A wastewater treatment system 1 includes: an acid fermentation tank 2; a methane fermentation tank 3 positioned under the acid fermentation tank, and configured to produce biogas, and an upper portion of the methane fermentation tank including an opening that communicates with the acid fermentation tank; and a gas type liquid partition valve 4 provided at the opening 35, including a gas storage portion 40 configured to store a predetermined amount of the biogas and discharge the biogas exceeding the predetermined amount to the acid fermentation tank, and configured to block the opening with the biogas stored in the gas storage portion.
