Sequential biological reactor technology is an optimized variant of conventional activated sludge technology. It is based on the use of a single reactor that works in a sequential discontinuous manner. The sequential biological reactor system, SBR, consists of at least four cyclical processes: filling, aeration, anoxia, decanting, and emptying, both of the effluent and of the sludge.

This technology is capable of tolerating load and flow variations and produces stabilized sludge as a product, and is sometimes the most suitable technology for the industry. The investment costs are lower, since they do not require the typical secondary decanters.

An SBR requires much less space than conventional systems such as activated sludge, in addition to being able to reach significant heights in the reactors, favoring the transfer of oxygen as a consequence of the elevation of the water column with the configuration of the biological reactor.