Improvement of methane production from rice straw with rumen fluid pretreatment: A feasibility study

Abstract

To overcome the inherent recalcitrance of rice straw during anaerobic digestion process, effective pretreatment is required for promoting methane production. In the present study, a biological pretreatment using rumen fluid was proposed. The rice straw was pretreated with the rumen fluid at 39 °C for 120 h under anaerobic conditions. Various volatile fatty acids, especially acetic acid and propionic acid, were produced by the rumen fluid pretreatment. The methanogenic process was carried out over a 30-day anaerobic digestion. The results indicated that the optimal pretreatment time for anaerobic digestion was 24 h, resulting in a biogas production increase of 66.5%, a methane yield increase of 82.6% and a technical digestion time decrease of 40.0%, compared with the control. At the end of anaerobic digestion, degradation efficiency of total solid and volatile solid was respectively improved by 16.4–33.3% and 14.8–31.7% for rumen fluid pretreatment. The promoted methane production and organic matter degradation could be mainly attributed to the effective hydrolysis of rice straw by the mixed microorganisms in rumen fluid. Methane production could be well explained by modified Gompertz model rather than the first order model, and a higher methane production rate of 29.31 ml/(gVS·d), a rapider hydrolysis rate of 0.09 1/d, and a shorter lag phase of 1.62 d were obtained after 24 h pretreatment. Therefore, the rumen fluid pretreatment is promising for effective production of methane from rice straw and reduction of rumen fluid discharge from slaughterhouse.