Effect of primary effluent coagulation on performance of laboratory-scale managed aquifer recharge system

Aluminum and iron salts are widely used as coagulants in water and wastewater treatment. Two identical soil columns were fed with coagulated and non-coagulated primary effluent (PE) to investigate effect of coagulation on removal of suspended solids, bulk organic matter, nitrogen, and pathogens indicators during managed aquifer recharge. Aluminum sulfate and iron chloride were used as coagulants. Experimental results showed considerable suspended solids removal of >65% by both coagulants at optimum doses. However, the overall suspended solids removal by infiltration and coagulation–infiltration was ~90%. Likewise, removal of phosphorus by coagulation was 80%, whereas total removal by coagulation–infiltration was >98% compared with ~30% by infiltration only. Coagulation of primary removed 16–22% of dissolved organic carbon whereas total removal of ~70% by coagulation–infiltration accounted to 1.4 orders of magnitude higher than infiltration only. Furthermore, removal of pathogens indicators increased considerably from 2.5 log10 units during infiltration only to 3.8 log10 units during coagulation–infiltration for Escherichia coli. Similarly, total coliforms removal increased from 2.6 to >4 log10 units. These results imply that coagulation of PE using both aluminum sulfate and iron chloride essentially gives similar contaminants removal. Removal of suspended solids improves operation of soil aquifer treatment site by reducing surface clogging while reduction of phosphorus through coagulation also improved removal of pathogenic micro-organisms.