This means that a biomethanation system consisting of a single BTF reactor cannot maintain a steady operation or CH 4 productivity. To overcome this shortcoming, a system of two or more BTF can be designed that undergo the vigorous nutrient supply method of flooding or flushing at alternative times. This system can be operated using a feed gas flowrate control scheme that shifts the feed gas flowrate to the reactor operating at a stable period and reduces the feed gas flowrate from the reactor that is under the transient period. Overall, the feed gas control scheme can ensure a steady conversion and outlet flowrate from the biomethanation system.