Multi-response optimization of Fenton process for applicability assessment in landfill leachate treatment

Fenton process, as a pretreatment method, was found to be effective in the primary treatment of mature/medium landfill leachate. However, the main problem of the process is the large amount of produced sludge that requires an accurate feasibility evaluation for operational applications. In this study, the response surface methodology was applied for the modeling and optimization of Fenton process in three target responses, (1) overall COD removal, (2) sludge to iron ratio (SIR) and (3) organics removal to sludge ratio (ORSR), where the latter two were new self-defined responses for prediction of sludge generation and applicability assessment of the process, respectively. The effective variables included the initial pH, [H2O2]/[Fe(2+)] ratio and Fe(2+) dosage. According to the statistical analysis, all the proposed models were adequate (with adjusted R(2) of 0.9116-0.9512) and had considerable predictive capability (with prediction R(2) up to 0.9092 and appropriate adequate precision). It was found that all the variables had significant effects on the responses, specifically by their observed role in dominant oxidation mechanism. The optimum operational conditions obtained by overlay plot, were found to be initial pH of 5.7, [H2O2]/[Fe(2+)] ratio of 17.72 and [Fe(2+)] of 195 mM, which led to 69% COD removal, 2.4 (l sludge/consumed mole Fe(2+)) of SIR and 16.5 (gCOD removed/l produced sludge) for ORSR in verification test, in accordance with models-predicted values. Finally, it was observed that [H2O2]/[Fe(2+)] ratio and Fe(2+) dosage had significant influence on COD removal, while Fe(2+) dosage and [H2O2]/[Fe(2+)] ratio had remarkable effects on SIR and ORSR responses, respectively.