泥-水界面微孔曝气对底泥重金属释放潜力的影响

采用自行研发的泥-水界面精准布氧系统研究了微孔曝气对安徽省合肥市南淝河城市重污染河段底泥重金属形态分布以及释放规律的影响.结果表明,微孔曝气明显改变了泥-水界面物理化学环境,增加了上覆水溶解氧(DO)质量分数和pH值,特别是显著提高了表层底泥氧化还原电位(ORP).泥-水界面微孔曝气处理显著改变了表层底泥重金属形态分布特征,显著降低了酸提取态重金属质量分数,而残渣态重金属的质量分数比例均出现不同程度增加.特别是镍(Ni)的形态变化对微孔曝气反应更为敏感,曝气前后残渣态质量分数比例由39.5%上升到55.0%.与对照组相比,在试验初期,泥-水界面微孔曝气处理下底泥间隙水重金属质量分数有所增加,但随着处理时间延长,这种增加效应逐渐减弱,至曝气处理10d以后,底泥间隙水重金属质量分数较对照组均有明显下降,尤其Ni下降更为明显.泥-水界面微孔曝气导致表层底泥中酸可挥发性硫(AVS)减少,但并没有促进底泥中重金属的释放.泥-水界面微孔曝气对底泥重金属生物有效性和释放风险的抑制效应主要归功于上覆水和表层底泥DO质量分数、pH和ORP等理化环境的改变.

Effects of Fine Bubble Aeration on Sedimentwater Interface on Release Potential of Heavy Metals in the Sediment from a Heavily Polluted Urban River

A simulation experiment with precision oxygen distribution system with nanopore was conducted to study the effect of fine bubble aeration on sedimentwater interface on species distributions and release potential of heavy metals in the sediment sampled from Nanfei River, a seriously polluted urban river in Hefei City, Anhui Province. The results showed that the concentration of dissolved oxygen (DO) and pH in the overlying water had been significantly increased with fine bubble aeration treatment on the sedimentwater interface, and the oxidation reduction potential (ORP) of the surface sediment also increased significantly. The fine bubble aeration on sedimentwater interface significantly changed the distributions of heavy metal species. The extractable heavy metals such as acid soluble and easily reducible fractions were decreased, while residual fractions increased at different degrees depending on the type of heavy metals through fine bubble aeration. The responses of Ni species were more sensitive to the fine bubble aeration treatment. Percentage of residual fraction increased from 39.5% to 55.0% before and after the fine bubble aeration treatment. As compared with the control, the contents of heavy metals in interstitial water increased during the early stage of aeration period, but the improvement effect declined markedly with prolonged aeration duration. After the fine bubble aeration treatment for 10 d, the interstitial water showed the significantly lower contents of heavy metals relative to the control, especially for Ni. The fine bubble aeration treatment reduced the content of the acid volatile sulfide (AVS), however, which did not necessarily result in the increase in release of heavy metals in the sediment. The above results indicated that the inhibition effects on bioavailability and release of heavy metals from the sediment under fine bubble aeration are mainly attributed to changes in physiochemical environment factors such as DO, pH and ORP on sedimentwater interface.