Abstract Description

Dry anaerobic digestion (DAD) offers a sustainable approach to organic waste management and biogas production, particularly in regions of the Global South, where resource constraints (such as energy, water and space) are significant. As part of the W3M-Dry AD (Water wise waste management) Africa-Japan collaboration project, this study addresses common limitations in DAD systems, such as high solid content and poor substrate mixing, which results in inefficient biogas production and slow biodegradation rates. The use of bulking agents (BAs) has been proposed as a solution to improve DAD efficiency. BAs may provide a supportive platform for DAD-promoting microorganisms to adhere, colonize and form biofilms under high solid stress, thereby fostering resilient microbial communities. They may also enhance substrate porosity, improving mass transfer, microbial activity and overall process stability. Despite their potential, the mechanisms through which BAs influence DAD are not fully understood, especially in low-resource settings where scalability and cost-efficiency are key. This study aims to investigate the role of BAs as microbial carriers in optimizing DAD of cattle manure and mixed vegetable waste (2:1, 20 % total solids). BAs derived from abundant agricultural residues accessible to smallholder farmers will be collected and characterized for surface area and porosity; size and morphology; and functional groups using Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy, respectively. Following pre-soaking in inoculum (cattle manure liquid digestate), the BAs will be applied for mesophilic (37 °C) batch DAD at three dosage ratios of BA to substrate (1:2, 1:1 and 2:1; control without BA - 0:1). Biofilm formation on the surface of the BAs will be assessed using SEM and crystal violet assays, while the impacts on biogas production, acid to alkalinity ratios and microbial community dynamics will be determined using gas chromatography and manometer; potentiometric titration and next generation sequencing and bioinformatics tools, respectively. It is anticipated that the BAs will enhance methane yield, process stability and digestion rates by creating a more favourable environment for microbial communities and improving mass transfer. The findings will provide insights into how BAs mediated improvements in DAD performance and their potential for low-cost, scalable applications in resource-constrained settings.