Insights into the rapid granulation for treating refractory wastewater under salt stress: Variation of sludge property, treatment performance and microbial community

Abstract

Industrial effluents often contain high total dissolved solids, which exhibit negative effects on microorganisms. In this study, the granulation process under salt stress in the presence of aniline (a common organic pollutant in several types of industrial wastewaters) was evaluated. The sludge properties, removal performance of pollutants and microbial community structure were investigated. Two reactors, namely R1 and R2 were set up, and influent in R1 contained 15 g L−1 of NaCl while R2 was in the absence of salt as contrast. Results showed that aerobic granules appeared within 20 d under saline conditions with 30 min sludge volume index (SVI30) below 36 mL g−1. High salinity led to larger granule size and extracellular polymeric substances was 1.3 times higher than those in R2. However, part of Ca2+ ions in the bio-aggregate matrix of granules were replaced by Na+ ions in the saline environment, resulting in the modestly higher SVI30. Regarding the treatment performance, high removal efficiencies of aniline and COD were observed (~100% and 93.7%, respectively) after 4-h treatment under saline condition while both nitrification and denitrification were slightly retarded. The average concentration of NH4+-N and TN in the effluent of R1 after formation of granules were 1.2 ± 0.4 and 17.3 ± 1.7 mg L−1, respectively. Microbial community analysis indicated that saline condition could facilitate microorganisms with high flocculation activity and high tolerance to salinity such as Paraclostridium, Citrobacter, and Flavobacterium, which contributed to simultaneous removal of organics and nitrogen in AGS process for treating saline refractory wastewater.