Household biogas digester

Problem statement

In Sub-Saharan Africa and especially Ghana, the use of renewable energy such as biogas is highly under-developed thus accounting for the country’s over-reliance on natural gas and other fossil-based fuels for electrical power generation . It is, therefore, very crucial for Ghana to expand the production of renewable energy such as biogas from food wastes, black water (waste water comprising human faeces, urine and flush water) for both industrial and household consumption. Consequently, coming up with an innovative and good technological design for household biogas production is very imperative.

Executive summary

Α household biogas digester piloted in a slum called Terterkessim in the K.E.E.A. Municipality of the Central Region of Ghana. A 2-seater toilet compartment was constructed on a pilot manually-stirred, fixed pyramidal-dome-shaped single-stage household biogas digester for a compound house of 32 persons in the Terterkessim slum. The pyramidal dome-shape biogas digester was constructed on an abandoned septic tank meant to contain faeces from the toilets. Blocks and concrete were used for the construction. The digester has a rectangular sub-surface base and a pyramidal gas holder above the surface of the soil. It also has a two-blade manual stirrer, a ball bearing affixed at the bottom and a handle to manually mix the content of the digester. A solar-photovoltaic was installed on the roof of the toilet connected to the digester to heat the content to a hyper-thermophilic condition for hygienising the digestate.

Technology description

The single-stage innovative household biogas digester constructed in Terterkessim slum composed of 3 chambers which were originally designed for a septic tank system. The septic tanks were connected to a two-unit toilet meant for that household. The first chamber was the biggest and was converted into the main single-stage household biogas digester in which the AD process occurred. It had a total volume of 8.64 m3. Adjoining the main reactor was a compensation tank which had a tunnel from the main digestion chamber. The compensation tank was about 3.17 m3. Within the compensation tank were steps designed to help with settling of particles as well as directing clear effluent to be discharged into the next chamber, the effluent collection and storage tank. The effluent collection and storage tank had a total volume of 4.52 m3. It had an effluent discharge pipe for overflow into a collection container for agricultural usage. Τhe digester could produce about 2.52 Nm3CH4/(kgCOD.d) which could be burnt for at least 8 hours for purposes such as cooking and heating in the households in the slum.

Market deployment considerations

Environmental considerations

An average COD removal of 97.6% was recorded for the digester.