Performance assessment of wastewater treatment plants with special reference to phenol removal

Abstract

This study investigated the performance of five different wastewater treatment plants (WWTPs) in some rural areas in the Eastern Cape, South Africa, through an assessment of the physicochemical qualities of the effluents and their removal capacity for selected phenolic compounds. Water samples were collected on a monthly basis (February–July 2016), and temperature, pH, turbidity, total dissolved solids (TDS), total suspended solids (TSS), electrical conductivity (EC) and dissolved oxygen (DO) were measured on-site using standard methods. Phenolic compounds were determined using the solid-phase extraction technique followed by derivatization and gas chromatography–mass spectrometry analysis. Recorded temperatures for all the WWTPs effluents were 29–30 °C in summer, 20–27 °C in autumn and 12–17 °C in winter, and the pH was between 6.8 and 9.1. The treatment processes increased only the DO of the final effluents, while TDS, EC, turbidity and TSS were considerably reduced. Out of the nine phenolic compounds investigated, 2,4-dimethylphenol (2,4-DMP), 4-chloro-3-methylphenol (4-C-3MP), 2-nitrophenol (2-NP) and pentachlorophenol (PCP) were prominent in the influent (17.3–42.1 µg/L) and concentrations of phenolic compounds in the effluents and receiving water bodies were mostly below the tolerable limits allowed internationally for a safe aquatic environment. Generally, the WWTPs removal capacities range between 33 and 96%, however, South Africa standard limits for discharged effluents were occasionally exceeded especially with some WWTPs. This poses health challenges to rural communities that rely heavily on surface water for domestic use.