城市污泥农用对土壤环境质量的影响评价

Evaluation of the effects of urban sewage sludge application in farming on the soil-environmental quality

为研究城市污泥连续农用情况下土壤环境质量存在的重金属污染风险,对河南省17个城市污水处理厂污泥样本中的重金属(Pb、Zn、Cu、Cd、Cr、Ni)质量比进行分析,利用重金属积累率推算污泥农用数年后土壤环境质量的变化,依据国家土壤环境质量二级标准评价其单项和内梅罗污染指数。结果表明,在每a施用当地城市污泥30t/hm^2的条件下,保证土壤污染等级在安全和警戒限内时,有10个点的污泥可以连续施用5 a,6个点的、污泥可以连续施用10 a,20 a后可能造成所有地市土壤被污染。研究表明,污泥连续农用土壤存在很大的Cd、Zn污染风险;要保持土壤环境二级质量标准,土壤污泥的使用年限要远小于设定的年限。

The present paper attempts to evaluate the effects of the application of urban sewage sludge in fanning in Henan on the soft environmental quality. When the sewage sludge samples were collected and tested in our experiments from the sewage treatment plants from the 17 cities in Henan, we have done a series of experiments and analyzed their contents of the heavy metals （ Pb, Zn, Cu, Cd, Cr, Ni）. It is found through careful measurements and calculation that the contents of the heavy metals in the sample soils prove the growing rate of accumulation of heavy metals, the patterns of plants, the characteristics of the soil samples as well as the change of the soil environment quality as a result of long years＇ sewage sludge＇ use in farming. When evaluating indexes of single contaminants and Nemerow pollution in accordance with the national standard for evaluating soil environmental quality, we have done observations and found some differences in assessing the heavy metal status in the farming soils by means of the Nemcrow pollution index and the single-factor pollution index, which indicates that it is better to evaluate the contamination of heavy metals by the mixed use of the comprehensive as well as the single-factor pollution indices. Our investigation results show that the contents of heavy metals in the sewage sludge prove greatly higher than that in the soil background and therefore failed to achieve the national standard in 8 cities out of 17. In addition, serious pollution hazards have also been caused by the sludge use in fanning, including exposure of the soil to overcontent of cadmium and zinc. On the condition of applying 30 t/hm^2 sewage sludge every year, the soil safety and security would reduce every 10 points every five years from pollution, 6 points attenuated for eery ten years. It can be inferred that such a tendency of soil deterioration would totally spoiled the quality of soil twenty years later if there were no protection measures to be taken. However, if the length of the application of the sludge in fanning were less than fixed and the content of heavy metals in the soil was lower than the secondary standard of soil environment quality, the pollution hazards would be less serious.