Pulse water inlet mode: The most striking feature of UASB reactors at home and abroad is that many of them adopt pulse water inlet mode. Some researchers believe that pulsed water inflow can make the sediment contract and expand alternately, which is helpful to the mixing of sediment. Fig. 3a is a schematic diagram of the pulse water distributor adopted by Beijing Academy of Environmental Sciences. This system draws lessons from siphon filter's water distribution method in water supply. Single-pipe porous water distribution mode: water is distributed by opening holes in the horizontal water distribution pipe at the bottom of the reaction tank. In order to distribute water evenly, it is required that the outflow velocity is not less than 2.0m/s, which can be used in pulse water intake system. The problem of porous water distribution in one pipe is that it is easy to block. Therefore, it is necessary to avoid too many orifices in a pipeline as much as possible.
Load of water distribution orifice plate: the large area problem of water inlet service should be deeply studied. Lettinga suggested that after the start-up of UASB reactor, the load of 2.0-4.0m2 per inlet was enough to obtain satisfactory removal efficiency. However, when the temperature is below 20℃ or the load is low, the gas production rate is low, and the sludge and influent are not fully mixed, a higher density water distribution point is needed. De Man and Van der Last (1990) suggested that urban sewage 1 ~ 2 m2/ hole. Table 4 is the inlet pipe load recommended by Lettinga et al. according to a large number of practices of UASB reactors.