TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The bio-gas plant further comprises a gas transfer line for transferring biogas in a biogas demand source, and collecting biogas from the anaerobic fermentor, the fermentation liquid conveying tank, and the flow rate adjustment tank, a hot water supply unit for supplying hot water to heat the anaerobic fermentor, the fermentation liquid conveying tank, and the flow rate adjustment tank, and hot water is heated using heat generated from the biogas demand source, a ground water supply unit for supplying hot ground to cool the anaerobic fermentor, the fermentation liquid conveying tank, and the flow rate adjustment tank, a fermentation liquid finishing bath for generating manure by aeration, and supplying the fermentation broth into the double jacket pipe from the fermentation liquid conveying tank, a liquid manure storage tank to store the produced manure, a solid-liquid separator for separating liquid water and solid, provided between the fermentation liquid finishing bath and the liquid manure storage tank, a level sensor for detecting output signal by measuring inner level of the anaerobic fermentor, a first valve for controlling flow of the raw water in the anaerobic fermentor from the flow rate adjusting tank, a controller for controlling the first valve according to detect signal of the level sensor, and a carrier pump for flushing of the conveying pipe, provided on the conveying pipe, and increasing amount of conveying fermentation broth via the conveying pipe from the fermentation liquid conveying tank by controlling the conveying pump or the second valve during falling temperature in the flow rate adjusting tank and the anaerobic fermentor. The anaerobic fermentor is supplied with the hot air from the mechanical room in order to compensate the heat loss of gas bubble during winter ambient temperature within the specified temperature. The anaerobic fermentor is connected in series with a single-stage anaerobic fermentor and double-stage anaerobic fermentor.