Formation of manganese phosphate and manganese carbonate during long-term sorption of Mn2+ by viable Shewanella putrefaciens: effects of contact time and temperature

Abstract

The influence of temperature (5, 10, 22 and 30 °C) on the long-term (30 days) sorption of Mn²⁺ by viable Shewanella putrefaciens was studied by FTIR and EXAFS. The additional Mn-removal capacity of these bacteria was found to result from the surface precipitation of Mn-containing inorganic phases. The chemical composition of the Mn-containing precipitates is temperature and contact-time dependent. Mn(II) phosphate and Mn(II) carbonate were the two major precipitates formed in 1000 mL batches at 10, 22 and 30 °C. The ratio of Mn(II) phosphate to Mn(II) carbonate was a function of the contact time. After 30 days, MnCO₃ was the dominant phase in the precipitates at 10, 22 and 30 °C; however, MnCO₃ did not form at 5 °C. Mn(II) phosphate was the only precipitate formed at 5 °C over 30 days. The biosynthesis of Extracellular Polymeric Substances (EPS) was much greater at the lowest temperature (5 °C); however, these polymeric sugars did not contribute to the additional removal of Mn(II) under the experimental conditions. This work is one of the first reports demonstrating the ability of microbes to bioprecipitate manganese phosphate and manganese carbonate. Because of the focus on interfacial processes, this is the first report showing a molecular-level mechanism for manganese carbonate formation (in contrast to the traditionally studied aged minerals).