BIOGAS

Biogas is produced by anaerobic bacterial digestion of organic material such as animal dung, human wastes and crop residues. The digestion slowly produces a gas which is roughly 60% methane and 40% carbon dioxide. Biogas is a well established fuel for cooking and lighting in a number of developing countries. Biogas makes a meaningful contribution to the energy supply and it saves fossil energy, such as wood, coal, oil and gas. It also makes a significant ecological contribution to heat and electricity production. Biogas is an environmentally friendly source of energy because it produces electricity and heat but still keeps carbon dioxide emissions neutral and emits no sulphur. As fossil based fuels become scarcer and more expensive and carbon dioxide emission levels become of greater concern, the benefits and potential of biogas as a source of energy supply are being increasingly recognized.

Biogas in Kenya

Pictures of smallholder dairy household biogas production and use in Embu Kenya

Photos taken by ABS TCM, Ltd. Representative – Ambrose Munene

General facts on biogas:

1m³ Biogas (approx. 6 kWh/m³) is equivalent to:

Wood (approx. 4.5 kWh/kg) 1.3 kg

Cow dung (approx. 5 kWh/kg dry matter) 1.2 kg

Plant residues (approx. 4.5 kWh/kg dry matter) 1.3 kg

Diesel, Kerosene (approx. 12 kWh/kg) 0.5 kg

Hard coal (approx. 8.5 kWh/kg) 0.7 kg

City gas (approx. 5.3 kWh/m3

Propane (approx. 25 kWh/m3) 0.24 m3) 1.1 m3

Kenya Dairy Industry

Kenya has an estimated smallholder dairy farmer population of 600,000 of which less than 2% are using biogas. Dairy activites are mainly in the high to medium potential regions. The smallholder dairy herd size ranges from 2 to 3 cows and calves. Generally farm size is in the range 1 to 3 acres. A survey of 250 dairy smallholder households from central province of Kenya, Nyeri (Technoserve, 2006) showed that over 80% used wood fuel and 74% were suffering from respiratory diseases. The demand for electricity, gas and fuel is rising and Kenya is recommended to pursue utilizing renewable sources of energy such as biogas to avoid overdependence on fossil fuel.

Small-scale biogas plants are cheap to establish (about US$75 to $100) and easy to maintain. A donor group GTZ is working with local partners to install bigger biogas units that can generate enough gas to run electricity generators. Some have been installed at Egerton University, Kilifi Sisal Plantation, Kiserian and Limuru. Since installation of biogas plant, Edgerton university has saved 30 per cent equivalent to Ksh300,000 (US$4,545) per month used on Liquid Petroleum Gas (LPG) for its student's kitchen (East African Standard Aug. 28, 2007).

Biogas Run Generator

Fertilizer Benefit

In addition to creating their own electricity and heating, the farmers produce a high quality and odorless fertilizer. The biologically recycled materials are carried to the fields and deliver high value nutrients to plants and crops which suit their growth. The left over sludge keeps its nutrients for the crops but with the gas removed, the fertilizer does not smell. The sludge is a valuable by-product and because it has lost its potent smell, it does not have to be dug into the earth like conventional sludge affording zero tillage for soil conservation. Instead, it can be sprayed directly onto the crops. The other advantage is that the sludge can be spread at any time of the year.

Observed improved yields in agricultural produce as a result using biogas digesta / bio-fertilizer are in the range 6 - 20 %. Biogas can substitute traditional cooking fuels such as wood fuel and charcoal but needs to be produced at a minimum amount of 0.8-1 m³ daily. To generate this amount of biogas, the household should have 20-30 kg of fresh dung available on a daily basis equivalent to 2 dairy cows fecal output per day.

Kenya Biogas Installations

Institutions that have played an active role in the promotion of biogas include:

1 Special Energy program (SEP), a joint effort between GTZ ,Ministry of Energy, Ministry of Livestock Development and Kenya Industrial Estates (KIE)

2 Kenya woodfuel and Agroforestry Project (KWAP)

3 Christian Intermediate Technology Center (CITC)

4 Tunnel Technology Ltd.

5 Biogas Africa

6 Kentainers Ltd.

The potential for agriculture is limited to agricultural areas with high population densities and is further restricted to farmers who can afford the high initial costs associated with biogas plants.

Major constraints to biogas technology dissemination include:

• High initial investment costs compounded with lacking credit schemes
• Negative image caused by failed biogas plants
• Limited private sector involvement

To increase viability the following avenues must be explored:

1. Resources should be directed to promoting the technology in high potential areas.
2. Private sector involvement in promotion and dissemination is necessary for successful adoption of the technology.
3. There is need to counter the already negative image of the technology that exist by promoting proven designs and providing post installation support.
4. Cheaper low costs designs need to be developed to lower the cost entry barrier
5. Access to credit for end-users and small enterprises promoting biogas
6. Promoting entities should develop sufficient capacity to advice potential users on available options.

ABS TCM Research on Biogas

ABS Kentainers Collaborative Work

KENTAINERS DOMESTIC BIOGAS PLANT:

Kentainers has now developed a small sized convenient to use biogas plant which uses food waste and manure as feedstock and supplies biogas for cooking as well as lighting. The plant is sufficiently compact to be used by urban as well as rural households.

The compact biogas plant works on the floating dome principle and is basically formed two linear low-density polyethylene (LLDPE) tanks, one tank being larger than the other. The larger tank is referred to as the “digester” and is 2,200 litres in capacity while the smaller tank is referred to as the “dome” and is 1,200 litres in capacity. The smaller tank is inverted and placed into the larger tank and acts as a gas holder.

The tanks are molded in a special design so as to allow for smooth operation as well as maximize the efficiency of gas trapping and pressurizing. The digester is fitted with an inlet pipe and funnel for easy pouring of food waste/manure slurry (mixture of manure and or food waste with water) into the tank and it also has on outlet pipe higher up the tank to remove digested residue. The dome has a provision for weight addition on the top of it to realize gas compression, it also comes with an outlet gas valve fitted as well as an ingenious mechanisms to address excessive gas production. A rubber pipe is fitted to the outlet valve and this pipe carries the gas to the kitchen where it can be used for cooking or to a lantern where it may be used for lighting. The gas holder gradually rises as gas is produced, and sinks down again as the gas is used.

The plant safely digests manure, kitchen waste, food waste or waste flour from mills, thus reducing the problem of waste disposal. A 1,000 litre plant produces sufficient biogas to relieve most of the use of LPG or kerosene or fire wood for cooking in a household, as well as a small amount of liquid effluent which can be used as fertilizer. The fact that it would save on LPG, kerosene or fire wood makes this energy use eco-friendly and helps protect the environment.

The gas produced in these plants has a high methane concentration and is odorless and burns blue when ignited hence the flame is hotter which serves to reduce cooking time as when compared to firewood or kerosene. Also, the gas burns smokeless and hence is eco-friendly by virtue of not polluting the atmosphere and is comfortable to be used in a household.

Initially, the plant is fed with slurry made of 25Kg of manure and is left for gas to start producing (usually takes 7-10days depending on climatic conditions). After realization of gas production, slurry made of 10Kg manure and any food waste (1Kg) is added on a daily basis to ensure continuous gas production. We estimate that a plant which is well fed and situated in hot climatic conditions will produce sufficient gas for 3 hours of cooking daily.

The plant is simple to operate and can be installed in a matter of hours by our technical staff who also educate the user on how to use the gas plant. It is sold as a kit and takes only two to three hours to install. It needs a space about 2 m square and 2.5 m high. The feed can be manure, waste flour, vegetable residues, waste food, fruit peelings and over-ripe or rotten fruit. Oil cake, left over from oil-pressing, is another useful feedstock.

Biogas Trials in Rwanda

Below are pictures of the Canvas Biogas Unit Installed in Rwempasha

There has been a lot of interest in setting up biogas units across the associations and among dairy farmers in Rwanda Cooperatives. However, there have been a few challenges that are facing the units and the beneficiaries. Gas production has remained somewhat low. The causes appear to be low energy content and digestibility of the cattle dung and possible contamination by acaricides and other chemicals. Boosting the quality of the dung through use of slaughter house rumen contents and wood ash (quenches acaricides and chemicals) improved the gas output. However, further investigation is required to optimize the output. As a result of this challenge, the cost of monitoring the biogas units has been higher than anticipated. Some biogas units have been vandalized. There is need to engage whole communities and extend the technology to them.