REMOVAL OF ARSENATES FROM CONTAMINATED WATER BY COAGULATION–DIRECT FILTRATION

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Abstract
The present study has been directed towards the removal of arsenic, applying a modification of conventional coagulation/flocculation process. The modifications refer to the introduction of “pipe flocculation” process in the first stage of the technique, whereas the second step has been performed by direct filtration with sand filters, instead of separation by sedimentation. Alum or ferric chloride was the coagulant agent used, enhanced in certain cases by the presence of cationic or anionic polyelectrolytes (organic polymers). The efficiency of coagulant/polymer addition was investigated, using different ratios and for different initial As(V) concentrations. The effect of linear velocity during sand filtration was also examined. In general, both the coagulants were found to be efficient regarding arsenic removal and in both cases the use of coagulant aids increased the overall efficiency of the method—reaching in some cases arsenic removals up to 99%.