Hydrothermal liquefaction of Scenedesmus abundans biomass spent for sorption of petroleum residues from wastewater and studies on recycling of post hydrothermal liquefaction wastewater

Application of microbial resources in biorefineries: Current trend and future prospects

The recent growing interest in sustainable and alternative sources of energy and bio-based products has driven the paradigm shift to an integrated model termed "biorefinery." Biorefinery framework implements the concepts of novel eco-technologies and eco-efficient processes for the sustainable production of energy and value-added biomolecules. The utilization of microbial resources for the production of various value-added products has been documented in the literatures. However, the appointment of these microbial resources in integrated resource management requires a better understanding of their status. The main of aim of this review is to provide an overview on the defined positioning and overall contribution of the microbial resources, i.e., algae, fungi and bacteria, for various bioprocesses and generation of multiple products from a single biorefinery. By utilizing waste material as a feedstock, biofuels can be generated by microalgae while sequestering environmental carbon and producing value added compounds as by-products. In parallel, fungal biorefineries are prolific producers of lignocellulose degrading enzymes along with pharmaceutically important novel products. Conversely, bacterial biorefineries emerge as a preferred platform for the transformation of standard cells into proficient bio-factories, developing chassis and turbo cells for enhanced target compound production. This comprehensive review is poised to offer an intricate exploration of the current trends, obstacles, and prospective pathways of microbial biorefineries, for the development of future biorefineries.

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.

Co-Hydrothermal Liquefaction of algal and lignocellulosic biomass: Status and perspectives

Hydrothermal liquefaction (HTL) effectively converts biomass to biofuels, thereby limiting the endless reliance on petroleum products derived from fossil fuels. However, the conversion is based on individual feedstock in the HTL process. In order to, further boost the conversion, HTL can be done by blending various feedstock, mainly algal and lignocellulosic biomass. Bibliometric analysis was carried out, and it was observed that there have been very few studies on Co-Hydrothermal Liquefaction (Co-HTL). There still exist several crucial gaps in process optimization when co-reactants are used due to their synergistic effects. The reaction kinetics and mechanism, catalyst screening and by-products application require further studies. Therefore, R&D is necessary to optimize the process to completely utilize the complementarity of the feedstocks under study resulting in better quality of products which require minor/ no upgradation steps.

Review on hydrothermal liquefaction aqueous phase as a valuable resource for biofuels, bio-hydrogen and valuable bio-chemicals recovery

Hydrothermal liquefaction (HTL) of biomass results in the formation of bio-oil, aqueous phase (HTL-AP), bio-char, and gaseous products. Safer disposal of HTL-AP is difficult on an industrial scale since it comprises low molecular acid compounds. This review provides a comprehensive note on the recent articles published on the effective usage of HTL-AP for the recovery of valuable compounds. Thermo-chemical and biological processes are the preferred techniques for the recovery of biofuel, platform chemicals from HTL-AP. From this review, it was evident that the composition of HTL-AP and product recovery are the integrated pathways, which depend on each other. Substitute as reaction medium in HTL process, growth medium for algae and microbes are the most common mode of reuse and recycle of HTL-AP. Future research is needed to depict the mechanism of HTL process when HTL-AP is used as a reaction medium on an industrial scale. Need to find a solution for the hindrance in commercializing HTL process and recovery of value-added compounds from HTL-AP from lab scale to industry level. Integrated pathways on reuse and HTL-AP recycle helps in reduced environmental concerns and sustainable production of bio-products.

Insights into the potential impact of algae-mediated wastewater beneficiation for the circular bioeconomy: A global perspective

Algae-based technologies are one of the emerging solutions to societal issues such as accessibility to clean water and carbon-neutral energy and are a contender for the circular bioeconomy. In this review, recent developments in the use of different algal species for nutrient recovery and biomass production in wastewater, challenges, and future perspectives have been addressed. The ratio and bioavailability of nutrients in wastewater are vital parameters, which significantly impact nutrient recovery efficiency and algal biomass production. However, the optimum nutrient concentration and ratio may vary depending upon the microalgal species as well as cultivation conditions. The use of indigenous algae and algae-based consortia with other microorganisms has been proved promising in improving nutrient recovery efficiency and biomass production in pilot scale operations. However, environmental and cultivation conditions also play a significant role in determining the feasibility of the process. This review further focused on the assessment of the potential benefits of algal biomass production, renewable biofuel generation, and CO₂ sequestration using wastewater in different countries on the basis of available data on wastewater generation and estimated nutrient contents. It was estimated that 5-10% replacement of fossil crude requirement with algal biofuels would require ~952-1903 billion m³ of water, 10-21 billion tons of nitrogen, and 2-4 billion tons of phosphorus fertilizers. In this context, coupling wastewater treatment and algal biomass production seem to be the most sustainable option with potential global benefits of polishing wastewater through nutrients recycling and carbon dioxide sequestration.

Using polypropylene needle punch nonwoven sorbents as the interceptor for oil in static and dynamic water experiments

This work was to determine the impact of pore size and thickness of sorbents besides the influence of oil properties on the performance of sorbents used as an interceptor barrier for oils in Static and dynamic water experiments. polypropylene needle punch sorbents were used. SEM test showed the porous structure of sorbents. Oil sorption test investigated that with sorbents had same thickness N1 absorbed oil 8.89 g/g of soybean oil and 7.15 g/g of motor oil. Meanwhile, sorbents with the same pore size, N6 absorbed oil 6.11 g/g of soybean oil and 5.13 g/g of motor oil. All sorbents showed a retention rate of over 75% after 24 h of dripping. Dynamic oil spreading revealed that smaller pore size and higher thickness exhibited higher height wicking. The static performance experiment showed motor oil and soybean oil started to leak at 38 and 32 min for N1, then prolonged with reducing pore size with intercepting efficiency around 70% after 600 min for motor oil and 540 min for soybean oil. In comparison, The motor oil and soybean oil started to leak at 49 and 40 min for N4 and then prolonged with increased thickness with intercepting efficiency around 70% after 480 min for motor oil and 360 min for soybean oil. Under the dynamic experiment, oils spilled quicker with initial leakage of sorbents N3 and N6 at rate flow 55.65 ml/s for motor oil and soybean oil were (41 min, 36 min) and (50 min, 41 min) while intercepting efficiency was (99%, 98.40%) and (99.33%, 98.40%).

Effect of algae (Scenedesmus obliquus) biomass pre-treatment on bio-oil production in hydrothermal liquefaction (HTL): Biochar and aqueous phase utilization studies

Environmental concerns due to fossil fuel usage has turned the research interest towards biomass and bioenergy field. Renewable biomass such as microalgae provides numerous advantages as they can grow in wastewater; sequester carbon dioxide, economical and eco-friendly. In this study, effect of pretreatment of microalgae (Scenedesmus obliquus) biomass using post-hydrothermal liquefaction wastewater (PHWW) for bio-oil production through hydrothermal liquefaction at a temperature of 300 °C was studied. Results showed liquefaction of pre-treated biomass yielded 48.53% bio-oil whereas 28.35% was resulted from biomass without pretreatment. The analysis of higher heating value of bio-oil showed that pretreated biomass oil has 36.19 MJ.Kg^-1 against non-pretreated biomass oil, which has 28.88 MJ.Kg^-1. Bio-oil (pretreated biomass) analysis revealed that 60% of compounds are in diesel and gasoline range with 58.09% of energy recovery. Bio-oil was rich in hydrocarbons of C₇-C₂₁ range with less oxygenated compounds. Carbon balance showed that an increase of 13% of carbon was sequestered in solid residue obtained from pretreated biomass and about 146% of increase also obtained in bio-oil.

Effects of aqueous phase circulation and catalysts on hydrothermal liquefaction (HTL) of penicillin residue (PR): Characteristics of the aqueous phase, solid residue and bio oil

Hydrothermal liquefaction (HTL) is a promising thermochemical technology for the treatment of hazardous wastes such as penicillin residue (PR). For the treatment of aqueous waste produced by PR in the HTL process, aqueous phase circulation is an attractive solution, both environmentally and economically. The present study shows that aqueous phase circulation can promote the transfer of organic matter from the aqueous phase to bio-oil. The content of organic acids and alcohols in the aqueous phase decreased significantly, and the bio-oil yield and energy recovery efficiency also increased. Under non-catalytic conditions, the bio-oil yield increased from 26.09 wt% to 33.72 wt%. The use of Na₂CO₃ as a catalyst further improved the bio-oil yield. After a single aqueous phase circulation, the bio-oil yield increased to 34.63 wt%, and the energy recovery efficiency increased to 66.94%. Under catalytic hydrothermal conditions, the content of organic acids in the bio-oil was reduced using aqueous phase circulations, which improved the quality of the bio-oil. At the same time, the Na₂CO₃ catalyst promoted the hydrolysis of PR to form small molecule organic matter, inhibited the formation of coke, and reduced the content of carbon, hydrogen and oxygen in the solid residue. An increase of cycle times led to excessive accumulation of Na₂CO₃, which had a negative impact on the yield of bio-oil. Nitrogen-containing compounds in the bio-oil increased to a certain extent, which renders it necessary to consider denitrification treatments in the future. The work provides a useful reference for further research on the preparation of high quality bio-oil by PR hydrothermal liquefaction.

Technical insights into the production of green fuel from CO2 sequestered algal biomass: A conceptual review on green energy

Algae a promising energy reserve due to its adaptability, cheap source, sustainability and it's growth ability in wastewater with efficient sequestration of industrial carbon dioxide. This review summarizes the pathways available for biofuel production from carbon sequestered algae biomass. In this regard, this review focuses on microalgae and its cultivation in wastewater with CO₂ sequestration. Conversion of carbon sequestered biomass into bio-fuels via thermo-chemical routes and its engine emission properties. Energy perspective of green gaseous biofuels in near future. This review revealed that algae was the pre-dominant CO₂ sequester than terrestrial plants in an eco-friendly and economical way with simultaneous wastewater remediation. Hydrothermal liquefaction of algae biomass was the most preferred mode for biofuel generation than pyrolysis due to high moisture content. The algae based fuels exhibit less greenhouse gases emission and higher energy value. This review helps the researchers, environmentalists and industrialists to evaluate the impact of algae based bio-energy towards green energy and environment.

Photocatalytic reforming of aqueous phase obtained from liquefaction of household mixed waste biomass for renewable bio-hydrogen production

In this study, hydrothermal liquefaction of household waste was performed to produce valuable liquid hydrocarbons with aqueous phase as by-product. Photocatalytic reforming of aqueous phase was carried out for hydrogen production. Liquefaction of 15 g waste at temperature of 320 °C and solvent to biomass ratio of 13.33 mL/g produced bio-oil of 32.4 wt% and hydrogen 21 wt% in gas product. Hydrogen production from aqueous phase was studied in presence of various concentrations of activated carbon doped Fe/TiO₂ catalyst (0.2-1 wt%). Hydrogen yield was 32 wt% when 0.6 wt% of catalyst was used to reform aqueous phase. To ease of operation in economical manner the reusability study of the catalyst was evaluated and it was found to be active for three consecutive cycles. As outcome of this study, household waste can serve for a whooping amount of hydrogen (53 wt%) production via liquefaction and photocatalytic reforming process.

The effect of aqueous phase recirculation on hydrothermal liquefaction/carbonization of biomass: A review

Aqueous phase (AP) recirculation is attracting increasing interest in hydrothermal process field as it has the potential to increase the yield of bio-crude and/or hydrochar and decrease the cost of hydrothermal wastewater disposal. This work summarizes the effect of AP recirculation on hydrothermal processing biomass, including the discussions on the mechanisms account for the increased yield and the changing properties of the hydrochar and bio-crude. However, the application of AP recirculation in hydrothermal process is limited by the enrichment of nitrogen in bio-crude and the applicability of only specific biomass type. To alleviate these limitations, the feasibility of combining AP recirculation with other strategies (e.g., co-solvent and co-feed) has been discussed. The possibility of using AP as a resource (e.g., nutrient source, and material mediator) can be increased by AP recirculation due to the accumulation of substances.

Hydrothermal liquefaction of Nostoc ellipsosporum biomass grown in municipal wastewater under optimized conditions for bio-oil production

Microalgae offer numerous potential applications, however the industrial scale-up of algal technology still remains a challenge due to high production cost. Optimization of growth conditions and integration with waste streams can improve the economic viability of microalgal production systems. This study investigated on the optimal growth conditions of microalgae Nostoc ellipsosporum cultivated in municipal wastewater with the objective of achieving maximum biomass production, nutrient removal efficiency and bio-oil yield. The effect of light intensity, photoperiod, wavelength, aeration and growth media composition were studied. Different formulations of municipal wastewater blended with Fog's nutrient were used as growth medium. Optimization of growth conditions and acclimatization to wastewater enhanced the biomass yield of Nostoc ellipsosporum from 1.42 to 2.9 g L^-1, achieving 87.59% of nitrogen removal and 88.31% of phosphate removal from wastewater. Furthermore, hydrothermal liquefaction of biomass produced bio-oil yield of 24.62% at 300 °C.

Review on sustainable production of biochar through hydrothermal liquefaction: Physico-chemical properties and applications

This review examines in detail the production and characteristics of biochar resulting from hydrothermal liquefaction. Specifically, the impact of feedstocks and different process parameters on the properties and yield of biochar by hydrothermal liquefaction has been thoroughly studied. Hydrothermal liquefaction derived biochars, relative to biochars from high-temperature thermochemical processes retain critical functional groups during carbonization and are therefore promising for a wide range of applications. Most of the review's efforts are to study possible hydrothermal liquefaction biochar applications in various fields, including fuel, metal and dye adsorption, pollutant reduction, animal feed, and biogas catalyst. The feasibility of biochar through the hydrothermal liquefaction process has been analysed via life-cycle assessment and energy evaluation. The article concludes with a brief discussion on possible issues and strategies for the sustainable development of hydrothermal liquefaction-based biochar.

Hydrothermal liquefaction of Scenedesmus obliquus using a novel catalyst derived from clam shells: Solid residue as catalyst for hydrogen production

This study explores the catalytic application of waste clam shell in hydrothermal liquefaction (HTL) of microalgae (Scenedesmus obliquus) for liquid hydrocarbons production. Novel catalyst (calcium hydroxide) was derived from clam shells. Catalytic HTL was performed at varying temperature of 240-320 °C for catalyst load (0.2-1 wt%) at a reaction time of 60 min. Bio-oil yield was maximum (39.6 wt%) at a temperature of 300 °C for catalyst load of 0.6 wt% at a reaction time of 60 min with calorific value of 35.01 MJ/kg. Compounds like phenols, aromatic hydrocarbons, acids and aldehydes were detected in bio-oil through Gas Chromatography Mass Spectrophotometry (GC-MS). Gasification of microalgae with waste solid residue obtained from HTL was carried out for hydrogen production. Valuable hydrogen gas production was maximum (37 wt%) at a temperature of 400 °C for 3 wt% of solid residue. Water-gas shift, methanation and steam reforming reactions favoured the hydrogen gas production.

Megamerger of biosorbents and catalytic technologies for the removal of heavy metals from wastewater: Preparation, final disposal, mechanism and influencing factors

Heavy metal pollution, because of its high toxicity, non-biodegradability and biological enrichment, has been identified as a global aquatic ecosystems threat in recent decades. Due to the high efficiency, low cost, satisfactory recyclability, easy storage and separation, biosorbents have exhibited a promising prospect for heavy metals treatment in aqueous phase. This article comprehensively summarized different types of biosorbents derived from available low-cost raw materials such as agricultural and forestry wastes. The raw materials obtained are treated with conventional pretreatment or novel methods, which can greatly enhance the adsorption performance of the biosorbents. The suitable immobilization methods can not only further enhance the adsorption performance of the biosorbents, but also facilitate the process of separating the biosorbents from the wastewater. In addition, once biosorbents are put into large-scale use, the final disposal problems cannot be avoided. Therefore, it is necessary to review the currently accepted final disposal methods of biosorbents. Moreover, through the analysis of the adsorption and desorption mechanisms of biosorbents, it is not only beneficial to find the better methods to improve the adsorption performance of the biosorbents, but also better to explain the influencing factors of adsorption effect for biosorbents. Especially, different from many researches focused on biosorbents, this work highlighted the combination of biosorbents with catalytic technologies, which provided new ideas for the follow-up research direction of biosorbents. Finally, the purpose of this paper is to inject new impetus into the future development of biosorbents.

Preparation of transparent anti-pollution cellulose carbamate regenerated cellulose membrane with high separation ability

In this study, cellulose pulp and urea were used to synthesize cellulose carbamate (nitrogen content reaches 4.5%) by low-cost and environmentally friendly solid-liquid phase method. Cellulose carbamate fluid was prepared by using sodium hydroxide aqueous solution as solvent. The fluid was regenerated and formed in a coagulation bath, and finally a regenerated cellulose membrane with high transparency and separation ability was obtained. The simple chemical treatment of cellulose not only greatly increased the mass fraction of cellulose dissolution (It has reached 15%) and retains the original crystal form and thermal stability of cellulose. The surface of the membrane was relatively dense, and the inside has regular microchannel. The factors affect the transparency and water flux of regenerated cellulose membranes were discussed by orthogonal experimental range analysis. The ability of the regenerated cellulose membrane to reject dyes was tested. The results showed that the rejection of methyl blue and congo red reached 100%, and the rejection rate of methyl orange reached 60%. The oil/water separation ability and the anti-pollution ability of the regenerated cellulose membrane were tested. The oil/water separation effect reached 100%. This membrane may have application prospect in water treatment, biotechnology.

Co-thermal liquefaction of Prosopis juliflora biomass with paint sludge for liquid hydrocarbons production

In this study, Prosopis juliflora biomass was co-liquefied with hydrocarbons rich paint waste for next generation fuel (bio-oil) production. Co-liquefaction (HTL) was performed at varying biomass to paint waste ratios (1:0, 0:1, 1:1, 2:1 and 1:2) at different temperatures from 340 to 440 °C for a holding time of 60 min. Bentonite catalyst was added from 1 to 5% wt. to the HTL reactor. Gas Chromatography-Mass Spectroscopy (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR) analysis were carried out for bio-oil and HTL aqueous phase. Maximum bio-oil yield was around 49.26% wt. at 420 °C, 2:1 blend and 4% wt. of bentonite catalyst. Energy and carbon recovery of bio-oil was around 70% and 96% respectively. Additionally, HTL aqueous phase was analysed and it showed presence of acids molecules in it. The gas from HTL process contained Carbon dioxide (46.25%), Carbon monoxide (6.38%), Methane (9.35%) and hydrogen (24.53%).