The Treatment Of Flowback Wastewater From The Hydraulic Fracturing For Shale Gas Extraction By Aerobic Granular Sludge SBR

China with the largest shale gas as important clean energy reserves in the word has begun to use of hydraulic fracturing technology for large-scale development and utilization.However,the treatment of flowback wastewater from the hydraulic fracturing for shale gas extraction become a core issue of environmental protection.Aerobic granular sludge(AGS)as a new technology of wastewater biological treatment was developed in 1980 s.In this thesis,aerobic granular sludge was cultivated in the sequencing batch reactor(SBR)using synthetic flowback wastewater(SFW).The performance and filamentous expansion control of AGS were explored and while the salinity changes,AGS's characteristics of extracellular polymeric substances(EPS)and microbial community structure were analyzed.This paper can provide technical reference to the treatment of flowback wastewater from the hydraulic fracturing for shale gas extraction.Main conclusions are as follows:(1)SBR1 with SFW as carbon source can cultivate AGS with the shape of the rules.Even though the AGS in SBR2 with glucose as carbon source formed faster than that in SBR1,the AGS in SBR1 had obvious larger average particle size.The filamentous bacteria emerged easier in SBR2.(2)The filamentous overgrowth in SBR with SFW as carbon source was effectively controlled through transforming superficial upflow air velocity from 0.7m/min up to 1.3m/min and the settling time of SBR from 2min to 1min after two weeks.Sludge volume index(SVI)decreased from 200ml/g in the period of Filamentous expansion to 30ml/g and the degree of filamentous overgrowth reduced from 3.07 to 1 approximately.This paper found that some filamentous fungi existing in SBR can promote the formation of aerobic granular sludge at the same time.(3)Aerobic granular sludge SBR had strong ability to adapt environment and removed COD efficiency stability.When SBR fed with influent chemical oxygen demand(COD)concentrations of 700mg/L,1200mg/L,2300mg/L respectively,the COD removal rate was 74%~81% and when hydraulic retention time(HRT)was 6h,12 h,24h and 48 h,average daily removal load was 1.96kgCOD/(m-3·d),1.11 kgCOD/(m-3·d),0.53 kgCOD/(m-3·d)and 0.27 kgCOD/(m-3·d)respectively,while SBR feeding with influent COD concentrations of 700mg/L and operating with 12 h HRT can run under the best performance.(4)Aerobic granular sludge SBR under 50 g/L NaCl can stably operation,and had a better effect to consume organic matter within a certain range to increase salinity and suited to treat flowback wastewater from the hydraulic fracturing.With sodium chloride concentration from 12.5 g/L to 50 g/L,the TOC removal rate rose from 53% to 64%;polyacrylamide removal rate increased from 5% to 20%;SVI reduced first then increased,but was still below 40 ml/g;the average settling velocity increased gradually.(5)Sodium chloride concentration increased can promote microbes to produce more extracellular polysaccharide and extracellular protein,and they had good linear relationship between them.With NaCl concentration from 12.5g/L to 50g/L,the extracellular polysaccharide of aerobic granular sludge in SBR1 were from 11.99 mg/gMLVSS rose to 32.31 mg/g MLVSS and extracellular proteins were from 6.42 mg/gMLVSS rose to 11.70 mg/gMLVSS and determination coefficient(R2)were 0.9051 and 0.8959 respectively.With salinity increased,the extracellular polysaccharide of aerobic granular sludge in SBR2 were from 9.44 mg/gMLVSS rose to 26.33 mg/gMLVSS and extracellular proteins were from 8.05 mg/gMLVSS rose to 13.51 mg/gMLVSS and R2 were 0.9532 and 0.8675 respectively.(6)Experimental result demonstrated that dominant bacteria of AGS were class Alphaproteobacteria,Gammaproteobacteria and Sphingobacteriia and With the increase of salinity,the abundance of class Alphaproteobacteria and Gammaproteobacteria rose and class Sphingobacteriia declined.The abundance of class Clostridia and Bacillia in high salinity started to increase while class Flavobacteria was suitable for existence in low salinity.In the subsystem,genus Vibrio,genus Halomonas,family Rhodocyclaceae and family Enterobacteriaceae were observed and they were likely to utilize guar gum,polyacrylamide and isopropanol in SFW.