Study On The Degradation Process Of Organic Matter In Shale Gas Produced By Electric Fenton Method

Shale gas is an important unconventional natural gas resource.A large number of produced waste water are produced inevitably in the Shale gas production process,which has the characteristics of difficult degradation,long-term residue and high salt content.Direct reinjection or discharge has an adverse impact on the ecological environment.Effective treatment of wastewater from shale gas exploitation is the bottleneck of shale gas exploitation and utilization To improve the biodegradability of wastewater and provide technical support for the follow-up treatment up to the standard,and promote the sustainable development of shale gas resources,the electrofenton technology is used to degrade the organic matter in shale gas produced water.In this paper,typical water samples sampling in different shale gas produced water sites and at different times in Yibin,Suining and Changning of Sichuan Province were selected to carry out routine water quality analysis and organic matter identification.The results show that the shale gas produced water is mostly acidic,sodium ions and a small amount of calcium and magnesium ions are the main system cations.The anions are mainly chloride ions,whose contents are about 150000ppm.The value of BOD5/CODcr is less than 0.3.Therefore,shale gas produced water belongs to high salt wastewater which is difficult to be biodegraded.The main organic pollutants in shale gas produced water are alkanes,esters,alcohols,phenols,amines and quinolines.Among them,aromatic compounds and silicones are most difficult to degrade.Based on the preliminary exploration and comprehensive efficiency analysis of the treatment of organic matter in shale gas produced water by the similar Fenton Method,the electro Fenton method was selected as an optimized method for the degradation of organic pollutants.The process optimization of shale gas produced water treatment by two-dimensional electric Fenton was carried out,and the optimum conditions of two-dimensional electric Fenton method were determined:graphite as cathode,titanium coated ruthenium dioxide as anode,current density of 187A/m2,aeration volume of 3L/min,Fe2+ dosage of 15mmol/L.The removal rate of CODcr was 45.1%and the biodegradability value of BOD5/CODcr increased from 0.28 to 0.57 when the reaction time was 3hours.In this paper,three-dimensional electric Fenton reactors to treat shale gas produced water were studied.The iron sludge particle electrode was prepared by using the waste iron sludge produced by the electric Fenton process as the raw material.The preparation process of particle electrode and its related factors were investigated.The process was determined as follows:using clay as binder,35%clay,iron mud and a small amount of iron powder as raw materials,adding water to mix,forming by pressing,roasting at 950?.On this basis,the single factor effects on the three-dimensional electric Fenton treatment process was investigated,and the operation parameters of three-dimensional electric Fenton were obtained,which were graphite was used as cathode,titanium coated ruthenium dioxide as anode,the corresponding current density was 250A/m2,the electrolyte concentration was 30g/L,and the aeration rate was 2L/min.The removal rate of CODcr was 45.7%in 2h reaction,and the current,the amount of divalent iron and the initial pH were optimized by response surface method.The optimal conditions were obtained:the initial pH value was 3.23,the amount of divalent iron was 14.07mmol/L,the current was 0.65A,and the removal rate of COD was 50.72%.In addition,the active substances in the process of three-dimensional electrofenton reaction were determined.It is speculated that free chlorine and ·OH with strong oxidation can degrade organics efficiently after electron transfer of water and free chlorine in the electrolyte.The main active substances of oxidative degradation of organics were free chlorine and OH.The degradation mechanism of organics was preliminarily explored.After the treatment by the electric Fenton process,the biochemical BOD5/CODcr value of shale gas produced water increased from 0.28 to 0.43,which significantly improved its biodegradability,providing the basis for the subsequent biochemical treatment of deep degradation of organic matter.