Thesis Format
Alternative Format
Degree
Master of Engineering Science
Program
Chemical and Biochemical Engineering
Supervisor
Nakhla, George
Abstract
The increasing demand for sustainable energy has highlighted the importance of utilizing renewable resources like cattle manure for biogas production. However, the recalcitrance of lignocellulosic biomass primarily composed of lignin, cellulose, and hemicellulose, limits its biodegradability and methane yield during anaerobic digestion (AD). This study explored chemical, thermal, and thermochemical pretreatment methods to enhance substrate digestibility and methane production.
Chemical pretreatment involved using NaOH at pH levels of 8, 10, and 12 for contact times of 6, 15, and 24 hours. In batch systems with a substrate-to-inoculum ratio of 2:1 at 35°C, optimal results were observed at pH 12 for 15 hours, yielding 149 mL-CH4/gCODadded and achieving a biodegradability of 43%. In fed-batch systems with an HRT of 20 days and OLR of 3.75 gCOD/L-d, maximum biodegradability reached 35%, 40%, and 37% for pH 8, 10, and 12, respectively. At pH 10 and 12, lignin, cellulose, and hemicellulose removal ranged from 12%-13%, 55%-58%, and 55%-58%, respectively, and were notably higher than at pH 8.
Thermal pretreatment was conducted at temperatures of 50°C, 70°C, and 90°C for contact times of 6, 15, and 24 hours. In batch systems, methane yields of 161 mL-CH4/gCODadded and biodegradability of 46% were achieved at 70°C and 90°C for 24 hours. In fed-batch systems under the same conditions, biodegradability reached 34%, 36%, and 37%, respectively, with the highest lignocellulosic removal observed at 90°C: 21% lignin, 63% cellulose, and 56% hemicellulose.
Thermochemical pretreatment combined NaOH (pH 8, 10, and 12) with temperatures of 50°C, 70°C, and 90°C for contact times of 6, 15, and 24 hours. The optimal conditions were pH 12, 90°C, and 24 hours, which resulted in a maximum biodegradability of 51% and a methane yield of 180 mL-CH4/gCODadded.
In conclusion, this study demonstrated that chemical, thermal, and thermochemical pretreatments improve the anaerobic digestion of cattle manure by enhancing lignocellulosic degradation. Among the methods tested, thermochemical pretreatment proved to be the most effective in maximizing methane production.
Summary for Lay Audience
Cattle manure is a valuable source of renewable energy, particularly methane (CH₄), which can be captured and used as biogas for power generation. However, maximizing methane extraction from manure is challenging due to its complex structure. Manure contains components such as lignin, cellulose, and hemicellulose, which are resistant to degradation, making it harder for microorganisms to break them down efficiently and produce methane. Thus, application of new technologies to break down the complex structure of cattle manure could improve its digestion.
To enhance methane production, researchers have investigated various treatments to improve the digestibility of manure components, focusing on lignin, cellulose, and hemicellulose degradation. Commonly used methods include chemical (pH adjustment using chemicals), thermal (heating), and thermochemical (a combination of chemicals and heat) pretreatments. In the present study, chemical, thermal, thermo-chemical pretreatments were applied to the cattle manure followed by anaerobic digestion in batch and continuous-flow modes.
The findings of this study showed that chemical, thermal, and thermochemical pretreatments improved cattle manure digestion by 26.4%, 27.7%, and 34.2%, respectively, compared to the untreated sample. The highest cattle manure digestion was observed at pH of 12 and temperature of 90 ﹾC for contact time of 24 hours, because of simultaneous heat and chemicals that facilitated lignin, cellulose, and hemicellulose degradation.
Recommended Citation
Kianizadeh, Seyedehfatemeh, "Evaluation of chemical, thermal and thermo-chemical pretreatment effects on lignocellulose in cattle manure for enhanced biogas production" (2024). Electronic Thesis and Dissertation Repository. 10835.
https://ir.lib.uwo.ca/etd/10835