Advancing the sustainability and cost-effectiveness of hydrothermal liquefaction of algal-bacterial biomass

Da Cruz Costa, Tiago Henrique

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https://hdl.handle.net/2142/129766 Copy

Description

Title

Advancing the sustainability and cost-effectiveness of hydrothermal liquefaction of algal-bacterial biomass

Author(s)

Da Cruz Costa, Tiago Henrique

Issue Date

2025-05-02

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

Schideman, Lance

Doctoral Committee Chair(s)

Zhang, Yuanhui

Committee Member(s)

• Rodriguez, Luis
• Davidson, Paul C.
• Rajagopalan, Nandakishore

Department of Study

Engineering Administration

Discipline

Agricultural & Biological Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Hydrothermal liquefaction
• Biofuel
• Sustainable energy

Abstract

Hydrothermal liquefaction (HTL) is an emerging thermochemical technology that converts wet biomass into a biocrude, which can be refined into drop-in liquid fuels with characteristics similar to those of their fossil counterparts. These biofuels require minimal to no modifications to existing fleets, while achieving significantly lower life cycle greenhouse gas (GHG) emissions. Because of its versatility and capability to handle high-moisture biomass, HTL is one of the most promising pathways for converting algal biomass into fuels and value-added chemicals. Due to elevated cultivation costs and competing demands of single-species microalgae cultivation, mixed algal-bacterial biomass from wastewater treatment systems has emerged as an attractive feedstock for HTL. Despite its great potential, HTL also produces a nutrient- and carbon-rich waste stream known as HTL aqueous phase (HTL-AP), which requires proper treatment and disposal. Addressing the treatment and valorization of this byproduct remains one of the key challenges impeding the widespread, full-scale implementation of HTL. Therefore, this study investigated the integration of membrane filtration as a valorization method for the HTL-AP of algal-bacterial biomass. In the proposed process configuration, nanofiltration concentrates organic compounds and separates nutrients from HTL-AP. The concentrated organics can be recirculated back into HTL as process water to improve biocrude conversion efficiency, while the nutrients can serve as a growth supplement in biomass cultivation. The research was structured into three main studies. In the first study (Chapter 3), the effects of filtration operational conditions (membrane type, pH, and filtration temperature) on separation efficiency and permeate flux were evaluated for two types of biomass: one from an algal wastewater treatment system and the other from harmful algal blooms (HABs). The impact of recirculating the concentrated HTL-AP back into HTL was assessed in terms of biocrude yield and quality over one recirculation cycle. Next (Chapter 4), humic acid precipitation was investigated as an HTL-AP pretreatment method to improve the efficiency and robustness of HTL-AP nanofiltration. Its effects on filtration performance and HTL efficiency parameters were evaluated over five consecutive recirculation cycles, and the nanofiltration permeate was tested as a growth supplement in algal-bacterial biomass cultivation. Finally (Chapter 5), techno-economic analysis (TEA) and life cycle analysis (LCA) were conducted to assess the process's economic feasibility and environmental sustainability, comparing it with other HTL-AP valorization strategies (catalytic hydrothermal gasification and untreated HTL-AP recirculation). The results of this research showed that nanofiltration is an effective strategy for valorizing the HTL-AP of algal-bacterial biomass. When optimized for maximum separation efficiency of organics from nutrients (pH 11 and filtration temperature of 45 °C), 99% of the organics were recovered in the retentate. Recirculating the retentate back to HTL increased biocrude yield by 70% to 116% while reducing biocrude nitrogen content by up to 12%. The carbon and energy capture in the biocrude also increased by 66% and 68%, respectively. Humic acid precipitation proved an effective and essential pretreatment for the nanofiltration of high-strength HTL-AP, allowing the process to sustain reasonable permeate fluxes over five consecutive recirculation cycles. Thermogravimetric analysis of the biocrude showed that 83% of its mass falls in the distillate range of sustainable transportation fuels. Additionally, biomass cultivation experiments showed that adding the permeate from the nanofiltration of HTL-AP to the cultivation medium at approximately 3 wt% increased the biomass growth rate by 89%. The TEA and LCA revealed that, compared to the other valorization strategies, integration of nanofiltration improves both the cost-effectiveness and sustainability of biofuels produced via HTL of algal-bacterial biomass. The analysis showed that this HTL configuration could produce net negative fuels at a minimum fuel selling price (MFSP) of $3.32 per gasoline gallon equivalent (gge).

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129766

Copyright and License Information

Copyright 2025 Tiago Da Cruz Costa

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