Material inter-recycling for advanced nitrogen and residual COD removal from bio-treated coking wastewater through autotrophic denitrification

For wastewaters containing high strength sulfide and nitrogen (e.g. coking wastewater), sulfide might be precipitated and recovered using ferrous salt. This study systematically investigated the feasibility of recovered and precipitated FeS (comparing to commercial FeS minerals) to support autotrophic denitrification for advance nitrogen removal from bio-treated coking wastewater in fluidized bed reactors. The reactor with precipitated FeS could achieve simultaneous removal of NO3--N and inert COD with high efficiencies of around 96.3% and 30.5%, at NO3--N and COD loading rates of 4.18 mg.L-1.h(-1) and 8.06 mg.L-1.h(-1), respectively. Whereas, the performance of commercial FeS reduced gradually and irreversibly after two days, which became completely ineffective after 40 days. Thiobacillus and Rhodanobacter dominated the biomass, which played a key role in the FeS-based denitrification process. This material inter-recycling concept benefits an advance and more sustainable treatment of wastewaters with high strength sulfide and nitrogen.