Occurrence and fate of VOCs in high concentration wastewater treatment plant of coal liquefaction

This study presents the occurrance,adsorption characteristic and fate of volatile organic compounds (VOCs) in wastewater and sludges collected from high concentration wastewater treatment plant of coal liquefaction. Twenty-six VOCs were detected cumulatively by headspace coupled with gas chromatography / mass spectrometry (HS / GC / MS) in the effluent of each treatment unit. The most abundant compounds are BTEX of Benzene,Ethylbenzene,Styrene,Tolu- ene and (O / M / P)xylene etc. with total concentrations ranging from 266. 22 to 527. 45 μg / L,and the total VOCs at concentrations from 339. 28 to 562. 36 μg / L;the highest concentration pollution in all sludges from four units of sludge generated is due to Benzene or Styrene,and both the maximal adsorption to ΣVOCs and the sludge-water partitioning coefficients (Kd ) of each VOC monomer are observed in 3T activated sludge. Under the relatively stable adsorbent,the adsorption would be stronger with the increase of octanol-water partition coefficient ( lg Kow ). In the process of wastewater treatment,wastewater-following discharge is the main fate pathway for the ΣVOCs (accounted for 60. 33%of the initial loadings),followed by the sludge adsorption and volatilization / biodegradation (22. 95% and 16. 72% re- spectively). With the increase of lg Kow ,the outflow discharge removal rate of VOC monomers decreased,but a gradu- ally increase of adsorption removal was found,and a peak in removal of VOCs through volatilization / biodegradation was observed around a lg Kow value of 3. 5.