Study on the Mass Transfer Enhancement in Biofilms Applied in Papermaking Wastewater Treatment

The research and refinement of papermaking wastewater treatment and reuse technology are important measures for energy conservation and emission reduction in the papermaking industry. This paper studied the process of biofilm formation and dissolved oxygen mass transfer of biofilms cultivated under different aeration intensities and attempted to enhance the biofilm reactor performance. The removal efficiencies of the chemical oxygen demand, total nitrogen, and ammonia nitrogen through biofilm treatment in two parallel biofilm reactors were higher under the larger aeration intensity (8 L/min) than under the smaller intensity (4 L/min). Macroscopically, this reflected the effect of dissolved oxygen on nitrogen removal. Microscopically, in terms of the dissolved oxygen profiles inside of the biofilms determined using a microelectrode probe, both aerobic and anaerobic layers occurred inside the biofilms, which suggested that simultaneous nitrification and denitrification occurred. The different aeration intensities led to differences in the internal and external dissolved oxygen concentrations in the biofilms, which affected the biofilm growth. This led to different micro-structures, and so the internal metabolism and wastewater treatment performance of the biofilms were not identical.