Use of recovered coagulant from water treatment sludge for greywater treatment

In the present study, the potential of aluminium recovered from water treatment sludge (WTS) as a coagulant was assessed for treating real greywater. Aluminium was first recovered from WTS by acidification at pH 1.0. Performance of the recovered coagulant (RC) was compared with that of fresh polyaluminium chloride (PAC) in removing different contaminants such as turbidity, COD, NH₄⁺-N, PO₄^3--P, and faecal coliforms from greywater. Results showed that RC was as good as or better than fresh PAC in removing various pollutants from greywater. Combined use of RC and PAC was attempted since this would reduce the demand for fresh coagulant. Response surface methodology was used to model and optimize the coagulation process using initial pH, RC dose, PAC dose, and initial turbidity as variables. Predicted outcomes for turbidity, COD, NH₄⁺-N, PO₄^3--P, and faecal coliforms removal were 94.2, 44, 83.5, 99.9, and 94.01%, respectively, at initial pH of 7, RC dose of 10 mg Al/L, PAC dose of 3.5 mg Al/L, and initial turbidity of 40 NTU. The results indicate that recovered coagulant can be effectively recovered from WTS and reused for greywater treatment, reducing the consumption of fresh coagulants. This approach transforms the waste into a valuable resource, promotes circular resource utilization, and offers a novel, sustainable solution for decentralized greywater treatment.