An approach to wastewater valorization in the cassava value chain through biorefineries based on anaerobic digestion

Abstract

The cassava value chain (VC) is essential for food security in developing countries. During cassava agro-industrial processing, wastewater (WW) is the main residue generated. Anaerobic digestion (AD) is an effective treatment for this WW, and modified AD (MAD) can produce valuable intermediates such as volatile fatty acids (VFAs). Although several studies have explored the valorization of cassava waste in the context of the circular economy, limited work has combined experimental results with techno-economic and environmental assessments of integrated AD-based biorefineries within the cassava VC. This study evaluates the feasibility and environmental impacts of incorporating AD-based biorefineries into the cassava VC. Experimental results from conventional AD (CAD) and MAD were used to simulate and assess multiple integration scenarios. Biorefineries were evaluated economically and environmentally, using cassava starch production as the base case. A biogas yield and mixed VFAs concentration of 5.57 ml/ml WW and 42.18 mg/ml WW was evidenced in the conventional AD (CAD) and MAD, respectively. Acetic acid was the most representative VFAs. The base case presented a payback period (PBP) of 10 years. CAD integration enhances economic performance by enabling the recovery of unconsumed mixed VFAs. MAD integration allowed a reduction of 18 % of the PBP. The cassava VC was found to have a carbon footprint of 2.63 kg CO₂ and a water depletion of 11.20 m³ per kilogram of WW. However, a 54.4 % reduction was achieved by integrating AD-based biorefineries. These results elucidate the potential of MAD-based biorefineries, showing favorable economic results, while environmental impact is reduced.