The MSL was constructed to treat rural domestic wastewater. Biofilm colonization, effects of hydraulic loading rate (HLR) on the treatment of domestic wastewater by the MSL, and biofilm characteristics during the working process of the MSL were investigated. The biofilm colonization was success after 28d of influent by "continuous manner", and at this moment, removal efficiencies of COD, ammonia, TN and TP reached 84.5%, 74.7%, 66.7%, and 76.4%, respectively. During the treatment process of the domestic wastewater, the MSL exhibited a strong adaptability on the variation of HLR. The average removal efficiencies of COD, ammonia, TN, TP reached 93.4%, 94.9%, 80.4%, and 94.7%, respectively, which meet to the 1A discharge standard of the Discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002), when the HLR was adjusted to 400L/(m2·d). Pathways of the removal of COD, ammonia, TN and TP by the MSL showed that the biological decomposition and biotransformation processes of microorganisms were the most important pathway for the removal of COD, ammonia, and TN, while TP was mainly removed by the chemical reaction with iron irons. q-PCR showed that the nitrifying bacteria in the biofilm were about 35.5% of the total flora.
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