Life cycle optimization model for rice straw utilization in the Philippines

• Main Author: Tan, Iliana Benice T.
• Format: text
• Language: English
• Published: Animo Repository 2020
• Subjects: Agricultural wastes—Environmental aspects; Organic wastes as fertilizer; Rice; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/5916; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/12896/viewcontent/Tan_Illiana_Benice_11699043_Redacted.pdf
• Institution: De La Salle University

Biomass waste utilization is being explored as a means to combat high greenhouse gas emissions. In the Philippines, one of the highest volumes of biomass waste is from rice straw. Rice straw can be converted to higher-value products such as fertilizer, electricity, and fuel through mechanical, thermochemical processes like combustion, gasification, or pyrolysis; and biochemical processes like fermentation and anaerobic digestion. However, there is no consensus on which is the best technology to adapt. Existing literature utilizes different reference units, there is lacking use of footprint indicators, and the uncertainties and sensitivities that exist within the supply chain are not adequately addressed. This study develops a model which optimizes the environmental performance of rice straw utilization using carbon and nitrogen footprints under demand considerations. The study examines the tradeoff between the carbon and the nitrogen footprint and investigates the sensitive parameters within the supply chain. The developed model utilizes life cycle optimization as its framework for single-objective optimization, it was then extended into a fuzzy optimization model to accommodate multiple objectives. Furthermore, Monte Carlo sensitivity analysis is performed to analyze the impact of variations in process efficiencies on footprint reduction. The results showed that overall, the model avoids open burning of rice straw and prefers to utilize the rice straw through gasification, pyrolysis, anaerobic digestion, and fermentation. The study considered two scenarios namely neglecting the additional emissions due to changes in fertilizer and including these additional emissions. These scenarios showed that emissions vary and show tradeoffs with the substitution of commercial fertilizer to rice straw fertilizer. Commercial fertilizer was preferred when the objective was to minimize carbon footprint, while rice straw fertilizer was preferred when nitrogen footprint was minimized. The sensitivity analysis showed that the rice straw fertilizer application phase greatly affects the nitrogen and carbon footprint reduction. While additional consideration for rice straw transport and collection should be placed as these can be sensitive parameters for the two footprints as well.