Algal biomass production inhibition and adaptive bioprocess pathways via reutilization of hydrothermal liquefaction wastewater

The increasing need to remediate waste and bolster food, energy, and water (FEW) resources for our global population necessitates research for sustainable development. New waste-to-energy technologies can improve the reutilization of resources within our circular bioeconomy and thus improve the resilience of our FEW systems. Hydrothermal Liquefaction (HTL) has shown promise to serve as a critical tool in the efficient conversion of organic wastes to renewable resources, including biocrude oil and a nutrient rich, toxic wastewater, known as Post HTL Wastewater (PHW). When coupled with biological treatment through systems like the Environment Enhancing Energy (E2E) Paradigm, biomass and nutrients may be recycled through the system repeatedly to create a wealth of sustainable bioproducts. HTL has been shown to covert agricultural wastes, such as animal manure, algal biomass, corn stalks, etc., using high heat and pressure (300C and 1400psi) into renewable biocrude and a toxic wastewater rich in nutrients and organic compounds. Food waste was identified as a promising feedstock given its diverse composition and yields of biocrude as high as 60% for lipid rich materials when HTL operational conditions are optimized. The present research collected food waste from two campus dining halls, at University of Illinois in Urbana-Champaign and University of São Paulo in Pirassununga, São Paulo, Brazil, and separated materials into groups based on proteins, lipids, and carbohydrates before performing HTL over a range of temperature and time to maximize biocrude yield and quality. Then, PHW was characterized for organic compounds, nitrogen content, and micronutrients to determine suitability for use as a substrate in downstream biological processes. The results showed that while PHW was replete with essential growth nutrients, there were also lacking elements that could hinder growth, based on optimal media composition for anaerobic digestion and algae. Algal growth assays have been performed to determine the toxicity of PHW and dilution necessary to allow for biomass production. A key set of analyses were performed to determine the effects of different PHW dilutions on algal physiology and metabolism for 5 different species. The results showed that individual species could survive in up to 1% PHW but this would result in decreases in cellular viability and photosynthesis. Modeling of the algal growth suing the Gompertz equation also quantified changes in adaptation (lag) phase and maximum growth rate. Notably, Chlorella sorokiniana (CS) was able to grow in 2% and increase biomass production while photosynthetic performance decreased, signaling mixotrophic metabolism. Mixotrophic metabolism is the combined autotrophy (photosynthesis) and heterotrophy (growth on organic substrates), proving that CS was able to enhance its biomass production by utilizing PHW compounds and adapting to the augmented media. The significant dilution required also prompts development of strategies to increase PHW utilization in such biological systems. Mixed cultures or polycultures have been shown to increase the resilience of microbial communities to system perturbations and acute toxic shocks. The present research and growth assays were expanded by mixing multiple algal species to achieve growth in as much as 5% with as few as 3 species. Chlorella spp. again proved to be the most dominant in the best performing cultures and were scaled up to measure changes in growth rates, photosynthetic performance, and biochemical composition. The results showed that while polycultures were more resilient to PHW, they still demonstrated the same negative effects on photosynthesis, suggesting that the algae utilize other mechanisms to maintain their growth despite toxicity. Similarly, combinations of 1, 2, or 3 species of algae all presented increased biomass and increased carbohydrates in biomass, suggesting that PHW derived algal biomass is not ideal for recycling back into HTL. In order to further increase PHW utilization, the Environmental Protection Agency’s (EPA) Toxicity Identification Evaluation (TIE) methodology was implemented as a novel pretreatment for improving algal biomass production. Shown previously to improve the ecotoxicity of municipal, agricultural, and industrial wastewater, TIE treatment methods including filtration, oxidation, chelation, and solid phase extraction (SPE), removed various potential toxins to improve algal viability. Through additional screening assays, SPE was shown to allow for algal growth in as much as 50% PHW. The results comparing control growth, 0.5% raw PHW, and 5% TIE SPE on algal metabolism showed that wastewater utilization was improved but growth and photosynthesis were still hampered. RNA sequencing (RNAseq) was used as a tool to quantify changes in gene expression to inform algae and wastewater researchers on how to carry out studies that will further improve utilization and biomass production. The complexities of waste management and reutilization for agricultural systems require input from multiple stakeholders and detailed, technical understanding of factors influencing biomass generation, processing, and valorization. Thus, the overall objective is to identify and evaluate a complete set of activities that support the enhancement of waste-to-energy systems for global sustainability.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Agricultural & Biological Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Stablein, Michael James

Contributors dc:contributor

• Rodriguez, Luis F
• Davidson, Paul
• Malvandi, Amir
• Tommaso, Giovana
• Lombardi, Ana Teresa

• algae
• wastewater

Statement dc:rights

• Copyright 2025 Michael Stablein

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129606

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129606