作 者 ：刘思辰,王莉玮,李希希,陈玉成,付茂梅
期 刊 ：植物营养与肥料学报 2014年 20卷 6期 页码：1517-1524
Keywords:biogas slurry, heavy metal, risk assessment,
摘 要 ：【目的】沼液含有丰富养分元素和生理活性物质,沼液灌溉不仅能消纳沼液,同时也可促进植物生长。但是在经济利益的驱使下,某些重金属元素由于人为的添加,不可避免地通过饲料—畜禽—粪便途径进入沼气发酵池,导致用沼液灌溉后土壤中重金属含量的超标。本文通过对不同沼气发酵规模和不同地区的沼液中重金属元素含量的分析,并对其污染风险进行评估,探索沼液灌溉的风险等级,以期为选择灌溉前对沼液的处理方法提供依据。【方法】采用文献调研与样品分析,对比分析全国部分地区户用沼气池沼液和沼气工程沼液中的重金属元素含量,收集和监测了全国部分地区户用沼气池和沼气工程近100个沼液样品的重金属含量数据,其中镉(Cd)、 铬(Cr)和铅(Pb)采用原子吸收分光光度法,砷(As)采用二乙基二硫代氨基甲酸银分光光度法,汞(Hg)采用冷原子吸收光谱法测定。采用不同风险表征指数(算术均值指数、 几何均值指数、 Nemerrow指数、 单位向量指数)评估重金属的风险等级。【结果】 1)搜集的户用沼液和沼气工程沼液中重金属数据均不符合正态分布,户用沼液中As、 Cd、 Cr、 Hg和Pb含量的中位值分别为0.312、 0.0195、 0.183、 0.025和0.330 mg/L,沼气工程沼液分别为0.110、 0.009、 0.218、 0.004和0.131 mg/L。除As外,后者平均含量明显高于前者。户用沼液中Cd、 Hg属高强度变异,As、 Cr和Pb属中度变异,而工程沼液中各重金属变异系数均属高强度变异。2)不同原料沼液重金属含量差异较大,其中猪场沼液重金属含量均高于牛场,风险相对较大。3)采用综合风险指数评价,户用沼液中Pb、 As的单位向量指数评价,属于低风险,其余重金属的各指标均小于0.2,无风险。工程沼液中Hg的算术均值指数、 几何均值指数、 Nemerrow指数、 单位向量指数均最高,按Nemerrow指数计算,工程沼液中Hg属较高风险,按均值指数和单位向量指数计算,Hg属于低风险等级。Cd的Nemerrow指数评价,属低风险,其余重金属的综合风险指数虽然随计算方法不同而变化,但其风险等级一致,均属于无风险。4)调查地区中,河南、 安徽的工程沼液中重金属的Nemerrow风险指数最大,属于较高风险,因此其沼液除了必要的物理处理外,还需利用化学方法进行处理,降低风险后才可进行灌溉;其次湖南、 浙江,属于低风险,这些地区沼液只需物理处理和简单化学处理后便可灌溉;其余地区Nemerrow风险指数评价,属于无风险等级。此外,内蒙古、 辽宁、 福建、 四川和重庆5个地区的户用沼液中重金属的Nemerrow风险指数均低于0.2,属于无风险状态,只需经过简单的物理处理便可直接进行灌溉。【结论】统计分析表明,沼液灌溉存在一定风险,主要发酵原料对沼液中重金属含量的影响较大,地域对沼液灌溉风险虽有一定影响,但南方片区与北方片区工程沼液重金属风险等级并没有显著性差异。户用沼气池沼液和沼气工程沼液中,含量相对较低的Hg、 Cd风险反而较大,建议在灌溉前通过化学方法予以去除。
Abstract:【Objectives】The biogas slurry contains abundant nutrients and physiological activators. Irrigation with biogas slurry is a cost-effective and environmental friendly way for biogas slurry disposing. However, there is always concern about the residual heavy metals brought through forage or animal feces, the contents of which sometimes exceed the up limit of standards. The risk of biogas slurry for irrigation is assessed to provide the basis for the selection of proper treatment methods. 【Methods】 One hundred samples of biogas slurry, from household marsh gas tank and biogas engineering in northern and southern parts of China were selected, the contents of total Cd, Cr and Pb are determined by atomic absorption spectrometry, Hg by cold atomic absorption spectrometry. The risk degree of heavy metal from different source of biogas slurry is evaluated using Geometric mean index, Nemerrow index and the unit vector index. 【Results】 1)The heavy metal contents from both of household marsh gas tanks and biogas engineerings are not conforming the normal distribution. The mid-value contents of As, Cd, Cr, Cu, Hg, Pb and Zn from household biogas slurry are 0.312, 0.0195, 0.183, 0.75, 0.025, 0.33 and 1.15 mg/L, respectively; from engineering biogas slurry are 0.110, 0.009, 0.218, 0.985, 0.004, 0.131 and 0.857 mg/L, respectively The average contents of the latter are higher than the former, except for As. In household biogas slurry, the Cd and Hg contents are varied strongly, As, Cr and Pb contents are less strong. All of heavy metal contents in the engineering biogas slurry are varied strongly. 2)The contents of heavy metals in the biogas slurry from different sources are different. The heavy metal contents from piggery are generally higher than from cattle farms, showing higher risk. 3)Evaluated by comprehensive risk index, the unit vector index of Pb and As in household biogas slurry is low in risk potential, and other ones are less than 0.2, indicating no risk. The Arithmetic Average Index, the Geometric Mean Index, Nemerrow Index and the Unit Vector Index of Hg in engineering biogas slurry are the highest. The content of Hg in engineering biogas slurry assessed by the Nemerrow Index is high in risk potential, however, it is low while assessed with the Arithmetic Average Index and the Unit Vector Index. The content of Cd in engineering biogas slurry assessed by the Nemerrow Index is low in risk. All the risk index values of other heavy metals are different when assessed with different methods, they are all in low degree of risk. 4)The risk of the biogas slurry among the investigated provinces is different for irrigation. The Nemerrow Index from Henan and Anhui Provinces is the highest (high risk), suggesting that physical and chemistry treatments are needed before the biogas slurry is used for irrigation. Those from Zhejiang and Hunan Provinces are low in risk, and from other provinces have no risk. In addition, the Nemerrow Indexes of the household biogas slurry form Inner Mongolia, Liaoning, Fujian, Sichuan Provinces are lower than 0.2, means only simple physical methods are needed before the biogas slurry irrigation. 【Conclusions】The heavy metal contents in the biogas slurry are mainly influenced by the sources of the raw materials. Although there are some differences in the risks of heavy metal among different areas, the difference between the northern and the southern China is not existed in the engineering biogas slurry. The Hg and Cd contents in the biogas slurry are low in concentration but still higher in risk, suggesting that they should be removed before application.
全 文 ：