The invention relates to the technical field of biological
fermentation engineering, and discloses a method for preparing clean biological
methane gas from duckweed residues, which comprises the following steps: fermenting anaerobic granular
sludge as an inoculant and duckweed residues as a
fermentation substrate in an anaerobic
fermentation tank to prepare
methane; the anaerobic fermentation tank comprises a tank body, a cover body and a regulation and
control unit, wherein the regulation and
control unit comprises a controller, a display screen, a
barrel, a telescopic device for driving the
barrel to lift, and a pH sensor, a
conductivity sensor and an acid and alkali liquor adding
pipe which are fixed in the
barrel; the liquid inlet end of the acid and alkali liquid adding
pipe is communicated with an acid liquid
pipe, an alkali liquid pipe and a flushing liquid pipe through a four-way valve; the telescopic device, the pH sensor, the
conductivity sensor, the four-way valve and the display screen are all electrically connected with the controller. According to the scheme, the regulation and
control unit is additionally arranged, so that the pH of the fermentation liquor is effectively and accurately regulated and controlled in real time, the pH of the fermentation liquor is ensured to be within the optimal active
pH range of methanogens, the activity of the methanogens and the
methane yield are further improved, and the production benefits are improved.