Phosphorus Trend Analysis and the Role of Wastewater Treatment Facilities in Attenuating Eutrophication of the Swakoppoort Reservoir, Namibia

<title>Abstract</title> <p> The study was carried out to assess the trend of phosphorus from the effluents of selected wastewater treatment facilities and their respective potential role in mitigating nutrient levels (i.e. eutrophication) of the Swakoppoort Reservoir. The phosphorus trend analysis of the industrial effluent and reservoir was assessed using the Mann-Kendall trend tests. Eutrophication potential (EP) of the selected industries was determined using a life cycle assessment approach embedded into the GaBi software. The severity of reservoir eutrophication was assessed using Carlson’s Trophic State Index. The results indicate that the Old Ujams Oxidation ponds and the Namib Poultry Industry’s (NPI) evaporation ponds systems were not effectively treating wastewater. This could be demonstrated by increasing trend of phosphorus levels. They were found to have the highest daily Eutrophication Potential (EP) of 60.9 kg PO ₄ ³ and 175.01 kg PO ₄ ³⁻ equivalents, respectively. The study also revealed that advanced treatment technologies that have tertiary treatment stages focusing on nutrient removal are very effective at reducing nutrients in the effluent. This was the case for the New Ujams wastewater treatment plant (UWTC), the NPI Reverse Osmosis (RO) Plant and the Otjomuise Sewage treatment plants (OSTP) that use membrane technology, Reverse Osmosis and biological nutrient removal technologies, respectively. The EP for the UWTC, NPI RO Plant and OSTP was 4.64, 0.051 and 11.05 kg PO ₄ ³⁻ Eq. respectively. Furthermore, the Swakoppoort dam was found to be in hypertrophic state. The study recommends application of lake restoration technologies to help improve further the reservoir’s current status. </p>