Modification of polyurethane sponge filler using medical stones and application in a moving bed biofilm reactor for ex situ remediation of polluted rivers

The application of moving bed biofilm reactors is a prospective water remediation technology, but its treatment efficiency needs to be further improved. In this study, moving bed biofilm reactors were applied for ex situ remediation of polluted rivers, and medical stones were newly used for modification of polyurethane sponge filler. The porosity, water-holding capacity and apparent density of the modified filler were 8.24%, 32.74% and 5.2 times higher than non-modified filler, respectively, which is more favourable to microbial attachment and growth. The developed moving bed biofilm reactors had a good removal effect on the chemical oxygen demand, ammonia, and total nitrogen of polluted urban-river water with hydraulic retention times of 12 h, 6 h, and even 3 h. The chemical oxygen demand, ammonia, and total nitrogen removal rates of moving bed biofilm reactors containing modified filler were 88.06%, 93.67% and 67.10%, respectively, which are 4.86%, 8.89% and 9.01% higher than moving bed biofilm reactors with non-modified filler, respectively, at the shortest hydraulic retention time, 3 h. In summary, this study provides a new kind of filler for moving bed biofilm reactors in ex situ remediation of polluted urban rivers, targeting rapid removal of chemical oxygen demand, ammonia, and total nitrogen.