Study On The Effect And Mechanism Of Two Typical Industrial Wastewater RO Concentrates Treated By PPFS Cooperated With H₂O₂

At present,Reverse Osmosis technology has been widely used in the advanced treatment of industrial wastewater and reused of reclaimed water.However,RO concentrate will be produced after used of this technology,which has the characteristics of high COD concentration,poor biodegradability,high salt content and so on,and the treatment is difficult.In this paper,two typical RO concentrate of industrial wastewater（coal chemical wastewater RO concentrate and desulfurization wastewater RO concentrate）were used as the research objects.The treatment of RO concentrate was carried out with polyphosphosulfate（PPFS）coagulant and H₂O₂.The removal effect of pollutants in the RO concentrate after treatment and the mechanism of coagulation and oxidation were studied.The main results are as follows:（1）Single factor experiment was conducted to analyze the removal efficiency of pollutants from RO concentrate of two typical industrial wastewater treated by PPFS/H₂O₂.The removal rates of COD,TP and DOC in coal chemical wastewater RO concentrate were 62.16%,93.05%and 41.37%,respectively,under the conditions of stirring speed of 70.0 r/min,the reaction time of 60.0 min,the standing time of 75.0 min,pH value of 5.0,PPFS and H₂O₂dosage of 168.60,166.50 mg/L.At the same time,SUVA also reached the highest value.The removal rates of COD,TP and DOC in desulfurization wastewater RO concentrate are 82.32%,98.68%and 41.02%,respectively,under the conditions of the stirring speed of 50.0 r/min,the reaction time of 45.0 min,the standing time of 45.0 min,the pH value of 5.0,the PPFS and H₂O₂dosage of 112.40 and 166.50 mg/L.At the same time,SUVA also reached the highest value.（2）Response surface methodology was used to analyze the removal efficiency of pollutants from two typical industrial wastewater RO concentrate treated by PPFS/H₂O₂.According to the fitting model equation and response surface analysis,the optimal process conditions for COD,TP and DOC removal in coal chemical wastewater RO concentrate are as follows:The reaction times were 60.00 min,62.00 min and 57.00 min,the initial pH values of the solution were 5.00,5.16 and 4.78,and the n(Fe³⁺)/n（H₂O₂）values were 1.72,1.73 and 1.90.The theoretical prediction values of COD,TP and DOC removal rates were 62.28%,93.20%and 40.89%,respectively.The theoretical optimum process conditions for COD,TP and DOC removal of desulfurization wastewater RO concentrate are as follows:The reaction times were 45.00min,37.00min,41.00min,the initial pH values of the solution were 5.00,4.50,4.95,and the n(Fe³⁺)/n（H₂O₂）values were 1.15,1.27,1.14.The theoretical predicted removal rates of COD,TP and DOC were 82.93%,98.91%and 41.31%,respectively.The deviation between the predicted and measured values of the two RO concentrates was less than 5.0%.（3）Comprehensive mechanism analysis.Appearance analysis:PPFS flocs have a unique spatial three-dimensional network structure with tight cross-linking,which can better absorb tiny particles in water;PPFS/H₂O₂is added to two kinds of industrial wastewater RO concentrates and the flocs become finer.A large number of salt particles are deposited on the surface of the floc.Analysis of inorganic pollutant removal mechanism:After the PPFS/H₂O₂process reaction,the concentration of TP,SO₄^2-,and Cl^-in the RO concentrate has decreased.The analysis shows that when PPFS is added to the RO concentrate,it will undergo an instant hydrolysis reaction with water to produce a large amount of new hydroxyl polymers.The hydroxyl groups on the polymer will polymerize with PO₄^3-,SO₄^2-and Cl^-in the RO concentrate,and the polymerization strength is PO₄^3->SO₄^2->Cl^-.Analysis of organic pollutant removal mechanism:UV-visible absorption spectroscopy shows that the complexity of organic molecules in the RO concentrate after coagulation and oxidation is reduced;analysis of hydrophilicity and hydrophobicity and molecular weight distribution of organic matter found that flocculation oxidation mainly removes strong hydrophobicity in water Macromolecular substances,but weakly hydrophobic substances and hydrophilic substances cannot be effectively removed in the RO concentrate.PPFS cooperated with H₂O₂to improve the removal effect of organic matter in RO concentrate.On the one hand,the strong oxidation of hydroxyl radicals generated between PPFS and H₂O₂.On the other hand,after PPFS reacts with RO concentrate,the flocs formed can affect organic matter because of good adsorptivity and it can remove organic matter after sedimentation,that is,it has strong adsorption,coagulation and sedimentation effects.However,the removal rate of COD and DOC in the RO concentrate is not high because the hydrophobic organic macromolecules in the water become small molecules which are easily soluble in water after flocculation and oxidation,but the small molecules are extremely stable in water.It is difficult to be completely mineralized and turned into carbon dioxide to escape,and it is also difficult to be removed by adsorption,coagulation and sedimentation.