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Mohd Nasir, Amirah Syafika

University of British Columbia

The integration of pyrolysis after anaerobic digestion offers the benefits of waste-to-resources and maximizing energy recovery from waste materials. The pyrolysis process converts the solid digestate into valuable products, including biochar. In this study, we examine the composition of primary solid digestate (PSD) and secondary solid digestate (SSD) from an on-farm anaerobic digester. The physiochemical properties of the biochar was analyzed to understand the impact of precursor characteristics on biochar properties. Both PSD and SSD contained high lignin content, but the SSD has higher ash content compared to PSD. The results revealed that biochar PSD-B500 exhibited superior characteristics with a higher specific surface (249 m²/g), micropore volume (0.106 cm³/g) and acidic functional groups (6.64 mmol/g) than SSD biochar (SSD-B500) (31.9 m2/g, 0.0019 cm3/g, 5.39 mmol/g). This suggests that PSD is a favourable feedstock for producing high-quality biochar. Adsorption is a promising technique for water treatment and has garnered attention, particularly in utilizing adsorbents derived from waste materials. The effectiveness of the two adsorbents was analyzed by investigating the removal of pollutants called polycyclic aromatic hydrocarbons (PAHs). Four compounds were selected: phenanthrene (PHEN), anthracene (ANT), fluoranthene (FLUO) and pyrene (PYR). The estimated adsorption capacities of PHEN, ANT, FLUO and PYR are 2991, 6059, 15590 and 7262 μg/g onto PSD-B500, which were 46-90% higher than SSD-B500. Thermodynamic studies demonstrated that PAHs adsorption onto PSD-B500 was spontaneous and feasible. Leachability of loaded biochar confirmed the strong bonding of PAHs to both biochars, with < 3% release ratio. The effect of pH, dosage, and humic acid had a limited effect on the percentage removal of PAHs using PSD-B500. The performance of PSD-B500 was analyzed under various conditions representing common produced water compositions. The results indicate that PSD-B500 is not significantly affected by the presence of salts and formic acids. However, notable reduction in removal efficiencies was observed with presence of Ca²⁺, Zn²⁺, Cu²⁺, and Pb²⁺. The comparative analysis between PSD-B500 with commercial activated carbon over three adsorption cycles, highlights the limitation of inactivated biochar, as PSD-B500 shows a significant decrease (~30%) in the efficiency after the first cycle compared to activated carbon.

Text

2024-02-21

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87463

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/