Enhanced denitrification of dispersed swine wastewater using Ca(OH)2-pretreated rice straw as a solid carbon source

Abstract

In a pilot-scale packed bed reactor, the denitrification performance and microbial community structure of the dispersed swine wastewater treatment using calcium hydroxide (Ca(OH)2) pretreated rice straw as a carbon source were investigated. In a Ca(OH)2-pretreated rice straw supported denitrification system (Ca(OH)2-RS), the removal efficiency of NO3−-N was 96.39% at an influent NO3−-N load of 0.04 kg/(m3•d). Meanwhile, there was no obvious accumulation of NO2−-N or chemical oxygen demand (COD) in the effluent of Ca(OH)2-RS. The contents of soluble microbial byproduct-like substances and tryptophan-like substances in the effluent of Ca(OH)2-RS were reduced by 46.2% and 43.4%, respectively, compared with the influent. Overall, the Ca(OH)2-pretreated rice straw system had a strong resistance to fluctuations in water quality conditions, such as influent NO3−-N and COD concentrations. According to the microbial assay results, the Ca(OH)2 pretreatment enriched more denitrifying bacteria. Among them, Proteobacteria (42.33%) and Bacteroidetes (35.28%) were the dominant bacteria. Moreover, the main denitrifying functional bacteria, generanorank_f_Saprospiraceae (13.32%), norank_f_Porphyromonadaceae (4.22%), and Flavobacterium (3.25%), were enriched in Ca(OH)2-RS. This suggested that using Ca(OH)2-pretreated rice straw as a carbon source was a stable and efficient technology to enhance the denitrification performance of dispersed swine wastewater.