Ensiling and Fermentation of Rice Hulls With Ruminal Fluid for Medium‐Chain Carboxylate Production

ABSTRACT Large quantities of rice hulls are common at milling sites in Nigeria. They are a by‐product of rice processing and can contribute to environmental degradation if not properly managed. In this study, rice hulls were pretreated by ensiling at ambient temperature and then used as substrate for medium‐chain carboxylates (MCCs) production employing batch and semicontinuous approaches. Ensiling was carried out with (TRT) and without (CTR) the addition of molasses to improve the water‐soluble carbohydrate content of the waste biomass. After 240 days, the study showed that ensiling significantly reduced the structural carbohydrate content of rice hulls. Batch fermentation results showed a total MCC yield of 54.69 g kg −1 VS from CTR, while TRT yielded 97.79 g kg −1 VS total MCCs. A kinetic evaluation showed that the modified Gompertz model predicted the production of MCCs better than the first‐order model. During the semicontinuous fermentation, which lasted for 100 days, an increase in HRT from 2 to 3 days significantly improved the yield of MCCs, with the production of 93, 49.5, and 69 g kg −1 VS of caproate, enanthate, and caprylate, respectively.