Wastewater treatment has been a challenge throughout the years due to varying inﬂuent chemical and physical characteristics and stringent efﬂuent regulations. Treatment systems using activated sludge have been able to handle many of these difﬁculties. Given the lack of on-line computer controls, continuous ﬂow systems have been mostly used for these purposes versus sequencing batch processes. The advancements in the ﬁeld of automation has now made the option of a SBR process more attractive thus providing better controls and results in wastewater treatment. This is coupled by the ﬂexibility of a SBR in the treatment of variable ﬂows, minimum operator interaction required, option for anoxic or anaerobic conditions in the same tank, good oxygen contact with microorganisms and substrate, small ﬂoor space, and good removal efﬁciency.
Conventional activated sludge systems require separate tanks for the unit processes of biological reactions (aeration of mixed liquor) and solids-liquid separation (clariﬁcation) and also require process mixed liquor solids (return activated sludge) to be returned from the ﬁnal clariﬁcation stage to the aeration tanks. In contrast to this GWT designs timer based Sequential Batch Reactors (SBR systems) in which all phases of the treatment process occur sequentially within the same tank.
Sequencing batch reactors operate by a cycle of periods consisting of ﬁll, react, settle, decant, and idle. The duration, oxygen concentration, and mixing in these periods could be altered according to the needs of the particular treatment plant. Appropriate aeration and decanting is essential for the correct operations of these plants. The aerator should make the oxygen readily available to the microorganisms. The decanter should avoid the intake of ﬂoating matter from the tank.