Hydrothermal Liquefaction Technology Research Articles

Advancements and challenges in catalytic hydrothermal liquefaction of lignocellulosic biomass: A comprehensive review

Hydrothermal liquefaction (HTL) is one of the leading technologies for converting lignocellulosic biomass waste into liquid bio-oil to meet the growing energy demands and alleviate environmental crises. In this comprehensive review, an examination and comparison were conducted on three distinct technologies: HTL, Microwave-Assisted Hydrothermal Liquefaction (MA-HTL), and Co-hydrothermal Liquefaction (Co-HTL). The assessment encompassed various parameters, including production efficiency, bio-oil quality, production cost, and operational conditions. Furthermore, the pivotal role of catalysts in enhancing the bio-oil quality was explored. The corresponding catalytic attributes, spanning homogenous, heterogeneous, and combined catalysts, along with the associated mechanisms such as depolymerization, decarboxylation, decarbonylation, hydrogenation, dehydration, deoxygenation, and hydrodeoxygenation, were thoroughly examined. Additionally, the review delved into upgrading technologies and potential applications of bio-oil to broaden its utility. The current challenges and future prospects concerning bio-oil production using HTL technologies were also addressed.

Continuous wet air oxidation of aqueous phase from hydrothermal liquefaction of sewage sludge

The conversion of organic waste into advanced fuels through hydrothermal liquefaction (HTL) is a promising route. However, for the commercialisation of HTL technology, treatment and valorisation of the generated aqueous by-product are required for its economic viability. This study investigates subcritical non-catalytic continuous wet air oxidation (WAO) for the treatment of the aqueous phase from hydrothermal liquefaction (HTL-AP) of sewage sludge. A custom-made tubular reactor was used at temperatures and residence times similar to the HTL process (300–350 °C; 6–50 min), with excess air equivalent to 1.5–2 times the oxygen demand. The WAO process removed up to 95.3 % of the chemical oxygen demand and 91.8 % of the total organic carbon, generating volatile fatty acids, mainly acetic acid, as intermediary compounds from the oxidation reactions, and CO2 and H2O from the pollutant’s complete degradation. The process effectively eliminated almost all of the organonitrogen compounds, generating NH4+, which reached values of up to 97 % of the total nitrogen. Comprehensive molecular characterization performed by FT−Orbitrap MS analysis revealed that the main basic organonitrogen compounds in HTL-AP are distributed in the O1N1, N2, O1N2, N1 classes. For neutral to acidic organonitrogen species, O3N1 is the most representative chemical class. The energy consumption for heating the WAO reactor was up to 40 % lower using HTL-AP compared to blanks experiments. Despite good process water clean-up, autothermal operation was not achieved, and improvements in the reactor design are suggested.

Aqueous-phase product treatment and monetization options of wet waste hydrothermal liquefaction: Comprehensive techno-economic and life-cycle GHG emission assessment unveiling research opportunities

While wet waste hydrothermal liquefaction technology has a high biofuel yield, a significant amount of the carbon and nitrogen in the feedstock reports to the aqueous-phase product. Pretreatment of this stream before sending to a conventional wastewater plant is essential or at the very least, advisable. In this work, techno-economic and life-cycle assessments were conducted for the state-of-technology baseline and four aqueous-phase product treatment and monetization options based on experimental data. These options can cut minimum fuel selling prices by up to 13 % and life-cycle greenhouse gas emissions by up to 39 % compared to the baseline. These findings highlight the substantial influence of aqueous produce treatment strategies on the entire wet waste hydrothermal liquefaction process, demonstrating the potential for optimizing economic viability and environmental impact through further research and development of milder treatment methods and diversified by-product valorization pathways.

Hydrothermal Liquefaction: How the Holistic Approach by Nature Will Help Solve the Environmental Conundrum.

Hydrothermal liquefaction (HTL) represents a beacon of scientific innovation, which unlocks nature's alchemical wonders while reshaping the waste-to-energy platform. This transformative technology offers sustainable solutions for converting a variety of waste materials to valuable energy products and chemicals-thus addressing environmental concerns, inefficiencies, and high costs associated with conventional waste-management practices. By operating under high temperature and pressure conditions, HTL efficiently reduces waste volume, mitigates harmful pollutant release, and extracts valuable energy from organic waste materials. This comprehensive review delves into the intricacies of the HTL process and explores its applications. Key process parameters, diverse feedstocks, various reactor designs, and recent advancements in HTL technology are thoroughly discussed. Diverse applications of HTL products are examined, and their economic viability toward integration in the market is assessed. Knowledge gaps and opportunities for further exploration are accordingly identified, with a focus on optimizing and scaling up the HTL process for commercial applications. In conclusion, HTL holds great promise as a sustainable technology for waste management, chemical synthesis, and energy production, thus making a significant contribution to a more sustainable future. Its potential to foster a circular economy and its versatility in producing valuable products underscore its transformative role in shaping a more sustainable world.

Agricultural Waste Liquefied Hydrothermally using Heterogeneous Catalyst

Due to its abundance and sustainability, lignocellulosic biomass is a possible replacement for petroleum oil in the production of energy and chemicals. Numerous thermochemical processes have been used in significant study to turn biomass into products with added value. One of the best methods for creating bio-fuels and bio-based compounds among them is hydrothermal liquefaction (HTL). However, a number of technological obstacles still need to be removed before HTL technology can be widely used in industry. Hydrothermal liquefaction is now thought to be amongst the most popular effective processes to converting moist biomass for bio crude, but it requires costly renovation procedures to be utilized as biofuel. It is crucial to employ catalysts that may straightforwardly improve the bio crude yield as well as the efficiency of the reaction process; the benefit of raising the operation’s overall production; the impacts of adding heterogeneous catalysts and how they affect the bio-crude yield. In lignocellulosic biomass hydrothermal liquefaction, a typical catalytic activity was discovered, dividing the various catalysts into four separate groups (transition metal, lanthanide oxide, alkaline metal oxide, and zeolite). The purpose study is to objectively evaluate the hydrothermal liquefaction of lignocellulosic biomass and know effecting of adding a zeolite catalyst on it, with a focus on increasing the production and efficiency of the biofuel. In addition, it has drawn attention to the natural stimulatory effects associated with zeolite catalysts.

Production of biocrude oils from various bio-feedstocks through hydrothermal liquefaction: Comparison of batch and continuous-flow operations

Laboratory- and pilot-scale hydrothermal liquefaction (HTL) of biomass has predominantly been carried out in batch reactor systems. However, the development of continuous-flow reactor systems is critical for industrial deployment of HTL technology in a cost-competitive manner. In this study, a continuous-flow HTL system (with a feed capacity up to 6 kg/h) was developed and employed to convert various types of bio-feedstocks (wood sawdust, cornstalk, and black liquor) into biocrudes in the presence of K2CO3 catalyst at 300 °C for 12 min. The produced biocrude oils were characterized in detail by using GC-MS, FT-IR, GPC, and elemental analysis. This work compared the performance of the continuous-flow HTL process with that of a batch HTL process under the same conditions in terms of the yields and chemistry of the biocrude products as well as the energy recovery potential. The results indicated that HTL of different bio-feedstocks, particularly cornstalk and pinewood, in the continuous-flow reactor led to a higher yield of biocrude (32.4 and 34.5 wt %, respectively) with lower molecular weights and less solid residue (2.9 and 4.6 wt%, respectively) as well as a higher energy recovery rate (53.3 and 52.0%, respectively) compared with those in the batch reactor (Cornstalk: 23.8 wt%, 6.2 wt% and 46.5%; Pinewood: 28.5 wt%, 10.3 wt% and 50.8%, respectively). These promising results shall advance the future development and deployment of the HTL technology in Canadian and global bioenergy sectors.

Catalytic hydrothermal liquefaction of Chinese herb residue for the production of high-quality bio-oil

In this study, the catalytic hydrothermal liquefaction technology was adopted to convert the Chinese herb residue (CHR) into liquid bio-oil. The effect of the reaction conditions was investigated including temperature, water/biomass mass ratio (W/B) and time. Different combinations of Fe, Ni and ZSM-5 molecular sieve catalyst were evaluated to improve the bio-oil quality. The optimized liquefaction parameters were determined through experiments, which were the reaction temperature of 320 °C, W/B of 15:1, and reaction time of 10 min; the yield and high heat value (HHV) of bio-oil were 24.7 wt% and 29.39 MJ/kg, respectively. There was a synergy between Fe and ZSM-5, and Fe/ZSM-5 can achieve in situ hydrodeoxygenation in the liquefaction process, increasing the HHV of bio-oil to 31.74 M J/kg at 10 wt% loading with the yield of 21.3 wt%. The enhancement of bio-oil quality by Ni/ZSM-5 was weak due to the cleavage of C–C bond by Ni, resulting in the poor HHV and a low yield; the catalytic performance of Fe–Ni/ZSM-5 was between the former two catalysts. Elemental analysis and GC-MS showed that Fe/ZSM-5 increased H/C and decreased O/C in bio-oil, and the content of aliphatic compounds in bio-oil increased to 72.96%. • Chinese herb residue can be efficiently utilized by hydrothermal liquefaction. • Reaction temperature and W/B have a significant effect. • The operating conditions were given for highest yields of bio-oil. • Fe/ZSM-5 exhibits synergistic effect of hydrodeoxygenation. • 10 wt% Fe/ZSM-5 increases the HHV of bio-oil to 31.74 MJ/kg.

Production of Sustainable Aviation Fuels from Lignocellulosic Residues in Brazil through Hydrothermal Liquefaction: Techno-Economic and Environmental Assessments

Decarbonization of the aviation sector relies on deployment of sustainable aviation fuels (SAF) at commercial scale. Hydrothermal liquefaction (HTL) has been recognized as a promising technology to help supply the increasing projected SAF demand. High availability of agro-industrial residues, combined with a well-established biorefinery system, makes the sugarcane industry in Brazil a good option for HTL technology deployment. Moreover, challenges regarding the economic feasibility of SAF from HTL could be partially addressed by the RenovaBio policy, a market-driven incentive mechanism of carbon credits implemented in Brazil. This study investigated both the techno-economic and life cycle assessment of SAF production from sugarcane lignocellulosic residues, considering HTL integrated to a first-generation ethanol distillery and a HTL stand-alone facility. The evaluated scenarios showed great climate mitigation potential, reaching a reduction of up to 73–82% when compared to fossil jet fuel. The minimum fuel selling price of SAF at 15.4 USD/GJ indicated potential of economic competitiveness with fossil jet fuel in the best integrated scenario. The economic benefits obtained from carbon credits are not enough to enable feasibility of HTL in the stand-alone scenarios, even with carbon prices projected at 125 USD/tonne CO2-eq avoided.

Hydrothermal liquefaction of waste Al-PE-Pa laminated packaging: Effect of Ni:Ce in Ni10Cex/Al2O3 catalyst

Hydrothermal liquefaction technology was applied for treating waste Al-PE-Pa laminated packaging for bio-oil production at 360 °C, 20 MPa and 30 min. Ni10Cex/Al2O3 catalyst was used to upgrade the quality of bio-oil. The effect of Ni:Ce on bio-oil yield, elements and compounds distributions were investigated. Results showed that the maximum bio-oil yield of 35.53 wt% was obtained with 5 wt% Ce loading. In addition, the O content decreased from 21 wt% without catalyst to 15% with Ni10Ce5/Al2O3 catalyst. The interactions between Ce and Ni facilitate the dispersion of the active metals and promoted the hydrodeoxidation reactions. The main content of the bio-oil produced with Ni10Ce5/Al2O3 catalyst was diesel oil, which mainly due to the accelerated degradation of the long chain C-C bond in paper fibre and PE. This study provided a new approach for waste Al-PE-Pa laminated packaging treatment.

Technology Selection of Microalgae Thermochemical Conversion to Bio-Crude Oil

Microalgae as a third-generation biofuel source with various advantages is a potential part of renewable energy resources. Various studies on the conversion process of microalgae into biofuels have been carried out, one of which is the thermochemical process. The thermochemical conversion process is considered better than the biochemical process which has a low conversion rate and higher production costs. Recent researches state that to obtain bio-crude oil from microalgae through a thermochemical process, there are two alternative technologies that can be used, which are pyrolysis and liquefaction. In this research, a selection was made to determine which technology was better using decision making tools of Analytic Hierarchy Process (AHP) method. The evaluation criteria that have been used are technological (readiness level, energy efficiency, pre-treatment process, and product output), operational complexity, environment, and economy (investment cost and operation cost). The alternative technologies evaluated were pyrolysis with bubbling fluidized bed reactor, pyrolysis with circulating fluidized bed reactor, and hydrothermal liquefaction. From the results of pairwise comparisons, the technological criteria had the highest weight (0.343) and hydrothermal liquefaction technology was the best alternative technology among other alternatives (0.420).

Valorization of Plastic Waste: A Lab-Scale Approach with the Aid of Solar Hydrothermal Liquefaction Technology

Valorization of Plastic Waste: A Lab-Scale Approach with the Aid of Solar Hydrothermal Liquefaction Technology

Renewable adsorbents from the solid residue of sewage sludge hydrothermal liquefaction for wastewater treatment

Solid residue from hydrothermal liquefaction (HTL) of nutrient rich feedstock presents a promising source to recover valuable nutrients, such as phosphorus, in the solid form. The present work shows for the first time the potential of utilizing the waste residue remaining after nutrients extraction from HTL of sewage sludge, as renewable adsorbents. A parametric study was undertaken to investigate the influence of chemical activation conditions (temperature, residence time, activation agent loading, washing after activation) on raw and partially demineralized HTL solids. Kinetic and equilibrium adsorption investigation was undertaken for the removal of methylene blue (MB) from aqueous solution. For comparison purposes, a commercial activated charcoal (AC) was used. Demineralization was found to have a significant influence in the adsorption capacity of the resultant adsorbents. Three adsorbents were found to follow the Langmuir adsorption model, while the acid washed demineralized adsorbent had higher adsorption capacity than AC and was found to follow the Freundlich adsorption model. The superior performance of the acid washed demineralized adsorbent was verified from the kinetic study where all adsorbents were found to best fit the pseudo-second order model. Adsorption capacities for MB at equilibrium were 367.1, 332.3, 297.4 and 87.6 mg/g, for acid washed demineralized adsorbent, AC, demineralized adsorbent, and raw adsorbent, respectively. Finally, the most promising adsorbents were assessed for their adsorption capacity to remove pharmaceuticals present in a real wastewater treatment effluent. Results indicated ultimate concentration for all targeted compounds below the detection limits for acid washed demineralized adsorbent, AC and demineralized adsorbent. Future implementation of HTL technology in wastewater treatment facilities, will not only provide an efficient way to valorize sewage sludge into bio-crude and nutrients, but can also enhance technology integration by providing the precursors for renewable adsorbents needed in tertiary treatment of wastewater.

Assessment of Product Yield and Characteristics of Biocrude from Hydrothermal Liquefaction

Biomass is a promising renewable energy source for fuel conversion. Hydrothermal liquefaction technology converts biomass into an energy-rich biofuel called biocrude which can potentially substitute fossil fuels. In this study, wet biomass namely water hyacinth, banana pseudostem, banana peduncle, wine waste and beer waste were investigated for biocrude production. The biomass macro molecules underwent anaerobic thermochemical disintegration to yield biocrude in the range of 7.3 to 16% at the hydrothermal liquefaction temperature and pressure of 275 ºC and 15 MPa respectively. Wine waste showed higher biocrude yield (16%) among the selected biomass materials with aqueous phase (63%) and char (3%) as by products. The recovered biocrude showed good quality fuel properties similar to diesel and bio-diesel with heating value of about 30 MJ kg-1. GCMS and FTIR analyses proved the biocrude to be rich in aliphatic and aromatic fuel and chemical derivatives of alkenes, alcohols, ketones and amines which necessitate its potential to drop in advanced fuels and chemicals for supplementing conventional resources.

Design and scale-up challenges in hydrothermal liquefaction process for biocrude production and its upgradation

• Hydrothermal Liquefaction (HTL) process has the ability to convert all kinds of biomasses to biocrude, which is comparable to fossil crude oil and can be upgraded in existing refinery set-up. • Article identifies various design, scale-up and operational challenges in HTL technology and proposes potential ways to mitigate those challenges. • Key challenges in the post processing of biocrude to make it refinery ready are the high amount of heteroatoms, moisture, ash, and acid content. Renewables are going to play an important role in meeting the greenhouse gas (GHG) emission targets to mitigate the effects of climate change. Most of the bioenergy production processes available today can be broadly categorized into two types of technologies - biological and thermochemical processes. Worldwide, the major practiced methods are Combustion/Incineration, Pyrolysis, Gasification, Anaerobic digestion, Fermentation etc. These methods have their own benefits and limitations based on their capability and capacity to process various feed stocks, energy efficiency, operational challenges, product quality and economics. Hydrothermal liquefaction (HTL) process is one such method, which has recently attracted attention of many scientific and practicing community across the world on various platforms. HTL process has the ability to convert all kinds of biomasses to crude bio-oil, which is comparable to fossil crude oil and can be upgraded in existing refinery set-up. Although it has significant benefits over other conversion technologies, HTL process is yet to be commercialized. Several technical and operational challenges have been reported in literature that need to be addressed for successful scale-up and design of continuous scale HTL process. Large number of review and research articles pertaining to batch and pilot scale are available on the process and product development aspect of HTL process. However, limited information is available on the design and scale-up issues that are envisaged in the scale-up of HTL technology. This review article identifies various design, scale-up and operational challenges in HTL technology and proposes potential ways to mitigate those challenges.

Wet oxidation of aqueous phase from hydrothermal liquefaction of sewage sludge

Hydrothermal liquefaction (HTL) is a thermochemical process for the conversion of biomass into bio-crude oil. However, treatment of post-HTL aqueous by-products is an emerging issue towards the commercialisation of HTL technology. This study investigates the use of non-catalytic wet oxidation (WO) for the reduction of organic compounds and heat production at different temperatures (200–350 °C), residence times (RT) (2–180 min) and excess oxygen. The aqueous phase from HTL of sewage sludge is investigated, and 97.6% of the chemical oxygen demand (COD) and 96.1% of the total organic carbon (TOC) were removed at the highest temperature and retention time. The minimum energy requirement achieved was 9.6 kWh/kg COD removed at 200 °C for 180 min, and the exothermic reactions of the process can generate 28.3% of the required heat. GC-FID and -MS analysis revealed that the degradation of different groups of organic compounds generates acetic acid as an intermediate by-product of WO, being further oxidised at temperatures higher than 300 °C. NH4+and NH3 are generated from the decomposition of nitrogenated organic compounds showing the highest concentration of 704.5 mg NH4+ /L at 350 °C after 180 min.

Techno-economic assessment of HTL integration to the Brazilian sugarcane industry: An evaluation of different scenarios

Hydrothermal liquefaction (HTL) has been identified as one of the most promising thermochemical technologies to produce liquid biofuels. Although the production cost of HTL biofuels has not yet reached a competitive price, Brazil is recognized worldwide by its mature and well-developed biomass chain, along with a very market-competitive sugarcane industry, which could be used to deploy HTL technologies in a large-scale. The present study carried out a techno-economic analysis to understand the economic performance of HTL in the Brazilian context and considered sugarcane bagasse as the feedstock in two main configurations: a HTL stand-alone facility and a HTL plant integrated with the Brazilian sugarcane industry. The integration of the HTL with a sugarcane ethanol distillery has significantly increased the internal rate of return (IRR) compared with the stand-alone, moving from 8.1%–12.6% per year, thus indicating that HTL have the potential of being economically feasible if integrated to a sugarcane mill. Moreover, the minimum fuel selling prices of biofuels (MFSP) produced in the best integrated scenario showed a very high market-competitiveness, estimated as 0.44, 0.48, 0.51 and 0.37 US$/L for gasoline, diesel, jet fuel, and marine fuel, which were slightly lower than fossil counterparts. This study has also demonstrated that the selection of liquefaction solvents is a highly sensitive parameter to the economic feasibility of HTL; water has showed the highest economic feasibility, suggesting that the utilization of ethanol as solvent may not be feasible at industrial scale.

Recycle of nitrogen and phosphorus in hydrothermal liquefaction biochar from Galdieria sulphuraria to cultivate microalgae

Hydrothermal liquefaction (HTL) of G. sulphuraria (GS) has been demonstrated to produce energy-dense biocrude oil, water-soluble chemicals, and biochar. The recycling of nutrients from HTL water-soluble chemicals for algae cultivation has been demonstrated. The current study evaluated the feasibility of using HTL biochar, a by-product to recover nutrients and use the nutrients to cultivate microalgae without inhibition. GS biomass was liquefied to produce biocrude oil, biochar, water phase, and gasses under subcritical water conditions (300 °C, 15 MPa & 30 min). The N and P content in the HTL biochar were ~5.27 wt.% and ~15.98 wt.%, respectively. Both nutrients were leached from the biochar at varied pH values with ~40.23% of phosphate and ~70.01% of ammoniacal nitrogen recovery obtained at a pH of 0.5. The leached phosphates and ammoniacal nitrogen were added to N and P free Cyanidium medium (CM) for cultivating GS. Growth experiments were carried out in microtiter plates and culture tube reactors at 40 °C and with CO₂ (2–3%) supplementation. Similar growth rates were observed in cultures supplemented with the leached nutrients when compared to controls in standard CM growth media proving the absence of inhibition in the former. Comprehensive characterization of HTL biochar by Inductively Coupled Plasma Optical Emission Spectrometry, bomb calorimeter, and Scanning Electron Microscope is also presented. This study confirmed the feasibility of recovering nutrients from GS biochar and using these nutrients to cultivate algae successfully without inhibition, thus supporting reduced steps for recycling, process optimization, and HTL technology commercialization.

Exploring the feasibility of producing sustainable aviation fuel in the UK using hydrothermal liquefaction technology: A comprehensive techno-economic and environmental assessment

Abstract Carbon emissions from the aviation industry are a significant concern and the adoption of sustainable aviation fuel has the potential of mitigating the environmental impacts. Hydrothermal liquefaction (HTL) has great potential to produce sustainable aviation fuel employing organic waste feedstock but requires further development to reduces costs and the environmental impact. This study focuses on examining the feasibility of an integrated HTL plant in the UK whilst investigating the potential to improve the energy efficiency of the process through heat integration and resource recovery from waste streams. The methodology adopted includes modelling an integrated HTL plant with a feed throughput of 10 ​t ​h−1 using Aspen Plus simulation approach. Techno-economic, regional resource and carbon footprint assessment are conducted on three different HTL configurations, i.e. a base case without energy and resource recovery; an HTL with heat integration; and an HTL with energy and resource recovery. Three different feedstocks (algae, food waste and sewage sludge) are investigated with sewage sludge feedstock found to have the lowest minimum fuel selling price of 0.50 £ l−1. Heat integration results in a 96.4% and 77.8% decrease in heating and cooling utilities and the economic assessment indicates that heat integration and resource recovery can reduce the minimum fuel selling price by 10.5% compared to the base case. The regional resource assessment reveals that 22.8% of UK jet fuel demand can be met with the technology. The carbon footprint assessment demonstrates that with maximum production, the technology can result in a 18.3% reduction of CO2 emissions relative to current aviation emissions. This study signifies that the integrated HTL process could play a pivotal role in mitigating carbon emissions in the aviation industry.

Conversion of sewage sludge from healthcare facility to bio-crude oil using hydrothermal liquefaction technology

Population growth, municipal waste management challenges, fossil fuel depletion and its associated pollution are increasingly becoming public health issues. These necessitate the production of renewable and sustainable biofuels. This study, therefore, employed the use of hydrothermal liquefaction for the conversion of sewage sludge to bio-crude oil. Samples of the sewage sludge were purposively collected from sewage treatment plant and subjected to laboratory analyses (in triplicates) using standard methods (ASTM and AOAC) to obtain the composition. Sewage sludge (25 kg) from the sewage treatment Plant of University College Hospital, Ibadan, was converted at 300oC to bio-crude oil and biochar using hydrothermal liquefaction. The bio-crude oil was analysed for its physico-chemical properties. Conversion product yield gave 34% bio-crude oil with cloud point, pour point, viscosity and density of -38.89oC, -36.11oC, 0.86cP and 1.04gml-1respectively. The Higher Heating Value (HHV) of the bio-crude oil was 30.60 MJ/kg. A total of 18 compounds were identified from the analysis of Total Petroleum Hydrocarbon (TPH) in the bio-crude oil with 17 compounds within the diesel range organics of crude oil which showed that bio-crude oil has great potential to serve as alternative to fossil fuels.

Municipal wastewater sludge as a renewable, cost-effective feedstock for transportation biofuels using hydrothermal liquefaction

U.S. municipal wastewater contains approximately 160 trillion Btu/y of influent chemical energy, but very little is recovered and utilized nationwide. Hydrothermal liquefaction (HTL) is a thermochemical process that converts biomass into a biocrude intermediate that can be upgraded to a variety of liquid fuels. HTL provides an opportunity to enhance energy recovery at wastewater treatment plants by transforming underutilized municipal wastewater solids into a renewable, cost-effective feedstock for transportation biofuels. In this study, we estimate total national economic sludge feedstock supply by performing discounted cash flow analyses at >15,000 U.S. wastewater treatment facilities to assess the net present value of 30-year HTL investments, with comparison to wider adoption of anaerobic digestion (AD). This analysis is the first to model HTL technology deployment across the real-world fleet of wastewater treatment plants. Analyses indicate treatment facilities ≥17 ML/d (4.6 million gal/d) could supply 9.77 Tg/y of dry solids feedstock to economically produce 3.67 GL/y of biocrude intermediate, thereby increasing energy, environmental, and financial sustainability of sludge treatment while reducing disposal costs and operational and environmental risk.