Assessment of the biological quality of raw and treated effluents from three sewage treatment plants in the Western Cape, South Africa

Abstract

Wastewater contains contaminants such as bacteria, heavy metals, industrial chemicals, pesticides, pharmaceuticals, personal care products, steroid hormones and surfactants. Pollutants enter receiving waters via agricultural run-off, wash-off from roadways, industrial wastewaters and domestic sewage. Pollutants can incur adverse effects to the environment, human and animal health. The aim of this study was to compare the water quality of raw wastewater and treated sewage effluents from three different sewage treatment plants in the Western Cape, South Africa. The treatment plants investigated are on the same river system. Sewage treatment plant 1 and 2 use older technologies, while sewage treatment plant 3 has been upgraded and new technologies (membrane bioreactor) were incorporated in the treatment processes. The first objective was to determine the occurrence of total coliforms, Escherichia coli (E. coli) and fluoroquinolone and sulfamethoxazole antibiotic residues in raw wastewater and treated sewage effluents. Bacteria in treated sewage effluents can result in diseases such as dysentery, gastroenteritis, and typhoid upon exposure. A chromogenic test was used to screen for coliforms and E. coli. Enzyme linked Immunosorbent Assays (ELISA) were used to quantitate antibiotic residues (fluoroquinolones and sulfamethoxazole) in raw wastewater and treated sewage effluents. This study showed that bacteria are present in raw wastewater and residual bacteria are released with treated sewage effluents from sewage treatment plant 1. Fluoroquinolones and sulfamethoxazole are present in raw wastewater entering all sewage treatment plants. Fluoroquinolones were not eliminated by the sewage treatment processes and detectable levels were released with treated sewage effluents. Sulfamethoxazole was eliminated by the treatment processes used by sewage treatment plant 2 and 3 only. The second objective of this study was to compare the occurrence of the steroid hormones estradiol, estrone and testosterone in raw wastewater and treated sewage effluents. Steroids in water bodies are associated with endocrine disruption. ELISAs specific for the steroid hormones were used to assess the samples collected from the sewage treatment plants. Estradiol, estrone and testosterone were detected in raw wastewater entering all sewage treatment plants. Sewage treatment plant 3 displayed low efficiencies for estradiol removal. Treatment plant processes at sewage treatment plant 1 and 2 removed estrone effectively. Testosterone was removed efficiently by the treatment processes. The third objective of the study was to determine the occurrence of the surfactants alkylphenol ethoxylates (APE) and alcohol ethoxylates (AE) in raw wastewater and treated sewage effluents. Surfactants in water bodies are associated with adverse effects in aquatic organisms. ELISAs specific for the selected surfactants were used to assay the sewage samples. APE and AE surfactants were detected in significant concentrations in raw wastewater entering all investigated sewage treatment plants. Results of this study showed that APE was not removed effectively by treatment plant 1. However, APE was removed by the treatment processes used in sewage treatment plant 2 and 3. In addition, this study showed that AE levels in treated sewage effluents for all sewage treatment plants were reduced, irrespective of treatment technology used. Biomarkers for toxicity are useful to determine potential adverse effects to humans and animals. Lactate dehydrogenase (LDH) release from cells is used as a biomarker to determine cellular cytotoxicity. Acetylcholinesterase (AChE) inhibition is used as a biomarker to determine neurotoxic contaminants in the aquatic environment. The SOS chromotest is often used to determine genotoxicity of samples. The fourth objective of this study was to validate and use these screening tests to determine the toxicity of raw wastewater and treated sewage effluents. Raw wastewater and treated sewage effluents were screened for cytotoxicity using LDH release as a biomarker. This study also focused on validating the AChE inhibition assay to screen raw wastewater and treated sewage effluents for potential AChE inhibitors. Raw wastewater and treated sewage effluents were also tested for genotoxicity using the SOS chromotest. The results of this study showed that raw wastewater and treated sewage effluents from all sewage treatment plants were not cytotoxic. Results of this study also showed that raw wastewater entering sewage treatment plants contain AChE inhibitors. The sewage treatment processes are ineffective in eliminating these inhibitors from treated sewage effluents. In addition, raw wastewater samples tested positive for genotoxicity. Treated sewage effluents from all sewage treatment plants displayed no genotoxicity. This indicates effective removal of genotoxins by all three sewage treatment plants investigated. This study makes use of only screening assays to determine toxicity therefore care should be taken into interpreting results. Results of this study could reflect unique characteristics of the analyzed samples and therefore not a true representation of raw wastewater and treated sewage effluents over an extended period of time. The fifth objective of this study was to screen raw wastewater and treated sewage effluents from three different sewage treatment plants for its toxic effects on specific immune pathways using an in vitro whole blood culture assay and cytokine monitoring. Mammals possess immune systems that are particularly vulnerable or sensitive to exposure to pollutants. Therefore, the immune system can be used to monitor pollutant exposure. Sewage effluents consist of a mixture of chemicals, pollutants, microorganisms, debris, heavy metals, pesticides and pharmaceuticals. These sewage effluents or environmental pollutants may have effects on the immune system of humans. Interleukin-6 (IL-6) was used as a biomarker for inflammation. Interleukin-10 (IL-10) was used as a biomarker for humoral immunity. ELISAs specific for these two cytokines were used to assay the samples. Results of this study showed that raw wastewater and treated sewage effluent samples produced an immunotoxic effect on the IL-6 and IL-10 immune pathways. Despite different technologies used by the sewage treatment plants in this study, contaminants in the effluents still resulted in immunotoxic effects. The final objective of this study was to determine the efficiency of activated charcoal for the removal of steroids and surfactants from treated sewage effluents from a sewage treatment plant. Several concentrations of activated charcoal were added to treated sewage effluents from the sewage treatment plant and allowed to incubate for 2 hours. Treated sewage effluents and activated charcoal adsorbed treated sewage effluents were assessed for the occurrence and removal of estradiol, estrone, testosterone and APE. Specific ELISAs were used to monitor estradiol, estrone, testosterone and APE. Results showed that activated charcoal is effective in removing the steroids and surfactants. Adding activated charcoal as a final sewage treatment step could potentially provide a method that could be employed by sewage treatment plants to reduce residual contaminants in treated sewage effluents.