煤化工高浓有机废水处理及特征性有机污染物降解机理研究现状

Research status of coal chemical high-concentrated wastewater treatment and degradation mechanism of characteristic organic pollutants

现代煤化工是实现煤炭清洁高效利用的重要途径,但煤化工废水难以经济有效处理,主要表现为特征性有机污染物浓度高,如杂环、芳香烃、长链烷烃等难以降解,严重制约了煤化工产业的可持续发展。介绍了煤化工高浓有机废水水质特点和废水中有机物逐级去除过程,论述了煤化工废水处理技术现状,并分析了各技术的特点及存在问题。脱酚萃取剂选择要根据废水中难挥发酚含量进行技术经济分析后确定;厌氧+多级好氧及在此工艺基础上的优化改进是目前煤化工高浓度有机废水处理的常用工艺,主要利用厌氧工艺提高废水可生化性的优点;基于无二次污染及不增加废水中盐含量臭氧催化氧化技术是深度处理合适的技术选择,但催化剂的作用效果有待进一步提高。着重论述了煤化工废水中典型有机污染物如酚类、苯系物、链烷烃、多环芳烃、杂环化合物的生物降解机制。苯酚首先羟化转化成邻苯二酚,而后在无细菌作用下进行间位裂解和邻位裂解2条路径;而间苯二酚是先转化为苯三酚然后进一步开环裂解;苯的好氧降解路径较为清晰,厌氧降解途径还未明确,但苯酚和苯甲酸是苯在厌氧降解过程中的重要中间产物;长链烷烃生物降解过程主要有4种氧化方式:单末端氧化、双末端氧化、次末端氧化和直接脱氢;多环芳烃降解首先生成不同的二氢二醇,然后进一步转化为儿茶酚或龙胆酸后开环降解;含氮杂环污染物的生化降解机理为反硝化菌利用有机物作为电子供体,硝态氮中的氧作为电子受体开展代谢活动。目前对特征性有机污染物降解机制、降解中间产物研究较多,已取得一定成果,但对中间产物毒性研究以及不同降解路径反应控制方面研究较少,有待深入探究,以寻找最有利的反应条件,强化或加速有机物降解。煤化工高浓有机废水处理应强化物化预处理过程,降低对生化系统水质、水量的冲击,充分利用厌氧工艺提高可生化性,减少处理过程中反复的pH调节,减少对系统盐的增加。建议开展煤化工废水特征难降解污染物降解中间产物解析、毒性对比及不同降解路径的优化控制研究,是煤化工废水开展强化处理工作的基础。

It is an important way to realize clean and efficient utilization of coal by the advanced coal chemical engineering,but coal chemical industry wastewater is difficult to be treated economically and effectively.That is mainly manifested in the high concentration of characteristic organic pollutants,such as heterocycles,aromatic hydrocarbons,long-chain alkanes,etc,which seriously restrict the sustainable development of coal chemical industry.The water quality characteristics of high concentration coal chemical wastewater and the step-by-step removal process of organic matter in wastewater were introduced,and the research status of coal chemical wastewater treatment was discussed.The characteristics and existing problems of each technology were analyzed.The selection of Dephenol extractant should be determined after technical and economic analysis according to the content of polyhydric phenol in waste water.At present,anaerobic+multi-stage aerobic process and the optimization and improvement process based on this process are the common processes for the treatment of high concentration organic wastewater in coal chemical industry,that mainly using the advantages of anaerobic process to improve the biodegradability of wastewater.Ozone catalytic oxidation technology based on no secondary pollution and no increase of salt content in waste water is a suitable choice for advanced treatment,but the effect of catalyst needs to be further improved.The biodegradation mechanism of typical organic pollutants such as phenols,benzene series,alkanes,polycyclic aromatic hydrocarbons and heterocyclic compounds in coal chemical wastewater was discussed emphatically.For example,phenol is first hydroxylated and transformed into catechol,and then metalytic and ortho cleavage can be carried out without bacteria.Resorcinol is first converted to pyrogallol and then further split in ring opening.The aerobic degradation pathway of benzene is relatively clear,however the anaerobic degradation pathway is not clear,but phenol and benzoic acid are important intermediate products in the anaerobic degradation process of benzene.There are four main oxidation ways of long-chain alkane biodegradation:single end oxidation,double end oxidation,secondary end oxidation and direct dehydrogenation.Firstly,different dihydrodiols are formed in PAHs degradation,which are further converted into catechol or gentianic acid for ring opening degradation.The biochemical degradation mechanism of nitrogen-containing heterocyclic pollutants is that denitrifying bacteria use organic matter as electron donor and oxygen in nitrate nitrogen as electron acceptor to carry out metabolic activities.At present,there are many researches on the degradation mechanism of characteristic organic pollutants and the analysis of degradation intermediates,and some achievements have been made.However,there are few researches on the toxicity of intermediates and the control of reaction in different degradation paths,which need to be further explored to find the most favorable reaction conditions and strengthen or accelerate the degradation of organic pollutants.The treatment of high concentration organic wastewater from coal chemical industry should strengthen the physicochemical pretreatment process,reduce the impact on water quality and quantity of biochemical system and make full use of anaerobic process to improve biodegradability,as well as reduce repeated pH regulation in the process of treatment,reduce the increase of salt in the system.It is also suggested to carry out the study on the analysis of the intermediate products,toxicity comparison and optimal control of different degradation paths of the characteristic refractory pollutants in coal chemical wastewater,which is the basis of strengthening the treatment of the coal chemical wastewater.