ABSTRACT
Mature landfill leachate is a refractory organic wastewater, and needs physical and chemical pretreatments contemporaneously, e.g. iron-carbon micro-electrolysis (IC-ME). In this study, a novel iron-carbon (Fe-C) material was synthesized from waste activated sludge to be utilized in IC-ME for landfill leachate treatment. The pyrolysis temperature, mass ratio of iron to carbon, and solid-liquid ratio in leachate treatment were optimized as 900 °C with 1.59 and 34.7 g/L. Under these optimal conditions, the chemical oxygen demand (COD) removal efficiency reached 79.44 %, which was 2.6 times higher than that of commercial Fe-C material (30.1%). This excellent COD removal performance was indicated to a better mesoporous structure, and uniform distribution of zero-valent iron in novel Fe-C material derived from sludge. The contribution order of COD removal in IC-ME treatment for landfill leachate was proven as coagulation, adsorption, and redox effects by a contrast experiment. The removal of COD includes synthetic organic compounds, e.g. carcinogens, pharmaceuticals and personal care products. The contents of CHO, CHON, and CHOS compounds of dissolved organic matter (DOM) in the leachate were decreased, and both the molecular weight and unsaturation of lipids, lignin, and tannic acids concentration were also reduced. Some newly generated small molecular DOM in the treated leachate further confirmed the existence of the redox effect to degrade DOM in leachate. The total cost of sludge-derived Fe-C material was only USD$ 152.8/t, which could save 76% of total compared with that of commercial Fe-C materials. This study expands the prominent source of Fe-C materials with excellent performance, and deepens the understanding of its application for leachate treatment.
ABSTRACT
A comparative study of the different advanced oxidation processes (Fe(II)-Oxone, Fe(II)-H2O2, and Fe(II)-NaClO) was carried out herein to analyze the characteristics of organic components and the migration of heavy metals in waste activated sludge. With the Fe(II)-Oxone and Fe(II)-H2O2 treatments, sludge dewaterability was significantly improved, however, sludge dewaterability was deteriorated by the Fe(II)-NaClO treatment. The enhanced sludge dewaterability by the Fe(II)-Oxone and Fe(II)-H2O2 treatments was strongly correlated with the shifted organic components, particularly proteins, in soluble extracellular polymeric substances (S-EPS), while the deteriorated sludge dewaterability by the Fe(II)-NaClO treatment was strongly correlated with the over release of organic components from bound EPS (B-EPS) to S-EPS. For both the Fe(II)-Oxone and Fe(II)-H2O2 treatments, the radicals preferentially attacked humic acid-like organic components over the protein-like organic components in S-EPS, while for the Fe(II)-NaClO treatment, interestingly, the radicals preferentially attacked the protein-like organic components in both S-EPS and B-EPS. The hydrophilic functional groups like phenolic OH and CO of polysaccharides may be more preferentially migrated to S-EPS of sludge by the Fe(II)-NaClO treatment compared to the other two treatments. With the Fe(II)-Oxone and Fe(II)-H2O2 treatments, the proportion of aliphatic compounds as well as the much oxygenated organic components with a low desaturation and a low molecular weight increased. While with the Fe(II)-NaClO treatment, the proportion of low oxygenated organic components with a high desaturation and a high molecular weight increased. The concentration of total organic carbon, particularly the concentration of proteins, may be the key factor determining the shift of Zn and Cu from sludge solid to liquid phase, along with the high oxidation extent of organic components and close binding to CHOS and CHON compounds as indicated by density functional theory (DFT) calculation. This study systematically revealed the simultaneous sludge dewatering and migration of heavy metals when the role of organic components was factored into herein.
