Landfill leachate treatment in-depth by bio-chemical strategy: microbial activation and catalytic ozonation mechanism

• Alternant bio-chemical strategy was effective on landfill leachate treatment. • Microorganism in sludge played key roles on refractory organic matters degradation. • The reactive oxygen species of ·OOH and ·O 2 - played key role on catalytic ozonation. • Changeable metallic oxide indicated the synergistic action of catalyst. The combination of activated sludge process and catalytic ozonation technology was used to treat the landfill leachate as bio-chemical strategy in this study. The technology of activated sludge pretreatment and catalytic ozonation post-treatment coupled with baffled membrane bioreactor (MBR) system was proposed. The COD, ammonia nitrogen and phosphate were removed in anaerobic and aerobic environments. At the same time, catalytic ozonation could significantly remove COD, colority, UV 254 , ammonia nitrogen, 3D fluorescence peak value, and fluorescence regional integration (FRI) of organic pollutants from landfill leachate. Ultimately, the maximum removal efficiencies of COD, ammonia nitrogen and phosphate were 98.46 ± 0.28%, 99.92 ± 0.01%, and 79.71 ± 1.62%, respectively. The heavy metal contents met the emission standards after treatment with this strategy. The removal of pollutants in landfill leachate could be attributed to the positive effect of microorganism in sludge and catalyst in ozonation: (1) The microorganism found in sludge all played different roles, Proteobacteria and Bacteroidetes accounted for the most, they could degrade organisms and even refractory organic matters. Though the number of Thauera, Acinetobacter , Nitrospira and Nitrosomonas was small, they played an important role on denitrification. (2) During catalytic ozonation, the hydroxyl radical ( OH) produced by ozone would combine with oxygen to generate hydrogen peroxide radical ( OOH) during the reaction, while unpaired electrons were trapped by surface adsorbed oxygen on the catalysts to produce superoxide radical ( O 2 – ). In addition, the active metal components, such as Ce 4+ /Ce 3+ redox pair, Mn 2+ , Mn 3+ and Mn 4+ on the catalyst surface were able to transform synergistically, which was able to maintain the catalyst activity and realize the removal of contaminants.