NOVELTY - The marsh gas tank comprises a tank body provided with a whole flat layer, a waterproof layer, a heat preservation layer and a thick sand layer from lower to upper, where the thick sand layer is embedded with multiple inner heat tubes. A biogas bag group comprises first methane gas unit and second methane gas unit, which are connected with the thick sand layer. The first methane gas bag unit is connected with the second methane gas unit through a pipeline. The first methane gas bag unit is provided with a sewage inlet and a first conveying pump.    USE - The marsh gas tank is useful for processing excrement sewage (claimed).    ADVANTAGE - The marsh gas tank high efficiently and rapidly process the sewage with greatly increased production efficiency in a less energy consumption and cost-effect manner.    DETAILED DESCRIPTION - The marsh gas tank comprises a tank body provided with a whole flat layer, a waterproof layer, a heat preservation layer and a thick sand layer from lower to upper, where the thick sand layer is embedded with multiple inner heat tubes. A biogas bag group comprises first methane gas unit and second methane gas unit, which are connected with the thick sand layer. The first methane gas bag unit is connected with the second methane gas unit through a pipeline. The first methane gas bag unit is provided with a sewage inlet and a first conveying pump. The second methane gas bag unit is provided with a sewage outlet that is connected with an inlet of a second conveying pump. An outlet of the second conveying pump is connected with a solid-liquid separator. The first methane gas bag unit and a top end of the second methane gas bag unit are provided with methane gas holes. The first methane gas bag unit and an inner bottom part of the second methane gas bag unit are paved with an aeration tube. The pipeline comprises first pipeline and second pipeline. An inspection well is connected with bottom ends of the first methane gas bag unit and the second methane gas bag unit through the first and second pipelines. The first pipeline extends into an end of the inspection well that is provided with a telescopic movable elbow. A water inlet and a water outlet of a heating furnace are connected with a heat tube. The water inlet of the heating furnace is connected with a methane gas hole or gas collector.