Study On Toxicity Analysis And Reduction Technology Of Key Pollutants In Coal Pyrolysis Wastewater

The composition of coal pyrolysis wastewater is very complex,the pollution load is high and the biological toxicity is strong.According to the current industrial situation,the effect of biochemical treatment is not ideal,and the growth inhibition and even mass death of microorganisms often occur when the conventional indexes are not significantly increased.In order to improve the biodegradability of wastewater,it is necessary to analyze the toxic sources and changes of wastewater.Coal pyrolysis wastewater has complex composition and large content differences.When using chromatographic analysis,there are often problems such as overlapping chromatographic peaks and large area differences,which are difficult to analyze.According to the characteristics of the main pollutants in coal pyrolysis wastewater,the pollutants were classified by trioctylamine extraction combined with macroporous resin fractional adsorption.Then the toxicity of the analyzed pollutants is evaluated by luminescent bacteria method,and the key pollutants in wastewater are determined.The results show that phenols are the most important pollutants contributing to the biological toxicity of coal pyrolysis wastewater,and p-cresol is the most toxic.The type,position and number of substituents on the benzene ring of phenolic compounds have a significant impact on biological toxicity.Heterocyclic compounds have more residues in biochemical effluent and contribute greatly to the toxicity of wastewater.Coal pyrolysis wastewater contains a variety of pollutants with strong biological toxicity,which makes the wastewater poor in biodegradability and cannot be directly biologically treated.Therefore,coal pyrolysis wastewater needs to be pretreated to reduce the biological toxicity of wastewater by digesting or recycling highly toxic pollutants.In this paper,the reduction of biological toxicity,chemical oxygen demand and key pollutant content of wastewater treated by two pretreatment processes commonly used in industry,liquid-liquid extraction and wet oxidation,are evaluated.so as to provide basic data for the improvement of pretreatment process.The results showed that the reduction rate of total phenol content in the wastewater after trioctylamine extraction is the highest,but the reduction rate of chemical oxygen demand and biological toxicity is the lowest,indicating that the complex extractant is not suitable for the treatment of complex phenol containing wastewater.The toxicity reduction rates of butyl acetate and MIBK to water samples are relatively high,96.6% and 95.1%respectively.Both of them can widely remove various key pollutants,which is suitable for the extraction treatment of pyrolysis wastewater.The mixed extraction system often has a synergistic effect.MIBK has a good extraction effect on phenolic and non-phenolic substances.Whether it is mixed with isopropyl ether or butyl acetate,the extraction effect is stronger than that of each extractant used alone.The wet oxidation process achieves the overall reduction of biological toxicity,which proves that it is technically feasible to use wet oxidation technology to treat pyrolysis wastewater.