非水相液体污染场地源区自然消除研究进展

Review on the Research Progress of Natural Source Zone Depletion in LNAPL Contaminated Sites

污染场地的健康风险和环境地质危害备受关注,自然衰减被公认是优选修复技术。对存在非水相液体的场地,源区非水相液体残余导致的“拖尾和反弹”问题对污染场地自然衰减技术提出了挑战。近年来源区自然消除技术的出现丰富深化了自然衰减修复的内涵,展现了解决“拖尾和反弹”问题的巨大潜力。本文综述了轻非水相液体(LNAPL)污染场地源区自然消除的研究历程和最新成果,研究显示:①2000年至今,自然衰减修复的相关研究逐渐从地下水污染羽衰减转向包气带源区自然消除;②包气带自然消除过程被证实是源区自然消除的关键生物过程,占LNAPL总质量损失的90%~99%;③LNAPL挥发过程中的生物降解是源区自然消除的主要研究对象。在以上研究过程中,建立的源区自然消除研究方法:①可分为LNAPL源区-羽识别、定性判断和定量估算三个部分;②包气带定量评估常用浓度梯度、二氧化碳通量(动态密闭室和静态捕集)和热力学梯度是量化评估的三类方法。综合已有的研究进展和难点,可以预见,在未来研究中,识别源区LNAPL的成分变化、明确源区自然消除的限速因子,以及开发恰当的气体脱气和气泡逃逸观测方法,是源区自然消除修复方法应用推广需解决的关键科学问题。

BACKGROUND:Human health risks and potential environmental geological hazards caused by contaminated sites have been paid much attention.Monitored natural attenuation(MNA)is recognized as a preferred remediation technique.However,for sites with non-aqueous phase liquids(NAPLs),the problem of“tailing rebound”caused by the residue of NAPLs in the source area poses a challenge to the MNA technology.In recent years,the emergence of natural source zone depletion(NSZD)enriches the connotation of MNA remediation,and it is a potential way to solve the problem of“Tailing&Rebound”.OBJECTIVES:To summarize the research process and latest achievements of NSZD for light non-aqueous phase liquid(LNAPL)contaminated sites.METHODS:A comprehensive review was conducted on the literature on NSZD for LNAPL contaminated sites from the end of the 1990’s.The conceptual models of vertical zoning natural elimination in LNAPL source areas have been reviewed.The key control factors on NSZD and main scientific and technological challenges for future research have been fully discussed.RESULTS:The research shows that:(1)since 2000,the research on MNA remediation has gradually shifted from groundwater pollution plume attenuation to natural depletion of vadose zone source areas;(2)The natural elimination process of aeration zones has proved to be the key biological process of NSZD,accounting for 90%-99% of the total mass loss of LNAPLs;(3)biodegradation in the volatilization process of LNAPL is the major research field of NSZD.The following research methods of NSZD are established:(1)the NSZD method can be divided into three parts:LNAPL source area plume identification,qualitative judgment and quantitative estimation;(2)The Concentration Gradient Method,CO_(2) Fluxes Method(including Dynamic Closed Chambers and CO_(2) Traps)and Thermal Gradient Method are three major methods for quantitative estimation.CONCLUSIONS:Based on the existing research progress and challenges,the key scientific problems to be solved in the application and promotion of NSZD include identifying the composition change of LNAPLs in the source area,clarifying the speed limiting factor for natural elimination in the source area,and developing appropriate monitoring methods for degassing and bubble escape.