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A laboratory-scale model for evaluating effluent toxicity in activated sludge wastewater treatment plants
Wat. Res. Vol. 24, No. 6, pp. 717-723, 1990 Printed in Great Britain.All rights reserved
0043-1354/90$3,00+ 0.00 Copyright © 1990PergamonPress plc
A LABORATORY-SCALE MODEL FOR EVALUATING EFFLUENT TOXICITY IN ACTIVATED SLUDGE WASTEWATER TREATMENT PLANTS DONALD J. VERSTEEG* and DANIELM. WOLTERING Environmental Safety Department, The Procter & Gamble Company, Ivorydale Technical Center, Cincinnati, OH 45217, U.S.A.
(First received May 1989; accepted in revised form December 1989) Abstract--Laboratory-scale wastewater treatment systems were used to assess the potential contribution of a specific waste source, a detergent manufacturing plant, to wastewater treatment plant (WWTP) effluent toxicity. Laboratory-scale, continuously-fed activated sludge treatment systems (CAS units) were established and seeded with sludge from one of two activated sludge WWTPs. The CAS units were fed influent from these WWTPs supplemented with detergent manufacturing plant waste (plant waste). CAS unit effluent toxicity was measured with the 7 day Ceriodaphnia dubia survival and reproduction test and the 4 day Selenastrum capricornutum population growth test. Control (ambient W~VTPinfluent) CAS unit and actual WWTP effluentshad similar toxicity, indicating the CAS units generated effluenttoxicologically similar to actual effluent for the two species tested. Untreated WWTP influent was supplemented with atypically high concentrations of plant waste in an attempt to establish a dose--response relationship between influent plant waste levels and effluent toxicity. However, there was no trend toward increasing effluent toxicity to Ceriodaphnia or algae with increasing influent plant waste concentrations. Thus, the detergent manufacturing plant waste is not contributing to the toxicity of the municipal WWTP effluent. This case study demonstrated the utility of CAS units for assessing the impact of WWTP influent sources on final effluent toxicity.
Key words--wastewater treatment, effluent toxicity, algae, invertebrates, Ceriodaphnia, surfactants, manufacturing plant
INTRODUCTION The U.S. Environmental Protection Agency water quality based toxics control strategy promotes the utilization of toxicity data on single species to assess and control the discharge of toxic substances into receiving waters (U.S. EPA, 1985). Whole effluent toxicity tests with the daphnid, Ceriodaphnia dubia, a green algae, Selenastrum capricornuturn and the fathead minnow, Pimephales promelas, are recommended to assess potential chronic effluent impacts on in-stream communities (Horning and Weber, 1985). Municipal wastewater treatment plant (WWTP) effluents have been observed to be acutely and chronically toxic to aquatic organisms, with up to 79% of effluents reported to be acutely toxic to aquatic life (Tebo, 1986; Neiheisel et al., 1988). Effluents exceeding permitted toxicity limits may be required to reduce effluent toxicity. Effluent toxicity reduction can be accomplished through a toxicity identification and reduction evaluation (TI/RE) in which toxicants are identified and toxicity is ameliorated by augmented treatment processes and programs designed to restrict sources of toxic compounds (Mount and Anderson-Carnahan, 1988), At municipal WWTPs, *Author to whom all correspondence should be addressed.
the TI/RE process may involve going "up the pipe" to identify industrial or commercial sources of toxicity (U.S. EPA Science Advisory Board, 1988). But, how should toxicity information on untreated waste be obtained and interpreted to accurately reflect toxicity in the final treated effluent? Toxicity tests on untreated wastes may not accurately assess the contribution of a waste to final effluent toxicity, especially in waste streams containing compounds removed by treatment processes. Knowledge of total waste treatability (e.g. BOD removal) might not always be useful as effluent levels of residual toxic compounds will not be known. The key parameter to understand is the quantity of final effluent toxicity a specific waste source contains. In this study, model waste treatment systems were used to assess the contribution of a detergent manufacturing plant waste to final effluent toxicity. This approach has been used successfully to evaluate the effect of treatment on the toxicity of a number of compounds (Horning et al., 1984; Botts et al., 1989). Predicting the potential contribution of the manufacturing plant waste to WWTP effluent toxicity is complicated by: (1) the chemical complexity of the manufacturing plant waste; (2) the differential WWTP removal of manufacturing plant waste components; and (3) the potential for toxicological interactions among components of the final WWTP
717
DONALD J. VERSTEEG a n d DANIEL M. WOLTERING
718 INFLUENT/SLUDGE SOURCE
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M AANNW UFACTURN IG PLO D SINTGASTE
~_~Mnnuf actuerlng Pla4X nt Wast
CASUNITS~~
~
~ ~
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EFFLUENT
EFFLUENT
TOXICITY
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~
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Fig. 1. Flow diagram of the experimental design demonstrating the source of sludge and influent, the addition of manufacturing plant wastes and the use of CAS unit effluents for toxicity testing. effluent. To conduct the most relevant testing possible, we reasoned that effluent toxicity should be assessed following actual or simulated wastewater treatment of the manufacturing plant waste. This research had two purposes. First, to assess the feasibility of coupling a laboratory-scale waste treatment system with effluent chronic toxicity assays to determine the contribution of an influent source to final W W T P effluent toxicity. This research was conducted using a detergent manufacturing plant waste as a case study. The manufacturing plant releases wastes along with other domestic, commercial and industrial sources to a municipal WWTP. Effluent from the municipal W W T P was observed to be toxic to aquatic life and the issue was the level of final effluent toxicity contributed by the manufacturing plant. The second objective of this study was to determine, under a realistic worst case scenario, i.e. a W W T P receiving both domestic waste and detergent manufacturing plant waste, whether surfactants, the major components o f the manufacturing plant waste, are likely to contribute to municipal W W T P effluent toxicity. MATERIALS AND METHODS Wastewater sources
Two wastewater treatment plant sludges and influent sources (A and B) were used to establish and operate six CAS (continuously-fed activated sludge) units. WWTP A is an approx. 20 million gallons per day conventional activated sludge treatment plant receiving waste from domestic (90%) and industrial (10%) sources. The industrial input includes wastes from the detergent manufacturing plant. WWTP B is a 1 million gallon per day, extended aeration activated sludge plant receiving wastes entirely from domestic sources. C A S units
Three CAS units were seeded with sludge from WWTP A (Fig. I). One unit was operated with WWTP A inflUent only. This influent contains ambient levels of the detergent manufacturing plant waste. Influent to the other two CAS units
were spiked with additional detergent manufacturing plant waste at 4 and 16 times the typical level of plant waste in WWTP A influent (Fig. 1). Three CAS units were set up with sludge from WWTP B and operated with WWTP B influent. One unit was operated with untreated influent alone (i.e. normal loading of domestic waste and no detergent manufacturing plant waste). Influent to the other two units were spiked with 4 and 16 times the plant waste levels in WWTP A influent (Fig. 1). Each laboratory-scale CAS unit consisted of a plexiglas aeration basin and a 21. cylindrical clarifier (Fig. 2). The aeration basin contained 61. of activated sludge dispersed by two aeration tubes. The aeration basin discharged through an overflow tube into a clarifier stirred by a shaft mixer. The Pump
InPlfluusn! se Pla(4oc) ntWast Compressed Air
Pump
Waste
~
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Aerati Sectioonn
/"
Effluent
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Fig. 2. Schematic diagram of the CAS units used in the treatment of the influent and th~ waste from a detergent manufacturing plant.
Waste contribution to effluent toxicity clarifier had a recycle discharge tube in the bottom and an overflow for effluent discharge. Sludge settling in the clarifier was periodically recycled (15 min per h) to the aeration basin by a peristaltic pump. Effluent from the clarifier was cornposited in a 201. polypropylene pail for toxicological and analytical sampling. Grab samples of WWTP inftuents were collected twice weekly, transported to the laboratory and stored in polypropylene containers at 4°C. Samples were fed into CAS units immediately upon receipt at the laboratory. Due to the influent feed rate, a portion of influent samples were 4 days old when treated. Influent was fed by peristaltic pump to the CAS units at a mean flow rate of 16.6 ml/min. Operational parameters in the CAS units were designed to be similar to actual conventional wastewater treatment plants (Table 1) (Metcalf & Eddy, 1979; Namkung and Rittmann, 1987). Wasting of sludge was carried out as needed to maintain the mixed liquor suspended solids (MLSS) limits. Influent, effluent and mixed liquor total suspended solids, and influent and effluent pH and total organic carbon were routinely monitored during the dosing period. Initially, CAS units were operated for 14 days with untreated influent only. This predose period allowed the CAS units to reach a state of equilibrium before dosing with plant waste. After the predose period, influents were supplemented with detergent manufacturing plant waste to approximate increases of zero (ambient influent), 4 and 16 times the level of manufacturing plant waste in WWTP A influent. The exaggerated doses of plant wastes were intended to generate effluents for toxicity testing which could be compared in a dose-related manner. Observation of a dose-response relationship between the concentration of the manufacturing plant waste and effluent toxicity would be substantial evidence of a cause and effect relationship. The dosing period lasted for 32 days allowing sufficient time for acclimation of the activated sludge microbial communities to plant waste under laboratory conditions. Control CAS unit effluent samples were collected for acute toxicity testing during the entire dosing period. Effluent samples for chronic toxicity testing were collected during the last 7 days of the dosing period.
Toxicity tests Control CAS unit influents and effluents were tested for acute toxicity to Ceriodaphnia dubia by the method of Peltier and Weber (1985). Grab samples of influent and 24h composite samples of effluent were used. Toxicity tests were initiated immediately after sampling and test samples were changed after 24 h with a fresh grab sample of influent and a second 24-h composite of effluent. These tests were conducted to determine the variability in influent toxicity and the ability of CAS units to remove toxicity, Effluent short-term chronic toxicity tests with Ceriodaphnia dubia and Selenastrum capricornuturn were used to assess the chronic toxicity of CAS effluents and final effluents from WWTPs A and B. Ceriodaphnia were chosen due to their generally greater sensitivity than fish to WWTP effluents (data not shown). Selenastrum was selected due to the sensitivity of algae to surfactants, the short duration of toxicity tests with algae, and their critical position in the ecosystem. These tests were conducted according to the Table 1. Operational conditions of the CAS units Parameter Aeration tank volume (litres) 6.0 Aeration rate (l/min) 6.0 Wastewater flow (I/d) 23.9 Hydraulic retention time (h) 6.0 Sludge retention time (d) 12.0 Mixed liquor suspended solids MLSS ( m g / l ) 2000-3000 Sludge volume index SVI (ml/I) < 100
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methods of Horning and Weber (1985) with the exception that Ceriodaphnia were cultured and tested in individual 30 ml plastic cups filled with 20 ml of test solution. Filtered Little Miami river water, a relatively clean source of natural dilution water, was collected at Xenia, Ohio and used for Ceriodaphnia and Selenastrum culture and as dilution water in toxicity tests. During Ceriodaphnia 7 day chronic toxicity tests, daily 24-h composited samples from each CAS unit effluent were used to make the daily renewals of test solutions. Observations on the survival and reproduction of Ceriodaphnia were made daily at the time of transfer. The 4 day algal tests were run concurrently with the Ceriodaphnia toxicity tests. Test solutions were not renewed during the test. Algae were incubated at 24°C and 86 #E s-1 m -2 (equivalent to 400 ft-c cool white fluorescent light) on a shaker table oscillating at 100rpm. After 4 days of incubation, population growth was assessed by quantifying algal biomass (chlorophyll a) fluorometrically on a Turner model 111 fluorometer (APHA, 1985).
Analytical Surfactant analytical samples were 24 h composites of CAS effluents. Samples collected for anionic and nonionic surfactant analyses were preserved with 1% formalin and stored at 4°C. Samples collected for cationic surfactant analyses were preserved with 1% formalin and 5 mg/l of alkyl ethoxylate (C14_15AE 7), and stored at 4°C. The samples were analyzed for total nonionic surfactants by a modification of the cobalt thiocyanate active substance method (APHA, 1985), linear alkylbenzene sulfonates (LAS) by desulfonation gas chromatography (Osborne, 1986), and the following cationic surfactants by a modification of the method of Wee (1984); ditallow dimethyl ammonium chloride, monotallow trimethyl ammonium chloride and dodecyl trimethyl ammonium chloride. Note that the analytical method for the nonionie surfactants is a nonspecific colorimetric method reported to overestimate the concentration of nonionic surfactant in WWTP effluents (Gledhill et al., 1989). Thus, results of nonionic surfactant analyses are reported in general terms only. Water quality parameters including hardness, alkalinity, dissolved oxygen, total organic carbon, total suspended solids, ammonia, conductivity and pH were measured in dilution water and CAS influent and effluent by accepted methods (APHA, 1985). CAS unit sludge volume index (SVI) was measured according to APHA (1985) using a 30 min settling time. Water quality parameters were measured at the beginning of the algal test and daily during Ceriodaphnia testing. Statistics Survival data were analyzed by the methods described in Peltier and Weber (1985). Ceriodaphnia young production and algal population growth data were analyzed by nonlinear multiple regression analysis on SAS (SAS, 1986). Toxicity test results are summarized in this study as the effective concentration of effluent reducing biological response, survival or reproduction, by 50% (ECs0 values) with 95% confidence intervals. The ECs0 statistic was selected to identify effluent concentrations causing a specific level of toxicity and does not indicate a toxicity threshold or biological relevance in the receiving environment. In using no observed effect (NOEC) and first observed effect concentrations (FOEC), biological effects varied greatly among CAS unit treatments with similar NOECs and FOECs. Others have observed this effect and recommend the use of a dose-response statistical approach in place of the hypothesis testing approach (Krump, 1984; Barnthouse et al., 1987). Thus, to make meaningful comparisons among CAS unit treatments in this study, biological effects were held constant at 50%. For Ceriodaphnia chronic tests, ECs0 values were calculated based on survival and young production. The lower of
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DONALD J. VERSTEEG a n d DANIEL M . WOLTERING Table 2. Concentration [mean (mg/l); (SD); n = 4] of surfactants* in CAS units and actual WWTP effluents Treatment system
Wastewater treatment plants WWTP A effluent (n = 7) WWTP B effluent (n = 3) CAS units WWTP A control WWTP A 4 × plant waste WWTP A 16 x plant waste WWTP B control WWTP B + 4 x plant waste WWTP B + 16× plant waste
DTDMAC
MTTMAC
CI:TMAC
LAS
0.038 (0.018) 0.025 (0.027)
<0.012t < 0.005"I"
<0.010t < 0.005t
<0.050t 0.130t
0.760 (0.39) 4.53(0.84) 20.3 (4.57) 0.550 (0.28) 2.98 (1.41) 10.7(3.66)
0.009 (0.002) 0.008(0.003) 0.024 (0.001) 0.010 (0.005) 0.011 (0.005) 0.046(0.035)
< 0.005t <0.005t <0.005t <0.005t <0.005"i" <0.007t
0.070 (0.032) 0.390(0.042) 3.10 (1.46) 0.140 (0.010) 0.340 (0.145) 2.05(1.00)
*Nonionic surfactant concentrations as assessed by a nonspecifi¢ method were less than 0.40 mg/l. Abbreviations: DTDMAC, ditallow dimethyl ammonium chloride; MTTMAC, monotallow trimethyl ammonium chloride; CI2TMAC, dodecyl trimethyl ammonium chloride; LAS, linear alkylbenzene sulfonate. t N o standard deviation, "less than" values included in calculation.
these two toxicity values was reported to insure the most sensitive toxic effect was selected. For algae, ECs0 values were based on a reduction in population growth. To determine if a relationship existed between manufacturing plant waste and toxicity, effluent toxicity to Ceriodaphnia and algae were regressed on influent manufacturing plant waste and effluent total surfactant concentrations using the linear regression analysis on SAS (SAS, 1986). RESULTS
CAS unit operation CAS units operated well during the study. Mean total organic carbon removals ranged from 76.8 to 83.7% among the CAS units. Total suspended solids removals were 81.9 and 87.7% in control CAS units A and B, respectively, however, due to the chemical and physical nature of surfactants, reliable total suspended solids removal values could not be determined in CAS unit receiving manufacturing plant waste. Mean sludge volume indices ranged from 46.8 to 66.7 ml/l and mean mixed liquor suspended solids levels ranged from 2141.7 to 2981.5mg/1 across all CAS units. The F / M ratio (lb BODs/Ib VSS.d) ranged from 0.28 to 0.37 in WWTP A CAS units and from 0.20 to 0.31 in WWTP B CAS units. The yield coefficient (mg SS/mg BODs) ranged from 0.19 to 0.20 in WWTP A CAS units and from 0.31 to 0.69 in WWTP B CAS units. Effluent surfactant concentrations at WWTP A and B were similar to each other and, with the exception of ditallow dimethyl ammonium chloride, similar to effluent concentrations in the control CAS unit effluents (Table 2). Addition of plant waste to CAS unit influents caused effluents surfactant levels
to increase greatly relative to the actual WWTPs and the control CAS units (Table 2).
Acute toxicity WWTP A influent toxicity was variable, Ceriodaphnia dubia 48 h LCs0 values ranged from 22 to > 100%, but was generally less toxic than WWTP influent B (Table 3). W W T P B infiuent was consistently acutely toxic to Ceriodaphnia; LCs0 values were less than 50%. Effluents from control CAS units were consistently of low acute toxicity indicating CAS units effectively removed acutely toxic components. More sensitive "chronic" endpoints, though, were needed to distinguish effluent toxicity among CAS units.
Chronic toxicity Toxicities of WWTP A and B effluents were similar to Ceriodaphnia (Table 4). EC50 concentrations were 24 and 22°/'0 effluent in W W T P A and B, respectively. Control CAS unit and actual effluents also had similar toxicities. For W W T P A, chronic ECs0 concentrations were 24% in the actual W W T P effluent and 33% in the control CAS unit effluent to Ceriodaphnia. For WWTP B, effluent ECs0 concentrations were 22 and 16% in the actual WWTP and control CAS unit effluents, respectively. In WWTP A CAS units, Ceriodaphnia chronic effluent ECs0 concentrations were 33% for the control CAS unit, 46% for the CAS unit receiving 4 x plant waste and 13% for the 16 x plant waste CAS unit (Table 4). In WWTP B CAS units, chronic effluent Ceriodaphnia ECs0 concentrations were 16% for the control CAS unit, 35% for the CAS unit receiving
Table 3. The acute toxicity of influents and effluents from control CAS units to Ceriodaphnia dubia 48-h LCs0 value (%) Sample type WWTP A control influent effluent WWTP B control influent effluent
Week:
1 22.2 (16.5-29.6) > 100 44.6 (32.9-92.3) 52.9 (0-100)
2
3
4
5
> 50
> 100
> 100
--
> 100
> 100
> 100
> 100
16.0 (12.0-25.0) > 100
38.0 (25.0-50.0) > 100
< 25
--
> 100
> 100
Waste contribution to effluent toxicity Table 4. Effect on the survivaland reproductionof Ceriodaphnia dubia and the growthof Selenastrum caprieornutum of effluentsfrom WWTPs and CAS units Ceriodaphnia Selenastrum ECs0 ECs0 Treatment (%) (%) Wastewater treatment plants
WWTP A effluent
24 (16.8-36.9) 22 (8.4-58.4)
WWTP B effluent CAS units
WWTP A control WWTPA + 4 x plant waste WWTP A + 16× plant waste WWTP B control WWTP B+ 4 x plant waste WWTP B+ 16x plant waste
33 (25.0-50.0) 46 (25.0-50.0) 13 (9.6-18.7) 16 (12.5 25.0) 35 (27.6-45.3) 28 (20.5-37.1)
> 100 13 (9.0-17.8) > 100 > 100 > 100 72 (60.8-86.1) 59 (46.%74.8) 58 (49.4-67.0)
4 x plant waste and 28% for the 16 x plant waste CAS unit effluent (Table 4). Toxicities of WWTP A and B effluents to S e l e n a s t r u m c a p r i c o r n u t u m differed (Table 4). The ECs0 concentrations were > 100% in WWTP A effluent and 13% in WWTP B effluent. The control CAS units reflected this difference in effluent toxicity. Effluent from the WWTP A control CAS unit were also nontoxic to algae with 4-day ECs0 concentrations exceeding 100% effluent. With WWTP B influent, the control CAS unit effluent was less toxic to algae than the actual WWTP effluent. The ECs0 concentration of the WWTP B effluent was 13% effluent while the control CAS unit effluent EC50 level was 72%. In WWTP A CAS units, all algal CAS unit effluent ECs0 concentrations exceeded 100% effluent (Table 4). In WWTP B CAS units, algal chronic ECs0 concentrations were similar at 72, 59 and 58% in the ambient, 4 x and 16 x plant waste units (Table 4). Regression of effluent toxicity to Ceriodaphnia and Selenastrum on infiuent manufacturing plant waste levels and effluent surfactant concentrations indicated the lack of a statistically significant relationship between toxicity and the level of plant waste components in the influent or effluent (Table 5). DISCUSSION Federal and state agency regulation of effluents has expanded to include the monitoring and regulation of whole effluent toxicity (U.S. EPA, 1984, 1985). TechTable 5. Regressionstatistics(r; Pearsoncorrelation coefficients) describing the regression of toxicity (ECs0)to Ceriodaphniaand Selenastrumon influent manufacturingplantwastelevelsand effluentsurfactant concentrations Correlation coefficient(r) Species Ceriodaphnia Selenastrum
lnfluent 0.03 0.28
Effluent 0.05 0.15
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niques used to control whole effluent toxicity at municipal WWTPs include utilization of alternative treatment options to remove final effluent toxicity and chemical identification and remediation of effluent compounds causing toxicity (U.S. EPA, 1985; Mount and Anderson-Carnahan, 1988). These techniques are useful and effective at controlling effluent toxicity. However, in some cases a more cost effective and direct approach to controlling effluent toxicity, source reduction, is recommended (U.S. EPA Science Advisory Board, 1988). In this approach, the waste streams contributing to final effluent toxicity would be identified and regulated. Interpretation of the results of toxicity tests on municipal WWTP influent waste streams is not straightforward. Due to the potential chemical complexity of a waste stream, the differential impact of treatment on the components of the waste, and the effect of the effluent matrix on the toxicity of waste components, the waste treatment process should be incorporated in evaluating the contribution of a waste stream to final effluent toxicity. Laboratory-scale, continuously fed activated sludge treatment systems (CAS units) have been validated as effective models of the activated sludge process giving removals of conventional parameters and consumer product chemicals similar to actual WWTPs (King, 1980; Vashon et al., 1982). In this study, we demonstrated the utility of CAS units to assess the contribution of a specific WWTP influent waste stream to post-treatment toxicity by verifying that, for Ceriodaphnia and Selenastrum, CAS units generate effluent toxicologically similar to actual WWTP effluents. For Ceriodaphnia, effluent toxicity in the control CAS units and the actual WWTPs were similar for both influent sources. For algae, although some differences between toxicity in the WWTPs and the control CAS unit effluents were observed, effluent toxicities were comparable for an influent source. At WWTP A, both control CAS unit and the actual WWTP effluents had similar toxicity to algae with ECs0 concentrations exceeding 100% effluent. The WWTP B control CAS unit effluent was less toxic to algae than the actual WWTP effluent. However, given the possible variability in effluent toxicity and in the toxicity test, algal toxicity of the control CAS units and the actual WWTP effluents were comparable. Effluents of increasing manufacturing plant waste strength were generated by exaggerating influent plant waste loadings to CAS units. There was no overall effect of plant waste components on toxicity. However, effluent from WWTP A CAS unit receiving the 16-fold addition of plant waste and having the highest effluent total surfactant concentrations did have increased toxicity to Ceriodaphnia relative to effluent from the WWTP A control CAS unit. A 4-fold addition of manufacturing plant waste to untreated influent had no effect on the toxicity of the WWTP A CAS unit effluent. Thus, the current level of detergent manufacturing plant waste being re-
722
DONALDJ. VERSTEEGand DANIELM. WOLTERING
ceived at WWTP A is not impacting effluent toxicity. In fact, a 4-fold increase in influent plant waste levels would not be expected to impact effluent toxicity. In the WWTP B CAS units, increases in plant waste levels including the 16-fold addition did not adversely impact effluent toxicity to algae or Ceriodaphnia. The reason for the 16 x plant level contributing to effluent toxicity in W W T P A but not WWTP B is not known but may have been due to increased levels of manufacturing plant waste in this effluent. Due to addition of plant wastes to CAS unit influents, CAS unit effluents contained greatly increased concentrations of two detergent actives, linear alkylbenzene sulfonate and ditallow dimethyl ammonium chloride (DTDMAC), in comparison to the actual WWTPs (Table 2). Despite these greatly elevated concentrations of surfactants, effluent toxicity to algae and Ceriodaphnia was not affected except in the CAS unit with the greatest effluent surfactant concentration (i.e. W W T P A 16 × plant waste CAS unit). In all CAS unit effluents, linear alkylbenzene sulfonate concentrations remained below levels reported to be toxic to aquatic organisms (Maki, 1979; Holman and Macek, 1980; Taylor, 1985). However, CAS unit effluent concentrations of D T D M A C exceeded levels reported to be toxic. Lewis and Wee (1983) observed that D T D M A C completely inhibited Selenastrum capricornutum growth (ECl00 or algistatic concentration) at concentrations ranging from 0.7 to 2.6 mg/l in filtered river water. In a chronic toxicity test conducted in river water, the D T D M A C ECs0 concentration to Daphnia magna was approx. 1.0 mg/1. In our study, D T D M A C concentrations up to 20.3 mg/l in a CAS unit effluent had no effects on Selenastrum. For Ceriodaphnia, a congeneric species to Daphnia, the effluent D T D M A C concentration at the ECs0 level of effluent reached a maximum of 3.0 mg/1. These observations indicate that the waste treatment process and effluent matrix may have reduced the apparent toxicity of D T D M A C . This effect on toxicity is presumed to be due to an effect on D T D M A C speciation and bioavailability. Similar results on the amelioration of the toxicity of cationic compounds by suspended solids and organic carbon have been reported (Cary et al., 1987). Since these factors affect the toxicity of these compounds in the environment, it is important to utilize the most environmentally relevant method to introduce these compounds into aquatic toxicity test systems. These results suggest that CAS units are an effective method for generating increased concentrations of test materials in an environmentally realistic matrix and that relevant safety data can be obtained with these methods. In this case study, effluent concentrations of the major plant waste components could be measured. However, if plant waste components could not be measured due to the number of compounds or the
inability to accurately quantify specific components, the CAS unit approach would remain valid. Due to the ability to manipulate influent waste loadings, the CAS unit approach can be a powerful tool to assess the contribution of waste contributors to effluent toxicity. In utilizing this approach, care should be exercised to avoid effects of the waste on the treatment process. Addition of waste at abnormally high levels could cause effects including toxicity to activated sludge organisms, alternative substrate utilization or dilution of influent and mixed liquor strength. These, and other potential effects, could ameliorate or potentiate the observed toxicity of the waste. The incidence of these effects can be reduced by proper selection of influent waste levels and monitoring of activated sludge processes. CONCLUSIONS Use of laboratory-scale, continuous activated sludge units coupled with effluent toxicity test procedures were effective methods to assess the contribution of an influent source to final WWTP effluent toxicity. CAS units provided treatment of influent waste streams and generated toxicologically relevant effluents for Ceriodaphnia and Selenastrum. A major component of the detergent manufacturing plant waste, DTDMAC, was less toxic as a component of a CAS unit effluent than has been reported in the literature in conventional laboratory toxicity tests suggesting that components of WWTP effluents ameliorate the toxicity of this surfactant. In this case study, the detergent manufacturing plant waste was not a significant contributor to WWTP effluent toxicity at current rates of manufacturing plant waste input to the WWTP. REFERENCES
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Waste contribution to effluent toxicity and receiving waters to freshwater organisms. EPA-600/485-014, U.S. EPA, Cincinnati, Ohio. Horning W. B., Robinson E. L. and Petrasek A. C. (1984) Reduction in toxicity of organic priority pollutants by pilot-scale conventional wastewater treatment process. Arch. envir, contain. Toxic. 13, 191-196. King J. E. (1980) Treatability of Type A zeolite in a wastewater--Part I. J. Wat. Pollut. Control Fed. 52, 2875-2886. Krump K. S. (1984) A new method for determining allowable daily intakes. Fund. appl. Toxic. 4, 854-871. Lewis M. A. and Wee V. T. (1983) Aquatic safety assessment for cationic surfactants. Envir. Toxic. Chem. 2, 105-118. Maki A. W. (1979) Correlations between Daphnia magna and fathead minnow (Pimephales promelas) chronic toxicity values for several classes of test substances. J. Fish. Res. Bd Can. 36, 411-421. Metcalf & Eddy (1979) Wastewater Engineering Treatment, Disposal, Reuse. McGraw-Hill, New York. Mount D. I. and Anderson-Carnahan L. (1988) Methods for aquatic toxicity identification evaluations. Phase I: toxicity characterization procedures. National Effluent Toxicity Assessment Center, Draft Technical Report 02 88, Duluth, Minn. Namkung E. and Rittmann B. E. (1987) Estimating volatile organic compound emissions from publically owned treatment works. J. Wat. Pollut. Control Fed. 59, 670~578. Neiheisel T. W., Horning W. B., Austern B. M., Bishop D. F., Reed T. L. and Estenik J. F. (1988) Toxicity reduction at municipal wastewater treatment plants. J. Wat. Pollut. Control Fed. 60, 57q57.
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Osborne Q. W. (1986) Analytical methodology for linear alkylbenzene sulfonate (LAS) in waters and wastes. J. off. analyt. Chem. Soc. 63~ 257-263. Peltier W. H. and Weber C. I. (Eds) (1985) Methods for measuring the acute toxicity of effluents to freshwater and marine organisms. EPA-600/4-85-013, U.S. EPA, Cincinnati, Ohio. SAS (1986) SAS User's Guide: Statistics. SAS Institute, Cary, N.C. Taylor M. J. (1985) Effect of diet on the sensitivity of Daphnia magna to linear alkylbenzene sulfonate. In Aquatic Toxicology and Hazard Assessment: Seventh Symposium (Edited by Cardwell R. D. et al.), pp. 53-72. ASTM STP 854, American Society of Testing Materials, Philadelphia, Pa. Tebo L. B. (1986) Environmental monitoring: historical perspective. In Environmental Hazard Assessment o f Effluents (Edited by Bergman H. L., Kimerle R. A. and Maki A. W.), pp. 13-31. Pergamon Press, New York. U.S. EPA. (1984) Development of water quality based permit limitations for toxic pollutants: national policy. Federal Register, U.S. EPA, 49 (48), 9016-9019. U.S. EPA. (1985) Technical support document for water quality-based toxics control. Office of Water, U.S. EPA, Washington, D.C. U.S. EPA Science Advisory Board (1988) Technical support document for water quality-based toxics control. Office of Water, U.S. EPA, Washington, D.C. Vashon R. D., Jones W. J. and Payne A. G. (1982) The effect of water hardness on nitrilotriacetate removal and microbial acclimation in activated sludge. Wat. Res. 16, 1429-1432. Wee V. T. (1984) Determination of cationic surfactants in waste- and river waters. Wat. Res. 18, 223-225.
0043-1354/90$3,00+ 0.00 Copyright © 1990PergamonPress plc
A LABORATORY-SCALE MODEL FOR EVALUATING EFFLUENT TOXICITY IN ACTIVATED SLUDGE WASTEWATER TREATMENT PLANTS DONALD J. VERSTEEG* and DANIELM. WOLTERING Environmental Safety Department, The Procter & Gamble Company, Ivorydale Technical Center, Cincinnati, OH 45217, U.S.A.
(First received May 1989; accepted in revised form December 1989) Abstract--Laboratory-scale wastewater treatment systems were used to assess the potential contribution of a specific waste source, a detergent manufacturing plant, to wastewater treatment plant (WWTP) effluent toxicity. Laboratory-scale, continuously-fed activated sludge treatment systems (CAS units) were established and seeded with sludge from one of two activated sludge WWTPs. The CAS units were fed influent from these WWTPs supplemented with detergent manufacturing plant waste (plant waste). CAS unit effluent toxicity was measured with the 7 day Ceriodaphnia dubia survival and reproduction test and the 4 day Selenastrum capricornutum population growth test. Control (ambient W~VTPinfluent) CAS unit and actual WWTP effluentshad similar toxicity, indicating the CAS units generated effluenttoxicologically similar to actual effluent for the two species tested. Untreated WWTP influent was supplemented with atypically high concentrations of plant waste in an attempt to establish a dose--response relationship between influent plant waste levels and effluent toxicity. However, there was no trend toward increasing effluent toxicity to Ceriodaphnia or algae with increasing influent plant waste concentrations. Thus, the detergent manufacturing plant waste is not contributing to the toxicity of the municipal WWTP effluent. This case study demonstrated the utility of CAS units for assessing the impact of WWTP influent sources on final effluent toxicity.
Key words--wastewater treatment, effluent toxicity, algae, invertebrates, Ceriodaphnia, surfactants, manufacturing plant
INTRODUCTION The U.S. Environmental Protection Agency water quality based toxics control strategy promotes the utilization of toxicity data on single species to assess and control the discharge of toxic substances into receiving waters (U.S. EPA, 1985). Whole effluent toxicity tests with the daphnid, Ceriodaphnia dubia, a green algae, Selenastrum capricornuturn and the fathead minnow, Pimephales promelas, are recommended to assess potential chronic effluent impacts on in-stream communities (Horning and Weber, 1985). Municipal wastewater treatment plant (WWTP) effluents have been observed to be acutely and chronically toxic to aquatic organisms, with up to 79% of effluents reported to be acutely toxic to aquatic life (Tebo, 1986; Neiheisel et al., 1988). Effluents exceeding permitted toxicity limits may be required to reduce effluent toxicity. Effluent toxicity reduction can be accomplished through a toxicity identification and reduction evaluation (TI/RE) in which toxicants are identified and toxicity is ameliorated by augmented treatment processes and programs designed to restrict sources of toxic compounds (Mount and Anderson-Carnahan, 1988), At municipal WWTPs, *Author to whom all correspondence should be addressed.
the TI/RE process may involve going "up the pipe" to identify industrial or commercial sources of toxicity (U.S. EPA Science Advisory Board, 1988). But, how should toxicity information on untreated waste be obtained and interpreted to accurately reflect toxicity in the final treated effluent? Toxicity tests on untreated wastes may not accurately assess the contribution of a waste to final effluent toxicity, especially in waste streams containing compounds removed by treatment processes. Knowledge of total waste treatability (e.g. BOD removal) might not always be useful as effluent levels of residual toxic compounds will not be known. The key parameter to understand is the quantity of final effluent toxicity a specific waste source contains. In this study, model waste treatment systems were used to assess the contribution of a detergent manufacturing plant waste to final effluent toxicity. This approach has been used successfully to evaluate the effect of treatment on the toxicity of a number of compounds (Horning et al., 1984; Botts et al., 1989). Predicting the potential contribution of the manufacturing plant waste to WWTP effluent toxicity is complicated by: (1) the chemical complexity of the manufacturing plant waste; (2) the differential WWTP removal of manufacturing plant waste components; and (3) the potential for toxicological interactions among components of the final WWTP
717
DONALD J. VERSTEEG a n d DANIEL M. WOLTERING
718 INFLUENT/SLUDGE SOURCE
[ 'A.OS'UO0'I ['.FLU
WWT A IL,'---JI ;,N.LUE..A"O.LUOOE
M AANNW UFACTURN IG PLO D SINTGASTE
~_~Mnnuf actuerlng Pla4X nt Wast
CASUNITS~~
~
~ ~
TESTS
EFFLUENT
EFFLUENT
TOXICITY
EFFLUENT
EFFLUENT
~
EFFLUENT
EFFLUENT
Fig. 1. Flow diagram of the experimental design demonstrating the source of sludge and influent, the addition of manufacturing plant wastes and the use of CAS unit effluents for toxicity testing. effluent. To conduct the most relevant testing possible, we reasoned that effluent toxicity should be assessed following actual or simulated wastewater treatment of the manufacturing plant waste. This research had two purposes. First, to assess the feasibility of coupling a laboratory-scale waste treatment system with effluent chronic toxicity assays to determine the contribution of an influent source to final W W T P effluent toxicity. This research was conducted using a detergent manufacturing plant waste as a case study. The manufacturing plant releases wastes along with other domestic, commercial and industrial sources to a municipal WWTP. Effluent from the municipal W W T P was observed to be toxic to aquatic life and the issue was the level of final effluent toxicity contributed by the manufacturing plant. The second objective of this study was to determine, under a realistic worst case scenario, i.e. a W W T P receiving both domestic waste and detergent manufacturing plant waste, whether surfactants, the major components o f the manufacturing plant waste, are likely to contribute to municipal W W T P effluent toxicity. MATERIALS AND METHODS Wastewater sources
Two wastewater treatment plant sludges and influent sources (A and B) were used to establish and operate six CAS (continuously-fed activated sludge) units. WWTP A is an approx. 20 million gallons per day conventional activated sludge treatment plant receiving waste from domestic (90%) and industrial (10%) sources. The industrial input includes wastes from the detergent manufacturing plant. WWTP B is a 1 million gallon per day, extended aeration activated sludge plant receiving wastes entirely from domestic sources. C A S units
Three CAS units were seeded with sludge from WWTP A (Fig. I). One unit was operated with WWTP A inflUent only. This influent contains ambient levels of the detergent manufacturing plant waste. Influent to the other two CAS units
were spiked with additional detergent manufacturing plant waste at 4 and 16 times the typical level of plant waste in WWTP A influent (Fig. 1). Three CAS units were set up with sludge from WWTP B and operated with WWTP B influent. One unit was operated with untreated influent alone (i.e. normal loading of domestic waste and no detergent manufacturing plant waste). Influent to the other two units were spiked with 4 and 16 times the plant waste levels in WWTP A influent (Fig. 1). Each laboratory-scale CAS unit consisted of a plexiglas aeration basin and a 21. cylindrical clarifier (Fig. 2). The aeration basin contained 61. of activated sludge dispersed by two aeration tubes. The aeration basin discharged through an overflow tube into a clarifier stirred by a shaft mixer. The Pump
InPlfluusn! se Pla(4oc) ntWast Compressed Air
Pump
Waste
~
/
Aerati Sectioonn
/"
Effluent
q I
J
SolPump idRecycl s e ~'
Fig. 2. Schematic diagram of the CAS units used in the treatment of the influent and th~ waste from a detergent manufacturing plant.
Waste contribution to effluent toxicity clarifier had a recycle discharge tube in the bottom and an overflow for effluent discharge. Sludge settling in the clarifier was periodically recycled (15 min per h) to the aeration basin by a peristaltic pump. Effluent from the clarifier was cornposited in a 201. polypropylene pail for toxicological and analytical sampling. Grab samples of WWTP inftuents were collected twice weekly, transported to the laboratory and stored in polypropylene containers at 4°C. Samples were fed into CAS units immediately upon receipt at the laboratory. Due to the influent feed rate, a portion of influent samples were 4 days old when treated. Influent was fed by peristaltic pump to the CAS units at a mean flow rate of 16.6 ml/min. Operational parameters in the CAS units were designed to be similar to actual conventional wastewater treatment plants (Table 1) (Metcalf & Eddy, 1979; Namkung and Rittmann, 1987). Wasting of sludge was carried out as needed to maintain the mixed liquor suspended solids (MLSS) limits. Influent, effluent and mixed liquor total suspended solids, and influent and effluent pH and total organic carbon were routinely monitored during the dosing period. Initially, CAS units were operated for 14 days with untreated influent only. This predose period allowed the CAS units to reach a state of equilibrium before dosing with plant waste. After the predose period, influents were supplemented with detergent manufacturing plant waste to approximate increases of zero (ambient influent), 4 and 16 times the level of manufacturing plant waste in WWTP A influent. The exaggerated doses of plant wastes were intended to generate effluents for toxicity testing which could be compared in a dose-related manner. Observation of a dose-response relationship between the concentration of the manufacturing plant waste and effluent toxicity would be substantial evidence of a cause and effect relationship. The dosing period lasted for 32 days allowing sufficient time for acclimation of the activated sludge microbial communities to plant waste under laboratory conditions. Control CAS unit effluent samples were collected for acute toxicity testing during the entire dosing period. Effluent samples for chronic toxicity testing were collected during the last 7 days of the dosing period.
Toxicity tests Control CAS unit influents and effluents were tested for acute toxicity to Ceriodaphnia dubia by the method of Peltier and Weber (1985). Grab samples of influent and 24h composite samples of effluent were used. Toxicity tests were initiated immediately after sampling and test samples were changed after 24 h with a fresh grab sample of influent and a second 24-h composite of effluent. These tests were conducted to determine the variability in influent toxicity and the ability of CAS units to remove toxicity, Effluent short-term chronic toxicity tests with Ceriodaphnia dubia and Selenastrum capricornuturn were used to assess the chronic toxicity of CAS effluents and final effluents from WWTPs A and B. Ceriodaphnia were chosen due to their generally greater sensitivity than fish to WWTP effluents (data not shown). Selenastrum was selected due to the sensitivity of algae to surfactants, the short duration of toxicity tests with algae, and their critical position in the ecosystem. These tests were conducted according to the Table 1. Operational conditions of the CAS units Parameter Aeration tank volume (litres) 6.0 Aeration rate (l/min) 6.0 Wastewater flow (I/d) 23.9 Hydraulic retention time (h) 6.0 Sludge retention time (d) 12.0 Mixed liquor suspended solids MLSS ( m g / l ) 2000-3000 Sludge volume index SVI (ml/I) < 100
719
methods of Horning and Weber (1985) with the exception that Ceriodaphnia were cultured and tested in individual 30 ml plastic cups filled with 20 ml of test solution. Filtered Little Miami river water, a relatively clean source of natural dilution water, was collected at Xenia, Ohio and used for Ceriodaphnia and Selenastrum culture and as dilution water in toxicity tests. During Ceriodaphnia 7 day chronic toxicity tests, daily 24-h composited samples from each CAS unit effluent were used to make the daily renewals of test solutions. Observations on the survival and reproduction of Ceriodaphnia were made daily at the time of transfer. The 4 day algal tests were run concurrently with the Ceriodaphnia toxicity tests. Test solutions were not renewed during the test. Algae were incubated at 24°C and 86 #E s-1 m -2 (equivalent to 400 ft-c cool white fluorescent light) on a shaker table oscillating at 100rpm. After 4 days of incubation, population growth was assessed by quantifying algal biomass (chlorophyll a) fluorometrically on a Turner model 111 fluorometer (APHA, 1985).
Analytical Surfactant analytical samples were 24 h composites of CAS effluents. Samples collected for anionic and nonionic surfactant analyses were preserved with 1% formalin and stored at 4°C. Samples collected for cationic surfactant analyses were preserved with 1% formalin and 5 mg/l of alkyl ethoxylate (C14_15AE 7), and stored at 4°C. The samples were analyzed for total nonionic surfactants by a modification of the cobalt thiocyanate active substance method (APHA, 1985), linear alkylbenzene sulfonates (LAS) by desulfonation gas chromatography (Osborne, 1986), and the following cationic surfactants by a modification of the method of Wee (1984); ditallow dimethyl ammonium chloride, monotallow trimethyl ammonium chloride and dodecyl trimethyl ammonium chloride. Note that the analytical method for the nonionie surfactants is a nonspecific colorimetric method reported to overestimate the concentration of nonionic surfactant in WWTP effluents (Gledhill et al., 1989). Thus, results of nonionic surfactant analyses are reported in general terms only. Water quality parameters including hardness, alkalinity, dissolved oxygen, total organic carbon, total suspended solids, ammonia, conductivity and pH were measured in dilution water and CAS influent and effluent by accepted methods (APHA, 1985). CAS unit sludge volume index (SVI) was measured according to APHA (1985) using a 30 min settling time. Water quality parameters were measured at the beginning of the algal test and daily during Ceriodaphnia testing. Statistics Survival data were analyzed by the methods described in Peltier and Weber (1985). Ceriodaphnia young production and algal population growth data were analyzed by nonlinear multiple regression analysis on SAS (SAS, 1986). Toxicity test results are summarized in this study as the effective concentration of effluent reducing biological response, survival or reproduction, by 50% (ECs0 values) with 95% confidence intervals. The ECs0 statistic was selected to identify effluent concentrations causing a specific level of toxicity and does not indicate a toxicity threshold or biological relevance in the receiving environment. In using no observed effect (NOEC) and first observed effect concentrations (FOEC), biological effects varied greatly among CAS unit treatments with similar NOECs and FOECs. Others have observed this effect and recommend the use of a dose-response statistical approach in place of the hypothesis testing approach (Krump, 1984; Barnthouse et al., 1987). Thus, to make meaningful comparisons among CAS unit treatments in this study, biological effects were held constant at 50%. For Ceriodaphnia chronic tests, ECs0 values were calculated based on survival and young production. The lower of
720
DONALD J. VERSTEEG a n d DANIEL M . WOLTERING Table 2. Concentration [mean (mg/l); (SD); n = 4] of surfactants* in CAS units and actual WWTP effluents Treatment system
Wastewater treatment plants WWTP A effluent (n = 7) WWTP B effluent (n = 3) CAS units WWTP A control WWTP A 4 × plant waste WWTP A 16 x plant waste WWTP B control WWTP B + 4 x plant waste WWTP B + 16× plant waste
DTDMAC
MTTMAC
CI:TMAC
LAS
0.038 (0.018) 0.025 (0.027)
<0.012t < 0.005"I"
<0.010t < 0.005t
<0.050t 0.130t
0.760 (0.39) 4.53(0.84) 20.3 (4.57) 0.550 (0.28) 2.98 (1.41) 10.7(3.66)
0.009 (0.002) 0.008(0.003) 0.024 (0.001) 0.010 (0.005) 0.011 (0.005) 0.046(0.035)
< 0.005t <0.005t <0.005t <0.005t <0.005"i" <0.007t
0.070 (0.032) 0.390(0.042) 3.10 (1.46) 0.140 (0.010) 0.340 (0.145) 2.05(1.00)
*Nonionic surfactant concentrations as assessed by a nonspecifi¢ method were less than 0.40 mg/l. Abbreviations: DTDMAC, ditallow dimethyl ammonium chloride; MTTMAC, monotallow trimethyl ammonium chloride; CI2TMAC, dodecyl trimethyl ammonium chloride; LAS, linear alkylbenzene sulfonate. t N o standard deviation, "less than" values included in calculation.
these two toxicity values was reported to insure the most sensitive toxic effect was selected. For algae, ECs0 values were based on a reduction in population growth. To determine if a relationship existed between manufacturing plant waste and toxicity, effluent toxicity to Ceriodaphnia and algae were regressed on influent manufacturing plant waste and effluent total surfactant concentrations using the linear regression analysis on SAS (SAS, 1986). RESULTS
CAS unit operation CAS units operated well during the study. Mean total organic carbon removals ranged from 76.8 to 83.7% among the CAS units. Total suspended solids removals were 81.9 and 87.7% in control CAS units A and B, respectively, however, due to the chemical and physical nature of surfactants, reliable total suspended solids removal values could not be determined in CAS unit receiving manufacturing plant waste. Mean sludge volume indices ranged from 46.8 to 66.7 ml/l and mean mixed liquor suspended solids levels ranged from 2141.7 to 2981.5mg/1 across all CAS units. The F / M ratio (lb BODs/Ib VSS.d) ranged from 0.28 to 0.37 in WWTP A CAS units and from 0.20 to 0.31 in WWTP B CAS units. The yield coefficient (mg SS/mg BODs) ranged from 0.19 to 0.20 in WWTP A CAS units and from 0.31 to 0.69 in WWTP B CAS units. Effluent surfactant concentrations at WWTP A and B were similar to each other and, with the exception of ditallow dimethyl ammonium chloride, similar to effluent concentrations in the control CAS unit effluents (Table 2). Addition of plant waste to CAS unit influents caused effluents surfactant levels
to increase greatly relative to the actual WWTPs and the control CAS units (Table 2).
Acute toxicity WWTP A influent toxicity was variable, Ceriodaphnia dubia 48 h LCs0 values ranged from 22 to > 100%, but was generally less toxic than WWTP influent B (Table 3). W W T P B infiuent was consistently acutely toxic to Ceriodaphnia; LCs0 values were less than 50%. Effluents from control CAS units were consistently of low acute toxicity indicating CAS units effectively removed acutely toxic components. More sensitive "chronic" endpoints, though, were needed to distinguish effluent toxicity among CAS units.
Chronic toxicity Toxicities of WWTP A and B effluents were similar to Ceriodaphnia (Table 4). EC50 concentrations were 24 and 22°/'0 effluent in W W T P A and B, respectively. Control CAS unit and actual effluents also had similar toxicities. For W W T P A, chronic ECs0 concentrations were 24% in the actual W W T P effluent and 33% in the control CAS unit effluent to Ceriodaphnia. For WWTP B, effluent ECs0 concentrations were 22 and 16% in the actual WWTP and control CAS unit effluents, respectively. In WWTP A CAS units, Ceriodaphnia chronic effluent ECs0 concentrations were 33% for the control CAS unit, 46% for the CAS unit receiving 4 x plant waste and 13% for the 16 x plant waste CAS unit (Table 4). In WWTP B CAS units, chronic effluent Ceriodaphnia ECs0 concentrations were 16% for the control CAS unit, 35% for the CAS unit receiving
Table 3. The acute toxicity of influents and effluents from control CAS units to Ceriodaphnia dubia 48-h LCs0 value (%) Sample type WWTP A control influent effluent WWTP B control influent effluent
Week:
1 22.2 (16.5-29.6) > 100 44.6 (32.9-92.3) 52.9 (0-100)
2
3
4
5
> 50
> 100
> 100
--
> 100
> 100
> 100
> 100
16.0 (12.0-25.0) > 100
38.0 (25.0-50.0) > 100
< 25
--
> 100
> 100
Waste contribution to effluent toxicity Table 4. Effect on the survivaland reproductionof Ceriodaphnia dubia and the growthof Selenastrum caprieornutum of effluentsfrom WWTPs and CAS units Ceriodaphnia Selenastrum ECs0 ECs0 Treatment (%) (%) Wastewater treatment plants
WWTP A effluent
24 (16.8-36.9) 22 (8.4-58.4)
WWTP B effluent CAS units
WWTP A control WWTPA + 4 x plant waste WWTP A + 16× plant waste WWTP B control WWTP B+ 4 x plant waste WWTP B+ 16x plant waste
33 (25.0-50.0) 46 (25.0-50.0) 13 (9.6-18.7) 16 (12.5 25.0) 35 (27.6-45.3) 28 (20.5-37.1)
> 100 13 (9.0-17.8) > 100 > 100 > 100 72 (60.8-86.1) 59 (46.%74.8) 58 (49.4-67.0)
4 x plant waste and 28% for the 16 x plant waste CAS unit effluent (Table 4). Toxicities of WWTP A and B effluents to S e l e n a s t r u m c a p r i c o r n u t u m differed (Table 4). The ECs0 concentrations were > 100% in WWTP A effluent and 13% in WWTP B effluent. The control CAS units reflected this difference in effluent toxicity. Effluent from the WWTP A control CAS unit were also nontoxic to algae with 4-day ECs0 concentrations exceeding 100% effluent. With WWTP B influent, the control CAS unit effluent was less toxic to algae than the actual WWTP effluent. The ECs0 concentration of the WWTP B effluent was 13% effluent while the control CAS unit effluent EC50 level was 72%. In WWTP A CAS units, all algal CAS unit effluent ECs0 concentrations exceeded 100% effluent (Table 4). In WWTP B CAS units, algal chronic ECs0 concentrations were similar at 72, 59 and 58% in the ambient, 4 x and 16 x plant waste units (Table 4). Regression of effluent toxicity to Ceriodaphnia and Selenastrum on infiuent manufacturing plant waste levels and effluent surfactant concentrations indicated the lack of a statistically significant relationship between toxicity and the level of plant waste components in the influent or effluent (Table 5). DISCUSSION Federal and state agency regulation of effluents has expanded to include the monitoring and regulation of whole effluent toxicity (U.S. EPA, 1984, 1985). TechTable 5. Regressionstatistics(r; Pearsoncorrelation coefficients) describing the regression of toxicity (ECs0)to Ceriodaphniaand Selenastrumon influent manufacturingplantwastelevelsand effluentsurfactant concentrations Correlation coefficient(r) Species Ceriodaphnia Selenastrum
lnfluent 0.03 0.28
Effluent 0.05 0.15
721
niques used to control whole effluent toxicity at municipal WWTPs include utilization of alternative treatment options to remove final effluent toxicity and chemical identification and remediation of effluent compounds causing toxicity (U.S. EPA, 1985; Mount and Anderson-Carnahan, 1988). These techniques are useful and effective at controlling effluent toxicity. However, in some cases a more cost effective and direct approach to controlling effluent toxicity, source reduction, is recommended (U.S. EPA Science Advisory Board, 1988). In this approach, the waste streams contributing to final effluent toxicity would be identified and regulated. Interpretation of the results of toxicity tests on municipal WWTP influent waste streams is not straightforward. Due to the potential chemical complexity of a waste stream, the differential impact of treatment on the components of the waste, and the effect of the effluent matrix on the toxicity of waste components, the waste treatment process should be incorporated in evaluating the contribution of a waste stream to final effluent toxicity. Laboratory-scale, continuously fed activated sludge treatment systems (CAS units) have been validated as effective models of the activated sludge process giving removals of conventional parameters and consumer product chemicals similar to actual WWTPs (King, 1980; Vashon et al., 1982). In this study, we demonstrated the utility of CAS units to assess the contribution of a specific WWTP influent waste stream to post-treatment toxicity by verifying that, for Ceriodaphnia and Selenastrum, CAS units generate effluent toxicologically similar to actual WWTP effluents. For Ceriodaphnia, effluent toxicity in the control CAS units and the actual WWTPs were similar for both influent sources. For algae, although some differences between toxicity in the WWTPs and the control CAS unit effluents were observed, effluent toxicities were comparable for an influent source. At WWTP A, both control CAS unit and the actual WWTP effluents had similar toxicity to algae with ECs0 concentrations exceeding 100% effluent. The WWTP B control CAS unit effluent was less toxic to algae than the actual WWTP effluent. However, given the possible variability in effluent toxicity and in the toxicity test, algal toxicity of the control CAS units and the actual WWTP effluents were comparable. Effluents of increasing manufacturing plant waste strength were generated by exaggerating influent plant waste loadings to CAS units. There was no overall effect of plant waste components on toxicity. However, effluent from WWTP A CAS unit receiving the 16-fold addition of plant waste and having the highest effluent total surfactant concentrations did have increased toxicity to Ceriodaphnia relative to effluent from the WWTP A control CAS unit. A 4-fold addition of manufacturing plant waste to untreated influent had no effect on the toxicity of the WWTP A CAS unit effluent. Thus, the current level of detergent manufacturing plant waste being re-
722
DONALDJ. VERSTEEGand DANIELM. WOLTERING
ceived at WWTP A is not impacting effluent toxicity. In fact, a 4-fold increase in influent plant waste levels would not be expected to impact effluent toxicity. In the WWTP B CAS units, increases in plant waste levels including the 16-fold addition did not adversely impact effluent toxicity to algae or Ceriodaphnia. The reason for the 16 x plant level contributing to effluent toxicity in W W T P A but not WWTP B is not known but may have been due to increased levels of manufacturing plant waste in this effluent. Due to addition of plant wastes to CAS unit influents, CAS unit effluents contained greatly increased concentrations of two detergent actives, linear alkylbenzene sulfonate and ditallow dimethyl ammonium chloride (DTDMAC), in comparison to the actual WWTPs (Table 2). Despite these greatly elevated concentrations of surfactants, effluent toxicity to algae and Ceriodaphnia was not affected except in the CAS unit with the greatest effluent surfactant concentration (i.e. W W T P A 16 × plant waste CAS unit). In all CAS unit effluents, linear alkylbenzene sulfonate concentrations remained below levels reported to be toxic to aquatic organisms (Maki, 1979; Holman and Macek, 1980; Taylor, 1985). However, CAS unit effluent concentrations of D T D M A C exceeded levels reported to be toxic. Lewis and Wee (1983) observed that D T D M A C completely inhibited Selenastrum capricornutum growth (ECl00 or algistatic concentration) at concentrations ranging from 0.7 to 2.6 mg/l in filtered river water. In a chronic toxicity test conducted in river water, the D T D M A C ECs0 concentration to Daphnia magna was approx. 1.0 mg/1. In our study, D T D M A C concentrations up to 20.3 mg/l in a CAS unit effluent had no effects on Selenastrum. For Ceriodaphnia, a congeneric species to Daphnia, the effluent D T D M A C concentration at the ECs0 level of effluent reached a maximum of 3.0 mg/1. These observations indicate that the waste treatment process and effluent matrix may have reduced the apparent toxicity of D T D M A C . This effect on toxicity is presumed to be due to an effect on D T D M A C speciation and bioavailability. Similar results on the amelioration of the toxicity of cationic compounds by suspended solids and organic carbon have been reported (Cary et al., 1987). Since these factors affect the toxicity of these compounds in the environment, it is important to utilize the most environmentally relevant method to introduce these compounds into aquatic toxicity test systems. These results suggest that CAS units are an effective method for generating increased concentrations of test materials in an environmentally realistic matrix and that relevant safety data can be obtained with these methods. In this case study, effluent concentrations of the major plant waste components could be measured. However, if plant waste components could not be measured due to the number of compounds or the
inability to accurately quantify specific components, the CAS unit approach would remain valid. Due to the ability to manipulate influent waste loadings, the CAS unit approach can be a powerful tool to assess the contribution of waste contributors to effluent toxicity. In utilizing this approach, care should be exercised to avoid effects of the waste on the treatment process. Addition of waste at abnormally high levels could cause effects including toxicity to activated sludge organisms, alternative substrate utilization or dilution of influent and mixed liquor strength. These, and other potential effects, could ameliorate or potentiate the observed toxicity of the waste. The incidence of these effects can be reduced by proper selection of influent waste levels and monitoring of activated sludge processes. CONCLUSIONS Use of laboratory-scale, continuous activated sludge units coupled with effluent toxicity test procedures were effective methods to assess the contribution of an influent source to final WWTP effluent toxicity. CAS units provided treatment of influent waste streams and generated toxicologically relevant effluents for Ceriodaphnia and Selenastrum. A major component of the detergent manufacturing plant waste, DTDMAC, was less toxic as a component of a CAS unit effluent than has been reported in the literature in conventional laboratory toxicity tests suggesting that components of WWTP effluents ameliorate the toxicity of this surfactant. In this case study, the detergent manufacturing plant waste was not a significant contributor to WWTP effluent toxicity at current rates of manufacturing plant waste input to the WWTP. REFERENCES
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