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Influence of toxicity on the performance of a trickling filter system
Agricultural Wastes 10 (1984) 221-228
Influence of Toxicity on the Performance of a Trickling Filter System
T. Viraraghavan Faculty of Engineering, University of Regina, Regina, Saskatchewan, Canada
& R. C. Landine & A. A. Cocci ADI Limited, Consulting Engineers, Fredericton, New Brunswick, Canada
ABSTRACT A potato processing wastewater treatment plant located in eastern Canada includes several unit operations--screening, primary settling, two-stage trickling filtration and secondary settling. Primary sludge is dewatered in a vacuum filter and the dewatered sludge is hauled away. The secondary sludge is usually pumped to a digestion and dewatering lagoon. The processing plant has been in operation since 1971; a new by-product line was commissioned in 1979. The main product isfrench fried potatoes, but instant potato flakes are also manufactured. The performance of the wastewater treatment plant, especially its BOD removal efficiency, significantly deteriorated during 1980. This paper presents the effect of toxicity (one of the causes examined) arising from farm and in-plant chemicals and heavy metals on the trickling filter system.
INTRODUCTION A large potato processing plant in eastern Canada became operational in the spring of 1971. The main product is french fried potatoes, but instant potato flakes are also manufactured and there is a starch recovery plant. 221 Agricultural Wastes 0141-4607/84/$03.00 © Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
222
T. Viraraghavan, R. C. Landine, A. A. Cocci TABLE 1 BOD Removal in Trickling Filters
Month
Mean BOD removal
(%) March, 1978 April, 1978 September, 1978 October, 1978 November, 1978 December, 1978
76.9 68.0 51.9 73.0 83.4 72-0
January, 1979 February, 1979 March, 1979 April, 1979 May, 1979 June, 1979 July, 1979 September, 1979 October, 1979 November, 1979 December, 1979
73.9 71.5 71.2 59.1 63.9 72.9 57.3 59-0 58.8 61.5 72.7
January, 1980 February, 1980 March, 1980 April, 1980 May, 1980 June, 1980 September, 1980 October, 1980 November, 1980 December, 1980
71.3 79"2 70.3 37.8 78.0 72.2 80.4 39.8 11.5 29.0
January, 1981 February, 1981 March, 1981 a April, 1981 b May, 1981 b June, 1981 c
23.8 18.0 38.1 67.3 88.9 35.2
a Half flow to trickling filter since 23 March, 1981. b Half flow to trickling filter for month. c Full flow until shut down--12 June, 1981.
Influence of toxicity on the performance of a trickling filter system
223
A new by-product line went into operation in the spring of 1979. A new pizza plant also discharges wastes to the wastewater treatment plant. The wastewater treatment plant is comprised of several unit operations --screening, primary settling, two-stage trickling filtration and secondary settling. Primary sludge is dewatered in a vacuum filter and the dewatered sludge is hauled away. The secondary sludge is usually pumped to a digester and dewatering lagoon. Details of the treatment plant are available elsewhere (Landine & Dean, 1973). The plant performance estimated by BOD removal dramatically deteriorated during October, 1980 and the reduction in performance continued until March, 1981, at which time half the flow entering the secondary system was diverted to the river directly and mud water was kept out of the treatment system. A monitoring programme was developed and put in place in April, 1981 to aid in the determination of the causes of the poor performance of the treatment system; this was continued until the seasonal closing of the factory in June, 1981. Possible causes of the poor performance of the treatment plant were examined; these included the loading rate, pH changes, mud water impacts, toxicity aspects, dissolved oxygen levels, grease and nutrient conditions. A general overview of this evaluation was presented at the 1983 Purdue Industrial Wastes Conference (Viraraghavan et al., 1983). This paper presents specifically the toxicity aspects that could have influenced, to some extent, the poor performance of the trickling filter system. PERFORMANCE OF THE TRICKLING FILTER SYSTEM Mean monthly BOD removal efficiency of the trickling filter system (Table 1) remained generally in the 60-80 ~o range from March, 1978 to September, 1980, except during April, 1980 when it dropped to approximately 40 ~o; however, the efficiency exhibited a downward trend from October, 1980 to March, 1981. In April and May, 1981, when only 50 ~ PCE flow was admitted to the filter, the efficiency improved to 70-90 ~. TOXICITY Toxicity considerations related to farm and in-plant chemicals and heavy metals are discussed in this section.
T. Viraraghavan, R. C. Landine, A. A. Cocci
224
TABLE 2 Heavy Metals in Primary Clarifier Effluent (PCE) (Results in mglitre- 1)**
Date
Cu
Zn
Cd
Fe
Mn
14 April 15 April 21 April 22 April 28 April 29 April 5 May 6 May 12 May 13 May 19 May 20 May 26 May 27 May
0.20 0.14 0.13 0.14 0.16 0.15 0.12 0.27 0.17 0.19 0.09 0.13 0.05 0.05
0.41 0.35 0-44 0.35 0.55 0.41 0.35 0.67 0-70 0.74 0.56 0.62 0.40 0.32
LT0.1 LT0-1 LT0-1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1
7.34 8.65 7.65 7.16 5.37 8.00 6.74 11.8 9.22 7.71 15.3 18.9 19.3 14.2
0"88 0.84 0.94 0"86 0.71 0.77 0.71 0.87 0.87 0.74 0.74 0-88 0.95 0.81
Average Permissible ** LT = Less than.
0-14 1.0
0.49 0.08-10
LT0.1 10-100
10.5 1 000
0.83 10
TABLE 3 Cu and Zn in Bioslimes and Secondary Sludge
No.
Tower 1 Bioslime TS Cu Zn (%) (ppm) (ppm)
1 10.6 2 8.32 3 11.10 4 8-47 5 8-19 6 8-70 7 8.54 Average 9.13 Average mg kg- 1
3.15 2.82 3.78 2.75 2.23 2.74 1.81 2.75 30.1
48.8 41.7 10.8 28.7 22.5 35.8 25.3 30.5 334
Tower 2 Bioslime TS Cu Zn (%) (ppm) (ppm)
Secondary sludge TS Cu Zn (%) (ppm) (ppm)
10.80 8.82 9-16 8.43 9.58 10.30 10.20 9.61
4.38 0.55 4.26 1.66 3.42 3.42 3-70 3.06
3.13 2.90 3-08 3.16 3-45 2.82 2.01 2.94 28.5
35-2 24.5 23.2 28.7 25.2 27.8 19.8 26.3 275
2.52 0'61 2-48 0.87 1.93 1-27 1-49 1"60 52.3
11.5 2-07 9-57 4.34 10.0 8.16 9-03 7.8 255
Influence o f toxicity on the performance o f a trickling filter system
225
Heavy metals Heavy metal concentrations in primary clarifier effluent (PCA) during April and May, 1981 are presented in Table 2, along with the range of permissible values reported in the literature. Concentrations of heavy metals as found were not likely to be toxic in the aerobic process according to published data. Table 3 shows concentrations of Cu and Zn in bioslimes and secondary sludge. Zn concentrations found in PCE (see high bioslime values also) could be a cause for concern. Although some possible heavy metal toxicity due to Zn could not be ruled out, heavy metal toxicity sufficiently significant to create such a condition of poor performance was not apparent.
Farm chemicals (CIPC and Mertect) Two farm chemicals extensively used in New Brunswick in potato production are CIPC (iso-propyl N-[3-chlorophenyl]carbamate) and Mertect (thiabendazole). These chemicals are sprout inhibitors, top killers or used for blight control. CIPC and Mertect concentrations in PCE and bioslimes are shown in Table 4. In comparison with average mud water concentrations of 4 to 5 mg litre-1 of CIPC and Mertect, TABLE 4 CIPC and Thiabendazole (Mertect) in PCE and in Bioslimes
Date
14-15 April, 1981 21-22 April, 1981 27-28 April, 1981 28-29 April, 1981 5-6 May, 1981 20 May, 1981 26 May, 1981
Concentration in P C E (mg litre - 1) C IPC Mertect ND ND ND ND ND 0.05 0-05
Concentration in bioslime (rag litre- 1) C IPC Mertect
ND 0.1 0.1 0.2 0-3 0-4 0.3 1"05 (11.30")
Average LT 0.05 0.2 * Dry matter basis (mg kg-1). N D - - n o t detectable (LT--less than 0-05 ppm).
0.26 (2-8*)
226
T. Viraraghavan, R. C. Landine, A. A. Cocci
average concentrations of CIPC and Mertect in PCE of less than 0.05 mg litre- 1 and 0.2 mg litre- 1 respectively indicated substantial reduction through dilution and settling in the primary clarifier. Using cultures of activated sludge and slime organisms from a polluted waterway, J. R. Schwartz, Jr. conducted sludies in a laboratory using 300-ml Erlenmeyer flasks and a gyratory shaker to investigate the rate of CIPC oxidation (Schwartz, 1967). The CIPC and microorganisms were added to an isotonic mineral salt solution supplemented by an organic nutrient broth in some test replicates. At CIPC concentrations of 0-15.4 mg litre - 1 and contact periods of 2-98 days, the rate of oxidation was monitored using radioactive tracer techniques. It was determined that CIPC degraded in a two-stage sequence. This study did not report any BOD removal information or the effect which these concentrations may h a v e h a d on BOD removal. Based on the author's lack of comment about any toxic effects to the activated sludge organisms by CIPC, it is possible to assume that none was apparently exhibited at the concentrations used in the study. An activated sludge metabolism study on CIPC was conducted by a manufacturer in 1978. It was concluded from this study that, with proper acclimitation procedures, CIPC exhibited no toxic effects on activated sludge microorganisms at concentrations of 100mglitre -1, as indicated by total microbial counts. It was found that CIPC caused toxicity in an anaerobic fermenter treating potato-processing wastewater at concentrations of 50-75 mglitre-1. CIPC is known to be inhibitory to the growth of nitrifying organisms (Dyer et al., 1981). No specific information is available in the literature on the effect of CIPC on the trickling filter biota. Thiabendazole (Mertect) is not active on bacteria, but is toxic to fungi, because the chemical binds the microtubules present in fungi. The toxicity of this chemical is specific to a wide range of plant pathogenic fungi, but its toxicity to fungi usually found in trickling filters is not known. As part of the investigation, microscopic examination of biota present in trickling filters 1 and 2 and secondary sludge was carried out. Sphaerotilus natans was predominant on most of the occasions in both filters. Although Sphaerotilus natans are associated with bulking of activated sludge, no adverse effect of these organisms on trickling filter performance is reported in the literature. In fact, these form the normal biota of trickling filters. It was found that these dominated over a wide range of PCE BOD values. A wide range of BOD removal values was also associated with their dominant presence; this indicated that their
Influence of toxicity on the performance of a trickling filter system
227
predominance cannot be linked to poor performance (low BOD removal). No specific patterns could be observed in the predominance of Sphaerotilus natans, Micrococcus and worms in trickling filters 1 and 2 during the study period. It was observed that the fungi (Geotrichum sp.) were present on only a few occasions and then only in small numbers. It was speculated that the absence of fungi on most of the occasions might have been due to the toxicity of Mertect, as larger numbers were always present when the filters were running normally. It would appear that toxicity by Mertect is more likely than by CIPC from the limited toxicity data related to CIPC in the literature. However, it is difficult to draw definite conclusions from the data available.
In-plant chemicals The toxicity of cleaning and sanitizing agents such as chlorine compounds, inorganic acids and anti-foam and other agents on the aerobic microorganisms could be due to slug doses of high concentration; such sludge doses could produce pH shock and toxicity conditions, upsetting the biological process for a period of time, after which the system would recover.
Oxygen uptake Simplified oxygen uptake tests were carried out as part of the toxicity investigations. Oxygen uptake levels were generally in the 1-2 mg litre- 1 min-1 range, much above the toxicity threshold level of 0.3 mg litre-a. However, on a few days, oxygen uptake rate reached very low values, but BOD removal through the filters during this period remained relatively high. The results show that the analysis of toxicity aspects and microscopic examination of trickling filter biota did not lead to any specific conclusions. However, toxicity, at least to some extent, might have contributed to the poor performance of the trickling filter system which was already under stress because of excessive loading rates.
REFERENCES Dyer, J. C., Vernick, A. S. & Feiler, H. D. 0981). Handbook of industrial wastes pretreatment. Garland STPM Press, New York, NY 10016, USA.
228
I". Viraraghavan, R. C. Landine, A. A. Cocci
Landine, R. C. & Dean, J. R. (1973). Waste treatment and solids recovery system at a potato processing plant. Industrial Wastes, 19, 12-17. Schwartz, Jr., H. G. (1967). Microbial degradation of pesticides in aqueous solutions. Journal Water Pollution Control Federation, 39, 1701-14. Viraraghavan, T., Landine, R. C. & Cocci, A. A. (1983). Performance of a potato processing wastewater treatment plant--A case study. Paper presented at the 38th Industrial Waste Conference, Purdue University, West Lafayette, Indiana.
Influence of Toxicity on the Performance of a Trickling Filter System
T. Viraraghavan Faculty of Engineering, University of Regina, Regina, Saskatchewan, Canada
& R. C. Landine & A. A. Cocci ADI Limited, Consulting Engineers, Fredericton, New Brunswick, Canada
ABSTRACT A potato processing wastewater treatment plant located in eastern Canada includes several unit operations--screening, primary settling, two-stage trickling filtration and secondary settling. Primary sludge is dewatered in a vacuum filter and the dewatered sludge is hauled away. The secondary sludge is usually pumped to a digestion and dewatering lagoon. The processing plant has been in operation since 1971; a new by-product line was commissioned in 1979. The main product isfrench fried potatoes, but instant potato flakes are also manufactured. The performance of the wastewater treatment plant, especially its BOD removal efficiency, significantly deteriorated during 1980. This paper presents the effect of toxicity (one of the causes examined) arising from farm and in-plant chemicals and heavy metals on the trickling filter system.
INTRODUCTION A large potato processing plant in eastern Canada became operational in the spring of 1971. The main product is french fried potatoes, but instant potato flakes are also manufactured and there is a starch recovery plant. 221 Agricultural Wastes 0141-4607/84/$03.00 © Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
222
T. Viraraghavan, R. C. Landine, A. A. Cocci TABLE 1 BOD Removal in Trickling Filters
Month
Mean BOD removal
(%) March, 1978 April, 1978 September, 1978 October, 1978 November, 1978 December, 1978
76.9 68.0 51.9 73.0 83.4 72-0
January, 1979 February, 1979 March, 1979 April, 1979 May, 1979 June, 1979 July, 1979 September, 1979 October, 1979 November, 1979 December, 1979
73.9 71.5 71.2 59.1 63.9 72.9 57.3 59-0 58.8 61.5 72.7
January, 1980 February, 1980 March, 1980 April, 1980 May, 1980 June, 1980 September, 1980 October, 1980 November, 1980 December, 1980
71.3 79"2 70.3 37.8 78.0 72.2 80.4 39.8 11.5 29.0
January, 1981 February, 1981 March, 1981 a April, 1981 b May, 1981 b June, 1981 c
23.8 18.0 38.1 67.3 88.9 35.2
a Half flow to trickling filter since 23 March, 1981. b Half flow to trickling filter for month. c Full flow until shut down--12 June, 1981.
Influence of toxicity on the performance of a trickling filter system
223
A new by-product line went into operation in the spring of 1979. A new pizza plant also discharges wastes to the wastewater treatment plant. The wastewater treatment plant is comprised of several unit operations --screening, primary settling, two-stage trickling filtration and secondary settling. Primary sludge is dewatered in a vacuum filter and the dewatered sludge is hauled away. The secondary sludge is usually pumped to a digester and dewatering lagoon. Details of the treatment plant are available elsewhere (Landine & Dean, 1973). The plant performance estimated by BOD removal dramatically deteriorated during October, 1980 and the reduction in performance continued until March, 1981, at which time half the flow entering the secondary system was diverted to the river directly and mud water was kept out of the treatment system. A monitoring programme was developed and put in place in April, 1981 to aid in the determination of the causes of the poor performance of the treatment system; this was continued until the seasonal closing of the factory in June, 1981. Possible causes of the poor performance of the treatment plant were examined; these included the loading rate, pH changes, mud water impacts, toxicity aspects, dissolved oxygen levels, grease and nutrient conditions. A general overview of this evaluation was presented at the 1983 Purdue Industrial Wastes Conference (Viraraghavan et al., 1983). This paper presents specifically the toxicity aspects that could have influenced, to some extent, the poor performance of the trickling filter system. PERFORMANCE OF THE TRICKLING FILTER SYSTEM Mean monthly BOD removal efficiency of the trickling filter system (Table 1) remained generally in the 60-80 ~o range from March, 1978 to September, 1980, except during April, 1980 when it dropped to approximately 40 ~o; however, the efficiency exhibited a downward trend from October, 1980 to March, 1981. In April and May, 1981, when only 50 ~ PCE flow was admitted to the filter, the efficiency improved to 70-90 ~. TOXICITY Toxicity considerations related to farm and in-plant chemicals and heavy metals are discussed in this section.
T. Viraraghavan, R. C. Landine, A. A. Cocci
224
TABLE 2 Heavy Metals in Primary Clarifier Effluent (PCE) (Results in mglitre- 1)**
Date
Cu
Zn
Cd
Fe
Mn
14 April 15 April 21 April 22 April 28 April 29 April 5 May 6 May 12 May 13 May 19 May 20 May 26 May 27 May
0.20 0.14 0.13 0.14 0.16 0.15 0.12 0.27 0.17 0.19 0.09 0.13 0.05 0.05
0.41 0.35 0-44 0.35 0.55 0.41 0.35 0.67 0-70 0.74 0.56 0.62 0.40 0.32
LT0.1 LT0-1 LT0-1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1 LT0.1
7.34 8.65 7.65 7.16 5.37 8.00 6.74 11.8 9.22 7.71 15.3 18.9 19.3 14.2
0"88 0.84 0.94 0"86 0.71 0.77 0.71 0.87 0.87 0.74 0.74 0-88 0.95 0.81
Average Permissible ** LT = Less than.
0-14 1.0
0.49 0.08-10
LT0.1 10-100
10.5 1 000
0.83 10
TABLE 3 Cu and Zn in Bioslimes and Secondary Sludge
No.
Tower 1 Bioslime TS Cu Zn (%) (ppm) (ppm)
1 10.6 2 8.32 3 11.10 4 8-47 5 8-19 6 8-70 7 8.54 Average 9.13 Average mg kg- 1
3.15 2.82 3.78 2.75 2.23 2.74 1.81 2.75 30.1
48.8 41.7 10.8 28.7 22.5 35.8 25.3 30.5 334
Tower 2 Bioslime TS Cu Zn (%) (ppm) (ppm)
Secondary sludge TS Cu Zn (%) (ppm) (ppm)
10.80 8.82 9-16 8.43 9.58 10.30 10.20 9.61
4.38 0.55 4.26 1.66 3.42 3.42 3-70 3.06
3.13 2.90 3-08 3.16 3-45 2.82 2.01 2.94 28.5
35-2 24.5 23.2 28.7 25.2 27.8 19.8 26.3 275
2.52 0'61 2-48 0.87 1.93 1-27 1-49 1"60 52.3
11.5 2-07 9-57 4.34 10.0 8.16 9-03 7.8 255
Influence o f toxicity on the performance o f a trickling filter system
225
Heavy metals Heavy metal concentrations in primary clarifier effluent (PCA) during April and May, 1981 are presented in Table 2, along with the range of permissible values reported in the literature. Concentrations of heavy metals as found were not likely to be toxic in the aerobic process according to published data. Table 3 shows concentrations of Cu and Zn in bioslimes and secondary sludge. Zn concentrations found in PCE (see high bioslime values also) could be a cause for concern. Although some possible heavy metal toxicity due to Zn could not be ruled out, heavy metal toxicity sufficiently significant to create such a condition of poor performance was not apparent.
Farm chemicals (CIPC and Mertect) Two farm chemicals extensively used in New Brunswick in potato production are CIPC (iso-propyl N-[3-chlorophenyl]carbamate) and Mertect (thiabendazole). These chemicals are sprout inhibitors, top killers or used for blight control. CIPC and Mertect concentrations in PCE and bioslimes are shown in Table 4. In comparison with average mud water concentrations of 4 to 5 mg litre-1 of CIPC and Mertect, TABLE 4 CIPC and Thiabendazole (Mertect) in PCE and in Bioslimes
Date
14-15 April, 1981 21-22 April, 1981 27-28 April, 1981 28-29 April, 1981 5-6 May, 1981 20 May, 1981 26 May, 1981
Concentration in P C E (mg litre - 1) C IPC Mertect ND ND ND ND ND 0.05 0-05
Concentration in bioslime (rag litre- 1) C IPC Mertect
ND 0.1 0.1 0.2 0-3 0-4 0.3 1"05 (11.30")
Average LT 0.05 0.2 * Dry matter basis (mg kg-1). N D - - n o t detectable (LT--less than 0-05 ppm).
0.26 (2-8*)
226
T. Viraraghavan, R. C. Landine, A. A. Cocci
average concentrations of CIPC and Mertect in PCE of less than 0.05 mg litre- 1 and 0.2 mg litre- 1 respectively indicated substantial reduction through dilution and settling in the primary clarifier. Using cultures of activated sludge and slime organisms from a polluted waterway, J. R. Schwartz, Jr. conducted sludies in a laboratory using 300-ml Erlenmeyer flasks and a gyratory shaker to investigate the rate of CIPC oxidation (Schwartz, 1967). The CIPC and microorganisms were added to an isotonic mineral salt solution supplemented by an organic nutrient broth in some test replicates. At CIPC concentrations of 0-15.4 mg litre - 1 and contact periods of 2-98 days, the rate of oxidation was monitored using radioactive tracer techniques. It was determined that CIPC degraded in a two-stage sequence. This study did not report any BOD removal information or the effect which these concentrations may h a v e h a d on BOD removal. Based on the author's lack of comment about any toxic effects to the activated sludge organisms by CIPC, it is possible to assume that none was apparently exhibited at the concentrations used in the study. An activated sludge metabolism study on CIPC was conducted by a manufacturer in 1978. It was concluded from this study that, with proper acclimitation procedures, CIPC exhibited no toxic effects on activated sludge microorganisms at concentrations of 100mglitre -1, as indicated by total microbial counts. It was found that CIPC caused toxicity in an anaerobic fermenter treating potato-processing wastewater at concentrations of 50-75 mglitre-1. CIPC is known to be inhibitory to the growth of nitrifying organisms (Dyer et al., 1981). No specific information is available in the literature on the effect of CIPC on the trickling filter biota. Thiabendazole (Mertect) is not active on bacteria, but is toxic to fungi, because the chemical binds the microtubules present in fungi. The toxicity of this chemical is specific to a wide range of plant pathogenic fungi, but its toxicity to fungi usually found in trickling filters is not known. As part of the investigation, microscopic examination of biota present in trickling filters 1 and 2 and secondary sludge was carried out. Sphaerotilus natans was predominant on most of the occasions in both filters. Although Sphaerotilus natans are associated with bulking of activated sludge, no adverse effect of these organisms on trickling filter performance is reported in the literature. In fact, these form the normal biota of trickling filters. It was found that these dominated over a wide range of PCE BOD values. A wide range of BOD removal values was also associated with their dominant presence; this indicated that their
Influence of toxicity on the performance of a trickling filter system
227
predominance cannot be linked to poor performance (low BOD removal). No specific patterns could be observed in the predominance of Sphaerotilus natans, Micrococcus and worms in trickling filters 1 and 2 during the study period. It was observed that the fungi (Geotrichum sp.) were present on only a few occasions and then only in small numbers. It was speculated that the absence of fungi on most of the occasions might have been due to the toxicity of Mertect, as larger numbers were always present when the filters were running normally. It would appear that toxicity by Mertect is more likely than by CIPC from the limited toxicity data related to CIPC in the literature. However, it is difficult to draw definite conclusions from the data available.
In-plant chemicals The toxicity of cleaning and sanitizing agents such as chlorine compounds, inorganic acids and anti-foam and other agents on the aerobic microorganisms could be due to slug doses of high concentration; such sludge doses could produce pH shock and toxicity conditions, upsetting the biological process for a period of time, after which the system would recover.
Oxygen uptake Simplified oxygen uptake tests were carried out as part of the toxicity investigations. Oxygen uptake levels were generally in the 1-2 mg litre- 1 min-1 range, much above the toxicity threshold level of 0.3 mg litre-a. However, on a few days, oxygen uptake rate reached very low values, but BOD removal through the filters during this period remained relatively high. The results show that the analysis of toxicity aspects and microscopic examination of trickling filter biota did not lead to any specific conclusions. However, toxicity, at least to some extent, might have contributed to the poor performance of the trickling filter system which was already under stress because of excessive loading rates.
REFERENCES Dyer, J. C., Vernick, A. S. & Feiler, H. D. 0981). Handbook of industrial wastes pretreatment. Garland STPM Press, New York, NY 10016, USA.
228
I". Viraraghavan, R. C. Landine, A. A. Cocci
Landine, R. C. & Dean, J. R. (1973). Waste treatment and solids recovery system at a potato processing plant. Industrial Wastes, 19, 12-17. Schwartz, Jr., H. G. (1967). Microbial degradation of pesticides in aqueous solutions. Journal Water Pollution Control Federation, 39, 1701-14. Viraraghavan, T., Landine, R. C. & Cocci, A. A. (1983). Performance of a potato processing wastewater treatment plant--A case study. Paper presented at the 38th Industrial Waste Conference, Purdue University, West Lafayette, Indiana.