Pilot-plant Design And Processing And Debugging Of Micro-pressure Internal Circulation Multiphase Bioreactor

Micro-pressure internal circulation multiphase bioreactor is a new type of bioreactor developed by Changchun Institute of Technology after twenty years of research. This bioreactor can provide anaerobic, anoxic, and aerobic environments simultaneously and features a low return sludge flow rate, improved efficiency of oxygen transfer, simultaneous phosphorus and nitrogen removal, and low energy consumption. Based on the results of previous bench tests, a pilot scale test, involving the pilot design, manufacturing, and commissioning, was conducted in order to further examine the treatment mechanism and performance of this bioreactor. The effluent from the aerated grit chamber at a municipal sewage treatment plant in Changchun was collected as the inflow to the bioreactor.Pilot process design, selection of water treatment equipment, and design of steel structure were in accordance with the Code for Design of Outdoor Water Supply Engineering, Codes for Design of Outdoor Wastewater Engineering, Water Supply and Drainage Design Handbook, and Code for Design of Steel Structures. In the design of pilot reactor, based on the parameters obtained from previous bench tests, the volume loading rate and sludge loading rate of the pilot reactor were calculated at 0.8 kgCOD/(m3·d) and 0.2 kgCOD/(kgMLSS·d), respectively. The key parameters of the pilot reactor were determined as follows: the rate of inflow Q was 300 m3/d; chemical oxygen demand(COD) of inflow was 250 mg/L; effective volume was 96 m3; mixed liquor suspended solids(MLSS) in the reaction tank was 3900 mg/L; and hydraulic retention time HRT was 9 h.The pilot plant was manufactured from Q235 structural carbon steel by skip welding and backstep welding; it was then manually brushed with glass-flake heavy anticorrosive paint. The finished reactor had a volume of 96 m3 and a seepage rate of less than 2 L/m2·d. The assembly unit deviation was 5 mm, the lateral shear deviation was 3.0 mm, and the welding gap deviation was 0.1 mm. An online monitor was installed in the reactor to record dissolved oxygen, turbidity, oxidation-reduction potential(ORP), pH and other data.During the pilot commissioning, the sludge in the reaction tank was sourced from an aeration tank at a municipal sewage treatment plant in Changchun. The COD of inflow was in the range of 90 to 130 mg/L, total phosphorus(TP) varied between 1 and 1.5 mg/L, and total nitrogen(TN) was 20-25 mg/L. In the commissioning stage, the sewage was pumped into the pilot plant continuously at a rate of 250 m3/d, with a HRT of 8 h, an aeration rate of 43 m3/h, and an initial MLSS of 3500 mg/L. A return sludge ratio of 100% and a return sludge flow rate of 12 m3/h were achieved, with a sludge age of 10 d and a daily sludge discharge of 10 m3/d. The results of water quality testing showed that the outflow from the reactor met the Standard A under Level I as specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant(GB18918-2002). The activated sludge in the reactor contained multiple biological phases, which exhibited great vitality, especially Vorticella, Rotifera and Nematode.