Physicochemical quality of an urban municipal wastewater effluent and its impact on the receiving environment

The physicochemical qualities of the final effluents of an urban wastewater treatment plant in South Africa were assessed between August 2007 and July 2008 as well as their impact on the receiving watershed. The pH values across all sampling points ranged between 6.8 and 8.3, while the temperature varied from 18 degrees C to 25 degrees C. Electrical conductivity (EC) of the samples was in the range of 29-1,015 mu S/cm, and turbidity varied between 2.7 and 35 NTU. Salinity and total dissolved solids (TDS) varied from 0.36 to 35 psu and 16 to 470 mg/L, respectively. The concentrations of the other physicochemical parameters are as follows: chemical oxygen demand (COD, 48-1,180 mg/L); dissolved oxygen (DO, 3.9-6.6 mg/L); nitrate (0.32-6.5 mg NO3- as N/L); nitrite (0.06-2.4 mg NO2- as N/L); and phosphate (0.29-0.54 mg PO43- as P/L). pH, temperature, EC, turbidity, TDS, DO, and nitrate varied significantly with season and sampling point (P < 0.05 and P < 0.01, respectively), while salinity varied significantly with sampling point (P < 0.01) and COD and nitrite varied significantly with season (P < 0.05). Although the treated effluent fell within the recommended water quality standard for pH temperature, TDS, nitrate and nitrite, it fell short of stipulated standards for other parameters. The result generally showed a negative impact of the discharged effluent on the receiving watershed and calls for a regular and consistent monitoring program by the relevant authorities to ensure best practices with regard to treatment and discharge of wastewater into the receiving aquatic milieu in South Africa.