History of mainstream wastewater treatment technology

(1.1) Development of SBR method

As an improvement of the traditional activated sludge process, the SBR process has a wide application prospect. SBR method is short for sequencing batch batch activated sludge method (also known as sequencing batch reactor), it is currently widely valued at home and abroad, research and application of a sewage biological treatment technology, especially with the development of advanced automatic control technology, the automatic management of sewage treatment plant greatly improved. It provides more favorable conditions for the popularization and application of SBR activated sludge process.

In the design and operation of SBR process, according to different water quality conditions, use occasions and effluent requirements, there have been many new changes and developments, and many variations have been produced. Compared with traditional SBR, ICEAS has an additional pre-reaction zone, continuous water intake and intermittent drainage, but the water quality of ICEAS is limited because the water intake affects the separation of mud and water during the precipitation period. The DAT-IAT process overcomes the shortcomings of ICEAS by changing the pre-reaction area into a pre-aeration tank DAT separate from the SBR reaction tank IAT. DAT is continuously injected and aerated, and the main batch reactor IAT is not affected by the influent during the precipitation stage and the reflux from IAT to DAT is increased. However, DAT-IAT can not achieve good results in the treatment of sewage containing biodegradable organic matter, while CASS process overcomes this shortcoming, innovates the pre-reaction zone of ICEAS into a small volume, more optimized and reasonable design of biological selector, and returns part of the residual sludge in the main reaction zone to the selector, so as to make the system more stable. It also has good nitrogen and phosphorus removal effect. IDEA is also a development of CASS, which mainly changes the biological selector into a premix pool separate from the main SBR structure. However, the above processes can only achieve continuous water intake and intermittent drainage. In order to overcome the shortcomings of intermittent drainage, UNITANK process integrates the advantages of SBR and three-ditch oxidation ditch, and the integrated design enables continuous water intake and continuous water discharge and automatic sludge reflux, which eliminates the need for sludge reflux equipment compared with CASS. However, the UNITANK process still has shortcomings such as low sludge concentration in the middle ditch and over-reliance on instrumentation. For example, once the inlet valve is damaged, the whole system will not work. In order to overcome the shortcomings of UNTANK process, a new SBR system MSBR has been developed. In essence, it is A/A/O process and SBR system in series, using a single pool multi-cell way, eliminating many valves and meters, increasing the sludge reflux and ensuring a high sludge concentration, has a good nitrogen and phosphorus removal effect. In recent years, many other SBR systems have also been studied deeply, such as anaerobic SBR, multistage SBR, etc., and have achieved good results. With the continuous progress of technology and in-depth research, more SBR modification processes will appear.

(1.2) Development of oxidation ditch

Oxidation ditch is a modification of activated sludge method, and its aeration tank is a closed ditch type, in which the mixed liquid of sewage and activated sludge is constantly circulating, so it is also called "ring aeration tank" and "non-terminal aeration system". The improvement and development of oxidation ditch process form is inseparable from the development and research of aeration equipment. In the late 1960s, DHV company in the Netherlands applied the vertical low-speed surface aerator to the oxidation ditch process, installed it at the end of the oxidation ditch center partition wall, and used the stirring driving force generated by it to circulate the water and increase the effective water depth of the oxidation ditch to 4.5m, which is the Carrousel oxidation ditch process, almost at the same time. Lecmple and Mandt applied the underwater aeration and push system to the oxidation ditch process for the first time, and developed the jet aeration oxidation ditch process, so that the effective water depth and width of the oxidation ditch are independent of each other, and its depth can reach 7~8m. In 1970, South Africa developed the turntable aerator and the Orbal oxidation ditch process appeared. In recent years, the Dutch DHV company has launched a two-layer turbine vertical aerator, and the German Passavant company has developed a fiberglass reinforced rotary brush blade with strong corrosion resistance, high strength and small weight. USFilter Envirex has developed a vertical circulation flow reactor (VLR) oxidation ditch process that combines aeration spinning dish (pushing water flow) and crude bubble aeration.

(1.3) Development of AB method

AB process is short for adsorption/biodegradation process. This sewage biological treatment technology was developed by Professor BothoBohnke of RWTH Aachen University in Germany in order to solve the problems of the removal of refractory organic matter, low efficiency of nitrogen and phosphorus removal and high investment and operating costs in the traditional two-stage biological treatment system, based on a large number of studies on the two-stage activated sludge method and high-load activated sludge method. A new biological wastewater treatment process developed in the mid-1970s and applied to engineering practice in the 1980s.