| Coal tar processing wastewater is a kind of non biodegradable wastewater, the levels of chemical oxygen demand (COD) and ammonia nitrogen(NH3-N) in the effluent from bio-chemical treatment are usually above the Wastewater National Emission. Powdered activated carbon adsorbent was an effective method to resolve this problem. However, this method was restricted because the technology of regeneration of powdered activated carbon is still imperfect. Therefore, to find a technolgical and economical regeneration method has theoretic and practical significance. The article investigated the biotreated coal tar processing wastewater using powdered activated carbon as adsorbent, chemical oxygen demand (COD) was used as the index for evaluating the treatment efficiency. The optimal adsorption conditions and the optimal regeneration conditions were researched,the adsorption equilibrium isothem and adsorption kinetics were studied, the thermal regeneration process was monitored by thermal analysis(TGA/DSC). Based on the experimental result, adsorbent of a countercurrent two-stage process was selected to treat the biotreated coal tar processing wastewater,and the economical feasibility was analyzed.The biotreated coal tar processing wastewater was used as research object. The removal rate of COD in wastewater influenced by the dose of activated carbon, wastewater temperature, pH and reaction time were investigated. The results showed that the primary and secondary factors were that the dose of activated carbon, reaction time, pH and wastewater temperature. The dose of powdered activated carbon was 2 g/L-1, and reacted 30 minutes at room temperature, pH used the raw wastewater’s pH, under this condition, the removal rate of COD in wastewater by powdered activated carbon adsorption was best, and the COD was 28 mg·L-1, the removal rate was 83.1%.The thermal regeneration of saturated powdered activated carbon was studied. The adsorption ability of regeneration by the regeneration temperature and regeneration time were discussed. Attention was paid to the effect of regeneration cycles on the adsorption capacity of powdered activated carbon. The results showed that the optimum regeneration conditions was heated 30 minutes under the temperature of 250 ℃. Under this condition, the regeneration efficiency of the first regeneration of powdered activated carbon was 105.1%. A good regeneration efficiencies could still be gotten after the activated carbon was regenerated repeatly for 7 times, and the regeneration efficiencies are more than 90%.The results showded that the powdered activated carbon can adsorb the biotreated coal tar processing wastewater effectively, and the adsorption isotherms was fit to the Freundlich. The kinetics of adsorption of COD from wastewater onto PAC was fit to the pseudo-second order model.The TGA/DSC curve of saturated powdered activated carbon was monitored. Thermal deadsorption profiles showded that the recovery of the regenerative adsorption capacity is mainly caused by the thermodeadsorption of pollutants, rather than decomposition. In most case the thermodeadsorption of pollutants occurred from 250 ℃ to 400 ℃, this was fitted to the experimental result of thermal regeneration.On the basis of powdered activated carbon was regeneration by. Using powdered activated carbon as adsorbent, selecting adsorbent of a countercurrent two-stage process to treat the biotreated coal tar processing wastewater, and the COD of the effluent can meet Comprehensive Discharge Standard of Water Pollutants along the Line in Shandong Section of South to North Water Diversion Project (DB37/599-2006). According to parameters from the Freundlich isotherm,the adsorptive capacity was calculated which can seek out the amount of fresh powdered activated carbon that add to the second stage adsorption.The saturated powdered activated carbon from the primary stage adsorption was regenerated by thermal regeneration at low temperature, the times of regeneration cycle was 7.The cost of per ton wastewater is 4.38 ￥RMB. |
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