Biocrude Yield Research Articles

Influence of Seawater and Reaction Temperature on Biocrude Yield and Composition During Hydrothermal Liquefaction of Spirulina sp. Microalgal Biomass

Influence of Seawater and Reaction Temperature on Biocrude Yield and Composition During Hydrothermal Liquefaction of Spirulina sp. Microalgal Biomass

Development of microalgal dual-cultures for enhanced productivity in sewage: An experimental study

Microalgae polycultures can be shown greater productivity than those that characterize monocultures. Nonetheless, rapid and ready identification of optimal microalgae combinations for highly productive polyculture systems remains a challenge. By assessing the corresponding nitrogen and phosphorus utilization efficiencies, this study aimed to identify microalgal combinations that might improve productivity. Ten high-biomass-producing microalgal species in municipal sewage habitats were cultivated in an artificial municipal sewage. Four high-yielding microalgae, which additionally showed complementary nitrogen and phosphorus nutrient utilization preferences, were selected for a subsequent dual-culture experiment. The D41 dual-culture system comprising Pediastrum sp. and Micractinium sp., showed the highest biocrude yield, at 17.5 mg/L/d, which was 13 % and 69 % higher than those of A4 and A1, respectively. Additionally, D41 showed the highest total phosphorus removal rate from artificial sewage, which was 27 % higher than that of Pediastrum sp. monoculture (A4) and 22 % higher than that of the Micractinium sp. monoculture (A1). Therefore, this study demonstrated that, (a) biomass production and nitrogen and phosphorus utilization rates of the constructed microalgae dual-culture systems were higher than those of monocultures, (b) phosphorus was identified as the limiting nutrient for further enhancing microalgae productivity, and (c) the dual-culture system showed intermediate characteristics between those of the constituent monoculture systems, suggesting that microalgae can influence community structure. Through the development of adequate software packages that can integrate microalgae nutrient utilization preference of and microalgae community structure, future research will enable the development of more productive microalgae culture combinations.

Production of phenolic monomers from lignin in hydrothermal medium: Effect of rapid heating and short residence time

This study investigates the influence of heating rate and short residence time (1–15 min) on the hydrothermal liquefaction (HTL) of alkali lignin, as a function of reaction temperature (280–320 °C). A novel induction-heating reactor system (IHRS) was designed and was used for rapid heating rate (∼100 °C/min), while a resistive-heating reactor system (RHRS) was used for slow heating rate (∼5.3 °C/min). The experiment using IHRS with a short residence time (1 min) resulted in the highest yield of carbon recovery in biocrude (52.2 ± 0.63 wt%) at 320 °C under autogenous pressure. In contrast, the experiments using RHRS or longer residence time (8–15 min) with IHRS showed lower biocrude yield due to the promotion of gasification and undesired secondary reactions. The detailed characterization of biocrude revealed that rapid heating rate improves the selectivity of compound in biocrude, such as phenol, while slow heating rate produced a broader distribution of compounds, including anisole and alkyl phenols at 320 °C for 1 min residence time. Furthermore, the usefulness of phenol as capping agent during IHRS of lignin was demonstrated in suppressing char formation and increasing biocrude yield.

Catalytic upgrading of biomass pyrolysis vapors for selective production of phenolic monomers over metal oxide modified alumina catalysts

This study investigates the catalytic vapor phase upgrading of sawdust to produce improved biocrude enriched in phenolic monomers. Various mixed metal oxide catalysts (MgO, CuO, Bi2O3, NiO, ZnO supported on Al2O3) were screened to determine the product composition. Further, the effect of different process parameters such as temperature (350 – 600 °C), metal oxide loadings (0 – 20 wt%), catalyst to biomass ratios (1:1–1:6), sweeping gas flow rates (0 – 15 LPH) were studied in terms of biocrude composition. Under non-catalytic conditions, maximum biocrude yields (∼39%) were obtained at an optimum temperature of 550 °C. The biocrude composition varied significantly with the type of metal oxide in which MgO and CuO produced higher amounts of phenolics (∼58%). Increasing MgO loading (5–20 wt%) and higher catalyst to biomass ratios (1:1) resulted in enhanced hydrocarbon yields to ∼15%. Premixing of biomass and catalyst in a fixed bed arrangement resulted in enhanced hydrocarbons/aromatics with simultaneous reduction in the phenolic content.

Unraveling the effects of sodium carbonate on hydrothermal liquefaction through individual biomass model component and machine learning-enabled prediction

Despite sodium carbonate (Na2CO3) being commonly utilized as a catalyst in actual biomass hydrothermal liquefaction (HTL), its impact on individual biomass components hasn't been well-examined. This study thus delves into the role of Na2CO3 in HTL of biomass model components (carbohydrate, lignin, protein, and lipid) at varying conditions. Na2CO3 at 5 wt% amplified carbohydrate degradation into biocrude and aqueous-gaseous products (AG), resonating with previous work on carbohydrate-rich feedstocks. While Na2CO3 has a marginal effect on lignin HTL, it negatively influences lipid HTL. Here, 5 wt% and 13.5 wt% Na2CO3 decrease the biocrude yield from 95.6% to less than 10%, simultaneously increasing the AG yield to approximately 90%. This is presumably due to the interaction of lipid decomposition intermediates (fatty acids) with sodium cations, resulting in water-soluble soap. For protein HTL, a low Na2CO3 concentration (5 wt%) has no significant impact on product formation, but excessive Na2CO3 (27 wt%) converts a considerable portion of biocrude into AG. In addition to these explorations that provided insights for actual biomass HTL, we also developed a machine learning model to adequately predict HTL biocrude yield by taking Na2CO3 effect into consideration. The Adaboost machine learning model displayed the most satisfactory prediction performance (training and testing R2: 0.96, 0.8) among the three investigated machine learning models. The feature importance analysis reveals lipid content and Na2CO3 concentration as pivotal factors over HTL process conditions and other biochemical components. This research provides fundamental insights into the Na2CO3 role in HTL product formation pathway and offers an intelligent and precise prediction model for HTL biocrude yield, thereby advancing the development of more efficient and sustainable bioenergy production processes.

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.

Solvothermal liquefaction of orange peels into biocrude: An experimental investigation of biocrude yield and energy compositional dependency on process variables

The efficient valorization of biomass for energy-derived biocrudes is essential for effective waste management. However, the production of biocrudes with high energy and reduced oxygen contents during the liquefaction process requires further insight. Therefore, the impact of reaction temperature, residence time, and ethanol: acetone on the energy compositions and bioproduct’s yield enhancement were investigated. The biocrudes obtained were characterized using elemental analysis, GC–MS, FTIR, GPC and TGA to understand the effects of process parameters on the biocrudes’ compositions. An improved HHV (38.18 MJ/kg) and lower O/C ratio (0.11) were obtained at 430 °C, 35 min and 50% ethanol with a significant improvement in the enhancement factor, deoxygenation, and percentage hydrogenation of 2.63, 36.88%, and 77.87%, respectively. The presence of ketones, hydrocarbons, phenolics and aromatics of 23.74, 4.28, 37.20 and 17.81% respectively indicate the potential of the obtained biocrude as renewable energy sources upon further upgrading.

Biorefinery integration of a green protein platform for maximum resource utilization

Biorefineries are often proposed to reduce environmental impact, enhance energy independence, and minimize waste generation while generating multiple valuable products. In this work, an integrated biorefinery approach is proposed to improve the overall process performance of a system combining a green biorefinery (GB), hydrothermal liquefaction (HTL), and anaerobic digestion (AD) to produce a leaf protein concentrate, bio-crude, and biogas. Festulolium and ryegrass, two varieties of forage grasses, were employed as feedstock. Two different maceration technologies were evaluated for protein recovery, more severe maceration led to a 75 % increase in protein content in the leaf protein concentrate (LPC) when compared to a standard maceration. The fiber residues produced by the grass processing were converted to biocrude using HTL. This step was not affected by the maceration step and the use of brown juice as HTL media proved to be beneficial. The bio-crude yield of the grass fiber residues was similar for both biomasses and maceration steps, ranging from 25.7 to 32.1 %. Finally, the HTL process water and the brown juice were subjected to anaerobic digestion to produce biogas. The brown juice from ryegrass resulted in higher methane production compared to HTL water but adding brown juice to HTL water did not reduce the lag times observed for pure HTL water. The integration of GB, HTL, and AD is shown to be effective in increasing the overall carbon and nitrogen recovery of the starting biomass.

Catalytic hydrothermal co-liquefaction of sewage sludge and agricultural biomass for promoting advanced biocrude production

Conventional hydrothermal liquefaction (HTL) technology is inhibited by the complicated feedstock properties, low biocrude yield, and poor biocrude quality. Herein, this work aimed to propose a novel catalytic hydrothermal co-liquefaction (catalytic co-HTL) route for enhancing high-quality biocrude production. Four representative biowastes were applied to determine the synergistic effects in co-HTL treatment. Binary sewage sludge (SS)/wheat straw (WS) presented the highest synergistic effect (14.05%) on biocrude production. Furthermore, homogenous and heterogeneous catalysts (i.e., Na2CO3, HY, SSB, CSB, and Ni@CSB) were comprehensively tested during catalytic co-HTL of binary SS/WS. Biocrude produced over Ni@CSB revealed the highest carbon content at 75.5% and HHV at 36.96 MJ/kg, due to the deoxygenation and desulfurization reactions enhanced by Ni@CSB. Thermalgravimetric behaviors and kinetic studies of biocrude degradation were further analyzed. Moreover, the byproducts (hydrochar and gaseous phase) were characterized. Overall, this study provides an effective and promising route to valorize biowastes into green high-quality biocrude.

Simultaneous production of bio-crude bio-oil via hydrothermal liquefaction and carotenoids via supercritical extraction from Nannochloropsis oceanica and recycling effluent to establish circular processes

Commercial production of microalgae biofuel is not economically feasible since it cannot compete with the price of fossil fuels. Algal biofuel could be cost-effective if high-value co-products are produced from microalgal biomass before it is converted into biofuel. Thus, this research aims to demonstrate a circular biorefinery process of producing bio-crude bio-oil as well as high-value products like carotenoids from a marine microalga Nannochloropsis oceanica. The microalga was cultivated in raceway ponds over the years with the highest biomass productivity of 30–40 g m−2 day−1 recorded in October and November of 2021, but it reduced in extremely high summer temperatures and low temperatures in winter of Delhi NCR, India. The annual average biomass productivity of 19.13 g m−2 day−1 was recorded, which is equivalent to 69825 kg ha−1 year−1. The algal biomass was processed for high-value carotenoids using a green process, i.e. supercritical carbon dioxide extraction. Carotenoid yield of 252 μg/g of biomass was obtained after optimizing temperature and pressure in the supercritical extraction process. The spent biomass after carotenoid extraction was used to produce bio-crude bio-oil using hydrothermal liquefaction. There was no significant difference between bio-crude oil yield and properties after carotenoid extraction and direct biomass use. A bioeconomic methodology for closing the circular loop involving recycling the effluent generated during hydrothermal liquefaction to re-cultivate the microalgae is demonstrated. This study highlights the potential of green technology, circular bioeconomy, and biorefinery practices in developing sustainable and environmentally friendly solutions for the chemical and energy sectors.

Hydrothermal liquefaction of Elaeis guineensis trunks: Lessons learned from a case study in Guatemala

The oil palm industry has been under public scrutiny during the last decades due to environmental and social issues related to its practices. Oil palm (Elaeis guineensis Jacq.) trunks (OPTs) are of special interest as they are left idle in the field after the replanting process which is performed every 25 years. This common practice results in harvesting challenges, phytosanitary risks, and a loss of bioenergy potential. Due to their high moisture content and fibrous nature, OPTs present a problem for traditional conversion processes that require a dry and homogeneous material. This study evaluates the feasibility of converting OPTs into a bio-crude oil and biochar to increase the sustainability of the oil palm sector. To date, research efforts have primarily focused on hydrothermal liquefaction (HTL) of OPT without catalysts, resulting in a limited understanding of the potential of OPTs. Thus, the main novelty of this work is the evaluation of the effects of catalyst dosage (0–5 wt%) on the bio-oil yield, reaction temperature (260–300∘C), and residence time (15–60 min) using a half-fraction experimental design methodology. For this, OPTs extracted from two plantations in Guatemala were used. The maximum bio-oil yield (26.77 ± 3.60 wt%) was found at 260∘C for 15 min and 5 wt% catalyst with a high heating value (HHV) of 19.29 ± 1.33 MJ kg−1. Nonetheless, the bio-oils produced without a catalyst at 300∘C and 15 min have higher HHV (27.63 ± 1.35 MJ kg−1) and are similar to Diesel fuel based on their H/C and O/C ratio. These results indicate that there is a potential trade-off between the bio-crude oil mass yield and HHV when using the catalyst.

Hydrothermal liquefaction of representative to Israel food waste model

In this study, we examined the hydrothermal liquefaction (HTL) pathway to reduce food waste environmental impacts by converting it into bio-crude and biochar. The yield and properties of these products depend on the composition of the feedstock and process parameters. We developed a model of household food waste based on Israel national waste survey. To investigate the effects of catalysts type, we examined the influence of dolime, dolomite, phosphate and potassium carbonate on products yields and composition. Additionally, we analyzed the role of the process parameters, including solid load, residence time, catalyst concentration, and temperature, on the yield and the properties of the hydrothermal liquefaction reaction products, such as bio-crude, biochar, and aqueous phase solubles. The experimental results show absolute bio-crude yield ranging from 6.61w% to 29.36w% and biochar yield ranging from 12.29w% to 40.73w% from the initial waste. Furthermore, 13.78w% to 33.98w% of the feed material was found in the aqueous phases and 6.15w% to 8.94w% was measured in the gas phase. The addition of catalysts positively influenced the bio-crude yield. A process temperature of 280 °C improved the energy recovery and increased product yield, resulting in a reduction in the oxygen content of the bio-crude. All bio-crudes showed undetectable sulfur levels and exhibited HHVs ranging from 30.24 MJ/kg to 37.94 MJ/kg, while biochar had HHVs of 31.29 MJ/kg to 31.84 MJ/kg. On the Israel national level, the bio-crude derived from food waste demonstrates the potential to meet up to 31.4 % of Israel's marine fuel demand assuming bio-crude yield of 29 %, as achieved in this study.

Process simulation for mass balance of continuous biomass hydrothermal liquefaction with reaction kinetics

Hydrothermal Liquefaction (HTL) process has been investigated for biomass conversion to bio-crude and other valuable materials. However, this process modeling remains a challenge due to the high complexity of its feedstock and product compositions and the numerous chemical reactions occurring simultaneously. Here, we investigate the mass balance of the HTL reaction using a process simulation with a kinetic model previously developed for the HTL of microalgae. This model was implemented in UniSim-Design software, and the simulation's performance was validated against published experimental results for various feedstocks, including microalgae, macroalgae, food waste, and model protein. Bio-crude had the best performance for predicting the products' yields from HTL of microalgae, and aqueous-phase had the poorest. For predicting the bio-crude yield from HTL of different feedstock categories, microalgae had the best performance, and model proteins had the poorest. Insights are suggested for improved modeling towards a more robust system-design-oriented approach for process simulations.

Production and characterization of biocrude from Persian Gulf Sargassum angustifolium using hydrothermal liquefaction: Process optimization by response surface methodology

In this study, the Sargassum angustifolium macroalgae was used as the feedstock of the hydrothermal liquefaction (HTL) process. The effects of operating conditions of temperature, residence time, and feedstock concentration on the yield of the HTL products were modeled using the response surface methodology of the Box-Benken design. Based on the proposed model, the maximum biocrude yield was predicted at 350 °C, 35 min residence time, and 8.6 wt% of the feedstock concentration, confirmed by the experiment. The biocrude has a higher heating value of 33.91 MJ/kg, with the main components including ketones and alkanes. Sensitivity analysis of operating conditions revealed that the HTL process temperature has the most effect on the yield of products, and increasing temperature causes an increase in the biocrude and gas phase yields while decreasing the aqueous and solid phase yields. Among the cross-effect of parameters, the temperature-residence time interaction has the highest impact on the biocrude and gas phase yields. A comparison of the structural analysis of the solid phase and the algae showed the solid residue of the HTL process is highly porous and potentially a good candidate as an adsorbent. The physicochemical properties of the aqueous phase revealed its potential application to algae cultivation. Finally, three pretreatment methods of ultrasonication, microwave irradiation, and size variation of the feedstock were used to increase the biocrude yield at both maximum and minimum yield conditions. The results showed that microwave-assisted HTL is the most effective process, increasing the biocrude yield from 26.15 wt% to 34.77 wt%.

Producing upgradeable bio-oil from food bio-waste via hybrid-assisted pretreatment coupled with catalytic hydrotreatment

Slurry food waste sourced from Renova (Gothenburg, Sweden) was investigated as a model for generating upgradeable bio-oil via a hybrid-assisted pretreatment along with a catalytic hydrotreatment process. Hybrid-assisted pretreatment has been examined for extracting and stabilizing of reactive-derived substances. For the resulting bio-crude and residual solids, the properties of the heteroatoms were also examined prior to the catalytic hydrotreatment experiments. Hybrid-assisted pretreatment is an interesting solution in that it maximizes the bio-crude yield and transfers significant amounts of the nitrogenous content (De-N ∼83.3 %, dry basis) into the residual solids. Nearly 87 wt% of the oxygenated monomers were found in the obtained bio-crude, which possessed 52.0 wt% of alcohols. The highest upgradeable bio-oil of 86.0 wt% was achieved during catalytic hydrotreatment of the bio-crude and residual solids jointly: producing blends of up to 78 wt% of hydrocarbons, 14 wt% oxygenated and <6 wt% of cyclic, aromatics, N-containing components.

Green and facile recycling of bauxite residue to biochar-supported iron-based composite material for hydrothermal liquefaction of municipal solid waste

Industrial and municipal wastes remain significant sources of air, soil, and water pollution, thus causing adverse climate and health impacts. EU faces challenges in developing green recycling processes and reducing GHG emissions. Innovation in green catalysis is a key driver toward the fulfilment of these goals. This study demonstrated a single-step “Green Recycling” route by which different wastes e.g., industrial and bioorganic wastes are treated to produce biochar/Fe(0) (BC-Fe(0)) material. Typically, three different biomass namely organic fraction of municipal solid waste (biopulp), wheat straw (WS), and microalgae (MA) were used as green reducing agents for reducing bauxite residue (BR). Among all biomass, the high reduction potential of amino acids present in biopulp facilitated the synthesis of BC-Fe(0). BC-Fe(0) material acted as an effective catalyst for HTL of biopulp as the results showed the highest bio-crude yield (44 wt%) at 300 °C for 30 min with 10 wt% BC-Fe(0) loading (containing 2.5 wt% Fe). Furthermore, BC-Fe(0) also assisted in-situ hydrogenation and deoxygenation of chemical compounds present in the bio-liquid product, therefore bio-crude exhibited a higher H/C ratio (1.73) and lower oxygen contents (9.78 wt%) in comparison to bio-crude obtained without catalyst. However, Raw BR and reduced BR (RED) as catalysts showed no significant effect on the yield and oxygen content of bio-crude, which confirms the high catalytic activity of Fe(0) containing BC-Fe(0). Therefore, this study demonstrates the greener path for the one-step valorization of industrial and organic wastes, as an alternative to existing chemical and high temperature-based waste recycling and catalyst synthesis technologies.

Hydrothermal liquefaction potential of wastewater treatment sludges: Effect of wastewater treatment plant and sludge nature on products distribution

The rapid growth of urban populations necessitates the development of more efficient and environmentally sustainable methods for waste treatment and resource recovery. Hydrothermal liquefaction (HTL) has emerged as a promising technology for converting organic waste into bio-crude oil. In this study, the HTL products of various waste fractions (Fat, oil, and grease (FOG), food waste, primary and secondary sludge, and digestate) produced or handled by four wastewater treatment plants in Denmark were analysed. Additionally, the effect of mixing the produced waste was investigated. The HTL experiments were conducted at temperatures 300, 325, and 350 °C, with a residence time of 20 min and dry matter content of 16.7%. The highest HTL bio-crude yields were obtained at a temperature of 325 °C for all feedstocks except FOG (300 °C). The mixing of wastes resulted in a positive synergistic effect, presenting an energy recovery between 62 and 76% and bio-crude yields higher than expected due to interactions between the feedstock's biochemical composition. Based on the biochemical composition and on the feedstocks fraction, two models are proposed for the prediction of bio-crude yields, with an error between 4 and 5% in absolute terms. In addition, important process water parameters, as well as the nutrient recovery and heavy metal load of the solid residues are analysed and discussed, giving a comprehensive overview of the potential of different wastewater treatment plant sludges.

Machine learning models for fast and isothermal hydrothermal liquefaction of biomass: Comprehensive experiment and prediction of various product fraction yields

Hydrothermal liquefaction (HTL) shows promise in biocrude productions from wet biomass. In this study, phycocyanin conversion was performed under an extensive range of conditions (set-point temperatures of 300–500 °C and holding times of 20–1800 s), covering both isothermal and fast HTL processes. Based on 226 sets of product fraction yields obtained from this study and literature, machine learning models, such as multiple linear regression, decision regression tree, random forest, gradient boosting regression, and support vector regression were developed. The model with the highest predictive accuracy for biocrude yield was further used to perform both single and multi-task predictions of other product yields. The results show that fast HTL at 500 °C and 40 s produced the highest biocrude yield (35.0 wt%) and energy recovery (55.2%), which were 11.9 wt% and 15.9% higher than those obtained by conventional isothermal HTL at 300 °C and 1800 s. Biocrude predominantly consisted of nitrogenous heterocyclic compounds, leading to its high nitrogen content (∼10 wt%). In addition, water quality analysis shows that the chemical oxygen demand, ammonia and total phosphorus contents of the aqueous phase by-products were much higher than the discharge standards and required further treatments. Cross-validation and testing error analysis show that the random forest model exhibited the highest predictive accuracy for the biocrude yield, with a testing R2 of 0.93. Additionally, the random forest model could predict other product fraction yields with desirable accuracies. According to the feature importance analysis, the most important factor for biocrude production from fast HTL was the residence time, followed by the reaction temperature.

Suppressing the formation of N-heteroaromatics during hydrothermal liquefaction of proteinaceous model feedstock

Hydrothermal liquefaction was applied to model mixtures containing lard oil (lipid), cellulose (carbohydrate), and bovine serum albumin (protein), representing biogenic organic waste feedstocks. The content of protein was kept constant for every experiment, while the lipid and cellulose content was changed, which is expressed by the lipid to protein (LtoP) or cellulose to protein (CtoP) ratio. The reactions were conducted at 350 °C with a residence time of 20 min in 25 ml micro autoclaves. Afterwards, the lumped recovery of carbon and nitrogen into the different product phases was investigated and representative compounds were identified to get an overview of the composition on a molecular level. A high LtoP ratio results in an increased biocrude yield and eventually higher carbon recovery, while the nitrogen recovery is slightly lowered. The formation of nitrogen containing heteroaromatic species could be suppressed by the addition of lipids from 6.10 to 0.03% for pyrazines and 2.69 to 0.43% for indoles. Consequently, the formation and nitrogen recovery by heteroaliphatic amide species increased from 0.00 to 8.77%. Different reaction pathways for the formation of the different species are proposed. It turned out that reactive amine from protein degradation can be “trapped” in stable amides, preventing the formation of nitrogen heteroaromatics with oxygenated from carbohydrates.Graphical abstract

Influence of processing conditions and biochemical composition on the hydrothermal liquefaction of digested urban and agricultural wastes

Hydrothermal liquefaction (HTL) of waste biomass is a promising technology to yield an energy dense biocrude oil and a nutrient rich solid phase. An abundant and problematic biomass waste stream potentially suited for HTL is digestate, the side stream of anaerobic digestion. HTL behavior of three digestates from urban and agricultural biogas plants has been studied using response surface methodology to investigate the influence of biochemical composition, temperature, and reaction time on biocrude yield and composition, energy recovery, as well as the mobility of nutrients (N, P, K) among the product phases using KOH as catalyst. A maximum energy recovery of up to 43% and a carbon recovery of 40% were achieved for the straw/manure digestate. Mass yields and biocrude composition by GC–MS analysis are shown to be heavily influenced by feedstock composition. High yields of > 80% for the main nutrients Ca, Mg, Fe, and P to the solid residue are observed.