某石油化工场地土层挥发性有机物的污染特征

在调查华北平原一个污染年限超过35年的石油化工场地时,采用便携式仪器土层测气方法,快速、准确地测定了场地内40多个钻孔不同深度土层中挥发性有机物(VOCs)的浓度。基于对场地地质水文地质条件的认识,以及通过对大量数据的分析对比和应用空间变异分析方法,得出了对场地土层介质中VOCs污染特征的如下认识:(1)土层VOCs浓度的垂向变化可概括为污染源淋滤型、包气带扩散污染型、地下水波动带污染型和混合污染型四种污染类型;(2)在包气带砂土层和粉土层中,VOCs的扩散规律可近似用指数模型描述;(3)包气带土层中VOCs优先积聚在渗透性强的砂性土层中,砂土层中VOCs浓度是粉土层中VOCs浓度的1.5～12倍,平均3.76倍;(4)土层VOCs浓度的水平变异性表现为包气带土层的变异性要比地下水波动带土层大,且水平变异性能在25m尺度内得到充分显示;而土层VOCs浓度的垂向变异性随地而异,变化复杂,很难用统一的一个量化尺度来表征。本文对这一典型污染场地的剖析,有助于从事污染场地调查人员认识我国华北平原石油化工类场地的污染特征,并为调查与治理类似污染场地提供技术依据。

高压旋喷注射修复技术的改进及应用

高压旋喷注射修复技术作为污染土层原位修复技术中的代表已在南京、宁波、青海等诸多工业污染土层中有所应用。但高压旋喷注射修复技术在污染土层应用时同样暴露了许多缺陷。针对其暴露的缺陷,比如作用时间短、药剂量难以控制、设备腐蚀严重等问题,进行了相应的技术改进和应用。通过将高压旋喷工艺与高压注射抽提技术相结合,利用高压旋喷工艺对中低渗透污染土层进行改造,增加了土层的渗透性和渗透范围,利用高压注射、抽提技术对污染土层进行长期注药中和,最终完成对中低渗透污染土层的长期、持续、稳定、充分的修复工作。

南方离子吸附型稀土尾矿不同土层氮污染现状的垂向特征

江西赣州地区分布着全球稀有的离子吸附型稀土矿,其开采工艺主要为原地浸矿,提取过程中主要使用硫酸铵,长期的原位浸提对当地的土壤环境造成的污染风险亟待评估。本研究以定南县原地浸矿工艺的典型离子吸附型稀土尾矿为研究对象,开展了矿区不同土层氮污染现状研究,设置了不同高程的采矿区(山顶、山腰、山脚)及附近未受浸矿干扰的山体对应深度的土柱进行对比研究,运用描述性统计、均值分析、Pearson相关性和主成分分析等方法,探索了定南原地浸矿的离子型稀土尾矿氨氮含量赋存现状,分析了定南该类稀土尾矿深层土壤氮化物污染特征。结果表明:顶子脑稀土矿山土壤Kj-N、NH+4-N和NO-3-N含量平均值分别为339.26 mg/kg、156.29 mg/kg和27.63 mg/kg,下茶坑稀土矿山土壤Kj-N、NH+4-N和NO-3-N含量平均值分别为226.42 mg/kg、100.46 mg/kg和18.20 mg/kg,两个对照区土壤Kj-N、NH+4-N和NO-3-N含量平均值为157.69 mg/kg、2.55 mg/kg和2.74 mg/kg;稀土矿山开采后山体深层土壤(4 m~12 m)中氨氮污染严重(顶子脑:744 mg/kg,下茶坑:374 mg/kg);顶子脑稀土矿山的山顶氮化物污染程度比山腰和山脚污染程度高(P<0.05),下茶坑稀土矿山山顶、山腰和山脚受氮化物污染程度近似(P>0.05);两座矿山山顶处凯氏氮与铵态氮含量之间存在显著的正相关性(P<0.01),山腰和山脚处铵态氮与硝态氮含量显著正相关性(P<0.01),两座矿山的铵态氮与土层深度之间存在显著的正相关性(P<0.01);稀土矿山中氮化物的存在形式主要是铵态氮,且铵态氮是稀土矿区判别污染的主要影响因素。

Remediation of Trichloroethylene and Monochlorobenzene-Contaminated Aquifers Using the ORC-GAC-Fe^0-CaCO_3 System: Volatilization, Precipitation, and Porosity Losses

The objectives of this study were to illustrate the reaction processes, to identify and quantify the precipitates formed, and to estimate the porosity losses in order to eliminate drawbacks during remediating monochlorobenzene （MCB） and trichloroethylene （TCE）-contaminated aquifers using the ORC-GAC-Fe^0-CaCO3 system. The system consisted of four columns （112 cm long and 10 cm in diameter） with oxygen-releasing compound （ORC）, granular activated carbon （GAC）, zero-valent iron （Fe^0）, and calcite used sequentially as the reactive media. The concentrations of MCB in the GAC column effluent and TCE in the Fe^0 column effluent were below the detection limit. However, the concentrations of MCB and TCE in the final calcite column exceeded the maximum contaminant level （MCL） under the Safe Drinking Water Act of the US Environmental Protection Agency （US EPA） that protects human health and environment. These results suggested that partitioning of MCB and TCE into the gas phase could occur, and also that transportation of volatile organic pollutants in the gas phase was important. Three main precipitates formed in the ORC-GAC-Fe^0-CaCO3 system： CaCO3 in the ORC column along with Fe（OH）2 and FeCO3 in the Fe^0 column. The total porosity losses caused by mineral precipitation corresponded to about 0.24% porosity in the ORC column, and 1% in the Fe^0 column. The most important cause of porosity losses was anaerobic corrosion of iron. The porosity losses caused by gas because of the production and entrapment of oxygen in the ORC column and hydrogen in the Fe^0 column should not be ignored. Volatilization, precipitation and porosity losses were considered to be the main drawbacks of the ORC-GAC-Fe^0-CaCO3 system in remediating the MCB and TCE-contaminated aquifers. Thus, measurements such as using a suitable oxygen-releasing compound, weakening the increase in pH using a buffer material such as soil, stimulating biodegradation rates and minimizing the plugging caused by the relatively high dissolved oxygen levels should be taken to eliminate the drawbacks and to improve the efficiency of the ORC-GAC-Fe^0-CaCO3 system.