Influence of particle size and pH on anaerobic degradation of cellulose by ruminal microbes

Batch experiments were performed to investigate the influence of cellulose particle size and pH on the anaerobic degradation of crystalline cellulose by ruminal microbes. At a particle size of 50 μm there was a higher hydrolysis and acidogenesis rate, and a reduced degradation time, than for 100-μm particles. Reduction in cellulose particle size resulted in decreased methane production, but an increase of soluble products. Cellulose degradation increased with pH from pH 6.0 to 7.5, whereas at pH⩽5.5 there was no degradation. The inhibitory effect of low pH (⩽5.5) on ruminal microbes was not completely remedied even when the pH of the medium was adjusted to a neutral range. In an anaerobic cellulosic waste degrading system inoculated with ruminal microbes the fermentation system should therefore be maintained above pH 6.0. In all cases, volatile fatty acids were the major water-soluble products of cellulose degradation; acetate and propionate accounted for more than 90% of the volatile fatty acid total.