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

Abstract:

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.