Enhanced Nitrogen Removal of Steel Rolling Wastewater by Constructed Wetland Combined with Sulfur Autotrophic Denitrification

Constructed wetlands (CWs), an ecological treatment technology, is suitable for advanced treatment, but has an unsatisfying denitrification performance for steel rolling wastewater with low C/N ratio. This study combined sulfur autotrophic denitrification (SAD) with conventional constructed horizontal subsurface flow wetlands to treat steel rolling wastewater, exploring the feasibility of applying SAD to enhance the denitrification performance of CWs. The reactor consists of two sections, one filled with manganese sand and gravel (HFC) and another filled with ceramic, sulfur, and lime (HFSAD). Results showed that HFC had a good performance on removing turbidity, DO, COD, and TP, while the average removal efficiency of total nitrogen (TN) in HFC was just 25.6%. On this basis, HFSAD could remove 45.6% of TN subsequently, whose denitrification rate was 4–6 times as high as that of HFC. Increasing hydraulic retention time could improve removal efficiency of contaminants in HFC and HFSAD in different degrees. The analysis of microbial community structure, observation results of fillers and monitored sulfate all provided proofs for the occurrence of SAD. CWs combined with SAD can be applied in the treatment of steel rolling wastewater with low carbon, which can provide reference for ecological wastewater treatment, water saving, and recycling in iron and steel enterprises.