Note: Descriptions are shown in the official language in which they were submitted.
DN 2-~665A
The suspended solids range in size from 10 8 microns to 100
microns and larger. Generally, solids 10 microns and larger are settle-
able and may be removed by gravity separation. Solids ranging from
10-3 micron to 10 microns normally will not settle, and generally
require coagulation and flocculation for removal. Solids 10-3 microns
and smaller are generally considered to be dissolved solids.
Most biological sewage treatment systems and processes are
designed to provide for separation of the large nonsoluble particles
and for biological treatment of the particles that will not settle.
Many of these systems are subject to erratic perfor~ance due to
general inflexibility of the prior separation process, i.e. primary
clarification and or screening.
- Primary processes may be subject to highly variable hydraulic
and/or organic loading, resulting in an effluent of varying quality.
lS The biological systems subsequently employed must operate within this
variation in load which may minimize the efficiency of the biological
system.
The suspended and colloidal solids not separated by either
screening or clarification must further be treated by one or more
biological systems in order to meet secondary treatment levels.
The energy, capital, and maintenance costs attendant to those systems
are substantial.
Two such generally accepted biological systems are the
suspended growth modifications of the activated sludge process, and
the rix~d growth system modifications of the trickling rilter process.
These systems can vary from rather crude to highly sophisticated
processes depending on the size of the plant and equipment involved.
The requirement of effluent nitrification will further complicate
the process with additional capital equipment and energy costs.
D~ 2-~665A
6~
--3--
Many attempts have been made to modify the treatmen-t pro-
cesses in order to reduce the energy costs of biological systems.
This has been generally attempted by modification of the process and
design changes of various mechanical components in order to improve
S the solids separation efficiency of the clarifier. An accepted and
effective solids separation technique has been the addition of chemical
coagulant to the influent wastewater which enters the gravity settl-
ing device or clarifier. This technique materially increases the
quantity of solids separated, and reduces the organic lo~d to the
biological system or subsequent treatment systems.
This reduction in load reduces the amoun: of energy re-
quired by the biological processes. Physical-chemical processes,
that have been recommended for the treatment of wastewater, generally
contempla~e the addition of a coagulant and the flocculation of
suspended particles. This is generally performed either in a zone
within the clarifier, or prior to the clarifier, to improve settling
of the suspended solids. The clarified wastewater then may be treated
in a number of ways, such as by adsorbing onto activated carbon or
even refiltering followed by carbon adsorption.
However, the addition of a chemical flocculant and/or a
coagulant adds chemical costs and creates very serious problems, in
many instances, far greater than the advantages obtained by the
reducing of the suspended solids discharged to the biological system.
The precipitation o-f the coagulant generates a chemical
sludge which can be very difficult and very expensive to treat and
dewater. Further, ~he chemical sludge generally adversely affects
the generation of sludge gas.
DN 2-4665
--4--
Organic material treated biologically in an activated sludge
system will generate new and additional cellular material. This
highly structured cellular material ultimately creates a potential
secondary polluting load, and therefore, must be carefully separated
and disposed of in a manner that will not affect the environment.
Therefore, in most biological systems, the activated sludge or
trickling filter humus, both consisting in major part of new cellular
material, ~ust be separated from the wastewater. This is generally
accomplished by secondary clarifiers. The settled sludge may be
returned to a digester for further biological reduction. The
digested sludge is ultimately withdrawn and dewatered by various
means. Ihe digestion, the dewatering and the disposal of the new
cellular materials are difficult and expensive processes.
Granular media ~ilters are currently used to remove
1~ suspended solids particles from wastewaters following other treatment
s~eps. One such filter effectively used in such applications is
described in U.S. Patent Reissue No. 28,458, issued July 1, 1975.
Improvements are shown in U.S. Patent No. 3,817,378, issued June
18, 1974 and U.S. Patent No, 3,840,117, issued October 8, 1974.
An effective method and apparatus for cleaning grease and
oil from the media of granular media filters is described in U.S.
Patent No. 4,032,443, issued J~me 28, 1977.
An apparatus and method ror separating and concentrating
solids from filter backwash liquid is disclosed in U.S. Patent No.
~5 3,792,773.
-5~
SUMMARY OF T~IE INVENTION
Many of the disadvantages of conventional systems of waste-
water treatment are overcome by the present invention which rela-tes
to an improved method for removing and collecting organic solids from
wastewater containing domestic sewage, without the use of coagulant
chemicals. A major improvement is the additional energy potential of
the increased quantity of chemical-free primary sludge. Another major
advantage is a corresponding reduction in production of new cellular
plant material.
The present invention is a wastewater treatment process for
the removal of suspended and colloidal materials, including greases
and oils, from previously untreated wastewater which contains domestic
sewage, comprising the steps of:
a. passing said wastewater containing domes-tic sewage
to a clarifier or screening device to remove a portion of the
materials and clarify said wastewater, without addition of
coagulating chemical;
b. passing clarified wastewater without addition
of coagulating chemical through a granular medium filter
comprising a single medium within a filter tan~ to an
underdrain cavity to produce filtrate containing less
suspended solids than present in the untreated wastewater;
c. intermittently passing air upwardly through the
granular medium to reduce resistance to flow through the
medium and inhibit anaerobic biological activity therein,
without disturbing the filter medium integrity; and
d. intermittently backwashing said filter with a
portion of said filtrate and a surfactan-t and/or oxidi~ing
agent to remove accumulated deleterious materials.
~0
DN 2-4665A
Thus, was-tewater con~aining domestic sewage from a device
such as a screen, seive and/or primary clarifier is passed through a
granular medium filter without prior biological, chemical or physical-
chemical treatment. Alternatively, the solids removal device may be
eliminated entirely; wastewater is passed directly to the inlet of
the filter and nonsettleable and colloidal solids are trapped by the
filter medium and adsorbed by the filter medium surface.
The effectiveness of the removal of these nonsettleable
solids is a function of the application rate and the physical char-
acteristic of the medium, typically sand. Generally, at least 60percent of the suspended material is remo~red by a single filter.
Solids are allowed to accumulate in the filter medium until the
resistance through the filter medium causes the water level above
the medium to reach a predetermined level, at which time the filter
is bac~washed, and the deleterio~ls materials previously trapped and
adsorbed are scrubbed and washed from the medium.
In accordance with the invention, there is also provided
an improvement in the interception æ.ld storage of colloidal and sus-
pended particles by periodically reducing the resistance of the fil-
tering medium, body and surface by passing air upwardly through themedium intermittently to improve the porosity and to retard anaerobic
deco~position. This air is motivated upwardly by filtrate rising
within the underdrain cavity and displ2cing the air. The upward
movement of air is sufficient to move deleterious materials into
the interior of the filter bed where such materials are temporari~y
stored, without disturbing the integrity of the filter mediu~.
DN 2-4665A
With another aspect of the present invention, there is
provided a method of bacl~ashing, utilizing vertical hydraulic jets
intermittently with air to provide high velocity agitation and medium
movement at a variable subfluidized rate to improve the effectiveness
of the backwashing system and utilize a minimum of backwash water.
In accordance with another aspect of the present invention,
the bac~ashed water is directed to a holding tank where the pre-
viously nonsettleable particles, now in the backwash water, agglo-
merate and settle. Greases and oils are also permitted to agglomer-
ate for skimming. The settled solids are allowed to concentrat~generally without the addition of chemicals. In accordance with
another aspect of the present invention, the backwashed solids are
pumped to a digester for anaerobic stabilization of the organic
material, and biological generation of a methane and carbon dioxide
fuel gas.
In accordance with another aspect of the present invention,
the clarified backwashed water may be directed back to the inlet of
the filter for refiltering and under some conditions, may be directed
to a receiving stream or water course such as a lake, riYer, ocean,
etc.
~ he polluting characteristics of the filtrate are materially
reduced by the removal of the colloidal and nonsettleable ~olids
present in the clarified wastewater.
In accordance with another aspect of the present invention,
2S oxygen is added to the liquid body by impingement, by diffuser and
by pulsing through the filtering medium, in order to minimize the
normal oxygen deficiency of clarified waste and counter anaerobic
conditions in the medium and liquid filter body.
DN 2-~665A
1 6~
In accordance with another aspect of the invention, there
is provided an improved medium regeneration cycle that removes grease,
oil and bio~a attached to the medillm surface by emulsification and
the hydraulic and pneumatically induced agitation of the medium bed.
Additionally, an o.~idizing agent such as hypochlorite with or without
a surfactant is used to regenerate the medium surfaces. Preferably,
however, a non-halogen oxidizing agent such as hydrogen peroxide,
oxygen containing gas or liquid, or ozone is used either with or
without the detergent or surfactant, thus avoiding the creation of
chlorinated hydrocarbons.
Another major aspect oE this invention is the staging of
the filtration processes in order to increase the quantity of unsettled
and colloidal solids removed from the liquid waste. Typically, in a
two-stage filter system, the secondary filtrate contains less than
25 percent of the suspended solids in the untreated ~ater, and the
accompanying low BOD. Such filtrate may generally be discharged
directly to a water course, without further biological treatment.
A further aspect of this invention is the use of very small
quantities of coagulant between the staging of the filter processes,
in ordeer to further reduce the very fine solids that will neither
be trapped nor adsorbed to the medium surface. The coagulation
chemical is rapidly mixed with the primary filtrate and passed to
the second filter without a flocculation step. Such a process will
typically result in a secondary filtrate having less than 20 mg/l
suspended solids and may contain less BOD than normally attributed
to secondary processes. The first stage filter removes the largest
portion of solids, and only very small quantities of coagulant are
required in the second stage. This the effect of such chemical
upon subsequent sludge treatment is negligible.
DN 2-~665A
Yet another object of the present invention is the use of
a filter to treat excess flows that may adversely affect an existing
or fixed design biological system by bypassing excess flows around
the biological system through a fine medium filter and remove suffi-
cient quantities of suspended solids from this bypassed wastewater,as well as from the biologically treated wastewater. This permits
the ~iltering of the treated and untreated wastewater to meet effluent
requirements. In this invention the efficiency of the biological
process is maintained. The biological process is protected against
hydraulic overload, and overall performance is ensured.
A further aspect of this invention is the combination of
two stage filtration within a single vessel providing for varying head
conditions relative to quantities of flow and designed to accept a
portion of extremely high flows through more coarse filtering media.
~le two stage filter provides the opportunity for more than
one sand size and varying application rates for a given filtering
load.
Another aspect of this invention is the scrubbing o~ the
vertical walls of the filter tank on an automatic select basis during
a backwash. A cleaning agent such as a detergent and oxidizing agent
or alternately a surfactant and an oxidizing agent may be added to
the backwash water to further clean the walls. Cleaning agent addition
may be controlled manually or on an automatic select basis. A non~
halogen oxidizing agent is preferred.
DM 2-~665A
G~
--10--
Another aspect of this invention is the addition of an
oxidizing or sterilizing liquid to the backwash liquid at the end of
the backwash cycle in order to control biota growth. This steriliz-
ing or oxidizing liquid will also cause the oxidation, emulsification
or removal of the previously attached organic substances on the
medium surfaces resulting from the filtration of the clarified waste
through the fine sand medium. The medium surfaces are e~fectively
utilized to adsorb some of the organic components that make up soluble
BOD.
Another aspect of this invention is the ability to minimize
the dele~erious effect of the colloidal and suspended particles which
plug the pores of activated carbon and coat the carbon surfaces with
organic substances that limit the effective use of activated carbon.
Another aspect of this invention is an improved underdrain
system that effectively distributes the oxidizing or sterilizing liquid
into the filter medium without premature mixing with backwash liquid
and detergent or surfactant.
BRIEF 3ESCRIPTION OF THE DRAWINGS
Figure l is a schematic line drawing of a conventional waste
water treatment system, employing as major elements a primary clarifier9
a biological treatment system, a final clarifier and a sludge digester.
Figure 2 is a schematic line drawing of the preferred embodi-
ment of the invention, illustrating the many alterr.ate treatment systems
that may be utilized.
DN 2-4665~
--11--
Figure 3 is a schematic line drawing of the invention,
combined with biological treatment.
Figure 4 i5 a schematic line drawing of the inventlon,
combined with a biological treatment system followed by a second filter.
Figure 5 is a schematic of a physical-chemical treatment
process placed between two filters.
Figure 6 is a schematic showing application of the invention
to a waste treatment system subject to high variations in influent
flows, illustrating treatment approaches for bypassed Elows.
Figure 7 is a sectional view of the invention utilized in
treating bypassed flows.
Figure 3 is a sectional view of the inventio~ illustrating
the wall washing and pulsed bed system.
Figure ~ is a sectional view of the underdrain support
system described in this invention.
Figure 10 is a sectional detail of an outlet nozzle of the
underdrain support system described in this invention.
Figure 11 is a sectional view of an alternate of the nozzle
detail of the underdrain support system described in this invention.
DESCRIPTIO~ OF THE PREFERRED E~BODrMENT
.
Reductions of total biochemical oxygen demand (BOD), suspend-
ed solids and soluble BOD of clarified domestic wastewater by parallel
granular medium filters are illustrated in Table I, in which the
filters utilized granular media consisting of quartz or 0.35 mm or
DN 2-4665A
6~
-12-
0.45 ~m effective size, respectively, 10 inch (25.4 cm) sand depth
and application rates of 80 liters per minute per square meter
(2 gpmlt2).
Table I
Filter Filter Filter
#1 #2
InfluentEffluentEffluent
Sand Size, mm 0.35 0.45
Suspended Solids, mg/l 81.3 20.8 25.7
10 Removal Efficiency ~ (74.6) (68.6)
Turbidity FTU 46 23 24
Total BOD5, mg/l 131.5 49.0 53.9
Removal Efficiencv ~ (62-7) (59.0)
Soluble BOD5, mg/l 35.3 23.3 24.9
15 Removal Efficiency ~ (34.0) (29.3)
Average Filter Run Length, hr. 3.0 6.0
Backwash to Filtrate Ratio, 1/1 0.168 0.088
A significant factor generally overlooked in the design and
development of waste treatment systems is tha-t the majority of the
organic polluting load in wastewater, either sho~n as Theoretical
Oxygen Demand (TOD), Chemical Oxygen Demand (COD), or Biochemical
Oxygen Demand (BOD), is contained in the nonsettleable suspended and
colloidal solids. Such solids are present in domestic sewage. For
example, wastewater solids that have been separated by size have the
~5 organic impact shown in Table II. Basically, 66 percent of the
organic polluting load is contained in the suspended solids of particle
~ ~ DN 2-4665A
-13-
size 8 microns and smaller as measured by COD. It is generally
conceded that suspended solids 8 microns and smaller are not settle-
able by themselves.
The significance of the polluting load of clarified or
S settled wastewater may be further illustrated by a size and weight
analysis of a clarified wastewater sample. The sample of Table II
was drawn from the Lorain Ohio Waste Water Treatment Plant, and is
not untgpical of clarified wastewater which contains domestic se~age.
The wastewater sample was then filtered progressively through increas-
ingly smaller pore membrane filters. The quantity of solids retainedon each filter was then determined, as well as the chemical oxygen
demand ~COD) for the solids retained.
Table II
Lorain Ohio Primary Effluent
Settled Wastewater TSS 84.5 mg/l; COD 182 mg/l
FILTE~ PORE TSS RETAINED BYCOD PASSED THROUGH
SIZE um FILTER, mo/l FILTER, mg/l
O
8.00 38.4 121.0
3.00 14.7 80.9
1.20 10.7 62.7
.80 11.5 62.7
.45 7.6 65.9
.22 1.6 48.9
The reduction of soluble BOD is another aspect of this
invention. The reduc~ion of soluble BOD by fine sand filtration is
quite significant, and becomes even more substantial at lower hydraulic
application rates. For example, tests have shown that the reduction
~8~ D~ 2-~665A
-14-
in soluble BOD ranges from a high of 34 percent reduction, to a low
of 5.6 percent. Soluble BOD is a definition rather than a true
description. Colloidal particles that can pass through a 0.45 micron
filter are calculated to be part of the soluble fraction which are
measured as soluble BOD.
A substantial quantity of the colloidal material that does
pass through a 0.45 micron membrane filter will attach itself and be
adsorbed to the grain surface in a granular medium filter. Some of
the organics in the solution are also rapidly biologically converted
to biomass as ~astewater is passed through a granular bed. The
quantity removed is a function of the application rate, and size and
depth of the sand. Table III, delineating a specific series of tests,
illustrates the effectiveness of the removal of soluble BOD by the
present invention. Therefore, sing1e or multi-stage filtering not
only removes the measurable non-settleable solids, but materially
reduces the soluble fraction of the organic load.
Table III
Soluble BOD5 Reduction (Percent)
FLOW RATE 0.35 mm 0.45 mm
2 GPM/FT2 34 29.5
5 GPM/FT2 18.3 15
8 GPM/FT2 7.2 5.6
Referring now to the drawings, wherein the sbowings are
for the purpose of illustrating the preferred embodiments of the
invention only, and not for the purpose of limiting same.
DN 2 ~665A
-15-
Referring to Figure 1, a conventional, biological waste
treatment process is delineated. The raw wastewater inlet conduit 10
is directed to the comminutor or screening device 20, and through a
conduit 11 to the primary settler or primary clarifier 100. The
clarified liquid is directed through conduit 110 to the biological
process 400, wherein the waste is biologically treated, generating
new cellular material, and is directed through conduit 410 to the
final settling tank 500. A major por~ion of the sludge solids is
settled in clariier 500 and withdrawn through conduit 520. A portion
of the sludge is recycled to the biological process via conduit 521.
The excess or waste sludge then mixes with the sludge that has ~een
withdrawn from primary clarifier 100 through conduit 120 and the ad-
mixture of the waste sludge and the primary sludge is directed through
conduit. 121 to digester 800, wherein the sludge is further treated,
1~ and a portion of the organics is converted to methane and carbon dioxide.
The excess waste sludge from clarifier 500 may be passed directly to
diges~er 800, and avoid the mixing process in conduit 121, depending
upon the Engineer's preference.
Figure 2 shows a schematic block diagram of the present
invention, wherein a ~ilter system 200 is placed following a primary
settling tank or clarifier 100. The wastewater treatment system in-
cludes an inlet wastewater conduit 10, wherein wastewater is directed
to comminuting and/or coarse screening device 20, then directed by
conduit 11 to a primary clarifier 100. The clarified effluent leaves
the primary clarifier 100 through conduit 110 to the inlet of filter
200.
in primary filtrate to nitrite and nitrate;
d. passing nitrified primary filtrate through a second granular
medium filter ~ a second filter tank to a second underdrain cavity, to
produce secondary filtrate containing less than 20 mg/l suspended solids.
e. intermittently passing air upwardly through each granular
medium to reduce resistance to flow through the media, and inhibit anaerobic
biological activity therein;
f. intermittently backwashing said Eirst filter with a portion
of said primary filtrate and a surfactant and/or oxidizing agent to remove
accumulated deleterious material; and
g. intermittently backwashing said second filter with a portion
of said secondary filtrate and a surfactant and/or oxidizing agenL to remove
accumulated deleterious material.
Such treatment readily produces a secondary filtrate containing
less than 20 mg/l suspended solids and typically less than 20 mg/l BOD5 when
the fixed media filter with appropriate depth of at least 4 feet is operated
at a rate equal to or less than 0.34 GPM per square foot typically 0.10 -
0.34 GPM/ft . With some wastewaters, high levels of nitrification can be
achieved at dosing rates as high as 1.0 GPM/ft . The secondary filtrate will
contain less than 1.5 mg/l NH4-N if the nitrification treatment temperature
exceeds 68 F, while the same fixed media filter treating unfiltered waste-
water at the same dosing rate will provide li-ttle if any nitrification.
Thus, adding the prior step of granular medium filtration in accordance with
this invention enables nitrification to proceed at a high rate in a fixed
media filter, where little or no nitrification would otherwise occur.
The backwash from filter 200 is discharged through conduit ~20 to
clarifier 300, wherein the backwashed solids are permitted to settle, and the
clarifier supernatant is returned to the inlet of filter 200 through conduit
310 and filter inlet conduit 110. The quality of the supernatant may be
enhanced by the addition of coagulation chemicals. The settled sludge from
clarifier 300 is withdrawn through conduit 320 and directed to the sludge
withdrawal line 122 which transports sludge from the primary clarifier 100
- 17 -
~,
DN 2 4665A
-16-
As shown in Figure 2, the filtrate in conduit 210 is directed
to one or more of subsequent elements of treatment, such as biological
treatment, which may be either the suspended growth or attached growth
systemO Alternately the filtration may be followed by second stage
filtration, and then -treated by activated carbon or biological treat-
ment for removal of organic matter and/or nitrogen, or discharged to
a receiving stream, or some other ~eans of treatment or reuse. The
necessity for the optional second stage filtration is a function of
wastewater quality and particle siæe distribution, as well as govern-
mental discharge requirements. In many cases the load to the biologi-
cal system is so reduced that adequate biological treatment is obtain-
ed, for example, in a trickling filter without any recirculation.
Another embodiment of this inYention is,a wastewater treat-
ment process for the removal of suspended and colloidal materials,
lS including greases and oils, proteinaceous compounds and ammonia
nitrogen from previously untreated wastewater which contains domestic
sewage, comprising:
a. passing said wastewater containing domestic sewage
to a clarifier or screening device to remove a portion of the
2~ materials and clarify said wastewater, without addition of
chemical;
b. passing clarified wastewater without addition of
chemical through a first granular fil~er within a first filter
` tank to a first underdrain cavity, to produce a primary filtrate;
c. passing said primary filtrate through a fixed
media filter such as a trickling filter having nitrifying micro-
organisms growing on said fixed media, to oxidize said nitrogen
D~l 2 /~665A
-18-
through conduit 120.
The filtrate quality will depend on the rate of wastewater
application, wastewater pollutant concentrations, the bed depth and
medium grain size utilized in filter 200. The filtrate quality can
be further enhanced by a series of subsequent treatment options,
depending upon the ultimate water quality requirement.
The energy requirement for subsequent treatment of clarified
wastewater will be materially reduced as a result of the reductlon in
organic polluting load of the clarified wastewater accomplished by
filter 200.
Additionally, the sludge created by the concentrated solids
in the backwash water f~-om filter 200 is added to the sludge removed
in the primary settling tank or clarifier 100. ~le total quantity
of primary sludge is the sum of the primary sludge developed by both
the gravity clarifier 100, and filter 200. The fact that no coagulant
is added to the inlet of either the primary settling tank or the
filter, ensures that the total sludge withdrawn shall contain a
minimum of treatment chemicals.
Anaerobic biological production of fuel gas methane from
sewage sludge is known to proceed more readily and efficiently when
the ratio of primary to secondary biological sludge is high. This
invention results in materially increased primary solids and signifi-
cantly reduced secondary solids quantities.
For example, a typical domestic wastewater contains 160 mgll
of suspended solids, one halE fo which is removed by simple primary
treatment without chemicals.
~ DN 2-~665A
--19--
The clarified wastewater typically has the following analysis:
Suspended Solids 80 mg/l
BOD5 130 mg/l
In standard treatment, the clarified ~7astewater is subjected
to activated sludge treatment to meet secondary governmental effluent
standards. Approximately 70 mg/l of biological sludge solids will be
produced. Thus the biological solids comprise nearly one half of the
total solids load which normally is anaerobically digested.
In the present invention the clarified wastewater is filtered
through a gr~nular medium to meet the secondary standards, thus re-
placing the biological step which has high equipment and operating
costs.
Additionally, no biological treatment solids are passed to
the anaerobic digester; therefore gas production and solids reduction
as well as subsequent solids dewatering are all enhanced.
~ dhere the biological treatment step is preceded by granular
medium filtration, the greatly reduced quantity of new cellular
materlal results in much improved digester performance.
Referring further to Figure 2, conduit 151 following second
stage filtration may direct the filtrate to an activated carbon con-
tactor. Filtrate may alternately be treated in a biological system
as further sho~n in Figure 3, or discharged to a stream or reused.
Alternately, second stage filtration may be omitted and single stage
filtrate be directed to the named alternate processes.
DM 2-4665A
20-
A major advantage of the invention is the reduction of the
organic pollu~ing load to all of the subsequent treatment systems by
filter 200, thereby reducing the energy and capital requirements.
Referring now to Figure 3, wherein the same type of secondary
biological process is illustrated as in Figure 13 the secondary treat-
ment plant process may now be modified by the use of a filter installed
in the clarified effluent conduit 110. The filtrate contained in
outlet 210 requires significantly reduced biological treatment.
Biologically treated wastes may be directed to a final settler or
clarifier 500, or directed to subsequent filter 700 as sh~wn in
Figure 4, and then to the chlorine contact tank 600.
Also, in accordance with this in~ention, the primary sludge
is withdrawn from the primary settling tank lO0 through co~lduit 120.
The generally nonsettleable and colloidal solids in the clarified
wastewater are intercepted then by filter 200, the filtrate from
filter 200 being then directed through conduit 210 to the biological
process 400. The backwashed water in conduit 220 i9 directed to the
inlet of backwash separator 300, wherein the backwashed solids are
allowed to settle, and are discharged and mixed with the solids of
the primary settling tank lO0, thus increaseing the total primary
solids removed from the process.
The organic load, based on the greater removal of organic
solids, is materially reduced to the biological process. Depending
again on the application and medium si~e, the residual organic load
to the biological process can be reduced to the point tha~ the new
cell growth may be effectively intercepted by a second filter of
D~l Z-4665A
-21-
generally the same type as utilized in filter 200 and a final settler
is not needed. The filter 700 will then intercept the admixture of
solids and new cells and return those solids to the inlet of the
biological process 400 through conduit 721 as shown in Figure 4.
Excess waste solids are then discharged to the backwash separator 300
through conduit 722,
In accordance with this invention, the potential for growth
of new cellular material has been limited by the reduction in suspended
and non-settleable matter by granular medium filtration. The growth
of new cells is proportional to the organic loading in the wastewater
entering the biological process through conduit 210.
For example, assuming a new cell growth rate of 0.4 lb.
new cells per lb. BOD removed, a filtrate residual containing 50 mg!l
o ~OD5 would generate only 20 mg/l of new cells. ~astewater with
suspended solids level of less than 30 mg/l of solids and proportion-
ate values of biochemical oxygen demand may be classified as second-
ary effluent. In the event that the suspended solids are in excess
of the permitted stream requirements of the particular water course,
a second filter may be added and the 20 mg/l of new ce1ls may easily
be separated out by the filter 700, and the filtrate through conduit
710 will meet a low solids stream requirement. Should stream re~
quirements be such that the solids to be discharged are not in excess
of the requirement, no additional treatment may be required.
Now referring to Figure 5, settled primary effluent ls
directed to the first stage filter 200 and the filtrate directed
through conduit 210 to mixing chamber 30 where very small concen-
trations of coagulant from vessel 40 are pumped into mixing chamber
30 through conduit 50. Coagulant is mixed in mixing chamber 30 with
DN 2-~665A
-22-
first-stage filtrate from filter 200 and the coagulant-filtrate ad-
mixture discharged to filter 700 through conduit 211, without a
flocculation step. The coagulant-filtrate admixture is then filtered
through filter 700, and the second-stage filtrate discharged through
conduit 710. The backwash liquid from the first stage filter 200 is
discharged to the backwash holding tank 300 through conduit 220, and
the backwash from filter 700 is also directed to the same backwash
solids separating device through conduit 720. The settled sludge in
vessel 300 is discharged through conduit 320 and mixed with the sludge
10 removed from the primary vessel 100 through conduit 120, and the
combined sludge volume is directed to the digester S00 through
conduit 123.
The effluent from conduit 710 may then be treated optionally
in a number of ways in accordance with the requirements of the ultimate
use or disposition of the treated wastewater. Water that is refiltered
may be directed as shown in ~igure 2 to a full series of further treat-
ment steps depending on ultimate use and requirement. This type of
system greatly reduces or completely eliminates the biological cellular
growth material normally associated with biological treatment plants,
and at the same time provides a high quali~y effluent. The limitation,
of course, will be the soluble constituents now not removable by
filtration. Wastewater effluent, from which the suspended solids
and colloidal solids have been removed by filtration, is readily
amenable to contact with activated carbon for the adsorption of
residual organics. This type of pretreatment can effectiYely save
tremendous space and energy and provide an effluent of controlled
quality. This is especially true in the many areas of water reuse.
DN 2-4665
-~3-
The filtering process will reduce the energy requirements normally
associated with conventional wastewater treatment providing similar
performance.
Reerri~g now to Figure 6, the primary filtration approach
may be applied most successfully to wastewater treatment systems that
are subjected to extremely high variations in flows, such as during
storms, wherein the existing biological processes are threatened by
a hydraulic overload. Now referring specifically to the drawing
Figure 6, influent conduit 10 represents the inflow conduit of the
wastewater, including variable volumes of storm water passing through
a comminuting or screening device 20, then through an alternate flow
diversion chamber and excess flow weir 60 into the primary settling
chamber 100. lhe clarified effluent in conduit 110 is directed to
hydraulic control chamber 80, wherein the first stage excess flow
will be directed around ~he biological process 400 and the final
clarifier 500 into conduit 510 which is the influent to filter 20G.
Backwash water is directed from filter 200 to conduit 220 to settling
vessel 300. The supernatant from settling vessel 300 is returned to
conduit 510 through conduit 310. The settled sludge is returned
through conduit 320 and mixed with che settled sludge from clarifier
100 through conduit 120 and directed for further treatment through
conduit 124 to a digester or other sludge treatment process.
In accordance with this invention, the excess flows are
directed around the biological process to protect the integrity of
the biological process from upset by hydraulic impact, and further
reduce the biochemical o~ygen demand of the bypassed flow passing
through conduit 90, by the action of filter 200 to reduce the
DN 2-4665A
-24-
suspended solids.
Referring again to Figure 6, excess flows may also be
directed around the primary clarifier 10~, in the event designs in-
dicate that maximum hydraulic conditions to clarifier 100 would be
exceeded. Therefore, a diverting chamber 60 may be installed ahead
of primary clarifier 1~0 and the flows beyond design values may be
directed through conduit 70 into bypass conduit 91 to conduit 510
into filter 200 for further improvement through the removal of sus-
pended solids by filtration.
Another aspect of this invention is the ability of the
filtering device to meet variable filtrate requirements as the influent
volumes change due to the impact of storm water flow and dry wea~h2r
flow. During dry weather, when wastewater flows are low, the residence
times of solids in the sewer lines is relatively long, resulting in
considerable solubilization of pollutant material. Wastewater BOD5
is high.
On the other hand, high water levels during wet weather
flush the sewer lines quickly. The wastewater is not only diluted
by the extra water but is more "fresh", e.g., less solubilization
has occurred.
While high flows hinder operation of con~entional biologi-
cal treatment systems, the pollutant materials in such high-flow
wastewaters are more amendable to removal by granular medium filtr-
ation than are pollutants in low-flow wastewaters. As a result,
bypassing excess flows of wastewater around biological treatment
systems to a granular medium filter will maintain a high biological
DN 2-4665~
treatment level while providing a high level of filtration ~reatment
to the excess ~lows. The result is a highly acceptable effluent at
a time when the effluent quality is normally deteriorated.
In another embodiment, the once-through granular medium
ilter of Figure 7 provides for effective and efficient treatment
of wastewater under highly variable flow rates. Referring to
Figure 7, the treated and bypassed influent flows are directed to
filter vessel 200 through conduit 510 as previously illustrated in
Figure 6. Referring back to Figure 7, a flow indicator 530 located
in conduit 510 signals the quantity of flow to the filter. Within
preset limits and at the lower levels of the range, valve 512 would
remain open and valve 514 remain closed. The dry weather flow at
low water levels from conduit 510 enters filter 200 at a low hydraulic
head level over the filter media 250. As the flows increase, flow
meter 530 would then signal valves 512 to close and valve 514 to
open, and allow the water level to enter filter 200 at a higher point.
Simultaneously, flow indicator 530 would change the operating
level from the previous operating water level indicated at level 240,
to level 242, and eventually to 244, thus increasing the capacity of
the filter. As the flow further increases, a signal from flow indicator
530 would then limit the flow through flow diversion bo~ 516 to filter
200 and cause a proportionate flow to pass through conduit 518 in~o
filter vessel 200A located entirely in the confines of fil-ter vessel
200. The filtrates from filter 200 and filter 200A passing through
conduits 223 and 223A are then blended together into a single conduit
for plant effluent. The operating le~els within filter 200, in turn,
DN 2~4665A
are changed proportional to the flow demand as indicated in control
by 10w indicator 530.
Referring again to Figur~ 7, backwash trough 260 is located
over the filter sand 250, and prior to backwash, the water level 240
5 i5 lowered to the level of the backwash trough weir 262. In the prior
art, this volume of water over the filter trough weir 262 is added to
the backwash water volume, thereby increasing the amount of bac~ash
water to be treated.
As the operating water level changes as directed by flow
indicator to 242 or 244 or to intermediatP levels, the volume of
wasted water is, of course, increased.
One aspect of this invention is the placement of filter
cell 200A entirely within the confines of filter 200 thus reducing
the volume of water over the filter bed 150 without reducing the
efficiency of the filter system. The volume of wasted water is thus
reduced.
Another aspect of this invention is the dumping of the
volume of water over trough weir 262 into 3 separate dump chamber
270 prior to the start of the bacl~wash pump 222, thus greatly re-
ducing the volume of bac~ash water to be treated. The sequenceof backwash operation is initiated by a backwash requirement signal
from level sensor 352, 354, or 356 proportionate to the appropriate
water level 240, 242, or 244 as controlled by the signal from flow
indicator 530. Upon signal, valve 277 opens and allows the body of
liquid over the trough weir 262 to drain through line 266 to waste-
water dump chamber 270 wherein the total volume of liquid over the
DN 2--4665A
-27-
weir 262 is ~ow retained. After the liquid body over weir 262 is
drained as provided by a signal from a timing device9 valve 277 is
closed and valve 278 is opened, backwash pump 222 is then energi2ed,
valve 226 is opened, valve 225 is closed, and the backwash liquid
is the~ directed into the underdrain ca~ity 208 and through the sand
bed 250 ta the overflow weir 262. The backwash liquid is then
directed to the backwash holding tank 290 and may be further treated
as described in my U.S. Patent 3,792,773. The liquid volume now
retained in tank 270 is pumped into filter 200 by pump 272 after
pump 2~22 has been shut down, valve 226 is closed and valve 225 has
opened, and the filtrate from filter 200 is again directed to the
filtrate holding tank "clea~ell" 280.
The volume of liquid over weir 262 contains materially
less solids than the backwash liquid. The mixing of these volumes
increases the total liquid volume and increases the cost of treating
that liquid volume by diluting the back~ash admixture. This dilution
will reduce the ability of the admaxture to reach the point of auto
flocculation without the addition of chemicals. Auto flocculation
or agglomeration proceeds much more readily as an increased concen-
tration of solids.
The filter chamber head water dumping, sho~n as part ofthe filter system in Figure 7 with other aspects of this invention,
may be used independently. This aspect of reduced volume of head
water results in an improvement i~ operating costs and efficiencies
in any system of filtration where volumes of water are stored over
the level of the backwash weir.
DN 2-4665A
-28-
By modification of the piping, this filter may also be
used to treat wastewater in two consecutive stages. In this case,
wastewater is first passed through the upper filter bed 250A and
then through filter bed 250. Granular medium in the first bed 250A
will be relatively coarse while bed 250 will be composed of finer
granules ~
Now, referring ~o Figure 8, another feature o filter 200
is illustrated. ~erimeter washing ring 226 is placed at the upper
wall of filter 200 with nozzles 228 placed to scour the walls of the
LO filter 200. Washing ring supply conduit 224 communicates with back-
wash pump 222 and chemical feed pump 262 through conduit 266. One
aspect of this invention is the utilization of a specialty cleansing
solution to bac~ash the walls of the filter at preselec-ted periods.
The filtering of primary waste contemplates the introduction of highly
contaminated biological wastes into the filter cell. Biological
wastes will coat the walls, whereon biota may grow. In turn, the
absence of oxygen will cause objectionable growths and odors. Effect-
ive cleansing and disinfection of the walls is necessary to improve
the total operation of the filter system.
Another aspect of this invention is the improved backwashing
system for removal of the particles that are tenaceiously attached to
the medium grains and the introduction of cleansing and disinfecting
solution into the medium at preselected periods to retard biota
grow~h.
DN 2-4665A
-29-
Now referring to Figure 8 and specifically drawing attention
to the backwash technique, a high pressure air system is alternately
provided through air pressure pump 280, directing air through conduit
282 to static mixer 284, mixing air and backwash water and directing
this admixture to the underdrain cavity 208.
The air intermittently fed into the static mixer 284 causes
an additional agitation of the medium 250, due to the pulsating vertical
rising jets 292 in the underdrain system. Thus the backwash more
thoroughly scours the medium, than has been previously possible, and
minimizes the need for frequent chemical cleaning. However, the same
system is designed so the chemical may be fed into the underdrair.
system from chemical holding tank 260 to adequa.ely disinfect the
filtering media, retarding a biota build up in either the medium or
filter surface.
The most serious problem associated with the filtering
process of wastewater is the adsorption and accumulation of colloidal
grease and/or oil films to the surcace of the medium grains. This
particular problem is magnified by the high percentage of colloidal
grease and oil present in primary or combined storm and primary flows.
Contact with and backwashing with a detergent solution or oxidant
and surfactant effectively removes colloidal grease and oil from
the surface of the medium grains.
Another aspect of this invention is thus an improvement
in the underdrain system described in my U.S. Patent 3,840,117 as
well as an improvement in the chemical clean system described in
my U.S. Patent 4,032,443. Frequent or excessive chemical clean cycles
~N 2-~665A
-30-
utilizing halogenated compounds can be detrimental to the operation of
a biologlcal system or the quality of filtrate of the wastewater treat-
ment system. Halogenated compounds such as those containing bromine
or chlorine can combine with nydrocarbons present in the wastewater to
form trihalomethanes which have been characterized b~ the Environmental
Protection Agency as carcinogens. Bromoforms and chloroforms are
examples of halogenated hydrocarbons that may result from the use of
halogenated compounds.
Now referring to Figure 9, a preferred embodiment of this
aspect of the invention, is shown. An improvement in the underdrain
system described in my patent 3,840,117 is illustrated, including the
modification by the addition of oxidant chamber 1000, inlet conduit
1100, and compound sleeves 1200. Chamber 1000 is formed of an upper
plate and a lower plate, generally coe~tensive with and supporting
a network of horizontal bars. The bars, in turn support the screen,
and the screen supports the granular medium bed. The plates are
separated in parallel relationship by non-limiting spacers.
Uniformly spaced sleeves 1200 extend vertically through
both upper and lower plates for ailowing a liquid or gas flow either
upward or downward.
Uniformly spaced air distribution chambers 208 are open at
the lower end and closed at their upper end by the lower oxidant
chamber plate.
A detergent, generally a linear alkyl sulfonate is intro-
duced into the underdrain. After a premeasured quantity of detergent
DN 2~4665A
-31-
is introduced into the underdrain cavity~ an oxidant solution such as
of hydrogen peroxide, or a gaseous o~idant such as o~one is fed into
conduit 1100, into chamber 1000, into noz71e 1400 through orifice
1420, and mixed with detergent and filtrate solution forced up into
air distribution chamber 208 and through orifice 1450. Alternate
construction of the sleeves 1200 and location of orifices 1450 are
shown in Figures 10 and 11.
De~ergents or surfactants such as ~.A.S. are biodegradable,
and oxidizing solutions as strong as hydrogen peroxide or ozone for
example will reduce the strength of the admixture if they are mixed
prior to entry into the granular medium, and permitted to remain in
a condition mixed prior to use in the medium. This apparatus protects
the strength of the chemicals and the use of a biodegradable detergent
with a strong oxidant by mixing them just prior to, at, or just
following passage of filtrate into the medium, yet provides a uniform
distribution into the medium of the admixture. rnis method reduces
the cost of chemical cleaning, eliminating formation of any ~rihalo-
methanes and problems in disposing of non-biodegradable or phosphate
type detergent. The chemical clean system will rapidly emulsify any
0 residual grease coating on the medium grains, and wash the surfaces
of the grains free of any grease or oil residual.
Another aspect of this invention as shown in Figure 9 is
the ultimate passage of air into the underdrain system through conduit
1500 and intermittently opera~ed valve 1510 into conduit 1100, which
causes a iet pulsa~ion. This jet pulsation more effectively removes
the grease and oil film from the sand medium.
