Study On The Treatment Of Refractory Wastewater By Chemical Flocculation And Electrocatalysis

Refractory wastewater treatment is one of the urgent issues to be solved in the field of environmental governance.Due to the complex composition and high pollutant concentration of refractory wastewater,the removal ability of pollutants by conventional biological methods is limited.Therefore,seeking efficient,fast and feasible physicochemical and other treatment methods has become the key to solving the problem.This study relies on the topic of“National Major R&D Program”to achieve the goal of discharging or reusing refractory wastewater,and proposes the strategy of using chemical flocculation and electrocatalytic oxidation technology to treat refractory wastewater.In order to solve the problem of the large amount of commonly used chemical flocculants and the large sludge yield,a chlorine-free polyaluminum ferric silicate（PSAF）flocculant with excellent flocculation performance was studied,and the preparation and application of the chlorine-free flocculant can effectively alleviate the corrosion problem of the facility caused by the chlorine-containing flocculant.For the wastewater that still couldn’t meet the discharge or reuse standards after chemical flocculation,Ti/SnO₂-Sb was selected as the anode to construct the electrocatalytic oxidation system which was used for the advanced treatment.The research on the water quality characteristics of typical refractory wastewater,Removal of refractory organic matter from wastewater by chlorine-free PSAF,the efficiency of chlorine-free PSAF pretreatment of refractory drilling water,and the advanced treatment of refractory wastewater by electrocatalytic oxidation technology have been carried out,which provided a practical basis for the practical application of chemical flocculation and electrocatalytic oxidation technology to treat refractory wastewater.The main research contents and achievements are as follows:（1）Conventional water quality analysis methods,3D-EEM,GC-MS and FT-ICR-MS were used to comprehensively analyze the water quality and characterize the pollutants in typical refractory wastewater（lubricating oil wastewater,drilling wastewater）.The study found that the concentration of pollutants in two types of wastewate is high,the stability of wastewater system is good,BOD₅/COD value is low,and there are a lot of refractory organic pollutants,such as hydrocarbons and CHO,CHON,CHOS,CHONS heteroatom organic pollutants,etc,which indicated that the two kinds of wastewater have the quality characteristics of refractory wastewater,and the non-biochemical treatment methods will be more efficient.（2）A chlorine-free PSAF flocculant was prepared,and the removal of refractory organic matter by PSAF was studied with simulated and actual refractory wastewater as the treatment target.The results showed that when p H was 7.0,the humus removal efficiency of PSAF was the highest,reaching 96.0%.Under the dosage of 396 mg/L,the COD removal efficiency of actual wastewater was 33.6%.PAMALAM combined with PSAF could improve the actual wastewater pollutant removal efficiency.Under the condition of PSAF+0.08%PAMALAM addition sequence and dose,turbidity,COD and TN removal efficiencies increased by 0.3,1.8 and 5.9 times,respectively.It was also found that more fulvic acid-like substances could be removed during this process.The analysis of zeta potential and floc properties revealed that charge neutralization,adsorption,sweep net capture,and bridging mechanisms existed during the single PSAF coagulation process,PAMALAM further enhanced the above effects.（3）The properties of PSAF flocculant were further optimized by increasing the activation p H and the molar ratio of metal ions to silicon.The chlorine-free PSAF-2flocculant was prepared when the activation p H was 4.0 and the molar ratio of metal ion to silicon was 0.9 and used to pretreat drilling wastewater.The study found that chlorine-free PSAF-2 flocculant had better flocculation effect than silicon-free PAF and chlorine-containing flocculant PAC.Compared with PAC,PSAF-2 produced less flocculant sludge and needed lower dosage of flocculant.At the same time,the study showed that the chlorine-free PSAF hardly released chlorine ions into the effluent water,which avoided the problem of chloride ion corrosion and showed better engineering application value.（4）Ti/SnO₂-Sb electrode was prepared by impregnation pyrolysis.The study found that it had a higher OEP value and a stronger ability to produce hydroxyl radical,dominating indirect oxidation.Using the Ti/SnO₂-Sb electrode as an anode of the electrocatalytic oxidation system,which was used for the advanced treatment of drilling wastewater.The refractory organic matter in the wastewater is further removed,and the COD concentration can be reduced to less than 50 mg/L.Finally,the drilling wastewater can be discharged or reused up to standard,which provides a reference for the application of electrocatalytic oxidation technology in the advanced treatment of refractory wastewater.