Improved lakeshore sediment microenvironment and enhanced denitrification efficiency by natural solid carbon sources

At present, the high level of nitrate in tailwater of wastewater treatment plants (WWTPs) has continued to cause serious environmental problems. In current study, wood chips and bark, serving as natural solid carbon source (NSCS), were applied to enhance the denitrification capacity of lakeshore sediment to remove superabundant nitrate in tailwater. The results show that NSCS had a positive effect on denitrification process for lakeshore sediment and increased the total phosphorus removal capacity by 212%–601%. Comparatively, wood chips were better in enhancing denitrification ability of lakeshore sediment for a longer time. At the 70th day, the nitrate elimination (NEL) of the wood chip-sediment integrated system (WSIS) was 20% and 9% higher than the control system (CS) and bark-sediment integrated system (BSIS), respectively. For the WSIS, the microbial activity and the abundance of nicotinamide adenine dinucleotide (NADH) were significantly increased, and the sediment anaerobic zone was rapidly formed, which were conducive to the denitrification of the sediment. At the DNA level, both groups presented an inconsistency in the abundance of functional denitrification genes with the NEL. At the enzyme level, wood chips significantly increased the nitrate and nitrite reductase activities of the sediment, and promoted denitrification. From the perspective of microbial communities, wood chips highly promoted the abundance of norank_f_BIrii41 Proteobacteria and Ruminclostridum more than other denitrifying and potential denitrifying bacteria in the process of sediment denitrification enhancement.