Start-up of anaerobic digestion of sulfate wastewater

During the anaerobic treatment of high sulfate content wastewater large amounts of sulfide are produced and cause unfavorable conditions. The start-up of such a digestion is often a critical step. This study provides key parameters for a proper start-up. The effect of the sludge and the influence of trace metals were investigated. Using discontinuous cultures it was shown that an addition of iron followed by a cobalt supply increased the Total Organic Carbon (TOC) - and acetate - removal rates, while an input of one metal alone remained inefficient. Nickel seemed not to be limiting. This treatment was successfully applied to Continuous Stirred Tank Reactors (CSTR). Finally, after modifying the design from a chemostat to an anaerobic contact reactor the digestion was immediately stabilized. This sudden behavior shift was unexpected. It was suggested that metal complexing agents produced by bacteria were recycled with the sludge and contributed to an increase of essential metals in the broth. (C) 1997 Elsevier Science Ltd.