The effect of low temperature (5-29 degrees C) and adaptation on the methanogenic activity of biomass

The influence of low temperature (5-29 degrees C) on the methanogenic activity of non-adapted digested sewage sludge and on temperature/leachate-adapted biomass was assayed by using municipal landfill leachate, intermediates of anaerobic degradation (propionate) and methane precursors (acetate, H-2/CO2) as substrates. The temperature dependence of methanogenic activity could be described by Arrhenius-derived models. However, both substrate and adaptation affected the temperature dependence. The adaptation of biomass in a leachate-fed upflow anaerobic sludge-blanket reactor at approximately 20 degrees C for 4 months resulted in a sevenfold and fivefold increase of methanogenic activity at 11 degrees C and 22 degrees C respectively. Both acetate and H-2/CO2 were methanized even at 5 degrees C. At 22 degrees C, methanogenic activities (acetate 4.8-84 mM) were 1.6-5.2 times higher than those at 11 degrees C. The half-velocity constant (K-s) of acetate utilization at 11 degrees C was one-third of that at 22 degrees C while a similar K-i was obtained at both temperatures. With propionate (1.1-5.5 mM) as substrate, methanogenic activities at 11 degrees C were half those at 22 degrees C. Furthermore, the residual concentration of the substrates was not dependent on temperature. The results suggest that the adaptation of biomass enables the achievement of a high treatment capacity in the anaerobic process even under psychrophilic conditions.