Landfill leachate treatment using hybrid coagulation-nanofiltration processes
In this study, treatment of landfill leachate using a novel electrocoagulation – nanofiltration (EC-NF) hybrid system was investigated. Leachate sample was collected from Whytes Gully landfill in Wollongong, Australia. The performance of electrocoagulation (EC) using aluminium electrodes as a pretreatment step for the nanofiltration process was compared against a conventional chemical coagulation (CC) process. Results reported here indicate that electrocoagulation is superior over the conventional coagulation process with respect to total organic carbon (TOC) and turbidity removal. At the optimum reaction time, TOC and turbidity removals by the electrocoagulation process were 67% and 80%, respectively. In comparison, at the optimum dosage of Al2(SO4)3 obtained by a standard jar testing procedure, TOC and turbidity removals by the chemical coagulation process were only 10% and 65%, respectively. It is noteworthy that the amount of aluminium released by the electrocoagulation process to the solution was significantly higher than the optimum dosage of the chemical coagulation process. Therefore, better performance of the electrocoagulation process can possibly be explained by the higher coagulation concentration and the formation of polymeric aluminium which is known to be more effective for small organic compounds which are prevalent in landfill leachate. A remarkable difference between electrocoagulation and chemical coagulation pretreatment was also observed with respect to fouling mitigation in a subsequent nanofiltration process. For the two different nanofiltration membranes (NF 270 and SR2) used in this study, severe membrane fouling was evident when filtering raw landfill leachate or chemical coagulation pretreated landfill leachate. In contrast, fouling was not observed with an electrocoagulation pretreated feed solution. However, the use of electrocoagulation pretreatment did not result in any improvement in treated effluent quality by the hybrid system. Over all, there was no discernible variation between the EC – NF and CC – NF hybrid systems in their TOC and turbidity removals, which were approximately 92% and 99%, respectively. The reported results demonstrate that an EC – NF hybrid system can be a promising candidate for landfill leachate treatment, particularly for small and decentralised landfills where simplicity and robustness are required.