蚯蚓作用下污泥重金属形态变化及其与化学生物学性质变化的关系

城市污泥处理是一项世界性难题,污泥农业利用是其最简单有效的资源化利用方式之一,但污泥中较高的重金属含量限制了其实际推广应用,利用蚯蚓-超富集植物联合修复污泥重金属的方法已引起国内外研究者的关注。以新鲜城市脱水污泥为研究对象,接种赤子爱胜蚓(Eisenia fetida)进行室内培养试验,系统研究蚯蚓作用下污泥重金属形态的变化,及其与污泥氧化还原条件、化学和微生物性质变化的关系,以期为蚯蚓-超富集植物联合修复技术在污泥重金属处理中的应用提供理论依据。结果表明,试验前期蚯蚓在污泥中能正常生长和存活,前20 d总生物量增加了52%。蚯蚓可以显著促进污泥中的Cu、Zn、Cd、Ni等重金属从残渣态和铁锰态等稳定形态向交换态和水溶态等有效形态转化。还可以显著降低污泥中还原性物质的含量,减缓p H值下降速度,降低总有机碳含量,促进铵态氮向硝态氮转化,减少污泥微生物的数量并增加其种群活性。蚯蚓作用下,污泥中重金属的活化程度与还原性物质的含量呈显著负相关,而与微生物种群的活性呈显著正相关(P0.05)。综上所述,蚯蚓可以促进污泥重金属的活化,并改善污泥的肥力条件,为修复植物在污泥中的正常生长和对重金属离子的快速吸收提供有利条件。

Remediating effluent sludge with earthworms: changes in heavy metal speciation and associated chemical and biological properties

The disposal of effluent sludge is a difficult problem throughout the world. Agricultural utilization of sludge as resources is one option. However, high levels of heavy metals pose difficulties in the safe use of sludge. To reduce the heavy metal content of sludge, a technique combining remediation with earthworms and hyperaccumulators has been suggested to be effective and is drawing the attention of scientists in the field. Therefore, an experiment was conducted to evaluate effect of earthworms on heavy metals in sludge. In the experiment, sludge was collected from a wastewater treatment plant in Dongguan, and 400g (dry weight) fresh sludge was put in a plastic pot. The earthworm Eisenia fetida was used. Twenty healthy earthworms were added to each replicate pot. Each earthworm weighed about (0.35±0.03)g, with total earthworm weight about 7g per pot. Control pots with no earthworms were set up too. Sludge measurements were made, including heavy metal speciation, redox conditions, chemical properties, enzymatic and microbial properties. The results showed that the earthworm Eisenia fetida could survive well and grow in the sludge. By the 20^th day, the earthworm weights were approximately 0.55g each (10.66g per pot). In the treatments with earthworms, the amount of Cu, Zn, Cd, and Ni in the form of residue, organic, and Fe-Mn bound metals significantly decreased, and those in the forms of exchangeable and water soluble metals significantly increased. However, earthworms had no significant effect on the speciation of Pb and Cr. The earthworms also significantly reduced the amount of total reductive substance, active reductive substance and active organic reductive substance, but had no significant effect on the ferrous iron (Fe²⁺), free iron oxide (Fe₂O₃), amorphous iron (Fe₂O₃) and complex iron (Fe) content. The pH of sludge with earthworms (pH = 5.62) was significantly higher than that of the control group (pH = 5.20) by the 80^th day, but both groups had significantly lower pH than the original sludge (pH = 6.49). The total organic carbon and fulvic acid content were reduced by earthworms, and earthworms promoted the conversion of ammonium nitrogen to nitrate nitrogen. Metabolic quotient and catalase were significantly increased, while microbial biomass carbon, invertase, and fluorescein diacetate enzymes were significantly reduced in the earthworm treated sludge. These findings suggest that earthworms reduced the number of microorganisms in the sludge, while increasing microbial activity. With the addition of earthworms, the activation of heavy metals in sludge had a significant negative correlation with reductive substance content, but had a significant positive correlation with microbial activity. In summary, earthworms could facilitate the activation of heavy metals in sludge, and improve its fertility. Thus, addition of earthworms to sludge could provide favorable conditions for the growth of hyperaccumulators, other plants, and the uptake of heavy metals from sludge.