In the realm of cassava-ethanol production, the byproducts hold untapped energy potential. Specifically, root fiber, constituting 30% of the dry weight organic matter, and wastewater (stillage), harboring 20%, emerge as valuable sources for biogas production.
For every tonne of fresh cassava root, a theoretical extraction of 42 m3 methane from the root and 28 m3 from the wastewater unveils a global biogas production potential of approximately 3,000 million m3. In this exploration, we delve into harnessing cassava ethanol waste streams for biogas production, evaluating two key options: biogas from ethanol stillage and biogas from root cake (cassava pulp).
Characteristics of Waste Streams
The cassava-to-ethanol process yields stillage, a by-product rich in pollutants, characterized by low pH, high temperature, dark brown color, and substantial organic and inorganic matter. Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) levels range significantly.
Biogas Production from Stillage
Anaerobic treatment stands as the primary method for distillery wastewater treatment, demonstrating high efficiency in removing COD. This method can yield up to 90% BOD removal, and the generated biogas could potentially satisfy 30% of distilleries’ fuel needs. Various reactor types influence treatment efficiency and methane yield.
Biogas Production from Cassava Pulp
Cassava pulp, a residue post-starch extraction, emerges as another promising source for biogas production. With a dry matter content of about 20%, it can potentially yield 350-450 m3 of methane per ton of dry matter. The global potential of biogas from cassava pulp surpasses that from stillage.
Global Biogas Potential
Assessing cassava-growing regions with high ethanol potential, Nigeria, Indonesia, and Mozambique emerge as key contributors, collectively offering a global biogas potential of approximately 3,000 million m3. Nigeria leads with 1,000 million m3/a, followed by Indonesia and Mozambique.
This investigation sheds light on the substantial energy reservoirs within cassava-ethanol waste streams, offering a sustainable avenue for biogas production.