Impact of microbial and physico-chemical qualities of treated wastewater effluent on receiving water bodies in Durban.
Increase in magnitude of the global freshwater crisis together with the constantly changing demographics, hydrological variability and rapid urbanization will allow for continuous over exploitation of existing water resources, in an attempt to satisfy the rising socioeconomic demands. Increasing pressure on existing wastewater treatment plants, together with inefficient hygiene practices have exacerbated the nutrient and microbiological loads constantly entering surrounding water systems. This, coupled with the use of outdated guidelines has resulted, not only in an increase in waterborne related diseases but also an increase in waterborne-disease-related deaths. The current study investigated the physicochemical and microbiological quality of treated effluent from two independent wastewater treatment plants as well as their impact on the receiving watershed within Durban, South Africa over a one year period. Microbiological and physicochemical profiles were determined using standard methods whilst conventional PCR was used for the seasonal detection of human enteric viruses. Monthly variations were observed for all parameters with eight and six out of 12 month samples exhibiting increases in turbidity at the discharge point for the NWWTP and NGTW respectively, relative to before chlorination. Similarly, increases in nitrate and phosphate levels at the discharge point were also noted with the highest being recorded during December (215.23%) and September (12.21%) respectively. Temperature profiles ranged between 12 – 26 °C and 12.7 – 26 °C for the NWWTP and receiving Umgeni River whilst for the NGTW and receiving Aller River, it ranged between 16.5 – 26 °C and 12 – 25.7 °C respectively. Seasonal averages revealed relatively high COD values downstream of the Umgeni River during winter (263.22 mg/l) and spring (177.93 mg/l). Eight out of twelve samples exhibited increases in turbidity at the discharge point for the NWWTP with the highest values obtained during April (76.43 NTU). Significant positive correlations (p ≤ 0.05) were observed upstream and downstream of the Umgeni River between temperature and BOD (r = 0.624); turbidity (r = 0.537); TDS (r = 0.437); TSS (r = 0.554) and DO (r = 0.516). Percentage reduction of bacterial indicators at the discharge point ranged between 0.52 – 100% and 41.56 – 100% across the sampling period for the NWWTP and NGTW, respectively. Treated effluent from both plants did not meet the required guidelines, with a 100% reduction in the faecal coliform load being detected only during October 2012 for both plants. In addition, higher levels of indicator bacteia were observed at the discharge point for the NWWTP during February 2013 with observed counts (in CFU/ml) as high as 12.27 x 103; 6.61 x 103; 2.99 x103; 1.6 x 103 and 1.17 x103 for total coliforms, E.coli, faecal coliforms, faecal streptococci and enterococci, respectively. Similarly, higher levels of both somatic and F-RNA bacteriophages were detected during April (106.67 PFU/ml), May (309.33 PFU/ml). June (346.67 PFU/ml) and August (126.67 PFU/ml) compared to samples collected before chlorination for the NWWTP. Enteroviruses were detected in 100% of unchlorinated final effluent samples, 87.5% of chlorinated final effluent and 93.75% of receiving river samples whilst human adenoviruses were detected in 50% of final effluent samples before chlorination, 62.5% in samples collected at the discharge point and 62.5% of river water samples. 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. Ensuring efficient surveillance and management of existing treatment plants coupled with guideline revision and monitoring compliance is imperative in preventing further risk of pollution to both the environment and human health.