Removal of refractory compounds from stabilized landfill leachate using an integrated H2O2 oxidation and granular activated carbon (GAC) adsorption treatment

This study investigated the treatment performances of H2O2 oxidation alone and its combination with granular activated carbon (GAC) adsorption for raw leachate from the NENT landfill (Hong Kong) with a very low biodegradability ratio (BOD5/COD) of 0.08. The COD removal of refractory compounds (as indicated by COD values) by the integrated H2O2 and GAC treatment was evaluated, optimized and compared to that by H2O2 treatment alone with respect to dose, contact time, pH, and biodegradability ratio. At an initial COD concentration of 8000 mg/L and NH3-N of 2595 mg/L, the integrated treatment has substantially achieved a higher removal (COD: 82%; NH3-N: 59%) than the H2O2 oxidation alone (COD: 33%; NH3-N: 4.9%) and GAC adsorption alone (COD: 58%) at optimized experimental conditions (p ≤ 0.05; t-test). The addition of an Fe(II) dose at 1.8 g/L further improved the removal of refractory compounds by the integrated treatment from 82% to 89%. Although the integrated H2O2 oxidation and GAC adsorption could treat leachate of varying strengths, treated effluents were unable to meet the local COD limit of less than 200 mg/L and the NH3-N of lower than 5 mg/L. However, the integrated treatment significantly improved the biodegradability ratio of the treated leachate by 350% from 0.08 to 0.36, enabling the application of subsequent biological treatments for complementing the degradation of target compounds in the leachate prior to their discharge.