Biodiesel Production Research Articles

Biodiesel Production from Soybean Oil Using a Free-Enzyme and Whole-Cell Dual Lipase System as a Biocatalyst.

A dual lipase system has been developed to convert soybean oil into biodiesel through synergistic catalysis of Thermomyces lanuginosus lipase (TLL) and Yarrowia lipolytica lipase 2 (YLL) in this study. Pichia pastoris recombinant strains expressing lipases were successfully constructed, and the activities of TLL and YLL in the fermentation supernatant reached 23,142.71 ± 280.54 U/mL and 895.44 ± 27.31 U/mL, respectively. Immediately thereafter, free lipase was used to catalyze the preparation of biodiesel from soybean oil. After optimizing reaction conditions, 80 U/g oil TLL and 20 U/g oil YLL were used to catalyze the production of biodiesel, and a 95.56% biodiesel yield was obtained at 40°C, 40% moisture content (water/oil, w/w), and stepwise addition of five molar equivalents of methanol. Double lipase plasmids (tll gene and yll gene in different proportions) were constructed in vitro and introduced into P. pastoris to construct a recombinant strain with optimal activity. Under the reaction conditions of 40% moisture content, 8% whole-cell biocatalyst dosage, and stepwise addition of five molar equivalents of methanol, the biodiesel yield reached 95.35% after 24h at 40°C. These results show that synergistic catalysis is an effective strategy for biodiesel synthesis and can not only improve the biodiesel yield but also shorten the reaction time. This study provides a scientific basis for biodiesel production by multi-enzyme compounding, with potential industrial applications.

The potency of oleaginous yeast Lipomyces starkeyi in organic waste valorization to biodiesel

Oleaginous yeast-derived biodiesel production utilizing zero-value organic waste biomasses has been prioritized to curb environmental pollution, global warming, and rising bioenergy demands. Lipomyces starkeyi is a promising lipid accumulator among various oleaginous yeasts due to its potency for lipogenesis utilizing a diverse variety of substrates and tolerating various fermentation inhibitors produced during biomass pretreatment. The prevalence of saturated and monounsaturated longer-chain fatty acids (C16–C18) in triglyceride of L. starkeyi improves the quality of the produced biodiesel. Nevertheless, variations in substrate types, fermentation conditions, and modes of fermentation influence the growth of L. starkeyi and its lipid productivity and profile. This review will comprehensively discuss the lipid production potency of oleaginous L. starkeyi during variations in substrate composition and fermentation conditions and their impact on lipid production and its quality to facilitate industrial production of L. starkeyi-derived biodiesel utilizing zero-value organic waste.

Impact of pH, nutrient, and salinity stress on lipid synthesis in Coelastrella sp. for sustainable biodiesel production

Impact of pH, nutrient, and salinity stress on lipid synthesis in Coelastrella sp. for sustainable biodiesel production

Study of the Effect of NaOH Type Alkaline Catalyst on the Physicochemical Characteristics of Used Cooking Oil Biodiesel

Dependence on fossil fuels causes significant environmental damage and increases costs and scarcity in the future. To overcome this problem, a transition to renewable energy is needed, one of which is biodiesel which can be obtained from used cooking oil. This study aims to convert used cooking oil that cannot be reused into biodiesel products. Biodiesel synthesis can be carried out by the transesterification process, using NaOH catalyst with concentration variations of 0.5%, 0.75%, 1%, 1.25%, and 1.5% of the total mass of oil. The test parameters are calorific value, density, viscosity and flash point as well as yield on used cooking oil biodiesel products. The test results show that the use of a catalyst concentration of 1% produces more optimal density, viscosity, and calorific value and flash point. Each value is 0.859 g / cm³, 2.34 cSt, 10,356 cal / g, and 139°C. However, the use of a catalyst concentration of 0.5% shows that the biodiesel product is less than optimal. This can be shown by the highest density, viscosity and flash point values of the catalyst concentration variations used. Each value is 0.88 g/cm3, 3.16 cSt and 178°C, while the calorific value is also low with a value of 9,689 cal/g. However, when viewed from the yield, the catalyst concentration of 0.5% produces the highest value of all catalyst concentration variations used with a value of 88%.

Preparation and Characterization of Sulfonated CaO Catalyst for Biodiesel Production from Waste Cooking Oil

Biodiesel production depends on raw materials. Low-quality oils, such as cooking oil, crude palm oil, and sludge oil, are used to reduce costs, and they contain free fatty acids (FFA) and water. Soap can be produced when using the alkaline catalyst during transesterification. In this work, the sulfonation method prepared the esterification of waste cooking oil by sulfonated CaO as a bifunctional catalyst. The sulfonated CaO catalysts were characterized by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), temperature-programmed desorption of carbon dioxide and ammonia (TPD), BET surface area, and scanning electron microscopy (SEM). It was observed that the specific surface area, pore volume, and pore diameter of the CaO increased after being sulfonated with a 2 M sulfuric acid solution. It showed a high total surface acidity and basicity, 7.22 and 3.86 mmol/g, respectively. The optimal FFA conversion (84.94 %) from the waste cooking oil was acquired at a reaction temperature of 65 ˚C, a 9:1 MeOH: Oil molar ratio, and 5 wt% catalyst loading for a 3 h reaction time. The 2 M sulfonated CaO catalyst can be reused twice with a high FFA conversion without further treatment under optimized reaction conditions. The 2 M sulfonated CaO catalyst has potential treatment for biodiesel production from high-FFA oils due to its lower production cost and high catalytic activity.

The Potential of Microwave Technology for Glycerol Transformation: A Comprehensive Review

Glycerol is a major by-product in biodiesel manufacturing, which accounts for around 10% of the biodiesel volume. A surplus of glycerol has led to the development of technologies for production of value-added products using glycerol as a raw material, following the “waste as a resource” strategy. Various techniques are available to carry out glycerol transformation, viz. carrying out processes under thermal heating, application of ultrasonic or hydrodynamic cavitation, microchannel technologies, etc. Microwave-assisted organic synthesis (MAOS) is a simple and innovative technology, which can be considered as a means of intensifying these processes. This review describes microwave irradiation as a valuable energy-efficient alternative to conventional heating for the production of value-added chemicals from glycerol via dehydration, hydrogenolysis, esterification, transesterification, etherification, and oxidation. In general, innovative and potential catalysts, approaches, and technologies are discussed and critically evaluated in terms of the possibilities and potential for further industrial implementation

Energy Utilization of Rapeseed Biomass in Europe: A Review of Current and Innovative Applications

Rapeseed (Brassica napus L.) biomass holds significant potential as a renewable energy resource in Europe due to its adaptability, high oil content, and role in biodiesel production. This review explores the energy applications of rapeseed biomass, examining its agronomic characteristics and environmental benefits. A detailed analysis of extraction processes—pressing, solvent extraction, and refining—highlights methods to optimize oil yield and quality. Additionally, the review addresses the use of rapeseed oil in various biofuel applications, including its direct use and in blends with fuels like alcohols and hydrogen, analyzing performance and emissions outcomes. Rapeseed cake, a valuable by-product, is discussed for its dual role as animal feed and as a moderate biofuel alternative. Emissions data and combustion efficiency metrics provide insights into the feasibility of rapeseed oil as a fuel substitute. Overall, this review aims to underscore the contributions of rapeseed biomass to sustainable energy and to identify gaps in current research that can guide future innovations in biofuel production and agricultural sustainability in Europe. Research in rapeseed biomass focuses on optimizing extraction methods, improving combustion efficiency and emission control, exploring advanced uses for rapeseed cake, developing higher-yielding and resilient varieties, conducting lifecycle sustainability assessments, and investigating new biofuel blends and applications.

Direct Synthesis of the Ce-SBA-15 Catalyst Doped with MoO3 for Application in the Transesterification Reaction of Soybean Oil

Objective: Synthesize and characterize the heterogeneous catalyst MoO₃/Ce-SBA-15, to be applied in the transesterification reaction of soybean oil. Theoretical Framework: The molecular sieve SBA-15 is a mesoporous silica used as a support for the dispersion of active metals. Modification with cerium (Ce) enhances the textural properties, while doping with molybdenum oxide (MoO₃) increases the catalytic activity. This catalyst is applied in transesterification for the production of biodiesel, a renewable and efficient biofuel to replace fossil diesel. Method: Ammonium cerium nitrate was introduced along with the silica source in the synthesis gel, evaluating different Si/Ce molar ratios (10, 20). The obtained material was doped with MoO3 using the pore saturation method and evaluated in the transesterification reaction at different temperatures. Results and Discussion: Characterization analyses indicated that the longer crystallization time (48h) and the introduction of Ce into the structure improved the crystalline and textural properties of SBA-15. The presence of MoO₃ in its orthorhombic phase was confirmed by X-ray diffraction analysis. The maximum yield of methyl esters was 86.56% at 150°C using the 15MoO3/10Ce-SBA-15 catalyst. Research Implications: This research developed a new catalyst efficient in biodiesel production, contributing to the field of catalysis. Promoting advances in renewable energy and sustainability. Originality/Value: This study reports the influence of Ce as a structural promoter in the synthesis of a new catalyst (MoO3/Ce-SBA-15) to be applied in the transesterification reaction for biodiesel production.

Biodiesel Production from Waste Oil Through Efficient Enzymatic Synthesis Using Yarrowia lipolytica Lipase 2 in the Presence of Glucose, β-Cyclodextrin, or G50.

In this study, the liquid lipase Yarrowia lipolytica lipase 2 (YLLip2) expressed by Pichia pastoris GS115 was used to produce biodiesel from waste oil. Four signal peptides were compared to express YLLip2 in P. pastoris, among which SP23 exhibited greater secretion performance. In a 1.3-L bioreactor with FM22 medium for 7days incubation, the maximum YLLip2 activity and total protein content reached 895.44 ± 27.31 U/mL and 3.83 ± 0.31g/L, respectively. Under the optimal reaction conditions of 30°C, 20% moisture content, 50 U/g oil of enzyme dosage, and distributed methanol addition, the reaction yield reached 80.99% after 12h. To further improve the biodiesel yield, some additives were used to assist with YLLip2. The results showed that adding G50 (approximately 1/20 of YLLip2) increased the yield by approximately 90% after 6h cultivation without changing the enzyme dosage. Compared with previous studies, the reaction time for biodiesel production from waste oil in this study was significantly shortened. This study provides a workable method for converting low-quality feedstocks containing high free fatty acids into biodiesel using a liquid lipase as the catalyst.

Sustainable Management of Fish Gut Waste Through Transesterification

Abstract: The fishing industry in Sri Lanka generates significant waste, presenting an opportunity to convert it into a sustainable energy source. This research investigates the production of biodiesel from fish waste, specifically fish oil, as an alternative fuel to reduce reliance on fossil fuels and improve waste management in the fish market. Fish waste, including non-edible parts such as fish heads, tails, fins, and internal organs, was collected from a local fish market and subjected to an extraction process using wet boiling. The extracted fish oil was then converted into biodiesel through a transesterification reaction with methanol in the presence of potassium hydroxide (KOH) as a catalyst. Two optimization experiments were conducted to determine the best methanol concentration (15%, 20%, and 25%) and KOH concentration (1g, 2g, and 3g). The results showed that the highest biodiesel yield was obtained using 20% methanol (producing 10.71g of biodiesel) and 1g of KOH as a catalyst, yielding a biodiesel production of 8.66g for 15% methanol and 6.89g for 25% methanol. The biodiesel produced exhibited promising fuel properties, with a flashpoint of 127.5°C, a calorific value of 39.248 MJ/kg, kinematic viscosity of 4.4107 mm²/s, and density of 0.8766 g/cm³, all of which were within the acceptable limits set by ASTM standards. Additionally, the FFA content of the extracted fish oil was initially 7%, which was reduced through a saponification process, making the oil suitable for biodiesel production. The study estimated that approximately 237 metric tons of biodiesel could be produced per month from the fish waste in Sri Lanka, based on the average monthly fish waste generated (50% of total fish production). The biodiesel production from fish oil thus holds significant potential as both a renewable energy source and a sustainable waste management solution, reducing the reliance on fossil fuels and addressing environmental challenges associated with waste disposal in the fishing industry.

Waste‐Derived Catalyst for Biodiesel Manufacturing in CO2‐Free Manner: Preparation, Catalytic Activity and Reuse Studies

Currently, CaO‐based catalysts for biodiesel manufacturing are produced by calcination of available limestone ore consisting of CaCO3. The production of 1 ton of CaO catalyst resulted in 0.89 tons of CO2 emission, and every ton of the catalyst provided only 20 tons of biodiesel in non‐reusable manner. In this work, a CaO‐based catalyst was obtained by calcination of Ca(OH)2, a large‐tonnage waste from acetylene manufacturing via calcium carbide route (carbide slag), producing H­2O as a by‐product instead of CO2. Amazingly, carbide slag – a waste – was active in catalytic transesterification of soybean oil skipping calcination or any pretreatment steps and provided biodiesel in 28% yield! Moreover, biodiesel was obtained in 98% yield after catalyst calcination at 600 °C for at least 4 times accompanying zero CO2 emission. The obtained catalysts were characterized by XRD, XRF, FTIR, TGA, SEM‐EDX and BET surface area analysis. The best conversion of soybean oil was achieved using 1 wt% CS600, MeOH:oil ratio of 12:1, by boiling at 65 °C for 2 h. The catalyst reuse was found out using two approaches: "catalyst isolation" (5 cycles with yield ≥ 80%) and "fresh start" (up to 7‐10 cycles with yield ≥ 80%).

Valorization of Dairy Wastewater into Microbial Lipid by Oleaginous Yeast Pseudozyma sp. for Sustainable Biodiesel Production

Valorization of Dairy Wastewater into Microbial Lipid by Oleaginous Yeast Pseudozyma sp. for Sustainable Biodiesel Production

Sustainable Processes Reusing Potassium-Rich Biomass Ash as a Green Catalyst for Biodiesel Production: A Mini-Review

To mitigate the emissions of greenhouse gases (GHGs) from fossil fuels, the use of biodiesel and its sustainable production have been receiving more attention over the past decade, especially for the reuse of waste cooking oils and non-edible oils as starting feedstocks. For the biodiesel production process, the suitability of a green catalyst is a core function in the transesterification reaction. Heterogeneous (solid-state) catalysts are generally superior to homogeneous (liquid-state) catalysts due to several significant advantages such as no saponification products formed, recyclability, and less equipment corrosion. Recent studies also revealed that heterogeneous solid base catalysts were widely used for the production of biodiesel. Furthermore, the use of biomass-based ash derived from herbaceous and agricultural biomass is increasing rapidly because of its environmental sustainability, high biodiesel yield, and low catalyst cost. To highlight alternative catalysts from biomass residues, this mini-review paper thus focused on a summary of various heterogeneous potassium-rich ash materials, which were used as green catalysts for the sustainable production of biodiesel. Due to the abundant quantity and chemical compositions, it was found that ash derived from cocoa pod husk may be the most commonly used solid base catalyst for producing biodiesel in the literature. Finally, future perspectives on biodiesel production by adopting emerging technologies and using high-potassium (K) biomass ash as a green catalyst were also addressed.

Sustainable production of a highly pure (R,R)-2,3-butanediol from crude glycerol using metabolically engineered Klebsiella pneumoniae GEM167 strain

BackgroundAmong 2,3-butanediol (2,3-BDO) stereoisomers, (R,R)-2,3-BDO is particularly noteworthy for its application in the agricultural industry. It is an eco-friendly plant immune system stimulant, promoting plant growth and enhancing resistance to biotic and abiotic stresses.ResultsThis study aimed to address the limitations of a previous study, which produced (R,R)-2,3-BDO with only 98% purity despite Kp-dhaD overexpression. First, BLi-gldA demonstrated significantly higher activity and selectivity in converting racemic acetoin to (R,R)-2,3-BDO compared to others among 2,3-BDO dehydrogenases (Kp-dhaD and Kp-gldA from Klebsiella pneumoniae, and BLi-gldA from Bacillus licheniformis). The K. pneumoniae GEM167 ΔadhEΔldhAΔbudC-BLi-gldA/pETM6 strain produced the highest (R,R)-2,3-BDO amount, with 99% purity (73.51 ± 1.69 g/L at 48 h), by isopropyl β-D-1-thiogalactopyranoside addition at the early exponential growth phase (6 h) compared to other cell growth phases. The availability of crude glycerol was investigated, and crude glycerol promoted cell growth resulting in efficient (R,R)-2,3-BDO in the early stage of culture [90.32 ± 1.12 g/L (R,R)-2,3-BDO with 99.0% purity after 60 h]. The productivity and yield remained comparable for crude glycerol (1.51 g/L/h, 0.41 g/g) and pure glycerol (1.53 g/L/h, 0.43 g/g).ConclusionsThis study successfully produced 99% enantiopure (R,R)-2,3-BDO from crude glycerol for the first time using the K. pneumoniae GEM167 ΔadhEΔldhAΔbudC-BLi-gldA/pETM6 strain. (R,R)-2,3-BDO production from crude glycerol, a biodiesel process byproduct, is expected to contribute to a sustainable and circular biomass supply chain and biodiesel production system by positively influencing the stable cultivation of biodiesel crops even under unpredictable climate conditions.Graphical abstract

Surfactant-modified ZnFe2O4/CaOPS porous acid-base bifunctional catalysts for biodiesel production from waste cooking oil and process optimization

Biodiesel production from waste cooking oil (WCO) with high acid value is useful for clean energy development and utilization. In this work, ZnFe2O4(5)/CaOPS porous bifunctional catalysts were prepared for catalytic production of biodiesel with the help of surfactants such as PVP, SDS and citric acid, using a sol-gel method. The ZnFe2O4(5)/CaOPS catalysts were characterized using XRD, SEM, EDX, NH3-TPD, and BET. The parameters (reaction temperature, catalyst dosage, methanol-oil ratio and reaction time) for the transesterification reaction to produce fatty acid methyl esters (FAMEs) were optimized for the optimal materials using a one-variable method. Experiments were designed using Response Surface Methodology (RSM) and Artificial Neural Network (ANN) for global optimization to obtain the best process parameters. The final average yield of FAMEs was 96.89% under the optimum reaction parameter of catalyst dosage of 5.06wt%, reaction temperature of 63.69°C, reaction time of 212.22min and methanol-oil ratio of 12.96:1. The prepared biodiesel was characterized using FT-IR, 1H NMR as well as 13C NMR and compared with international standard ASTM D6751. The ZnFe2O4(5)/CaOPS catalyst has excellent stability in biodiesel production and has some free fatty acid tolerance. In addition, a cost analysis and sensitivity analysis were done for the production of WCO biodiesel. It is hoped that the research results in this paper can provide a theoretical basis for biodiesel production from WCO with high free fatty acid content.

Enhanced catalytic performance of methanol-tolerant Rhizopus stolonifera immobilized on polyurethane foam with hydrophobic coating for biodiesel production

The limited methanol tolerance and glycerol adsorption tendency of whole-cell catalysts are the main factors contributing to the extended catalytic cycle and limited catalyst reusability in biodiesel preparation. In this study, a 7.5 % methanol-tolerant Rhizopus stolonifera mutant (MTS2) was developed through the atmospheric and room temperature plasma (ARTP), exhibiting a 1.5-fold increase in methanol tolerance compared with the wild type strain (WT-RS), along with a 93.5 % increase in lipases activity. Polyurethane foam PF3 with an average pore size of 0.15 mm and 90 A rigidity is optimal for MTS2 immobilization (MTS2 @PF3), enabling its application in continuous processing for industrial applications. Utilizing soybean oil as a substrate, the catalyst MTS2 @PF3 produced 95.5 % of fatty acid methyl esters (FAME) in 36 hours under optimal conditions (30°C, 180 r/min, catalyst dosage of 15 % g/g oil, 30 % water content, and methanol addition in Scheme 3), achieving over a 50 % reduction in reaction time compared with WT-RS@PF3. To address limitations in catalyst reusability due to glycerol adsorption, various modifiers, including rosin-based modifier (RM), amino silicone oil (ASO), graphene (GRA), betaine and Tween 80 were evaluated. The glycerol adsorption rates experienced substantial reductions (39.3 % with RM and 85.6 % with betaine), and the catalysts maintained above 60 % FAME yield even after 8 reaction cycles. The combination of enhanced methanol tolerance, lipase activity, and reduced glycerol adsorption contribute to enhanced catalytic efficiency and reusability, which can reduce production costs for biodiesel manufacturing. The composite of these attributes makes MTS2 @RM1-PF3 and Betaine-MTS2 @PF3 as promising candidate for industrial biodiesel production, addressing previous limitations in catalyst performance and sustainability. The developed immobilized whole-cell catalysts exhibit promising potential for more sustainable and cost-effective processes in biodiesel manufacturing.

Sulfonic-acid-functionalized lignin-derived LC900@SO3H: A promising catalyst for the efficient production of biodiesel via the esterification of oleic acid

The renewable and clean biodiesel production makes higher demands for cheap, green and efficient catalysts. A sulfonic-acid-functionalized LC900@SO3H catalyst was prepared using alkali lignin as the carbon source, which was applied in the esterification of oleic acid to produce biodiesel. The yield of biodiesel reached 96.3% under mild conditions (Temperature = 95 ◦C, Catalyst dosage = 3.5wt%, MeOH/Oleic acid = 11.2:1, Time = 1.5h). The catalysts were reused at least 3 times with a high biodiesel yield of over 80%. The morphological and spectral analyses of the catalysts were conducted using BET, TGA, Raman, SEM, FTIR, and XPS, and the products were analyzed by GC and GC-MS. Characterizations indicated that the huge specific surface area (1618.68 m2/g) and large pore volume (0.8573 cm3/g) endow the LC900@SO3H with abundant sulfonic-acid-functionalized active sites for excellent catalytic activity. In addition, the response surface method (RSM) revealed the interaction of different reaction conditions for biodiesel production. The cost of 1kg catalyst was estimated as $3.59, showing good economic viabilities.

Biodiesel production from the transesterification of waste cooking oil via CaO/HAP/MnFe@K magnetic nanocatalyst derived from eggshells and chicken bones: Diesel engine and kinetic studies

This study focuses on the biodiesel generation from waste cooking oil (WCO) utilizing eggshells/chicken bones-derived magnetic nanocatalyst (CaO/HAp/MnFe@K). Various assessments were applied to demonstrate the CaO/HAp/MnFe@K nanocatalyst surface. These assessments showed that CaO/HAp/MnFe@K nanocatalyst has considerable catalytic attributes (e.g., highly crystalline, suitable surface area, and favorable porosity). The highest biodiesel efficiency employing CaO/HAp/MnFe@K magnetic nanocatalysts was 99.10%, which was obtained at a molar proportion of 15.24:1, catalyst content of 2.97 wt.%, reaction time of 175.72 min, and temperature of 67.72 °C (optimal conditions). Further, the reaction kinetics demonstrated that the transesterification of WCO in the attendance of CaO/HAp/MnFe@K nanocatalyst follows the pseudo-first-order model. Besides, the activation energy and exponential factor reflection reveal that the conversion of WCO to biodiesel is 41.51 kJ/mol and 1.66×105 min-1, respectively. By adding WCO-derived biodiesel to diesel, the release of carbon dioxide (CO2) and nitrogen oxides (NOx) increases while the carbon monoxide (CO) and unburned hydrocarbon (UHC) amounts diminish. By boosting biodiesel in the fuel combination, the quantities of brake specific fuel consumption (BSFC) and exhaust gas temperature (EGT) increased while the Brake Thermal Efficiency (BTE) amount decreased. Moreover, reusability of the CaO/HAp/MnFe@K nanocatalyst revealed that the magnetic particles were considerably stability.

Process Optimization for Madhuca indica Seed Kernel Oil Extraction and Evaluation of its Potential for Biodiesel Production

The current research aims to optimize the solvent-based oil extraction process from Mahua (Madhuca indica) seed using response surface methodology and biodiesel production using heterogeneous catalysts. The oil extraction was varied through the levels of process parameters including extraction temperature (60 to 80°C), solvent-to-seed ratio (3 to 9 wt/wt), and time (2 to 4 h). The experiments were designed following the Central Composite model. The regression model provided optimal values for the selected process parameters based on the extraction yield percentage. To ensure the model’s reliability, it was experimentally validated. Maximum experimental oil yields of 50.9% were obtained at an optimized extraction scenario of 70 °C extraction temperature, solvent-to-seed ratio of 6 wt/wt, and time 4 h. The extracted oil’s physicochemical properties and fatty acid composition were tested. Also, using copper-coated dolomite as a catalyst, the extracted oil was transformed into biodiesel via transesterification. The FAME (94.31%) content of the prepared biodiesel was determined via gas chromatography. As a result, the findings of this study will be useful in further research into the use of Madhuca indica as a potential feedstock for biodiesel production.

Enhancing bioremediation of diesel/biodiesel blend (B20) impacted sites using in situ bioreactors: A nature-based solution for sustainable groundwater management

The rise of biodiesel content in diesel/biodiesel blends as a viable alternative to traditional diesel fuel presents several advantages, particularly in terms of reduced emissions of pollutants like carbon monoxide (CO), hydrocarbons (HC), and smoke. However, the increased production and utilization of biodiesel raise concerns about potential environmental impacts, such as groundwater pollution. This has led to a growing need for sustainable and effective bioremediation techniques to address these issues and ensure the safe closure of contaminated sites in accordance with environmental regulatory criteria. Two experimental areas contaminated with B20 (80% diesel and 20% biodiesel v/v) to evaluate ammonium acetate biostimulation (B20_BAA) and natural source zone depletion (B20_NSZD) as remediation strategies were monitored for 10 and 12 years, respectively. Although the benzene half-life was 1.49 and 4.08 years, respectively, hydrocarbon concentrations remained above the maximum contaminant level (MCL) allowed in Brazil for groundwater, requiring additional technologies for site cleanup. Then, two pilot-scale airlift bioreactors were employed as nature-based solutions (NbS) to reduce the concentration of persistent contaminants for site closure. Indeed, concentrations of benzene and 2-methylnaphthalene decreased significantly after the bioreactors began operation, reaching values below their respective MCL. 16S rRNA gene sequencing showed a beneficial response of microbial communities composed of Massilia, Burkholderia-Caballeronia-Paraburkholderia, Mycobacterium and Bacillus genus involved in hydrocarbons aerobic biodegradation. Moreover, predicted functional genes analysis demonstrated that the relative abundances of key aerobic degradation pathways for benzene and 2-methylnaphthalene increased, supporting the hypothesis that the NbS stimulated the hydrocarbons biodegradation. These findings demonstrated that combining different nature-based solutions (NbS) can effectively remediate petroleum hydrocarbons in contaminated groundwater through geochemical characteristics and exploration of indigenous microorganisms. To the best of the authors’ knowledge, this is the first study to employ bioreactors to treat B20-contaminated groundwater at a field scale.