Biomembrane wastewater treatment by activated sludge method

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The paper compares the biomembrane and classical activated sludge methods of wastewater treatment and presents the influence of ultraffltration on the ...
DESALINATION ELSEVIER

Desalination 107 (1996) 83-95

Biomembrane wastewater treatment by activated sludge method Michal Bodzek*, Zuzanna Debkowska, Ewa Lobos, and Krystyna Konieczny Silesian Technical University, Faculty of Environmental and Energy Engineering, Konarskiego 18, 44-100 Gliwice, Poland. Tel.: +48-32-371698 Fax: +48-32-371047

Received 22 February 1996; accepted in revised form 26 May 1996

Abstract

The paper compares the biomembrane and classical activated sludge methods of wastewater treatment and presents the influence of ultraffltration on the activated sludge condition. It specifies the difference of enzymatic activity of activated sludge in both systems. In effect of both activated sludge performance and separation properties of the ultrafiltration membrane, the effluent from the biomembrane system is less loaded. Keywords: Wastewater treatment; Activated sludge; Ultraftitration; Biomembrane method; Membranes

1. Introduction In spite of a significant decrease of BOD and s u s p e n d e d matter c o n t e n t s after biological treatment, there still remain in wastewaters s o m e s p a r i n g l y d e c a y i n g pollutants, fine suspensions and, moreover, some water microflora and fauna metabolites, as well as bacteria and viruses. For this reason, further development of biological processes of wastewater treatment is necessary. Modern wastewater treatment methods aim at the removal of residual impurities and biogenic substances resulting in the eutrophication of tanks. Phosphorus c o m p o u n d s are most frequently removed by means of chemical processes, however, for nitrogen removal, the

*Corresponding author,

biological nitrification-denitrification process is usually used [1, 2]. Apart from this, some processes aiming at a decrease of residual impurity concentrations increasing BOD, COD and intensifying the colour of treated wastewaters areused [3]. One of the examples of modernization of biological wastewater treatment consists in the incorporation of ultrafiltration into the activated sludge method treatment [4]. The process combining the biological system with ultrafiltration has been called biomembrane process. Such a solution concept with regard to a waste treatment plant having the capacity of several m3/d is the result of studies aiming to find compact purification systems of wastewaters containing organic compounds. The membrane processes, and, in particular, ultrafiltration, may be integrated both with anaerobic fermentation processes and aerobic

0011-9164/96/$15.00 Copyright© 1996ElsevierScienceB.V. All fights reserved. PH S0011-9164(96)00153-1

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processes of pollution removal. The biom e m b r a n e systems, in which anaerobic fermentation processes are utilized, are now used in the treatment of domestic sewage [5], food industry wastewaters [6] and other wastewaters containing organic compounds [5]. In the case of aerobic w a s t e w a t e r treatment plants, the biomembrane systems are combined with various system operating on the basis of activated sludge. The aim of the studies was to compare the effects of wastewater treatment in the classical and b i o m e m b r a n e s y s t e m s o f activated sludge. Also, the investigations determining the influence of ultrafiltration, introduced instead of a secondary settling tank, on the condition o f activated sludge have been carried out, i.e. the formed populations of microorganisms have been compared. The classical activated sludge system operated in the conditions analogical to the biomembrane one. 2. Experimental 2.1. Apparatus

Fig. 1 presents the diagram of a test stand enabling to carry out comparative studies in the b i o m e m b r a n e and classical activated sludge systems. A tank combined with a settling tank was used as the aeration tank in the classical system. Active capacity of the aerated part was 25 dm 3, and the capacity of the settling tank 8 dm 3. In the biomembrane system, a 40 dm 3 tank was used as the aeration tank, and the aerated volume was also 25 dm 3. Both systems were supplied by means of peristaltic pumps, from one, c o m m o n raw wastes tank. Treated wastes from the classical and biomembrane systems were carried off to separate tanks. Aeration of the activated sludge was carried out by means of air pumps. Identical quantity of air was supplied to both tanks, its flow rate being measured by means o f rotameters. Medium bubble aeration mode was used in the system. The submersion of the aeration grate was 0.28 m. An impeller pump was used for the pumping

of the activated sludge suspension. The bypass conduit of the pump made it possible to maintain a suitable volume flow rate through the ultrafiltration module at proper pressure. T w o ultrafiltration tubular m o d u l e s of membrane diameter 0.016 m and length 0.5 m were used in the system. The membrane area in one module was 0.025 m 2. The retentate stream was divided into two parts. The first was directed to the aeration tank through the return conduit, the other through the recirculation conduit again to the pump, by-passing the tank. The system was also e q u i p p e d with a c o o l e r e n s u r i n g the maintenance of suitable temperature, rotameters for the measurement of flow rate, as well as manometers and a thermometer. 2.2. Membranes and their characteristics

Tubular membranes made in our laboratory from p o l y a c r y l o n i t r i l e (PAN) poly(vinyl chloride) (PVC) and copolymer vinyl chloride-vinyl acetate (WlNICET) were used in the investigations. The phase-inversion method [7-9] was used to make membranes; it consists of casting the film from the polymer solution in d i m e t h y l f o r m a m i d e and gelating in a nonsolvent (water). The membranes were tested with deionized water, determining the dependence of the volumetric water flux (Jw) on transmembrane pressure (AP). Potential dependence of the function Jw = f(AP) has been obtained for all used membranes: PAN membranes: Jw = 25.5 × (AP) °.68 PVCmembranes: Jw = 39.2x (AP) °7° WINICETmembranes: Jw = 10.0× (AP) 073 The c o r r e l a t i o n and d e t e r m i n e d coefficients, exceeding the value of 0.99 in all cases, prove that there is good conformity of the results with the potential function equation. The obtained results show that PVC and PAN membranes are characterized by the highest volumetric water flux, while WINICET membranes are the most compact ones.

M. Bodzek et al. /Desalination 107 (1996) 83-95

t5

85

tS t2

Fig. 1. S c h e m a t i c d i a g r a m o f t h e b i o m e m b r a n e a n d c l a s s i c a l a c t i v a t e d s l u d g e s y s t e m o f w a s t e w a t e r t r e a t m e n t . 1 = Aeration tank of classical system; 2 = Aeration tank of biomembrane system; 3 = Ultrafiltration module; 4 = Raw w a s t e w a t e r tank; 5 = Purified w a s t e w a t e r tank; 6 = P e r m e a t e tank; 7 = W a s t e w a t e r m e t e r i n g p u m p ; 8 = A i r rotameter; 9 = A e r a t i o n p u m p s ; 10 = I m p e l l e r p u m p ; 11, 12, = M a n o m e t e r s ; 13 = T h e r m o m e t e r ; 14 = D e - a e r a t i o n ; 15 = Telerotameter.

2.3. Activated sludge and its characteristics

2.4. Methods of wastewater treatment

The activated sludge from the housing estate biological treatment plant near Gliwice (Poland) was selected for the investigation purposes. The dark-brown sludge was characteristic of good settling properties, its floccules being compact and of large and medium size. No sewage fungus or fauna was found in the sludge. The sludge was retained in an aerated tank to which nutrient medium was added p e r i o d i c a l l y . B e f o r e the initiation o f investigations, the sludge was washed with water, divided into two equal parts and introduced into the aeration tanks of the classical and biomembrane activated sludge s y s t e m s . T h e initial c o n c e n t r a t i o n o f suspension in both system was 5.3 g/dm 3, including 3.9 g/dm 3 of organic suspension, The ratio of organic and inorganic suspension was constant in the course of investigations and amounted to 3:1.

Process parameters of ultrafiltration in the biomembrane system were constant and had the following values: - Transmembrane pressure: 0.2 MPa - Cross-flow velocity of wastes over the membrane surface: 2 m/s - V o l u m e flow rate o f wastes through modules: 2.83 m3/h - Volume flow rate of wastes recirculated through the tank: 0.58 m3/h - Recirculation degree: 5:1 - Temperature: 24-28°C. The above parameters were chosen on the basis of our earlier investigations [8, 10-12] as well as from literature data [13, 14]. To c o m p a r e the p e r f o r m a n c e of the classical and b i o m e m b r a n e s y s t e m s of activated sludge, the same parameters and working conditions of activated sludge were applied (Table 1).

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Table 1 Working parameters of activated sludge Parameter

Flow rate of wastewaters, dm3/h Retention time, h Aeration intensity, dm3/h Oxygen content, mg O2/dm3 Temperature,°C pH Suspension, g/din3: Total Organic Dissolved solids, g/din3: Total Organic Aeration tank loading with impurities, mg O2/dm3: Momentary Average (after 24 h) Activated sludge loading with impurities, g COD/gTSd: Momentary Average (after 24 h)

Initial (first 2 weeks) BM system CL system

After 4 weeks of working time BM system CL system

1.89 13.3 390 6.0

1.63 15.6 390 4.7

8.0

23.5 8.0 5.05 3.72 1.03 0.51

7.9 23.5

7.6 5.14 3.71 1.06 0.50

1,580 520

8.0 3.86 2.93 0.98 0.43

7.9 4.58 3.45 0.99 0.46

1,330 445

0.42 0.14

0.42 0.14

0.46 0.15

0.39 0.13

BM = Biomembrane system, CL = Classical system, TS = Total solids. The table presents average values. The values of temperature, pH, oxygen and suspension concentration were measured before the system has been taken into operation.

Model wastewaters (COD - 860 mg O2/dm 3 and total solids 1.4 g/dm 3) were used in the investigations. Both systems were working as periodic systems, Identical quantities of raw wastes were fed to both systems over 8 hours a day. After the experiment had been completed, the samples were taken for analysis, and the activated sludge from the b i o m e m b r a n e system was r e m o v e d to the aeration tank. T he n the membrane was cleaned by means o f direct flushing of the permeate over the membrane surface without pressure and at cross-flow velocity amounted to 2 m/s. Any chemicals were used to this procedure. After cleaning, the membrane was stored under the deionized water during 16 h out of operation, In the biomembrane system the volume of the outflowing per m eat e was measured in time, and, basing whereon, the volumetric permeate flux was calculated (the capacity of the process),

2.5.

Analytical m e t h o d s

In both treatment methods, the chemical o x y g e n d e m a n d (COD), the cont ent s o f suspension and di ssol ved substances, the contents of total ammonia, nitrate and nitrite nitrogen, and the contents of total phosphorus w ere d e t e r m i n e d for raw and p u r i f i e d wastewaters. The analyses w ere made in a c c o r d a n c e with [15]. Also pH and the temperature of wastewaters were determined. In the course of testing, measurements were made to determine the di fferences in the physiological state o f both populations o f activated sludge. T he m e a s u r e m e n t s were carried out immediately before the activation o f the systems. T he following has been d e t e r m i n e d : pH, t e m p e r a t u r e , o x y g e n concentration, respiratory activity, settling ability [16], the concentration o f suspensions and dissolved substances [15], the activity of dehydrogenase [17, 18] and catalase [19] and

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the contents of nucleic acids and D N A [20]. Also, the respiratory activity and o x y g e n concentration were s u b j e c t e d to analysis during the operation of the system and during the ultrafiltration of activated sludge alone. The investigation was complemented by an additional analysis - a microscopic assessment of the formed biocenoses,

3. Results and discussion

3.1. Capacity of the biomembrane process For the biomembrane process, the daily and average volumetric permeate flux (mean value during the process) was determined. It was defined as permeate volume passing through the membrane per unit area and unit time. The results have been presented in Table 2.

Table 2

Volumetric permeate flux obtained during biomembrane

process Membrane

Temperature, °C Min.-Max. (Average)

Volumetric permeate flux, 105 (m3/m 2 s) Min.-Max. (Average)

of m e m b r a n e s [7]. P V C membranes, as opposed to PAN membranes, have structures characteristic of large macropores (voids) susceptible to pressure compaction. In the course of biomembrane wastewater treatment, there occurs initially a violent decrease of the volumetric permeate flux in time (Fig. 2). The decrease of the volumetric permeate flux over the first 1-1.5 hours is somewhat higher. Later, however, its decrease is continual, but constant value o f this parameter is not achieved. The permeate flux decrease does not exceed 2 0 - 3 0 % of the initial value over 8 h of working time. A similar p h e n o m e n o n was observed during direct ultrafiltration o f activated sludge [11] without nutrient medium (Fig. 2). Basing on the obtained results, we may conclude that the formation of a polarization layer during b i o m e m b r a n e treatment is d i f f e r e n t from that e f f e c t e d by direct ultrafiltration o f w a s t e w a t e r s [11]. The polarization layer of activated sludge settles on the membrane as early as during the first moments of the operation of the system, and the decrease of volumetric permeate flux may ~ i.~ ~ ~ ~

! [ ,

,,= I

Polyacrylonitrile 24-28 (26) 0.95-1.18 (1.05) Poly(vinyl chloride) 24-25 (24.5) 0.87-1.01 (0.94) WINICET 23.5-27 (25.5) 0.73-0.93 (0.82)

~_j d 4.c ~

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1

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2-

1 During the b i o m e m b r a n e treatment of wastewaters, there occur some fluctuations of the volumetric permeate flux. Table 2 presents minimum and maximum values, as well as mean values for the whole sequence of measurements. PVC membranes with higher water p e r m e a b i l i t y are characterized by smaller volumetric permeate flux as compared to P A N membranes (Table 2). This effect seems to result from higher affinity of activated sludge with PVC membranes and differences in porous structure of both kinds

3

4

s

T,,,~ "_,3

8

Fig. 2. Changes of the volumetric permeate flux (Jw) during biomembrane wastewater treatment. 1 = Polyacrylonitrile membrane; 2 = Poly(vinyl chloride) membrane; 3 = Winicet membrane; 4 = Ultrafiltration of activatedsludge alone; Winicet membrane.

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be associated both with the decrease of its thickness and its character (as a result of the change of physicochemical properties of activated sludge during the operation of the system). However, the decrease of volumetric permeate flux is not connected with settling of impurities from the wastewaters on the membrane surface,

Table 4 Comparison of removal degree of pollutants during wastewater treatment by biomembrane and classical activated sludge methods Pollutants, mg/dm 3 Removal degree, %

Biomembrane

Classical

system

system

3.2. Results of wastewater treatment using a classical method as compared to the biomembrane method of activated sludge

COD Total nitrogen Total phosphorus Suspension

98.5-99.0 81.0-89.0

The investigations had two basic aims, i.e. to find out which of the effects of treatment are independent of the activated sludge performance, and to specify the benefits of introducing the ultrafiltration process in place of the secondary settling tank in the classical activated sludge method of wastewater treatment. Table 3 presents the compilation of load components of raw and treated wastewaters for the classical and biomembrane systems of activated sludge, and Table 4 shows the degrees in which particular components for both systems of activated sludge were removed,

The elimination of impurities denoted as COD is very high in both systems. In the biomembrane system the degree of COD elimination reaches 99%, with the permeate COD being only 10 mg O2/dm 3. In the classical activated sludge system the values are 97% and 20 mg O2/dm 3, respectively. This was, to a high extent, affected by the applied operational parameters of activated sludge (Table 1), i.e., long retention time in the aeration tank and settling tank, with the activated sludge loaded with a small amount

40.0-48.0

100

96.3-98.0 55.0-58.0

0-11

-

Table 3 Comparison of effectiveness of model wastewater treatment by biomembrane and classical activated sludge methods Pollutants, mg/dm 3

Temperature, °C pH COD Total nitrogen Organic nitrogen Ammonium nitrogen Nitrate nitrogen Nitrite nitrogen Total phosphorus Organic suspensions Organic dissolved solids

Raw wastewaters

7.4-7.6 860 22.9-30.7 21.6-27.7 1.66-2.58 0.4-0.5 0.01-0 6.89-10.1 0.11-0.16 0.72-0.90

Treated wastewaters Biomembrane system

Classical system

24-26 7.8-8.0 9-12 2.70-4.62 1.53-1.85 0.79-1.42 0.36-1.64 0.03-0.04 3.82-6.20 0 0.28-0.48

23-26 7.8-7.9 25-29 11.0-12.8 1.89-2.79 1.00-1.15 7.81-9.10 0.05-0.065 7.44-9.00 trace 0.48-0.53

M. Bodzek et al. /Desalination 107 (1996) 83-95

of impurities. The removal of compounds measured as COD is caused principally by the performance of activated sludge, since, in the course of direct ultrafiltration of the investigated wastewaters, only 50% of COD is removed [11]. However, a basic difference in the performance of both systems was found when analyzing the results concerning the elimination of nitrogen and phosphorus compounds, The removal of nitrogen compounds is much lower in the classical system than in the biomembrane system. In both systems, the organic nitrogen is removed for the most part. In the classical system a nitrification process takes place, and large amounts of nitrates appear in the effluent. In the biomembrane system the nitrification process is insignificant and smaller amounts of nitrates appear in the permeate. As a result of the transformations of nitrogen compounds in the biomembrane system, over 80% of nitrogen is eliminated from the wastewaters, and only 55% in the classical system. We may state that the introduction of the membrane to the system plays a decisive role here since, in the course of direct ultrafiltration, the removal of nitrogen compounds amounted to 70% [11]. Also the elimination of phosphorus c o m p o u n d s is much higher in the biomembrane system than in the classical one. The degrees of elimination are respectively 45 % and several percent. Since the removal of phosphorus compounds in the biomembrane system is comparable to their retention by the membranes during ultrafiltration (about 43%) [11], we may state that the transportseparation properties of the membrane play a decisive role here. In the biomembrane system the suspensions were completely eliminated (the permeate is clear). In the classical system, a small amount of sludge appears in the effluent causing insignificant increase of COD values alone, The removal of suspensions during direct ultrafiltration is also complete [11]. The amount of inorganic substances in the effluent of both systems is practically the

89

same. The effects of wastewater treatment in the biomembrane system are better than in the classical system of activated sludge and in direct ultrafiltration. It results both from the performance of activated sludge and from the separation properties of ultrafiltration membranes. The integration of the process of biological treatment of wastewaters with the ultraflltration makes it possible to increase the effects of treatment achieved separately in these processes and offers new possibilities in the technology of biological treatment of wastewaters.

3.3. Application of ultrafiltration in view of its influence on the condition of activated sludge (comparison of the formed microorganism populations) Both systems of activated sludge (classical and biomembrane) operated with the same working parameters. In comparison with the classical system, the biomembrane one is characterized by the occurrence of an increased turbulence and higher pressure resulting from the character of ultrafiltration performance. The obtained populations of activated sludge varied decisively, both in the enzymatic aspect, biocenoses composition and physical properties. The activated sludge in the classical system was of brown colour with compacted floccules of various size, mostly large and medium. Very rich accompanying fauna developed in the sludge. It resulted in the creation of amoebas (Mastgoamoeba limax, Arcella sp.,

Diflugia sp., Placocysta sp., Amoeba proteus), ciliates (Vorticella campanula, Vorticella convolaria, Vorticella microstoma, Aspidisca proteus) and rotiferes (Habrotricha triples, Philodina nitida, Monostyla sp., Habrotrocha sp.)(Fig. 3). Also sewage fungi accompanying the activated sludge floccules developed very intensively (Fig. 3). However, the intensive evolution of fungi did not result in any deterioration of sedimentary properties of the sludge. Over the whole period of

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M. Bodzek et al. / Desalination 107 (1996) 83-95

Fig. 3. Activated sludge from aeration tank of the classical system, a. Presence of monocells (ciliates) as well as multicella (rotiferes) microorganisms; b. Floccules of the accompanying settling fauna amoebas (globular shape) and settling ciliates (cup-shaped).

testing Mohlmann's index varied within 69113 cm3/gTS (86 cm3/gTS on average), The activated sludge f o r m e d in the biomembrane system was of milky brown colour. The sludge floccules were small and the sludge was much more dispersed (Fig. 4). No accompanying organisms were found: there was neither fauna nor fungi there. All the time M o h l m a n n ' s index showed an increasing tendency, from 190 cm3/gTS to 270 cm3/gTS . The sludge in the biomembrane system was dispersed only a few minutes after the activation of the system, as a result of turbulence and increased pressure,

Fig. 5 presents the sedimentation curves for both systems: the initial ones, after 24 hours, 20 hours and after 38 days of performance. The initial sedimentation curves (before the activation of the system) are practically the same. After the activation of the system, as a result of dispersion, the activated sludge in the biomembrane system exhibited weak sedimentation capacity. However, in the classical system, in spite of the development of fungi, the sludge had good sedimentation characteristics until the end. The sedimentation curves maintained the same character for both systems over the whole

M. Bodzek et al. /Desalination 107 (1996) 83-95

91

activated sludge activity from the classical system corresponded with the increase in the biom system andalso e

aevels

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t..

.

~

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............. Fig. 4. Activated sludge from biomembrane system,

period of testing, Table 5 presents the parameters of the physiological state of activated sludge. In the course o f testing, the occurrence of two activated sludge performance periods was determined. During the first period - the period of entering the process, which lasted two weeks, the sludge was being adapted to working conditions. In this period, over the first week, there occurred an increase of enzymatic activity of the sludge, and next - its decrease. In the second w e e k - after the period of entering the process, the enzymatic activities were stabilized at a constant level. It is significant that the changes in both systems occurred in a similar way, i.e., the increase of

orbothsystemscorrespon

edwith

each other. Also the stabilization in both systems occurred in the same time. Basing on the obtained data, it has been found that there is a basic difference in enzymatic activities of the activated sludge. The sludge from the classical system had higher r e s p i r a t o r y a c t i v i t y ( A O ) and dehydrogenase activity (AD) than the sludge from the biomembrane system, whereas the catalase activity (AK) was higher for the biomembrane system. The content of nuclei acids was different for these two kinds of sludge. The sludge from the b i o m e m b r a n e system contained more DNA than the sludge from the classical system, whereas the R N A content was the opposite: the sludge from the classical system contained greater amount of RNA. The i n c r e a s e d contents of D N A and decreased contents of RNA, as well as higher catalase activity together with biomass drop, prove that the d e c o m p o s i t i o n o f organic substances takes place more quickly in the biomembrane system than in the classical one. The sludge in the biomembrane system, as compared to the conventional one, is in the state of "hunger", in spite of the same amount of substrate supplied. This was probably e f f e c t e d b y c h a n g e s in the e n z y m a t i c functioning of the cells due to increased pressure in the b i o m e m b r a n e system. The change in the enzymatic functioning of the cells is also responsible for the formation, by means of selection, of a specific population of bacteria in the biomembrane system, with all consequences affecting the state of biocenose and the obtained purification effects. Since the t e s t i n g was conducted periodically, measurements were made to determine differences in the functioning of the systems during substrate batching. Fig. 6 presents the dependence of the respiratory activity on the duration of the process in the course of wastewater treatment and ultrafiltration of activated sludge without

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substrate batching. On the basis of the obtained results it has been found that the respiratory activity increases in both systems after they have been supplied with substrate, On the other hand, oxygen concentration in the aeration tanks decreases in these conditions. However, there is a basic difference in the functioning of both systems, The increase of the respiratory activity in the classical system results only from adding the substrate, whereas in the biomembrane system also from other factors like the activation of the system and the increase of pressure during the operation (Fig. 6). The increase of activity as a result of subjecting the sludge to an increased pressure and turbulence confirms the conclusion that the sludge changes its enzymatic functions in these conditions,

30

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Fig. 5. Sedimentation curves of activated sludge coming from biomembrane and c l a s s i c a l systems. a. Initial; b. After 24 h of working time; c. After 20 days of w o r k i n g time; d. After 38 days of working time.

Summing up the obtained results it should be stated that, in spite of maintaining the same operational parameters of both systems, a specific population of activated sludge was formed in the biomembrane system, which was decidedly different from the activated sludge in the classical system. The formation of the specific activated sludge is the result of the ultrafiltration process of applied parameters, i.e., pressure and turbulence. These two kinds of sludge are different both with regard to biocenoses composition and enzymatic functioning, which is probably not without influence on the obtained effects of wastewater treatment. The quality of permeate is thus affected both by the retention of the impurities by the membrane, and also by the physiological state of activated sludge.

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Table 5 Physiological state parameters of activated sludge in classical (CL) and biomembrane (BM) systems Parameter

Settling, cm3/dm3 Molhman's index, cm3/gTS Respiratory rate: AOv, mg O2/dm3h AOx, mg O2/goTsh Dehydrogenase activity: ADv, mg TF/dm3h ADx, mg TF/gOTSh Catalase activity: AKv, imp/dm3s AKx, imp/goTss Nucleic acids content: KNv, g/din3 KNx, mg/goTs DNA content: DNAv, g/din3 DNAv, mg/gOTS RNA content: RNAv, g/din 3 RNAx, mg/goTs

Initial (first 2 weeks) BM system CL system 450 86

960 191

After 4 weeks of working time BM system CL system 390 86

940 248

30.8 8.21

16.3 4.28

18.4 5.37

12.0 4.17

29.0 7.60

12.8 3.26

15.9 4.63

5.70 2.00

8.60 2.22

15.4 4.45

8.20 2.37

13.4 4.66

303 80.1

256 66.8

261 75.3

228 77.0

-

-

122 36.2

135 48.4

-

-

137 41.0

78.0 27.6

BM = Biomembrane system; CL = Classical system; TS = Total solids; OTS = Organic total solids; "IF = Triphenylformazan; imp. = Impulse. The table presents average values.

4. C o n c l u s i o n s In t h e c o u r s e o f t h e b i o m e m b r a n e treatment, the e f f i c i e n c y o f the process does not d e p e n d o n its c o m p a c t n e s s or the kind o f membrane-forming polymer, T h e p e r f o r m a n c e o f activated sludge has an e s s e n t i a l i n f l u e n c e o n the e l i m i n a t i o n o f impurities m e a s u r e d as COD. T h e elimination o f C O D as a result o f ultrafiltration o f wastes a m o u n t s to a b o u t 50%, w h e r e a s during the b i o m e m b r a n e t r e a t m e n t and in the classical s y s t e m o f a c t i v a t e d s l u d g e the d e c r e a s e o f C O D reaches the value o f 9 7 - 9 9 % . The elimination of nitrogen and p h o s p h o r u s c o m p o u n d s in the b i o m e m b r a n e s y s t e m is m u c h h i g h e r than in the classical one. T h e d e g r e e o f e l i m i n a t i o n o f n i t r o g e n

and p h o s p h o r u s c o m p o u n d s is close to the retention coefficients of these compounds during d i r e c t ultrafiltration. Thus, b o t h the separating p r o p e r t i e s o f the m e m b r a n e and the p e r f o r m a n c e o f activated sludge play an important r o l e in t h e m e c h a n i s m of elimination of nitrogen and phosphorus compounds. M e m b r a n e s r e t a i n 100% o f s u s p e n s i o n , w h e r e a s the e f f l u e n t f r o m the classical a c t i v a t e d s l u d g e s y s t e m c o n t a i n s small quantity o f suspension. In spite o f the a p p l i c a t i o n o f initially h o m o g e n e o u s activated sludge and the same o p e r a t i o n p a r a m e t e r s for b o t h systems, the p o p u l a t i o n o f activated sludge created in the b i o m e m b r a n e s y s t e m is d e c i d e d l y different f r o m the population in the classical system.

94

M. Bodzek et al. / Desalination 107 (1996) 83-95

~

,~

ct.

r7

E

o 25ic zo

i~o ,' . . . . .

J

".

E

"~ z~l

~

b.

1~-1

~

',

",

i

2o !

[-.. 5.. Z '

5..2

--

o

.......

,

:

I\,,,

'--..

-_

BIOM~F_.~B~.AHE .~9,~TE.A,~

1

Oj,

._C ........

CONVF_..HIIONAL

T- -'i'

~UJ&TE..U~,

Fig. 6. Dependence of respiratory activity of activated sludge coming from biomembrane and classical systems on working time. a. During wastewater treatment; b. During ultrafiltration of activated sludge alone. AO = Respiratory activity; DB = Wastewater dosage start; DE = Wastewater dosage end.

This is the result of an increased pressure and turbulence, and, probably, the result of the retention of impurities by the membranes. As a result of higher pressure in the biomembrane system, enzymatic activity of the activated sludge differs from the activity of sludge from the classical system. Due to this, the decomposition of organic substances in the biomembrane system proceeds faster than in the classical system, which influences the effects of treatment. The effects of wastewater treatment in the biomembrane system are better than in the

[2]

Y. Suwa, T. Yamagisiki, Y. Urushigawa, and M.

Hirai, Simultaneous organic carbon removal

-

nitrification by an activated sludge process with

[3] [41 [5] [6]

cross-flow filtration. J. Ferment. Bioeng. 67 (1989) 119-125. R.F. Madsen, Membrane technology as a tool to prevent dangers to human health by water-reuse.

Desalination 67 (1987) 381-393. M. Bodzek and Z. Debkowska, Biomembrane

organic wastewater treatment. Biotechnologia 34 (1991) 74-89 (in Polish). M. Cheryan, Ultrafiltration Handbook. Technomic Publ. Co., Lancaster, 1986. T.J. O'Sullivan, A.C. Epstein, S.R. Korchin, N.C.

Beaton,

Application

of ultrafiltration in

biotechnology. Chem. Eng. Prog. 80 (1985) 68-

classical one. The quality of effluent is dependent both on the activated sludge performance and the separation properties of the membrane,

[7]

75. M. Bodzek, Preparation, structure and transport properties of ultrafiltration membranes made of

References

[8]

polyacrylonitrile and poly(vinyl chloride). In: B. Sedlacek and J. Kahoves (eds.), Synthetic Polymeric Membranes, Walter de Gruyter, BerlinNew York, 1987, pp. 193-202. M. Bodzek and K. Konieczny, Ultrafiltration membranes made of vinyl chloride-vinyl acetate copolimer. J. Membr. Sci. 76 (1993) 269-280. S. Loeb and S. Sourirajan, High-flow semipermeable membranes for separation of water from

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F. Boudon, M. Faivre, and H. Paillard, Innovations dans les techniques du traitment de l'eau et repuration. La Technique Moderne 80 (1988) 46-48.

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[16] J. Gancarczyk, Wastewater treatment with activated sludge. Arkady, Warszawa, 1963 (in Polish). [17] K. Miksch, The influence of the TTC concentration on the determination of activated sludge activity. Acta Hydrochim. Hydrobiol. 13 (1985) 67-73. [18] K. Miksch, Auswahl einer optimalen Methodic fiir die Aktivit~itsbestimmung des Belebtschlammes mit Hilfe TTC-Testes. Vom Wasser 64 (1985) 187-198. [19] Z. Debkowska, Application of bioluminescence reactions to determination of microorganisms activity, Master's Thesis, Silesian Technical University, Gliwice, Poland 1987 (in Polish). [20] E, Thomanetz, Untersuchungen zur Charakterisierung und quantitativen Erfassung der Biomasse von belebten Schlammen, Oldenburg, Munich, Germany, 1982.