EFFECTS OF MAGNESIUM ON THERMOPHILIC ACETATE-DEGRADING GRANULES IN UPFLOW ANAEROBIC SLUDGE BLANKET (UASB) REACTORS

Maintenance and growth of Methanosarcinae-dominated granules under different Mg2+ concentrations (0-100 mM) were investigated in 0.2-l acetate-fed UASB reactors at 55-degrees-C. In the absence of Mg2+ in the medium, a decrease in the conversion of acetate was observed and 50% of the biomass was washed out from the reactor. Furthermore, a change in the bacterial flora occurred, giving rise to fluffy granules consisting mainly of rod-shaped methanogens. The addition of 100 mM Mg2+ caused disaggregation of Methanosarcina packets and release of a high number of single cells, corresponding to 20% of the biomass, which were washed out from the reactor. No wall growth or washout of biomass could be seen when the Mg2+ concentration was under 30 mM. An increase in the Mg2+ concentration from 0.5 to 10 mM resulted in better performance of the UASB reactor.