Integration of water hyacinth plants into waste stabilization ponds: a case study of Donnybrook 4 Sewage Ponds in Mabvuku-Tafara, Harare, Zimbabwe

Abstract

Donnybrook Waste Stabilization Ponds (WSP) are overloaded and water hyacinth plants have infested the ponds. The study assessed the feasibility of integrating the problematic water hyacinth plants into the current treatment process. Grab samples of influent and effluent for each pond were collected between 28 March and 23 April 2019 and the analysis was done following standard APHA methods. Parameters considered include pH, turbidity, TDS, TSS, TN, TP, BOD, and COD. The raw sewage mean pH, turbidity, TDS, TSS, TN, TP, BOD, and COD were 8.08, 580 NTU, 1639mg/L, 1294mg/L, 78mg/L, 8.16mg/L, 287mg/L, and 887mg/L. The mean pH, turbidity, TDS, TSS, TN, TP, BOD, and COD in the effluent from the existing maturation pond, control pilot pond, and water hyacinth pilot pond were 7.7, 7.7, and 7.3; 75, 67, and 47 NTU; 861, 758, and 668mg/L; 276, 172, and 82mg/L; 27, 28, and 17mg/L; 4, 5.28, and 4mg/L; 114, 52, and 30mg/L; and 243, 122, and 81mg/L. It was concluded that the water hyacinth may be integrated into the WSP system to enhance contaminant removal. The water hyacinth in the ponds should be harvested periodically to avoid secondary organic and nutrient loading from dead plants.