Bioaugmentation using salt-tolerant bacteria in a dual-stage process for high-salinity wastewater treatment: Performance, microbial community, and salt-tolerance mechanism

Abstract

To address the challenges of nitrogen removal and stability problems in biological treatment of high-salinity wastewater, a new technology based on salt-tolerant aerobic denitrifying (SAD) bacteria to strengthen the two-stage bio-contact oxidation reactor (TBOR) and moving bed biofilm reactor (MBBR) dual-stage process was proposed. The results showed that the NH4+-N removal rate of TBOR and TN removal rate of MBBR increased by 26.05 % and 15.90 %, respectively, after bioaugmentation with SAD bacteria at salinity of 5 %. The COD, NH4+-N and TN removal rates in real wastewater (at salinity of 4 ~ 5 %) treatment were 93.45 %, 97.57 % and 90.83 %, respectively. Microbial analysis showed that at salinity of 5 %, SAD bacteria Halomonas and Truepera were the main functional bacteria responsible for nitrogen removal. Microbial functional analysis and metabolic predictions further revealed that bioaugmentation enhanced the expression of the nir gene, thereby further promoting the process of dissimilatory nitrite reduction to ammonium (DNRA). Furthermore, bioaugmentation can also resist the external high-salinity environment by exporting Na+ extracellularly, promoting extracellular polymeric substances (EPS) secretion and amino acid metabolism. This study demonstrates that bioaugmentation with SAD bacteria is a suitable approach for nitrogen and carbon removal of high-salinity wastewater.