Researches On Electrocatalytic Combined With AGS-SBR For Treatment Of Flowback Water From Shale Gas Extraction

The development of shale gas is a state key energy strategy in China.In recent years,large-scale development has progressed rapidly,but the potential water resources and water environment problems brought by hydraulic fracturing have gradually become prominent and attract attention.Shale gas flowback water has the characteristics of high salt,complex organic components,many potential risks,and large water quality variability.It is difficult to handle and has a large amount of production.It is one of the key issues that shale gas needs to be solved in the current scale development.The paper is aimed at the organic pollutants in the flowback water,electrocatalytic degradation and transformation of complex refractory organics to promote the biological treatment of flowback water,and the development of electrocatalysis and biological treatment technology as potential technical targets.The response surface optimization experiment of the reaction parameters of shale gas flowback water is used to identify the effects of electrocatalysis on the removal of organic matter and biodegradability in the flowback water and its influencing factors and laws.The electrocatalytic treatment of different pollutant concentrations is carried out.Flowback water experiment with different pollutant concentrations,investigate the adaptability of the effect of electrocatalytic treatment of shale gas flowback water to the change of water quality itself;carry out electrocatalytic pretreatment and aerobic granular sludge sequencing batch reactor?AGS-SBR?combined batch treatment and process experiments to determine the effect of electrocatalytic pretreatment on aerobic granular sludge for shale gas flowback water,and verify the treatment effect of the combined process.The main findings and conclusions of the study include:?1?Three factors including electrode spacing,voltage and reaction time were selected as variables,the B/C value and COD removal rate were simultaneously used as screening conditions for response surface optimization experiments.The results showed that the plate spacing improves the B/C value of flowback water by electrocatalysis.The effect is the most significant,while the effect of voltage on the effect of electrocatalytic removal of COD flowback water is most significant.For the experimental flowback water,the optimum conditions for electrocatalytic treatment are:plate spacing 2.5cm,voltage 12.5V,reaction time 60min,under this condition COD removal rate is 38.2%,B/C value is increased from 0.27 of raw water to 0.64.?2?Comparative analysis of the organic matter in flowback water before and after electrocatalytic treatment found that electrocatalytic changes the organic components in the flowback water,and the polycyclic aromatic hydrocarbons,phenolic compounds and long-chain aliphatic hydrocarbons decreased.It may be the reason why electrocatalysis improves the B/C value of flowback water.?3?The results of electrocatalytic treatment of multiple flowback water samples with different water quality differences showed that the salinity and organic matter of all water samples are removed,and the biodegradability of most water samples can be improved.The electrocatalytic treatment effect has wide water quality adaptability.However,the increase of COD removal rate,BOD₅ and B/C value is negatively correlated with TDS and Cl^-concentration.The higher the TDS,especially the Cl^-concentration,the more unfavorable the removal of organic matter and the increase of B/C value in the flowback water.?4?The batch experiment used the treated aerobic granular sludge to treat the flowback water after electrocatalytic pretreatment showed that the aerobic granular sludge adsorbed to the organic matter at an early stage,and the organic matter degraded rapidly within 4 hours,and the degradation reached stability in 12 hours;after electrocatalytic pretreatment,the COD removal rate of aerobic granular sludge to flowback water increased by 185.70%.During the 192 h period of the batch experiment,the shale gas flowback water before and after electrocatalytic treatment had little effect on the sedimentation velocity of aerobic granular sludge,and there was no significant difference in the sedimentation velocity of the two groups of sludge.After the batch experiment,the particle size of the aerobic granular sludge changed,and the particle size decreased.However,the treated flowback water can better maintain the particle size of the aerobic granular sludge and keep the particle size stable.?5?Gradient substitution method was adopted to gradually convert the influent of the AGS-SBR reactor treated with simulated flowback water to the actual flowback water with a COD concentration of 800 mg/L.The COD removal rate was continuously reduced from 80%to about 20%.The electroless catalysis was used to pre-treat the actual flowback water into the AGS-SBR reactor.The COD removal rate was about50%,and the effluent COD was 265 mg/L.The experimental results showed that the electrocatalytic effect on the removal of organic matter in the flowback water and the improvement of biodegradability can be used as pretreatment to reduce the influent organic matter load and enhance the biological removal effect of the subsequent aerobic granular sludge system.Electrocatalytic-aerobic particles Sludge combined process for shale gas flowback water has good technical potential.