The effects of Bacillus subtilis on nitrogen recycling from aquaculture solid waste using heterotrophic nitrogen assimilation in sequencing batch reactors

A sequencing batch reactor (SBR) supplied with Bacillus subtilis (treatment group) was employed to treat the sludge from a re-circulating aquaculture system (RAS). The crude protein content of bio-flocs from the treatment group increased from 21.52% ± 1.5% to 29.65% ± 13.34%, which was 23.97% ± 11.62% greater than that of the SBRs without B. subtilis (control group). The removal rate of dissolved inorganic nitrogen (RRDIN) for the treatment group was 0.41 ± 0.079 mg L−1 d−1, which was 1.17 times greater than that of the control group. The utility rate of total organic nitrogen (URTON) for the treatment group was 1.42 ± 0.33 mg L−1 d−1, which was 1.71 times greater than the control. The removal rate of dissolved organic carbon (RRDOC) for the treatment group was 138.39 ± 7.77 mg L−1 d−1, which was 1.95 times greater than the control. The extra-cellular polymer substance (EPS) was primarily composed of polysaccharides. The flocs volume after 5 min (FV-5 min) reached 22.67% ± 2.08% at 19 days. ⺠Bio-floc technology could remove C and N from aquaculture solid waste. ⺠Removal rates of C and N were higher in reactors with Bacillus subtilis. ⺠Inoculating with B. subtilis could inhibite autotrophic nitrification. ⺠Crude protein and EPS contents were higher in reactors with B. subtilis.