Kinetic and process considerations on biological reduction of soluble and scarcely soluble sulfates

Discharging of sulfur compounds, which may occur in both liquid and solid phases, can cause severe environmental pollution problems. Biological sulfate removal processes are demonstrated to be suitable even for industrial effluents or industrial derived sulfate-rich solutions. In this work a culture from anaerobic treatment plant has been employed to reduce soluble sulfate (Na2SO4) and scarcely soluble sulfate (CaSO4) using propionate as carbon source. The Pr-/SO42- inlet ratio influence on the process was studied anti when a complete selection of sulfate reducing bacteria (SRB) reached a ratio value equal to the stoichiometrical one, it was registered (about 1). A removal yield higher than 98% with a hydraulic retention time of 2 days was observed. The increased selection in SRB biomass allowed a sulfate reduction rate of 0.7 kg(SO4)/m(3) per day which corresponds to a upsilon(max) of 3.2 g(SO4)/g(vss) per day and to a K-s of 24.5 mg(SO4)/l. (C) 2000 Elsevier Science B.V. All rights reserved.