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Fluctuation of effluent quality from activated sludge plants
Waste Water Treatment
52
GrLs H. W. VAN(1964) Bacteriology o f Activated sludge. IG-TNO Report No. 32. LErct~RD G., NOURSE L. D. and SCHWARTZH. M. (1964) The measurement ofdehydrogenase activity of activated sludges. 2nd Int. Conf. on Water Pollut. Res. Tokyo, 1964. MANCY K. H. and Wr:STGART~W. C. (1962) A galvanic cell oxygen analyser. J. Wat. Pollut. Control Fed. 34, 1037. TENeH H. B. and MORTON A. Y. (1962) The application of enzyme kinetics to activated sludge research. Proc. Inst. Inst. Sew. Purif 5, 478.
F l u c t u a t i o n o f effluent quality f r o m activated sludge plants. IVAN ~PI~KA, C z e c h o s l o v a k i a
As the demand for water increases, both sewage and river water will be used more extensively. The municipal sewage plants manager of the future may therefore be called upon to produce an effluent which can be used either directly in industry and agriculture or indirectly as a source of raw water. The great majority of the streams to which Czechoslovakian communities discharge their sewage effluent are small. It is obvious that, due to variable flow conditions, quality requirements of biological plants effluent based on the average concentrations of unremoved polluting matter, measured by means of BOD, COD, or volatile suspended solids, (VSS), might not be a satisfactory estimate for determining the adequate function of purification plants. As far as effluent BOD is concerned, it has been found that the unremoved hourly BOD (i.e. kg BOD/hr) in a 24-hr period varies from about 60 to 160 per cent, 60 to 170 per cent and 35 to 185 per cent of the average hourly unremoved BOD (i.e. kg BOD/hr) for extended aeration plant, conventional activated sludge plant and high-rate activated sludge plant, respectively. The literature furnishes little information on the effect of a primary design and operating variable for the activated sludge process (i.e. kg BOD/kg mixed liquor volatile sludge solids, MLVSS, and the detention period) on the fluctuation of effluent impurities. As yet, almost all mathematical models of activated sludge process published so far were developed for steady-state systems. However, in practice biological systems operate at a steady-state different from equilibrium, and the operational and cultural conditions are partly random. This paper is concerned with the effect of BOD and COD loading and detention period on the diurnal and hourly fluctuation of effluent BOD, filtrate BOD, COD, filtrate COD, and VSS. Experimental data have been obtained for five years of full-scale research in a P~ibram activated sludge plant and for three years full-scale operation in a Kralupy n. Vlt. activated sludge plant. The different experimental series with the activated sludge stabilization, conventional activated sludge process and high-rate activated sludge process were carried out with sufficient analytical and operational control to justify detailed statistical analysis of results. The following relationships are proposed: Variety index (VI) -- variety in:fluent-variety effluent = ,=n ~ ~ ,=nbtb, = Y~ log ]~ ~ l o g . ~ , i=1
t:1
where: n A at B bt
= number of grab samples in sampling period T(usually 24 hr); = kg of influent impurities (e.g. kg BOD) per sampling period T; T = kgofinfluentimpuritiesper- ; n = kg of effluent impurities per sampling period T; T = kg of effluent impurities per - . n
Dl Resistance index (RI) = Do. S ' where:
Dl D, S
= dispersion variance of a set of values at; = dispersion variance of a set of values bt; = kg MLVSS in activated sludge system.
Waste Water Treatment
53
With decreasing "damping effect" VI decreases and vice versa. Some typical results obtained are as follows" 1. With constant loading of about 0.035 kg BOD/day per kg MLVSS and decreasing detention period within the limits of 24 to 13 hr, RI decreases. 2. With detention periods ranged from 1"2 to 2.2 hr and increasing loading from about 0.4 to 20 kg BOD day/per kg MLVSS RI increases. 3. With constant detention period of about 3.4 hr and loading within the limits of 0"5 to 1"6 kg BOD/day per kg MLVSS the change of RI was only negligible. 4. With detention periods within the limits of 0"6 to 0'97 hr and increasing loading from about 0.33 to 29 kg BOD/day per kg MLVSS RI increases. Within this limits the following equation fits the experimental data satisfactorily: L = 0"27 • o'a7 RI, where: L = loading, kg BOD/day per kg MLVSS; RI = Resistance index for T = 24 hr and n = 12. 5. The cyclic variation in effluent VSS from extended aeration was noted. It is not clear what mechanism causes these effects. Further experimental results will be discussed in the paper. At the same time, the rate of effluent quality fluctuation due to various mixing patterns in aeration units, obtained from full-scale tracer studies, will be discussed. The results indicate new possibilities for appropriate estimate of various modifications of activated sludge process. With increasing organic loading RI usually increases, however, VI decreases due to decreasing weight of biomass in the system; even with little average purification efficiency shift (i.e. with loading within the limits of 0.5 to 1-5 kg BOD/day per kg MLVSS) a decrease in VI usually ,OCCURS.
M e t a b o l i s m of suspended matter in the activated sludge process. SHUNZO TAKAHASHI, TOSHIHIKO FUnTA, M I c r u o KATO a n d TAKASHI SAIKI, W a t e r W o r k s a n d S e w a g e B u r e a o f N a g o y a City, N a g o y a , J a p a n The purification mechanism of sewage by the activated sludge is classified roughly into two categories: (a) removal and metabolism of suspended and colloidal matters, (b) adsorption, absorption and metabolism of soluble matters. A good deal of work has been done on the latter subject but only a little on the former. However, the proportion of suspended and colloidal organic matter in the total organic matter of sewage is very high, namely about 50 to 80 per cent in the raw sewage and about 50 per cent in the primary effluent. Therefore, the metabolism of suspended and colloidal matters may represent a large portion of the purification of sewage. Further, the metabolism of this suspended matter attached to the activated sludge seems to have an important role not only in recovery of the ability of activated sludge to remove suspended matters, but also in adsorption, absorption and metabolism of soluble matter. In order to elucidate the purification mechanism by the activated sludge, it is important to know the behaviour of suspended matter. In the present report, the metabolism of suspended matter by the activated sludge will be dealt with in relation to the size and composition of the suspended matter, its loading on the activated sludge and the condition of metabolism. Further, the interaction between suspended and soluble matter in the metabolism and the role of bacteria and protozoa will also be reported. EXPERIMENTAL The suspended matter was prepared by cultivating bacteria (Escherichia coli) and activated sludge in media containing organic compounds labelled with 14C. After growing, the bacteria were boiled and washed repeatedly on a membrane filter until the filtrate showed no radioactivity. The suspended matter thus obtained was mainly composed of protein. Starch labelled with 14C was also used as the suspended matter. The apparatus used for the experiment consisted of an air compressor, air-flow
52
GrLs H. W. VAN(1964) Bacteriology o f Activated sludge. IG-TNO Report No. 32. LErct~RD G., NOURSE L. D. and SCHWARTZH. M. (1964) The measurement ofdehydrogenase activity of activated sludges. 2nd Int. Conf. on Water Pollut. Res. Tokyo, 1964. MANCY K. H. and Wr:STGART~W. C. (1962) A galvanic cell oxygen analyser. J. Wat. Pollut. Control Fed. 34, 1037. TENeH H. B. and MORTON A. Y. (1962) The application of enzyme kinetics to activated sludge research. Proc. Inst. Inst. Sew. Purif 5, 478.
F l u c t u a t i o n o f effluent quality f r o m activated sludge plants. IVAN ~PI~KA, C z e c h o s l o v a k i a
As the demand for water increases, both sewage and river water will be used more extensively. The municipal sewage plants manager of the future may therefore be called upon to produce an effluent which can be used either directly in industry and agriculture or indirectly as a source of raw water. The great majority of the streams to which Czechoslovakian communities discharge their sewage effluent are small. It is obvious that, due to variable flow conditions, quality requirements of biological plants effluent based on the average concentrations of unremoved polluting matter, measured by means of BOD, COD, or volatile suspended solids, (VSS), might not be a satisfactory estimate for determining the adequate function of purification plants. As far as effluent BOD is concerned, it has been found that the unremoved hourly BOD (i.e. kg BOD/hr) in a 24-hr period varies from about 60 to 160 per cent, 60 to 170 per cent and 35 to 185 per cent of the average hourly unremoved BOD (i.e. kg BOD/hr) for extended aeration plant, conventional activated sludge plant and high-rate activated sludge plant, respectively. The literature furnishes little information on the effect of a primary design and operating variable for the activated sludge process (i.e. kg BOD/kg mixed liquor volatile sludge solids, MLVSS, and the detention period) on the fluctuation of effluent impurities. As yet, almost all mathematical models of activated sludge process published so far were developed for steady-state systems. However, in practice biological systems operate at a steady-state different from equilibrium, and the operational and cultural conditions are partly random. This paper is concerned with the effect of BOD and COD loading and detention period on the diurnal and hourly fluctuation of effluent BOD, filtrate BOD, COD, filtrate COD, and VSS. Experimental data have been obtained for five years of full-scale research in a P~ibram activated sludge plant and for three years full-scale operation in a Kralupy n. Vlt. activated sludge plant. The different experimental series with the activated sludge stabilization, conventional activated sludge process and high-rate activated sludge process were carried out with sufficient analytical and operational control to justify detailed statistical analysis of results. The following relationships are proposed: Variety index (VI) -- variety in:fluent-variety effluent = ,=n ~ ~ ,=nbtb, = Y~ log ]~ ~ l o g . ~ , i=1
t:1
where: n A at B bt
= number of grab samples in sampling period T(usually 24 hr); = kg of influent impurities (e.g. kg BOD) per sampling period T; T = kgofinfluentimpuritiesper- ; n = kg of effluent impurities per sampling period T; T = kg of effluent impurities per - . n
Dl Resistance index (RI) = Do. S ' where:
Dl D, S
= dispersion variance of a set of values at; = dispersion variance of a set of values bt; = kg MLVSS in activated sludge system.
Waste Water Treatment
53
With decreasing "damping effect" VI decreases and vice versa. Some typical results obtained are as follows" 1. With constant loading of about 0.035 kg BOD/day per kg MLVSS and decreasing detention period within the limits of 24 to 13 hr, RI decreases. 2. With detention periods ranged from 1"2 to 2.2 hr and increasing loading from about 0.4 to 20 kg BOD day/per kg MLVSS RI increases. 3. With constant detention period of about 3.4 hr and loading within the limits of 0"5 to 1"6 kg BOD/day per kg MLVSS the change of RI was only negligible. 4. With detention periods within the limits of 0"6 to 0'97 hr and increasing loading from about 0.33 to 29 kg BOD/day per kg MLVSS RI increases. Within this limits the following equation fits the experimental data satisfactorily: L = 0"27 • o'a7 RI, where: L = loading, kg BOD/day per kg MLVSS; RI = Resistance index for T = 24 hr and n = 12. 5. The cyclic variation in effluent VSS from extended aeration was noted. It is not clear what mechanism causes these effects. Further experimental results will be discussed in the paper. At the same time, the rate of effluent quality fluctuation due to various mixing patterns in aeration units, obtained from full-scale tracer studies, will be discussed. The results indicate new possibilities for appropriate estimate of various modifications of activated sludge process. With increasing organic loading RI usually increases, however, VI decreases due to decreasing weight of biomass in the system; even with little average purification efficiency shift (i.e. with loading within the limits of 0.5 to 1-5 kg BOD/day per kg MLVSS) a decrease in VI usually ,OCCURS.
M e t a b o l i s m of suspended matter in the activated sludge process. SHUNZO TAKAHASHI, TOSHIHIKO FUnTA, M I c r u o KATO a n d TAKASHI SAIKI, W a t e r W o r k s a n d S e w a g e B u r e a o f N a g o y a City, N a g o y a , J a p a n The purification mechanism of sewage by the activated sludge is classified roughly into two categories: (a) removal and metabolism of suspended and colloidal matters, (b) adsorption, absorption and metabolism of soluble matters. A good deal of work has been done on the latter subject but only a little on the former. However, the proportion of suspended and colloidal organic matter in the total organic matter of sewage is very high, namely about 50 to 80 per cent in the raw sewage and about 50 per cent in the primary effluent. Therefore, the metabolism of suspended and colloidal matters may represent a large portion of the purification of sewage. Further, the metabolism of this suspended matter attached to the activated sludge seems to have an important role not only in recovery of the ability of activated sludge to remove suspended matters, but also in adsorption, absorption and metabolism of soluble matter. In order to elucidate the purification mechanism by the activated sludge, it is important to know the behaviour of suspended matter. In the present report, the metabolism of suspended matter by the activated sludge will be dealt with in relation to the size and composition of the suspended matter, its loading on the activated sludge and the condition of metabolism. Further, the interaction between suspended and soluble matter in the metabolism and the role of bacteria and protozoa will also be reported. EXPERIMENTAL The suspended matter was prepared by cultivating bacteria (Escherichia coli) and activated sludge in media containing organic compounds labelled with 14C. After growing, the bacteria were boiled and washed repeatedly on a membrane filter until the filtrate showed no radioactivity. The suspended matter thus obtained was mainly composed of protein. Starch labelled with 14C was also used as the suspended matter. The apparatus used for the experiment consisted of an air compressor, air-flow