Application of Stabilization Pond Effluent Quality Parameters in Assessing Treatment Efficiency, Disposal Safety and Irrigation Suitability

摘要

Physico-chemical and microbiological parameters of treated pond effluent and effluent-receiving stream water were assessed for their suitability for irrigation and effluent for discharge safety. The study was done at stabilization ponds in northern Zimbabwe. Monthly effluent and stream water samples were collected between May and October, 2011 from the 5th maturation pond outlet of a 2A-4F-5M stabilization pond system and at a point that was 4 km downstream. Overall pond treatment efficiency estimates were ＞89% with respect to BOD_5 TSS and faecal coliforms (FCs). Mean treated effluent parameters (22.18±1.64mg/L BOD_5, 17.00±1.19mg/L TSS and 37.33±2.99 cfu/100 mL FCs) were significantly lower (p＜0.05) than safe surface disposal limits. Treated effluent and stream water were both non-saline (mean electrical conductivity: effluent = 779.50±37.79 μS/cm and stream water = 470.33±41.83 μS/cm) with a low sodium hazard (mean SAR: pond effluent = 1.71±0.06 and stream water = 1.08±0.10). Residual Sodium Carbonate (RSC) values were negative indicating safe water. Non-toxic levels of Cl~-and Na~+ were observed in stream water but slight restrictions for irrigation use were observed for the effluent. Effluent was slightly alkaline (pH 8.30±0.13) and safe. Stream water and effluent quality parameters were significantly different (p＜0.05) except for FCs, CO_3~(2-), Cd~(2+), K~+, Pb~(2+) and PO_4~(3-). Treated effluent was suitable for both surface discharge and for irrigation. Strong relationships were observed between effluent parameters and also between stream water parameters. Treated effluent from Woodbrook waste stabilization ponds can periodically be used for irrigation. This may help to restore stream water quality with a view to public health protection and environmental preservation.