An economic assessment of coagulant recovery from water treatment residuals

Coagulant recovery from waterworks sludge for re-use is a key option towards the reduction of chemical usage in the water industry. Whilst this concept is not novel, process economics and recovered product quality issues have limited its implementation. Ion selective membranes have recently been shown to satisfactorily address the latter, but economic feasibility remains a key issue which has been largely overlooked. This study used empirical data taken from bench-scale tests of coagulant recovery using Dorman dialysis (DD) with bulk chemical prices to determine the operational expenditure (OPEX) for full-scale recovery. Calculated values were compared with existing coagulant dosing procedures, as well as potential alternative recovery technologies based on electrodialysis (ED) and ultrafiltration (UF), to determine the cost benefit. It was determined that under current commodity and technology prices, coagulant recovery by DD offers no cost benefit in comparison to conventional practice. Process improvements, such as incorporating acid recovery, identifying alternative waste disposal routes and improving membrane performance, can significantly increase economic viability. UF was shown to provide OPEX reductions of around 40% when compared to conventional practice, and ED was found to be cost neutral. None of the assessed technologies are currently able to offer cost benefit for ferric coagulant. (C) 2011 Elsevier B.V. All rights reserved.