Two methods of surface modification of polyethylene biocarriers, chemical oxidation-surface covering with ferric ion (CO-SCFe) and chemical oxidation-surface grafting with gelatin (CO-SGG), were studied for improving the efficiency of wastewater treatment by moving-bed biofilm reactors. The results showed that two surface modifications caused corrosion pits to increase surface roughness, and brought –(C=O)–/–O–C–O– groups and ferric ions to the biocarrier surface, respectively. The positively charged surface increased the hydrophilicity and biological affinity of the biocarrier. The biofilm formation rate was improved by 37.5 and 60% after surface modifications of CO-SCFe and CO-SGG; the concentration of biomass on the biocarriers was improved by 54.8 and 76.1% and the COD removal efficiencies were increased by 10.63 and 8.64%, respectively. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis showed that the microbial populations in the biofilm were almost the same after surface modifications, but the biomass concentration was greatly increased.

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