The treatment of stabilized landfill leachate using iron-activated persulfate and peroxymonosulfate oxidation

The feasibility of sulfate radical-based advanced oxidation process (SR-AOP) in the reduction of chemical oxygen demands (COD) of pre-treated landfill leachate was evaluated. Nearly 70 % of COD from raw leachate was successfully removed by coagulation-flocculation pre-treatment. However, the COD concentration was still exceeded the discharge limit for most of the countries and required further treatment. The pre-treated leachate was then further treated with SR-AOP. In this work, Fe(II) activated persulfate (PS) and peroxymonosulfate (PMS) were used to generate the sulfate radical. The results indicated that the COD reduction efficiencies for both PMS/Fe(II) and PS/Fe(II) treatment systems were influenced by the oxidant to Fe(II) ratio, the dosage of oxidants, and reaction time. The initial pH of leachate and types of oxidants did not significantly influence the COD reduction. By using the optimal condition, nearly 83 and 84% of COD were reduced by the coagulation-flocculation coupled with SR-AOP. Ecotoxicity analysis by zebrafish showed that the toxicity was significantly reduced after coagulation-flocculation was done. However, the formation of residual sulfate ion after SR-AOP treatment slightly increased the toxicity of the final effluent.