Treatment Of Reverse Osmosis Concentrate From Coal Chemical Industry Using The Combination Of Coagulation And Ozonation

The membrane technology becomes a mainstream process during the treatment of wastewater from coal chemical industry due to the pressure of"zero emission"policy.However,reverse osmosis concentrate?ROC?produced from the membrane technology has high COD,high salinity and high chroma,and then a pretreatment is needed for this ROC before its evaporative crystallization.Coagulation is usually used as a pretreatment.Ozone is efficient in remove color and organics,but there is selective in ozonation.Catalytic ozonation can overcome this shortcoming.In present work,the combination of coagulation and ozonation was applied to treat the ROC from coal chemical industry,and the effect of ozonation with activated carbon was also studied.The effect of the types and dosage of coagulants,pH,hydraulic conditions,temperature and PAM on the organics removal in ROC were investigated.At pH=5,the addition of 3mM FeCl₃ and AlCl₃ can remove 30%and 14%of total organic carbon?TOC?,respectively.A highest removal efficiency on organics was obtained at initial pH 5,either increasing or decreasing pH value would result in a decrease of removal efficiency.The Ultaviolet-Vis?UV?absorbance of the solution in the 185-450 nm was reduced obviously after coagulation.The results of the high performance size exclusion chromatography?HPSEC?evidenced that Al coagulant is efficient in the removal of organic matter with molecular weight>2 kDa,and Fe coagulant is efficient in the removal of organic matter with molecular weight>500Da.The results of fluorescence excitation-emission matrix spectra?EEM?demonstrated that the ROC contains many humic acid-like and fulvic acid-like matters.Fe coagulant has shown a better removal on these two kinds of organics compared with Al coagulant.Secondly,the effects of ozone dosage,pH,and temperature on the removal of organics from the ROC were studied in ozonation.The results indicated that the highest degradation efficiency on organics is obtained at initial pH9.More hydroxyl radicals will be quenched by carbonate at initial pH11compared with pH9 in ozonation.With the increase of temperature,the higher degradation efficiency of organics was achieved in ozonation.The UV results revealed that the absorption peak of the UV spectra was red-shifted from 199nm to 220 nm with the extension of the oxidation time.Besides,the results from the HPSEC showed that the amount of organics with a molecular weight>2 kDa was decreased gradually,while the amount of small molecular weight?<2 kDa?organic matter increased significantly in the ozonation.The EEM results demonstrated that reaction between ozone and either humic acid-like or fulvic acid-like is fast,resulting in a effectively removal on these two types of organics.Finally,the effect of ozone dosage,activated carbon dosage,pH,and temperature on the removal of organics from ROC was examined during ozonation in the presence of activated carbon.A highest degradation efficiency on organics was obtained at initial pH 9.The removal efficiency of organics increases with the increase of temperature.The UV spectra result showed that the absorption peak of the UV spectra was red-shifted from 199nm to 223 nm with the extension of the oxidation time.In addition,the result of HPSEC indicated that the amount of organic matter with molecular weight>2 kDa decreased gradually,and the amount of small molecular weight?<2 kDa?organics increased obviously during ozonation with activated carbon,but the accumulation of small-molecule organics was less than that in the ozonation.The result of EEM indicated that ozonation with activated carbon could efficient in the removal of humic acids-like and fulvic acids-like matters.