The effect of recycling untreated filter bachwash water through Nabajjuzi river on the quality of final water in Masaka District.

Abstract

Background to the study: Water treatment plant in Masaka is currently recycling untreated spent filter backwash water through Nabajjuzi River and yet the plant does not have any treatment facility to treat the filter backwash waste water. Studies in USA indicates that recycling untreated filter backwash waste water will contaminate the corresponding incoming raw water and this overwhelms the water treatment plant’s effectiveness and efficiency in removal of pathogens and the final water may no longer be safe for public health consumption. Objective of the study: To assess the effect of recycling untreated spent filter backwash water through Nabajjuzi River on the quality and safety of final water in Masaka. Methodology: An experimental study design was used to determine the effect of recycling untreated spent filter backwash water on the quality and safety of final water in Masaka. The effects of recycling untreated spent filter backwash water was assess using univariate and bi-variate analysis. All variables having p-value ≤0.05 at the bi-variate level using ANOVA were taken as significant predictors. Results: Returning untreated spent filter backwash water made the raw water at intake point dirtier; colour increased by 68%, turbidity by 55% Iron by 51% and faecal coliform bacteria by 94.6%. Statistical analysis indicated significant difference in raw water quality before and after discharge of untreated spent filter backwash water. No bacterial was detected in all final water samples analyzed however; colour and iron in final water failed a couple of times to meet the National Standard for Potable water. Conclusion and recommendations: Since colour and iron affects aesthetic property of water and non toxic at concentrations detected in final water, it is safe to conclude that despite recycling of Sent Filter Backwash Water, Masaka final water quality is safe for human consumption.To improve the quality of corresponding raw water and improve treatment efficiency to consistently produced clean and safe water, the filter waste water needs to be treated by constructing a pre-settlement tank or by using a dewatering press before recycling. 1