128
CHAPTER FIVE
GENERAL DISCUSSION AND CONCLUSION
129
Despite numerous reports on the poor physicochemical and microbial quality of treated effluents from wastewater treatment plants and receiving watersheds in other South African provinces (Samie et al., 2009; Igbinosa and Okoh, 2009; Preez et al., 1987), the efficiency of wastewater treatment plants and the impact of treated effluent discharge on the quality of surface waters, particularly within the Umgeni River, Durban has not been adequately investigated. Hence, the main focus of this study was to determine the microbiological and chemical quality of treated final effluent being discharged from two independent wastewater treatment plants into receiving water bodies in the Durban area and to ascertain if these plants contribute significantly to the poor quality of the receiving aquatic milieu. The results obtained in this study revealed that whilst the independent treatment plants monitored, exhibited effluent qualities that met acceptable standards for some parameters such as pH and temperature, the effluent quality fell short of other standard requirements such as turbidity, orthophosphate, nitrate, COD and faecal coliforms, with values as high as 76.43 NTU, 3.99 mg/l, 8.22 mg/l, 313.89 mg/l and 3.97 × 103 CFU/ml obtained respectively. From the results presented in chapter two, it is clear that tertiary treatment processes exhibited a limited impact on certain physico-chemical parameters such as turbidity, whereby an increase in turbidity at the discharge point was observed 66.7% of the time throughout the sampling period relative to before chlorination. Similarly, increases in nutrient levels were also noted at the discharge point over several months with a 215.23% increased nitrate and a 12.21% increased phosphate concentration observed in December and September, respectively. In addition, point and diffuse sources of pollution coupled with a range of peripheral factors such as changing tides, atmospheric deposition and surrounding industrial and anthropogenic activities may have further contributed to the fluctuating physical, chemical and nutrient profiles observed within the receiving watershed.
130
Similarly, results presented in chapter three and four highlighted the increased levels of microbial indicators, poor reduction efficiencies and the presence of faecal coliforms and enteric viruses at the discharge point, indicative of health and environmental risk. Higher levels of certain indicator bacteria were observed at the discharge point compared to before chlorination across various months with February 2013 exhibiting increases for all enumerated indicators namely, total coliforms (21.73%); E. coli (72.14%), faecal coliforms (5.65%), faecal streptocci (100%) and enterococci (108.93%) for the NWWTP. In addition, despite the South African guideline for treated effluent stipulating that no faecal coliforms should be present in treated effluent being discharged into any receiving water body, this guideline was only met in October 2012 for the NWWTP. Similarly, high counts of both somatic and F-RNA coliphages were detected at the discharge point throughout the sampling period with coliphages being detected during July in the absence of faecal coliforms indicating the need for a combination of indicators.
Despite the long term use of bacteria as indicators of water quality, numerous studies have reported on their inadequacy to accurately determine the presence of enteric viruses or protozoa, with more research being required on currently monitored indicators (Gironez et al., 2010).
Hence, chapter four focused on determining the presence of enteroviruses and human adenoviruses which have been commonly implicated in disease outbreaks in South Africa.
Results obtained indicated the presence of both viruses within collected samples, with human adenovirus being detected in 62.5% of all samples collected for both plants and enteroviruses in 100% and 87.5% of samples collected from NWWTP and NGTW respectively. Similar to other findings, results presented in chapters three and four of this study revealed that whilst detected bacterial indicators provided an overall indication of the water quality within the receiving
131
watersheds, there was no link between the presence of bacterial indicators monitored and that of coliphages and enteric viruses in certain months. This further confirmed the possible need for the use of coliphages as indicators of faecal contamination, reinforcing their potential to serve as a valuable model for predicting the presence of enteric viruses in contaminated water due to the many similarities between the two groups (Grabow, 2001).
In order for sewage treatment plants to meet national and international standards, there is a growing need to improve current treatment processes and to adopt more rigid methods for monitoring final effluent being discharged into any receiving water body. The design and implementation of affordable and suitable equipment and wastewater technologies in conjunction with adequate training of workforce within treatment plants will further aid management and treatment efficiencies, especially in developing countries. In addition, the privatization of treatment plants as well as the inclusion of suitable penalties such as the ‘polluter-pays’ principle together with a bottom-up approach involving community education and involvement may further aid the overall improvement and prevention of further contamination of existing water bodies (Doughari et al., 2007). Accurate and timeous information on the quality of water is necessary to develop a sound public policy and to ensure the implementation of efficient water quality improvement programmes. In addition, ensuring effective societal communication measures through the introduction of simple easy to understand water quality indices will allow for ease of understanding regarding water quality trends. Ensuring rigorous water quality monitoring is imperative for the provision of reference data that will aid policy development as well as the protection and management of existing water resources (Varunprasath and Daniel, 2010). Therefore, more stringent monitoring of wastewater treatment plants is required to ensure
132
compliance with current guidelines. In addition, current legislation should be enforced and industries discharging toxic wastes should be registered according to the effluent they discharge with toxic chemicals being used in agriculture and industry being monitored and intensely studied. Without an adequate water supply of good quality, surrounding communities as well as further agricultural developments will suffer and the overall economy affected.