Treatment Of Reverse Osmosis Concentrate From Wastewater Treatment Plant By Countercurrent Adsorption Dependent On Powdered Activated Carbon

Reverse osmosis concentrate(ROC)has been a bottleneck,which restricted the application of reverse osmosis in the field of wastewater treatment.ROC has a high content of refractory organics,which contributes to a severe irreversible fouling to the modules of reverse osmosis.As a result,in order to prolong the life of reverse osmosis,it is a key factor to select a proper method and reduce the concent of refractory organics in ROC.The purpose of the dissertation is to find a reasonable process to remove the organics in ROC,so that ROC could return to the inlet of reverse osmosis system,and reduce the fouling of RO membrane that is attributed to the organics in ROC.In the jar tests,several methods including Fenton oxidation,ozone oxidation,powder activated carbon(PAC)adsorption,and ozone oxidation-PAC adsorption,were used for the treatment of ROC.The optimum parameters for Fenton oxidation are as follows:the molar ratio of H2O2 to Fe2+ is 1:1,the dosage of H2O2 is 100 mg/L,the initial pH is 8.0,the reaction time is 20 minutes,with a higher removal of 60 percent on the organic carbon cannot be purged.(NPOC).Addionally the molar ratio of H2O2 to Fe2+ is the key factor to control Fenton oxidation.The PAC adsorption of organics in ROC follows the pseudo-second-order kinetic model and Freundlich adsorption isotherm.Removal of NPOC using the two-stage countercurrent adsorption dependent on PAC is as high as 60%,when the PAC dosage is 0.15 g/L,with the adsorption time for 20 min and the dilution factor F equal to 0.3.The three-dimensional fluorescence spectrum and the molecular weight distribution of the organics in ROC was analyzed.Most of the organics in the ROC were humic acid with a molecular weight of less than 1k Da,which could be well adsorbed by PAC adsorption.In a comprehensive comparison,Fenton oxidation and PAC adsorption have a better removal on organics in ROC,while ozone oxidation has a lower removal.The combination of ozone oxidation and PAC adsorption depends on the PAC adsorption.As a consequence,PAC adsorption with a short process and simple operation,was selected for the subsequent lab-scale test schemesIn the lab-scale test,four-stage countercurrent adsorption dependent on PAC was used for the treatment of ROC,when the PAC dosage is 0.086 g/L.The test removals on NPOC is 57%,which is very close to the calculated value based on the four-stage countercurrent adsorption model.Turbidity in the effluent is below 0.2 NTU,and the mean fouling rate is 0.048/(h m).According to the linear relationship between NOPC and COD,the COD in the effluent of the ROC after four-stage countercurrent adsorption dependent on PAC could be calculated as 41.7 mg/L,which could meet the Grade A of Discharge Standard of Pollutants for municipal Wastewater Treatment Plants(GB 18918-2002).When the four-stage countercurrent adsorption dependent on PAC is used for the treatment of organics in ROC raw water,the costs is ￥0.894/m3,which is lower than ￥1.78/m3 for Fenton oxidation.