Investigation of the response mechanisms of halophilic and mixed culture aerobic granular sludge under hypersaline conditions

The high salinity of brine wastewater generated by industrial processes could limit options for biological treatment and reuse of these wastewaters. In the present study, several bioresponse mechanisms to cope with high osmotic pressure created in hypersaline wastewater were investigated. Production of extracellular polymeric substances (EPS), microbial community shifting, and intracellular accumulated cations were compared between aerobic granular reactors seeded with activated-sludge and an enriched halophilic culture to investigate different adaption strategies. The selected cultures exhibited different responses toward the gradually increased salt content (1 – 85 g. L-1 as NaCl). EPS production was consistently higher in enriched halophilic culture under hypersaline conditions (≥ 40 g. L-1 NaCl), which corresponded with better granule size and integrity in this same region. Microorganisms in the activated sludge culture relied on higher concentrations of intracellular cations to cope with high osmotic extracellular pressure. Genomic analysis showed that salinity had a significant influence on microbial community composition, resulting in both communities becoming dominated by halophilic organisms, with the richness of the two cultures converging at hypersaline conditions. Despite these broad similarities in the microbial communities, the use of halophilic inoculum resulted in measurable differences in microbial response and better maintained granule structure under hypersaline conditions.