Study On Biodegradabiliity Of Coal Gasification Wastewater

Lurqi coal gasification craft is one of the most widely used gasification processesin the world, and it is effective to utilize the low-grade coal. However, the wastewatergenerated in gasification process is very complex and contains high level of variouspollutants, such as phenols, NH3-N etc. This kind of wastewater is difficult to deal withnormal treatment. Although the coal gasification wastewater was treated by steamstripping and solvent extraction, its COD was still not low, and its biodegradabilitywas still not good. Thus, the polish way needed to treat the biochemical effluent. Inview of this problem, the effect of coal gasification and solvent process on thepollutants and biodegradability of the wastewater was studied, then the effect ofFenton reagent chemical oxidations on the extracted wastewater was also investigated.The results showed that:1．Coal gasification wastewater extracted with solvents showed that about15%ofCOD had low distribution coefficient into solvents, even with the pH of the wastewaterchanged, and most of the non-extracted COD were non-volatile substances. Theorganic nitrogen analysis in wastewater also showed that a fraction of nitrogencontaining organics had low distribution coefficient into solvents. Finally, the threestages count-current extraction process was simulated by different solvents, andshowed that the biodegradability of the wastewater treated by different solvents wasstill not high.2. The biodegradability of the extracted wastewater was not high, hence thefenton oxidation was adopted to improve its biodegradability. The effects of Fe2+dosing quantity、H2O2dosing quantity、reaction initial pH、reaction time and reactiontemperature on wastewater treatment were studied. The optimal process conditions were: Fe2+and H2O2dosing quantity being0.5g/L and3.0g/L respectively, initial pHvalue being7, the reaction time being45minutes, reaction temperature being30centigrade, in this condition, CODcrremoval efficiency were as high as30%, andbiodegradability of the treated wastewater can be more than0.46. Then theintermediate products of phenols during fenton oxidation was ananlysed, it showed themain products were organic acids.3. Based on the principle of Gibbs free energy minimization, the coal gasificationand the second reaction of tars were simulated. The results showed that coalgasification was simulated good with the Gibbs reactor, while the the second reactionof tars was not good. The tars in the gas decreased with the increasing temperature.