Reuse of ferric sludge as an iron source for the Fenton-based process in wastewater treatment

A mature municipal landfill leachate (S1), a wood soaking basin effluent from a plywood manufacturing plant (S2), and a leachate collected from a semicoke landfill area of an oil-shale thermal treatment plant (53) were subjected to the Fenton/Fenton-based treatment (H2O2/Fe2+, H2O2/Fe3+ and H2O2/sludge systems). The results of ferric coagulation trials indicated a high efficacy in S2; thus, only pre-coagulated samples (cS2) were further treated by the H2O2/iron systems. Irrespective of reaction duration, 51 was more recalcitrant to oxidation than cS2 and S3. The optimal COD/H2O2 weight ratio for cS2 and S3 was 1:1 with respective 21(35) and 36(45)% residual COD(DOC). In the case of 51, the COD/H2O2 w/w of 1:3.45 proved the most efficient with 30 and 35% residual COD and DOC, respectively. The results also indicated an increase in BOD7/COD ratio and a reduction in the acute toxicity to Daphnia magna of the studied wastewater samples after the Fenton/Fenton-based treatment. The application of the Fenton-based process catalysed with iron-containing sludge exhibited efficacies similar to classical Fenton treatment over four reuse cycles. The reuse of ferric sludge without any regeneration as an iron source in the Fenton-based process was displayed as a feasible solution to minimise the production of hazardous ferric waste and reduce the overall cost of the treatment process. (C) 2014 Elsevier B.V. All rights reserved.