No abstract

Cassava is one of the main processed crops in Thailand, but this generates large amounts (7.3 million tons in 2015) of waste cassava pulp (WCP). The solid WCP is sold directly to farmers or pulp-drying companies at a low cost to reduce the burden of on-site waste storage. Using an integrated direct and environmental cost model, fermented animal feed and mushroom growth media were compared as added-value waste management alternatives for WCP to mitigate environmental problems. Primary and secondary data were collected from the literature, field data, and case studies. Data boundaries were restricted to a gate-to-gate scenario with a receiving capacity of 500 t WCP/d, and based on a new production unit being set up at the starch factory. The total production cost of each WCP utilization option was analyzed from the economic and environmental costs. Fermented animal feed was an economically attractive scenario, giving a higher net present value (NPV), lower investment cost and environmental impact, and a shorter payback period for the 10-year operational period. The selling price of mushrooms was the most sensitive parameter regarding the NPV, while the NPV for the price of fermented animal feed had the highest value in the best-case scenario.

Adoption of the circular economy concept to utilize wastes and by-products from the cassava starch industry for biogas production has been considered a viable option. The annual generation of wastewater and cassava pulp in Thailand is reported to be approximately 21 million m3 and 9.5 Mt, respectively. This research therefore aimed to analyze the key drivers and challenges in implementing the circular economy concept in the cassava starch industry in order to generate higher demand for biogas systems, increase the energy security and resource efficiency, and combat the environmental problems associated with cassava wastes. The following three scenarios were analyzed in this study: (1) a factory without integrated biogas system, (2) a factory with integrated biogas installation using wastewater as a raw material, and (3) a factory with biogas system using both wastewater and cassava pulp as raw materials. The assessment of economic feasibility, resource efficiency, water recovery, land use, and global warming potential was performed to compare different scenarios. This study found that Scenario 3 generated the highest net present value and the shortest payback period of 6.14 million USD and 4.37 yr, respectively, for the 10-yr operational period. Moreover, Scenario 3 had the highest resource efficiency and water recovery with the lowest land use (1.89 × 105 m2 at 5 × 105 kg of starch d− 1) and the lowest global warming potential (0.14 kg CO2eq kg− 1 of starch).

This research integrated the circular economy (CE) concept in the cassava starch industry in Thailand, and revealed the benefits of biogas generation from both the wastewater and waste cassava pulp with a focus on the identification and analysis of the key drivers and challenges to increase the efficiency of the biogas system. The research methodology applied the CE concept for scenarios of cassava pulp utilization for biogas production, compared to the no waste treatment and anaerobic wastewater treatment scenarios, in termsof an economic assessment, resource efficiency, water recovery, land use, and global warming potential. Proposed options mainly involved the conservation of energy, water, land use, and reduction of greenhouse gases emissions. These included the reuse and recycling of water and use of biogas to substitute for fuel oil for burners and electricity in the cassava starch production process.

An adoption of the circular economy concept to utilize the wastes and by-products in the cassava starch industry to produce the biogas is a high potential option. Thai cassava starch industry generates wastes and by-products, as such the wastewater of 21.00 million m3 y-1 and the cassava pulp of 9.50 million t y-1. This research analyzed the key drivers and challenges to increase the demand of biogas system, increasing the energy security, resource efficiency, and decreasing the environmental problem. Three-scenarios of (1) a factory has no biogas system, (2) a factory produces biogas using wastewater as a raw material, and (3) a factory produces biogas using both wastewater and cassava pulp as raw materials, were analyzed. The economic assessment, resource efficiency, water recovery, land use, and global warming potential were the parameter of comparison. Scenario 3 generated a highest net present value, and a shortest payback period for the 10-year operational period with 6.14 million USD and 4.37 y, respectively. Moreover, scenario 3 had the highest resource efficiency and water recovery with the lowest land (18.90 ha with 500 t starch d-1) use and global warming (144.33 kg CO2eq t-1 starch).