Researches On Pollution Characteristics And AGS-SBR Treatment Of Flowback Water From Shale Gas Extraction

With the development of shale gas,the environmental problems associated with it are widely concerned.Because of the large amount,high salt,complex compositions and potential environmental toxicity,the flowback water has become the focus.Firstly,the organic and inorganic components of the flowback water from the shale gas recovery in Chongqing area are analyzed,the pollution characteristics and the key organic pollutants of the flowback water are identified.Secondly,the the inhibition to activated sludge microorganisms are evaluated by respiration measurement.And finally,the influence of quaternary ammonium salt on the AGS-SBR system is studied and the AGS-SBR reactor is used to treat the real flowback water.The main conclusions are as follows:?1?The quality of the flowback water from shale gas recovery in Chongqing is close to neutral,showing high salinity,high COD,complex chemical composition and organic components.There are certain uncertainties in the time and space,the major indexes that changed over time are mainly Cr,Zn and petroleum,the major indexes that changed over space are mainly heavy metals.From the point of view of wastewater treatment,the indexes of SS,TDS,COD,petroleum and NH₄⁺should be listed as the key indicators of shale gas flowback water.From the environmental risk point of view,we should pay attention to Hg,Cr,Fe,Pb,Cl^-,Ba²⁺and other indicators.Compared with the American region,the organic matter,salinity and heavy metal contents in the flowback water of Chongqing area are relatively low,and the difficulty and environmental risk of the flowback water treatment are relatively low.?2?There are 190 kinds of organic compounds in the flowback water,and the species and content of organic matter are different in different areas,but the main organic compounds are alkane?C9-C44?,accounting for 54.2%of the total amount of organic matter.The key organic pollutants identified are phenol,trichloromethane,PAEs?DMP,DBP,DEHP?,benzene series?1,2,4,5-four toluene,2-ethyl p-xylene,1,2-two methyl-4-ethyl benzene,1,2-two methyl-3 ethyl benzene?,polycyclic aromatic hydrocarbons?naphthalene,1-methylnaphthalene,2-methylnaphthalene 2,3-two methylnaphthalene,1,3-two methylnaphthalene,1,4-two methylnaphthalene,1,7-two methylnaphthalene?,2-methionyl benzothiazole,2,4-ditert butylphenol,bactericide?quaternary ammonium salt?,2-butoxyethanol,etc.?3?The flowback water has a certain inhibitory effect on activated sludge microorganisms.The semi inhibitory volume concentration IC50 for activated sludge heterotrophic bacteria is 52.96%?TDS 12352.39mg/L,chlorine ion 7522.06mg/L,COD 582.89mg/L?,and the semi inhibitory volume concentration of activated sludge autotrophic bacteria is 9.69%?TDS 5988.44mg/L,chloride ion 4223.41mg/L,COD25.57mg/L?.The inhibitory effect on activated sludge heterotrophic bacteria was affected by the development area and storage time,the main possible inhibitory factor is organic,the main possible inhibition factor for the activated sludge autotrophic bacteria is chlorine ion,and the semi inhibitory concentration is 3.76g/L.?4?In the short term,quaternary ammonium salt has a certain inhibitory effect on the performance of AGS-SBR system,but it has little effect on long term operation.AGS-SBR can be well adapted to the toxic impact of quaternary ammonium salt.For long term operation,with the increase of quaternary ammonium salt concentration,SVI is always under 40mL/g,the sedimentation rate of granular sludge is always above80m/h,and the effluent TOC is basically stable in 56.9mg/L.Granular sludge always maintains good sedimentation performance and slight promotion effect.The morphology of sludge is not changed significantly,and extracellular polymeric substances is increased significantly.?5?The cultivated granular sludge has the potential to deal with the real flowback water and has good organic removal effect.The BCOD in the flowback water is18.22%of the total organic matter,and the biodegradability is poor.The removal rate of TOC is60%-80%,the effluent TOC is maintained at about 113mg/L and the organic matter can be removed by aerobic granular sludge is 74.42%.The microbial community structure in the granular sludge domesticated by simulated reactivated sludge is consistent with the real flowback water.