Environmental Water Treatment Knowledge: Meaning and Function of the Sequencing Batch Reactor (SBR) Process
Chinese definition: An activated sludge wastewater treatment method in which, within the same reaction tank (vessel), five basic processes—influent, aeration, settling, decanting, and idle—are performed in time sequence; abbreviated as the SBR process. [1]
This process is an activated sludge wastewater treatment technology that operates on intermittent aeration. [1] Its core is the SBR reaction tank, which integrates the functions of water equalization, primary sedimentation, biodegradation, and secondary sedimentation, and typically has no sludge return system. [11] The operation proceeds intermittently in time sequence; a complete operating cycle generally includes five basic stages: influent, aeration (reaction), settling, decanting (or draw), and idle. [15]
This process replaces the spatial plug flow of traditional continuous-flow processes with temporal plug flow, achieving a complete activated sludge treatment process within a single reactor. [11][15]
In 1914, the sequencing batch reactor (SBR) activated sludge process was invented by British scholars Ardern and Lockett. [1][3][12] In 1915, a similar activated sludge wastewater treatment plant was built in Milwaukee, USA. [12]
In the early 1970s, American scholar R. Irvine and others re-studied the SBR process. [10][14] In 1980, Culver, Indiana, USA built the world’s first automatically controlled SBR wastewater treatment plant. [5-6][12]
Around the 1980s, with the development of automation technology, the SBR process achieved major progress and was widely applied. In Australia, the SBR process is widely used, with more than 600 SBR wastewater treatment plants built, including a large-scale SBR plant with a daily treatment capacity of 210,000 tons. [12][14] China began researching the SBR process in the mid-1980s, with application examples in many places, such as the third wastewater treatment plant in Kunming using ICEAS technology, the Tianjin Economic-Technological Development Area wastewater treatment plant using DAT-IAT technology, the second-phase project of the Guangzhou Liede wastewater treatment plant using UNITANK technology, and the leachate treatment system of the Guangzhou Xingfeng sanitary landfill using the classic SBR process. [14]
The SBR process developed rapidly and spawned various modified processes, such as the Intermittent Cyclic Extended Aeration System (ICEAS), the Cyclic Activated Sludge System (CASS), the Demand Aeration Tank-IAT, the UNITANK unit tank activated sludge treatment system, and the Modified Sequencing Batch Reactor (MSBR). [5-6][14]
The sequencing batch reactor is an activated sludge wastewater treatment technology based on intermittent aeration; its core SBR reaction tank integrates equalization, biodegradation, and solid-liquid separation. [1][3] The SBR process offers the advantages of simple flow scheme, fewer structures, compact footprint, and lower investment and operating costs. The ideal plug-flow process increases the driving force of biochemical reactions, resulting in high treatment efficiency and good purification. It is flexible in operation and has strong resistance to shock loads. Through time control, anaerobic, anoxic, and aerobic states can alternate, achieving good nitrogen and phosphorus removal. [10-11][17][24] The sludge has good settling performance and can effectively inhibit filamentous bulking. [11][24] It is suitable for small- and medium-scale wastewater treatment, especially for intermittent discharge and situations with large flow variations. [10-11][14]
The SBR process has high requirements for automatic control. [15-16][24] Nitrogen and phosphorus removal efficiency may be limited in certain cases. [20-21][24] Variable water-level operation may increase power consumption. [16][24] The equipment idle rate is relatively high. It is not suitable for ultra-large-scale continuous influent projects. [14-15]
The SBR process, characterized by compact flow scheme, flexible operation, and good nitrogen and phosphorus removal, is widely used in multiple fields. [10-11][14]
Main application areas and suitable scenarios
The SBR process is suitable for domestic sewage from small- and medium-sized towns and industrial wastewater from factories and mines, especially where discharge is intermittent and flow varies greatly. [10-11][14] The process is also used where higher effluent quality is required, such as scenic tourist areas, lakes, and harbors, to remove organic matter and achieve nitrogen and phosphorus removal. In areas with scarce water resources, the SBR system facilitates water recycling. Where land is tight, the SBR process is applicable due to its compact layout and small footprint. The process can be used to retrofit existing continuous-flow wastewater treatment plants. It is very suitable for treating small-volume, intermittently discharged industrial wastewater and dispersed point-source pollution. [10-11][14] Depending on wastewater volume (e.g., less than 1,000 m³/day) and regional characteristics (e.g., coastal areas, hot and humid southern regions), the SBR process is also often chosen. [20-21]
In the rural domestic sewage treatment of Xinyang City, Henan Province, an integrated facility of "pretreatment + SBR + sand filter" was adopted, with a treatment scale of 3 m³/day. [18] Hejin City, Shanxi Province, adopted the SBR process at wastewater treatment stations with a daily treatment capacity greater than 500 m³; the process degrades organic matter in the wastewater through microorganisms to meet water quality requirements, with very good nitrogen and phosphorus removal and PLC fully automatic control. [19]
Application in specific wastewater treatment
The SBR process is one of the most commonly used methods in biological treatment and has been widely applied in the treatment of landfill leachate, a type of high-concentration, refractory organic wastewater. [23] In addition, in the treatment of industrial wastewater such as slaughtering, food, pharmaceutical, petroleum, and chemical industries, the SBR process is also an important method. [9][15]
The core innovation of SBR technology lies in adopting time-segmented operation to replace space-segmented operation, achieving non-steady-state biochemical reactions and ideal static settling. [11] This theoretical innovation promoted the development of subsequent improved processes, such as the continuous-influent ICEAS process, the CASS/CAST process with added biological selector, and the UNITANK system and improved MSBR process that combine the advantages of time plug flow and space plug flow. [13][22]
These derivative processes expanded the application scope of SBR technology, extending it from small- and medium-sized treatment facilities to large wastewater treatment plants. [14] In industry technology selection, SBR and its modified processes are often recommended for the treatment of domestic sewage and industrial wastewater with a volume of less than 1,000 m³/day, especially in scenarios with nitrogen and phosphorus removal needs, tight land, or large water fluctuations, due to their compact flow scheme, good nitrogen and phosphorus removal, and shock-load resistance. [20-21]
The periodic operation characteristic of the SBR process places high demands on automatic control, promoting the application and development of automatic control technology in wastewater treatment plants. [26]
The SBR process, due to its flexibility and high efficiency, has attracted widespread attention and research at home and abroad in recent years. [9] Research directions mainly focus on process energy-saving optimization control, automatic control system design, advanced nitrogen and phosphorus removal technology, and enhanced treatment processes for specific wastewater.
In process energy-saving optimization control research, the energy consumption of the blower aeration system accounts for more than 50% of the total energy consumption of the SBR process, so energy-saving optimization for the aeration stage in the aerobic phase is the focus. Research involves designing fuzzy adaptive PID controllers, fuzzy neural network controllers, etc., to achieve better energy-saving effects and operational stability. [25]
In automatic control system design and implementation, to improve the reliability and efficiency of SBR process operation, research on automatic control systems is an important direction. A fully automatic control system based on PLC and a host computer was designed and implemented, realizing automatic control of pretreatment, aeration, pH neutralization, and sludge discharge processes, improving treatment capacity and operational stability. [26]
1 SBR is suitable for wastewater treatment plants of construction scale III, IV, and V categories and medium- and small-sized wastewater treatment stations, and is suitable for the treatment of intermittently discharged industrial wastewater.
In enhanced treatment processes for specific wastewater, research studied the biological phosphorus and nitrogen removal efficiency of a two-stage SBR process for high-concentration, refractory pig farm anaerobic digestion liquor. Such research aims to improve the treatment efficiency of specific industrial or agricultural wastewater through process modification (e.g., separating the cultivation of nitrifying bacteria and phosphorus-accumulating organisms). [28]
In advanced nitrogen and phosphorus removal technology, research explored simultaneous nitrification and denitrification (SND) nitrogen removal technology within an SBR reactor. By controlling sludge age, dissolved oxygen (DO), pH, and other conditions, total nitrogen is efficiently removed within a single reactor; its denitrification mechanism involves micro-environment theory and biological theory. [27]
2 The number of SBR reaction tanks should not be less than 2.
3 The design parameters of SBR reaction tanks include cycle number, fill ratio, oxygen demand, sludge load, sludge production, sludge concentration, and sludge age.
4 When SBR aims primarily at nitrogen removal, a low sludge load and low fill ratio should be selected; when aiming primarily at phosphorus removal, a high sludge load and high fill ratio should be selected.
5 The design of SBR shall comply with the provisions of HJ 577-2010 and relevant process engineering technical specifications. [2]
