Characterisation and Energy Valorisation Trials of Septic Tank Sludge from Urban Areas in Benin, West Africa

Abstract

Introduction: Population growth is accompanied by a significant increase in waste production of all kinds, including that from latrines, which raises serious health and environmental issues. Furthermore, in today’s energy-intensive lifestyle, the exploration and utilisation of new renewable, sustainable, and environmentally friendly energy sources is imperative. Aims: This study aims to explore the potential for energy recovery (biogas) from septic tank sludge in Benin. Place and Duration of Study: Liquid sludge samples were collected from 29 May to 2 June 2023 at the Sludge Treatment Station (STS) in Adjagbo, within the commune of Abomey-Calavi. Methodology: Sludge is subjected to anaerobic co-digestion with simple fruit waste and in the presence of iron filings. The process lasted between 17 and 24 days, depending on the composition of the digester. Results: The raw biogas obtained comprises methane and carbon dioxide in proportions ranging from 55.2% to 65.3% and 34.7% to 44.8% for simple co-digestion, respectively, and between 60.82% and 71.35% and 28.65% to 39.18% in the presence of iron filings. The results demonstrated the effectiveness of iron filings in biogas production and a reduction in process duration during co-digestion compared to simple digestion of fruit waste. Conclusion: This study provides avenues for exploring the valorisation of sludge into renewable energy and considers the use of biodigesters in households as an alternative to conventional septic tanks. The results of this study provide valuable insights to guide effective sludge waste management practices in Benin.