Background Research

Anaerobic Baffled Reactor

What is ABR?

An Anaerobic Baffled Reactor (ABR) is a variation of a septic tank, which collects waste and can lead to a cleaner effluent than a septic tank.  This ABR is one of five main components that make up the Decentralized Wastewater Treatment System (DEWATS), whose goal is to produce a sustainable sanitation system.


Anaerobic Baffled Reactors consist of two major parts: a settling tank and a series of collection chambers. The first, a settling tank, is where the wastewater originally enters the system and larger waste products sink to the bottom, creating the first step in the filtration process. Next the water is forced through a series of compartments. Baffles are used to force the water in an upflow pattern, and the gaps between chambers are located toward the bottom to increase contact between the wastewater and sludge. This sludge, formed at the base of each compartment, contains microorganisms that are responsible for the anaerobic digestions of organic waste (Ferraz, et. al ,2009).

Each chamber provides a different level of filtration. The larger, more easily removed wastes are removed in the first chamber, and in each following chamber smaller, less degradable substances begin to decompose. By filtering the water through the sludge multiple times, a larger number of pollutants can be filtered out and a cleaner product will result.

Why use ABR?

There are many advantages to the use of an Anaerobic Baffled Reactor as a method of waste filtration.  First, the physical construction of the system does not require any electricity or power tools. The materials are basic and can easily be found, making it a system that has the potential to be built anywhere. It is not difficult to operate, and once constructed, the system requires very little maintenance, just emptying the tank every few years. The tank is smaller than most of the comparable options and can be located underground, conserving physical space. The system is self-contained, and does not interfere with any natural waterways.  If constructed correctly, the ABR is a reliable way to consistently provide filtration of wastewater. As a part of the DEWATS, the use of an ABR could provide a sanitary way to dispose of, and potentially even recycle, wastewater in any environment.

Although the ABR is a beneficial system, there are a few characteristics that need to be considered when creating this reactor.  If not designed or constructed correctly, the system could fail, resulting in leakages of the wastewater and sludge contained in the tank. Expert design is recommended to prevent this type of failure from occurring. Also, to maintain the tank the sludge will need to be removed regularly, so the tank must be in a location that will allow access for the necessary tools, such as a pump truck, to remove the sludge.

Learn more about the Chemical Process of ABR.

Past ABR Research done by WPI Students.

Drainage Systems

Leach field

A leach field is where the out flow from a septic tank is distributed and allowed to filter through the soil to be purified. Also known as a septic drain, a leach field consists of a series of trenches where perforated pipes are laid that filter the wastewater from the septic tank back into the ground(Septic Drainfield Design, 2010).

A non-perforated outlet pipe comes from the septic tank and leads into a junction pipe.  This junction pipe then branches out in a “T” shape to cover a larger area over the field, and all of the perforated pipes are connected to it.  The outside of the pipes are surrounded by a larger set of gravel stones to act as one last filtering level before the water is absorbed into the soil. On top of the trenches grass seeds are planted to add structure to soil below without large roots interfering with the underlying pipes.


A soakaway is a water filtration system designed to disperse effluent without a high concentration of solids into sub-soil near the tank.  The effectiveness of a soakaway depends on three main factors: sub-soil porosity (how quickly effluent can soak through the sub-soil), the number of residents the property is serving and the storage system (septic tank or sewage plant).  The sustainable operation and effectiveness of the soakaway is dependent on how high the permeability of the sub-soil is.   Since sand has high permeability it makes it an ideal solution for this location.  Having a system such as a soakaway allows for grey- and blackwater to be filtered naturally back through the earth.

The proposed soakaway used in the alternative designs consists of a trench running parallel to the tank system which will be located adjacent to the East fence.  Bordering the trench will be different size stones (Border Rocks) that will act as the first layer of the filtering system to block out larger solids.  Along with the stones certain types of foliage will be planted along this border to serve as structural support, a way to address the issue of excess water as it is released, as well as an aesthetically pleasing addition around the trench.   Concrete blocks will line the trench end to end with holes facing to the side to create a natural pathway into the soil for the water to flow.  Once the cinder blocks are in place the trench will be filled with an assortment of smaller and finer rocks and pebbles, thus completing the filter (AJ McCormack & Son, 2010).


Leach Field vs. Soakaway

Leach fields were chosen as the most practical and beneficial way to dispose of wastewater after it has been filtered through the tanks. Although soakaways are most commonly used in South Africa, we chose to construct leach fields because they release filtered wastewater over a larger area and have more potential for future sustainable projects, such as growing grass.