Rapid cultivation of aerobic granular sludge for shale gas flowback water treatment by bioaugmentation with inoculating multifunctional fungal pellets

Aerobic granular sludge (AGS) technology showed great potentials in treatment of hypersaline industrial wastewater such as shale gas flowback water (SGFW), while long start-up period was still a major bottleneck. To both strengthen its granulation and pollutant removal efficiency, herein, one multifunctional fungus Aspergillus sydowii NCSL-XY1 was first isolated with the capacities including formation of fungal pellets, salt tolerance, and efficient degradation of organics in SGFW. Subsequently, its appropriate fungal pellets were used to try to shorten the start-up period of AGS in SGFW. The results showed that inoculating fungal pellets evidently accelerated the formation of AGS from 41 to 16 days. Also, it could enhance the TOC removal from ∼30% to ∼45% in the initial start-up period (Day 2-Day 11). Mechanisms analysis showed that the inoculation of fungal pellets increased EPS secretion and microbial community diversity. When the reactor stabilized, both of the AGS in R1 and R2 had similar D50 (∼1200 μm), SVI30 (∼30 mL/g), and SVI30/SVI5 (∼0.95). Also, the TOC and PAM removal in R1 and R2 were also similar and maintained at ∼71% and ∼20%. Overall, the inoculated fungal pellets played significant roles of both biomass carrier and synergistic degrader in facilitation of AGS start-up, while it had limited functions after the granules maturation. This study provided a universally effective bioaugmentation mode (screening degrading fungus and inoculating its fungal pellets) for AGS cultivation in treatment of refractory industrial wastewater.