污染底泥原位覆盖中可降解有机污染物扩散解析解

Analytical solutions for degradable organic contaminant diffusion in in-situ capping of contaminated sediments

运用分离变量法,推导出了针对三层介质体系的底泥水下原位覆盖可降解有机污染物扩散解析解,该三层介质体系由上至下包括覆盖层、污染底泥和洁净底泥.运用既有的污染底泥覆盖室内试验以及已被广泛验证的CST3数值模型对所提解析解进行了验证.基于所提出的解析解,分析了覆盖层厚度、污染底泥厚度、洁净底泥厚度和污染物降解速率等参数对萘扩散过程的影响.计算结果表明:在100 a时,不施加覆盖层情况下累计萘流出质量为施加1 m厚砂质覆盖层情况下的近9倍;污染底泥越厚,则萘流出覆盖层上边界的速率越快;洁净底泥越厚,底边界条件对萘迁移的影响就越小;降解对萘迁移影响显著,不考虑降解时萘的最大流出速率为萘半衰期10 a时的3倍.

An analytical solution for the diffusion of degradable organic pollutants was derived by using the method of separation variables for in-situ capping of sediment under water in a three-layer medium system, including clean cap, contaminated sediment and uncontaminated sediment from top to bottom. The analytical solution was verified by the existing laboratory test of contaminated sediment capping and the widely validated CST3 numerical model. Based on the proposed analytical solution, the effects of the cap thickness, the thickness of contaminated sediment, the thickness of uncontaminated sediment, and the contaminant degradation rate on the diffusion process of naphthalene were analyzed. The results indicate that at the 100 a, the cumulative outflow mass of naphthalene without cap is nearly 9 times that of applying 1 m thick sandy cap;the thicker the contaminated sediment is, the faster the naphthalene flows out of the upper boundary of the cap;the thicker the uncontaminated sediment is, the less the influence of bottom boundary conditions on naphthalene transport is;the effect of degradation on naphthalene transport is significant, the maximum outflow rate of naphthalene without considering degradation is 3 times that of the naphthalene with a half-life period of 10 a.