Abstract
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.
Highlights
The iron and steel industry is one of the pillar industries of China’s national economic development, with its productivity ranking first steadily in the whole world in recent years [1,2]
The composite constructed wetland reactor was operated continuously for over three months in three kinds of operation conditions in turn, and the concentrations of different contaminants in the influent and effluent were monitored and analyzed, as shown in COD biodegradability was poor, and the water-soluble trace S may be included in COD
The analysis indicated that the removal rates of nitrogen contaminants decreased with increasing HRT
Summary
The iron and steel industry is one of the pillar industries of China’s national economic development, with its productivity ranking first steadily in the whole world in recent years [1,2]. In the steel production process, as great quantity of freshwater required and wastewater emitted, it’s significant to improve water recycling for improving the sustainability of iron and steel industry. Steel rolling, coking, and iron exchange are several significant processes in the iron and steel enterprises, in which an overwhelming majority of wastewater emits [3]. After two-stage treatment, these kinds of wastewater are relatively stable and considerable in terms of quality and quantity [4], with great potential of advanced treatment and reuse, being a prominent part of saving water resources in iron and steel enterprises. With the improvement of wastewater effluent quality standards and the large demand of water resource in iron and steel enterprises, advance treatment and reuse of steel rolling wastewater become more important.
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