Engineering Research: Perspectives on Recent Advances Vol. 12

Third-world areas are facing a two-fold problem in terms of how the organic waste streams can be handled and how they can be provided with predictable and decentralised energy. This research paper is a comparative kinetic evaluation of the anaerobic co-digestion of cow dung (CD) with 2 different high-carbon feedstuffs, cassava peel (CP) and water hyacinth (WH), on the stability, performance, and fuel quality of biogas produced under mesophilic batch anaerobic digestion. Three digestion systems were operated for 30 days: cow dung alone (CD), cow dung with cassava peel (CD+CP), and cow dung with water hyacinth (CD+WH). Daily monitoring of temperature, pH, total dissolved solids (TDS), electrical conductivity (EC), and gas yield provided insights into microbial activity and substrate behaviour. All digesters maintained constant mesophilic conditions (25 - 32 °C) and buffered pH values (7.2 - 8.9) for most of the retention period, with a final decline (≈5.2 - 6.1) marking substrate depletion. Co‑digestion markedly improved biogas productivity compared to mono‑digestion. The CD+WH blend produced 4,810 L of biogas (72.8% increase), with steady gas release linked to the gradual breakdown of lignocellulosic material. The CD+CP blend achieved the highest yield at 5,042 L (81.1% increase), driven by the rapid fermentation of cassava starch. Gas composition analysis showed methane concentrations peaking at 61.0% in CD+CP, compared with 52.0% in CD alone. However, all raw gases contained critically high hydrogen sulfide (5,000 - 8,000 ppm). A low-cost, locally designed and fabricated iron-oxide scrubber used during this work successfully eliminated H₂S by reducing the concentration from about 8000 ppm to 0 ppm. Post-scrubbing flammability tests confirmed high-quality fuel, with co‑digested gases producing strong blue flames characteristic of methane-rich biogas. Beyond energy recovery, the study also demonstrated the agronomic value of the digester effluents. The nutrient-rich slurry was applied as fertiliser to plants, improving soil quality and supporting healthy growth, thereby closing the resource loop between waste management, energy generation, and agriculture. In addition to energy recovery, the nutrient-rich digester effluents were applied as fertiliser, improving soil quality and supporting plant growth. The findings demonstrate that co-digestion of cow dung with cassava peel or water hyacinth enhances biogas yield, methane content, and process stability while generating valuable organic fertiliser. This integrated approach supports decentralised renewable energy and sustainable agriculture in biomass-rich regions.