The purposes for which biogas technology was introduced at household level were multiple but the major and direct one was to provide a clean and sustainable energy, thereby reducing the reliance on wood fuel. From the socio-economic studies that have been carried out, biogas end-users and technicians continue to be blamed for technical factors hindering its adoption and use. However, the ways these factors hinder biogas adoption and use plus the linkage between them seem not well understood right from policy to end-users. A technical survey was carried out on household biogas digesters to evaluate the adoption, use and management factors and their implications on the future of household digesters. Over-designed digesters in relation to family size yet not producing enough biogas, dependence on cow dung as the feedstock, 75% of users not being sure of loading rate and mixing ratios, not feeding the digesters daily by all households were found to be the main causes of why biogas was not enough for 87.5% of the respondents and digesters were abandoned in Kampala, Uganda. All surveyed digesters were characterized by starvation-overfeeding problem. Wood fuel was found still dominating in these households with biogas. Given that end-users had no options of digester types from which to select, but handed-over with over-size fixed dome digesters, there is need for all biogas stakeholders to come together as the reality on ground reveals that right from inception to management, everyone is to blame for the technical failures.
In the need to provide sustainable clean energy to the ever growing population, biogas technology has been seen as one of the renewable energy sources that can cause a paradigm shift on communities, especially in the developing countries. However, its adoption and use seem not to be advancing in most of these developing countries where it was hoped to have an impact. This has led to a number of researchers to carry out in-depth studies on socio-economic factors hindering biogas adoption and use with little on technical factors where biogas users and technicians are always blamed [
To carry out the technical evaluation, a questionnaire was designed for households with biogas digesters either working or not working. The questionnaire was divided into five sections. The first part was intended to capture demographic information and resources available that directly or indirectly affect the type and size of the biogas digester. The next section considered biogas systems and status. The third section looked at information related to biogas use practices and behaviour that help to understand the potential of the digester to supply the needed energy as well as the safety of the users. The fourth section collected data on operation and management practices that influence the efficiency of digesters. The last section was meant for digesters that were not working. The questionnaire was pretested and administered in two divisions in Kampala city and two sub-counties in Wakiso district neighbouring Kampala city that had been selected randomly. The study intended to have at least five households with biogas digesters from each of the selected divisions to make twenty in total. However, only ten in total were found basing on the informers in each of the selected divisions.
Statistical Package for Social Sciences (SPSS) was used in data entry and analysis. Descriptive statistical analysis using frequencies was applied to questions that needed one response while for questions that necessitated multiple responses, multiple response analysis was used.
implies total disregard by the biogas implementers (government, NGOs and research centres) in involving the users or community. As it can be seen in
where, V is the volume of digester (m3), Fs is family size, pb is per capita biogas usage (m3/d) and vr is volumetric biogas production rate (m3/m3・d). From these results digester size and family size were found not to have any relationship given that 80% of the digesters were of 8 m3 while family size varied mainly from 5 to 10. This is an indication of either over design or under design as the demand (family size) does not march with the size of digester. However, Rajendran [
A household using a mixture of cow dung and pig manure or more than one feedstock will never know the optimal ratio that favours anaerobic process for maximum biogas/methane unless the researcher comes in the equation. This is in light of the much available literature on synergetic effect of co-digestion on methane yield with little mention on the antagonistic effects [
explained in Section 3.1, limited diversity in feedstock supply presents great challenges on the continuity of biogas digesters. The question who uses biogas was asked to understand the level of responsibility in energy saving. A worker or children may switch on the stove before cooking pot is ready fail to switch off the stove immediately after cooking. This contributes to biogas not being enough for the task. Results show that over 75% of the households, everyone is free to use biogas which is good. However, this compromises on energy saving unless the techniques of energy saving are emphasized. Another important factor was the freedom to use biogas anytime of the day represented by 62.5%. This is an indication that these digesters had a potential to supply most of the energy requirements of these households, if not all. Majority of the households (66.7%) were found to be using biogas for cooking while 22.2% use it for both cooking and lighting and 11.1% use it only for boiling water. Diversifying biogas applications has been suggested by some researchers [
Section 3.2, the question on who feeds the digesters was meant to capture the level of risk associated with less responsible people who may not know the impact of changing defined parameters. Feeding a biogas digester is a dirty activity that follows specified guidelines which requires someone responsible and knowledgeable. Therefore, assigning children or workers to feed the digester daily may require supervision occasionally. In regard to the how much question, which refers to an important parameter of loading rate, 75% of the households were not sure of how much the feed the digester per unit time. Only 25% was in position to specify the quantity in terms of wheel borrows. The size and performance of any digester are based on the loading rate. There is a lot of literature showing the effect of loading rate on digester performance [
Similarly, 75% of the households were not sure of the mixing ratio of water to feedstock. Equally so, this affects digester performance as concentrated mixture or feed slow down the anaerobic digestion process while over diluted feed is associated with scum formation [
Like most of the questions, the question on how often the digesters are fed was an open ended one. Respondents gave varying responses like once in 2 days, once in 3 days, on every Sunday to mention but a few. These responses were then categorized into more than a week, once a week, twice a week and thrice a week. From
Having presented technical factors affecting biogas right from adoption through use to management, this section presents the implications of these factors on the future of household biogas digesters. From adoption, it was shown that all the digesters under use were of the Chinese fixed dome type. This type of digester requires a big space and probably this could be one of the factors why only three digesters were found in the two selected divisions in Kampala city where space is limited than the other sub-counties in Wakiso district which are just beginning to be occupied (
positive trend. However, the limiting factor is the reliance on cow dung as the main feedstock which even from the survey is responsible for abandoning a working digester after the death of animals. Several researchers have suggested diversification of biogas feedstock by exploiting household waste.
that have been presented in this work are not to be blamed on the end-user nor the technician but on all stakeholders. This therefore, calls for extension workers not necessarily in agriculture alone but in energy saving and performance efficiency areas.
There is a need for a shift from the common fixed dome type of digester to small and compact types which do not require large spaces in addition to substrate diversification and process optimisation and control. Majority of the household biogas digesters are over designed and cannot adapt to any unexpected reduction in feedstock supply. Over 70% of biogas users were found not to know how much is needed to feed their digesters and mixing ratios. This is not to mention
that none was found to be feeding the digester daily. All this coupled with the oversize problem seem to be the major causes of why biogas is not enough for 87.5% of the households and responsible for the situation presented in
This research was funded by the Office of Research and Development (ORD) University of Botswana and Support made possible through a capacity building competitive grant Training the next generation of scientists provided by Carnegie Cooperation of New York through the Regional Universities Forum for Capacity Building in Agriculture (RUFORUM). Peter is a METEGA sponsored graduate student at University of Botswana.
Tumutegyereize, P., Ketlogetswe, C., Gandure, J. and Banadda, N. (2017) Technical Evaluation of Uptake, Use, Management and Future Implications of Household Biogas Digesters― A Case of Kampala City Peri-Urban Areas. Computational Water, Energy, and Environ- mental Engineering, 6, 180-191. https://doi.org/10.4236/cweee.2017.62013