Sequential Batch Reactor (SBR) Technology

Abstract The Sequencing Batch Reactor (SBR) is a widely adopted aerobic treatment technology for municipal and industrial wastewater. As a variant of the activated sludge process, SBR operates in time-sequenced steps within a single or multiple tanks. These tanks can function as either plug flow or completely mixed reactors, receiving raw wastewater (influent) at one end and discharging treated effluent at the other. In multi-tank configurations, while one tank undergoes settling and decanting, the other fills and aerates, ensuring continuous treatment. Some designs incorporate a bio-selector—comprised of a series of baffles or walls—that directs the flow in a zigzag pattern. This enhances mixing of incoming influent with returned activated sludge (RAS), initiating biological digestion early in the treatment cycle. SBR systems treat wastewater in discrete batches, including sewage and effluent from anaerobic digesters or mechanical biological treatment plants. Oxygen is introduced into the tank to stimulate microbial activity, which breaks down organic matter, measured by reductions in Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). The treated effluent is often clean enough for safe discharge into surface water bodies or, in some cases, for reuse on land. Key Words: Sequential Batch Reactor (SBR), Wastewater Treatment, Activated Sludge Process, Aerobic Treatment, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD).