酸去除剩余活性污泥重金属效果及农用安全性

污水处理厂剩余污泥中的重金属是污泥农用的潜在危害之一,因此如何有效去除污泥中的重金属以保证其农用安全性是当前迫切需要解决的问题。采集污水处理厂二沉池的活性污泥,比较不同物质的量比的盐酸和硝酸(1∶2、1∶1、2∶1)浸取污泥中重金属Pb、Zn、Cd、Cu和Mn的效果,采用Tessier连续提取方法定时检测污泥重金属相态分布,分析混合酸对污泥EPS结构和质量比的影响,并检验了处理后污泥对菠菜生长及重金属富集的影响。结果表明:1)盐酸/硝酸物质的量比为2∶1时效果最佳,重金属浸出率从高到低依次为Pb、Zn、Cd、Mn、Cu;2) Pb的可交换态和碳酸盐结合态比例最高,Cu的残渣态比例最大,可交换态、碳酸盐结合态和FeMn氧化物结合态比例越大,重金属的浸出率越高;3)酸浸试验期间EPS总量减少,黏液层和LB-EPS层易脱落;最后盆栽试验表明处理后污泥中重金属的潜在迁移性风险大大减弱,且污泥对菠菜生长有明显的促进作用。因此混合酸处理后污泥可以安全用于农业种植,且污泥与土壤干重比为1∶1时效果最佳。

Approach to the heavy metal contaminants removal from the residual activated sludge by acid and its agricultural application safety

This paper aims to explore and determine a method that can effectively remove the heavy metal contaminants from the sewage treated sludge so as to ensure its agricultural use safety.For the said research purpose,we have collected the activated sludge from the secondary sedimentation tank of the sewage treating plant to compare the removal efficiency of Pb,Zn,Cd,Cu and Mn in the sludge by the mixed hydrochloric acid and nitric acid in different molar ratios( 1: 2,1: 1,2: 1). At the same time,we have also managed to detect the redistribution situation of the heavy metal contaminants by using the continuous extraction method by analyzing the effects of the mixed acid on the structure and content of EPS so as to define and examine the effects of the sludge treatment on the growth and heavy metal enrichment of the Spinach sp. The results of our experimental study demonstrate that:( 1) The removal efficiency would be the best when the molar concentration ratio of the hydrochloric acid/nitric acid is 2: 1,with the order of removal rate being Pb > Zn > Cd >Mn > Cu;( 2) The proportion of the exchangeable state and carbonate binding state of Pb would be the highest when the proportion of the residual state of Cu tends to be the greatest. The removing rate of the heavy metals tends to increase with the proportion of the exchangeable state,whereas the carbonate binding state and the Fe-Mn oxide-bound state tend also to increase;( 3)In the process of the acid leaching test,the total amount of EPS tends to decrease. However,the slime and LB-EPS layers tend to be easy to fall off,which can probably promote the release of Zn and Mn from the sludge. Thus,finally,our potted experiment has shown that the potential migration hazards of the heavy metal contaminants can be greatly released,whereas the growth of Spinach sp. can probably be promoted by the sludge obviously. It would be working best when the dry weight ratio of sludge to soil can be increased to the ratio of 1: 1. Therefore,from the point of view of availability,the sludge treated by the mixed hydrochloric acid and nitric acid can be made safely adopted for the agricultural and farming cultivation,which can be expected to have a broad application prospect.