生物淋滤法去除骨灰中重金属的研究

Study on removal of heavy metals from the ashes with bioleaching method

遗体富集了人一生中从环境中摄取的多种有毒有害物质,即使在火化后重金属仍会持续残留在骨灰中。近年来,大量骨灰的累积给我国环境带来了巨大的压力。针对高浓度重金属在骨灰中的残留问题,本文采用生物淋滤技术使骨灰中的重金属溶出,从而达到脱除重金属毒性的目的。将在酸性培养条件下从生活污泥中筛选出来的微生物菌群和不同浓度的底物S粉添加到质量浓度为20g/L的骨灰浆液中组成5个生物淋滤处理,考察了15 d振荡培养条件下,不同浓度的S0(0、2、4、6和8 g/L)对重金属Zn、Cu、Pb和Cr去除效果的影响。研究结果表明,生物淋滤法可有效去除骨灰中的重金属,S0的添加浓度能明显影响淋滤体系中的pH和氧化还原电位(ORP),进而影响各种重金属的溶出效率。在0 g/L的淋滤处理中,由于底物S0的缺乏达不到生物淋滤启动条件,重金属的去除率低于2%;随着S0浓度增加,其他4个处理中的pH值由初始5.0左右分别降至1.29、0.93、0.70和0.54,添加底物浓度越高,pH值下降越明显,ORP上升趋势也越显著,重金属的溶出效果越好。当淋滤实验结束时,S0投加量为2、4、6和8 g/L的4个处理中,Zn去除(溶出)率分别为68.4%、82.6%、89.0%和94.7%,Cu去除率分别为54.8%、80.6%、88.9%和94.2%,Pb的去除率分别为25.1%、39.4%、42.2%和43.5%,Cr的去除率分别为71.4%、93.2%、98.6%和99.5%。重金属去除率与pH的相关性分析也表明,淋滤过程中重金属的去除率受pH的影响显著。尽管增加S0的添加量可以提高重金属Zn、Cu、Pb和Cr的去除效果,但也同时降低了底物S0的生物利用率,因此,综合考虑骨灰生物淋滤过程中S0利用率和重金属的去除效果,发现4 g/L的S粉投加比例较为合适,可同时兼顾淋滤效果和运行成本。

Human remains accumulate various toxic and hazardous substances uptake from the environment during its life. Even after a human has been cremated, the heavy metals are still remained in the ashes. Therefore, the accumulation of a great amount of ashes has caused serious environmental issues in our country. The aim of this study was to investigate the effect of substrate concentration on the removal of heavy metals Zn, Cu, Pb and Cr from ashes with bioleaching method. Groups of microorganisms that would work as inoculum in this study were screened and isolated from municipal sludge by adding sulfur powder as their energy substance. Five bioleaching treatments, each containing ground ashes, inoculum, and SM culture mediums, were set up. Batch experiments were conducted over 15 days to optimize substrate （sulfur powder） concentrations of 0 g/L, 2 g/L, 4 g/L, 6 g/L and 8 g/L, respectively for the bioleaching processes. Experimental results showed the effectiveness of bioleaching method for removing heavy metals from ashes. The pH and ORP that involved in the leaching effect of heavy metals in different bioleaching treatments was significantly affected by the concentration of added substrate. For the treatment free of sulfur powder, the removing rates of all measured heavy metals were less than 20 g/L due to a futile bioleaching process, while pH decreased from the same initial value of 5.0 to 1.29, 0.93, 0.70 and 0.54, respectively for the treatments as the addition of sulfur powder at a concentrate of 2 g/L, 4 g/L, 6 g/L and 8 g/L over bioleaching process of 15 days. The higher concentrate of added substrate meant lower pH and higher ORP. Accordingly the leaching effect of heavy metals from ashes was better. When bioleaching process was finished, the removing rates of Zn were 68.4%, 82.6%, 89.0% and 94.7%, respectively for four treatments. Similarly, the removing rates of Cu were 54.8%, 80.6%, 88.9% and 94.2%, of Pb were 25.1%, 39.4%, 42.2% and 43.5%, of Cr were 71.4%, 93.2%, 98.6% and 99.5%, respectively for the four different treatments. Correlation analysis results indicated that removing rate of heavy metals was significantly correlated with pH of bioleaching system. Furthermore, the inherent characteristic and chemical speciation of various heavy metals also related to their removing rates from ashes during bioleaching process. To optimizing substrate concentration, the sulfur utilizations that declined as the increase of added sulfur powder were determinated for different treatments. The result suggested that the concentrate of 4 g/L was suitable for removing heavy metals from ashes with bioleaching method in consideration of leaching effect and capital cost of a bioleaching operation