METHANOGENIC FERMENTATION AND GROWTH OF GRANULAR METHANOGENIC SLUDGE ON A METHANOL-PROPIONATE MIXTURE

The effect of methanol on the methanogenic fermentation of propionate and the growth of granular methanogenic sludge on a methanol-propionat e mixture was studied. Degradation of propionate was markedly inhibite d by the addition of methanol (0.5 to 8.6 g/l) to the synthetic propio nate basal wastewater. When the methanol was completely consumed by me thanol-degrading bacteria, propionate degradation was restored. Upflow anaerobic sludge blanket (UASB) reactors were operated at a volumetri c loading rate of 7.3 g propionate/l.d with and without addition of me thanol at a space velocity of 2.2 d(-1). In a run of propionate basal wastewater, a propionate removal efficiency of more than 96% could be maintained, while efficiency decreased gradually to 25% with increasin g methanol concentrations up to 8.6 g/l, giving methanol removal effic iencies of more than 85%. In all runs, granular growth of methanogenic sludge occurred successfully, and larger-sized granules were obtained on methanol-propionate mixtures rather than on propionate basal waste water. Microscopic observation and identification of corrinoid showed that Methanosarcina spp. was the predominant species of methanol-degra ding bacteria, indicating that methanol was directly converted to meth ane. The results indicated that spontaneous growth of granules occurre d on methanol-propionate mixtures and that methanol inhibition was due to the toxicity of methanol to propionate-degrading bacteria.