may also be
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utilized to remove other objectionable ancUor odor causing compounds from
contaminated air streams, for example, compounds resulting from the
volatilization of
reduced sulfur compounds in a sewage or wastewater stream such as any one or
more
of carbon disulfide, dimethyl sulfide, dimethyl disulfide, dimethyl
trisulfide, methyl
mercaptans, ethyl mercaptans, butyl mercaptans, ally' mercaptans, propyl
mercaptans,
crotyl mercaptans, benzyl mercaptans, thiophenol, sulfur dioxide, and carbon
oxysulfide, or hydrogen sulfide generated from any of these compounds by
sulfate
reducing bacteria. For the sake of simplicity, however, aspects and
embodiments
disclosed herein will be described as removing hydrogen sulfide from
contaminated
gas streams.
As illustrated schematically in FIG. 1, a system 10, for example, a wastewater
treatment system or a sewer system has an inlet 5 in fluid communication with
a
source 50 of, liquid, for example, wastewater. The system 10 includes a space
15, for
example, a conduit, a lift station, a wastewater treatment basin, etc., that
includes
liquid 25, for example, wastewater, that generates one or more objectionable
gaseous
species, for example, hydrogen sulfide or any one or more of the other
compounds
discussed above. A biofilter, or in some embodiments, a biotrickling filter
100 may
be provided to remove one or more of the objectionable gaseous species from
air in or
exiting the space 15. As used herein, the term "biofilter encompasses
"biotrickling
filters." A contaminated air inlet 195 in fluid communication with an internal
volume
of the biofilter 100 vessel may be coupled to a headspace of the space 15 by a
conduit
20 providing fluid communication between a process gas outlet 30 of the space
15 and
the contaminated air inlet 195. In other embodiments, the biofilter 100 may be
disposed within the space 15. The biofilter 100 draws contaminated air from
the
headspace of the space 15 into the contaminated air inlet 195, treats the
contaminated
air to remove the one or more of the objectionable gaseous species, for
example, by
oxidation by sulfur compound oxidizing bacteria, and releases the resultant
treated air
though a treated air outlet 150 in fluid communication with the internal
volume of the
biofilter 100 vessel into the environment 145 and/or back into the space 15.
In some
embodiments, the system 10 further includes a source 165 of an alkali material
configured to provide alkaline material to the biofilter 100 vessel.
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As discussed with reference to FIG. 2A, the biofilter 100 may include a water
introduction system configured to introduce water from a source of water into
the
biofilter vessel and an alkaline material introduction system configured to
introduce
an alkaline material from the source of alkaline material into the vessel. As
further
discussed with reference to FIG. 2A, the biofilter 100 may include a sensor
configured
to measure a pH of a liquid within the vessel and to provide an indication of
the pll to
a controller configured to regulate a rate of introduction of the water and a
rate of
introduction of the alkaline material into the vessel. The controller may be
configured
to regulate the rate of introduction of the water and the rate of introduction
of the
.. alkaline material into the vessel based on an output of a fuzzy logic
algorithm
utilizing the indication of the pH as an input parameter.
Hydrogen sulfide may be formed in wastewater streams by the conversion of
sulfates to sulfides by sulfide reducing bacteria (SRBs) under anaerobic
conditions.
Hydrogen sulfide is dissolvable in water (up to about 0.4 g/100 ml at 20 C
and 1
is atmosphere). In water, hydrogen sulfide exists in equilibrium with the
bisulfide ion,
HS-, and the sulfide ion, S2-. Unlike sulfide and bisulfide, hydrogen sulfide
is
volatile, with a vapor pressure of about 1.56 x l0 mm Hg (2.1 MPa) at 25 C,
and
may emerge from aqueous solution to form gaseous hydrogen sultidc. The
presence
of hydrogen sulfide in sewer systems is undesirable due to its offensive odor,
toxicity,
and corrosivity.
Gaseous hydrogen sulfide exhibits a characteristic unpleasant odor suggestive
of rotten eggs. Humans can detect this odor at hydrogen sulfide concentrations
as low
as four parts per billion (ppb). Hydrogen sulfide is considered toxic.
Extended
exposure to a few hundred parts per million (ppm) can cause unconsciousness
and
death. Accordingly, the presence of hydrogen sulfide in sewer systems is found
objectionable to people who may come into contact with the gaseous effluent
from
such sewer systems.
Hydrogen sulfide also supports the growth of organisms such as thiothrix and
beggiatoa. These are filamentous organisms which are associated with bulking
.. problems in activated sludge treatment systems.
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Various methods and apparatuses are used to control H2S emissions. One
such apparatus is a biofilter. A biotrickling filter is one kind of biofilter.
A
biotrickling filter utilizes a population of hydrogen sulfide oxidizing
bacteria to
remove hydrogen sulfide from the vapor phase by converting it to sulfuric
acid. The
production of sulfuric acid lowers the pH of the biofilter bed. Constant
dilution and
recirculation of water over the bed facilitates stabilization and maintenance
of the pH
of the Not-titer bed at a level conducive for the bacteria to thrive.
Traditionally the
introduction of fresh water, called make-up water, is done at a constant,
unchanging
flow set by a manually operated valve.
Hydrogen sulfide loadings change in a cyclical manner to reflect high and low
usage of the sewage collection system throughout the day. This cyclical
increase and
decrease in hydrogen sulfide loadings may result in a cyclical rise and fall
of pH of
the biofilter bed. By using a fixed flow rate of make-up water, the system is
incapable
of dynamically adjusting to the changes in hydrogen sulfide loadings. The
result is
that the flow of make-up water will at times be insufficient for meeting the
demands
of high loadings of H2S in the system, while at other times be excessive
during low
loadings of H2S. This results in previously unappreciated problems such as
difficulties in maintaining a desired pH in the system or removing a desired
amount of
H2S. Further, using a fixed flow rate of make-up water to a biofilter often
results in a
previously unappreciated significant amount of water waste.
A biotrickling filter comprises a vessel including a media bed compartment
packed with media. A source of liquid constituting a treatment water is
sprayed on
top of the media and this liquid trickles down through the media to a sump to
become
a treatment water effluent. In a biotrickling filter, at least some of this
treatment water
effluent is recirculated. By providing a moist environment, bacteria are
encouraged to
grow on the media. Air laden with H2S is introduced to the bottom of the
vessel. As
the air rises through the media, an exchange between the gaseous and liquid
phase
occurs where 112S is removed from the air, either by dissolving or direct
biotreatment.
Air, low in H2S concentration, exits the top of the vessel. Alternatively, top
down air
flow through the biofilter could be used.
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During biotreatment, H2S is oxidized to H2SO4 (sulfuric acid). H2S or its
ionic
forms HS- or S2- are used as an energy source by litho-autotrophic bacteria
such as
thiobacillus. These bacteria require a carbon source which may be carbon
dioxide or
dissolved carbonate as well as organic carbon compounds. There are several
possible
intermediate sulfur species such as S , S2032-, and S032- that may be produced
during
the oxidation process. Their production depends on the 11.2S loading, p11,
oxygen
concentration, and temperature within the biofilter.
The use of a biofilter represents a continuous process to remove H2S from
emissions from a wastewater stream by biotreatment. This biotreatment utilizes
bacteria to oxidize the H2S to sulfuric acid and then flushes the sulfuric
acid out of the
system as a liquid solution.
Aspects and embodiments disclosed herein may remove hydrogen sulfide
from a contaminated gas stream by the biological conversion of the hydrogen
sulfide
into less objectionable or less odorous compounds. In some embodiments,
hydrogen
sulfide oxidizing bacteria, for example, one or more of ancalochloris
beggiatoa,
beggiatou alba, sulfobacillus, thiobacillus denitrificans, thiohalocapsa
halophila,
thiomargarita, or thioploca oxidize hydrogen sulfide into sulfuric acid
(H2SO4). En
some embodiments, the hydrogen sulfide oxidizing bacteria (referred to
hereinafter as
simply "bacteria"), are present on a media material disposed in a body of a
biofilter.
The bacteria may form a biofilm on surfaces of the media material.
Contaminated air
passed through the biofilter contacts the bacteria contained therein and the
bacteria
remove hydrogen sulfide from the contaminated air by oxidizing the hydrogen
sulfide
into sulfuric acid. In some embodiments, the biofilter is supplied with water
and
various nutrients, for example, nitrogen, potassium, and phosphorus compounds,
to
provide an environment within the biofilter conducive for the maintenance
and/or
growth of desirable bacteria populations. The supply of water and nutrients to
the
biofilter is, in some embodiments, controlled in response to the results of
measurements of parameters including, for example, pH and nutrient
concentration of
liquid within various portions of the biofilter and/or of effluent or waste
liquid drained
from the biofilter.
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In new installations, bacteria may migrate into a new biofilter along with
water
vapor from an environment in which the new biofilter is installed to establish
a
bacterial population effective for the removal of odorous compounds from
contaminated air from the environment. The establishment of a sufficiently
large
bacterial population within the biofilter (referred to herein as "acclimation"
of the
biofilter) may take between about a few days and about a week. In some
implementations, a biofilter may be "seeded" with desirable bacteria to
shorten the
time period required for the biofilter to acclimate.
One important aspect of the operation of biofilters is the control of the pH
of
to the liquid in contact with the media. The pH may be measured in the
effluent or
blow-down or purge from the biofilter. For a given vessel, there is a range of
pH that
is conducive to acceptable operation. This pll may be in the range of from
about 0 to
about 4 or from about 1.6 to about 2.2. It has been found that flowing liquid
having a
pH in the range of from about 0 to about 4 or from about 1.6 to about 2.2
through the
media bed of a biofilter is conducive to growing and/or maintaining a
population of
hydrogen sulfide oxidizing bacteria on media in a media bed of a biofilter. It
has been
found that if the pH is too low, fouling of the media occurs. If the pH is too
high, the
removal efficiency of H2S drops. Thus, it is important to control the pII in
the
biofilter, for example, as determined by a measurement of pH of effluent from
the
Walter. Normally, in previous implementations, pH is controlled by varying the
rate
of addition of make-up water to the biofilter. If the pH is too low, the flow
rate of
make-up water to the biofilter is increased. If the pH is too high, the flow
rate of
make-up water is decreased.
The cost of water is a significant part of the operational costs of a
biofiltration
system and a target for improvement. A typical system may use from 53,000 L
(14,000 gallons) per day for smaller units to 120,000 L (30,000 gallons) per
day for
larger units depending on loadings and limits of a water supply at a site.
This
amounts to up to about 9 million gallons of water consumed per year for some
systems. For one municipality in Florida, the cost of water alone in operating
a 3-
stage biotrickling filter system (BTF) is roughly $67,000 per year. Reducing
the
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usage of water in these systems to lower operation costs and better use scarce
water
resources is an important goal in the sustainable design of these systems.
Aspects and embodiments disclosed herein are directed to systems and
methods for achieving and/or maintaining a desirable pH in a biotrickling
filter by
partial neutralization of sulfuric acid produced during operation by dosing
alkaline
material into the biotrickling filter. In implementations where the site
supply of
make-up water is not sufficient, this would allow a biotrickling filter to
function as if
it had an adequate water supply. Dosing a sufficient amount of alkaline
material may
achieve an aggressive reduction in water usage, however, in some embodiments,
the
entire balance of make-up water is not replaced with alkaline material due to
system
losses from evaporation and to prevent concentration of salts within the
biofiltcr.
Aspects and embodiments disclosed herein achieve significant water reduction
as
compared to systems that do not utilize alkaline material to partially
neutralize the
sulfuric acid generated in the biofilter, for example, greater than 50%
reduction in
water usage, greater than 99% reduction in water usage, or up to about 99.9%
reduction in water usage, without negatively impacting system performance.
In some embodiments, alkaline material is added to the makeup water that is
used to control the pH within a biotrickling filter. The alkaline material may
include a
water soluble or partially water soluble alkaline material, or a material that
may form
a slurry when mixed with water. Examples of alkaline materials that may be
utilized
with various embodiments disclosed herein include, but are not limited to, any
one or
more of magnesium hydroxide, potassium hydroxide, calcium hydroxide, sodium
hydroxide, potassium carbonate, and sodium carbonate. In some embodiments, the
alkaline material forms a water soluble sulfate upon reaction with sulfuric
acid.
In some embodiments, the alkaline material is added to the biotrickling filter
manually. For example, an operator may monitor the pH of one of the
recirculation
water, the treatment water effluent, or water in a sump of the biotrickling
filter. When
the pH is not within a desired range, or is observed to be approaching a limit
of a
desired range, makeup water including alkaline material is introduced into the
system.
When the pH is within the desired range, the makeup water with the alkaline
material
is not introduced into the system, or is introduced into the system at a
reduced rate or
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a substantially constant rate that has been determined sufficient to maintain
the pH
within the desired range. The alkaline material may be introduced into the
makeup
water using a chemical feed pump in fluid communication with a source of the
alkaline material and/or by manual adjustment of a flow valve in a conduit
fluidly
connecting the source of alkaline material to a conduit through which the
makeup
water flows. In some embodiments, the operator may introduce the alkaline
material
into the system by introducing the alkaline material into a conduit carrying
the
recirculation water or directly into the sump of the biotrickling filter.
In other embodiments, the alkaline material is added to the biotrickling
filter
to automatically as needed. In an automatically operating system, a pH
probe is located
within the system, for example, in the sump of the biotrickling filter or in
fluid
communication with a conduit carrying the recirculation water or the treatment
water
effluent. An electronic controller, for example, a programmable logic
controller
(PLC) receives a signal from the pH probe and compares the pH value to a
setpoint or
target pH value or to a range of desirable pH values. If the pH is off target,
out of the
desired range, or approaching a limit of the desired range, the PLC opens a
makeup
water valve and starts a chemical injection pump or opens an alkaline material
flow
control valve to introduce makeup water and/or the alkaline material into the
biotrickling filter system. Once the pH is within the desired range or at the
target pH
value, the controller stops the makeup water and alkaline material addition or
sets the
rate of introduction of the makeup water and/or alkaline material into the
system at a
rate that has been determined sufficient to maintain the p1 -I within the
desired range.
This rate may vary according to changes in H2S loading to the biofilter. In
some
embodiments, the controller may introduce the alkaline material into the
system by
introducing the alkaline material into a conduit carrying the recirculation
water or
directly into the sump of the biotrickling filter.
In various aspects and embodiments disclosed herein, a fuzzy logic controller
is used to monitor the pH of the drain water, the recirculation water, the
treatment
water effluent, or water in a sump of the biotrickling filter and dynamically
adjust the
flow of make-up water and/or alkaline material to the biotrickling filter to
stabilize
operating parameters, for example, the pH within the biotrickling filter. The
disclosed
CA 02911534 2015-11-05
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fuzzy logic controller achieves a more precise and narrow control of pH within
a
specified range, by, for example, increasing make-up water and/or alkaline
material
flow during high H2S loadings, and decreasing or turning off make-up water
and/or
alkaline material flow during periods of low H2S loadings. This results in
better
.. control of the pH of the biotrickling filter while using significantly less
water.
FIG. 2A illustrates one embodiment of a biofilter, indicated generally at 100,
for the treatment of contaminated air. The biofilter (also referred to as a
biofiltration
system) 100A is supplied with contaminated air 105, for example, air from the
headspace of a sewage system or a wastewater treatment system. The
contaminated
to air 105 contains unwanted or odorous compounds including, for example,
hydrogen
sulfide. While FIG. 2A is described with reference to hydrogen sulfide, the
biofilter
100A may alternatively or additionally be used to mitigate other chemical
species.
The contaminated air 105 is blown through a blower 110 and through a
contaminated
air inlet 195 into a lower plenum 115 of a vessel 120 of the biofilter 100A.
Alternatively or additionally, the contaminated air 105 may be pulled through
the
biofilter vessel 120 by a fan or blower located at a treated air outlet 150 of
the biofilter
vessel 120. The contaminated air passes through the lower plenum 115 and into
a
media bed compartment 125 of the biofilter 100 that is disposed within the
biofilter
vessel 120 in fluid communication between the contaminated air inlet 195 and
the
treated air outlet 150.
The media bed compartment 125 includes a bed of media, for example,
particulate media, on which bacteria reside. The media is retained in the
media bed
compartment 125 by a lower screen 130 and, optionally, an upper screen 135.
The
contaminated air passing though the media bed compartment 125 contacts the
media
and the bacteria on the media and in the water in the media bed compartment
125.
The bacteria in the media bed compartment 125 consume hydrogen sulfide in the
contaminated air, removing the hydrogen sulfide from the contaminated air and
converting the contaminated air into treated air.
The treated air passes through an upper plenum 140 of the biofilter 100A and
is released to the external environment 145 or a polishing unit through the
upper gas
outlet 150 of the biofilter vessel 120. A lower portion of the plenum 115 may
- 16 -
function as a sump 117 which may retain fluid draining from the media bed
compartment 125. Sulfuric acid produced by the bacteria, water, unutilized
nutrients,
and other waste fluids exit the sump 117 through either a drain outlet 170
connected
to drain line 172 or through an effluent outlet connected to a recycle line
176.
Alternatively, a single effluent outlet connected to the sump 117 could
deliver liquid
both to the drain line and recycle line. The waste fluid in drain line 172 may
be
returned to a sewage system or wastewater treatment system from which the
contaminated air was withdrawn or may be otherwise treated, for example, to
neutralize the acid in the waste fluids, or disposed of. The effluent in the
recycle line
to 176 may be returned to the vessel 120, for example, to the top of the
media bed
compartment 125, via inlet 182.
The materials of construction of the biofilter vessel 120 are desirably
resistant
to attack by acid which is generated by the bacteria in the biofilter vessel
120. The
walls of the biofilter vessel 120 and the upper and lower screens 130, 135 may
be
foimed from, for example, fiberglass and/or an acid resistant polymer and/or
may be
coated with an acid resistant material.
Media used in the media bed compartment 125 of the biofilter vessel 120 may
be composed of various organic and/or inorganic materials, including, for
example,
wood mulch, pine bark, gavel, pumice, expanded shale, fired clay, and
polymeric
open celled foam (referred to hereinafter as "traditional media materials").
The media
is referred to synonymously herein as "biofiltering media." The biofiltering
media is
configured to support growth and maintenance of a population of hydrogen
sulfide
oxidizing bacteria on the biofiltering media. To support growth and
maintenance of a
population of hydrogen sulfide oxidizing bacteria, the biofiltering media may
be
porous or fiberous to provide a large surface area on which the hydrogen
sulfide
oxidizing bacteria may grow, and may be resistant to degradation by acid
and/or non-
reactive with acids, for example, sulfuric acid in an operating pH range of
the biofilter
(in some instances, from about 1.6 to about 2.2).
Glass (5i02) media, for example, sintered glass media, foamed glass media or
other silica based media, may be utilized in place of traditional media
materials in
biofilters for the removal of odorous compounds, for example, hydrogen
sulfide, from
Date Recue/Date Received 2022-03-02
CA 02911534 2015-11-05
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contaminatcd air. The characteristics of embodiments of glass-based biofilter
media
are discussed in detail in U.S. Patent Application No. 14/270,461 and U.S.
Patent
Application No. 14/920,407.
To provide an environment conducive to the maintenance and/or growth of a
desirable bacterial population within the biofilter 100, the biofilter may
include a
water introduction system configured to introduce water from a source of water
into
the biofilter vessel. Water from a source of make-up water 155 and/or
nutrients, for
example, nitrogen, potassium, and/or phosphorus compounds from a source of
nutrients 160 is introduced into the biofilter vessel 120 through an inlet 182
of the
.. biofilter vessel 120. In some embodiments, the source of make-up water 155
and/or
source of nutrients 160 are external to the biofilter vessel 120. In some
embodiments,
the nutrients are supplied as an aqueous solution. The liquid entering through
inlet
182 may generally be referred to as a treatment liquid.
The source of make-up water 155 and the source of nutrients 160 are
illustrated in FIG. 2A as being in fluid communication with the same inlet 182
of the
biofilter vessel 120 that is also used to introduce recirculated effluent into
the
biofilter, but in other embodiments the source of make-up water 155 and the
source of
nutrients 160 may be fluidly connected to different inlets of the biofilter
vessel 120.
Upon entering the biofilter vessel 120, the make-up water and/or nutrients are
distributed over the top of the media bed in the media bed compartment 125 by,
for
example, a fluid distributor, sprayer. or sprinkler (not shown). The water
and/or
nutrients are periodically or, alternatively, continuously provided to the
media bed in
the media bed compartment 125.
In some embodiments, the biofilter includes an alkaline material introduction
system configured to introduce an alkaline material from a source of alkaline
material
into the biofilter vessel. As illustrated in FIG. 2A, a source of alkaline
material 165 is
in fluid communication with a conduit 155C fluidly connecting the source of
make-up
water 155 to the inlet 182 of the biofilter vessel. The source of alkaline
material 155
may include, for example, one or more of magnesium hydroxide, potassium
.. hydroxide, calcium hydroxide, sodium hydroxide, potassium carbonate, and
sodium
carbonate. In some embodiments, the alkaline material is present in the source
of
- 18 -
alkaline material 165 as a slurry or dissolved in a solvent, for example,
water.
The alkali material is periodically or, alternatively, continuously provided
to the
media bed in the media bed compainnent 125 to control the pH of fluid in the
media
bed 125. In some embodiments, the alkali material is distributed over the top
of the
media bed in the media bed compartment 125 by the same fluid distributor,
sprayer,
or sprinkler as the make-up water and/or nutrients. In some embodiments, the
alkaline material introduction system of the biofilter is configured to
introduce the
alkaline material into the vessel 120 with the water from the source of water
155. In
other embodiments, the alkali material is alternatively or additionally
introduced
to separately into the biofilter, for example, into the sump 117 through
conduit 165C and
inlet 118, illustrated in FIG. 2A. The alkaline material may thus be
indirectly added
to the media bed compaitinent of the biofilter.
In some embodiments, flow control devices 155F, 160F, and 165F may be
utilized to control the flow of make-up water, nutrients, and alkaline
material,
respectively, from the sources of make-up water, nutrients, and alkaline
material 155,
160, 165. In some embodiments, one or more of the flow control devices 155F,
160F,
and 165F are manually controlled flow valves or pumps. In other embodiments
one
or more of the flow control devices 155F, 160F, and 165F are flow valves or
pumps
that are automatically controlled by an electronic control system 175,
described
below. In other embodiments one or more of the flow control devices 155F,
160F,
and 165F include flow meters to measure the flow of make-up water, nutrients,
and
alkaline material, respectively, through the flow control devices 155F, 160F,
and
165F.
A portion of the fluid in the sump 117 of the biofilter vessel 120 may be
recycled, for example, from lower fluid outlet through recycle line 176 and
pump 178
into an inlet 182 proximate an upper end of the biofilter vessel 120. Residual
nutrients remaining in the fluid exiting the media bed 125 are thus re-
introduced into
the biofilter vessel 120, retaining the bioculture and reducing the need for
"fresh"
nutrients to be introduced into the biofilter vessel 120 from the source of
nutrients
160, reducing operating costs of the biofilter 100A. Acid in the fluid exiting
the
media bed 125 is also re-introduced into the biofilter vessel 120, which may
facilitate
Date Recue/Date Received 2022-03-02
CA 02911534 2015-11-05
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maintaining the pH within the media bed 125 and/or biofilter vessel 120 at a
desired
level. Water and/or nutrients and/or alkaline material from the source of
water 155
and/or source of nutrients 160 and/or source of alkaline material 165,
respectively,
may be introduced into the biofilter vessel 120 the same inlet 182 as the
recycled
liquid from the sump 117 and may be distributed onto the top of the media bed
compartment 125 utilizing a common fluid distributor, sprayer, or sprinkler as
the
recycled liquid from the sump 117. In some embodiments, the alkaline material
introduction system of the biofilter is configured to introduce the alkaline
material
into the vessel 120 with the recycled liquid from the sump 117 and the sump
117 may
be considered a source of water for the biofilter. Biofilters configured as
illustrated in
FIG. 2A may be referred to as trickling biofilters or biotrickling filters.
Water and/or nutrients and/or alkaline material from the source of water 155
and/or source of nutrients 160 and/or source of alkaline material 165, may be
mixed
with effluent in the recycle line 176 and delivered back to the vessel 120 via
inlet 182.
The biofilter 100A may be provided with one or more sensors which provide
information to the controller 175. The controller 175 analyzes the information
from
the one or more sensors and adjusts a timing/and or rate of introduction (or
more
generally, an amount per unit time added to the biofilter) of water and/or
nutrients
and/or alkaline material from the source of water 155 and/or source of
nutrients 160
and/or source of alkaline material 165, respectively, into the biofilter
vessel 120
responsive to an analysis of the information. In some embodiments, one of the
alkaline material and the water may be added or introduced to the biofilter at
a fixed
rate and the other of the alkaline material and the water may be added or
introduced to
the biofilter at an amount per unit time or flow rate controlled by the
controller 175.
The control of the flow rate of make-up water into biofilters in prior known
systems has been performed manually with infrequent adjustments to flow rate
of the
make-up water. This practice has often led to the problems discussed above. It
has
been discovered that methods of operation of a biofilter may be improved by
using
automated fuzzy logic control process that will control the effluent pI1, for
example,
to maintain the effluent pH within a desired range.
CA 02911534 2015-11-05
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In some embodiments, the controller 175 may also control a speed of the
blower 110 responsive to an analysis of information provided from one or more
sensors associated with the biofilter 100A, for example, one or more sensors
may
provide information regarding a concentration of H2S entering ancUor exiting
the
biofilter 100A or a percent of H2S from contaminated air removed by the
biofilter to
the controller 175.
The biofilter 100A may include one or more pH sensors (also referred to as
"pH probes") 180, positioned downstream of the media bed and configured to
measure a pH of liquid having passed through the media bed and to provide an
indication of the pH to the electronic control system. The one or more pH
sensors
180 may be positioned in, for example, sump 117 and/or in fluid communication
with
the drain line 172 and/or on the recycle line 176 or otherwise positioned
downstream
of the media bed of the biofilter. A nutrient concentration sensor 185
configured to
measure a concentration of one or more components of a nutrient supplied to
the
biofilter 110 may be provided in fluid communication with fluid within and/or
drained
from the biofilter vessel 120 through either the drain line 172 or the recycle
line 176.
Sensor 185 is illustrated as coupled to the drain line 172 in FIG. 2A, but in
other
embodiments may be located or configured to measure parameters of fluid within
the
media bed 125, lower plenum 115, sump 117, or other portions of the biofilter
100.
The pH measured by the pH sensor(s) 180 may be utilized by the controller
175 to control or regulate a flow rate and/or frequency of addition of water
from the
source of make-up water 155, and/or nutrients from the source of nutrients
160, and/or
alkaline material from the source of alkaline material 165 into the biofilter
vessel 120.
Controlling the flow of make-up water and/or alkaline material may, in turn,
aid in
.. controlling the pH within the vessel 120. In some embodiments, the
controller 175 is
configured to maintain an acidic pH within the biofilter vessel 120. A pH of
between
about 0 and about 4 in the fluid within the biofilter vessel 120 and/or in the
sump 117
may be indicative of a pH level within the media bed conducive for hydrogen
sulfide
consuming bacteria to grow. More particularly, a pH between about 1.6 and
about 2.2
may be desired. According to some embodiments a pH set point of about 2.0 may
be
desired. The controller 175 may be configured to control the introduction of
water
CA 02911534 2015-11-05
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and/or alkaline material and/or contaminated air into the biofilter to
maintain the pH
in the biofilter, for example, in the media bed, within these desired ranges
or at about
this desired set point.
One or more pH sensors 180 in communication with the controller 175 may be
placed at various locations in the system to measure pH. For example, in FIGS.
IA
and 1B pH sensor(s) 180 are located in sump 117 and/or in fluid communication
with
the drain line 172 and/or the recycle line 176.
The controller 175 may control the flow of water and/or alkaline material into
the biofilter vessel 120 according to a fuzzy logic algorithm in response to
the
to measurements of the pH sensor(s) 180 as discussed in greater detail
below. However,
the controller 175 is not limited to using pH as an input parameter. Nor is
the
controller 175 limited to controlling the output parameters of water flow
and/or
alkaline material addition to the biofilter. In some embodiments, the
controller 175
may respond to other input parameters, including without limitation, pressure
values,
hydrogen sulfide concentrations in the air stream, nutrient concentration, and
air flow
or water flow values. The controller 175 may respond to input from any sensor
of the
system. Further, the controller 175 may be implemented to control any output
parameter of the system, including without limitation, water flow rate of any
system
stream, air flow rate, nutrient addition rate, and/or alkaline material
addition rate.
Another type of sensor that may be used in the system 100A includes one or
more flow meters. As discussed above, flow meters may be included in one or
more
of the fluid flow control devices 155F, 160F, and 165F. Alternatively or
additionally,
a flow meter 168 may be placed elsewhere, for example, along recycle line 176
to
measure the flow rate of recycled effluent from sump 117.
The nutrient concentration measured by the nutrient sensor 185 is utilized by
the controller 175 to control a flow rate and/or frequency of the flow of
nutrients from
the source of nutrients 160 into the biofilter vessel 120. A nutrient
concentration or a
concentration of a component of nutrient supplied to the biofilter 100A below
a lower
threshold within the biofilter vessel 120 and/or exiting the drain 170 of the
biofilter
vessel 120 may be indicative of insufficient nutrients being supplied to the
bacteria.
A nutrient concentration or a concentration of a component of nutrient
supplied to the
CA 02911534 2015-11-05
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biofilter 100A above an upper threshold in fluid within the biofilter vessel
120 and/or
exiting the drain 170 of the biofilter vessel 120 may be indicative of an
excessive
amount of nutrients being supplied to the bacteria. The controller 175 may
control the
flow of nutrients into the biofilter vessel 120 according to a fuzzy logic
algorithm in
response to the measurements of the nutrient sensor 185, as discussed in
greater detail
below.
Pressure sensors 190a, 190b provide an indication of the differential pressure
across the biofilter vessel 120 and/or media bed compartment 125. A pressure
differential exceeding an upper threshold value, for example, between about
two
to inches (5.1 cm) and about 10 inches (25 cm) of water (four degrees
Celsius) (between
about 498 Pascal and about 2,491 Pascal) may be indicative of the biofilter
vessel 120
and/or media bed compartment 125 being blocked, for example, by contaminants
or
by over-packing of media in the media bed compartment 125. Responsive to the
detection of a pressure differential exceeding an upper threshold, the
controller 175
may increase the speed of the blower 110 to maintain an air flow through the
biofilter
vessel 120 within a desired range and/or may shut down the biofilter 100A
and/or
provide an indication to an operator that the biofilter 100A may be in need of
service.
A pressure differential which decreases over time may be indicative of the
biofilter
vessel 120 and/or media bed compartment 125 exhibiting channeling, for
example,
due to channels forming through the media bed and/or by poor distribution or
mispacking of media in the media bed compartment 125. Responsive to the
detection
of a drop in the pressure differential, the controller 175 may shut down the
biofilter
100A and/or provide an indication to an operator that the biofilter 100A may
be in
need of service.
In some embodiments, the controller 175 is configured to control a rate of
introduction of the alkaline material and a rate of introduction of water into
the
biotrickling filter to be sufficient to both maintain the pH of the liquid in
the biofilter,
for example, in the media bed, within a range conducive to maintain a
population of
hydrogen sulfide oxidizing bacteria in a media bed of the biotrickling filter
and to
prevent clogging of the media bed, for example, by providing sufficient water
to rinse
salts which may accumulate in the media bed from the media bed. In some
CA 02911534 2015-11-05
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embodiments, water soluble salts (for example, sulfates) may accumulate in the
media
bed as alkaline material introduced into the biofilter reacts with and
neutralizes a
portion of the acid (e.g., sulfuric acid) in the media bed. Water introduced
into the
biofilter may rinse accumulated salts from the media bed before the salts
accumulate
to a degree which causes significant blockage to flow of air or liquid through
the
media bed or clogging of the media bed.
In some embodiments, as illustrated in the biofilter generally indicated at
100B in FIG. 2B, which is substantially the same as biofilter 100A, the
recycle line
176 of FIG. 2A is eliminated, and no fluid from the sump 117 of the biofilter
vessel
to 120 is recycled. Instead, water and/or nutrients and/or alkaline
material from the
source of water 155 and/or source of nutrients 160 and/or source of alkaline
material,
respectively, may be introduced into the biofilter vessel 120 through the
inlet 166 and
may be distributed onto the top of the media bed compartment 125 utilizing a
fluid
distributor, sprayer, or sprinkler (not shown). The discussion of features and
operation of the biofilter and components thereof herein applies equally to
both
biofilters 100A and 100B.
The controller 175 used for monitoring and controlling operation of the
biofilter 100A or 100B may include a computerized control system. Various
aspects
of the invention may be implemented as specialized software executing in a
general-
purpose computer system 200 such as that shown in FIG. 3. The computer system
200 may include a processor 202 connected to one or more memory devices 204,
such
as a disk drive, solid state memory, or other device for storing data. Memory
204 is
typically used for storing programs and data during operation of the computer
system
200. Components of computer system 200 may be coupled by an interconnection
mechanism 206, which may include one or more busses (e.g., between components
that are integrated within a same machine) and/or a network (e.g., between
components that reside on separate discrete machines). The interconnection
mechanism 206 enables communications (e.g., data, instructions) to be
exchanged
between system components of system 200. Computer system 200 also includes one
or more input devices 208, for example, a keyboard, mouse, trackball,
microphone,
CA 02911534 2015-11-05
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touch screen, and one or more output devices 210, for example, a printing
device,
display screen, and/or speaker.
The output devices 210 may also comprise valves, pumps, or switches which
may be utilized to introduce water and/or nutrients and/or alkaline material
from the
source of water 155 and/or the source of nutrients 160 and/or the source of
alkaline
material 165 into the biofilter and/or to control the speed of a blower of the
biofilter.
One or more sensors 214 may also provide input to the computer system 200.
These
sensors may include, for example, pH sensor(s) 180, nutrient sensor 185,
pressure
sensors 190a, I90b, sensors for measuring a concentration of an undesirable
to component of contaminated and/or treated air, for example, H2S, and/or
other sensors
useful in a biofilter system. These sensors may be located in any portion of a
biofilter
system where they would be useful, fbr example, upstream of a media bed,
downstream of a media bed, in communication with a liquid waste outlet of a
biofilter
vessel, and/or in communication with an air or gas inlet and/or outlet of a
biofilter
vessel. In addition, computer system 200 may contain one or more interfaces
(not
shown) that connect computer system 200 to a communication network in addition
or
as an alternative to the interconnection mechanism 206.
The storage system 212, shown in greater detail in FIG. 4, typically includes
a
computer readable and writeable nonvolatile recording medium 302 in which
signals
are stored that define a program to be executed by the processor or
information to be
processed by the program. The medium may include, for example, a disk or flash
memory. Typically, in operation, the processor causes data to be read from the
nonvolatile recording medium 302 into another memory 304 that allows for
faster
access to the information by the processor than does the medium 302. This
memory
304 is typically a volatile, random access memory such as a dynamic random
access
memory (DRAM) or static memory (SRAM). It may be located in storage system
212, as shown, or in memory system 204. The processor 202 generally
manipulates
the data within the integrated circuit memory 204, 304 and then copies the
data to the
medium 302 after processing is completed. A variety of mechanisms are known
for
managing data movement between the medium 302 and the integrated circuit
memory
clement 204, 304, and aspects and embodiments disclosed herein are not limited
CA 02911534 2015-11-05
- 25 -
thereto. Aspects and embodiments disclosed herein are not limited to a
particular
memory system 204 or storage system 212.
The computer system may include specially-programmed, special-purpose
hardware, for example, an application-specific integrated circuit (ASIC).
Aspects and
embodiments disclosed herein may be implemented in software, hardware or
firmware, or any combination thereof. Further, such methods, acts, systems,
system
elements and components thereof may he implemented as part of the computer
system
described above or as an independent component.
Although computer system 200 is shown by way of example as one type of
io computer system upon which various aspects and embodiments disclosed
herein may
be practiced, it should be appreciated that aspects and embodiments disclosed
herein
are not limited to being implemented on the computer system as shown in FIG.
3.
Various aspects and embodiments disclosed herein may be practiced on one or
more
computers having a different architecture or components that that shown in
FIG. 3.
Computer system 200 may be a general-purpose computer system that is
programmable using a high-level computer programming language. Computer system
200 may be also implemented using specially programmed, special purpose
hardware.
In computer system 200, processor 202 is typically a commercially available
processor such as the well-known Pentium Tm or CoreTm class processors
available
from the Intel Corporation. Many other processors are available, including
programmable logic controllers. Such a processor usually executes an operating
system which may be, for example, the Windows 7, Windows 8, or Windows 10
operating system available from the Microsoft Corporation, the MAC OS System X
available from Apple Computer, the Solaris Operating System available from Sun
Microsystems, or UNIX available from various sources. Many other operating
systems may be used.
The processor and operating system together define a computer platform for
which application programs in high-level programming languages are written. It
should be understood that the invention is not limited to a particular
computer system
platform, processor, operating system, or network. Also, it should be apparent
to
those skilled in the art that aspects and embodiments disclosed herein are not
limited
CA 02911534 2015-11-05
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to a specific programming language or computer system. Further, it should be
appreciated that other appropriate programming languages and other appropriate
computer systems could also be used.
One or more portions of the computer system may be distributed across one or
more computer systems (not shown) coupled to a communications network. These
computer systems also may be general-purpose computer systems. For example,
various aspects of the invention may be distributed among one or more computer
systems configured to provide a service (e.g., servers) to one or more client
computers, or to perform an overall task as part of a distributed system. For
example,
to _________________________________________ various aspects and embodiments
disclosed herein may be perfoi wed on a client-
server system that includes components distributed among one or more server
systems
that perform various functions according to various aspects and embodiments
disclosed herein. These components may be executable, intermediate (e.g., IL)
or
interpreted (e.g., Java) code which communicate over a communication network
(e.g.,
the Internet) using a communication protocol (e.g., TCP/IP). In some
embodiments
one or more components of the computer system 200 may communicate with one or
more other components over a wireless network, including, for example, a
cellular
telephone network.
It should be appreciated that the aspects and embodiments disclosed herein are
not limited to executing on any particular system or group of systems. Also,
it should
be appreciated that the aspects and embodiments disclosed herein are not
limited to
any particular distributed architecture, network, or communication protocol.
Various
aspects and embodiments disclosed herein are may be programmed using an object-
oriented programming language, such as SmallTalk, Java, C-HF, Ada, or C# (C-
Sharp). Other object-oriented programming languages may also be used.
Alternatively, functional, scripting, and/or logical programming languages may
be
used, for example ladder logic. Various aspects and embodiments disclosed
herein
are may be implemented in a non-programmed environment (e.g., documents
created
in HTML, XML or other format that, when viewed in a window of a browser
program, render aspects of a graphical-user interface (GUI) or perform other
CA 02911534 2015-11-05
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functions). Various aspects and embodiments disclosed herein may be
implemented
as programmed or non-programmed elements, or any combination thereof.
The controller may be operated under a "fuzzy logic" regime. Fuzzy logic is a
problem-solving control system methodology that lends itself to implementation
in
systems ranging from simple, small, embedded micro-controllers to large,
networked,
multi-channel PC or workstation-based data acquisition and control systems. It
can
be implemented in hardware, software, or a combination of both. Fuzzy logic
provides a way to arrive at a definite conclusion based upon vague, ambiguous,
imprecise, noisy, or missing input information. A fuzzy logic approach to
control
to problems mimics how a person would make decisions, only much faster.
In a standard bivalent set theory, an object cannot belong to both a set and
its
complement. When describing temperature, for example, using sets such as "hot"
and
"cold" a certain temperature value either belongs to the "cold" set or the
"hot" set, and
never both at the same time. The boundaries of standard sets are exact.
However,
standard bivalent set theory is not descriptive of the real world. In the real
world
boundaries in sets are not exact and often blur together. Objects can belong
to many
sets to varying degrees. By using fuzzy logic one can build devices capable of
reasoning with fuzzy sets and judge how they should operate or shift from one
setting
to another even when the criteria for making those changes are hard to define.
In a fuzzy logic algorithm, a crisp input value is first converted to fuzzy
sets in
a process called "fuzzification." The algorithm then uses rules to associate
these
fuzzy input sets to fuzzy output sets representing some control value, for
example,
motor speed or fluid flow rate.
Fuzzy logic incorporates a rule-based IF X AND Y THEN Z approach to
solving a control problem rather than attempting to model a system
mathematically.
The fuzzy logic model is empirically-based, relying on an operator's
experience rather
than their technical understanding of the system. For example, rather than
dealing
with pH control in terms such as "Set_Point =2.0", "pH <1.6", or "pH 1.6 <pH
<2.2",
terms like "IF (process is too acidic) AND (process is getting more acidic)
THEN
(increase water flow rate to the process),'' "IF (process is too basic) AND
(process is
getting more basic rapidly) THEN (reduce the water flow rate to the process
CA 02911534 2015-11-05
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quickly)." "IF (process is too acidic) AND (process is getting more acidic)
THEN
(increase addition of alkaline material to the process)," or "IF (process is
too basic)
AND (process is getting more basic rapidly) THEN (reduce the addition of
alkaline
material to the process quickly)"are used. These terms are imprecise and yet
very
descriptive of what desirably should happen.
Fuzzy logic controllers are typically provided with some numerical parameters
to facilitate operation, for example, what is considered significant error and
significant
rate-of-change-of-error. Exact values of these numerical parameters are
usually not
critical unless very responsive performance is required in which case
empirical tuning
to would determine them. For example, a pH control system could use a
single pH
feedback sensor whose data is subtracted from the command signal to compute
''error' (a degree of deviation of measured pH from a desired center point of
a range
of pH values) and then time-differentiated to yield the error slope or rate-of-
change-
of-error, hereafter called "error-dot." Error might have units of pH and a
small error
may be considered to be about 0.1 pll units while a large error might be about
0.5 pH
units. The "error-dot" might then have units of pH units/min with a small
error-dot
being about 0.2 pH units/min and a large one being about 1.0 pH units/min.
These
values do not have to be symmetrical and can be altered once the system is
operating
to improve or optimize performance. Generally, fuzzy logic is inherently
robust since
it does not require precise, noise-free inputs and can be programmed to fail
safely if a
feedback sensor quits or is destroyed. The output control is a smooth control
function
despite a wide range of input variations. Since the fuzzy logic controller
processes
user-defined rules governing the target control system, it can be modified to
improve
or alter system performance. New sensors can easily be incorporated into the
system
simply by generating appropriate governing rules.
In one embodiment, a fuzzy logic controller 175 is interfaced with a biofilter
100. The system comprises a pH monitoring device 180 in contact with the
effluent
of the biofilter 117. Flow meters are positioned to measure the flow of make-
up water
from source of make-up water 160 and/or a rate of addition of alkaline
material from
source of alkaline material 165. A flow meter may additionally or
alternatively be
placed along recycle line 176. Flow control devices 155F and/or 165F are
positioned,
CA 02911534 2015-11-05
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for example, downstream of the source of make-up water 155 and/or the source
of
alkaline material 165 to regulate flow of make-up water and/or alkaline
material into
recycle line 176 or into the biofilter vessel 120 through inlet 182, 166,
and/or 118.
The flow control device 155F and/or 165F may comprise, for example, an
automated
control valve such as a motorized valve, a solenoid valve, or a pneumatic
valve. The
flow control device 155F and/or 165F is interfaced with the fuzzy logic
controller
175. The pH monitoring device(s) 180 may measure the pH of effluent at one or
more
points in the system 100, for example, in the sump 117. The controller 175
receives
the pH value via an input signal from the pH sensor(s) 180. Based on a pre-
to determined set point, the controller 175 sends a signal to the flow
control device 155F
and/or 165F that either causes the make-up water and/or alkaline material flow
rate to
increase or decrease depending on the pH of the effluent, or causes the flow
rate of the
recycled effluent in recycle line 176 to increase or decrease, according to an
alternative embodiment. In some embodiments, the controller utilizes an
indication of
pH from the pH sensor(s) 180 as an input parameter in an algorithm used by the
fuzzy
logic-based controller to automatically control one of the amount of water
introduced
to the biotrickling filter per unit of time and/or the amount of the alkaline
material
added to the biotrickling filter per unit of time.
The following examples are given by way of illustration of working one
embodiment in actual practice and should not be construed to limit the scope
of the
presently disclosed aspect and embodiments in any way.
Example 1: Fuzzy Logic Control Scheme
A non-limiting example of a fuzzy logic control scheme for controlling the pH
in a trickling biofilter is described as follows. This control scheme is
designed to
maintain a pH in a biotrickling filter system within a range of +/- 0.4 pH
units of a set
point of 2.0 pH units by adjusting the flow rate of fresh make-up water into
the
biofilter using a motorized controller actuated valve. Advantages of using a
fuzzy
logic control scheme in this setting include:
1. pH behavior is non-linear. Using a fuzzy system circumvents mathematical
modeling of the pH behavior of the system.
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2. The pH target set point and the allowable threshold of variation can
remain as
variables in the control logic.
The algorithm of the controller receives two crisp inputs, error and error-
dot.
Crisp inputs maybe defined herein as actual measured inputs having defined
values.
Error is calculated by subtracting a measured pH (also referred to as a
feedback pH)
from the user programmed pfl set point. Error-dot is calculated as the change
in error
over a time period. From these two inputs the algorithm calculates an output
control
value. In this particular implementation, the output control value corresponds
to a
change in the position of a motorized control valve on a flow control valve
that
controls the flow rate of the make-up water and/or alkaline material into the
biofilter.
Finally, based on the output control value, the controller sends an output
signal to the
control valve and the flow rate of make-up water and/or alkaline material is
adjusted
accordingly. The algorithm waits for a defined period of time for the changes
in the
flow of make-up water and/or alkaline material to be reflected in the system
pH, and
after this period of time, the algorithm repeats this procedure.
Error, which is the first of the two crisp input variables, is defined as the
difference between target pH and measured, or feedback, pH, and may be
calculated
according to the following equation:
Error = target pH ¨ feedback pH.
Having obtained the pH measurement and calculated the error, the controller
algorithm places the error in one or more fuzzy sets shown in TABLE I.
TABLE 1: Fuzzy Error Sets
Set Name Error Type Description
pH_Low positive error Measured pH is
lower than target
pII_Iligh negative error Measured pH is
higher than target
pli_Good zero error Measured pH is same as target
A characteristic of fuzzy set theory is that the error value need not belong
to
only one set but may be a member of multiple sets to differing degrees.
Membership
functions are used to determine the degree to which the calculated error is a
member
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of each of the error sets. Using error as an example, there are three sets
that input
"error" can belong to: pH_Low, pH_High, and pH_Good. Membership functions
define which fuzzy sets a given input belongs to, and the degree to which it
belongs to
that particular set (degree of membership).
FIG. 5 depicts a graph showing the relationship between error and the degree
of membership in a fuzzy set. For this example, the predetermined desired pH
range
is plus/minus 0.4 pH units from the pH set point. Where error is zero, the
error
belongs one hundred percent in the pil_Good set. Where the error is +0.4 pH or
greater, the error belongs one hundred percent in the pH Low set. (Referring
to
Equation 1, error is defined as target pH minus measured pH, therefore if the
measured pH is below the set point, the error will be positive.) Where the
error is -0.4
pH or more negative, the error belongs one hundred percent in the pH_High set.
Where the error is 0.0 pH, the error belongs one hundred percent in the
pH_Good set.
Where the error is between 0.0 pH and +0.4 p11, the error will be a member of
both the pH_Good set and the pH Low set. The percent membership in the pH_Good
set decreases linearly from 100% where error is 0.0 pH to 0% where error is
+0.4 pH.
Meanwhile, the percent membership in the pH Low set increases linearly from 0%
where error is 0.0 pH units to 100% where error is +0.4 pH units. Analogous
relationships apply between the pH_Good set and the pH_High set where error is
between -0.4 pH units and 0.0 pH units.
Error-dot, which is the second of the two crisp input variables, is defined as
the change in error over a pre-determined time period, and may be calculated
according to the following equation:
Error-dot = d Error / di
The error-dot may belong in three different fuzzy sets shown in TABLE 2:
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TABLE 2: Fuzzy Error-Dot Sets
Set Name Error Type Description
pfl_getting _lower positive error-dot Error is
changing with
positive slope
pH_getting_higher negative error-dot Error is
changing with
negative slope
pil_no_change zero error-dot Error is not
changing
FIG. 6 depicts a graph showing the relationship between error-dot and the
degree of membership in a fuzzy error dot set. For this example, the pre-
determined
desired range for error-dot is plus/minus 0.1 delta pH units/minute.
Where the error-dot parameter is +0.1 d error/min or greater, the error-dot
parameter belongs one hundred percent in the pH_getting_lower set. Where the
error-
dot is -0.1 d error/min or more negative, the error-dot parameter belongs one
hundred
percent in the pfl_getting_higher set. Where the error-dot is 0.0 d error/min,
the
to error-dot parameter belongs one hundred percent in the pH_no_change set.
Where the error is between 0.0 d error/min and +0.1 d error/min, the error
will
be a member of both the pH_no_change set and the pH_getting_lower set. The
percent membership in the pH_no_change set decreases linearly from 100% where
error is 0.0 d error/min to 0% where error is +0.1 d error/min. Meanwhile, the
percent
membership in the pH_getting_lower set increases linearly from 0% where error
dot
is 0.0 d error/min to 100% where error dot is +0.1 d error/min. Analogous
relationships apply between the pH_no_change set and the pH_getting_higher set
where error dot is between -0.1 d error/min and 0.0 d error/min.
Thus far the controller has received crisp input signals describing pH values
of
the effluent. The controller used these crisp inputs to calculate error and
error dot and
determined degrees of membership in the various fuzzy error sets and fuzzy
error dot
sets based on the inputs and pre-determined ranges. Now that the degrees of
membership have been determined, the controller may use this information to
determine an output control value.
The output control value determines the output signal delivered to the control
valves. Change in control valve positions may be calculated as a percentage of
total
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valve span from 0% to 4/-100%. A positive percentage represents opening of the
valve, and a negative percentage representing a closing of the valve. This
percentage
is converted to a milliamp change in valve position. For a 4-20 milliamp (mA)
actuated valve the total span of movement of the valve is 16mA, therefore the
controller adjusts the current valve position by changing the applied current
as a
percentage of 16 mA.
A series of steps are performed in the controller algorithm to arrive at an
output control value based on the input values. The fuzzy logic controller
incorporates a rule-based IF X AND Y THEN Z approach to determining the output
control value, rather than relying on a mathematical model of the system, the
way
other control processes do. The controller uses this rule-based approach to
associate
input signals with specific output actions.
For this system, there are five fuzzy output sets. Each fuzzy output set has a
rule associating it with one or more fuzzy input sets.
Because this system includes five fuzzy output sets, it has five rules, shown
in
TABLE 3:
TABLE 3: Rules
Input Fuzzy Set Antecedent Output Set Consequent Action.
condition. If... Then...
pH_Good Do_Nothing
pil_High Close fast
p14_Low Open_fast
pH_Good AND getting_lower Open_slow
pH_Good AND getting_higher Close slow
Each fuzzy output set is associated with a numerical output value constant.
For example, the output' set Open_fast is associated with the constant 1.0,
which
indicates that the output set is associated with opening an associated valve
100%. The
output set Do_Nothing is associated with the output set constant, 0,
indicating that it
corresponds to an output of a 0% change in the valve position. The output set
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Close_slow is associated with an output in which the valve is closed 50% from
its
current position. Each of the associated output constants is shown in Table 4.
TABLE 4: Output Set Constants
Fuzzy Output Set Associated Fuzzy Output Set Constant
Open_valve_fast; 1.0
Open_valve_slow 0.5
Do_nothing 0.0
Close_valve_slow -0.5
Close_valve_fast -1.0
While there are five fuzzy output sets, ultimately, a single crisp output
control
signal for controlling the valve must be determined.
This single crisp output signal is determined by calculating a degree of
membership for each fuzzy output set and then taking a weighted average of the
fuzzy
output set constants. The degree of membership in the fuzzy output set serves
as the
weighting coefficient.
The degree of membership in each respective fuzzy output set is a function of
the degree of membership of the input sets that serve as conditions for the
output set.
For example, the rule associated with the Do_nothing output set is:
IF pH Good THEN Do_nothing.
This output results from an input designating that pH error parameter is in a
good range. Therefore the degree of membership in the output set Do_nothing is
a
function of the degree of membership of the fuzzy input set pH_Good.
The logical operations shown in TABLE 5 below are evaluated to determine a
degree of membership (and therefore a weighting coefficient) for each of the
five
fuzzy output sets based on the rule statements. In TABLE 5, "x" corresponds to
an
error parameter membership value and "y" corresponds to an error-dot parameter
membership value.
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TABLE 5: Logical Operations
Logical Operation Membership Value
x AND y (Intersect) min(x,y)
x OR y (Union) max(x,y)
NOT x (Compliment) I - x
Combining the logical operations shown in TABLE 5 with each associated
rule provides the equation for determining the output membership.
For example, the rule governing the Open_slow output set is:
IF pll Good AND Getting_Lower THEN Open_slow.
Because the Open_slow output requires two antecedent conditions, the
intersect operation must be performed to determine the degree of membership
for the
Open_slow output set as follows:
Open_slow degree of membership = min(pH_good membership,
Getting_lower membership).
An analogous operation is performed on each of the five output sets.
Once the degree of membership for each fuzzy output set is determined, a
weighted average of the fuzzy output set constants is taken, and the result is
the output
control value. The output control value represents a percentage by with the
valve(s)
will be opened or closed from its present position. After a predetermined
amount of
time passes, the process is repeated and a new valve position is determined.
The
period of time may be determined by a determination of how long it would take
a
change in make-up water flow and/or alkaline material addition to the
biofilter to case
a steady pIl in biofilter to he re-established.
Applying specific values for illustrative purposes, if Feedback pH = 1.8, and
Target pH = 2.0, then Error = Target ¨ Feedback = 2.0 - 1.8 = 10.2 p11.
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This error value would have the following degrees of membership in the fuzzy
error sets:
Membership(pn_high) = 0;
Membership(pFl_good) = 0.5; and
Membership(pH_low) = 0.5.
If four minutes earlier the pH reading had been 1.6, then d error/dt = Error-
dot
= (-.4 - -0.2)/4 = -0.05. This error-dot value would have the following
degrees of
membership:
Membership(Getting_higher) = 0.5;
to Membership(No_change) = 0.5; and
Membership(Getting_lower) = 0.
TABLE 6 shows the weighting values for each output set detennined from the
intersect, union and complement operations found in the rule base evaluated
using the
.. corresponding input set degree membership.
TABLE 6: Degrees of Membership in Output Sets
Rule Evaluate to find a weighting Degree of
value for the output set Membership
(Weighting Value)
IF pH_Good THEN MAX (0.5, N/A) 0.5
Do_nothing
IF pH_High THEN MAX (0, N/A) 0.0
Close _fast
IF pH_Low THEN MAX (0.5. N/A 0.5
Open_fast
IF pH_Good AND MIN (0.5, 0) 0.0
Getting_Lower THEN
Open slow
IF pH_Good AND MIN (0.5, 0.5) 0.5
Getting_l ligher THEN
Close_slow
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Evaluating the rule for Do_nothing, the membership value of pH_Good is 0.5,
therefore the weighting value for the fuzzy output set of Do_nothing is 0.5.
Evaluating the rule for Close_fast, the membership value of pli_High is zero,
therefore the scaling or weighting coefficient for the fuzzy output set of
Close_Fast is
zero.
Evaluating the rule for Open_fast, the membership value of pli_Low is 0.5,
therefore the weighting coefficient for the fuzzy output set of Open_fast is
0.5.
Evaluating the rule for Open_Slow, the membership value for pH_Good is 0.5,
while the membership value for Getting_Lower is 0Ø Taking the minimum of
these
two values, the weighting coefficient for Open_Slow is 0Ø
Evaluating the rule for Close_Slow, the membership value for pH_Good is
0.5, while the membership value for Getting_Higher is also 0.5. Taking the
minimum
of these two values, the weighting coefficient for Close Slow is 0.5.
Once the algorithm finds the weighting coefficient of each fuzzy output set by
evaluating the rules in the rule base, each fuzzy output set is scaled
according to the
weight of its corresponding rule. For example, the rule corresponding to the
fuzzy
output set "do nothing" evaluated to 0.5, so this fuzzy set is scaled to 50%.
Once all
fuzzy output sets are scaled appropriately, the algorithm calculates the
centroid, or
center of mass, or the weighted average of output set constants, according to
the
equation:
Ei.5=1 Ci * Mi
5
where,
i = fuzzy output set;
C = output set constant; and
M = degree of membership.
The sum is divided by the number of output sets, which is five in this case.
Application of the above equation to the given values for this scenario
results
in an output value of 0.167.
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With a low of 1.8 (target of pH 2.0) with the pH rising at a rate of
0.05
pH/min, the algorithm therefore responds by opening the valve(s) from present
position(s) by 16.7 cYo of the total valve capacity or span range to increase
make-up
water flow and/or alkaline material addition and raise the pH within the
Walker. The
logic takes into consideration both the current state of the system (pH is
low) and the
behavior of the system (pH is getting higher) to calculate a suitable blended
control
value for the valve position(s).
Total valve capacity is span range: 20mA - 4ma = 16mA. Therefore valve
position is increased by:
to +16mA * 0.167 = +2.672 mA (a crisp output value of the algorithm)
The controller reads the current presently applied to the valve and adds an
additional 2.672 mA to further open the valve.
In instances where a full open position of the valve corresponds to an input
current of 20 mA, limits are set in the programming so that final valve
position is not
set higher than 20mA. When the valve is already opened to its fullest extent
in the 20
mA position but the maximum flow rate of water and/or alkaline material
through the
valve(s) is not sufficient in raising the feedback pH to the target, the
algorithm may
recommend the valve position(s) be increased by a value that comes out of the
fuzzy
logic process, but the actual position(s) of the valve(s) will remain
unchanged.
FIG. 7 shows the resultant "surface" of the output for all combinations of
error
and error-dot in the defined range, based on the rules described above. As
shown in
FIG. 7, the output control value is a function of both the error value and the
dot error
value.
Example 2 Test of Effectiveness of Alkali Addition for Maintaining
Biofilter pH
Alkaline material has not been utilized in the past for neutralizing portions
of
acid within biofilters or biotrickling filters for a number of reasons. One of
these
reasons was a concern that the addition of alkaline material to the media bed
of a
biofilter including HS oxidizing bacteria could negatively affect the health
of the
bacterial population, killing or otherwise deactivating a portion of the
bacterial
CA 02911534 2015-11-05
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population and thus decreasing the ability of the bacteria to remove FLS or
other
undesirable compounds from a contaminated air stream. Accordingly, testing was
performed to determine if the pH of fluid within and/or exiting a biofilter
could be
controlled by the addition of alkaline material to the biofilter media bed
(and a
reduction in make-up water addition) without negatively impacting the
performance
of the biofilter.
Testing was performed in early summer using a 3-stage 3.7 m (12 ft) diameter
biotrickling filter (BTF) in Florida, using 50% caustic soda (sodium
hydroxide) as the
alkaline material in conjunction with a pH control system. Initial water usage
at the
site was 17 gpm on average. After addition of caustic soda and utilizing pH
control,
the water usage dropped to an average of 5 gpm, a 60% reduction, while
maintaining
previous levels of hydrogen sulfide removal.
Testing was conducted over the course of about 5 days (about 120 hours). For
the first 74 hours the system was operated at the maximum site-available make-
up
water rate of roughly 16.9 gpm. From hour 74 to hour 103 the system was
operated
with addition of 50% caustic soda (sodium hydroxide) fed at a rate of 30
gallons per
day (78 mL/min) into the sump of the biofilter. The rate of make-up water was
controlled using an actuated globe valve and a fuzzy logic controller
attempting to
maintain a pH in the sump of the biotrickling filter at 1.72. From hour 103
until the
.. end of testing caustic addition was ten-ninated, but the fuzzy logic
controller was
allowed to continue to adjust make-up water addition as necessary in attempt
to
maintain the pH 1.72 set point.
Prior to addition of caustic the site available water rate of 16.9 gpm was
insufficient to achieve a pH of 1.72, as illustrated in FIG 7.
Make-up water rate during the pre-caustic period averaged 16.3 gpm. The
average pH was 1.61 with a high of 1.70 and a low of 1.56. Average H2S
loadings
were 150 ppm. At hour 74, caustic addition was initiated and the system was
placed
in automatic pH control. This allowed an actuated globe valve to throttle
water in
response to changing pH in attempt to keep pH within a user specified set-
point range.
Water usage dropped to 4.96 gpm and pH was maintained at an average value of
1.73
with a low of 1.70 and a high of 1.78. Average FI2S loadings were 130 ppm,
slightly
CA 02911534 2015-11-05
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lower than the pre-caustic levels of 150 ppm, but comparable. It was important
to
establish that loadings were comparable during these two periods so that the
reduction
in water usage can be attributed primarily to the caustic addition and pH
control and
not a drop in H2S loading. A chart of H2S loading and water flow rate is shown
in
FIG. 9.
At hour 103 the caustic soda feed was terminated, while the pH logic control
was allowed to continue to operate. A steady drop in pH was observed,
beginning as
soon as the caustic soda feed was terminated (FIG. 10). The impact on water
usage is
immediately observable as without the additional neutralization provided by
the
caustic the logic control commanded the water valve to open 100% in attempt to
bring
the pH back up to the 1.72 set point. Even at.maximum flow, the site-available
flow
rate of 16.9 gpm was not sufficient to maintain the 1.72 set point and as a
result, the
valve remained open at maximum flow for the remainder of the testing (FIG. 8).
The final parameter that was evaluated in this test was the inlet H2S vs.
outlet
H2S before, during, and after the caustic addition. It was important to
establish that
the addition of caustic would not have a negative impact on the biology of the
BTF,
and that the reduction in water would not decrease the performance of the BTF.
As
can be seen from FIG. 10, H2S removal was maintained during the experiment
without any large fluctuations in performance during or after caustic
addition. The
one caveat to this is the brief and small rise in outlet 142S from hours 71 ¨
80, which
was a result of a depleted nutrient reservoir. As soon as the nutrient
reservoir was
replenished, the outlet H2S dropped to previous levels, and was maintained to
the end
of the testing.
30
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TABLE 7: Example 2 Operation Summary
Start End Caustic Make- Average Minimum Maximum Average
Time Time Soda Up pH pH pH Influent
Feed Water H2S
(GPD) Feed (PPM)
(GPM)
0 Hours 74 0 16.9 1.61 1.56 1.70 150
Hours
74 103 30 4.96 1.73 1.70 1.78 130
Hours Hours
103 118 0 16.9 1.62 1.52 1.68 150
Hours hours
Example 2 Conclusion
Optimizing water usage in biofiltration systems using fuzzy logic pH control
and alkaline addition is a large step forward in the sustainable design of
these
systems, and exhibits tangible economic and environmental benefits. The pH
control
system allows the water usage to be adjusted automatically to match demand,
reducing unnecessary water expenditures. The alkaline addition reduces water
usage
by neutralizing sulfuric acid instead of simply diluting it. Addition of
caustic soda, to
neutralize a portion of the sulfuric acid, is shown to decrease make-up water
demand.
It is expected that the use other alkaline materials would show a similar
benefit.
lJsing fuzzy logic and alkaline addition together, water usage can be
optimized.
Is Aspects and embodiments disclosed herein are not limited by the type of
biofilter, the media used within the biofilter, the type and location of pH
monitoring
device, the type and location of the control valve and the type of fuzzy logic
controller
used. It is not limited to the removal of H2S and can be used to remove any
compound capable of being removed by a biofilter. More than one biofilter can
be
used in a staged configuration. If a staged configuration is used, the
parameter of
interest, for example, pH, is monitored and controlled from each stage.
Multiple
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fuzzy logic controllers can be used in a staged configuration. An acid and/or
a base
may be introduced into the make-up water to control the pH.
The phraseology and terminology used herein is for the purpose of description
and should not be regarded as limiting. As used herein, the term "plurality"
refers to
.. two or more items or components. The terms "comprising," -including,"
"carrying,"
"having," "containing," and "involving," whether in the written description or
the
claims and the like, are open-ended terms, i.e., to mean "including but not
limited to."
Thus, the use of such terms is meant to encompass the items listed thereafter,
and
equivalents thereof, as well as additional items. Only the transitional
phrases
in "consisting of' and "consisting essentially of," are closed or semi-
closed transitional
phrases, respectively, with respect to the claims. Use of ordinal terms such
as "first,"
"second," "third," and the like in the claims to modify a claim element does
not by
itself connote any priority, precedence, or order of one claim element over
another or
the temporal order in which acts of a method are performed, but are used
merely as
is labels to distinguish one claim element having a certain name from
another element
having a same name (but for use of the ordinal term) to distinguish the claim
elements.
Having thus described several aspects of at least one embodiment, it is to be
appreciated various alterations, modifications, and improvements will readily
occur to
20 those skilled in the art. Any feature described in any embodiment may be
included in
or substituted for any feature of any other embodiment. Such alterations,
modifications, and improvements are intended to be part of this disclosure,
and are
intended to be within the scope of the invention. Accordingly, the foregoing
description and drawings are by way of example only.
25 What is claimed is:
