Nitrogen removal and biofilm structure affected by COD/NH4+–N in a biofilter with porous sludge-ceramsite

Self-made sludge-ceramsite was tested as carrier in biofilter to investigate its biogenic stimulating properties for obtaining high biomass concentration, and the performance of Guangzhou ceramsite, Jiangxi ceramsite, and Shanxi activated carbon were provided as a baseline for comparison. Results show that the removal efficiencies of COD and total nitrogen (TN) increase along with the increased COD/NH4+–N ratio (4, 5.7, 8, and 10) in the four biofilters. On average, the sludge-ceramsite biofilter converts 79.1–86.4% of NH4+−N to NOx−−N and removes 43.9–51.0% of TN at COD/NH4+–N ratios of 4–10, which are slightly better than the other biofilters. The well-developed porous structures (0.5 μm < pore size < 10.0 μm) of sludge-ceramsite is propitious to develop many microbial communities and to improve the permeable capacity of biofilm layers and the pollutants removal efficiencies, as they determine the pollutants mass transfer and the biological contact-reaction that occur in the aqueous phases, liquid–solid boundary, and biofilm interior. It is concluded that these results can be considered as basic understanding for utilization of this porous and lightweight (bulk density of 668.2 kg m−3 and particle density of 1251.2 kg m−3) sludge-ceramsite as carrier in biological wastewater treatment.

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► Porous structure of sludge-ceramsite improves the mass transfer efficiencies.
► Sludge-ceramsite promotes the permeable capacity of biofilm layer.
► TN removal performance of sludge-ceramsite biofilter is better than the other three biofilters with commercial carriers.
► Pore size-range of sludge-ceramsite is propitious to develop many microbial species.
► Biogenic stimulating characteristic of sludge ceramsite makes it to be an excellent carrier.