Pollution Characteristics Of Adsorbable Organic Chlorides And Chlorobenzenes In Textile Dyeing Wastewater

Textile dyeing industry is one of the major industries in China,but its output is large(about 1.9 billion tons were discharged in 2018),ranking the third in the national industrial industry.The organochlorine compounds are often used in the textile dyeing industry,or some by-products of organochlorine compounds are produced in the production process.At present,the main pollutant control targets are conventional wastewater discharge indicators,such as COD,NH₃-N,etc.However,the toxic and carcinogenic organics contained in it have not yet become the control target and need to pay attention.In view of the potential pollution hazards of organic chlorides in textile dyeing wastewater,the Pearl River Delta textile dyeing wastewater treatment plants are selected as the research object.According to the discharge standard of textile dyeing wastewater and the list of priority pollutants in China,the adsorbable organic chlorides(AOCl)and chlorobenzenes(CBs)in textile dyeing wastewater are regarded as the target pollutants.Aimed to explore the pollution level and removal characteristics of AOCl and CBs in the process of textile dyeing wastewater treatment,and to assess the ecological risk of CBs in the effluent.The main conclusions are as follows:(1)The pollution level and removal efficiency of AOCl in different units of textile dyeing wastewater treatment plants were analyzed by adsorption-pyrolysis-ion chromatography.The adsorption efficiency of aocl on four adsorption methods,namely oscillating adsorption,ultrasonic adsorption,packed activated carbon column adsorption and graphitized carbon black small column adsorption,was compared by single factor experiment.The experiment was carried out after the graphitized carbon black column with the lowest bottom chlorine value(17.7?g/L)and the most stable recovery(RSD<10%,the recovery is 87.5-113%)was determined as the adsorption method.(2)The results show that although organic chlorides are often used in textile dyeing and finishing industry,the AOCl content in the original textile dyeing wastewater is low,with an average value of 436-2130?g/L,which is far lower than that in pharmaceutical wastewater and pulp and paper wastewater.In the conventional treatment process,the total AOCl decreased,and the content of AOCl in the effluent is 310-975?g/L,which were lower than the national AOX special discharge limit(8 mg/L).Although the processes used in textile dyeing wastewater plants are different,most of the AOCl removal rates are contributed by anaerobic aerobic processes,ranging from 32.57-51.97%.After anaerobic-aerobic treatment,the AOCl value of the wastewater does not fluctuate much until it is discharged.After anaerobic aerobic treatment,the aocl value of the wastewater does not fluctuate much until it is discharged.In the subsequent treatment process,only the secondary sedimentation tank has an obvious removal effect on AOCl(17%).It was found that the concentration of AOCl in the discharge water was higher than that of the pretreatment equipment,which was due to the addition of chlorine containing disinfectant before discharge.(3)The pollution level of 12 kinds of CBs in textile dyeing wastewater treatment plants was determined by liquid-liquid extraction and gas chromatography.The pollution characteristics of CBs in textile dyeing wastewater were analyzed based on the experimental results of AOCl and the index value of total organic matter in textile dyeing wastewater.The results show that trichlorobenzene(three kinds),tetrachlorobenzene(three kinds),pentachlorobenzene and hexachlorobenzene are common in textile dyeing wastewater,and CBs only accounts for a small proportion(less than 0.5%)in AOCl due to its low concentration.The content of hexachlorobenzene in the original wastewater in the oil-water mixed state is 9.277?g/L,which is hundreds of times higher than that in the remaining original wastewater.The concentration level of CBs in other wastewater is similar,all of which are lower than 0.1?g/L,and the composition is similar.Monochlorobenzene and dichlorobenzene were not detected,which may be related to their strong volatility,biochemical characteristics and weak instrument sensitivity.(4)The removal of CBs only be found in the anaerobic system,mainly by the biodegradation of anaerobic organisms and adsorption of sludge.The aerobic system with excellent removal effect on aocl and total organic matter has no corresponding effect on CBs.Therefore,CBs did not have the same removal trend with total organic matter or AOCl.In the process of treatment,the CBs concentration increased.It is speculated that the improper selection of coagulant and process has a negative impact on the removal of CBs.Although the individual processes of the treatment plant are different,the content and composition distribution of CBs in the effluent are similar.Trichlorobenzene is the main pollutant,accounting for 38.68-39.19%of the total CBs.Because conventional wastewater treatment plants can not improve the pollution of CBs in wastewater,the content and composition of CBs in effluent are not significantly different from that in influent water.(5)The ecological risk of CBs in textile dyeing wastewater was assessed by water environmental impact degree(Amibient Severity,AS)and risk quotients(RQs).According to the assessment results of AS,the single or overall CBS will not cause serious potential harm to human health(AS<1),but the as value of the overall CBs is one order of magnitude higher than the single as value.According to the results of RQs assessment,although the concentration of CBs in the textile dyeing wastewater after conventional treatment is very low,it still poses a medium risk to the ecological environment(0.1<RQs<1).