Occurrence And Removal Characteristic Of BTEX, Anilines And Heavy Metal In Coking Wastewater During Treatment Process

Coking wastewater is a kind of typical industrial organic wastewater, whichcontains not only amounts of refractory organic contaminants such as BTEX, PAHsand PCBs but inorganic pollutants such as heavy metal, SCN^-1and CN^-1. To today,COD、NH3-N、SS and total oil are generally employed to assess the treatmenttechnology for coking wastewater. The traditional indicators are not efficient toforcast the environmental effects for the discharge of wastewater, and in fact that thecontaminants with low concentration and high toxic should be in the center of concern.These high toxic contaminants could be concentrated in organism and theircarcinogenicity-mutagenicity-teratogenicity effect is a serious threat for organism inenvironment once discharged into environment. Benzene and PAHs were listed in thenewly implemented emission control regulations. Therefore, it is crital to investigatethe removal characteristic of these high toxic contaminants in coking wastewaterduring treatment process in order to remove these contaminants more efficently.In this work, referred to the priority controlled contaminants list in our country,6BTEX,19anilines and8heavy metals were selected as typical nonpolar organic,polar organic and inorganic contaminant in coking wastewater, respectively. Twocoking wastewater treatment plants based on three phases biological fluidized bedA/O/O and A/O/H/O process, were selected as model plants. The three typicalcontaminants in water and sludge were analyzed by gas chromatography, gaschromatography-mass spectrometry and atomic adsorption spectrometry to investigatetheir removal characteristic during the treatment procedure.The content of BTEX in the coking wastewater was15.9-257μg.L^-1, andbenzene was the dominant compound. For BTEX, the proportion was similar fot thethe two investigated plants. As the representative of nonpolar organic contaminant incoking wastewater, BTEX was all effectively removed through the treatment by threephase biological fluidized bed A/O/O and A/O/H/O process. The BTEX removal ratewas higher than85%, and for some compounds of BTEX the removal rate was indeedhigher than95%. The benzene removal rate was the lowest among BTEX which were 86.5%and88.4%for the two plants. It is proved that the alkyl accelates thebiodegradation of BTEX by the higher removal rate of xylene.The removal rate ofBTEX for aerobic process was observably higher than that for anaerobic process, andthe aerobic process was the main process for BTEX removal. There were BTEX in thedischarged coking wastewater, although the concentration was much lower thanemission control regulations. According to the study, it was found that the BTEXremoval was caused by biodegradation and adsorption on sludge. Thepartition coefficients of BTEX between sludge and water were high and some of thosewere even up to2000due to the high adsorption ability of the sludge. The partitioncoefficients were well linear with the Kow of BTEX. The relativity of BTEX in waterand sludge phase was distincted revealed by the relativity investigation.The concentration of aniline was the highest one among anilines in the two rawcoking wastewater, which was up to31234μg.L^-1and59078μg.L^-1, respectively. Thedifferences of concentration and buildup of anilines in the two raw coking wastewaterproved that the coal and technics were very important for the production of anlines.As the representative of polar organic contaminant in coking wastewater, very higheven higher than99%removal rate of anlines was achieved through the treatment bythree phase biological fluidized bed A/O/O and A/O/H/O process. The dominantanilines in the discharged coking wastewater was aniline which concentration was8.56μg.L^-1and6.01μg.L^-1, respectively. It was low down to the detection limit forthe concent of anilines in sludge and it was speculated that biodegradation was themain removal way for anilines. The polar organic contaminant was much easierbiodegradated than non polar organic contaminant in coking wastewater.There are Cd、Cr、Hg、Cu、Ni、Zn、Pb and As in raw coking wastewater andwhich concentrations were0.104-81.5μg.L^-1. As the representative of inorganiccontaminant in coking wastewater, the concent of heavy metals in the dischargedcoking wastewater was much lower than that in raw coking wastewater but theremoval rates were much lower than that of BTEX and anilines, through the sametreatment by three phase biological fluidized bed A/O/O and A/O/H/O process. Theheavy metals could not be biodegradated by activated sludge, and the removal in water phase was mainly achieved by adsorption to sludge. It was found that thedistribution characteristic differed greatly for different heavy metals in the sameprocess, and the distribution characteristic for the same heavy metal in differentprocess also showed much deviation. For the two different treatment plants, notabledifferences for distribution characteristic were found for the same heavy metals.Further SPSS clustering analysis proved that the characteristic of heavy metal and thecondition of different process were the two main determinant factors for heavy metaldistribution characteristic.