Effect of magnetic powder on denitrification using the sludge alkaline fermentation liquid as a carbon source.

This work evaluates the impact of the different concentrations of Fe3O4 on nitrate removal and organic matters utilization in the sequencing batch reactors (SBRs) using the sludge alkaline digestion supernatant as external sludge carbon source. Results indicated that the optimal concentration of Fe3O4 was 1 g/L for enhancing denitrification with NO3--N removal efficiency of 93.13% (up to a 11.93% increase) and without NO2--N accumulation after 18 days. The changes of soluble chemical oxygen demand (SCOD), protein, and carbohydrate during denitrification process were analyzed to gauge the utilization of sludge fermentation products by denitrifiers. The SCOD was consumed for organisms involved in NO3--N removal and the Fe3O4 could promote the utilization of carbohydrate better than protein by denitrifiers during denitrification process. Denitrification rate (VDN) and the nitrate-to-nitrite transformation ratio (NTR), as the kinetics parameters, were also investigated in different concentrations of Fe3O4.