Reduction of reagent requirements and sludge generation in Fenton's oxidation of landfill leachate by synergistically incorporating forward osmosis and humic acid recovery

Abstract

Applications of Fenton's oxidation of landfill leachate is limited by both high reagent requirements and a large amount of sludge generation. To address those issues, forward osmosis (FO) and humic acid (HA) recovery were incorporated with Fenton's treatment. In the FO, leachate was concentrated by 3.2 times in 10 hours using a 5-M NaCl draw solution. The HA recovery increased from 1.86 to 2.45 g L^-1 at pH 2 after FO concentration, mainly because of the replacement of O in the HA structure by other inorganics (i.e., Cl, Na, K) with higher molecular weights. Due to the movement of alkalinity causing species (i.e., HCO₃^-, CO₃^2-) to the draw side driven by a concentration gradient, the H₂SO₄ requirement per g of recovered HA and per g of removed COD decreased by 46.4% and 17.1%, respectively. The HA recovery also decreased sludge generation by 30%. At a dimensionless oxidant dose of 0.5, the proposed system reduced the overall requirement of H₂SO₄ by 25.2%, NaOH by 34.6%, and both FeSO₄.7H₂O and H₂O₂ by 35%, compared to the standalone Fenton's treatment of raw leachate. Those results have demonstrated that the proposed system could greatly decrease the leachate volume, lower the reagent requirements, and reduce the sludge production towards sustainable leachate treatment.

Keywords: Fenton's oxidation; Forward osmosis; Humic acid; Landfill leachate; Sludge reduction.