SBR reactor

SBR reactor

Introduction to SBR Process

SBR stands for Sequential Batch Reactor Activated Sludge Process. It was originally proposed by British scholars Ardern and Lockett in 1914, but due to the easy clogging of aerators, low level of automatic control, and complex operation and management at that time, it was quickly replaced by continuous activated sludge process. Until the 1970s, with the development of various new aerators, floating effluent weirs (decanters), and hardware and software technologies for automatic control and monitoring, especially the continuous improvement of computer and industrial automation technology, automatic operation of sewage treatment processes had become possible. The SBR process, with its unique advantages, received widespread attention and rapidly developed and applied. Now, hundreds of SBR sewage treatment plants have been successfully operated in the world. The US Environmental Protection Agency (EPA) considers the SBR process to be a low investment, low operating and maintenance cost, and high-efficiency environmental remediation technology.

SBR belongs to a type of activated sludge process, and its reaction mechanism and pollutant removal mechanism are basically the same as traditional activated sludge process, except for significant differences in operation mode. It divides the process into units in chronological order, and the entire process is intermittent for a single operating unit. Typical SBR combines aeration and sedimentation in one tank, without the need for a secondary sedimentation tank or sludge return equipment. In this system, the reaction tank is filled with sewage at certain time intervals and operated in an intermittent treatment mode. After treatment, the mixed liquid is precipitated, and the supernatant is discharged with the help of specialized drainage equipment. The settled biological sludge is left in the tank for further mixing with sewage for treatment. This process is repeated in sequence, forming a batch process. A typical SBR system operates in five stages: inflow, reaction, sedimentation, drainage, and idle. The basic operating mode of typical SBR technology for wastewater treatment is shown in the following figure:

The SBR process has the following main advantages:

1. There are few structures to be treated, and an SBR reactor integrates aeration and sedimentation, eliminating the need for a primary sedimentation tank, a secondary sedimentation tank, and a return sludge pump room. Therefore, it greatly saves the floor area of processing structures, connecting pipelines between structures, and fluid transportation equipment, and can generally reduce the total project investment by 10% to 20%.

2. Due to the intermittent inflow of water during this period, the length of time and the amount of water can be adjusted, so it has strong adaptability to changes in water quantity and quality, and there is no need to set up a separate regulating tank.

3. It occupies less land, 30% -50% less than traditional activated sludge process, and is currently one of the most land saving processes among various sewage treatment processes.

4. It can remove nitrogen and phosphorus. By adjusting the aeration time and interval time, the sewage in the reaction tank is in alternating aerobic, anoxic, and anaerobic states, creating conditions for nitrogen and phosphorus removal in the process. At the same time, changes in environmental conditions can effectively inhibit the growth of filamentous bacteria and reduce the impact of sludge expansion.

When the sewage treatment plant is first built and put into operation, the flow rate is generally lower than the design value. SBR can increase or decrease the number of operating tanks according to the needs of water quantity and quality, which can avoid unnecessary energy consumption, which is not available in other processes.

The main disadvantages of SBR process are:

The inflow, aeration, and drainage processes of the reaction tank change frequently and cannot be manually managed. Therefore, high requirements are placed on the equipment and instruments of the sewage treatment plant, and management personnel are required to have a certain level of technical proficiency.

When the water volume is large, it will expose the problem of low capacity utilization.

1.2 Introduction and Comparison of SBR Improvement Process

The operation mode of SBR is flexible and adaptable. In order to meet the requirements of different water quality and practical engineering, the process can be improved. With the continuous progress of basic research and the gradual understanding of the mechanism of activated sludge removal of pollutants, in view of the certain limitations of classical SBR technology in practical engineering applications, SBR technology has gradually derived various new forms to meet the needs of practical engineering.

The currently widely used improved processes include ICEAS, UNITANK, DAT-IAT, CAST (CASS), etc.

1.2.1 ICEAS Process Principle

ICEAS, also known as Intermittent Cycle Extended Aeration, is characterized by the addition of a pre reaction zone at the inlet of the reactor. It operates in a continuous inflow mode (with continuous inflow during sedimentation and drainage periods) and intermittent drainage, without obvious reaction or idle stages. Wastewater enters the main reaction zone at a very low flow rate from the pre reaction zone, which does not have a significant impact on the separation of sludge and water in the main reaction zone. Due to its simple facilities and convenient management, especially in the treatment of municipal and industrial wastewater, ICEAS has received widespread attention both domestically and internationally, as it is more cost-effective than classical SBR systems. Since its rise in Australia in the early 1980s, over 300 sewage treatment plants have been built and put into operation.

The operation mode of ICEAS is shown in Figure 1-2:

Divide the SBR reaction tank into two parts along the length direction, with the front part being the pre reaction zone and the rear part being the main reaction zone. The pre reaction zone can regulate the water flow, while the main reaction zone is the main body for aeration and sedimentation. ICEAS is a continuous water inlet process, which not only introduces water during the reaction stage, but also during the sedimentation and decanting stages. After entering the pre reaction zone, the sewage enters the main reaction tank in a laminar flow state through the connection port at the bottom of the partition wall. Intermittent aeration and sedimentation/decanting are carried out in the main reaction tank, forming a continuous inlet and intermittent outlet SBR reaction tank, greatly simplifying water distribution and making operation more flexible.

The roles of each operating unit in the ICEAS process are:

A、 During the aeration stage, oxygen is intermittently supplied to the reaction tank by the aeration system. At this time, organic matter is oxidized by microorganisms, while ammonia nitrogen in the sewage is denitrified by microbial nitrification and denitrification, achieving the effect of nitrogen removal.

B、 At this stage of sedimentation, oxygen supply to the reaction tank is stopped, and the activated sludge descends in a static state, achieving sludge water separation.

C、 After the sludge settles to a certain depth during the decanting stage, the decanting system starts working and discharges the supernatant from the reaction tank. During the decanting process, due to the sedimentation of sludge at the bottom of the tank, the concentration is relatively high. The sludge pump can be activated as needed to discharge the remaining sludge into the sludge tank to maintain a certain concentration of activated sludge in the reactor. After the decanting process is completed, the next cycle begins with aeration, repeating the cycle to complete the treatment of wastewater.