Sustainable valorization of macroalgae residual biomass, optimization of pyrolysis parameters and life cycle assessment.

The major challenges for the current climate change issue are an increase in global energy demand, a limited supply of fossil fuels, and increasing carbon footprints from fossil fuels, which have necessitated the exploration of sustainable alternatives to fossil fuels. Biorefineries offer a promising path to sustainable fuel production, converting biomass into biofuels using diverse technologies. Aquatic biomass, such as macroalgae in this context, represents an abundant and renewable biomass resource that can be cultivated from water bodies without competing with traditional agricultural land. Despite this, the potential of macroalgae for biofuel production remains largely untapped, with very limited studies addressing their viability and efficiency. This study investigates the efficient conversion of unexplored macroalgae biomass through a biorefinery process that involves lipid extraction to produce biodiesel, along with the production of biochar and bio-oil from the pyrolysis of residual biomass. To improve the effectiveness and overall performance of the pyrolysis system, Response Surface Methodology (RSM) was utilized through a Box-Behnken design to systematically investigate how alterations in temperature, reaction time, and catalyst concentration influence the production of bio-oil and biochar to maximize their yields. The results showed the highest bio-oil yield achieved to be 36 %, while the highest biochar yield reached 45 %. The integration of Life Cycle Assessment (LCA) in the study helps to assess carbon emission and environmental burdens and identify potential areas for optimization, such as resource efficiency, waste management, and energy utilization. The LCA results contribute to the identification of potential environmental hotspots and guide the development of strategies to optimize the overall sustainability of the biofuel production process. The LCA results indicate that the solvent (chloroform) used in transesterification contributes significantly to greenhouse gas emissions and climate change impacts. Therefore, it is crucial to explore alternative, safe solvents that can mitigate the environmental impacts of transesterification.

Direct conversion of apricot seeds into biodiesel.

Using edible lipids for biodiesel production has been criticized, causing biodiesel production from inedible food resources to be desirable. Lipid extraction must be prioritized to produce biodiesel using an acid/base-catalyzed transesterification process, but this conversion process suffers from technical reliability. Therefore, this study introduced non-catalytic conversion of oil-bearing biomass into biodiesel. Apricot seeds were used as a model compound (oil content 44.3 wt%). The non-catalytic transesterification of apricot seed oil recovered 98.28 wt% biodiesel at 360 °C for 1 min, while alkali-catalysis of apricot seed oil recovered 91.84 wt% at 63 °C for 60 min. The direct conversion of apricot seeds into biodiesel was attempted. The trends in the yields of biodiesel from apricot seeds and seed oil obtained by non-catalytic transesterification as a function of reaction temperature were similar. The yield of biodiesel from apricot seed was 43.06 wt%, suggesting that 97.20 wt% of lipids were converted into biodiesel.

Enhancement for the synthesis of bio-energy molecules (carbohydrates and lipids) in Desmodesmus subspicatus: experiments and optimization techniques.

Microalgae are regarded as renewable resources of energy, foods and high-valued compounds using a biorefinery approach. In the present study, we explored isolated microalgae (Desmodesmus subspicatus) for the production of bio-energy molecules (carbohydrate and lipid). Optimizations of media (BG-11) components have been made using the Taguchi orthogonal array (TOA) technique to maximize biomass, carbohydrate and lipid production. Optimized results showed that biomass, carbohydrates and lipid productivity increased by 1.3 times at optimal combinations of media components than standard BG-11 media. Further, the influence of various carbon and nitrogen sources as nutritional supplement with optimum media composition under different light intensities was investigated for productivity of carbohydrate and lipid. Results demonstrated that 1.5 times higher productivity of carbohydrate and lipids were achieved in the presence optimum BG-11 under a broad range of light intensities (84-504 µmol m-2 s-1). Among different nitrogen sources, glycine was found to give higher productivity (1.5 times) followed by urea. Use of the cellulose as a carbon source in the media significantly increases biomass (2.4 times), carbohydrates (2.3 times) and lipids (2.3 times) productivity. Investigations revealed that cultivating Desmodesmus subspicatus under optimum culture conditions has the potential for large-scale bio-ethanol and bio-diesel production.

Co-pyrolysis of sewage sludge and biomass waste into biofuels and biochar: A comprehensive feasibility study using a circular economy approach.

Enormous annual sewage sludge (SS) volumes pose global environmental challenges owing to contamination and significant greenhouse gas emissions. Here, we investigated the economic viability of co-pyrolyzing SS and biomass waste to produce biofuels (bio-oil and gas) and biochar. Net present worth (NPW) analysis, the sale product break-even price, and sludge handling price (SHP) were used to determine the profitability of co-pyrolysis compared with SS pyrolysis alone and conventional treatment methods. In this study, the sale prices of biochar based on quality (i.e., stability, carbon sequestration effectiveness, and heavy metal content) were estimated to be 2.24, 1.44, and 0.98 CAD/kg for high-, medium-, and low-grade biochar. The bio-oil prices, estimated based on the higher heating values of bio-oil and diesel, ranged from 0.80 to 1.22 CAD/kg. Sawdust (SD) and wheat straw (WS) were the chosen co-pyrolysis feedstocks, with four mixing ratios (20, 40, 60, and 80 wt%). Economically, SD (40 wt% mixing ratio) co-pyrolysis achieved the best performance, with a maximum NPW of 8.71 million CAD. SD single and co-pyrolysis were the only profitable scenarios. Moreover, SS single pyrolysis and WS co-pyrolysis exhibited higher profitability than conventional SS treatment methods, with SHPs of 65 and 40 CAD/1000 kg dry sludge, respectively. Sensitivity analysis highlighted the dependence of economic performance on biochar and bio-oil market value. This study offers the first economic analysis of this approach and enhances our understanding of the potential of co-pyrolysis for biofuel and biochar production, providing innovative solutions for the environmental challenges of SS disposal.

Challenges and prospects of yeast-based microbial oil production within a biorefinery concept.

Biodiesel, unlike to its fossil-based homologue (diesel), is renewable. Its use contributes to greater sustainability in the energy sector, mainly by reducing greenhouse gas emissions. Current biodiesel production relies on plant- and animal-related feedstocks, resulting in high final costs to the prices of those raw materials. In addition, the production of those materials competes for arable land and has provoked a heated debate involving their use food vs. fuel. As an alternative, single-cell oils (SCOs) obtained from oleaginous microorganisms are attractive sources as a biofuel precursor due to their high lipid content, and composition similar to vegetable oils and animal fats. To make SCOs competitive from an economic point of view, the use of readily available low-cost substrates becomes essential. This work reviews the most recent advances in microbial oil production from non-synthetic sugar-rich media, particularly sugars from lignocellulosic wastes, highlighting the main challenges and prospects for deploying this technology fully in the framework of a Biorefinery concept.

Production of fungal phytases in solid state fermentation and potential biotechnological applications.

Phytases are important enzymes used for eliminating the anti-nutritional properties of phytic acid in food and feed ingredients. Phytic acid is major form of organic phosphorus stored during seed setting. Monogastric animals cannot utilize this phytate-phosphorus due to lack of necessary enzymes. Therefore, phytic acid excretion is responsible for mineral deficiency and phosphorus pollution. Phytases have been reported from diverse microorganisms, however, fungal phytases are preferred due to their unique properties. Aspergillus species are the predominant producers of phytases and have been explored widely as compared to other fungi. Solid-state fermentation has been studied as an economical process for the production of phytases to utilize various agro-industrial residues. Mixed substrate fermentation has also been reported for the production of phytases. Physical and chemical parameters including pH, temperature, and concentrations of media components have significantly affected the production of phytases in solid state fermentation. Fungi produced high levels of phytases in solid state fermentation utilizing economical substrates. Optimization of culture conditions using different approaches has significantly improved the production of phytases. Fungal phytases are histidine acid phosphatases exhibiting broad substrate specificity, are relatively thermostable and protease-resistant. These phytases have been found effective in dephytinization of food and feed samples with concomitant liberation of minerals, sugars and soluble proteins. Additionally, they have improved the growth of plants by increasing the availability of phosphorus and other minerals. Furthermore, phytases from fungi have played an important roles in bread making, semi-synthesis of peroxidase, biofuel production, production of myo-inositol phosphates and management of environmental pollution. This review article describes the production of fungal phytases in solid state fermentation and their biotechnological applications.

Valorization of onion peel waste: From trash to treasure.

Globally, fruits and vegetables are consumed as raw, processed, or as an additive, accounting for approximately 50% of total food wastage. Among the fruits and vegetables, onion is well known for its potential bioactive components; however, peels of onion are a major concern for the environmental health and food industries. Effective utilization methods for valorizing the onion peel should be needed to develop value-added products, which are more eco-friendly, cost-effective, and sustainable. Therefore, this review attempts to emphasize the conventional and emerging valorization techniques for onion peel waste to generate value-added products. Several vital applications including anticancerous, antiobesity, antimicrobial, and anti-inflammatory activities are thoroughly discussed. The findings showed that the use of advanced technologies like ultrasound-assisted extraction, microwave-assisted extraction, and enzymatic extraction, demonstrated improved extraction efficiency and higher yield of bioactive compounds, which showed the anticancerous, antiobesity, antimicrobial, and anti-inflammatory properties. However, in-depth studies are recommended to elucidate the mechanisms of action and potential synergistic effects of the bioactive compounds derived from onion peel waste, and to promote the sustainable utilization of onion peel waste in the long-term.

Effect of crude glycerin supplementation via drinking water on feed intake, water intake and productive performance of dairy ewes.

This study was performed to determine the effects of crude glycerin (CG) supplementation in drinking water on DM and nutrient intake, milk production, milk composition, and serum glucose. Twenty multiparous Lacaune × East Friesian ewes were randomly distributed into four dietary treatments throughout the lactation cycle. Treatments consisted of doses of CG supplementation via drinking water as follows: (1) no CG supplementation, (2) 15.0 g CG/kg DM, (3) 30.0 g CG/kg DM, and (4) 45.0 g CG/kg DM. DM and nutrient intake were reduced linearly with CG supplementation. CG linearly reduced water intake when expressed as kg d-1. However, no effect of CG was observed when it was expressed as a percentage of body weight or metabolic body weight. The water to DM intake ratio was increased linearly with CG supplementation. No effect of CG doses on serum glucose was observed. The production of standardized milk decreased linearly with the experimental doses of CG. Protein, fat, and lactose yield were linearly reduced with the experimental doses of CG. Milk urea concentration was quadratically increased with CG doses. Feed conversion was quadratically increased by treatments during the pre-weaning period (P < 0.05), in which the worst values were observed when the ewes were supplemented with 15 and 30 g CG/kg DM. The N-efficiency was linearly increased with CG supplementation in drinking water. Our results suggest that dairy sheep can be supplemented with CG up to 15 g/kg DM in drinking water. Greater doses are not beneficial for feed intake, milk production, and the yield of milk components.

Optimization of biodiesel production, engine exhaust emissions, and vibration diagnosis using a combined approach of definitive screening design (DSD) and artificial neural network (ANN).

In this study, definitive screening design (DSD) optimization and artificial neural network (ANN) modelling techniques are applied for the production of palm oil biodiesel (POBD). These techniques are implemented to examine the vital contributing factors in achieving maximum POBD yield. For this purpose, seventeen experiments are conducted randomly by varying the four contributing factors. The results of DSD optimization reveal that a biodiesel yield of 96.06% is achieved. Also, the experimental results are trained in ANN for predicting the biodiesel yield. The results proved that the prediction capability of ANN is superior, with a high correlation coefficient (R2) and low mean square error (MSE). Furthermore, the obtained POBD is characterized by significant fuel properties and fatty acid compositions and observed within the standards (ASTM-D675). Finally, the neat POBD is examined for exhaust emissions and engine cylinder vibration analysis. The emissions results confirm a significant drop in NOx (32.46%), HC (40.57%), CO (44.44%), and exhaust smoke (39.65%) compared to diesel fuel at 100% load. Likewise, the engine cylinder vibration measured on top of the cylinder head reveals a low spectral density with low amplitude vibrations observed for POBD at measured loads.

Genotoxicity by rapeseed methyl ester and hydrogenated vegetable oil combustion exhaust products in lung epithelial (A549) cells.

Biofuel is an attractive substitute for petrodiesel because of its lower environmental footprint. For instance, the polycyclic aromatic hydrocarbons (PAH) emission per fuel energy content is lower for rapeseed methyl ester (RME) than for petrodiesel. This study assesses genotoxicity by extractable organic matter (EOM) of exhaust particles from the combustion of petrodiesel, RME, and hydrogenated vegetable oil (HVO) in lung epithelial (A549) cells. Genotoxicity was assessed as DNA strand breaks by the alkaline comet assay. EOM from the combustion of petrodiesel and RME generated the same level of DNA strand breaks based on the equal concentration of total PAH (i.e. net increases of 0.13 [95% confidence interval (CI): 0.002, 0.25, and 0.12 [95% CI: 0.01, 0.24] lesions per million base pairs, respectively). In comparison, the positive control (etoposide) generated a much higher level of DNA strand breaks (i.e. 0.84, 95% CI: 0.72, 0.97) lesions per million base pairs. Relatively low concentrations of EOM from RME and HVO combustion particles (<116 ng/ml total PAH) did not cause DNA strand breaks in A549 cells, whereas benzo[a]pyrene and PAH-rich EOM from petrodiesel combusted using low oxygen inlet concentration were genotoxic. The genotoxicity was attributed to high molecular weight PAH isomers with 5-6 rings. In summary, the results show that EOM from the combustion of petrodiesel and RME generate the same level of DNA strand breaks on an equal total PAH basis. However, the genotoxic hazard of engine exhaust from on-road vehicles is lower for RME than petrodiesel because of lower PAH emission per fuel energy content.

Unlocking the potential of transesterification catalysts for biodiesel production through machine learning approach.

The growing demand for fossil fuels has motivated the search for a renewable energy source, and biodiesel has emerged as a promising and environmentally friendly alternative. In this study, machine learning techniques were employed to predict the biodiesel yield from transesterification processes using three different catalysts: homogeneous, heterogeneous, and enzyme. Extreme gradient boosting algorithms showed the highest accuracy in predictions, with a coefficient of determination accuracy of nearly 0.98, as determined through a 10-fold cross-validation of the input data. The results indicated that linoleic acid, behenic acid, and reaction time were the most crucial factors affecting biodiesel yield predictions for homogeneous, heterogeneous, and enzyme catalysts, respectively. This research provides insights into the individual and combined effects of key factors on transesterification catalysts, contributing to a deeper understanding of the system.

Response surface optimization of product yields and biofuel quality during fast hydrothermal liquefaction of a highly CO2-tolerant microalgae.

The effects of biochemical components and processing variables (e.g., temperatures, solid-liquid ratio, ethanol concentration, and time) during fast hydrothermal liquefaction of a highly CO2-tolerant microalgae (Micractinium sp.) on the product yields and biofuel quality were explored using response surface methodology coupled with central composite design. Results showed that the maximum bio-oil yield (51.4 %) was obtained at 321 °C for 49 min at ethanol concentration of 75 % and solid-liquid ratio of 15.3 %. Among different studied parameters, ethanol concentration showed the highest significant impact on the bio-oil yield due to the low P-value and high F-value in ANOVA analysis. Furthermore, the chemical compositions of bio-oils were determined, which showed that the increase of ethanol concentration in the solvent not only increased the bio-oil yield but also promoted the bio-oil quality by reduction of carboxylic acids and nitrogen-containing compounds with simultaneous enhancement of esters in the bio-oil. The present results show that fast hydrothermal liquefaction is a promising approach to convert the microalgae into high quality biofuels rich in esters.

The coexpression of two desaturases provides an optimized reduction of saturates in camelina oil.

Reducing the saturate content of vegetable oils is key to increasing their utility and adoption as a feedstock for the production of biofuels. Expression of either the FAT5 16 : 0-CoA desaturase from Caenorhabditis elegans, or an engineered cyanobacterial 16 : 0/18 : 0-glycerolipid desaturase, DES9*, in seeds of Arabidopsis (Arabidopsis thaliana) substantially lowered oil saturates. However, because pathway fluxes and regulation of oil synthesis are known to differ across species, translating this transgene technology from the model plant to crop species requires additional investigation. In the work reported here, we found that high expression of FAT5 in seeds of camelina (Camelina sativa) provided only a moderate decrease in saturates, from 12.9% of total oil fatty acids in untransformed controls to 8.6%. Expression of DES9* reduced saturates to 4.6%, but compromised seed physiology and oil content. However, the coexpression of the two desaturases together cooperatively reduced saturates to only 4.0%, less than one-third of the level in the parental line, without compromising oil yield or seedling germination and establishment. Our successful lowering of oil saturates in camelina identifies strategies that can now be integrated with genetic engineering approaches that reduce polyunsaturates to provide optimized oil composition for biofuels in camelina and other oil seed crops.

Evaluation of fatty acid profiles of Chlorella Vulgaris microalgae grown in dairy wastewater for producing biofuel.

Biodiesel is a biofuel made from plant oils and animal lipids. Utilization of lipid accumulation in algae biomass as biodiesel is a good alternative to fossil fuels. In this research Chlorella vulgaris microalga was applied after planting in BG11 culture medium in effluent and wastewater of dairy industry after preparation of 25, 50, and 75% dilutions. Algae in two concentrations with low (13 million cells/mL) and high density (26 million cells/mL) were injected. According to the results obtained in the wastewater environment the highest amount of C16:0 fatty acid was observed in F2 25% treatment, and C18:0 fatty acid is related to F1 75% treatment. In the effluent environment, the highest amount of fatty acids C16:0 and C16:1n7 occur in P1 50% treatment, and C18:0 and C18:3n3 fatty acids are related to P1 50% treatment, respectively. The highest amount of saturated fatty acids (SFA) was reported at P2 75% treatment (56.25%) and monounsaturated fatty acids (MUFA) has accumulated in F175% (40.13%) treatment. Chlorella vulgaris microalgae can be considered as a rich source of lipid and fatty acid profiles in both wastewater and effluents, and it can be regarded as potential significance source for biodiesel production.

A critical review of Pongamia pinnata multiple applications: From land remediation and carbon sequestration to socioeconomic benefits.

Pongamia pinnata (L.) Pierre (Pongamia) is a tree native to Southeast Asia. Recently, interest in Pongamia focused on its potential as a biofuel source as its seeds contain around 40% oil. However, Pongamia has multiple applications beyond biofuel production. It is a legume, can form symbiotic associations with mycorrhizal fungi, has been shown to be tolerant to drought, salinity, and heavy metals in soil, and has potential to mitigate climate change. Additionally, Pongamia oil has medicinal properties, can be used as biopesticide, insect repellent, to produce soap, and as a source of edible grade vegetable oil. The seed cake can be used as a source of bioenergy, food and feed protein, and organic fertiliser, and the flowers are a good source of pollen and nectar. Pongamia can also bring socio-economic benefits as its ability to restore degraded and contaminated land provides opportunities for local communities through novel valorisation pathways. These multiple applications have potential to form part of a circular bioeconomy in line with sustainable development goals. Although research on the multiple applications of Pongamia has grown considerably, knowledge gaps remain and these need to be addressed so that the full potential of Pongamia can be achieved. Further understanding of the mechanisms underlying its resilience to abiotic stresses, phytoremediation potential and biotic interactions should be a priority, and co-ordinated breeding efforts will be key. Here, we critically review the available literature on Pongamia and highlight gaps in knowledge in which future research should focus on to ensure that the full potential of this versatile tree can be achieved. We conclude that Pongamia can potentially form part of a circular bioeconomy and that harnessing the multiple applications of Pongamia in a holistic manner, with collaboration among key stakeholders, is crucial for the successful application of its benefits far beyond biofuel production.

Onion waste based-biorefinery for sustainable generation of value-added products.

Waste derived from the onion processing sector can be harnessed for the production of organic acids, polyphenols, polysachharides, biofuels and pigments. To sustainably utilize onion processing residues, different biorefinery strategies such as enzymatic hydrolysis, fermentation and hydrothermal carbonization have been widely investigated. This review discusses the recent advances in the biorefinery approaches used for valorization of onion processing waste followed by the production of different value-added products from diverse classes of onion waste. The review also highlights the current challenges faced by the bioprocessing sector for the utilization of onion processing waste and perspectives to tackle them.

Integrated biorefinery development for pomegranate peel: Prospects for the production of fuel, chemicals and bioactive molecules.

Current experimental evidence has revealed that pomegranate peel is a significant source of essential bio compounds, and many of them can be transformed into valorized products. Pomegranate peel can also be used as feedstock to produce fuels and biochemicals. We herein review this pomegranate peel conversion technology and the prospective valorized product that can be synthesized from this frequently disposed fruit waste. The review also discusses its usage as a carbon substrate to synthesize bioactive compounds like phenolics, flavonoids and its use in enzyme biosynthesis. Based on reported experimental evidence, it is apparent that pomegranate peel has a large number of applications, and therefore, the development of an integrated biorefinery concept to use pomegranate peel will aid in effectively utilizing its significant advantages. The biorefinery method displays a promising approach for efficiently using pomegranate peel; nevertheless, further studies should be needed in this area.

Aluminum phosphate sludge as a phosphorus source for maize production under low soil phosphorus availability.

Background: With increasing food demand as a consequence of the growing world population, there is a corresponding demand for additional sources of phosphorus (P). Alum-phosphate (Al-P) sludge is a by-product of wastewater treatment and can be a good source of P. In this study, the response of maize (Zea mays L.) to Al-P sludge was tested. Maize was chosen as the test crop due to its prevalent use as human and animal food and as a source of biofuel. The objective of the study was to investigate Al-P sludge as a source of P compared to a commercial fertilizer (monoammonium phosphate, MAP). Methods: A growth chamber assay was conducted over four cropping cycles (45 d each). The application rate was 9.7, 19.4, 29.1 and 38.8 mg P kg-1 dry soil. Amendments were applied once at the start of the first cropping cycle. Plants were harvested after each cycle and pots were re-seeded. Dry matter yield (DMY), total P uptake, Al-P uptake, soil total P and Olsen-P concentrations, pH, and EC were measured. Results: DMY was significantly greater in pots amended with Al-P sludge than in pots treated with MAP. There was a significant rate × cropping cycle interaction effect on DMY with the differences among rates in cycle 1 different from those in cycle 4. Phosphorus uptake depended on cropping cycle, P source and P application rate. With sludge uptake higher than MAP in all cycles, the highest P uptake was observed at the highest application rate except for cycle 2 where this was observed at the rate of 29.1 mg kg-1. For MAP, phosphorus recovery efficiency (PRE) at the highest rate was significantly greater than that at the lowest rate whereas PRE in cycle 1 was significantly higher than that in cycle 4. In the first two cycles, aluminum uptake was negligible in both MAP and Al-P sludge treatments; however, in cycles 3 and 4, there was significantly more Al in maize from sludge amended pots. Our results show that Al-P sludge was as effective as MAP in supplying enough P for biomass yield. We, therefore, conclude that Al-P sludge could be an alternative source of P, especially for growing maize as feedstock for bioenergy.

Mineral-hydrogel composites for mitigating harmful algal bloom and supplying phosphorous for photo-biorefineries.

Harmful algal blooms (HAB) are a major environmental concern in eutrophic aquatic systems. To mitigate HABs and recover the phosphorus that drives algal growth, this study developed hydrogel composites seeded with calcium phosphate and wollastonite particles, which first adsorb phosphate (P) and then precipitate it as calcium phosphate. Using a fast-growing cyanobacterium, Synechococcus elongatus 2973, as a model microalga, we found that the mineral-hydrogel composites reduced dissolved P in BG11 media from 5.1 mg/L to 0.31 mg/L, initially reducing the biomass growth rate by up to 73 % and ultimately reducing the total biomass concentration by 75 %. When applied to municipal wastewater and agricultural run-off, the composites removed 96 % and 91 % of the dissolved P, respectively. Moreover, when the recovered P-enriched composites were reused as a slow-release bio-compatible fertilizer in a photobioreactor, they effectively supported algal growth without blocking light and interfering with photosynthesis. The P-enriched composites could tune the P concentration in the culture medium and significantly promote algal lipid accumulation. This study demonstrates the mineral-hydrogel composites' potential to treat point sources of P pollution and subsequently facilitate photoautotrophic biofuel production as a nutrient, effectively recycling the captured P.

Acid-mediated hydrothermal treatment of sewage sludge for nutrient recovery.

Hydrothermal carbonization allows material valorization and energy recovery from wet biomass waste. In this study, the hydrothermal treatment of dewatered waste-activated sludge (DWAS) was evaluated at several temperatures (170-230 °C) and reaction times (5-60 min) in an acid-free medium or in media such as citric acid or HCl (0.1-0.5 mol/L). Compared with the DWAS, an increase in the fixed carbon content (>45 wt%) and heating value (18.9-22.9 MJ/kg) was observed in the hydrochar; however, their ash content remained high, which is the main drawback hindering their direct use as a biofuel. The addition of acids during hydrothermal treatment favored the solubilization of N and P in the process water, which required strict control of the reaction time to avoid the recrystallization of P in the hydrochar. Under optimum operating conditions (230 °C, 15 min, 0.5 mol/L HCl), 94 % of P (as of PO4) and almost 100 % of N (14 % as NH4-N) present in the feedstock were concentrated in the process water.