Data on effluent toxicity and physicochemical parameters of municipal wastewater treatment plant using Daphnia Magna

Toxicity of Municipal Wastewater Treatment Plant Effluent (MWWTPE) was evaluated using bioassay with Daphnia Magna (D. Magna). Acute toxicity tests were performed on effluent samples of Urmia municipal wastewater treatment plant (Biolac system) according to the USEPA methods and 24, 48, 72, and 96 hr lethal concentration 50% (LC50) were calculated by application of Probit analysis. Also interrelationship between main effluent physicochemical parameters of wastewater (BOD5, COD, and TSS) and 24hr-LC50, were studied. Results showed that the effluent was safe to be discharged to the surface water in regard to physicochemical parameters and acute toxicity unit (TUa), according to the standards of Iranian Department of Environment (DOE). Relationship between effluent COD and 24hr-LC50 show that, increase in effluent COD resulted in increase in wastewater toxicity and there was not relationship between BOD5, TSS and toxicity of effluent.


a b s t r a c t
Toxicity of Municipal Wastewater Treatment Plant Effluent (MWWTPE) was evaluated using bioassay with Daphnia Magna (D. Magna). Acute toxicity tests were performed on effluent samples of Urmia municipal wastewater treatment plant (Biolac system) according to the USEPA methods and 24, 48, 72, and 96 hr lethal concentration 50% (LC 50 ) were calculated by application of Probit analysis. Also interrelationship between main effluent physicochemical parameters of wastewater (BOD 5 , COD, and TSS) and 24hr-LC 50 , were studied. Results showed that the effluent was safe to be discharged to the surface water in regard to physicochemical parameters and acute toxicity unit (TUa), according to the standards of Iranian Department of Environment (DOE). Relationship between effluent COD and 24hr-LC 50 show that, increase in effluent COD resulted in increase in wastewater toxicity and there was not relationship between BOD 5  Bio-Assay method with D. Magna may be applied to quality control of MWWTPE before discharge to the aquatic ambient as valuable tools for bio-monitoring of wastewater treatment plant effluent, as it is highly sensitive to pollutants These data are valuable to researchers investigating LC 50 related to the bio-chemical parameters of WWTPs effluents.

Data
Chemical characteristics of Urmia wastewater treatment plant are presented in Table 1. The data of 24, 48, 72, and 96 h toxicity test of Urmia wastewater treatment plant effluent are presented at Fig. 1. In this Figure, lethal concentration 50 (LC 50 ) of UWWTPE for 24, 48, 72, and 96 h exposure time are presented. This figure also presents the highest and lowest levels for 95% confidence. As well, a regression analysis was performed to examine possible correlations between exposure time and LC 50 . LC 50 of Urmia wastewater treatment plant effluent was between 594 to 326 ml/l from exposure time of 24 to 96 h. Correlations between exposure time and LC 50 show that there is non-linear regression between exposure time and LC 50 (R-squared is 0.97).
According to the light microscope images of D. Magna, large amounts of dark material were found in the gut tract of D. Magna after effluent wastewater exposure but not in the control. According to these images (Fig. 2), D. Magna after 96 h exposure time was destructed. The acute toxicity test were carried out to evaluate the inter-relationship between physicochemical parameters of effluent and toxicity of Urmia wastewater treatment plant effluent at various operational condition of wastewater treatment plant with different Biochemical Oxygen Demand (BOD 5 ); (20-40 mg/l); Chemical Oxygen Demand; (COD) (30-50 mg/l); Total Suspended Solids (TSS); (15-25 mg/l) concentrations. These results are presented in Figs. 3-5. In addition, Relationship between BOD 5 and 24h-LC 50 are presented in Fig. 3. According to the results, there is no direct relationship between BOD 5 concentration and acute toxicity of Urmia wastewater effluent (R-squared is 0.19). Relationship between COD and 24h-LC 50 are presented in the Fig. 4. According to the results, there are linear and direct relationships between COD concentration and acute toxicity of Urmia wastewater effluent (R-squared is 0.93). Relationship between TSS and 24h-LC 50 are presented in the Fig. 5. According to the results, there are not any linear and direct relationships between TSS concentration and acute toxicity of Urmia wastewater effluent (R-squared is 0.005) and this means that non settleable organic materials remain in effluent of wastewater have not acute toxicity effect on D.Magna. Total suspended solids (TSS) include all particles suspended in water which will not pass through a filter. After biological treatment of wastewater, some of the biological flocs (these flocs are mainly of biological origin) are not able to be settled in secondary sedimentation tanks and have not toxicity effects ( Table 2).

Wastewater treatment plant
Wastewater treatment system in the city of Urmia (One of the great western cities of Iran in west Azarbaijan province) that designed to serve 950,000 persons was selected to toxicity evaluation. Wastewater flow is about 77,000 m 3 /day mainly of domestic origin. This system consists of 2 mechanical coarse screening, Flow meter, Grit chamber, Biolac lagoon that have 5 part (Phosphor removal, Aeration, Sedimentation, Secondary aeration, Clarifier) and disinfection. In recent years to access the reclamation strategy for the Urmia Lake, these effluents were discharge to the lake. According to the Iranian Department of Environment (DOE) report this wastewater treatment plant effluents have standards for discharge to surface water.

Sampling
Samples were collected at different operational conditions from effluent of wastewater treatment plant in Jun 2015 based on the grab sampling, also known as a catch sampling that consists of a single sample taken at a specific time. All samples were collected and transport to laboratory according to the standards.    To support the growth of D. Magna during the day after the initial culture, one mg of dry yeast was added to each bottle every other day. Identification of D.Magna was carried out according to the US-EPA [4,5].
In order to determine of LC 50 , different concentrations (sample and distilled water) of effluent were prepared using distilled water. The effluent samples were used at 20%, 30%, 40%, 50%, 60% and 70% and control samples according to the EPA recommendations for a toxicity test [4,6]. Ten D. Magna were added to each dilution and the results of D. Magna mortality were recorded after exposure time. Magna in the blank tubes were observed to have a mortality rate of less than 10% [7]. It should be noted that temperature was checked regularly using a thermometer in the culture medium, Temperature of ambient test was measured during the experiments, culture medium of D. Magna were prepared according to the guideline [2], All experiments are repeated three times and average of data were report. An aerator pump was used to provide oxygen.

Statistical analysis
LC 50 and their corresponding 95% confidence intervals were calculated by probit analysis (SPSS 16 version). Acute toxic unit (TUa) of effluent wastewater treatment plant was calculated as following equation [3,8]: Toxicity classification is reported as follows: Each species endpoint per effluents solution sample was compared to the corresponding reference sample mean using a Students't test. The difference was significant than p o 0.05.

Physicochemical analysis
Effluent samples from the Urmia wastewater treatment plant were collected simultaneously in clean plastic cans and taken for physicochemical analysis following standard procedure [4]. Samples were preserved using preservatives as required, separately (for BOD 5 , COD, and TSS estimation).