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Distribution States of Phenols and Heavy Metals from Coking Wastewater Sludge

Author: HeJingYing
Tutor: WeiChaoHai；DuCanYang
School: South China University of Technology
Course: Environmental Engineering
Keywords: coking wastewater sludge phenols heavy metals distribution states
CLC: X784
Type: Master's thesis
Year: 2011
Downloads: 81
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Abstract

With the fast development of cocking industry, the content of coking wastewater and the sewage sludge were dramatically increased. Phenols of coking wastewater are most important hazardous materials and highest amount of organic contamination, which have the toxic effects on creatures. The content of phenols is usually considered as an important index to evaluate the performance of coking wastewater system.In the previous study, people only pay attention to the concentration of phenols in aqueous phase. So far, there are no related reports, which study on the actual process of cocking wastewater treatment by combing with phenols residues in sludge. The study on the actual process of coking wastewater treatment by combing with phenols residues in sludge was not reported. In addition, the content and states distribution of heavy metals in final sludge is an important factor efftcting its reuse and safe disposal. For this scenario, the main reseaerh contents were as follows by investigating the actual coking wastewater treatment. The main research contents based on the actual cocking wastewater treatment were carried out.Firstly, by analyzing the process principle and statistics of Shaogang three-phase biofluidized bed coking wastewater treatment plant, the removal efficiency of pollutants and the pathways of sludge were studied. The operation data shows that biological fluidized bed A/O1/H/O2 combined process was efficient for removal of the organic matters in the designed condition. Up to 88.5% of COD and 99.9% of phenols was removed.Secondly, the pre-treatment and determination procedure were developed for the 11 phenols emerged both in water and sludge. The chromatographic peaks of the phenols were completely separated and the correlation coefficients were high, when the optimizing the mobile phase and gradient elution of HPLC. The recoveries of water sample were in the range of 88.1%~101.3% and sludge sample were in the range of 82.9%~101.6%. The method shows a good accuracy for sample determination. In order to know the distribution of phenolic compounds between the sludge samples and wastewater water samples, sludge production units in Shaogang coking wastewater treatment plant was selected and the analysis methods of the front was adopted. The results showed that phenol and 2, 4-Dimethylphenol were the two main phenolic compounds in raw coking wastewater, the sum of which can reflect the total quantity of the phenolic compounds in wastewater. Chorophenols were the main compounds in sludge while the proportion of phenol, methyl-phenol and nitrophenol were smaller. Combined with analysis data, we can found that the removal of phenolic compounds maily affected by the biological degradation effects instead of sludge adsorption effects, which contributive percentages was up to 99.94%.Sludge samples from the Shaogang coking wastewater treatment plant were analyzed to determine the chemical forms of heavy metals (Cd, Hg, Pb, Cr, As, Ni, Zn ,Cu and Mn) using the BCR (European Community Bureau of Reference) sequential extraction procedure. The index of geo-accumulation (Igeo) and potential ecological risk (RI) were used to evaluate their potential environmental risks to the soil environment. The results showed that the heavy metals including Cd, Hg, Pb, Cr, As, Ni, Cu and Mn were mainly existed in residual fraction, and Ni was mainly in oxidizable fraction. The concentrations of these heavy metals in the sludge were lower than the levels recorded in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002). The concentrations of Pb, Cr, Zn and Cu were lower, but the concentrations of Cd, Hg and Mn were higher as compared to those in relation to the heavy metals in the municipal sludge. The results of Igeo and RI for Cr and Hg suggested that they posed certain environmental risks, and thus concerns should be raised when considering their downstream migration. It can be concluded that the environmental risks of the sludge in the Shaogang coking wastewater treatment plant are not high because the heavy metals existed were mainly in residual fraction. Indeed, more attention should be paid on the distribution and environmental risk assessment of organic pollutants especially POPs contained in the coking wastewater sludge when selecting the methods for its disposal.

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