| The sludge from chemical industrial wastewater treatment containing a large amount of toxic contaminants which migrating from wastewater, particularly toxic organic pollutants, since not been effectively cut, the hazards of these pollutants persist in the environment. Although in recent years the amount of wastewater generated in the chemical industry and wastewater treatment rate continued to increase, the environmental risks of chemical wastewater treatment sludge began get attention, people still focused on the environmental toxicity caused by heavy metals, on the study of lower concentrations but more toxic organic pollutants still remain in the investigation stage of contamination levels, and lack of understanding on the cumulative process and migration regularity during transfer from waster to sludge. All of these make it difficult to management attribute identified and disposal of sludge. So it is necessary to study the enrichment mechanism, influencing factors and distribution characteristics of organic pollutants in chemical wastewater treatment sludge during migration from waster to sludge phase.In this paper, wastewater and sludge generated from the production process of coal liquefaction, PTA and caprolactam were selected, combining with qualitative analysis and pollutant toxicity profiles, VOCs, PAHs and phenol were screened as the featured pollutants of follow-up study. The pollution level and removal effect in the wastewater treatment process, and the enrichment concentration in the sludge were analyzed, on the basic of above analysis a preliminary exploration was conducted about the regulation of sludge-water transport and transformation, the contribution of sludge adsorption in the fate analysis and the distribution of featured pollutants in each component of activated sludge.The VOCs in three kinds of chemical waste water and sludge were mainly dominated by BTEX, PAHs were mainly composed of lower molecular weight monomers of naphthalene and phenanthrene, etc.,which enrichment factor in the sludge as high as several hundred even thousand times,and showed a significant perniciousness. ΣVOCs had a limitted removal efficiency with aqueous removal rate less than 40% during whole treatment process,which even in some extent promote theproduction of some toxic contaminants such as chlorinated hydrocarbons; the aqueous phase removal rate of low molecular weight PAHs were relatively high, but with the increase of ring and molecular weight, the difficulty of its degradation also increased; a relatively higher concentration of phenol in coal liquefaction wastewater was found, although easy to cut and had a thorough removal, the highly enriched in the sludge increased its environmental risks.The adsorption capacity of three kinds of sludges was closely related to their physicochemical properties: the adsorption capacity of activated sludge on VOCs(especially BTEX) and PAHs was stronger than inorganic sludge; the VOCs adsorption capacity of aerobic sludge was stronger than anaerobic sludge, but its capacity on PAHs is less than the latter; the PAHs adsorption capacity was enhanced in mixed sludge, even beyond the purely activated sludge adsorption; the adsorption of phenol in sludge was only related to the sequence of its production process, whereas little to do with the sludge’s physicochemical properties. The sludge-water partitioning coefficients(Kd) were quite different in several featured pollutants and sludge production processes, which mainly effected by the physicochemical properties of both sludge and pollutant: in the same adsorbate, the adsorption would be stronger with the increase of the organic carbon content(Foc) and the specific surface area, whereas when the adsorbent is relatively stable, the adsorption would be stronger with the increase of octanol-water partition coefficient(log Kow).In the fate analysis of coal liquefaction wastewater, the main fate pathway of ΣVOCs was wastewater-following discharge(60.33%), with the contribution rate of volatilization and biodegradation less than 17%, although not played a leading role(22.95%), the sludge adsorption still had a higher fate contribution than previously reports; the sludge adsorption was the main fate to Σ16PAHs(51.90%), followed with the water discharge(22.17%) and chemical oxidation degradation removal(17.41%); phenol was mainly removed by the chemical degradation(95.31%), followed by volatilization and biodegradation(4.59%), whereas a small removal by water discharge and sludge adsorption, but due to the huge amount of phenol in the influent, the adsorption content of phenol in the sludge can not be ignored. Thus, it’s necessary to strengthen the management and control on the adsorption of above mentioned organic pollutants in sludge. In terms of the relationship between the Kow and each fate removal rate, with the increase of Kow, the water discharge removal of VOCs and PAHs monomers decreased, but a gradually increase of adsorption removal was found, and a peak in removal of VOCs through this pathway was seen around a log Kow value of 4.5, whereas the fate of PAHs was always dominated by sludge adsorption removal in the whole increasing process of Kow.The enriched PAHs and VOCs in the activated sludge which generated from three types of wastewater treatment were mainly distributed in the intracellular, and the adsorption on VOCs was more dominant, but solely on the PAHs, the adsorption capacity of intracellular material in aerobic sludge was slightly stronger than the anaerobic sludge; although the relative adsorption amount of EPS for PAHs was secondary, it may play an important role in the initial adsorption process, and the performance of SEPS and BEPS in the activated sludge with different physicochemical properties was also inconsistent: the PAHs adsorption capacity of SEPS which extracted from coal liquefaction 3T mixed activated sludge and PTA jet aeration sludge was stronger than BEPS, but that was opposite in the anaerobic sludge and equal in the microporous aeration sludge. As greater solubility, phenol mainly distributed in the SEPS and intracellular, but difficult to adhere on the BEPS. In addition, with related researches it also found that within a certain time, there was a tendency of pollutants in sludge transferred from outer EPS to inner cells, which provide some ideas for the activated sludge disposal. |
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