Activated sludge reactors are aerobic suspended-growth type processes. Large amounts of injected oxygen allow maintaining aerobic conditions and optimally mixing the active biomass with the wastewater to be treated. Activated sludge systems are highly efficient for organic matter and nutrient removal, though pathogen removal is low. In the view of reuse of the effluent in agriculture, it is not beneficial to remove all nutrients while standards for pathogen removal are barely met. The contents of this factsheet are results of the Indo-European Project NaWaTech- “Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India”, co-financed by the EC and the DST – India.
The Sequencing Batch Reactor (SBR) is a different configuration of the conventional activated sludge systems, in which the process can be operated in batches, where the different conditions are all achieved in the same reactor but at different times. The treatment consists of a cycle of five stages: fill, react, settle, draw and idle. During the reaction type, oxygen is added by an aeration system. During this phase, bacteria oxidise the organic matter just as in activated sludge systems. Thereafter, aeration is stopped to allow the sludge to settle.
In the next step, the water and the sludge are separated by decantation and the clear layer (supernatant) is discharged from the reaction chamber (ASANO et al. 2007). Depending on the rate of sludge production, some sludge may also be purged. After a phase of idle, the tank is filled with a new batch of wastewater (UNEP and MURDOCH UNIVERSITY 2004). At least two tanks are needed for the batch mode of operation as continuous influent needs to be stored during the operation phase. Small systems may apply only one tank. In this case, the influent must either be retained in a pond or continuously discharged to the bottom of the tank in order not to disturb the settling, draw and idle phases. SBRs are suited to lower flows, because the size of each tank is determined by the volume of wastewater produced during the treatment period in the other tank (UNEP and MURDOCH UNIVERSITY 2004). Pollutants removal efficiency: BOD5: 95%, COD: 90%, TSS: 95%, Pathogen: N/A.
Figure 1: Sequencing Batch Reactor. Source: Own illustration (2015)
Operation and Maintenance
Mechanical equipment, such as pumps, aerates and mixers, require continuous maintenance and control, and supply of oxygen and sludge is essential (WSP 2008). Control of concentrations of sludge and oxygen levels in the aeration tanks is required and technical appliances (e.g. pH-meter, temperature, oxygen content, etc.) need to be maintained carefully. To make sure that optimal living conditions for the required bacteria are guaranteed and a satisfying effluent quality is met, the influent as well as the effluent should be supervised and controlled constantly (e.g. by a centralised computerised monitoring system).
Construction and maintenance costs are high as activated sludge treatment units are highly mechanised. Operation costs have been usually expensive due to the requirement of permanent professional operation, high electricity consumption (pumping and aeration) and costly mechanical parts (SANIMAS 2005), but in the last years the development of cheaper and more energy efficient equipment has reduced significantly the operational cost.
Experiences in India
The following are some of the known experiences in India with regard to the use of Sequencing Batch Reactors (SBR):
- Mundhwa Sewage Treatment Plant, Pune, India. The results are yet to be available as a published source, but it is stated that the raw BOD, SS and TKN of 205, 262 and 45 mg/l are reduced to less than 10 mg/l with phosphorous being 2.3 in the inlet and 0.7 in the outlet. The raw sewage MPN Faecal coliform of 230,000/100 ml was reduced to 7,500/100 ml but was still much higher than the NRCD limitations of 1000/100 ml.
- Sewage Treatment Plant (SBR) Kalpataru Construction Overseas, Mumbai. Capacity 65 m3/day. For the Commercial and residential building at the Camlin compound in Andheri, Mumbai. Sequential Batch Reactor (SBR) was chosen because of its compact footprint and ability to achieve enhanced nutrient removal. Also the output water needed to be used for a multiple of uses – right from toilet flushing, landscaping and cooling towers.
- Magarpatta City: SBR treating 3,000 m3/d of wastewater produced by the city. The treated water is used for lake recharge and secondary uses.
- Noida City: SBR built in Noida City to treat 35,000 m3/d of wastewater corresponding to the current and the expected wastewater to be produced by some areas of the city in the next years.
Fill-and-draw batch processes similar to the SBR are not a recent development as commonly thought. Between 1914 and 1920, several full-scale fill-and draw systems were in operation. Interest in SBRs was revived in the late 1950s and early 1960s, with the development of new equipment and technology. Improvements in aeration devices and controls have allowed SBRs to successfully compete with conventional activated sludge systems.
The Sequencing Batch Reactor (SBR) process has been successfully applied to more than 1,300 plants in the U.S., Canada, and Europe within the last 25 years. In particular, the number of SBR plants in North America is growing rapidly. Many of these facilities have been constructed for small communities, producing less than 4,500 m3/d of wastewater, although larger plants (up to 870,000 in Dublin, Ireland) have used SBR technology with similar effluent quality results (TOPRAK 2005).
Further examples of the compact design of the SBR process can be found in Bangkok, Thailand (average daily flow of 200,000 m3/d and peak flow of 500,000 m3/d) utilise tanks stacked on 4 levels to achieve a treatment plant footprint of 6,000 m2.
Environmentally sound technologies in wastewater treatment for the implementation of the UNEP Global Programme of Action (GPA) "Guidance on Municipal Wastewater"
Most small wastewater treatment plants , which are based on the activated sludge or variants of the activated sludge process, are generally designed as smaller versions of large-scale plants but without primary settling facilities.GORONSZY, M.S. (1979): Intermittent Operation of the Extended Aeration Process for Small Systems. In: Research Journal of the Water Pollution Control Federation: Volume 51 , p. 274-287. URL [Accessed: 04.08.2023]
This paper represents a six month study of waste characterization and design criteria for effluent discharges from two widely different processes involved in the corn refining wet milling industry.IRVINE, R.L. DAVIS, W.B. (1971): Use of Sequencing Batch Reactors for Waste Treatments - CPC International, Corpus Christi, Texas.. Engineering Extension Series No. 140. (= Proceedings of the 26th Industrial Waste Conference, Purdue University ). West Lafayette: Anna Arbor Science Publishers URL [Accessed: 23.03.2015]
The mass of contaminants present in domestic and industrial wastewaters, in leachates, groundwaters, and in soils naturally varies with either time or space. These natural and sometimes severe variations are coupled with the uncertainties associated with direct exposure to the environment. In the face of such an unsteadystate behavior, facilities used for the removal of contaminants are often designed with the potentially unrealistic expectation that they can be operated as steady-state systems.IRVINE, R.L.,WILDERER, P.A. and FLEMMING, H.C. (1997): Controlled Unsteady State Processes and Technologies. An Overview. In: Water Science and Technology: Volume 35 Issue 1, p. 1-10. URL [Accessed: 04.08.2023] PDF
This compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.TILLEY, E., ULRICH L., LÜTHI, C., REYMOND P. and ZURBRÜGG C. (2014): Compendium of Sanitation Systems and Technologies. 2nd Revised Edition. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag) URL [Accessed: 03.05.2023] PDF
A Directory of Environmentally Sound Technologies for the Integrated Management of Solid, Liquid and Hazardous Waste for SIDS in the Caribbean Region
This directory is part of UNEP collaboration with SIDS on the implementation of the Waste Management chapter of the Barbados Programme of Action. It focuses primarily on proven sound environmental technologies for solid, liquid and hazardous waste management plus those currently successfully being used in SIDS within the Caribbean Region.UNEP (2004): A Directory of Environmentally Sound Technologies for the Integrated Management of Solid, Liquid and Hazardous Waste for SIDS in the Caribbean Region. Nairobi: United Nations Environment Programme Global Programme of Action (UNEP-GPA)) and Caribbean Environmental Health Institute (CEHI) URL [Accessed: 04.08.2023] PDF
Compendium of Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India
The Compendium of NaWaTech Technologies presents a list of solutions (appropriate water and wastewater technologies) to treat and recover water suitable to be used in urbanised areas in India. It was created with the contribution of several experts in the sector and it is intended as a reference for water professionals in charge of planning, designing, and implementing sustainable water systems in the Indian urban scenario, based on a decentralised approach. It includes design principles, operation and maintenance requirements and cost considerations.BARRETO DILLON, L., DOYLE, L., LANGERGRABER, G., SATISH, S. and POPHALI, G. (2013): Compendium of Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India. Berlin: EPUBLI GMBH. URL [Accessed: 03.05.2023] PDF