The influence of metal ion addition on the anaerobic treatment of high strength, soluble wastewaters

Anaerobic technology is well suited for biological wastewater treatment of industrial effluents due to its low biological sludge production and energy consumption However, problems can occur with this technology when the fina l step of the process, methanogenesis, becomes unbalanced. Due to a combina tion of their relatively slow growth rates: and more stringent growth requi rements, the methanogenetic microorganisms are more sensitive Co fluctuatio ns/deficiencies in their environment than are the other bacteria involved. Therefore, the aim of this work was to gain a better understanding of the m etal ion nutrient requirements of the methanogenic phase when heating very high strength soluble feeds. A synthetic feed based on sucrose was supplied to six continuously stirred tank (CSTR) anaerobic digesters operating at 3 5 degreesC with an hydraulic retention time (HRT) of 20 days. This feed con tained 30gCOD l(-1), requiring the methanogenic biomass to achieve acetate utilisation rates (AURs) of between 0.25 and 0.5 g.gVSS(-1) day(-1). It was found that the growth of the methanogenic population was limited by a lack of available nutrients. Growth limitation was indicated by rapid accumulat ion of high concentrations of acetate, due to a fall in acetate utilisation rates (AUR). The cause of the growth limitation was investigated in experi ments using both batch assays and continuous reactor systems. Limitations i n methanogenic activity were prevented and/or restored by the addition of a solution of metal salts into the reactors.