Assessment of compatible solutes to overcome salinity stress in thermophilic (55¡C) methanol-fed sulfate reducing granular sludges

Abstract

High NaCl concentrations (25 g.L^-1) considerably decreased the methanol depletion rates for sludges harvested from two lab-scale sulfate reducing UASB reactors. In addition, 25 gNaCl.L^-1 strongly affected the fate of methanol degradation, with clear increase in the acetate production at the expense of sulfide and methane production. The addition of different osmoprotectants, viz. glutamate, betaine, ectoine, choline, a mixture of compatible solutes and K⁺ and Mg²⁺, slightly increased methanol depletion rates for UASB reactors sludges. However, the acceleration in the methanol uptake rate favored the homoacetogenic bacteria, as the methanol breakdown was steered to the formation of acetate without increasing sulfate reduction and methane production rates. Thus, the compatible solutes used in this work were not effective as osmoprotectants to alleviate the acute NaCl toxicity on sulfate reducing granular sludges developed in methanol degrading thermophilic (55°C) UASB reactors.