Thesis Defence: Pretreatment of Hydrothermal Liquefaction Aqueous from Municipal Sludge by Hydrogen Peroxide for Enhanced Biological Treatment

Nahian Rahman, supervised by Dr. Cigdem Eskicioglu, will defend their thesis titled “Pretreatment of Hydrothermal Liquefaction Aqueous from Municipal Sludge by Hydrogen Peroxide for Enhanced Biological Treatment” in partial fulfillment of the requirements for the degree of Master of Applied Science in Civil Engineering.

An abstract for Nahian Rahman’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Please email cigdem.eskicioglu@ubc.ca to receive the Zoom link for this defence.

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ABSTRACT

Wastewater treatment plants (WWTP) generate mixed sludge (MS) containing high volumes of organic and inorganic pollutants posing treatment and disposal challenges. Hydrothermal liquefaction (HTL) is a potential thermo-chemical technology for converting sludge to fuel (bio-crude 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 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 and sodium sulphite, were used to remove the residual hydrogen peroxide 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 hydrogen peroxide/g COD of HTLaq, followed by a quencher addition (hydrogen peroxide: 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 hydrogen peroxide/g COD with sodium carbonate as a quencher. Additionally, pretreated HTL at 0.5 g hydrogen peroxide/g COD with sodium carbonate 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 hydrogen peroxide/g COD with sodium carbonate 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 hydrogen peroxide can be suitable for pretreating HTLaq before downstream biological treatment.