CA1295058C - Biological treatment of wastewater - Google Patents

Abstract

BIOLOGICAL TREATMENT OF WASTEWATER
Abstract of the Disclosure A wastewater treatment reaction vessel is operated with repeated sequences of aeration and`
non-aeration, using a single vessel or multiple vessels alternately t activated sludge which is acclimated for BOD
reduction, nitrification or biological denitrification and phosphorus removal is absorptively reacted with influent wastewater, and the combined flow is passed into subsequent absorptive reactor volumes, reducing the BOD
such that the effluent BOD is less than twenty percent that of the influent.

Description

5~58 .~
BIOLOGICAL TRE:ArME~3T OF W~STE:WP.TER
F1 eld of the Invention This invention relates to activated sludge wastewater treatment systems. Specifically, this 5inYention relates to treatment of municipal sewage and industrial wastewater using dispersed yrowth and/or attached growth biomass to generate a high quality effluent from which nitrogen and phosphorus removal has been ef~ected and which is cost and energy ef~icient.
Abbreviations The following abbreviations are used in this speclfication:
ATP Cellular Adenosine TriPhospha-te BOD Biochemical Oxygen Demand (mg/L) BWL 80ttom Water Level COD Chemical Oxygen Demand (mg/L) F Floc-Load; substrate to biomass ratio, mg BOD/mg MLSS or mg ~OD/mg MLYSS
MCRT Mean cell residual time (days) 2GMLSS Mixed Liquor Suspended Solids MLVSS Mixed Llquor Volatile Suspended Solids PV Permanganate Value SOUR Specific Oxygen Uptake Rate TKW Total K~eldahl Nitrogen (Total Nitrogen as ~determined by standard Kjeldahl analysi~
TOC Total Organic Carbon TWL ~Top Water Level Con~entional : dimensional abbreviations, e.g.
g-graml mg=milligram, L=llter, m~=milliliter, etc. are 30 also usedO
Back~round of_the I~vention Previous activated sludge methodolo~y has u~ed various continuous flow configurations comprising a primary soliqs settlement tank, an aeratlon tank~and a .3ssecondary solids settlement tank. Solids are removed from the secondary solids settlement tank and returnecl to the aeration tank in order to maintain a stable solids concentration therein. Treatment of wastewater has also been achieved in intermittently aerated activated sludge systems both with and without primary solids settling.
sW:ith all activated sludge configurations, their process efficiency is dras-tically affected by sludge bulking conditions, a situation where activitated sludge solids exhibit a low zone settling velocity, sufficient to cause these ~olids to be lost from the treatment system. This l0loss of solids and associated treatment process upsets take considerable time to rec-tify.
For a biologicaI treatment process in general and particularly the activated sludge process to be effec-tive and economically viable, it is essential that lSthe biomass exhibit good settling properties in order that efficient gravitational solids-liquid separation can be prac-ticed. A number of circumstances can arise which have been reported -to contribute to the generation of a non-flocculating biomass (bulking s}udge~ which has poor 20settling properties and thus impose an impediment to the cost effectiveness of th0 activated sludge process as a method of biological wastewater treatment. The number and type of microorganisms which can contribute to or cause a non-flocculating biomass are numerous and quite prolific.
25~he growth of such organisms is known to be associated with the treatment of domestic wastes, readily degradable ;~ high strength predominately carbohydrate type of wastes such as those generated in the food, potato, milk, brewing and similar processing industries, or an admixture of such 30wastes in any proportion. ~ i i~ ~ A number o~ approaches have been suggested since the activated sludge process was initaIly developed, in order to alleviate sludge bulking conditions, the majority having been modifications to the conventional continuous 35feed continuously aerated configuration with separate clarifier and continuous return activated sludge. Some o*

~29~ 58 these include tapered feed and aeration combinations, the use of aerobic and ano~ic subreac-tors or zones, initial snlall volume anoxic, aerobic or anaerobic reactors for contacting the return activated sludge with the influent 5 waste flow and various chemicals to selectively limi-t or kill the growth of non-flocculating portion of the biomass. The success of these modifications and variations has been varied and often has produced inconsistent results.
In order to achieve best possible solids-liquid separation Lk ls necessary that the biomass contaLn a relatively small portion of -the non-flocculating type of orgclrlisms. This enhances the ability of the biomass to entrap coarse, fine and colloidal particulate matter 15 which, if not removed in the solids-liquid separation unit operation, requires a separate costly filtration or other type of process unit operation for its removal. The nature of the non-flocculating biomass enables strong solid bridging mechanisms, with high intra solid 2~ attractive forces assisted by micro particulate biocoagulation involving extra cellular polymer compounds, ~o -take place within the biomass. The absence of some non-flocculating microorganisms in the biomass leads to pin-point type of sludge or to a type that results in a 2~5 turbid liquid layer during and following the settling operation. This also means that the e~ficiency of the process is reduced necessitating the addi~ion of other processes or unit operations to remedy the deleterious situation. One solution to poor sollds-liquid separation 30 has been to increase the area and liquid depth of the solids-liquid separation unit and thus the hydraulic re-tention time of the unit. There is a limit to the hydraulic retention time that can be used in practice due to anaerobic and/or anoxic biological transformations 3S which can take place within the biomass. Too low a solids flux cosnbined wi-th too long a period whereby the biomass 3L2~

is in a non-aerobic condition only leads to a further 105s in process efficiency and cost effectiveness due to the need to use additional processes or unit operations.
In conventional activa~ed sludge wastewater 5 treatment methodology two flow configurations can be described, complete mix or plug-flow. Tracer studies to deterlnine hydraulic residence time distributions and dispersion number characteristics, a dimensionless number describing diffusive mixing and transport, essentially 10 descr:ibe the flow predominance of -the configuration. A
~ispersion number of or near to 0 essentially describes a plug-flow configuration while a large value of the dispersion number, approaching infinity, describes an essentially completely mixed configuration. Activated lS sludge systems operating, or predominantly operating, in the cornplete rnix configuration are very prone to ; generation of sludges which bulk and which are identified as having a low zone settling velocity i.e. poor solids-liquid separation. Such configuration is specially 20 unsuited to the treatment of readily degradable food processing types of wastes or to domestic wastewaters where a high level of ammonia removal is required. In such cases bulking sludge or biomass exhibi.ting poor solids-liquid separation severely limits the efficacy of 25 the process.
The hydraulic residence time distribution can also be used to fit various hydraulic models, which also describe -the degree of plug-flow, in the form of a certain number of smaller completely mixed reactors connected in ~0 series which in total exhibit the plug-flow behavior. An e~uivalent four reactors in series is known to approximate a plug-flow hydraulic configuration. Added to this type of rnodel, is the ability to be able to describe, bypass, backmix, bypass and dead volume fractions in the flow 35 configuration.
Wastewaters are characteristically described by 5~

parame-ters which quantify their oxygen eonsuming po-tential, solids content and the availability of other essential nutrients necessary for a healthy and efficiently opera-ting biological treatment process. The 5 concen-tration terms in domestic wastewaters are a function of the volume ratio of water that is used to transpor-t the was~es to the treatment facility, the diet o the population contributing to the system and the residence time of the combined water and wastes in the sewerage 10 systern. 'rhe prineipal treatment parameters are henee the carborl~.lceous oxygen eonsun~ing fraetion (or organies) variously determined as BOV (Biochemieal Oxygen Demand), COD (Chemieal Oxygen Demand), PV (Permanganate Value), TOC
~Total Organic Carbon) and the nitrogenous oxygen 15 consuming fraction deseribed as ~KN ~total Kjeldahl nitrogen), organie nitrogen, ammonia nitrogen or free and saline ammonia, and nitrite nitrogen. These parameters can be used as a measure of the soluble, eolloidal and particulate forms and their various fraetions. For 20 example, domestie wastewaters may have an assoeiated BOD
and a suspended solids eontent ranging from some 350 mgjL
to a low value of about 90 mg/L for eaeh parameter depending on the amount of water in the earrier system.
: 'rKN is similarly variable from about 80 mg/L to lower;
25 concentrations, On a praetieal basis partieulate matter : contributes to about 50 percent of the BOD (or other . ~ parame~ters). The soluble and eolloidal matter makes up the other 50 pereent with the eolloidal fraetion : ~ : contributing about 15: pereent. Domestic sewage may contain less then about 60 mg/L of soluble BOD (or other : parameterj.
1`he characteristies of industrial wastewaters are a function of the process they are derived from.
Industrial wastewaters from the food industries, sueh as ~, 35 pota-to, milk, vegetable, brewery industries have a high BOD (or other parame-ter) in which the soluble fraetion .

~6-also leads to a high BOD ~or other parameter) in the range of 200 to 2000 mg/L. Wastewaters having a total BOD (or o~h~r equivalent parameter) in excess of about 3000 mg/L
are generally not economically amenable to biodegradation 5 by an aerobic process alone such as the activated sludge process. For the purposes of demonstrating this invention a -typical domestic wastewater having a total BOD o~ about 300 mg/L. will be considered; however, the invention and :its application is not limited to this strength or type of 10 waste.
It is generally observed that BOD removal by the acti.vated sludge and o-ther biological processes takes place by storage, synthesis and oxidation mechanisms in which all three processes occur simultaneously. These 15 assu~ned basic mechanisms can be enhanced, the extent of which is determined by the net hydraulic flow configuration. Absorption of soluble substances (organics) by microorganisms is thought to take place by enzyme transport together with diffusive mechanisms. It is a rapid interaction the amount of which is determined by the ability o the active organisms of the biomass to absorb; the latter is functional on the population of intra and extra cellular enzymes that are available, the fraction of receptive transport sites or centers associated with the microorganisms, the fraction of previously absorbed material that remains in an unrnetabolized state, i.e. the concentration driving forces, all of which are related to the active mass fraction of the biomass. The active mass fraction has 30 sometimes been described as the viable fraction or the degradable fraction. This invention provides a process whereby the degradable ~raction property of biomass and its ability to absorb soluble substra-te is maximized.
The transport o~ soluble substrate (organics) by enzymdtic mechanisms, or absorp-tion, is an energy intensive react:ion, the magnitude of which can be shown by , the specific oxygen uptake rate (SOUR) of the biomass before and after substrate contact. Synthesis reactions and cellular growth do not necessarily occur on the onset of absorption. Cellular growth mechanism do not begin to function for some considerable time lag after absorptive:
transport saturation as can be evidenced by cellular Adenosine Tri-Phosphate (ATP) concentrations.
A typical bioresponse profile during and Eoll.owinc~ absorption is described in Figure 1. Two s:Ltuat:ions are shown in Figure 1, one where aeration of the biomagg i5 in the presence of residual unabsorbed substrate (curve I) and one where aeration of the biomass takes place in the absence of residual unabsorbed substrate (curve II~. The second bioresponse was obtained by centrifugal separation of biomass and substrate whereby the volume of removed substrate was replaced with distilled water containing a supply of necessary nutrien-ts. Bioprofile I therefore describes the oxygen mass required for substrate absorbed together with biodegrada-tion of residual substrate not initially absorbed. Bioprofile II essentially describes the oxygen mass required to me-tabolize initially absorbed substrate.
'I'he mechanism of absorption is quite different from that of adsorption. Adsorption is a surface attraction : 25: phenomena which only~ accounts for very minimal substrate : removal on contact with biomass. A maximum of about 3 -to 5 percent under optimum circumstances can be realized. On -the other hand, absorption of soluble substrate of up to 90 percent at practical floc-loading can be achieved.
It has been mentioned that the absorption ` potential or efficiency of a biomass is measurable by the initi.al magnitude of and the resul-ting elevation of the specific oxygen utlilization rate (SOUR) of that biomass.
rf'he absorption potential of a biomass is also functional 35 on the. fraction of that biomass that is active and degradable, the latter being determined by the organic ~;Z951~5~3 loading or mean cell residence time of the biomass. This is graphically depicted in Figure 2.
The rnagnitude of the elevation in the SOUR
bioprof:ile is also dependen-t on the initial substrate to 5 biomass ratio termed -the floc-load (F). This is shown schesna~ically in Figure 3. Units of floc-load are described as mg BOD, COD, TOC, PV per g biomass. Biomass may be described as mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids, (MLVSS). The 10 degr~ldclbL~ rnass of ei-ther ML.S~ or MLVSS on the surface or near surface layers of biomass in an attachecl growth sys-tem expressed in the same terms of oxygen utilization provides a measure of the substrate saturation capacity of that particular biomass. The initial absorption mechanism 15 is ~uick, the major fraction of substrate transport taking place in only abou-t 10 to 20 minutes. Little absorption takes place after about 45 minutes. Therefore the absorption mechanism results in a reduction in substrate concentration as shown generally in F'igure 4.
The percentage removal and floc-load relationship is waste specific and also functional on the ac-tive or degradable fraction of the biomass and the relative rnagnitude of SOUR existing on initiation of absorption mechanisms with respect to the magnitude 25 ~ssc~ciated with viable biomass in a nonabsorption state viz ini-tial value of SOUR. The absorption potential of a biomass is limited in the first instance, as shown in Yigure 5, by the active or degradable fraction of the biomass, by the floc-load and by the availability of 30 receptor transfer sites or storage capacity for that degradable fraction of biomass.
Ex-tended periods of aeration of the contacting biomass or contacting of biomass which has experienced prolonged periods without the presence of oxygen reduces 35 the absorption potential of that biornass, as depicted in Eigure 6.

~5~S~ -g The magnitude of percent of substrate absorbed, relative to the criteria described above, at a specific floc-load is instrumental in determining the sludge settling characteristics of the biomass following 5 eonverltional aeration periods.
Ior some time now it has been recognized that ~tlere is d need to improve activated sludge wastewater treatment methodology, for both domestic and high soluble BOD industrial wastewaters, in order to be able to 10 economiYe on both capital equipment and operating costs.
'I`lli~ may be brought about by manipulating and optim:Lzing the biological processes in order to provide consistent degradation -together with consistent and good sludge settlement behavior.
The following patents and publications provide various background information and details of certain ~pparatus, systems and processes which may be used in connection with the present invention.
U.S. Patents Nos. 2,852,140, MacLaren, 20 3,053,390, Wood, 3,202,285, Williams, 3,415,378, Fukuda, and 3,433,359, Lundin et al. Tank structure and aeration apparatus are disclosed.
U.S. Patent No. 3,264,213, Pav. Describes an activated sludge process.
U.S. Pa-tent No. 3,524,547, Nicol. A sewage treatment plant utilizing aeration is described, which includes an inlet compartment and two treatment compartrnents. Sewage from the inlet compartment is transferred substantially contemporaneously from -the inlet 30 compartment into the first of the treatment compar-tments and from first treatment compartment to the second treatment compartment and treated sewage is removed rom ~the second treatment compartment. The flow is then reversed, -flow being from the inlet compartment to the 35 second treatrnent compartment to the first compartment and then from the system. The two treatment compartments thus serve, alternately, as the first and second treatment stages.
U.S. Patent No, 3,530,990, Grimshaw. An aeration system and apparatus is described which, if 5 deslred, could be adapted to provide for aeration in the present invention. Aeration apparatus per se is not part of the present invention, however, and any aeration apparatus may be adapted for use in the present invention.
U.S. Patent No. 3,73Z,160, Klock, ~ fixed film 10 d:igestion material, referred to as a "filterl', whlch presents absorption medla to the sewage is described. 'rhe substrate for the film may be plates, spheres, etc.
U.S. Patent No. 3,805,957, Oldham. Tank structure, aeration and circulation are described.
U.S. Patent No. 4,069,147, Abrams, et al.
Multiple tank system with aeration is described.
U.S. Patent No. 4,081,368, Block et al.. A
multiple compartment activated sludge treatment system with recycle of activated sludge is described.
U.S. Patent No. 4,206,047, Mandt. A multi-stage waste water treatment system involvirg aeration and rnixing, utilizing pure oxygen is described.
U.S. Patent No. 4,152,259, Molvar. Aeration apparatus.
U.S. Patent No. 4,290,887, Brown, et al. A weir arrangemen-t for decanting treated wastewater may optionally be used with the present invention; however, any decanting apparatus may be used.
U.S. Patent No. 4,468,327, Brown, et al. A
30 single vessel treatment process is described. Aeration, decantin~ and various other apparatus may be used with the present invention. Reference is made to the subject patent for a discussion of various aspects of the activated sludge digestion process which, in a very broad 35 serlse, relates to -the present invention. U.S. Patent No.
G"4~8,327 utilizes a single reaction vessel and the ~2~ 8 process is carried out with continuous inflow and in-termit-tent aeration and decanting. In contrast, the pre~ent :invention is a multiple reaction vessel process in wh:ich ~he process variables differ substantially from the process of the subject patent.
oxIDAlrIoN DITCHES IN WASTEW~TER TREATMENT, D.
Barnes, C.F. Forster, D.W.M. Johns-tone, Pitman Press, llath, Avon, U.K.
"Dove:lopment of the Passveer Extended Aerat.ion ~ysteln", Batty, J.A., Coronszy, M.C., Clarke, R., The Sh:ire_and Municipa:L Record (Australia), November, 1974.
"Continuous Intermittent Wastewater Systems for Municipal and Industrial Effluents", Barnes, D. and Gorons~y, M.C., Oxford District Centre, October 4, 1979, Institute of Public Health Engineers, London.
"Con-trol of Activated Sludge Filamentous Bulking", Chudorba, J., Grau, P., Ottova, Blaha, J., Madera, V., Water Research; Part I, Vol. 7, pp 1163-1182;
Part II, Vol. 7, pp 1389-1406; Part II, Vol. 8, pp 231-237 (1973), "Single Vessel Activated Sludge Treatment for Small Systems", Goronszy, M.C., Journal WPCF, Vol. 51, pp 27~-287; presented October 6, 1977, 50th Annual Conference of the Water Pollution Control Federation, Philadelphia, Pa.
: "The Activated Sludge Process: State of the Art", W. Wesley Eckenfelder, Jr., et al., CRC Critical Reviews in Environmental Control, Volume 15, Issue 2, 1985.

3~ "PRINCIPLES OF WATER QUALITY MANAGEMENT", W.
Wesley Eckenfelder, Jr., CBI Publishing Company, Inc., Boston (1980).
- 'I'he foregoing publications describe the basic theory and operat:ion of the activated sludge process and the extended aeration process for treatment of sewage.

~2~5~S~

~12-Brief Description of the Drawings In the graphs of the figures and in the description, typical or average valves are used. Many data are specific -to a particular sludge, etc., and the actual valves may vary greatly from the data presented 5 which exemplify phenomena not valves per se.
Figure l graphically depicts a typical bioresponse profile during and following absorption.
Curve I shows the results of aeration of the biomass in the presence of residual unabsorbed substrate. Curve II
lO shows the results of aeration in the absence of unabsorbed substrate. 'r'he vertical ax:is indicates Specific Oxygen Uptake Rate, increasing upwardly, and the horizontal axis indicates tirne, increasing to the right. SOUR typically exhibi~ maxirnum valves of up to 200 mg 02/g MLVSS/hr.
Figure 2 graphically depicts the decrease in active fraction, i.e! degradable content of the biomass, wi-th the mean time the biomass resides in the system, of a typical system. The vertical axis indicates the Active F'raction, increasing upwardly, and the horizontal axis 20 indicates time, increasing to the right. At ~3 days Mean Cell Residual Time (MCRT), the degradable fraction is typically 0.66.
Figure 3 graphically depicts the change in floc loading (F) with time for three different initial floc 25 loads, as measured by Specific Oxygen Uptake Rate in a typlcal system. ~ The vertical axis indicates Specific Oxygen Uptake Rate, increasing upwardly, and the horizontal axis indicates time, increasing -to the right, Fl C F2 < F3.
; F'igure 4 graphically depicts a typ1cal reduction in substrate concentrat~ion, measured as percent of organic content remo~ed, with increasing floc load. The vertical axis indicates Percent Organic Compound Removed increasing upwardly, and -the horizontal axis indicates floc load, 35 increasing to the right.
F'igure 5 graphically depicts the reduction in )5~S~

substrate concentration for various initial substrate concentrations with time. The vertical axis indicates the logri-thm of the Substrate concentration, increasing logri-thmically downwardly, and the horizontal axis indicates time, increasing to the right.
Figure 6 graphically relates the amount of organic substrate removed with increasing floc load for aerobic conditions, Curve I, and anaerobic conditions, Curve II for the same active fraction of biomass.
10Figure 7 is a partially schematic depiction o~ a baslc apparatus in which the process of this invention may be carried ou-t. 'rhe presentation o structure, however, is without particular significance since the process may be carried out in virtually any structure which provides the reac-tion zones of the present process.
Figure 8 is a cut away perspective of a portion of a weir of the type which may be used in this invention, showing portions in cross-section. This weir is the ~oint invention of the inventor of the present invention with Olavarria and Piccioli.
Fi~ure 9 is a side view of the weir showing its orientation at two positions, the second position being shown in phantom line, the inflow to the weir at all times being on the same leading edge side of the weir.
25Figure 10 graphicaily depicts, in somewhat idealized curves, the loading reduction profile in the ;~ process of the invention as carried out in a two-stage, thr;ee zone system as depicted in Figure 7. The vertical axis indicates Biological~ Load of the wastewater 30 undergoing~treatment in the three zones, ~, B and C, increasing upwardly, and the horizontal axis indicates time, increasing to the right. Process changes A and B in Figure 10 typically take place in from about 5 to 20 Ininutes respectively.
35Figure 11 schematically depicts an alternative embodirnent of Zone B of the system of Figure 7 wherein uy .

. , .

to ninety-five percen-t of the space below the Bottom Water Level (RWL) is occupied by a fixed film growth media which may be fixed, mobile or in the form of mobile particles.
Figure 12 schematically depicts an al-ternative 5 ernbodiment of the invention comprising two digestion zone defining tank systems which may operate alternate from an inle~ zone.
Figure 13 schematically depicts the operation d~lrin~ cyclic periods of time oE the system of Figure L2.
Figure 14 schematically depic-ts yet another ernbodiment of the :invention in which the inlet zone is subdivided into separate zones.
Figure 15 graphically depicts the removal of biolo~lcal phosphorus with time, using the present 15 inverl-tion, The vertical axis indicates percent or ratio of phosphorus removed, increasing upwardly, and the horizontal axis indicates time, increasing to the right.
Summary of the Invention The invention relates generally to improvements in -the trea-tment of municipal sewage and/or industrial wastewater using dispersed growth and/or attached growth biomass. The invention enables a high quality effluent to be genera~ted whereby substantial biological deni-trification and phosphorus removal is consiste~tly 25 achieved and provides a process which is more cost and ~ energy effective for the treatment of domestic and ; industrial wastewaters.
This invention provides a method for achieving a minimum of two successive stages of biomass absorption in 30 a reaction vessel whereby conditions which favor sludge ; bulking are avoided. It is therefore possible to use the sarrle reaction vessel `to carry out the solids-liquid separation function to thereby produce a treated effluent which is removed by a surface liquid removal device. This ,. . .
J5 invention ensures that biomass absorption mechanisms are maxlrnized.

~2~56~

The reaction vessel is operated with repeated sequences of aeration and non-aeration which, combined witl~ the maximization of biomass absorption mechanisms in a series arrangement, provides a method of wastewater 5 treatrnent that is superior to existing conventional, :intermit-tent activated sludge and sequencing batch reactor methodology.
By proper manipulation of floc-load, mean cell res:i.dence time and cyclic aeration periods, it is possib].e 10 to provide a me~thod oE treatment such -that biological dc~ractat:i.on processes of carbonaceous oxiflation, nitrogenous oxidation, substantial biological denitrification and phosphorus removal, together with good biomass liquid separation can be accomplished in a common 15 variable volurne reactor, being one embodiment of the invention. The common variable volume reactor in its preferred form is subcompartmentalized in at least two hydraulically distinct sections in concurrent liquid flow cornmunication to permit certain floc-loading conditions to 2Q be yenerated in each section. The number and configuration of subcompartments, formed as separated vessels or by the use of sectioned walls is primarily determined by the magnitude of the average daily flow and the duration of peak continuous ~lows together with the 25 total and soluble BOD (or other) fraction associated with : : the hydraulic load. A basic feature of this invention is -to provide sequenced ,and/or staged absorption in a configuration which maximizes the removal of pollutants in ::
a manner that also permits the use of a variable volume 30 reactor. A further basic feature of this invention is the : ability to use the variable volume reactor for both :: biological degradation and soli~s liquid separation ; functions. A minimum of two stages of absorption are required in this invention in the case of domestic 35 wastewaters. For higher strength readily degradable w stewaters additional stages oE absorption are provided, .

the number depending on the ratio of soluble to total BOD
(or other pararneter).
A simple embodiment of two stage absorption is shown schematically in Figure 7.
Referring to Figure 7, the process of the invention proceeds as follows: Wastewater to be treated enters in-to a ~irst reaction zone A which is defined in a first vessel 110 and, as will be described, flows .int;ermittently into a second reaction zone B, in a second lO vesse:L 120 and, through the second reaction zone, into a thircl react:iorl ~.one C in a third vessel 130. The first of .influent zone A serves as the initial contact of the in~luent wastewater with activated sludge. The organic biological load of the wastewater, which is typically 15 reported as Biochemical Oxygen Demand and/or Chemical ~ Oxygen Demand, is at its maximum upon entry and decreases : very rapidly in the first reaction zone A, as depicted in :: portion A o~' the graph of Figure 10, will vary periodically as the associated flow is periodically held 20 and then dumped into the succeeding reaction zone B before pdssing into C. It will be understood that the confi.guration of the first reaction zone is not, per se, cr:itical. This zone may be confined in a vessel as indi.cated in Figure 7, which may be a compartment, . 25 definirlg a separate vessel, in a larger structure or a separate tank entirely. The zone may even be a high capaci-ty inlet conduit system lOO.
After a residence per.iod, generally not exceeding five minutes, the wastewater flows into the 30 second reaction æone B. Schematically, a valve mechanism ~ ~ .
: 10~ is shown which periodically opens and closes to direc-t total inflow into another small vessel durin~ the effluent : decantation sequence. During the aeration sequence this stored influent is directed to zone B by a valving or 35 purllpirlg arrangement to mix wi-th additional flow from zone ; A. The stored effluent may be dumped directly into zone B

~s~

or, as shown, flow through zone A to zone B. ~ valve, gate, movable weir, or any other means for periodically permitting and preventing flow from the first zone A to the second zone B may be used. Additional activated S sludge, if needed, may be mixed with the wastewater in the second reaction zone B and the mixture is aerated. There is a very high BOD reduction in the second reaction zone B
as indicated in the portion o~ the graph marked "B" of F;ig~lre 10.
'l'he second reaction ~one B is in fluid comlllun:ication with -the third reaction zone C. ~igure 7 shows a single multiple-vesseI tank structure, and there are certain economies in this kind of structure, in that one need not construct as many hydraulic bearing walls as 15 would be necessary using separate tanks. This principle, mu:Ltiple vessel tanks, has been used for decades if not centuries in sewage treatment facilities. In terms of operation, however, each compartment may be treated as a separate tank, with continuous flow communication.
2~ As shown in the portion of the graph marked C in ~igure lO, the rate of BOD reduction in the third reaction ~one C is very much lower than in the first and second reaction zones A and B. Of course, the active biological load of the wastewater entering the third reaction zone C
25 lS much lower than that enterlng the preceeding zones.
The wastewater in the third reaction zone C will have developed a very high activated sludge content and the principle functions of the third reaction zone C are -two-~old: ~ first to complete the oxidation of the 30 biochemical oxygen load of the wastewater and, second, to permi-t the sludge to settle leaving a clear upper layer ; which forms the effluent from the process and system of the invention. This effluent is removed through any convenient decanting device. An exemplary type of weir is 35 shown in Figures a and 9. Scum guards, etc. are typically provided to prevent floating debris, etc., from being ~Z~5~5~

decanted. The decanting apparatus is not, per se, part of this :invention, however, and any suitable decanting ~pparatus may be used. The decanted effluent exi-ts the sys-teln as ecologically acceptable water which may be 5 reprocessed, used for irrigation or simply disposed of.
Activa-ted sludge is removed from the third reaction zone C and may be introduced into the second reaction ~one B. Likewise, activated sludge may be introduced into the first reaction zone A. Similarly, if 10 desired, t~le activated sludge may be mixed w:Lth the inf1uent wastewclter even before the wastewater actually enters the holding portion of the first reaction zone A, ancl may also be introduced into a holding tank. Surplus activated sludge is removed and treated in the 15 cc)rlven-tional ~lanner.
A blower or air pump forces air, or oxygen containing gas into the second reaction zone. Likewise, air may flow in the third reaction zone C.
~ The time sequence of the process during normal, 20 average dry wea-ther operation, is as follows: Influent was-tewater is continuously received into the first reaction vessel A where it is mixed! either in the vessel or before, with activated sludge. If there is excess inflow, it is held in the holding tank. During a first 25 period of time, the BOD reduced wastewater flows into the second reaction zone B and then into the third reaction zone C where, during a second time period, it is subjected to aeration and may, in zone B, have additional activated ; slud3e actded. During a third time period, the outflow 3Q frolll zone A is stopped. During this third time period, effluent from the system is decanted from zone C thus lowering the water level in zones B and C. The level of water ir-, zones B and C will periodically raise from the 8Ottoln Water Level (BWL) to the Top Water Level (TWL), as i~ 35 shown in F`igure 7.
~ With specific reference to Figure 7 and the ~Z~ 8 apparatus shown therein schematically, it will be understood that the invention resides principally in the process and that any apparatus which provides the necessary reaction zones and conditions may be used to 5 carry out the invention. As depicted in Figure 7, the inf].ow of wastewa-ter from sewerage line 102 may pass through a val.ve 104, or equivalent s-top-flow mechanism, into vesseL 110, zone A, or through a valving mechanism .I.O~j :i.rlL;o a ~old:ing tank 108. The holding tank is not 10 nece~-s~clry to operation during Average Dry Weather (ADW) op~r~tj.on if the si~e of vessel 110 is adequate; however, during periods of abnormally high input extra holding cap~city may be required. The holding tank per se is not an essential feature of the invention, although it mya, in effect, serve as an extension of zone A if desired.
Aera-tion is provided into vessel 110, zone A, from a blower 112 and nozzle 114 which forces air or oxygen into zone A from inlete 116. A valving mechanism, gate or other stop-flow mechanism or arrangement 11~ permits the aera~ed eEfluent from zone A to flow into zone B, vessel 120.
~: ~he contents of zone B, in vessel 120, are aera-ted from blower 112 and nozzle 122 and sludge may selec-tively be introduced into zone B from sludge inlet 124. The level of wastewater being treated in zone B
variesj as described, from a TWL 126a to a BWL 126b as the corltents of vessel 120 flow through any desired type of fluid communication 128 into zone C. The fluid COITlmuniCation 128 may be passageways in a weir, a conduit, a gate, or any other form of fluid communication. In a : pre~ferred embo~iment the communication is such that sludge ., may flow in -two directions to and from zone B to zone C.
If this sludge fl.ow is adequate, it may not be necessary to ad(l addit:i.onal sludge via the conduit port 124.
Zone C, in vessel 130, serves as a aeration, seLt:Ling arlcl decanting zone. Aeration is provided by a ~:
~.

no~l.e 132 and decantation is provided by a wèir 134 which, in the embodim~nt schematically shown in F`igure 7, is a~tached to a telescoping conduit system 136 and 138 is drivin by any de~ired means up and down to decant the 5 wastewater into the outflow line 140, which is connected to -the ul-timate disposal or reprocessing system, between a TWL, 142a and a BWL 142b, as described before.
'rhe aeration is controlled to re-ackivate the s:Luclge which ~s then removed through conduit 144 and any lO su:Ltclble mechan:L3m and recycled and/or disposed as require~. An exemplary rnechanism for this purpose inc:l.udes a pump 146, sludge holding tank 148, conduit 150 arld pumps 152, 154, 156 and 158 which, selectively as des-ired, introduces açtivated sludge into zone B, zone A, the sewerage inlet line 102 to zone A and, if desired, into the holding tank 108. Excess sludge is disposed of via sludge exit line 160.
The decanting assembly which is depicted in FicJure~ 8 and 9 may be, bu-t is not necessarily, used with 20 the present invention. The decanting assembly is the joint invention of the present invention with others and is shown here merely to exemplify the type of decanting :?earls which may be used. The decanting arrangement is : ~ shown in a wastewater treatment tank which includes a 25 sidewall 162 and an endwall 164 and contains a body of : ~ :wastewater 166. The decanting assembly comprises a removal conduit 16a mounted for rotation to which one or more downcomer pipes 170 and 172 are connected in fluid ~; ::communication therewith. A weir comprising structure 30 fornling a leading edge 174 and a trailing edge 176 and end struc-ture 178~form a weir which is in fluid communication : with the downcomers 170 and 172 to permit the liquid which flows over the leading edge 174 to 10w through the downc~orners and out the removal condui-t 168. A scum guard 180, rneans of an arrn 182 to the end of the tank as shown at la4 such t;hat a-t all orientations of the weir the plank will lie substantially in the.veritcal plane and, thus, prevent floating debris from entering the decanting apparatus. The decanting assembly is moved pivotally about a pivot point 186 positively up and down by any 5 desired moving means, a hydraulic or air actuated ram 188, connected to the wall at 190 and the downcomer pipe 170 as shown at 192, being shown as rnerely exemplary.
Figllre 9 shows the positioning of weir during operation. 'l`he solid line position of the weir shows the :LO we:ir as it would be oriented at or near the TWL. The phantotll view shows the weir ak or near BWL. Two :Fcatures of ~Ihis decanting mechanisrn are pointed out here. First, the we.ir is always under positive drive control, the scum guard providing no bouyant support at all. Second, the 15inflow into the weir is always over the leading edge 174.
It will be understood that this is merely one o any number of decanting mechanisms which may be used.
Thus, flow is accepted continuously at A.
Bion~ass is continuously (or intermittently) directed from 20C ~the main aeration section) to mix with.untreated wastes at a point A before entering the reactor system. At A
rllixing i.s caused whereby absorption mechanisms take place with the biomass. A may be a length of influent line with or without an in-Iine mixing device, or a separate reactor 25volwne with or without a mixing device and with or without aeration. The mean contact time at this point is up to 5 : ~ minutes whereby substantial initial absorptive removal of soluble BOD (or other parameter) takes place. The flow of biornass from C is only minimal when compared to 30conventional technology, being up to 20 percent, by volurne, of the inflow to the system. In most applications the flow is only 5 to 10 percent. This may be compared to conventional systems where the flow from the separate clarifier returned to the aeration vessel is of the order 350f or in excess of 100 percent. The combined flow at A
passes to a subsection B for admixture with additional ~s~

biomass. In a preferred embodiment of the invention biolrlass -transfers from C to B as a result of backmixing and diffusion; in the absence of sufficient backmixing, additional biomass may be pumped. From B the flow passes 5 into C. Flow and floc-loading for the schematic systems shown in Figure 7 is designed to effect a loading reduc-tion profile schematically shown in Figure 8.
~ rom Figure 8, it will be seen that the b:i.ol.oy:Lcal load, whether measured by biochemical oxy~en 10 delnancl, chemical oxygen demand, or otherwise, decreases very rapidly with titne in Zone A and also decreases rap.idly in Zone B, most of the oxygen consuming biological material having been -transferred from the soluble state, ~he ~OD decreases at a lower rate in Zone C which effects 15 s~ttling, decantation and restores the absorptive potential of the biomass.
A further embodiment of the invention, as depicted schematically in Figure 11, places fixed-film (~rowth rnedia into cornpartment B to provide an additional 20 or a:Lternative rneans of ensuring an available biomass for sequential absorption. The placement of such fixed-film growth media in conjunction with biomass (in suspended form~ transfer frorn C provides another equivalent stage of ~ absorption and is hence a simple method for increasing the : 25 biological absorp-tive load capacity of the first system.
: Subsequent compartments both with and without fixed-film grow-th media are contemplated, depending on the strength of initial wastewaters and the quality of effluent that is desired. The media may be stationary or of the moveable 30 type, devices such as described in PRINCIPLES OF WATER
QUALITY MANAGEMEN~, iS preferrably placed such that it is subrnerged below the designated bottom water leve pos:i.tion. Moveable fixed-film growth media so operates duri.ng aeration sequences as to assist with mixing the .~5 blomass ~nd aicl i.n slud~e trans:Eer from Zone C.
The volume and specific area of -the fixed-film 5~SI!~

growth media is determined by wastewater strength cor~sicler~ions and may occupy a volume percen-tage of up to 95 percent of the bottom water volume of compartrnent B (or subsequerlt compartments). The fixed-film growth media may ~have a surface to volume ratio of up to 400 square fee-t :per cub:ic foot of media.
The preferred embodiment of this invention operat;es with sequential periods of aeration and non-aeration. During the non-aeration portion of the 10 sequerlce, d:ispersed solids in compartments B and C (Eor the example shown schem~tlcally in Figure 7) are caused to settle arld after a requisite time clear surface liquid is removed from compartment C by a moveable weir device.
Wl-en the liquid level shown as bottom water level is 15 re~ched the moveable weir returns to its resting position at a level in the reactor which is above the designated ` ,operating top water level of the reactor. The effluent removal operation may also be achieved by other devices, such as valves or other moveable decanters. It is 20 specific to this embodiment of the invention that the reac-tor opera-tes with variable volume between a designated top and bottom water level.
In order to discount any possibility o hydraulic short-circuiting or disruption of settled 25 biomass during surface liquid removal, inflow to B and : subsequen-tly -to C (in the embodiment shown in Figure 7) is ::shut off. In this one tan~ embodiment the flow from A is collected in a very small vessel or sub-compartment during ; the effluent removal portion of the sequence. This volume 30 of biomass and influent~: wastewater is directed into compartment B on completion of: effluent removal and : rei.nitiation of the aeration sequence. This inflow f'raction is only interrupted during effluent removal, 'I'his flow interruption is beneficial as it permits a h:i,gher rate of surface liquid removal and obviates any possib:Le form of short-circuitin~ from influent to ~z~s~

effluen-t ends of the variable volume reactor during surface liquid removal.
Another embodirnent of the invention, termed the two tank system, is schematically depicted in Figure 10.
5 The invention is not restricted to the geometrical shapes shown, and can be applied in any number of multiple tank arrangements. In this embodiment, the general operation describe~d wi~h reference to F:igure 7 is also used. There is no fixed-f:ilm growth media shown, but fixed-film growth lO med~ nay l:ike~wLse be used.
Re~ferring now to Figure 12, it will be understood that the unit operations described for the single reactor embodiment of Figure 7 are the same. In flow of untreated waste water from conduit 201 enters tank 15 A. During one period of time, the flow is from tank A, which defines a wastewater influent zone A, indicated at numeral 203 , through a conduit 205, into a tank 207, which defines a first stage B'l of a first reaction zone B. 'rhe second phase of zone ~1 vessel 209, B'1, is shown 20 onLy to indicate that subsequent absorption reaction zones or sub-zones, may be so provided. Multiple staged absorption zones would not normally be required for municipal wastewater. Decantation is effected from zone C, vessel 211, in the same manner as previously described, 25 the decanter apparatus being omitted from this drawing for clarity.
During another period of time, the flow is from the tank 203, zone A, through a conduit 213, into the first stage oE a second reaction zone in tank 215, zone . ~
~ ~2 Another tank 217, reaction zone B'2 may optionally be provided. Flow is then into the third reaction zone C, tank 219. As previously described, decantatlon from zone ~2~5~

C, vessel 219, is periodically effected.
Sludge pumped from tank 211 by a pump 221 and may be discharged through a valve ~23 or returned through a valve 225 to the tank 209 or valve 227 to the tank 207, 5 or to both tanks, and may also be introduced through a valve 229, into a tank 203. In a similar manner, the sludge pump 231 may pump sludge which may be removed from the system through a valve 233 or returned through valve 23S to tank 217 or valve 237 to tank 215 or valve 239 to tank 203.
The mode of operation of this kind of system is the same, functionally, as that described previously;
however, this system has a higher capacity because it has a duplicate series of reaction zones which are periodically operated. In flow is continuous from conduit 201 into tank A. During one period of time, the waste water is treated through the series of tank Bl and Cl.
During another period of time, while tank Cl is being decanted, the sewage is being treated in tanks B2 and C2.
Thus, it will be seen that the tanks are alternately operated to effect aeration of the waste water in one series of tanks while the other is being decanted, then the position is reversed and the other series of tanks is aerating the sewage while the first series is being 2s decanted.
Typical floc-loading patterns for assumed ideal steady-state flow conditions are shown schematically in Figure 11. Real flow conditions vary from the ideal.
Floc-load criteria and volumetric sizing of reactor absorption components Bl and B2, etc. are selected to ensure that remaining BOD (or COD) is less than 20 percent by concentration of influent BOD prior to the flow entering compartments Cl and C2.
For the two-tank embodiment, aeration and non-aeration periods are sequenced 50 that while reactor 1 i5 undergoing aeration, reactor 2 is undergoing non-aeration. This effects an ec:onomy on aeration equipment which permits the use of lower horsepower aeration units by virtue of the 24 hour continuous aeration duty. Multiple vessel embodiments are similarly phased to permit the same 24 hour duty aeration to take place.
It will be understood that treatment times will vary with the parameters of the particular system. In general terms biomass concentration, relative to the designa-~ed bottom water level in the third reactor C may be up to S,OOO mg/L although values in excess of lO,OOO
mg/L can be maintained. The duration of contact of biomass solids fxom Cl or C2 with influent wastewater at A
will generally not exceed 5 minutes, shorter times will still give the desired level of absorption. For the cited 5jOOO mg/L concentration of biomass in the reactor and a flow of biomass from Cl and C2 of up to 20 percent of the influent wastewater flow an approximate 2 minute initial absorption time will suffice. For the same biomass concentration cited Bl and ~2 would typically provide a retention time equal to the surface li~uid removal period, calculated on the designated bottom water level and the combined average inflow from the flow splitting device~
The hydraulically distinct sections in concurrent 1iquid ~flow communication in each vessel, following the flow splitting device, simultaneously and together offer alternating periods of aeration and non-aeration. The duration of these relative~ periods is determined by a number~of factors. ~In practice a minimum total aeration period would be 50 minutes~ followed by a minimum non-aeration period of approximately 50 minutes, after which aera~ion etc. is repeated. Other aeration time periods can be used, being typically 1.5 to 6 hours duration. In such cases, the non-aeration period would not normally exceed 2 hours but could be arrange~ to do so if process conditions so require. Under certain ~ S~

circumstances the aeration period may be 22 hours ollowed ~y a non-aeratlon period of up to 2-3 hours. Any suitable combinatlon of these periods may be used.
The bacterial sludge ~biomass) after passing through the absorption units will contain the a~sorbed but essentially unmetabolized organic material. This biomass passes into the final compartment where its absorption potential is restored by virtue of the aeration and metabolic reactions. Compartment C therefore provides a lO pool from which to take the requisite amount o biomass to ensure the reductions in organic content previously described. Before entering Compartment C the liquid phase will have a greatly reduced content of BOD amounting to at most only 20 percent, by concentration, of the influent 15 vaIue. By example a domestic wastewater having an enfluent strength of 300 mg/L BOD and suspended solids would after two successive stages of absorption as described before have a BOD of less than 60 mg/L in the liquid phase as it passes into the final compartment C, at 20 average flow conditions. Correspondingly an influent strength of 150 mg/L BOD would be reduced to less than 30 mg/L BOD in the liquid phase. Higher strength industrial wastewater would similarly have the BOD reduced, the number of absorption stages being sized to ensure the 20 25 percent criteria previously described. Residual organics (measured as ~OD or other parameter) are degraded by the biomass in Compartment C.
Figure 13 depicts the operation of a system such as shown in Figure 7, with normalize times and assuming 30 ADW operation. It should be recognized that during periods~ of high wastewater inflow,~ such as might occur, for~ example during rain storm, or during periods of low wastewa-ter inflow such as might~ occur during a period drought, holiday periods, etc. The time cycles may vary 35 and, indeed, a cycle may be abbreviated or omitted or extended depending upon the. flow rate at a given ~ime.

.

~2~

Overall, however, the time periods of Figure 13 may be considered typical of a mode of operation of the invention.
At a top of Figure 13, one complete cycle is shown. During the period To-T1/ which may be an hour plus or minus a half-hour generally, Zone A is receiving inflow, zone Bl is receiving inflow and zone C is receiving inflow. During this period, To~Tl, zone B2 is se~ttling and may be receiving inflow. Durin~ the time per:iod, Tl~T2, zone A continues to receive inflow, zone Bl and zone Cl receive inlfow and ~2 and C2 are being decanted and there is no inflow from zone A to these zones. During the period T2-T3, A continues to receive inlfow, sl and Cl are settling, B, continues to receive inflow B2 and C2 are being aerated and receive inflow from zone A. During the period T3-T4, A continues to receive inflow, Bl and Cl are being decanted and receive no inflow from A, and B~ and C2 are being aerated and receive inflow from A.
It wlll be seen that, as to each flow stream, there are three time periods. During the flrst itme : period, B and C are being aerated either during all or some of the period, and B and C receive inflow from A.
During the second period of time, B and C are settling and ~:25 would receive inflow from A. During the third period of time, B and C àre being decanted and there is no inflow from~A. By overlapping the three time periods for the flow streams 1 and 2, continuous inflow to A is accomodated with intermittent and alternatingly sequenced flow to path 1 and path 2, i.e. Bl - Cl and B2 ~ C2. The floc load in the zones are depicted qualitatively in the : graphs of Figure 13, increasing upwardly on the abscissa and to the right on the ordinate, the time periods:being about one hour plus or minus a half or three-quarters of : 35 an hour each, as may be required in a given installation.
r~ach flow path cycles full in a time period of from about 3L29~

two to a~out five hours, a four hour period being used in Figure 13 merely to depict the sequencing and not the time per se of the steps of the process. Equal intervals of time are indicated in Figure 13 but would not necessarily 5 be used. The decant time may be from about one-half hour more or less to one and one-half hours more or less. The settling time may be generally equal to or longer than the decanting ~ime. The settling time could be shorter also, but this would not be a usual or common case. Aeration time would be from about one to three times the time length of the combined settling and decanting time, though the ratio is optimized at one to one. The time-determining criteria are set forth elsewhere herein in -terms of the operation of the pracess and the sludge quality requirements, Figure 13 being provided to show sequencing rather than to define specific times.
Another embodiment of the invention provides for ; absorptive and subsequent reactive degradation to take place in a plug-flow configured, cyclically aerated water retaining structure, from which the flow is split for direction to either one of two sequentially aerated water retaining structures schematically shown in Figure 14.
Referring now to Figure 14, the influent waste water enters through the conduit 301 and to tank 303, reaction zone A. Reaction zone A is actually divided into sub-zones, shown as ~tank A, tank Al, and tank A2, indieated by numerals 303, 305 and 307. The flow ~is divided between tank Al, and tank A2. From tank Al, 305, the flow~ is through a conduit into the first stage of second reaction zone in tank 307, zone Bl, and then lnto the second stage of the second reaction 20ne in tank 311, zone Bl prime and ~hen into tank 213, the third reaction zone Cl in like manner, the flow, during a different ; period of time, is through a conduit into tank 315 and into tank 31~, which defined, respectively, reaction zones ~2 and B'2, and then into tank 319 which defines the third lZ95~58 reaction zone C2. As pointed out before, the sub-zones or phases within a zone, e.g. B'l and B'2 (311 and 317) are shown only to make the point that subsequent absorption zones may or may not be used as required. It is important 5 to recognize that the number of zones will be determined to the influent into the zone. The influent raw waste will control whether more than one zone is require. High carbohydrate content, e.g. potato processing water, would require more sub-zones or phases than municipal 10 wastewater, for example. The sludge handling is the same as previously described. Specifically, the 81udge pump 321 pump~ khe sludg~ which may be removed through the system through valve 323 or returned to the second reaction zone through either or both of valves 325 and 327 15 and to the first reaction zone indicated ln this particular embodiment as being introduced into the in flow conduit through a valve 329. The sludge pump 33} with the associated valves 333, 335, 337 and 339 function in the same manner with respect to the second series of tanks.
Water retaining structure A/ A2,~ A3 is a high rate absorptive~degradation reactor with partial segregation walls extending from the floor of the vessel to a height exceeding the designated top water level of that vessel.
~ ~nit operations described for the single reactor ' embodiment and the two tank system embodiment are :
~ essentially ~he same. ~ ~ ~
:
Flow of influent wastewater ~to Al and A2 i9 continuous, on an as received basis, through the initial ~, 30 mixing ;zone A. Flow from~ sludge~ pumps to A is also continuous. Biomass f;rom~Cl~and C2 can either be totally irect~ to A, and ~partially directed to B1 and B2. For short periods, sludge is also wasted~from the system.
; Wasting ~rom a reac~or vessel takes place either ~S in the aerat:ion or~non-aeration periods, but is preferred during non-aeration as a more concentrated biomass is ~: :

~Z~5~5~3 , generated resulting in more cost effective sludge management.
Flow from A to Al and A2 is directed to permit flow division to either of two water retaining reactors, 5 Bl -~ Cl or B2 + C2. While surface liquor is being removed ,~
from Cl the total flow from A + Al + A2 is directed to B2 etc; while surface liquor is being removed from C2, the total flow from A ~ Al -~ A2 is directed to Bl etc, This two tank embodiment, with high rate initial plug-flow 10 continuously aerated reactor provides the advantage that uninterrupted ~lows are accepted by the system and that reduced overall reactor volumes are required which has significant capital cost benefit.
This embodiment may also have fixed-film growth 15 media in Bl and B2, and subsequent absorptive reactor sections. This embodiment also operates with aeration and non-aeration sequencing such that while reactor 1 is undergoing aeration, reactor 2 is undergoing non-aeration.
During the decant sequence of reactor 1, total flow from A
20 + Al -~ A2 is directed to reactor 2; and while reactor 2 is in the decant sequence, total flow from A + Al + A2 is directed to reactor 1.
By the use of these concepts, vessel sizes can be reduced with the result that high quality effluents 25 having been biologically denitrified can be produced at overall average hydraulic reten~ion times as low as 9 ` hours ~for domestic wastewatersj as opposed to hydraulic retention times previousIy accepted by the industry of about 24 hours or more; hydraulic retention relating to 30 daily average day weather f 10wr Compartment C serves as the metabolism and absorptive capacity regenerator reactor for organics which are removed in the absorption stages.
Where attached growth absorption takes place, subsequent metabollsm of removed organics takes place in situ.
35 Attached growth solids are eventually displaced from the media due to aging and selective sloughing and flow ~ .

s~ :

contiguously with other dispersed growth solids. The proportion of displaced attached growth solids in the total is a very small proportion at any one time being only about some 10 percent.
During the non-aeration period before effluent removal, absorption mechanisms ta]ce place in the first stclge as be~ore. Second stage absorption takes place in Compartment s with biomass that is contained therein.
This compartment is sized to also ensure that leakage of 10 thè influent liquid phase to, and subsequent increase in the concentration of soluble organics in, final Compartment C is minirnal during the non-aeration period before effluent removal. As stated flow to B is shut off during surface liquid removal.
The repeated cycles of aeration followed by non-aeration expose the biomass to alternating periods whereby oxygen is present and absent. During the initial and subsequent period of the aeration sequence there are miriads of micro regions of depleted oxygen presen-t in the 20 bulk of the biomass. Such absence or near absence of n!olecular oxygen results in substantial biological denitrification, which takes place concurrently with the biological nitrification reactions and also during the non-aeration period. With a minimum of 2 stages of Z5 absorption, it is possible to operate this form of cyclic activated sludge system at mean bulk dissolved oxygen concentrations such that the oxygen demand rate is just ;
exceeded by the oxygen input rate. This has not been ; possible with conventional activated sludge methodology ~O~because of the generation of poor settling biomass. A
feature of this invention is its ability to permit such operations. Operation during the initial period of aeration does not normally show more than about 0.2 - 0.7 mg/L of dissolved oxygen in bulk liquid phase. During the 35 final 25 percent of the aeration period~the dissolved oxy~en concentrations of around 2 mg/L existr Si2ing and 5~

aeration is such that dissolved oxygen concentrations of 2 mg/L exist for approximately 25-33 percent of the total aeration time per day. The growth of non-flocculating organisms that are selected by growth conditions at 5 continuous low dissolved oxygen concentrations is hence negated. In this way, conditions are also generated which promote essentially simultaneous biological nitrification-denitrification reactions and enhanced biological phosphorus removal in this one sludge system.
10 l~uring the non-aeration sequence conditions for anaerobiosis are rapidly achieved within the s,ludge b]~nket in which the oxidation reduction potential is negative and which approaches - 150 millivolts.
Nitrate nitrogen is totally removed within the 15 sludqe during the non-aeration sequence~ Vessel sizing and aeration sequencing is such that bulk nitrate nitrogen, during the aeration sequence is variablP to a concentration less that 2 mg/L. Because of the oxygen demand conditions which exist nitrate nitrogen 20 concentration within microzones of the biological floc are reduced to less than 0.3 mg/L. In the 1 tank system, holding of the mixed influent (anoxic biomass and sewage) for the duration of the decant sequence results in additive anaerobiosis of that fraction. In the two tank 25 system, direction of the total mixed influent flow (anoxic , biomass and sewage) to one vessel, during the decant period of the other vessel, promotes additive macro anaerobiosis conditions in that portion of flow and particularly in the second and subsequent absorption 30 stages. It has been found that percentage biological phosphorus removal mainly varies with the magnitude of the duration of the non-aeration sequence, particularly when aeration and non-aeration sequences are equal or approximately so. Typical biological phosphorus removal 35 for the two s~age absorption configuration described as the preferred embodiment is shown in Figure lS.

~2~

Enhanced biological phosphorus removal can be achieved ~y addition of acetic acid at appropriate concentrations up to about 30 mg/L at the first absorptive mixing state during the on-off sequences. This markedly 5 increases the percent oE biological phosphorus removal and enables the system to be operated at lower non-aeration periods. This enables smaller tank volumes to be used which has a capital cost benefit.
The systems described may also be desirable 10 where carbonaceous oxygen demand only needs to be supplied. Activated sludge processes have not found wide acceptance for treating high-carbon wastewaters such as result from agricultural processes, e.g. fruit canning, potato processing, etc. A feature of this invention which 15 is of potentially great importance is that the absorption may be sequenced such that the BOD of the influent into the last zone, zone C, is low and the settling qualities of the sludqe are high.
To recapitulate, the invention may be regarded 20 as a continuous inflow, intermittent flow path, sequential cycle, activated sludge waste water process for treating wastewa-ter. The process includes continuously receivin~
wastewater into a first zone ~A) into which activated sludge from a subsequent zone is mixed and is retained ~.
~.
~;

r t ';
~S '.

~ .
'' 9)5~

in the firs~ zone for a period of from a~ lea~t approxima~ely two to 20 minutes~ typically about five minute6 or longer, sufficient to for~ a non-bulking sludge and ab~orb oxldizable di~olYed compound~ into the activated sludge. The wastewater, wlhich i8 then undergo$ng ~rea~ment, fro~ the first zone (~) i8 pa~sed in~o a ~econd zone (B) during at lea~t a fir~t aerating time period in o which second zone oxygen i8 transferred inte the wastewater. Oxygen may betran~ferred into thewastewater undergoing treatment by pumping air or oxygen intothe body of water, spraying the water into tha air! or in any other desired manner~ The wastewater is pa~sed into sald second zone during a ~econd quie~cent time period during which Bettlln~ of slud~e is cau~ed by maintaining a quie~cent condition in naid ~econd zone. ~he wa~tewater ~rom the ~econd zone ~B) i~ pa~ed lnto a third zone (C) during ~aid first and second time period~, and is characterized in that it ha~ les~ than approximately twen~y pe~cent of the biochemical oxygen demand the wa~tewater origi~ally contained and further characterized ln that sludge a~ociatedtherewith i8 non-bulking and has a high settling veloci~y. The third zone (C) i~ aerated during the first aerating period of time to regenerate the ab~orption 25 capacit~ of the sludge and i~ settled during the ~econd quiescent period of time. The upper portion of the wa~tewater from the third zone tC) i8 decanted during a third decas~ting p~:riod of time during which there i~ no inflow into the ~econd zon~ (B) from the fir~t zone. The ~teps, except the lnflow into zoneAwhich i8 continuous, i~
repeated ~equentially ln a cyclic manner a8 a cyclioally aerated proce6s, influent wa~tewater being retaine~ in or before the fir~t zone ~A) or dlrected elsewhere therefrom during the third decanting ~ime per~od~
Preferably~ the ~econd zone ~B) and the third zone (C) are in free fluid communlca~ion with each other. It 1 ~:~95~5~

al~o advantageous to effect aera~ion by injecting a s~ream of o~ygen containing gas into a portion of the third zone (C) regenerating the activated ~ludge and inducing backflow of regenerated sludge from the third ~one (C) to the ~Pcond ~one (B) Regensrated activated sludl3e i~ returned from the third zone (C) to the fir~t zone (A~ and, either by speclal pumps, conduits, etc., or by ~ree-~low through the fluid communic~tion between the zoneR, to the ~econd zone (B~.
The the second zone (B) may additionally include a f ixed ilm growth support matrix whlch occupie~ from approxim~tely twenty to approximately 90 percent o~ the portion ofthe secondzone ~B) below th~ bottomwater level.
~hl~ matrix may be a rotating drum type dev~e as de~cribed by Eckenfelder~ or ~ny other device or mechani~m.
Fre~ ~loat~ng su~pended support or ~ixed support may be used. It ls advantageous to rotate the drumt as ~hown in E~igure 11, in a direction which pumps ~ludge from zone C to zone B. The u~e of the matrix ~or dePinlng a f~xed film growth zone on the surface thereo~ i~ particularly beneficial in the treatement of wastewater contalninghigh soluble BOD components, e.g. wherein the total BOD i~ from abou~ 250 to about 2/000 mg/L or even ~omewhat higher and the soluble ~OD component i8 about 50% or more of the total BOD biological component.
~ he proce~s may advantageou~ly oper~te in amanner wherein the second zone tB) comprlse~ a pl~rality of ~ub-zones, (B, B'~ each ~ub-zone abso~ptively tran6porting ~oluble oxygen d~mand of ~he wastewat~r entering ~uch sub~
zone until ~he wa~ewat~r flowing from the la~t ~ub-~one contains no more than twenty percent of the biochemica~
oxygen demand of the orlginal in~luent wa~tewater into ~he proce~s.
The wherein the optimum hydraul ic retention time at mean flow conditions and t~e d~signat~d bottom water ~z~s~

level in th~ ~econd zone (B) is sub~tantially qual to the ~econd quie~cent timeO
Acetic acid may be added to the second zone for thereby improving the phosphoru~ re~oval characteristics of the proc~ss.
. The process i~ highly advantageous for treating municipal wastewater to reduce biochemical oxygen demand and remove ammonia, nitrate nitrogen and phosphoru~. ~he most e~ficient opera~ion i~normally obtainedwhen thefloc load of the influent into the first zone i~ less than approximately 250 mg chemical oxygen demand~gm MLVSS. ~he proce~s involve~ mul~lple stage absorptive reac~ion, metaboliRm o~ the removed biochemical oxygen demand lS a~sociated with sludge, regeneration o~ the ab~orptive capaci~y o~ the ~ludge, and ~et~ling o~ solid~ and decanting of wa~tewater and i~ most econo~ically carried out ina ~ingle water retaining ~tructure having partition~
dividiny said zones from each otherO
Tbe procefis i~ very advantageously carried out uPing parallel intermi~tent flows and lncludes, in thl~
embodiment, con'cinuou~ly receiving wastewater in~o a initial ab~orption zone (A) into which activated sludge from a ~ubsequent zone i8 mi~ed and retainlng the wastewater in the initial ab~orption zone for a period of from at leaRt approximately two to 20 minute~ sufficient to form a non-bulking sludge and ab~orb oxidizable d$ssolved compound~ into the activated sludge. The wastewater undergoing ~reatment i8 then pa~sed from the lnitial absorption zone (A) into at least one of two or more a sequenced ab~orption zones (Bl, B2) during aeration thereof and pa~sing w~stewater into ~he re~pective sequenced absorp~ion zones durlng re~pective quiescent time period~ during which ~ettling of ~ludge 18 caused in the respectlve sequenc~d ab~orptlon z~ne~ by ~aintain~ng a quiescent Gondition in the ~equenced ab~orption zonesD

~2~ S~

The wastewa~er from one sequenced ab~orption zone (Bl) is passed into one biological degrad~ltion zone (Cl) and the wastewater from anot~er sequenced absorption zone tB2) i8 pas~ed into another biological degradation zone (C2)~ the wastewater pa~6ing into the biological deg~adation zone~
be~ng characterized in that it ha~ le~s than approximately twenty percent of the biochemical oxygen demand the . wastewater originally contained and is further characterized in that ~ludge assoc:iated there with i~ non-bulking and has a high ~ettling velocity, the biological degradation zones (Cl, C2) being aerated to regenerate the absorption capaci~y of the ~ludge and being ~ettled during re~pectivequie~cent perlod~. ~he upper portion o~
thewastewAter i~ decanted from on~ biologic~.l degradation zone ~Cl) during one period of tlme and the wa~tewater ~rom the o~her biological degradation zone (C2) i8 decanted during ~nother period of ~ime, there being no inflow ~rom the intlal absorp~ion zone (A) into the one se~uenced ab~orption zone (~1) during the decanta~ion of the one biological degradatlon zone ~C}~D There i~ no inflow into the other ~equ~nced absorption zone (~2) from the inltial absorption zone ~A) during the decantation of the other biological degradation zone ~C2). The decantation o~
the respectlve biological ~b~orption zone~ (Cl and C2) i8 carried out at difPerent time perlod~.
~ he sequenced absorp~ion zones ~Bl and B2) and the biological degradation zone~ (Cl and C2) re~pectively are preferrably i~ free ~luid communication with each other, and, a8 to each o~ the flow path~ Bl - Cl and B2 ~ C2 respectively, they are a~ previou~ly described and may include fixedfilm grow~h media, e~c. ~ inthe previou~ly de&cribed embodimen~ o~ th~ proce$~, regenera~edactivated sludge i~ returned fro~ the respective biological degradation zone~ tCl and C2) to the initial absorptlon zone (A~ and to the re~peGtive ~quenced absorption zone~

~29S~5~3 lBl and ~2)- Similarly, the respective sequenced ab~orption zones tBl and B2) may compri~e a plurality of sub-zone~, (Bl, B'l and B2, B'2 respectively) each sub-zo~e absorptively transporting soluble oxygen demand ofthe wa~tewater entering such ~ub-zone until thewastewater flowing from thelast sub-zone contains no mor~ than twenty percent o~ the biochemical oxygen clemand of the original influent wastewater into the proces~. Typically, the retention time o~ the bioma~Q in the ~equenced ab~orption zone (Bl and B2) respectively are ~ub~tantially equal to the ~ue~cent settling time~
. _ --, . .

:' ., 3 U '`

f.

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Claims (49)

1. A continuous inflow, intermittent flow path, sequential cycle, activated sludge waste water process for treating wastewater, comprising the steps of:
(a) continuously receiving wastewater into a first zone (A) into which activated sludge from a subsequent zone is mixed and retaining said wastewater in said first zone for a period of from at least approximately two to 20 minutes sufficient to form a non-bulking sludge and absorb biodegradable dissolved compounds into the activated sludge;
(b) passing wastewater from the first zone (A) into a second zone (B) during at least a first aerating time period into which second zone oxygen is transferred into the wastewater, and passing was-tewater into said second zone during a second quies-cent time period during which settling of sludge is caused by maintaining a quiescent condition in said second zone;
(c) passing wastewater from the second zone (B) into a third zone (C) during said first and second time periods, the wastewater passing into the third zone being characterized in that it has less than approximately twenty percent of the biochemical oxygen demand the wastewater originally contained and further characterized in that sludge associated therewith is non-bulking and has a high settling velocity, said third zone (C) being aerated during the first aerating period of time to regenerate the absorption capacity of the sludge and being settled during the second quiescent period of time;
(d) decanting the upper portion of the was-tewater from the third zone (C) during a third decanting period of time during which there is no inflow into the second zone (B) from the first zone (A); and (e) repeating in cyclic manner steps (b), (c) and (d), the operation of said steps being charac-terized as a cyclically aerated process, influent wastewater being retained in or before the first zone (A) or directed elsewhere therefrom during the third decanting time period.

2. The process of Claim 1 wherein the second zone (B) and the third zone (C) are in free fluid communication with each other.

3. The process of Claim 2 wherein oxygen is trans-ferred into the wastewater in the third zone (C) regenerating the activated sludge and inducing backflow of regenerated sludge from the third zone (C) to the second zone (B).

4. The process of Claim 1 wherein regenerated activated sludge is returned from the third zone (C) to the first zone (A) and to the second zone (B).

5. The process of Claim 1 wherein the second zone (B) comprises additionally a fixed film growth support matrix which occupies from approximately twenty to approximately 90 percent of the portion of the second zone (B) below the bottom water level.

6. The process of Claim 5 wherein the fixed film growth support matrix is moveable.

7. The process of Claim 1 wherein the second zone (B) comprises a plurality of sub-zones, (B,B') each sub-zone absorptively transporting soluble biochemical oxygen demand of the wastewater entering such sub-zone until the wastewater flowing from the last sub-zone contains no more than twenty percent of the biochemical oxygen demand of the original influent wastewater into the process.

8. The process of Claim 1 wherein the hydraulic retention time at mean flow conditions and the designated bottom water level in the second zone (B) is substantially equal to the second quiescent time.

9. The process of Claim 1 comprising the further step of adding acetic acid to the second zone for thereby improving the phosphorus removal characteristics of the process.

10. The process of Claim 3 wherein regenerated activated sludge is returned from the third zone (C) to the first zone (A) and to the second zone (B).

11. The process of Claim 3 wherein the second zone (B) comprises additionally a fixed film growth support matrix which occupies from approximately twenty to approximately 90 percent of the portion of the second zone (B) below the bottom water level.

12. The process of Claim 11 wherein the fixed film growth support matrix is moveable.

13. The process of Claim 3 wherein the second zone (B) comprises a plurality of sub-zones, (B, B') each sub-zone absorptively transporting soluble biochemical oxygen demand of the wastewater entering such sub-zone until the wastewater flowing from the last sub-zone contains no more than twenty percent of the biochemical oxygen demand of the original influent wastewater into the process.

14. The process of Claim 3 wherein the hydraulic retention time at mean flow conditions and the designated bottom water level in the second zone (B) is substantially equal to the second quiescent time.

15. The process of Claim 3 comprising the further step of adding acetic acid to the second zone for thereby improving the phosphorus removal characteristics of the process.

16. A process for treating municipal wastewater to reduce biochemical oxygen demand and remove ammonia, nitrate nitrogen and phosphorus, comprising the steps of:
(a) in a first zone (A) injecting regenerated activated sludge from a subsequent zone;

(b) flowing wastewater from the first zone (A) to a second aerated zone (B) into which additional regenerated activated sludge is introduced;
(c) flowing wastewater from the second zone (B) to a third zone (c) which is aerated to regenerate the activated sludge absorption capacity which is injected into the first zone (A) and introduced into the second zone (B);
(d) settling the sludge and particulate matter in the second zone (B) and the third zone (C) and thereafter decanting fully wastewater from the upper layers of the third zone (C), there being no inflow from the first zone (A) to the second zone (B) during decantation; and (e) cyclically repeating steps (b), (c) and (d)?

17. The process of Claim 16 wherein the second zone (B) and the third zone (C) are in free fluid communication with each other.

18. The process of Claim 17 wherein oxygen is transferred into the wastewater in the third zone (C) regenerat-ing the absorptive capacity of the activated sludge and inducing backflow of regenerated sludge from the third zone (C) to the second zone (B).

19. The process of Claim 16 wherein the second zone (B) comprises additionally a fixed film growth support matrix which occupies from approximately twenty to approximately 90 percent of the portion of the second zone (B) below the bottom water level.

20. The process of Claim 19 wherein the fixed film growth support matrix is moveable.

21. The process of Claim 16 wherein the hydraulic retention time at mean flow conditions and the designated bottom water level in the second zone (B) is substantially equal to the settling time.

22. The process of Claim 16 comprising the further step of adding acetic acid to the second zone for thereby improving the phosphorus removal characteristics of the process.

23. The process of Claim 16 wherein the floc load of the influent into the first zone is less than approximately 250 mg chemical oxygen demand/gm MLVSS.

24. The process of Claim 16 wherein multiple stage absorptive reaction, metabolism of the removed biochemical oxygen demand associated with sludge, regeneration of the absorptive capacity of the sludge, and settling of solids and decanting of wastewater is carried out in a single water retaining structure having partitions dividing said zones from each other.

25. A process for treating wastewater having a high biochemical oxygen demand of from approximately 250 mg/L to approximately 2,000 mg/L and a high soluble biochemical oxygen demand fraction of approximately 50% or more, comprising the steps of:
(a) in a first zone (A) injecting regenerated activated sludge from a subsequent zone;
(b) flowing wastewater from the first zone (A) to a second aerated zone (B) into which additional regenerated activated sludge is introduced, said second zone comprising a multiplicity of sub-zones each of which is aerated and into each of which additional regenerated activated sludge is introduced.
(c) slowing wastewater from the second zone (B) to a third zone (C) which is aerated to regenerate the activated sludge which is injected into the first zone (A) and introduced into the second zone (B);
(d) settling the sludge and particulate matter in the second zone (B) and the third zone (C) and thereafter decanting fully wastewater from the upper layers of the third zone (C), there being no inflow from the first zone (A) to the second zone (B) during decantation; and (e) cyclically repeating steps (b), (c) and (d).

26. The process of Claim 25 wherein the second zone (B) and the third zone (C) are in free fluid communication with each other.

27. The process of Claim 26 wherein oxygen is transferred into the wastewater in the third zone (C) regenerat-ing the absorptive capacity of the activated sludge and inducing backflow of regenerated sludge from the third zone (C) to the second zone (B).

28. The process of Claim 25 wherein the second zone (B) comprises additionally a fixed film growth support matrix which occupies from approximately twenty to approximately 90 percent of the portion of the second zone (B) below the bottom water level.

29. The process of Claim 28 wherein the fixed film growth support matrix is moveable.

30. The process of Claim 25 wherein the hydraulic retention time at mean flow conditions and the designated bottom water level in the second zone (B) is substantially equal to the settling time.

31. The process of Claim 25 wherein multiple stage absorptive reaction, metabolism of the removed biochemical oxygen demand associated with sludge, regeneration of the absorptive capacity of the sludge, and settling of solids and decanting of wastewater is carried out in a single water retaining structure having partitions dividing said zones from each other.

32. A process for treating wastewater comprising the steps of:
(a) continuously receiving wastewater into an initial absorption zone (A) into which activated sludge from a subsequent zone is mixed and retaining said wastewater in said initial absorption zone for a period of from at least approximately two to 20 minutes sufficient to form a non-bulking sludge and absorb biodegradable dissolved compounds into the activated sludge;
(b) passing wastewater from the initial absorp-tion zone (A) into at least one of two or more sequenced absorption zones (B1, B2) during aeration thereof and passing wastewater into said respective sequenced absorption zones during respective quiescent time periods during which settling of sludge is caused in the respective sequenced absorption zones by maintaining a quiescent condition in said sequenced absorption zones;
(c) passing wastewater from one sequenced absorption zone (B1) into one biological degradation zone (C1) and passing wastewater from another se-quenced absorption zone (B2) into another biological degradation zone (C2) the wastewater passing into the biological degradation zones being characterized in that it has less than approximately twenty percent of the biochemical oxygen demand the wastewater original-ly contained and further characterized in that sludge associated there with is non bulking and had a high settling velocity, said biological degradation zones (C1, C2) being aerated to regenerate the absorption capacity of the sludge and being settled during respective quiescent periods; and (d) decanting the upper portion of the wastewater from one biological degradation zone (C1) during one period of time and decanting the upper portion of the wastewater from the other biological degradation zone (C2) during another period of time, there being no inflow from the intial absorption zone (A) into the one sequenced absorption zone (B1) during the decantation of the one biological degradation zone (C1), and there being no inflow into the other sequenced absorption zone (B2) from the initial absorption zone (A) during the decantation of the other biological degradation zone (C2), the decantation of the respective biological absorption zones (C1 and C2) being at different time periods.

33. The process of Claim 32 wherein the sequenced absorption zones (B1 and B2) and the biological degradation zones (C1 and C2) respectively are in free fluid communication with each other.

34. The process of Claim 33 wherein aeration is effected by inducing backflow of regenerated sludge from the biological degradation zones (C1 and C2) to the respective sequenced absorption zones (B1 and B2)

35. The process of Claim 33 wherein regenerated activated sludge is returned from the biological degradation zones (C1 and C2) to the initial absorption zone (A) and to the respective sequenced absorption zones (B1 and B2).

36. The process of Claim 33 wherein the respective sequenced absorption zones (B1 and B2) comprises additionally a fixed film growth support matrix which occupied from approximately twenty to approximately 90 percent of the portion of the respective sequenced absorption zones (B1 and B2) below the bottom water level.

37. The process of Claim 36 wherein the fixed film growth support matrix is moveable.

38. The process of Claim 33 wherein the respective sequenced absorption zones (B1 and B2) comprises a plurality of sub-zones, (B1, B'1 and B2, B'2 respectively) each sub-zone absorptively transporting soluble biochemical oxygen demand of the wastewater entering such sub-zone until the wastewater flowing from the last sub-zone contains no more than twenty percent of the biochemical oxygen demand of the original influent wastewater into the process.

39. The process of Claim 33 wherein the hydraulic retention time at mean flow conditions and the designated bottom water level in the respective sequenced absorption zones (B1 and B2) is substantially equal to the respective settling times.

40. The process of Claim 33 comprising the further step of adding acetic acid to the respective sequenced absorp-tion zone for thereby improving the phosphorus removal charac-teristics of the process.

41. The process of Claim 32 wherein regenerated activated sludge is returned from the respective biological degradation zones (C1 and C2) to the initial absorption zone (A) and to the respective sequenced absorption zones (B1 and B2).

42. The process of Claim 32 wherein the sequenced absorption zones (B1 and B2) respectively comprise additionally a fixed film growth support matrix which occupies from ap-proximately twenty to approximately 90 percent of the portion of the respective sequenced absorption zones (B1 and B2) below the bottom water level.

43. The process of Claim 42 wherein the fixed film growth support matrix is moveable.

44. The process of Claim 32 wherein the respective sequenced absorption zone (B1 and B2) comprises a plurality of sub-zones, (B1, B'1 and B2, B'2 respectively) each sub-zone adsorptively transporting soluble biochemical oxygen demand of the wastewater entering such sub-zone until the wastewater flowing from the last sub-zone contains no more than twenty percent of the biochemical oxygen demand of the original influent wastewater into the process.

45. The process of Claim 32 wherein the retention time of the biomass in the sequenced absorption zone (B1 and B2) respectively are substantially equal to the quiescent settling time.

46. The process of Claim 32 comprising the further step of adding acetic acid to the second zone near this beginning of the first time period.

47. The process of Claim 1, Claim 16, Claim 25 or Claim 32 further comprising the steps of positioning in the second aeration absorption zone (B) a rotatable fixed film growth support matrix and rotating the matrix in a direction to effectively introduce regenerated activated sludge from the third zone (C) into the second zone (B).

48. The process of Claim 47 wherein the rotatable fixed film growth support matrix is in the form of a rotatable drum-shaped body having a multiplicity of surface forming elements 190 mounted for rotation on a shaft 192 and rotating the body in a direction such that the portion of the body most adjacent the fluid communication means between the second zone (B) and the third zone (C) rotates away from said fluid com-munication means to effectively pump sludge from the third zone (C) to the second zone (B) and mix the sludge in the second zone (B).

49. The process of Claim 1, Claim 16, Claim 25 or Claim 32 further comprising the step of substantially con-tinuously aerating the first zone (A) or zone (B) or both into which regenerated activated sludge is substantially continuously introduced into zone (A) and optionally into zone (B).