The primary system mainly adopts physicochemical treatment method, which can be used as the pre-treatment stage of wastewater. Some of the processes are parallel operation, and processes can be selected according to different water quality, including mechanical flocculation tank, sedimentation, air flotation and other processes. The secondary system adopts the mainstream biological treatment process, with anaerobic aerobic treatment as the core, including UASB, MBR, SBR, BAF, oxidation ditch, A2O, etc., which can be used to treat domestic sewage, high concentration organic wastewater, high ammonia nitrogen wastewater, etc. typical applications include small-scale treatment and research of oil wastewater, beer wastewater, garbage percolate, tannery wastewater, etc. As the advanced treatment stage, the three-stage system is also the treatment system for reclaimed water reuse. For the further treatment of the secondary effluent, the physicochemical method is adopted. The quartz sand filtration and activated carbon adsorption can be operated in series or in parallel; and a membrane separation unit is set, including microfiltration, ultrafiltration, reverse osmosis, etc., which can remove colloids, insoluble organic matters, salts, etc. the effluent can be Sampling research or reuse.