Assessment of Smallholder Biogas Systems under Variable Feedstock in Sub-Saharan Farms

Thesis Abstract

Smallholder biogas systems offer a potential pathway to improved energy access, waste management, and greenhouse gas mitigation in Sub-Saharan farms; however, their performance under variable feedstock and on-farm management practices remains inadequately understood. This study addresses the problem of inconsistent biogas output, substrate utilization inefficiencies, and limited adoption by smallholders due to feedstock variability, seasonality, and socio-technical constraints. The aim is to evaluate how feedstock variability affects the operational performance, user practices, and socioeconomic outcomes of smallholder biogas systems in Sub-Saharan farms. Specific objectives are (i) to quantify biogas yield, retention time, and digester stability across a spectrum of locally available feedstocks (animal dung, crop residues, and kitchen waste) and mixtures; (ii) to identify on-farm management practices and seasonality factors influencing system performance; (iii) to assess the economic viability and household energy security implications of biogas use under different feedstock scenarios; (iv) to examine perceived barriers and enabling factors for technology adoption using a theoretical lens grounded in Technology Acceptance Model and diffusion of innovations; and (v) to develop evidence-based recommendations for feedstock optimization and policy support. The methodology adopts a mixed-methods cross-sectional design combining quantitative performance testing of 120 operated biogas units across three Sub-Saharan countries with qualitative reflections from 60 household interviews and 20 focus group discussions. The population comprises smallholder farmers owning household biogas plants with a capacity range of 2–6 m3. Purposive and stratified random sampling ensure representation across seasons and agro-ecological zones. Data collection instruments include calibrated gas meters and flow sensors for real-time biogas yield, digestate analysis for stability indices (volatile fatty acids/alkalinity ratio, pH), feedstock characterization protocols (proximate and ultimate analysis), structured household surveys, semi-structured interview guides, and focus group prompts. Instrument validity is established through expert review and pilot testing, while reliability is evaluated via test-retest procedures and Cronbach’s alpha for attitudinal scales. Analytical approaches comprise descriptive statistics and multivariate regression models to quantify relationships between feedstock composition, operating parameters, and biogas performance; repeated-measures ANOVA to detect seasonal effects on yield and digester stability; and time-series analyses for yield trends across months. A stochastic frontier analysis will estimate technical efficiency relative to feedstock mix and operating practices. For the qualitative strand, thematic analysis will identify patterns in adoption behavior, maintenance practices, and perceived constraints, with triangulation conducted against quantitative indicators. The study engages the Theory of Planned Behavior and the Diffusion of Innovations framework to interpret behavioral determinants and technology uptake, complemented by a system dynamics perspective to illustrate feedback loops between feedstock management, digester performance, and household energy outcomes. A conceptual model links feedstock variability, technical performance metrics, and socio-economic impacts. Key expected findings include (i) quantification of optimal feedstock blends that maximize gas yield and stability while minimizing process inhibition under suboptimal ambient temperatures; (ii) evidence that seasonality and feedstock supply chain characteristics significantly modulate digester performance and maintenance costs; (iii) demonstration of a positive correlation between stable biogas supply and reductions in traditional fuel expenditure, time savings, and improved indoor air quality; (iv) identification of user-centered design and capacity-building gaps that hinder sustained adoption, with actionable mitigation measures such as simplified feeding protocols and community-based feedstock sharing models; and (v) a policy-relevant framework for feedstock management and financing mechanisms that improve economic viability for smallholders. The study contributes to knowledge by providing empirically grounded, context-specific insights into how feedstock variability shapes technical performance, economic viability, and user acceptance of smallholder biogas systems in Sub-Saharan Africa, bridging engineering performance with socio-technical adoption dynamics. The main conclusion anticipates that targeted feedstock optimization, coupled with practical maintenance training and supportive policies, can substantially enhance biogas reliability and household energy outcomes. Recommendations include developing region-specific feedstock mix guidelines, scalable maintenance services, micro-financing arrangements for digester upgrades, and integration of biogas performance monitoring into extension programs to promote sustainable adoption and resilience in smallholder farming systems.