Study On The COD Reduction Technology Of Shale Gas Produced Water By Advanced Oxidation Methods

Taking produced water in Fuling shale gas field as an example,the treat effectiveness of chemical coagulation,Fenton oxidation,electrochemical oxidation,coagulation and Fenton-oxidation and electrochemical-oxidation coagulation is discussed on the basis of the physical and chemical properties and characteristics of the produced water.And the key is to reduce the amount of COD in it.High COD,TDS,SS concentrations are characteristics of Fuling shale gas produced water.Organic compounds are mainly tryptophan,aromatic and humic acid.The effectiveness order of COD efficiency reduced by chemical coagulation is PAC concentration>PAM concentration>pH.The optimum conditions are pH 6,PAC concentration of 30mg/L,and PAM concentration of 1mg/L and the removal ratio of COD is 38.9%.In the sludge after coagulation,there are Ba,Br,Ce,Mn,Nd,Ti,etc.,as well as some non-metal elements like Cl,P,S,Sr,etc.The effect of coagulation on turbidity removal was high and that of COD,nitrogen,and other pollutants was weaker.In Fenton oxidation,the order of Fenton removal factors of COD are:H₂O₂/Fe²⁺?molar ratio?>pH>reaction time>H₂O₂/COD?concentration ratio?.The optimal operation parameters are:H₂O₂/COD=6,pH=2,H₂O₂/Fe²⁺?molar ratio?=6,and reaction time is 120min.After treatment the COD reduced by 80.84%.The pollutants in the original water are mainly small organic molecules.Fenton oxidation can effectively degrade the dissolved degradable organic matter in water samples.Particles and colloids account for minor COD change,after oxidation,the COD percentages of both increase compared to original samples.Fenton method removes TOC of low weight molecules,COD and UV₂₅₄ more efficiently.The optimal treatment conditions of shale gas field produced water using electrochemical oxidation technology to reduce TOC and COD are current density of 50mA/cm²,pH=7?does not need to adjust pH?,electric plate spacing is 1 cm,and the electrolysis with stirring method 180 min.In this way,82.5%COD in the produced water is remove.After reaction,there was no obvious corrosion on the surface of the electrode,and the method has good stability in addition to some sediment.Electrochemical oxidation can effectively reduce the dissolved degradable organic matters in water samples causing great change to the COD distribution,however,the oxidized pollutants are among the small molecule range.After electrochemical oxidation,the process for mineralization are high weight organics,small organics,and carbon dioxide and water.For the treatment of produced water using Fenton oxidation and coagulation,the optimal treatment conditions during coagulation are pH=6,PAC=3mg/L,and PAM=1mg/L.In this stage,the removal rates for turbidity,COD,and total COD are 98.1%,10.2%,and 83.38%without flocculant.This method has poor capacity in removing the amount of ammonia nitrogen in the water samples.Electrochemical oxidation and coagulation method has the best performance in treating produced water from shale gas field under the following conditions during coagulation:pH=6,PAC=3mg/L,and PAM=1mg/L.In this stage,the removal rates for turbidity,COD,and total COD are 97.03%,13.33%,and 85.2%.Although the five methods above are effective in removing the COD,TOC,turbidity,and suspended solids from the water samples,the electrochemical oxidation coagulation method is superior than the other three methods in removing ammonia nitrogen.