Valorization of hydrothermal liquefaction aqueous phase via bio-electro-chemical processes

Wang, Zixin

Permalink

https://hdl.handle.net/2142/125819 Copy

Description

Title

Valorization of hydrothermal liquefaction aqueous phase via bio-electro-chemical processes

Author(s)

Wang, Zixin

Issue Date

2024-07-12

Director of Research (if dissertation) or Advisor (if thesis)

Zhang, Yuanhui

Doctoral Committee Chair(s)

Zhang, Yuanhui

Committee Member(s)

• Cai, Ximing
• Chu, Maria L.
• Davidson, Paul C.
• Yang, Hong

Department of Study

Engineering Administration

Discipline

Agricultural & Biological Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Hydrothermal liquefaction aqueous phase
• Waste valorization

Abstract

Hydrothermal liquefaction (HTL) is a promising approach for converting wet biomass into biocrude oil, which can serve as a precursor for the production of transportation fuel and valuable chemicals. However, an inevitable byproduct of HTL process is the post-HTL aqueous phase (HTL-AP), which is a waste stream containing toxins and pollutants that must be mitigated before discharge. On the other hand, HTL-AP is rich in nutrient and energy contents that can be recovered for reuse. Approximately 20-40% of the total energy from the original biomass remains in the HTL-AP, presenting a huge potential for valorization. This study explored different treatment approaches, including biological and electrochemical, to elucidate the potential of the HTL-AP valorization. The first approach involved anaerobic digestion (AD) of HTL-AP with the presence of biochar. Adding biochar to AD was reported to facilitate the digestion, but its role has not been explicitly determined. The added biochar could promote direct interspecies electron transfer (DIET), while the adsorption and detoxification effects of biochar cannot be overlooked. Results showed that the total pore volume and adsorption capacity of biochar played the most influential role. DIET was very likely not dominant since the limited electrical conductivity and electron-donating/accepting capacities of biochar. The microbial analysis further indicated that mediated interspecies electron transfer remained as the primary mechanism rather than DIET. The addition of facilitative biochar enriched Thermovirga and Methanosaeta, whereas a suppressive biochar can promote activities of microbes such as Asaccharospora, Clostridium, and Methanobacterium. The second approach involved two stage fermentation of HTL-AP with crude glycerol as the co-substrate. Compared with single stage, the biogas production from two stage mono-fermentation of HTL-AP was improved by 25.5%, and it was further increased to 1.85 times when crude glycerol was added at a ratio of 1:1 with HTL-AP. The addition of co-substrate crude glycerol helped relieve the acidic stress, adjust the nutrient supply, and dilute the concentration of toxic chemicals in HTL-AP. The initial pH of the fermentation was also controlled, with the highest hydrogen production achieved at an initial pH of 5.5. The pH control optimized the metabolic pathways during the first stage of hydrogen production and provided desirable intermediates for the second stage of methanogenesis. Accompanied with the enhanced biogas yield, the organic conversion, energy generation, and energy recovery from two stage co-fermentation were improved by 48.6%, 84.9%, and 40.1% compared to single stage fermentation, respectively. The third approach involved the electrochemical oxidation of HTL-AP under four different current densities to degrade the organics and generate the clean energy – hydrogen, and the electrodialysis to separate and recover the nutrients from HTL-AP. At the current density of 0.15 A/cm2, the anodic COD removal efficiency reached 76.49% with acetic acid accounting for over 75% of the remaining COD after 8 hours of electrooxidation. Nitrogen compounds were also efficiently decomposed into nitrate and ammonia: at low current density of 0.025 A/cm2, ammonia accumulation in the catholyte was detected via the diffusion of ammonia from anode to cathode under the acidic environment; while at high current densities, nitrate was generated via the efficient oxidation process. Electrodialysis facilitated the further recovery of anions in the post-oxidation HTL-AP that all the phosphorus and nitrate were separated and collected in the anolyte with KH2PO4, making the solution suitable for fertilizer production. The current efficiency of COD removal and energy efficiency of hydrogen production could achieve their highest at 87.82% and 23.14%, respectively. These results demonstrated that the coupling of electrooxidation and electrodialysis could benefit the enrichment and refinement of acetic acids as well as the recovery of various nutrients, including phosphorus, nitrogen, and potassium, from the HTL-AP which can be further used for the production of several valuable chemicals and fertilizers. Additionally, production of the high purity hydrogen can be utilized for biocrude upgrading via hydrocracking, integrating downstream HTL-AP treatment with upstream HTL as a complete waste valorization system. Findings of this study contributed to the sustainable and economically viable approaches for wastewater treatment and resource recovery in HTL processes. By optimizing HTL-AP valorization through various pathways, this study enhanced the efficiency and environmental impacts of HTL technology, promoting its wider adoption for biomass conversion.

Graduation Semester

2024-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/125819

Copyright and License Information

Copyright 2024 Zixin Wang

Owning Collections