Treatment of old landfill leachate by persulfate enhanced electro-coagulation system: Improving organic matters removal and precipitates settling performance

Electro-coagulation process is an alternative method for the treatment of old landfill leachate. However, limited removal of chemical oxygen demand (COD) and long solid-liquid separation times are the key technical problems hindering its practical application. In this study, a persulfate-enhanced electro-coagulation system (PECS) was constructed to improve the removal of COD and shorten the settling time of the flocculation precipitates. Compared with the traditional electro-coagulation process, the PECS can improve the COD removal from 41.1% to 72.6% (60 min reaction and current density of 50 mA/cm(2)) using activated persulfate oxidation process. The PECS process involves the formation of sulfate and hydroxyl radicals as the main oxidants. The dissolved organic matter in the old landfill leachate mainly consisted of macromolecular humus-like substances. PECS can reduce the aromaticity and the complexity of organic matter, and generated small molecular-weight organic matter, which was helpful in further alleviating the pressure of subsequent treatment of the leachate. The evolution path of precipitates in PECS followed the process of alpha- FeOOH/Fe2O3 center dot H2O -> Fe3O4, which promoted the formation of Fe3O4, improved the precipitation performance, and reduced the volume of precipitates. PECS could improve the degree of degradation of organic matter, increase the removal of COD, and shorten the separation time of precipitates under similar treatment costs to conventional processes. The results of this study provide an important theoretical basis for improving the performance of existing electro-coagulation equipment in practical engineering applications.

Automated summary

In this study, a persulfate-enhanced electro-coagulation system (PECS) was constructed to improve the removal of COD and shorten the settling time of the flocculation precipitates. By using activated persulfate oxidation process, PECS can reduce the aromaticity and complexity of organic matter, generating small molecular-weight organic matter to alleviate the pressure of subsequent treatment of the leachate. The results suggest that PECS could improve the removal of organic matter, increase the COD removal, and shorten the separation time of precipitates under similar treatment costs to conventional processes.