Proceedings Biodigester Workshop March  2002

Evolution of biogas technology in South Sudan; current and future challenges

David Kuria Njoroge

UNICEF/OLS, South Sudan



Sudan is the largest country in Africa with a total area of 2.5 million km² with a population of 35 million people.  The population comprises of mainly 65% Christian and Animist Africans and 35% Arabs who are predominantly Muslims. 

Sudan has suffered an on-going civil war for 18 years that has resulted in; 2 million people dead, 1 million Displaced Persons (DPs) and 3 million Internally Displaced Persons (IDPs).  The effect of this long conflict has been to totally impoverish the people of South Sudan and escalate the effects of natural calamities such as disease and famine. Physical infrastructures such as roads and buildings have largely collapsed. Technological development has also been a key victim in this conflict, archaic methods such as grinding grain between 2 stones and pounding by mortar and pestle are used today. 

To save lives and alleviate the suffering of the war-affected civilian population in South Sudan; the international community provides humanitarian assistance through the Operation Lifeline Sudan (OLS). OLS has been instrumental in opening up access into the war-torn south by air, road and to a small extent by river so that relief supplies and services reach the needy. The work of OLS is based on the guiding principle of humanitarian neutrality that transcends political and/or military considerations. OLS works hand in hand with the Sudan Relief and Rehabilitation Agency (SRRA) as the local counterpart.


The fuel mainly used for cooking in homes and public institutions of South Sudan is firewood. Firewood is collected from the forests and bushes by women and children -- sometimes as far as 6 km away. Large tracts of unutilized bush land resulting from displaced populations are a common feature in South Sudan. As a result, availability of firewood is not a constraint today. This however may change in future as more trees are cut down. 

The main fuel used for lighting in homes and Schools is kerosene. Some rural households also use grass torches and firewood for lighting. The disadvantages of firewood and kerosene as fuels include: 

Introduction of biogas technology

Biogas technology was introduced in South Sudan during the year 2001 through a UNICEF/OLS-supported Biogas Pilot Project at the Rumbek Secondary School. In February 2001, UNICEF/OLS engaged the services of a Kenyan based company (Project Assessment Services (PAS)) to identify an appropriate biogas system for South Sudan. PAS was also required to construct and demonstrate the working of the biogas plant at Rumbek Secondary School. An agricultural consultant (Mr. David Njoroge) was assigned to carry out this task. 

The choices of biogas plants available for selection included; the floating drum system (fairly common in neighboring Kenya), the fixed dome system (not common in Kenya) and the Tubular Plastic Biodigester (TPB). The TPB system has not been tested in Kenya but some work had been done and documented by Preston in neighboring Tanzania ( Bui Xuan An et al 1997).  It was from the work of Dr. Preston that the UNICEF consultant knew of the existence of the TPB system. Through Email contact between the UNICEF consultant in Sudan and Mr. Nguyen Khang in Vietnam, at the University of Agriculture and Forestry, PAS imported a 7m3 TPB unit from Vietnam to South Sudan. The package included a 45 minutes Videotape in Vietnamese language detailing the plant installation procedure. 

Using a laptop computer and CD-ROM copies of the Video, the consultant trained 20 students and 2 Teachers of Rumbek Secondary School, first on the theory of biogas and then on installation of the TPB. This training took a period of 3 weeks. The team involved in this activity then became known as the Rumbek Secondary School Appropriate Technology Club (ATC).  

Under the supervision of the UNICEF consultant and guidance from Mr. Khang via Email, the members of the ATC installed the TPB near one of the school kitchens. Subsequently, the team fed the digester with cow dung at the rate of 20 kg (1 bucket) per day. On the 25th day, the plant was tested by lighting the burner and the result was successful. This was the first ever practical experience with biogas technology in South Sudan. This TPB plant is today used as a biogas demonstration for the local community and visitors. It is also used to cook breakfast for 50 students.  The ATC students teachers operate and maintain the TPB plant on a daily basis. 

In 2002, UNICEF/OLS plans to support installation of 2 more 12.7m3 digesters at Rumbek School, (ie: phase 2 of the biogas project). The aim is to reduce firewood use for cooking in the School by up to 80%. Currently, the School uses about 50 tonnes of firewood per year to cook for 400 students. The target group for training in the phase 2 of the biogas project will be the cooking staff in the School.

Experiences with the Pilot Plant

The Biogas plant has performed satisfactorily for purposes of demonstrating that Biogas technology works. However, it has some significantly serious limitations as a cooking facility for the School.

Gas pressure problem

After about 40 minutes of cooking, gas pressure falls drastically and the flame at the burner becomes very low. Common Sudanese meals require more than 2 hours of cooking. Often, the cook has to remove the food from the biogas burner after 40 minutes and transfer to the 3-stone firewood place. There is an urgent need to solve the gas pressure drop problem so that a sufficiently high cooking flame is maintained for 2 hours of cooking. 

Loss of bacteria and gas

It was observed that when the gas was not used, the digester expanded excessively and much of the digester material was expelled out through the outlet. The result was that active bacteria and undigested matter were lost with the effluent and low gas production followed. Adding fresh dung from animal rumen (from the local abattoir) solved this problem. Also, when much effluent was lost in this way, the level of digester slurry fell below the level of inlet pipe and gas was lost through the inlet. Adding water to compensate the lost effluent solved this problem.


There is encouraging proof that the TPB can be a resilient and durable plant. Towards the end of 2001, Rumbek School was closed for about 3 months. During this time, the biogas plant was left unattended because all teachers and students went away. On return of the students, the plant was revived to full gas production capacity in only 3 days.

Utilization of digester effluent

The ATC students have established a ¼ acre vegetable garden next to the biogas plant where they grow popular local vegetables such as Amaranthus and Okra. The students use the rich natural fertilizer from the Biogas plant to improve the soil on this plot.  The vegetables are bought by local people and institutions, which provides some cash income for the Biogas team. UNICEF/OLS aims to support this initiative by providing high value crop seed such as Onion and Tomato to the students.

Community Response

A Biogas Technology Community Awareness workshop named “towards intensified use of Biogas in South Sudan” was held in Rumbek between 13 and 15 of Februray, 2002. The workshop objective was to gauge the level of acceptance of Biogas technology by the Sudanese community taking Rumbek County as a microcosm. Participants were shown the TPB installation Video and conducted on a tour of the Pilot Plant at Rumbek School where the working of the plant, including the fertilizer use,  was explained. The general response of the participants was as follows: Participants felt that biogas technology could: