挥发性有机污染土壤开挖异味风险评估及控制对策

为应对挥发性有机物(VOCs)污染土壤修复开挖过程中的异味污染问题，建立异味风险预测模型，评估其潜在风险具有重要的现实意义. 本文通过构建异味暴露概念模型，综合考虑土壤气扩散、土壤VOCs挥发、地下水溶质挥发等过程以估算污染源强释放速率，并结合高斯扩散模型模拟污染源向周边区域扩散过程，再以臭气强度作为异味表征手段，预测得到周边环境中的VOCs大气浓度及其对人体的嗅觉感官效应. 某修复地块土壤开挖面积为2 800 m2，深度3 m，涉及苯、甲苯、乙苯等9种异味物质，对其开挖过程中的异味扩散风险进行预测. 结果表明:在开挖速率为150 m3/h的情况下，VOCs快速释放并扩散至周边20 m处某居民点形成的混合气体中以氯苯、苯、乙苯、甲苯这4个组分为主，浓度分别为6.86、2.35、1.56、0.85 mg/m3. 进一步采用异味活度值(OAV)及ln(OAV)对VOCs的异味特征进行分析，识别得到乙苯为混合体系中的关键致嗅物质，故以该组分来表征VOCs的气味特性. 由此得到，居民点呼吸区VOCs对应的臭气强度为3.09，开挖过程中周边居民将明显感到臭味. 基于模型敏感性分析识别了影响异味风险的关键参数，主要为敏感目标距离(x_air)、土壤污染浓度(C_s)、土壤开挖速率(Q)、土壤空气体积比(θ_air)及大气风速(U_air)等. 从降低公众受异味影响的角度出发，提出了包括优化土壤修复工艺、控制区域土壤状况以及关注气象影响等控制对策，以期有效控制土壤中异味扩散引起的负面效应. 

Risk Assessment and Control Strategies for Odor Pollution during Excavation of VOCs-Contaminated Soils

In order to deal with the odor pollution during the excavation of VOCs-contaminated soils, the establishment of its risk predication model and the evaluation of its potential risk is of great practical significance. In this study, a conceptual model of odor exposure was developed to estimate the emission rate of pollution source, with the processes of soil gas diffusion, VOCs volatilization, and groundwater solute volatilization comprehensively considered. Combined with the Gaussian diffusion model, the diffusion process of pollution sources to the surrounding area was simulated, and then the odor intensity was used as the characterization means to predict the atmospheric concentration of VOCs in the surrounding area and its olfactory effect on human body. The risk of odor diffusion in a remediation plot was predicted during its excavation. The excavation area was 2800 m2 and the depth was 3 m. The odorous substances included 9 BTEXs such as benzene, methylbenzene and ethylbenzene. The prediction results showed that when the excavation speed was 150 m3/h, VOCs were rapidly released and diffused to the surrounding residential area at 20 m away. The main VOCs compounds were chlorobenzene, benzene, ethylbenzene, and toluene, and their contents were 6.86, 2.35, 1.56 and 0.85 mg/m3, respectively. The odor characteristics of VOCs were analyzed using odor activity value (OAV) and ln(OAV), which identified as the key odorous substance in the mixture. Therefore, ethylbenzene was chosen to represent the odor characteristics of VOCs. Accordingly, the odor intensity of the residents in the breathing area was 3.09, indicating the surrounding residents could obviously smell the odor during the excavation. Moreover, based on the model sensitivity analysis, the key parameters impacting the odor risk were identified, mainly including the sensitive target distance (x_air), soil pollution concentration (C_s), excavation speed (Q), soil air content (θ_air), and ambient air velocity (U_air). To effectively control the negative effects of the diffusion of odor in soil, from the perspective of reducing odor nuisance to the public, the study proposed several control strategies, such as the optimization of soil remediation technologies, control of regional soil conditions, and consideration of weather effect.