Special Energy Programme Columbia
In May 1985 the Special Energy Programme Columbia located in Barranquilla began work. This resulted in the project concept "investigation of the possibilities of producing and using biogas" in the Valle de Cauca. A German consulting company (Oekotop) was commissioned with carrying out the project as a subcontractor. The executing organisation on the Columbian side was the Corporacion Autonoma Regional del Cauca (CVC). A German long-term expert was active locally within the project from November 1985 to April 1987. Another long-term expert was involved from November 1987 until the contract with the consulting company ended in March 1989. During this period, the central problem was the "pollution of water resources"; the project purpose was to "disseminate modified biogas technology". Until this time, the activities within the project were marked by a great deal of research and development. Investigations were also carried out into the use of slurry.
From November 1989 to the beginning of 1992, a new consulting company (BioSystem), closely related in a personnel aspect with the original company, was commissioned with implementing a further project phase. During this time in which a "contribution to the improvement of the rural energy situation and the conservation of water resources by the use of biogas plants" was to be attained, another long-term expert was involved locally. This phase was marked by efforts to demonstrate the efficiency of biogas technology under dissemination conditions. I.e it was mainly a rehabilitation programme for non-functioning plants and set up a central area for a dissemination structure. The building of demonstration plants on selected farms was to establish biogas technology in the rural region. The involvement which was planned in the agro-industrial sector was suspended due to its complexity (initial investigations on the fermenting of agro-industrial wastewater had been carried out). Between 1985 and the beginning of 1992 a total of 25 biogas plants were built.
Types of Plants
A floating-drum plant of the BORDA type, a tunnel plant, various fixed-dome plants, a balloon plant and a UASB (upflow anaerobic sludge blanket) plant were built during this time. The type of plant was standardised in 1988. When the project was handed over in 1992 this consisted of 4 fixed-dome plants of 14 to 48 m3 and three fixed-dome plants of between 67 and 115 m3 with a separate gasholder.
In line with the heterogeneity of biogas users' agricultural household and farm systems, the integration of biogas technology into agricultural and farm systems was very varied. The plants were mainly built for medium-sized and larger pig and cattle breeders who had between 20 and 2,000 head of animals. The heterogeneity of the farms was also reflected in the pattern of utilisation and the condition of the plants.
Especially farm management had a considerable influence on the degree of effectiveness of biogas technology. The plants were normally filled by labourers. The administrator played a central role in instructing the staff in the function of the biogas plants due to the high rate of staff fluctuation in some cases. An extensively constant solids content i.e. the separation of long-fibred material (scum formation) is important for the ability of the biogas plant to function. Scum formation and the washing out of substrate could be observed on some plants. Especially uncontrolled inflow of washing water confronts conventional fixed-dome plants with "digestive problems". Labourers who were not instructed sufficiently and were not bothered, washed out the stables with large amounts of water which resulted in drastically reduced retention times. Adequate attention to the plants is impeded by different staff involved in filling and in using the gas. Not the workers, but the owner of the Finca or the administrator profits from the gas. Without the "long arm" of the farm management, proper filling and thus reliable function of the plant is not possible.