Algae removal from effluents of waste water stabilization ponds utilizing intermittent sand filtration

Abstract

The principle objective of this research was the removal of algae from effluents of waste water stabilization ponds. There are many possible ways of achieving this removal but problems such as of economics, technological appropriateness and maintenance requirements have to be considered before making a choice of the method to be adopted. The use of intermittent sand filtration has been shown to be cheap and easy to maintain, but research has centered chiefly on Pond effluents with low suspended solids concentrations. In this research work, relatively higher values for the suspended solids concentrations have been used. It was observed that the filtration runs for the two filters used were shorter than have been reported in the literature for corresponding hydraulic loading rates but with different effective sand sizes. However, the percentage removals achieved were high and within the ranges reported in the literature. The length of the filter runs for the two filters ranged from 35 to 38 days. The BODs removal of above 89.5 %, chlorophyll-a removal of above 86.9% and suspended solids removal of above 72.8% were achieved at a hydraulic loading rate of 20cm2 /cm2 /d. The effluent obtained was often clear and odourless. A conclusive observation was that although single stage intermittent sand filters can achieve high removal of algae from pond effluents, they are not suitable for upgrading effluents whose suspended solids concentration is high since the quantities of BODS' chlorophyll-a and suspended solids in the effluent were still significant and the length of filter runs achieved was low.