Seasonal influence on the nutrient removal efficiency of a SPRAS wastewater treatment plant in the Free-State Province, South Africa

S.  Mofokeng; P.  Oberholster; L.  Hill

S. Mofokeng
P. Oberholster
L. Hill

Keywords: Wastewater discharge, Water quality guidelines, Wastewater Treatment Plant (WWTP), Sludge Process Reduction Activated Sludge (SPRAS), Activated Sludge (AS), Sludge Reduction, Ineffective WWTP

Abstract

In Africa, untreated sewage discharge is one major source of water pollution that contributes to high oxygen demand and nutrient loading on the receiving water bodies, which threatens aquatic ecosystem and human health. Sludge Process Reduced Activated Sludge (SPRAS) plant could potentially address
this challenge as a technology that has been found effective in the removal of nutrients from wastewater. The objective of the current study was to investigate the nutrient removal and treatment efficiency of a SPRAS treatment plant as a case study during the cold and warm seasons in the Free State Province,
South Africa. The treatment effectiveness of the SPRAS plant was assessed by comparing the final effluent data to the South African General Authorization (SAGA) guidelines for discharging wastewater into water resources. Treatment efficiency was determined by comparing raw influent to the final effluent data. Ammonia was efficiently removed from wastewater in the colder seasons compared to the warmer seasons, at 97-99% and 87-89% removal efficiency range, respectively. Suspended solids, Carbon Oxygen Demand (COD), and ortho-phosphates were efficiently removed from wastewater during both warm and cold seasons, with efficiency ranges of 97-98%, 87-89%, and 67-98% respectively. E. coli in the final effluent was reduced to concentrations below the set SAGA limit during both warm and cold seasons. However, SPRAS was ineffective in nitrates removal during both seasons, where the final effluent concentration failed to meet the set SAGA limits. The observed nitrates removal ineffectiveness may be attributed to operating temperatures (minimum average range of 10.5 -13.5 °C) that were not
optimal for the activity of the microbial communities driving the treatment process. It was evident from the analysed data that climatic conditions may influence the treatment efficiency of SPRAS technology, with treatment efficiency reduced when air temperatures were below optimal temperatures for the growth of the microbial communities.