Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 3 f i 1 ~ ~
FIELD OF THE IN~ENTION
This invention relates to aerobic and ensuing
treatments of domestic sewage and wastewater, and certain
types of industrial wastewaters, and to the renovation of
polluted water in ganeral.
BACKGROUND ART
The most common method for on-site treatment of
domestic sewage and wastewater is a conventional septic
system using a septic tank for anaerobic treatment and a
tile bed, raised hed, or sand filter for aerobic
biofiltration. These solid particle aerobic filters are
readily constructed, and are passive, single-pass
biofilters which require little maintenance. However,
even in ideal conditions, nitrate and phosphorus are
released to the groundwater because the treated water
cannot be collected for further treatment. Loading rates
of potent wastewater such as sept:ic tank effluent in
solid particle media are low, usually 1 5 cm/day (cm3
volume/cm2 area~, and treatment beds therefore require
large volumes of filter media. A tile bed requires
~0-400 m3 of unsaturated soil, and a sand filter requires
about 25-35 m3 of sand and gravel. Signi~icantly higher
loading rates are required for the biofilter to be
transportable. The physical characteristics of natural
filter media such as soil and sand are highly variable.
The large volumes and natural variations preclude pre-
manufacturing the biofilters to consistent specifications
so that performance can be guaranteed at any site.
Aerobic package plants that are manufactured off-site are
generally highly mechanical units with high capital cost
and h gh maintenance requirements.
There is a need for a low-maintenance single-
pass aerobic biofilter with a filter medium that has
predictable physical properties and therefora predictable
2 0 ~
treatment performance. It shou:Ld withstand high loading
rates so it can be pre-manufactured to consistent
specifications in a small volume and transported to site.
Burial of the system and removal of nitrate and other
undesirable contaminants after aerobic treatment is also
advantageous.
In certain countries, polluted water is used
directly for human consumption and cooking, resulting in
sickness and death from water--borne diseases. There is a
need for a low-cost, low-technology, and transportable
aerobic treatment system which removes substantial
amounts of biological pathogens.
An at-grade peat system uses natural peat as
the filter medium and removes nutrients such as nitrogen
and phosphorus. It requires a very specific peat and the
loading rate for septic tank effluent is only 4-5 cm/day,
thereby precluding central manufacture and transport of
the ~50-m3 volume. The peat also requires special handling
to avoid over-compaction. The syst:em cannot be buried and
it removes a significant area of t:he property
(-200-300 m2) from use.
United States patent no. 5,049,265 (Boyd et
al.), granted in 1991, uses biologically active young
sphagnum peat in containers which can be buried. The
increased water-holding capacity enables treatment to
occur at what are stated to be "very high loading rates".
~he peat is mixed with a non-specific amount of peat
fibre to reduce the tendency to clog and pond on the
surface. It is compacted by a non-specific amount to
prevent channelling i~ undercompacted, and clogging if
over-compacted. Because the medium is inconsistent,
treatment performance cannot be assured. Loading rates
of only 7-15 cm/day are cit~d with a preferred rate of
<11 cm/day, which is insufficient to allow pre-
construction and transport of the 20-30 m3 volume to site.
~ 3~ 7~
Synthetic filter media have heen used for
treating relatively clear water. In U.S. patent no.
4,427,5~ uick), granted in 1984, a slab of
polyurethane foam is used as a physical and biological
filter to remove solids and ammonium from aquarium water.
The slab filter must be removed and cleaned frequently
and does not constitute an alternative biofilter for
treating potent wastewater with high solids and
biochemical oxygen demand. Under high loading rates of
potent wast~water, solid foam soon plugs up and becomes
anaerobic, similar to a solid particle biofilter.
DISCLOSURE OF INVENTION
It is an object of the invention to provide a
single-pass aerobic treatment method and apparatus for
potent wastewater in a small contained volume, in view of
the above deficiencies of the prior art. Another object
is to collect the aerobically treated water for removal
of other undesirable contaminants.
The invention includes a high-efficiency
biofiltration module which provides thorough wastewater
treatment in a relatively small contained volume, because
of the distinctive physical properties of a special
absorbent filter medium. It also includes preferably at
least one water-saturated module which further renovates
wastewater while isolated from the natural environment.
Each module generally has a specific treatment function,
including aeration, nitrate or phosphorus removal,
organi~ solvent removal, etc. Modules of similar
function (e.g., two or more aerobic modules and/or two or
more saturated modules) may be combined for larger
capacity.
Wastewater such as septic tank effluent, or any
water which contains biodegradable matter, is introduced
into a free-draining aerobic module which contains the
~ 3 i~ 3~
special absorbent biofilter medium. The aerobic filter
medium is a material with superior water retention and
air-permeability properties, such as polyurethane foam
particles or a foam slab with aeration conduits formed
through it. The particles have open cellular interiors so
that the wastewater is transferred through the interiors
of the particles or through the foam slab, while the
large voids between the particles or the aeration
conduits remain open, precluding plugging by biomat
development and allowing for simultaneous wastewater
loading and air ventilation. By contrast, solid particle
media must be loaded intermittently, then allowed to
drain free to be ventilated. They cannot be loaded and
ventilated at the same time, and therefore have much
~5 lower potential loading rates. In the invention, the
combination of water retention and ventilation allows for
greatly increased loading rates (consistently 10 times or
more higher) over that of solid particle media such as
sand or a solid slab of foam without aeration conduits.
The small voids between solid particles are
readily bridged by biomat. No plugging of the foam
particles in the invention has occurred in laboratory and
field experiments even after 10 months of ~0 cm/day
loading rates and 18 months of continuous use~ Field
units have incurred 10 months of loading at 55 cm/day of
potent wastewater, with 95-9~% removal of total suspended
solids and BOD, and with no sign of plugging (Table 1).
They have incurred surges of 170 cm/day for several days
with insignificant effect on performance. On the other
hand, peat and sand filters plugged up within one month
of use at these high loading rates. In the invention, the
superior physical properties of high surfa~e area, high
water retention, and permeability to air allow treatment
within a small contained volume in a single pass.
2 ~
TABl,e 1: Avcra~ecd r~ s Or i~o~ml ficl~l unit trcating pr;mary clarificr
crf1ucnl(T = 5-14 ~) ~low r~tcs avc~g~ 2(l()0 L/day, or a very
high l~ading rale of 54 cm/day.
n Inrlll~nt Efflu~nt ~/o Rcmov~l
BO~7 (mg/L) 9 123 2.~ 97-99
TS~; 10 ~2 2.X 9~ )8
NH4-N 7 5.9 I.-I -
NO3-N 1() 0.2 22.5
Total coliform ~CFU/lO()mL) lO -1.6c7 7.lc4 99.3-99. 7
10 ~ec~ll colifo~m -lO 5.6ct) 3.4c4 99.5-99.7
The wastewater percolates slowly downwardly
through the unsaturated filter medium in the aerobic
module, during which time it is renovated by microbial
activity. Natural air convection through vents in the
15 container wall ordinarily provides ade~uate treatment of
organic matter, solids, and pathogens. However, to
achieve full nitrification and ammonia removal at low
temperatures, the air flow through the medium should be
increased by means of larger voids between particles or
hy artificial forced air means. If the wastewater
contains adequate dissolved oxygen for the treatment
process, simple vents through th~ container provide
adequate aeration by natural convection.
The aerobically treated water collects at the
bottom of the aerobic module and passes to the next
treatment module in series, usually a saturated module
with a reactive medium for removal of nitrate,
phosphorus, or other constituents. ~lternatively the
aerobically treated water may be discharged directly to
the environment in some cases.
The use of contained volumes enables the
wastewater to be nitrified, collected, and then
denitrified before discharge. Denitrification and
further biological filter treatment can be provided by
one or more saturated modules containing a suitable
2 ~ ~ 6 ~
filter medium. In the water-saturaked module(sl~ non-
reactive media such as synthetic foam particles provide a
protected attachment means for microhes to biodegrade
nitrate or chemicals. Reactive or absorbing media such
as coal, limestone, cellulose, or iron oxides provide a
variety of treatments for removal of unde~irable
constituents.
The invention works effectively in drainage and
soil conditions which are otherwise inappropriate for
conventional, engineered, or peat tile beds. The modules
can be place~ above or below ground and can be designed
to operate with or without electricity.
The invention provides a high rate, single-pass
aerobic biofilter for potent wastewater treatment which
has low main~enance demands, and which can be pre-
manufac~ured off-site and transported to the site for
consistent performance. The invention replaces and
improves upon tile beds and sand filters, and has fewer
maintenance re~uirements than mechanized aeration
systems.
Additional features of t:he invention will
become apparent from a consideration of the drawings and
the ensuing detailed description.
BRIEF DESCRIPTION OF DRAWINGS
Preferred and alternative embodiments of the
invention will now be described in detail, with reference
to the accompanying drawings, in which:
Fig. 1 is a schematic cross-section of the
modular treatment invention which replaces the
conventional tile bed with an aerobic biofilter, and
removes additional constituents in subsequent treatment
modules;
Fig. 2 shows the invention in a vertical
configuration for above-ground installation. Ventilation
3 '~ ~
pipes enhance the aerobic treatment, especially to
provide thorough nitrification at low temperatures;
Fig. 3 is a perspective drawing of an
unsaturated aerobic module with a low profile des~gned
specifically for burial. Wastewater and ventilation air
flow paths through the treatment medium are indicated;
Fig. 4 is a perspective drawing of a water-
saturated module for burial or surface instal'ation.
Water flow paths are circuitous through the module to
10 r~;mi ze contact with the treatment medium;
Fig. 5 is a schematic cross-section showing a
prior art medium such as sand, and
Fig. 6 is a schematic cross-section showing an
example of the medium in the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
A detailed description of the best mode for
carrying out the invention/ and of variations on the
invention, is as set out below:
Basic structure of the aerobic moclule
The aerobic module 100 (shown schematically in
Figs. l and 2 and in detail in Fig. 3) is the key element
in the treatment process and preferably includes a
container 100, a distribution header llO, a treatment
medium 115, and a ventilation means 175. The structure
25 of the container 100 includes a wastewater inlet 105, a
treated water outlet 125, and an optional inspection or
access port 150. It may be buried, as illustrated in
Fig. 1, if the water table is sufficiently low, or
installed on the surface.
The distribution header 110 is embedded
proximate the top of the treatment medium 115 and is
connected to the wastewater inlet 105. The distribution
header 110 is supported by any suitable means.
~ 3 ~
The air ventilation means 175 preferably
includes an air collection header 155 embedded proximate
the hottom of the medium 115, an air inlet 150, an air
outlet 170, and an air ventilation fan 165. The air
collection header 155 is supported by any suitable means.
In another embodiment in which adequate
aeration can be provided by natural convection, the air
ventilation means 175 includes the air inlet 150 or air
outlet 170. In another embodiment, ventilation air may
be introduced through the distribution header 110 along
with the wastewater by means of a pump using compressed
air as a driving means.
The treatment med~um 115 substantially fills
the module 100.
Function/process of the aerobic module
Wastewater 130 is introduced to the aerobic
module 100 through the inlet 105, into the distribution
header 110. The water percolates slowly downwardly
through the absorbent medium 115 where treatment is
efEected, and is discharged through the outlet 125 to
another treatment module, such as a water-saturated
module 200 as shown in Figs. 1 and 4, or to the
environment.
Ventilation air 145 is preferably brought in
through the inlet ~50 and is drawn through the permeable
medium 115 to the collection header 155, and is
discharged through the outlet 170. Alternatively, air
may be introduced by a fan or with the wastewater by
means of an air-driven pump.
Details of the aerobic module elements - Container
The container used for the aerobic module 100
is enclosed and made of any suitable material which is
preferably impermeable, non-reactive, durable, and
structurally sound, such as plastic or concrete.
Tha container may be of any reasonable shape,
and the size of the container is typically approximately
3-5 m3 for a flow of 2000 L/day of potent wastewa~er.
Larger or more numerous modules can be used for larger
flows.
The water and air inlets and outlets 105, 125,
150, 170 are through-wall fittings of durable materials
such as plastic, are appropriately sized, and are
connected by any suitable means.
The inlet 105 is preferably located proximate
the top oE the module and the outlet 125 is located
proximate the bottom, ensuring free drainage of the
wastewater through the module 100. When pump dosed, the
inlet 105 may be proximate the bottom for convenience or
to prevent freezing, although the distribution header
will of course still be proximate th~ top.
The access port 150 should allow for inspection
and maintenance and can double as the air inlet for
ventilation air 145.
Details of aerobic module elements - Distribution header
As seen in Fig. 3, the distribution header 110
is a means to distribute the wastewater evenly and
directly into the upper portions of the medium 115. The
header 1~0 can be made of perforated tubes of durable
plastic such as PVC, appropriately sized, connected by
any suitable means and supported by any suitable means.
If dosing is by pump or siphon surge, the header 110 can
be a series of spray nozzles, preferably discharging onto
splash plates (not shown).
The distribution header 110 is shaped and
perforations therein are sized and positioned so that the
wastewater is evenly distributed onto the medium 115. In
another embodiment, the spray nozzles and splash plates
'. 7 ~ 3
11
in header 110 are arranged to spray evenly onto the
medium 115.
Details of aerobic module elements -
Structure of ventilation means
The air ventilation means 175 preferably
includes a ventilation air inlet 150 (previously
described), an air collection header 155, a ~an 165, and
an air outlet 170 (previously described).
The air collection header 155 is preferably
made of perforated plastic tubes of appropriate size,
connected by any suitable means, and support~d by any
suitable means~ Appropriate perforations are positioned
uniformly along the tubes, such as every 10-20 cm, for
example. Durable screen preferably covers the perforated
tubes to prevent clogging by the medium 115 which
preferably surrounds the header 155.
The air collection header 155 is shaped so that
the ventilation air is distributed as evenly as possible
through the medium 115. For example, in field trials of
the configuration shown in Fig. 2l a long, narrow
rectangular loop of perforated tube was found to be
effective in ventilating a long narrow tank.
In one embodiment, a fan 165 is located
proximate the air outlet 170 to facilitate ventilation of
the module 100. The fan 165 can be electric or wind-
driven.
In another embodiment, the air ventilation
means 175 includes the air inlet 150 or air outlet 170.
In another embodiment, the air ventilation
means 175 includes an air-driven pump and the air outlet
170.
Function - air flow through media and ventilation system
The ventilation air is brought into the module
1~
100 to sustain aerobic biotic activity within the medium
115 and to aerate the water.
Flow can be directed upwardly or downwardly
through the medium 115, but odour in the vented air 148
is minimized if the air flow follows the path of the
wastewater. Odour removal can also be effected by
passing the discharged air 148 through a de-odourizing
media such as natural peat or activated charcoal (not
shown).
Details of aerobic module elements - Structure of media
The treatment medium 115 is a means for
conveying the wastewater 510wly downwardly through the
aerobic module 100 and promoting aeration. Water
treatment within a module of reasonable size is possible
only with the use of medium 115 which has superior water
retention and air permeability properties. Preferred
materials for the medium 115 incl~lde particles of open
cellular synthetic ~oam such as flexible polyurethane
foam, modified synthetic foam, sponge, or other similar
materials. These absorbent particles transmit water
through their interiors by way of the open cells, and
also have high water-retention capacity. The particles
remain water-saturated, but air ventilation occurs
simultaneously through the open voids between t~e
particles. For example, excellent aerobic treatment was
attained in laboratory and field experiments with
particles of polyurethane foam of mixed sizes ranging
generally between about 0.5 and 5 cmO A narrow size
distribution of larger particles provides larger and more
open void spaces between the particles for ease of
aeration, whereas a distribution of small and large
particles provides smaller void spaces and more
restricted air flow.
The medium 115 does not necessarily require a
5~
13
particulate form, but could rather be a solid slab of
plastic foam, for example, with aeration conduits formed
substantially through it to allow diffusion of oxygen
from the conduits to the water contained in the foam
interior. This format would ease the fabrication of the
aerobic module 100. The size and separation of the
aeration conduits would depend on the loading rate and
wastewater potency hut could be 2 cm in diameter, and
distributed through the slab every 10 to 20 cm, for
example. To promote ventilation, the conduits would
preferably be oriented approximately vertically with
optional hori~ontal interconnections.
The medium material preferably should be
durable enough to retain these superior properties over
the expected life span of the system (e.g., 20-30 years)~
Function of the media
The unsaturated aerobic module 100 reproduces
the processes of a conventional tile bed in a small,
aerobic container 100 (e.g., 3-5 m3 for a typical
domicile).
The medium 115 sustains diverse populations of
beneficial biota by providing protection from
desiccation, extreme temperatures, and washouts by
increased flow of wastewater. As can be seen from Fig.
6, the medium 115 allows entry of ventilation air through
the large air-filled ~oid spaces 116 between the water-
filled foam particles 117 (or through the aeration
conduits in the case of solid foam blocks), provides
nutrient-rich wastewater to sustain the biotic
populations, and retains it long enough to be thoroughly
treated in the biofilter. In Fig. 6~ the large arrows
illustrate air flow through the voids, and the small
arrows illustrate wastewater flow through the particles.
By contrast, as can be seen from Fig. 5 (prior
~ ~ r~ ~ 3 7 ~
14
art), ventilation air cannot flow, since the space
between particles is filled with the wastewater.
Basic structure of the saturated module
The saturated module, shown in Fig. 4, includes
a container 200~ and a treatment medium 215 and
preferably, vertical flow baffles 210. The structure of
the container 200 includes a water inlet 205 and a water
outlet 225.
The flow ba~fles 210 are preferably fastened to
the interior walls.
The treatment medium 215 substantially fills
the module.
Th~ module 200 can be placed either adjacent to
or under the aerobic module 100 as desired or as space
limitations demand.
Function/process of the saturated module
The saturated module 200, if used, receives
aerobically treated water through the water inlet 205 and
guides it through the treatment medium 215 around the
flow baffles 210, and discharqes it through the outlet
225. The circuitous flow path ~i izes exposure of the
water to the medium 215.
The saturated module 200 promotes anaerobic
biological activity to remove additional undesirable
constituents discharged from the aerobic module 100.
The saturated module 200 is convenient for
abiotic removal of phosphate and other contaminants,
although an anaerobic environment is not a requirement.
The saturated module 200 is a self-contained,
water-saturated module containing media conducive to the
growth and maintenance of beneficial anaerobic bacteria
and biota. Water is passed to it at a rate sufficient to
allow the media to retaln the effluent to further treat
7 ~
the water before displacement by additional aerobic
effluent.
Details of the saturated module elements - Container
The container used for the saturated modul~ 200
is made of any suitable material which is preferably
impermeable, non-reactive, durable, and structurally
sound, such as plastic or concrete.
The container may be of any reasonable shape,
and the size of the container should be adequate for a
residence time of a~out 1 day.
The containers require an access port (not
shown) with a removable cover for filling and inspection.
The water inlet and outlets 205, 225 are
through-wall fittings of durable materials such as
plastic, are appropriately sized, and are connected by
any suitable means.
The inlet and outlets 205, 225 are proximate
the top of the container to maintain saturated
conditions. The inlet 205 brings aerobically treated
water into the saturated module 200.
Durable screen preferably covers the inside of
the inlet and outlet 20~, 225 to keep the medium 215
inside module 200.
Details of the saturated module elements
Structure and function of the media
The treatment medium 215 includes any natural
or artificial material which promotes biotic and abiotic
treatment under water-saturated conditions, and which is
sustainable over the expected life of the system (e.g.,
20-30 years).
Removal of phosphorus from wastewater is an
abiotic chemical reaction process which occurs when
dissolved phosphorus reacts with calcium carbonate to
2 ~ . '7 ~
16
create a calcium phosphate mineral. Crushed limestone
can therefore be used as a treatmen-t medium 215 to remove
phosphorus. Phosphorus is also adsorbed onto iron oxy-
hydroxides in aci~ic conditions, and therefore certain
crushed iron ores, pellets~ or similar material can ~e
used as treatment media. Organic solvents can be
absorbed onto media such as coal particles which may be
mixed with other media in the saturated modules. Foam
particles may be mixed in with the reactive media to
promote microbial populations.
Polluted water treatment
This is an additional use using the same
apparatus.
The aerobic module 100, with or without the
saturated mvdule 200, can be used to renova~e polluted
water for domestic consumption. Inorganic matter such as
clay and mud is first removed by any suitable
conventional filtration means. Laboratory experiments
show that at 20 C, coliform bacteria are reduced by 5-6
orders of magnitude in <1 m thickness of polyurethane
foam medium 115. The medium 115 acts as a physical
filter as well as a biological filter, and is able to
retain and remove larger harmful biota, such as Giardia
cysts. Tropical climates are ideal for this invention
and are the areas where water-borne diseases are most
prevalent.
Summary
The invention provides a means for single-pass
aerobic treatment of potent wastewater at high loading
rates in a small, contained and transportable volume, by
way of a special absorbent filter medium and ventilation
means. The aerobically treated water can be collected and
further treated in water-saturated modules to remove
.7 ~
17
undesirable constituents such as nitrate and phosphorusO
The invention i5 independent of the natural environment
and does not re~uire high maintenance mechanical devices.
Anaerobic septic tank effluent i5 an obvious wastewater
source for the invention, but any water containing
undesirable biodegradable matter can be treated, such as
polluted surface water. The apparatus can be placed
above or below ground and is equally effective in all
drainage and soil or rock conditions, even conditions
which are inappropriate for conventional or engineered
tile beds.
Accordingly, advanta~es of the invention are
possibly that the wastewater treatment system may:
(1) allow thorough and flexible treatment of
domestic wastewater and certain industrial wastewaters,
including aerobic and ensuing treatments in successive
modules, independently of soil type, precipitation, and
drainage conditions;
(2) treat polluted surface water or groundwater for
disposal or for subsequent use;
(3) treat the wastewater in a small~volume aerobic
module by using absorbent particles instead of solid
particles;
(4) not require a large lot, and not remove any land
from use when buried;
(5) be low-technology, low~maintenance, and easily
installed by semi-skilled workers, and not rely on
mechanical devices or chemical additives, although either
could be included;
(~) not depend on a particular tank shape, size, or
composition for the treatment modules t and may use
common, sustaina~le, and inexpensive materials for the
modules and for the aerobic and saturated treatment
media;
(7) be customized to treat a particular type or
~ '7l~3
18
volume of wastewater by adding a particular treatment
module or by linking modules together;
(8~ be connected directly to a conventional septic
tank for easy retrofitting and not require special
plumbing in the house or building;
(9) be a factory-made standardized product for
predictable performance, ease of inspection and approval,
and is easily transportable; and
(10) be installed above ground or below ground, may
be disguised with attractive panelling or wall cavering,
may be shaded easily from the sun, and may be insulated
and heated easily in permafrost areas.
It should be recognized that not all of the
above advantages will necessarily be achieved
simultaneously in any given installation.
It will be appreciated that the above
description relates to the preferred embodiment by way of
example only. Many variations on the invantion will be
obvious to those knowledgeable in the field, and such
obvious variations are within the scope of the invention
as described and claimed, whether or not expressly
described.
For example, although the above description
refers to the aerobic and saturated modules being defined
by containers, it should be readily appreciated that in
some soil conditions, it may be acceptable to simply
excavate a containment volume, defined by the walls of
the excavation, and position and support the various
components within that excavated containment volume, with
a suitable cover or lid being provided.
It should also be appreciated that although the
preferred embodiment of the invention contemplates
combining aerobic and ensuing treatment stages, an
aerobic stage only may be sufficient for certain
applications.
