重金属在氧化沟式污水处理工艺中的迁移转化

Migration and transformation of heavy metal pollutants in the sewage-oxidation treating tunnel

对焦作市污水处理厂各操作单元的污水和污泥进行了24 h连续采样,并测定了重金属元素镉、铬、砷、铅、镍、铜、锌、锰的含量、形态及去除率。结果表明,污水处理厂进水中各重金属元素总量的差别很大,其中镉质量浓度最低,锌质量浓度最高;二沉池出水中铅质量浓度最低,锌质量浓度最高。污水处理厂进水和二沉池出水中各重金属元素总量随时间变化有所波动,日变异系数在11.4%~88.9%。二沉池出水满足GB 18918—2002《城镇污水处理厂污染物排放标准》对重金属质量浓度的要求。该厂污水处理工艺对于各重金属元素总量的去除率在25.4%~99.5%,其中锰、砷和镍的去除率较低(<40%),铅、镉、铬去除率较高(>90%)。现有污水处理工艺去除的主要是以颗粒态形式存在的重金属元素,去除过程主要发生在二级处理工段,现有工艺对除铜以外的溶解态重金属没有明显的去除效果。与进水相比,二沉池出水中各重金属元素溶解态占总量的比例均有不同程度的提高。沉砂池污泥中各重金属元素质量比在(0.88±1.08)^(867.7±321.8)mg/kg,压滤污泥中各元素质量比在(2.98±2.15)^(2587±225.3)mg/kg。与沉砂池污泥相比,压滤污泥中各元素质量比更稳定。压滤污泥中重金属质量比均满足国家标准(GB 18918—2002)规定的污泥农用(碱性土壤)限值要求。

This paper is aimed to present an investigation of the migration and transformation of heavy metal pollutants in the sewage-oxi dation treating tunnel. For the research purpose, we have collected sewage and sludge samples from all the operation points of the Jiaozuo Sewage Treating Plant in a 24-hour sampling campaign and then analyzed the samples so as to make known the removal efficiency of heavy metal contents. As a result, we have found that the heavy metal contents in the untreated sewage varied greatly in such kinds of heavy metals as Cd, Cr, As, Pb, Ni, Cu, Zn, and Mn. Among them, Cadmium has been found lowest whilst the highest is that of Zn. In the effluent of the secondary sedimentation tank, Pb has been found lowest with that of Zn being the highest. In both the untreated sewage and the effluent, the content rates of all the heavy metal elements vary during the sampling periods in a given coefficient of variance （CV） between 11.4%- 88.9%. Thus, the quality of the effluent can be regarded as regular as compared to the ＂Urban sewage treatment plant pollutant discharge standard＂ （GB 18918-2002） in terms of heavy metal residues. The removal efficiency of the heavy metals from the point of view of the treatment technological standard proves varied from 25.45 % to 99.5 %. Individually speaking, the removal efficiency accounting for Mn, As, and Ni is less than 40 % from the untreated sewage, whilst that of Pb, Cr, and Cd accounts for less than 90%. The speciation analysis reveals that the removal of the heavy metal contents in particulate phase results in the major contribution to the total removal efficiency, with the main removal efficiency achieved as the result of the secondary treating process. As the treating facilities and technical conditions are concerned, it can be said that no specific removal efficiency for dissolving the heavy metal residue from the sewage, though the secondary sedimentation tank accounts for the higher rate of the said heavy metal residue from the effluent than that in the untreated sewage. Therefore, the heavy metal contents in the grit chamber sludge have been worked out at about （0.88 ± 1.08）-（867.7± 321.8） mg/kg, while those in the pressure-filter sludge were equal to （2.98 ± 2.15）-（2587 ±＋ 225.3） mg/kg. However, the heavy metal content rates in the pressure-filter sludge were fluctuating in a smaller range than that in the grit cham- ber. Thus, it can be concluded that the heavy metal content level in the pressure-filter sludge can be made to meet the national standard of sludge for farming application （for alkaline soil） with the help of the given technology of ours.