Study On Promotion Mechanisms And Methods Of Fenton System For Degradation Of Polymer-Containing Wastewater

Many oil fields in China enter the middle or late stages of mining,and the water content of output liquid is generally high.Some are even as high as 95%or more.Due to the huge amount of oil and gas exploitation in China,the annual oilfield wastewater generated is about 1.0 to 1.2 billion cubic meters,which has become one of the sources of pollution that cannot be ignored in China's environment.Unlike other industrial wastewaters,the composition of oilfield wastewater is extremely complex and the concentration of organic pollutants such as oils and polymers are high.The concentration of polymer is increasing with the popularization of polymer flooding technology,and it has become one of the difficulties and focuses of oilfield wastewater treatment.Traditional oxidants are difficult to effectively remove organic pollutants,and are not suitable for polymer-containing wastewater treatment.It is extremely urgent to develop new oxidation technologies that have obvious effects on polymer removal.Advanced oxidation technology represented by the Fenton system is one of the effective methods for degradation of organic pollutants.However,the low utilization rate of oxidant H₂O₂ is a bottleneck that Fenton system is difficult to overcome.This bottleneck involves the generation and effective utilization of active free radicals.Combined with the characteristics of polystyrene in the oilfield,it is an effective method to improve the oxidation capacity and the H₂O₂ utilization ratio of the system by regulating the reaction path of Fenton system,accelerating the generation rate of active free radicals and avoiding the useless consumption of active radicals.In order to analyze the mechanism of the additive to the oxidizing ability of Fenton system,the spectrophotometric method of Fenton system and·OH concentration was studied firstly via experimental method,and the proposed modified method was used to detect the·OH concentration in Fenton system.Methylene blue?MB?was used as the typical organic pollutants to study the mechanism and basic rules of degradation of organic pollutants by Fenton system.On the basis,the promotion methods of Fenton system for degradation of organic pollutants,the main reaction parameters and the way of reactant addition to the degradation of pollutants in Fenton/additive system were studied.Finally,the effect of Fenton/additive system on simulated oily wastewater was verified using experimental methods.The problem of the existing spectrophotometric method based on the Russell reaction mechanism for·OH concentration detection in solution under neutral condition was analyzed.It was found that the chromogenic agent fast BB salts?FBBs?interfered with the detection of the end product diazonium sulfone,which affected the detection accuracy of the existingmethod.It was found that FeSO₄ could effectively inhibit the extraction of FBBs by extractant,which greatly decreased the interference and increased the measurement accuracy to 7%.The effect of dimethyl sulfoxide?DMSO?on the detection was related to the concentration of the system.When the concentration was lower than 1945 mmol·L^-1,the detection of diazo sulfone was not affected.The H₂O₂concentration had a significant effect on the test results,and low concentrations of H₂O₂did not interfere with the test.On this basis,the modified method of detecting the·OH concentration in the Fenton system was proposed,that is,the H₂O₂ solution with concentration of 0.5¹ mmol·L^-1 was slowly(0.5 mL·min^-1)injected into the Fenton system.O₂^-·had a strong ability to oxidize MB,but because of its extremely low concentration,it was not the main active substance for MB degradation in traditional Fenton system.The main active substance for MBdegradation in the Fenton system were·OH radicals.The degradation process of MB in Fenton system was divided into rapid reaction phase and uniform reaction phase.The utilization efficiency of H₂O₂ in the initial rapid reaction phase was much higher than that in the uniform reaction phase because of the fast formation rate of·OH.The reaction·OH+HO₂·?H₂O+O₂ was the main reason for H₂O₂ useless consumption of Fenton.Attenuating the ineffective reaction between·OH and HO₂·was a feasible method to improve the utilization efficiency of Fenton H₂O₂.As the temperature increased,the degradation rate of MB in the Fenton system decreased.The degradation ability of MB to the system increased first and then decreased with the increase of H₂O₂ initial concentration.The degradation capacity of MB in the system increased monotonously with the increase of the initial concentration of Fe²⁺.The MB degradation rate increased as the initial concentration of MB increases.Inhancing the rate of formation of H₂O₂ to·OH by additives and reducing the formation of HO₂·were effective measures to improve the oxidation capacity of the system and the utilization ration of H₂O₂.The effects of hydroxylamine hydrochloride,sodium sulfite,hydroquinone and ascorbic acid on the degradation of simulated pollutants in Fenton system were compared.Ascorbic acid was chosen as the final additive due to the obvious promotion effect and its environmental friendliness.The·OH concentration was significantly increased after adding ascorbic acid.The reason was that the added ascorbic acid reduced Fe³⁺to Fe²⁺in the system,which accelerated the formation rate of·OH and greatly increased the oxidation capacity of the system.As the temperature increased,the MB degradation rate of the system with additive increased.The degradation ability of MB increased first and then decreased with the increase of initial H₂O₂ concentration and the initial concentration of Fe²⁺in the system.The MB degradation rate increased as the initial concentration of MB increased.When the temperature exceeded 30?,the stepwise addition method of ascorbic acid promoted the degradation of pollutants in the system.The degradation effect of Fenton/C₆H₈O₆ system on polymer-containingwastewater was studied.The degradation ratio of the Fenton/C₆H₈O₆ system was of great significant higher than that of the Fenton system,and the highest degradation ratio was close to95%.The addition amount of C₆H₈O₆ had a certain effect on the degradation effect,and the best[C₆H₈O₆]₀:[Fe²⁺]₀ was 3:1.With the increase of temperature,the degradation ratio of the polymer-containing wastewater increased.With the increase of initial concentration of H₂O₂ and Fe²⁺,degradation ratio of the polymer-containing wastewater increased first and then decreased.As the initial concentration of polycondensation increased,the amount of degradation increased,but the degradation ratio decreased.The degradation effect of adding C₆H₈O₆ by two times was better than that of adding C₆H₈O₆ by one time.Compared with the Fenton system,the polymer removal ratio of the Fenton/C₆H₈O₆ system was increased by nearly 1.4 times,and the H₂O₂ utilization ratio was increased by nearly 2 times.