Updated on January 15, 2024


Created on September 1, 2021

Anaerobic Baffled Reactor

Upcoming Update

An Anaerobic Baffled Reactor (ABR) is an upgraded version of a septic tank and consists of a series of baffles designed to treat wastewater.

Developed By Unknown
Tested By
  • Environment & Public Health Organization (ENPHO)
  • University of Kwazulu-Natal
Content Partners


Product Description

Anaerobic baffled reactors (ABR) are a sanitation technology designed to treat wastewater and fecal sludge through both physical and biological treatments. ABRs are improved versions of septic tanks where the addition of baffles in series increases contact time of wastewater and active biomass (sludge), which results in improved treatment.

The physical process includes settling. Prior to entering the ABR, the wastewater travels through a settling tank (sedimentation chamber), which removes the bulk of settleable solids. The biological treatment incorporates anaerobic digestion, which is more effective at warmer temperatures. As the wastewater travels through the baffles, the alternating upward and downward flows increases contact time between the wastewater and the residual sludge, which contains the microorganisms that anaerobically digest organic pollutants.

ABRs are relatively simple to operate and are resistant to hydraulic and organic shock loads, require no energy, have low operating costs, result in high reduction of BOD, and produce low amounts of sludge. The wastewater effluent and sludge from the ABR still require additional treatment. Therefore, ABRs are best used in combination with other treatment technologies and can be incorporated into decentralized wastewater treatment systems (DEWATS).

The price will depend on costs for local labor, local materials, and expert design.

Target SDGs

SDG 6: Clean Water and Sanitation

Target Users (Target Impact Group)

Household, Community

Distributors / Implementing Organizations

Numerous organizations work on designing and implementing ABRs, some of which include: the Sustainable Sanitation and Water Management (SSWM), seecon, Bremen Overseas Research and Development Association (BORDA), and the Environment and Public Health Organization (ENPHO).

Manufacturing/Building Method

This product is manufactured globally, typically using locally available resources and labor.

Intellectural Property Type


User Provision Model

Requires expertise in design and construction, but local technicians, NGOs, and governments have assisted in implementing ABRs.

Distributions to Date Status


Flow rate (L/min)

1.4 – 140 L/min

Power Supply Type

No power needed

Technology type

Sedimentation, Anaerobic treatment

BOD Removal Efficiency

70% to 95%

COD removal efficiency

65% to 90%

NH4-N Removal Efficiency

Can cause increase when ABR only, but when combined with additional or hybrid treatments can result in 36-44% removal

TSS removal efficiency


Total Phosphorus Removal Efficiency

Can cause increase when ABR only, but when combined with additional or hybrid treatments can result in 17-26% removal

Fecal Coliform Removal Efficiency


Design Specifications

Possible influents: blackwater, greywater, brownwater, and fecal sludge Byproducts: biogas in addition to biosolids and effluent which require additional treatment for pathogen removal. Typical inflows: 2 - 200 m3/day. Hydraulic retention time (HRT): 48 - 72 hours Upflow velocity: less than 0.6 m/hr (not to exceed 2 m/hr) Organic load should be below 3 kg COD/m3/day Number of chambers: at least 1 sedimentation chamber & between 2 to 5 upflow chambers. Chamber sizes: less than 75 cm in length and less than 60% of the total height. In order to keep upflow velocities slower, the tanks should be kept shallow but can be made wider to adapt for larger loads. Vertical pipes or baffles can be used to connect chambers. Access ports are located on top of each chamber for maintenance. Venting is required to release the buildup of gases formed as a byproduct of anaerobic digestion. Although not typically collected, biogas can be collected and used to power certain power needs like operating pumps or cooking. No electricity required. Treatment process: The process should start with a settling chamber for removal of larger solids. Wastewater flows upward through the tanks, starting at the bottom where the wastewater is forced to pass through the sludge and interact with the activated biomass. As the wastewater travels through the baffles, the alternating upward and downward flows increases contact time between the wastewater and the residual sludge, which contains the microorganisms that anaerobically digest organic pollutants. The separate compartments allow for the HRT and SRT to be decoupled, enabling the wastewater to be treated on shorter time scales (hours). Start-up period for the ABR can be long due to slow growth of the anaerobic biomass. This start-up period can be shortened by inoculating the ABR with anaerobic bacteria from fresh animal dung. Use of the ABR should be incrementally increased over months to allow for new growth of anaerobic biomass.

Product Schematics

Technical Support

Support provided by implementer or user.

Replacement Components



Generally long lasting, but depends on ABR size, number of chambers, and frequency of sludge removal.

Manufacturer Specified Performance Parameters

ABRs are designed to treat wastewaters, achieving up to 90% removal of BOD and TSS, and sludge, producing low amounts that are stabilized. ABRs have low operating costs, require no energy inputs, and are simple to operate.

Vetted Performance Status

Applicability of ABRs as solutions for handling blackwater treatment system with infiltration or effluent transport was discussed in Eawag’s Compendium of Sanitation Systems and Technologies (2nd Revised Edition). The appropriateness of anaerobic baffled reactors (ABRs) for on-site primary sanitation in low-income communities was evaluated using a pilot project testing COD removal in domestic wastewater. Results indicate that COD removal was sufficient for agricultural reuse but insufficient for discharging into surface or groundwater. The following study reports on the effectiveness of ABRs in removing organic pollutants.


Effluent and sludge must be handled with care since pathogens and nutrients are not removed. Effluent and sludge requires additional treatment.

Complementary Technical Systems

Requires water for flushing. Sludge and scum require regular removal (every 1 to 3 years). Sludge and scum removal strategy and technology including: road access for vacuum trucks (e.g. a Motorized Emptying and Transport technology) or a Human-powered Emptying and Transport Technology.

Academic Research and References

Tilley, E., Ulrich, L., Lüthi, C., Reymond, P., & Zurbrügg, C., 2014, Compendium of Sanitation Systems and Technologies (2nd Revised Edition), Swiss Federal Institute of Aquatic Science and Technology (Eawag), Duebendorf, Switzerland.

Khalekuzzaman, Md. et al., 2018, Performance comparison of uninsulated and insulated hybrid anaerobic baffled reactor (HABR) operating at warm temperature, Water Science & Technology 78(9): 1879-1892.

Foxon, K. M., Pillay, S., Lalbahadur, T., Rodda, N., Holder, F., & Buckley, C. A., 2004, The anaerobic baffled reactor (ABR): An appropriate technology for on-site sanitation, Water SA 30(5): 44–50.

Sasse, L., 1998, DEWATS: Decentralised Wastewater Treatment in Developing Countries, Bremen Overseas Research and Development Association (BORDA), Germany.

Morel, A. and Diener, S., 2006, Greywater Management in Low and Middle-Income Countries: Review of different treatment systems for households or neighbourhoods, Sandec (Water and Sanitation in Developing Countries) at Eawag (Swiss Federal Institute of Aquatic Science and Technology), Dübendorf, Switzerland.

Singh, S., Haberl, R., Moog, O., Shrestha, R. R., Shrestha, P., & Shrestha, R, 2009, Performance of an anaerobic baffled reactor and hybrid constructed wetland treating high-strength wastewater in Nepal—A model for DEWATS, Ecological Engineering 35(5): 654–660.

Bachmann, A. ; Beard, V. L. ; McCarty, P. L., 1985, Performance Characteristics of the Anaerobic Baffled Reactor, Water Research 19(1): 99-106.

Barber, W.P. ; Stuckey D.C., 1999, The use of the anaerobic baffled reactor (ABR) for wastewater treatment: A review, Water Research 33(7): 1559-1578.

BORDA, 2009, EmSan—Emergency Sanitation—An innovative & rapidly applicable solution to safeguard hygiene and health in emergency situations, Bremen Overseas Research and Development Association (BORDA) & BORDA BNS Network.

Stuckey, D. C., 2010, Anaerobic Baffled Reactor (ABR) for Wastewater Treatment, Environmental Anaerobic Technology, 163-184.

Compliance with regulations

Depends on national regulations. Can sometimes meet standards for agricultural application, but not surface water or groundwater discharge.

Evaluation methods

ABRs are primarily evaluated for removal and digestion of organic matter.

Other Information

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