Synergistic effects of digestate-derived biochar and free nitrous acid on biogas production from sewage sludge | |
| Author | Shakya, Stuti |
| Call Number | AIT Thesis no.EV-25-16 |
| Subject(s) | Sewage sludge--Purification Biotechnology Biogas |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Abstract | Effective and sustainable sludge management has become increasingly challenging with rapid urbanization and the expansion of wastewater treatment facilities. This study explores a method that integrates pretreatment techniques with additives to enhance biogas generation from sewage sludge, aligning with circular economy principles. Free Nitrous Acid (FNA) pretreatment and digestate-derived biochar were applied to thickened waste activated sludge (TWAS). Batch experiments tested varying FNA concentrations (0.5–5.93 mg N/L) and biochar dosages (2–14 g/L), with optimization conducted using Response Surface Methodology (RSM). Higher FNA concentrations significantly increased sludge solubilization, with soluble chemical oxygen demand (SCOD) release rising by 2.21%–7.78%, while thermal treatment at 90°C had minimal additional impact. Combined pretreatment at 5 mg N/L FNA and 2 g/L biochar resulted in biogas and methane yield improvements of 168.9% and 233%, respectively. However, methane content remained modest (17.2%–26.6%) due to the low biodegradability (VS/TS = 0.45) and long sludge age. Higher biochar dosages negatively affected biogas production, likely due to microbial competition favoring denitrifiers over methanogens, evidenced by extended lag phases up to 5 days and the absence of nitrite and nitrate in the digestate. RSM optimization identified 5.93 mg N/L FNA without biochar as the optimal condition for biogas enhancement. Economic analysis showed a negative energy balance across treatments, primarily due to the high energy demands of biochar production and thermal pretreatment. However, biochar application offered advantages in phosphorus capture and sludge volume reduction, supporting resource recovery goals. Future work should optimize biochar production methods, explore semi-continuous operation, evaluate impacts on sludge with higher organic content, and investigate microbial community dynamics to further enhance energy recovery and system sustainability. |
| Year | 2025 |
| Type | Thesis |
| School | School of Engineering and Technology |
| Department | Department of Water Resources and Environmental Engineering (DWREE) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Ghimire, Anish;Cruz, Simon Guerrero (Co-chairperson); |
| Examination Committee(s) | Chongrak Polprasert;Thammarat Koottatep; |
| Scholarship Donor(s) | Global Water & Sanitation Center (GWSC);AIT Scholarship; |
| Degree | Thesis (M. Eng.) - Asian Institute of Technology, 2025 |