Resistance and adaptation of mature algal-bacterial granular sludge under salinity stress.

The study investigated the response characteristics of algal-bacterial granular sludge (ABGS) under salinity stress (0 % → 2 %). At 1 % salinity, the sludge performance was inhibited, while recovered rapidly, indicating the ABGS exhibited resistance. However, at 2 % salinity, the suppressed performances did not recover until the stress was eliminated. Under salinity stress, the nutrient removal capacity of the system and the composition and chemical characteristics of extracellular polymers substances also changed. Meanwhile, the ABGS formed adaptation to salinity stress in the early coping process. As a result, the effect of the second 2 % salinity on ABGS was significantly weakened. High-throughput sequencing results showed that the microbial community in ABGS shifted under salinity stress, and the halophilic bacteria genera Arcobacter, Denitromonas, Azoarcus, etc. were enriched, which might be the genetic basis of the adaptation.

Role of cycle duration on the formation of quinoline-degraded aerobic granules in the aspect of sludge characteristics, extracellular polymeric substances and microbial communities.

This study investigated the culture and characteristics of quinoline-degraded aerobic granular sludge (AGS) under 8-h and 12-h cycle duration. According to results, the cultivation of an 8-h cycle duration enhanced the growth of quinoline-degraded AGS, as well as the settleability of sludge and the retention of biomass. Quinoline can be removed from mature AGS at a rate of more than 90%, but it is removed at a rate slightly higher when the AGS are cultured for 12-h. Compared to 12-h cycle duration, 8-h cycle duration result in a greater increase in the production of extracellular polymeric substances, particularly extracellular proteins. In these two systems, Acidovorax and Paracoccus dominated the quinoline degrading bacteria. In addition, analysis by non-metric multidimensional scaling (based on Bray-curtis distance) showed significant differences of community structure between the two reactors. Clostridia and Acidaminobacter are different bacteria with an 8-h cycle duration compared to 12 h. Relative abundance of nitrogen metabolism genes based on PICRUSt2 prediction, which explain the better total nitrogen removal for an 8-h cycle duration compared to a 12-h cycle duration. Finally, the KEGG pathway was analyzed in order to confirm the results of the microbial analysis.