Modeling the microbial fate and transport in rivers of South Africa

Abstract: In recent years, surface water used for domestic, industrial, and irrigation purposes in South Africa has deteriorated due to inadequate wastewater treatment, urban and agricultural runoff, and rural settlements with deficient sanitation. Access to safe drinking water and sanitation is a basic human right, and if waterborne pathogens are present in the water environment, they compose a human health risk. With some hydrological models, e.g., Hydrological Predictions of the Environment (HYPE), it is possible to model microbial water quality and predict how land use and climate changes affect recipient water sources. In this thesis, waterborne pathogen transport in South Africa is investigated using World-Wide HYPE (WWH), to increase the understanding of the largest sources affecting pathogen concentration in surface water and processes affecting pathogen transport. Initially, a literature study was performed with emphasis on finding the most suitable pathogen to simulate. Because of the amount of available data, the indicator microorganism, E. coli, was chosen. Observed E. coli concentrations in surface water were used to evaluate the conformity of the simulated concentration, and contributions from separate sources were analysed. A sensitivity analysis was performed to increase the understanding of process parameters affecting the transport of E. coli in WWH. The findings of this project show that the largest contributions of E. coli originate from humans with unsatisfactory waste management, where wastewater is partially released directly to surface water. The largest deviation in average E. coli load per year was obtained when altering t1expdec, which denotes the half-life time of the simulated microorganism. The half-life time was also the process parameter with the most significant effect on the simulated concentration. In addition, when the parameter that specifies the fraction of E. coli that is released directly to surface water was altered, which affects one of the largest E. coli sources, a large deviation in average E. coli load per year was observed. This finding shows the importance of estimating the load from contamination sources accurately. The conformity of simulated and observed E.coli load was acceptable, but the simulated discharge needs to be improved to achieve better conformity of the E. coli concentration in surface water. WWH has great potential to simulate waterborne pathogens, but further developments to improve the simulated discharge are encouraged to obtain more reliable results.