The Use of Recovered Coagulants in Wastewater Treatment

A programme of study was conducted to evaluate the feasibility of recovering iron coagulants from waterworks sludge for wastewater treatment. The purpose was to use the recovered coagulants to help meet the UWWTD discharge standards, at minimal cost and eliminate the need for disposal of the waterworks sludge. Acidic extraction of coagulant was performed varying contact time and solution pH to optimise the recovery process. A maximum of 350 mg of Fe was extractable from 5 g of waterworks sludge. When the efficacy of the recovered coagulant was considered, it was determined that the use of recovered coagulant was viable on performance grounds, but that commercial coagulants perform better than recovered coagulants. The performance of the recovered coagulants can be improved significantly by neutralising prior to use and blending with commercial coagulants. Recovered ferric sulphate when blended 50:50 with commercial coagulant removed over 90% of suspended solids and phosphorus and over 50% of the COD.