Biotransformation of sulfate in elemental sulfur in SBBR: Effects of feed strategy, temperature and microaeration

Abstract

The objective of this work was to assess the biotransformation of sulfate into elemental sulfur in a sequencing batch biofilm reactor (SBBR) with recirculation of the liquid phase and containing immobilized biomass on polyurethane foam. The reactor was inoculated with anaerobic biomass from an upward-flow anaerobic sludge blanket (UASB) reactor and treated 2.0 L synthetic wastewater in 8-h cycles. Two feed strategies at temperatures of 30 and 15oC were assessed: (a) batch and (b) batch followed by fedbatch. In strategy (a) the reactor was fed in 10 minutes with 2 L wastewater containing sulfate and carbon sources. In strategy (b) 1.2 L wastewater containing only the sulfate source was fed during the first 10 minutes of the cycle and the remaining 0.8 L (containing only the carbon source) in 240 minutes. Two microaeration strategies were assessed for the oxidation of sulfate to elemental sulfur: a) forced aeration, by bubbling air into the liquid medium, and (b) natural aeration, by natural oxygenation of the liquid phase during recirculation between the reactor and the side reservoir. Based on the volume fed and on the concentrations of organic matter (1.5 and 11.25 gCOD/L) and sulfate (0.5 and 2.5 gSO4 2-/L), the sulfate and organic matter loading rates applied were 1.5 and 4.5 gSO4 2-/L.d and 4.5 and 13.5 gCOD/L.d. Sulfate reduction efficiencies exceeding 90% were obtained, regardless of feed strategy and temperature used. Higher organic matter removal efficiencies were obtained when reactor feeding was gradual (strategy b) at 1.5 gCOD/L/0.5 gSO4 2-/L. In this case efficiency increased from 57.4 to 71.8%, when the reactor was operated at 15 °C. At the same COD/SO4 2-ratio the efficiency of sulfate oxidation to elemental sulfur was almost 100%. © 2013 Nova Science Publishers, Inc.