飞灰道路利用的环境风险及其时空分异特性

Environmental risk characteristics and temporal and spatial differentiation characteristics of fly ash road filling and utilization

为在综合考虑长期风化导致的污染物释放变化、区域气候条件差异、以及参数不确定性影响下,精细评估飞灰道路基材资源化利用过程对浅层地下水资源(在饮用水质量方面)潜在风险及其时空分异特性,提出了一种综合的基于风险的方法,可用于评估碱性废料(如焚烧飞灰)部分替代公路垫层材料的回收潜力.将估算源浓度的浸出试验结果与风险评估程序中通常采用的归趋-迁移模型相结合,通过实验室浸出试验模拟未风化和风化条件下的污染物释放,采用Monte Carlo方法模拟参数不确定性对风险的影响,针对不同气候特征对环境风险区域特性的影响进行评估.结果显示:在华北地区典型气候条件下,所识别的7种目标污染物中,Zn、Cd和Pb存在暴露点预测浓度超标的可能,超标概率分别为34%、96%和7%,导致其暴露浓度(以95%分位值表征)均超标,环境风险不可忽视;碳酸化作用会使得部分污染物的溶出特性发生变化,并导致长期风险的变化,具体到碳酸化后的暴露浓度,Cd呈下降趋势,Ni和Zn基本不变或变化较小,Cr、Cu、As明显增加但仍显著低于标准限值,而Pb离子暴露浓度显著增加的同时超标情况从1倍增加到3.5倍,需要引起重点关注;由于降雨等区域差异化参数的影响,不同区域之间风险差异较大,差异最大的干旱区和半干旱区暴露浓度相差近2倍;不同区域超标的共性污染物为Zn和Cd,另外,湿润/半湿润区域还存在Pb暴露浓度超标.

A comprehensive risk-based method was proposed to assess the potential risk and spatio-temporal differentiation of shallow groundwater resources(in terms of drinking water quality)in the process of recycling fly ash road base materials under the influence of comprehensive consideration of pollutant release changes caused by long-term weathering,regional climate conditions and parameter uncertainty.It could be used to evaluate the recovery potential of alkaline wastes(such as incineration fly ash)to partially replace highway cushion materials.The results of the leaching test for estimating the source concentration were combined with the fate migration model commonly used in the risk assessment procedure.The pollutant release under unweathered and weathered conditions was simulated through the laboratory leaching test.The impact of parameter uncertainty on the risk was simulated by Monte Carlo method,and the impact of different climatic characteristics on the characteristics of environmental risk areas was evaluated.The results showed that under the typical climatic conditions in North China,among the seven identified target pollutants,the predicted concentrations of Zn,Cd and Pb at the exposure points might exceed the standard,with the probability of exceeding the standard of 34%,96%and 7%respectively.As a result,their exposure concentrations(represented by 95%quantile)exceeded the standard,and the environmental risk could not be ignored;Carbonation would change the dissolution characteristics of some pollutants and led to changes in long-term risks.Specifically,with regarded to the exposure concentration after carbonation,Cd showed a downward trend,Ni and Zn remained basically unchanged or changed slightly,Cr,Cu and as increased significantly but were still significantly lower than the standard limit,while the exposure concentration of Pb ions increased significantly and the exceeding standard increased from 1 to 3.5 times,which requires special attention;Due to the influence of regional differential parameters such as rainfall,the risk difference between different regions was large,and the exposure concentration difference between the arid and semi-arid regions with the largest difference was nearly 2 times;The common pollutants exceeding the standard in different areas were Zn and Cd.In addition,there were Pb exposure concentrations exceeding the standard in humid/semi humid areas.