Open Collections

Rahman, Nahian

University of British Columbia

Wastewater treatment plants (WWTP) generate mixed sludge (MS) containing high volumes of organic and inorganic matter, posing treatment and disposal challenges. Hydrothermal liquefaction (HTL) is a potential thermo-chemical technology for converting sludge to fuel (biocrude oil) offering a smaller footprint alternative to typical sludge digestion methods such as anaerobic digestion (AD) for treating high-volume sludge. However, the large amount of aqueous by-product (HTLaq) from the HTL poses challenges for industrial-scale use. Onsite biological treatment can be a low-cost and effective solution for HTLaq. Whereas, complex substances and highly soluble organic compounds in HTLaq inhibit downstream biological treatment processes, making pretreatment of HTLaq before biological treatment a necessity for commercializing HTL in sludge management. This study used hydrogen peroxide (H₂O₂) to pretreat HTLaq, derived from municipal sludge cake at HTL conditions of 350ºC for 15 min residence time, and the biodegradability efficiency of pretreated HTLaq was evaluated. Previous studies used HTLaq from other feedstocks. Quenchers, such as sodium carbonate (Na₂CO₃) and sodium sulphite (Na₂SO₃), were used to remove the residual H₂O₂ from the pretreated HTLaq, which caused discrepancies in total chemical oxygen demand (tCOD) results and additional inhibition in downstream biological treatment. Pretreatment of aqueous for 2 h at dosages of 0.25, 0.50, and 0.75 g H₂O₂/g COD of HTLaq, followed by a quencher addition (H₂O₂: quencher at 1:1 (w/w)) and 3 h waiting period, achieved the highest efficiency in tCOD removal from HTLaq. Approximately 18% of tCOD removal was achieved from pretreated HTLaq at 0.75 g H₂O₂/g COD with sodium carbonate as a quencher. Additionally, pretreated HTL at 0.5 g H₂O₂/g COD with Na₂CO₃ as a quencher achieved a reduction of phenolics by 50% compared to unpretreated HTLaq. Further biological degradability assessments using mesophilic and thermophilic biochemical methane potential (BMP) assays yielded 16% and 63% higher specific cumulative methane yield, respectively, for pretreated HTLaq at 0.25 g H₂O₂/g COD with Na₂CO₃ quencher. Additionally, the aerobic biodegradability index, estimated by the ultimate biochemical oxygen demand (BOD)/tCOD ratio, increased from 0.75 to 0.85 for HTLaq pretreated assays. Results indicate that low-dosage H₂O₂ can be suitable for pretreating HTLaq before downstream biological treatment.

Text

2024-10-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89586

Civil Engineering

University of British Columbia

UBCO

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