Production of Hydroxyl Radicals From Oxygenation of Simulated AMD In Presence of Extracellular Polymers Substances

Abstract

While the reaction mechanisms Fe(II) abiotic oxidation produce ·OH by CaCO3-induced in AMD are well-documented, little is known about the influence of extracellular polymeric substances (EPS) secreted by microorganisms on Fe(II) oxidation in AMD. Given the recent finding, this study experimently measured the cumulative concentrations of ·OH produced from oxygenation of simulated AMD in the presence of EPS. Results of this study show that the cumulative ·OH increased from 56.75 to 158.70 μM within 24 h at pH 3 with the increase in EPS concentration from 0 to 12 mg/L. An appropriate pH (about 6) and EPS (6 mg/L) concentration were required for the moderate rate of Fe(II) oxidation, corresponding to the maximum production of ·OH. The presence of EPS enhanced the ·OH production from Fe(II) oxidation in simulated AMD under acid conditions. In the presence of EPS, ·OH production is attributed mainly the complexation of Fe(II) with EPS, of which is rich of carboxyl and hydroxyl groups. Besides, the yield of ·OH increased remarkably with the addition of Fe3+. It is most likely that EPS can contribute to reduce Fe(Ⅲ) to Fe(II), which is beneficial to the production of ·OH. The findings reveal from this study supplement the fundamental of ·OH production from Fe(II) oxidation by microorganisms in natural AMD.