FINE BUBBLE AERATION AT SEDIMENT-WATER INTERFACE INHIBITS RELEASE OF HEAVY METALS IN SEDIMENT FROM A HEAVILY POLLUTED URBAN RIVER

A simulation experiment was conducted to assess the effects of fine bubble aeration at the sediment-water interface (SWI) on the fraction distributions and release patterns of heavy metals (Pb, Cu, Ni and Cr) in sediment from a heavily polluted urban river. The results showed that an increase occurred in the dissolved oxygen content and pH of the overlying water, with a significant elevation in the oxidation-reduction potential of surface sediment. Moreover, fine bubble aeration at SWI significantly altered the distributions of heavy metals fractions and resulted in lower acid-extractable metal contents, while the proportion of the residual fraction increased to varying degrees. In particular, the response of Ni fractions was sensitive to fine bubble aeration, and the proportion of residual Ni fraction increased from 39.5% before treatment to 55.0% after treatment. Aeration treatment also increased heavy metal contents in the porewater of sediment compared with the non-aeration control. However, this increase was gradually attenuated with prolonged duration of treatment. After 10 days of treatment, the heavy metal contents of sediment pore water significantly declined, especially Ni. Fine bubble aeration at SWI resulted in decreased acid-volatile sulfide (AVS), but did not necessarily increase the release of heavy metals from surface sediment. The results indicate that fine bubble aeration at SWI inhibits bioavailability and release risk of heavy metals in river sediment. This inhibition is mainly attributed to dynamic changes in the physiochemical factors of the environment, such as dissolved oxygen, pH, and oxidation-reduction potential in the overlying water and surface sediment.