The effect of bentonite-bound oil on thermophilic anaerobic digestion of cattle manure was investigated. In digestor experiments, addition of oil was found to be inhibitory during start-up and the inhibitory effect was less pronounced when the oil was added in the form of bentonite-bound oil compared to when the oil was added alone. After adaption of the digestors, very rapid degradation of oil was observed and more than 80 of the oil was degraded within a few hours after daily feeding. In batch experiments, glyceride trioleate was found to be inhibitory to thermophilic anaerobic digestion when the concentrations were higher than 2.0 g/l. However, addition of bentonite (a clay mineral) at concentrations of 0.15 and 0.45 was found to partly overcome this inhibition. Addition of calcium chloride in concentration of 3 mM(0.033 w/v) showed a similar positive effect on the utilization of oil, but the effect was lower than with bentonite.
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