Study On Removal Of Organic Pollutants From Reverse Osmosis Concentrate By Powered Activated Carbon And Regeneration Of Spent Powered Activated Carbon By A Multiple-stage Countercurrent Process With Solvent

In recent years, due to its good effluent quality and high recovery ratio, reverseosmosis technology was applied widely in wastewater reclamation. At the same time,reverse osmosis process generated huge amount of reverse osmosis concentrate(ROC), containing salts and refractory organics that were difficult to biodegrade. TheROC was difficult to treat, and direct emission could also severely impact theenvironment. How to treat the ROC and dispose it has become a popular issue. In thispaper, powdered activated carbon (PAC) adsorption-microfiltration (MF) combinedprocess was used to remove the organic pollutants from the ROC, which was takenfrom a petrochemical wastewater reuse plant in Tianjin. A study on the regeneration ofloaded PAC was also carried out.The results indicated that PAC-MF accumulative countercurrent four-stageadsorption process could remove the organic pollutants from the ROC efficiently. Theremoval ratio of chemical oxygen demand (COD) and dissolved organic carbon (DOC)could reach to70.13%and80.46%respectively when the dosage of PAC was0.2945g/L. Silt density index (SDI) of the effluent was lower than5.0, which indicated thatthe effluent could meet the requirements of RO influent. PAC-MF accumulativecountercurrent four-stage adsorption process utilized the difference of ROCconcentration and PAC adsorption equilibrium concentration, making full use of thePAC adsorption capacity. At the same dose of PAC, compared with the PAC-MFaccumulative countercurrent two-stage adsorption, the COD and DOC removal ratioof PAC-MF accumulative countercurrent four-stage adsorption could increase by10%.Thus, if the effluent quality standard was the same, the dosage of PAC in the processwas saved. In addition, adding PAC also slowed the membrane fouling. The specificflux (SF) of the MF membrane could recover to98%of the original one only byphysical cleaning after the bench-scale test.The treatment effect of high salinity ROC and raw ROC by PAC-MFaccumulative countercurrent four-stage adsorption process was essentially unchanged.SDI of the effluent was lower than5.0, which indicated that the effluent could be usedas the influent of RO system. But the SF in the high salinity ROC treatment testdecreased faster than that in the raw ROC test, and its SF could recover to88%of theoriginal by physical cleaning, a little lower than the raw ROC test.A multiple-stage countercurrent regeneration method was used to recover the loaded PAC whose adsorption capacity was exhausted. The optimal regenerant wasdetermined by comparing the regenerative effect of different regenerants. Theinfluence factors and parameters for PAC regeneration were analyzed in the paper.The results indicated that the regeneration efficiency of organic solvents was betterthan that of inorganic solvents, and methanol was the best among the three organicsolvents used in the study. The optimal regeneration time was30min when methanolwas used as the regenerant. When the ratio of PAC to methanol was5g/L, theregeneration efficiency could reach to75%. At the same dosage of regenerant, theregeneration efficiency of two-stage countercurrent regeneration was higher thansingle-stage regeneration. Regeneration efficiency decreased with the number ofregeneration cycle, and increased with the regeneration temperature.