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The extensive growth of energy and plastic demand has raised concerns over the depletion of fossil fuels. Moreover, the environmental conundrums worldwide integrated with global warming and improper plastic waste management have led to the development of sustainable and environmentally friendly biofuel (bioethanol) and biopolymer (lactic acid, LA) derived from biomass for fossil fuels replacement and biodegradable plastic production, respectively. However, the high production cost of bioethanol and LA had limited its industrial-scale production. This paper has comprehensively reviewed the potential and development of third-generation feedstock for bioethanol and LA production, including significant technological barriers to be overcome for potential commercialization purposes. Then, an insight into the state-of-the-art hydrolysis and fermentation technologies using macroalgae as feedstock is also deliberated in detail. Lastly, the sustainability aspect and perspective of macroalgae biomass are evaluated economically and environmentally using a developed cascading system associated with techno-economic analysis and life cycle assessment, which represent the highlights of this review paper. Furthermore, this review provides a conceivable picture of macroalgae-based bioethanol and lactic acid biorefinery and future research directions that can be served as an important guideline for scientists, policymakers, and industrial players.

Biodiesel was prepared by transesterification process using heterogeneous catalyst has received a lot of interest lately as a sustainable source of biofuel. Hence, there is a need to study a generalized reaction kinetic model that can be used for all the reactions involved in biodiesel production. This study produces biodiesel by transesterifying palm oil using magnetic palm kernel shell-potassium hydroxide. The catalyst recorded a BET surface area of 47.72 m2/g. The maximum biodiesel yield, 95.78%, was obtained when reaction temperature and time were 55°C and 2 hours, respectively.

Energy plays an important role in sustaining humanity. With rising worldwide energy demand and the great dependence of energy generation on fossil fuels, it is inevitable that enhanced oil recovery must be deployed to recover more possible reserves. This report focuses on reviewing publications related to enhanced oil recovery from 2007 to 2020 through the utilization of bibliometric analysis. Of the 5498 documents retrieved from Web of Science, 569 journals, 90 countries, 2025 organizations, and 8684 authors are involved. China, the United States, Iran, Canada, and India published the most documents. The United States has the highest h-index at 61. The analysis of keywords had shown that the hot issues lie around four main domains namely carbon capture, utilization, and sequestration (CCUS), microbial enhanced oil recovery (MEOR), development of unconventional reserves, and chemical enhanced oil recovery. This study provides some useful insights for future research directions. From there, discussions were subsequently placed on chemical EOR.

In recent years, utilization of renewable sources for biofuel production is gaining popularity due to growing greenhouse gases (GHG) emissions which causes global warming. There has been a great effort in exploring alternative feedstock for bioethanol production. In this context, the production of third-generation bioethanol from macroalgae has emerged as an alternative feedstock to food crop-based starch and lignocellulosic biomass. This is mainly due to the fast growth rate of macroalgae, no competition with agricultural land, high carbohydrate content and relatively simple processing steps compared to lignocellulosic biomass. This review paper provides an insight of recent innovative approaches for macroalgae bioethanol production, including conventional and advanced hydrolysis process to produce fermentable sugar, various fermentation technologies, economic analysis and life cycle assessment. With the current technology maturity, efficient utilization of macroalgae as sustainable source for bioethanol and other value-added chemicals production could be achieved in the near future.

Catalytic deoxygenation is a biofuel upgrading process to eliminate the high oxygen content which will lead to corrosion, instability and lower heating value problems. Biofuel have a high oxygen content, which deteriorates the biofuel quality. Therefore, the upgrading of biofuels via catalytic deoxygenation is necessary. Metal oxide such as TiO2, Al2O3, SiO2, ZrO2 and CeO2 is known as a promising support for the production of hydrocarbon-graded biofuel via deoxygenation process. The choice of support is significant to provide the maximum acid strength for the hydrogenolysis of C-O bonds. Al2O3 supported catalyst has drawn attention due to the high acidity. However, the high acidity leads to coke deposition, unstable and deactivation of the catalyst. Thus, it is important to develop methods to reduce catalyst coking and enhance the lifetime of the catalyst. Recently, Al2O3-TiO2 supported catalyst has drawn increasing attention in deoxygenation process owing to its unique properties which can solve the issues from Al2O3. Controlled synthesis method is significant to improve the effectiveness of Al2O3-TiO2 in catalytic reaction since the physicochemical properties of the catalyst are co-related to the processing methodology. Hence, this review describes the use of selected metal oxide supported catalyst for biofuel conversion in deoxygenation process. Moreover, the synthesis method of Al2O3-TiO2 is comprehensively discussed. The physicochemical properties of Al2O3-TiO2, metals and metal oxides supported on Al2O3-TiO2 are further discussed. Finally, future prospective and challenges of deoxygenation process for biofuel synthesis are discussed in order to produce quality hydrocarbon like biofuel using metal oxide supported catalyst.

The declaration of 2016, third year in a row, as the warmest year ever recorded, the rising of CO2 concentration, increasing of seawater acidity as well as sea surface temperature are among the worst scenarios of global warming. One of the ways to reduce the harmful emissions is to use renewable energy sources. Biodiesel, being one of the less environment-damaging options to fuel diesel engines, is making its way globally as a greener portion of diesel engines emissions. For countries where utilization of high technological energy sources is a real challenge, then vegetable oils and waste oils from local sources are the possible option. This greener fuel has been mandated of its usage in many countries across the continents in a blending range up to 20% with petro-diesel. The concept of biorefinery is a must as to make the biodiesel industry viable, and to gauge its practicability, Biorefinery Complexity Index (BCI) is a way to go. Production and the use of biodiesel are not without challenges; challenges in term of cost, cold performance, storage stability, engine warranty, post production issues, boundary setting in life cycle analysis and public perceptions. Without an overall assessment, the benefits of biodiesel are not guaranteed; as such, this review is aimed to discuss those challenges, in addition providing possible options as to make this greener fuel into reality in much wider scope.

This study aims to establish an efficient pretreatment method that facilitates the conversion of sugars from macroalgae wastes, Eucheuma cottonii residues (ECRs) during hydrolysis and subsequently enhances L-lactic acid (L-LA) production. Hence, ultrasonic-assisted molten salt hydrates (UMSHs) pretreatment was proposed to enhance the accessibility of ECRs to hydrolyze into glucose through dilute acid hydrolysis (DAH). The obtained hydrolysates were employed as the substrate in producing L-LA by separate hydrolysis and fermentation (SHF). The maximum glucose yield (97.75%) was achieved using UMSHs pretreated ECRs with 40wt% ZnCl

The synthesis of Janus nanosheets using κ-carrageenan (κ-Ca) as a green template endows a greener and more straightforward method compared to traditional approaches of using wax template. We hypothesize that the hydrogen bonding interaction between κ-Ca and graphene oxide (GO) allows partial masking of GO’s single facet, paving the way for the asymmetric modification of the exposed surface. GO is first encapsulated within the porous hydrogel matrix formed by κ-Ca to isolate one of the facets. The exposed surface was then selectively hydrophobized to produce an amphiphilic asymmetrically modified graphene oxide (AMGO). The properties of AMGO synthesized under different κ-Ca/GO ratios were studied. The κ-Ca/GO interactions and the properties of GO and AMGO were investigated and characterized. AMGO was successfully produced with a yield of 90.37 % under optimized synthesis conditions. The separation of κ-Ca and AMGO was conducted without organic solvents, and the κ-Ca could be subsequently recovered. Furthermore, the porous hydrogel matrix formed by κ-Ca and GO exhibited excellent shape-retaining properties with high thermal tolerance of up to 50 °C. Given these benefits, this newly developed method endows sustainability and open the possibility of formulating more flexible material synthesis protocols.

Managing plastic waste remains an urgent environmental concern and switching to biodegradable plastics can reduce the dependence on depleting fossil fuels. This study emphasises the efficacy of macroalgae wastes, Eucheuma denticulatum residues (EDRs), as potential alternate feedstock to produce l -lactic acid ( l -LA), the monomer of polylactic acid, through fermentation. An innovative environmental friendly strategy was explored in this study to develop a glucose platform from EDRs: pretreatment with microwave-assisted autohydrolysis (MAA) applied to enhance enzymatic hydrolysis of EDRs. The results indicate that MAA pretreatment significantly increased the digestibility of EDRs during the enzymatic hydrolysis process. The optimum pretreatment conditions were 120 °C and 50 min, resulting in 96.5% of enzymatic digestibility after 48 h. The high l -LA yield of 98.6% was obtained using pretreated EDRs and supplemented with yeast extract. The energy analysis implies that MAA pretreatment could further improve the overall energy efficiency of the process.

The accumulation of conventional petroleum-based polymers has increased exponentially over the years. Therefore, algae-based biopolymer has gained interest among researchers as one of the alternative approaches in achieving a sustainable circular economy around the world. The benefits of microalgae biopolymer over other feedstock is its autotrophic complex to reduce the greenhouse gases emission, rapid growing ability with flexibility in diverse environments and its ability to compost that gives greenhouse gas credits. In contrast, this review provides a comprehensive understanding of algae-based biopolymer in the evaluation of microalgae strains, bioplastic characterization and bioplastic blending technologies. The future prospects and challenges on the algae circular bioeconomy which includes the challenges faced in circular economy, issues regard to the scale-up and operating cost of microalgae cultivation and the life cycle assessment on algal-based biopolymer were highlighted. The aim of this review is to provide insights of algae-based biopolymer towards a sustainable circular bioeconomy.

Microalgae-based biodiesel has gained widespread interest as an alternative energy source. Low-cost microalgae harvesting technologies are important for economically feasible biodiesel production. This study investigated, for the first time, the impact of adaptation period and height to diameter (H/D) ratio of a reactor on the growth and self-flocculation of microalgae, without the addition of bacteria. Six reactors were grouped into three sets of experiments, and each reactor was operated for 30 days at similar operating conditions (volume exchange ratio = 25% and settling time = 30 min). In set 1, two 8-L reactors, H5a (H/D ratio: 5) and H8a (H/D ratio: 8), were operated under batch operation. In set 2, reactors H5b and H8b were operated as sequential batch reactors (SBRs) without an adaptation period. In set 3, the reactors H5c and H8c were operated as SBRs with an adaptation period. The findings showed a threefold improvement in biomass productivity for the higher H/D ratio (H8c) and a reduction in biomass loss for microalgae. The H8c reactor exhibited 95% settling efficiency within 5 days, in comparison to 30 days for the H5c reactor. This study demonstrated that a higher H/D ratio and the introduction of an adaptation period in SBR operation positively influences growth and self-flocculation of enriched mixed microalgae culture.

H2-Free catalytic deoxygenation of biomass-derived organic compounds is an important technology to produce green hydrocarbons without the relevant carbon footprint associated with H2. In this work, the effects of the crystal size of zeolite Y (Y20: 20 nm, Y65: 65 nm, Y380: 380 nm and Y2750: 2.75 μm) on the deoxygenation reaction of triolein are reported. The reaction is performed under solvent-free conditions without the addition of hydrogen. As the crystal size decreases, the triolein conversion and the yield of deoxygenated products increase. In addition, better product quality is obtained: higher hydrocarbon formation, higher diesel formation, lower formation of heavy hydrocarbons and higher diesel-to-gasoline ratio are observed. The high activity is related to the high concentration of acid sites, with accessible medium acid strength comprised of Bronsted and Lewis acid sites located on the external surface of the crystals. A linear relationship is observed between the rate constant of triolein depletion and the amount of medium strength acid sites. Further conversion of the fatty acids which are obtained from the hydrogenolysis of triolein (first rate-determining step) to deoxygenated products occurs on the surfaces of the zeolite crystals. The better accessibility of the Y20 sample with the smallest crystal size leads to improved catalytic performance. In comparison with previously reported catalysts, H2-free deoxygenation over nanosized zeolite Y appears to be an interesting industrial option to obtain high yields of green diesel.

Cultivation of microalgae using wastewater has received considerable attention around the globe as a platform to remove inorganic nutrients from the wastewater and producing microalgae biomass for biodiesel production. This can be done by converting freely available nutrients from the wastewater (particularly nitrogen, N and phosphorus, P) into microalgae biomass with concomitant carbon dioxide (CO2) sequestration via photosynthesis process. In fact, microalgae biodiesel could help to reduce greenhouse gas (GHG) emissions to the atmosphere through the replacement of fossil diesel as it is made from renewable resources. Despite the various benefits to produce microalgae biodiesel, a number of technical hurdles such as complex processes, requirement of high energy input during cultivation and dewatering (harvesting steps) need to be addressed for commercialization purpose. Besides, additional pre-treatment step is necessary to disrupt the microalgae cell wall to enhance lipid extraction efficiency. Hence, this paper is aims to reveal in-depth analysis and discussions on the process of microalgae-based wastewater treatment as well as microalgae cells disruption technology for lipid extraction. The paper also includes several new directions for technological improvements to improve commercialization potential of microalgae biodiesel.

Biodiesel is gaining attention as a remedy for the increasing demand of fossil fuels which is depleting rapidly. Commercial homogeneous catalysts in the biodiesel production industry are facing challenges such as separation difficulties and severe corrosion which will lead to the increment of production and maintenance cost. Herein, this paper focuses on the comprehensive review of literature reported on the usage of biomass as the precursor for the catalyst used in biodiesel production. Compared to other commercial catalysts, the usage of biomass as catalyst precursor possesses several advantages such as abundantly available, cheaper raw materials, reusable, non-toxic and biodegradable. Carbon material synthesized from biomass which acts as the efficient support for active sites due to its high porosity and surface area characteristic has been studied widely. The latest development of biomass derived basic, acidic and magnetic heterogeneous catalyst through several state of the art synthesis pathways starting from the synthesis of the supporting material (carbon) until the functionalization process to form the complete catalyst was reviewed. Apart from direct sulfonation using sulfuric acid, sulfonation by reduction and arylation were less hazardous and provided comparable active sites activity. Most biomass based catalysts exhibited good catalytic performance by providing high biodiesel yield of above 80% at optimum conditions. Besides that, various kinetic models developed from the reaction kinetic study catalyzed by biomass based catalyst were also reviewed as a preparatory stage for the scaled-up commercialization process of the studied catalyst in the biodiesel production sector. This catalyst could assist to lower the activation energy required for the reactions and thus enables higher reaction rate to reach equilibrium. Continuous research on producing high performing biomass based catalyst with minimum resources is needed in order to achieve the ultimate goal of green and sustainable biodiesel industry.

In the present study, cultivation of Chlorella vulgaris was extensively explored under semi-continuous approach to enhance its growth. The microalgae were cultivated in a photobioreactor supplemented with compost derived from chicken waste as an alternative nutrients source in both batch and semi-continuous cultivations. It was found that Chlorella vulgaris grew well up to 17 cycles of semi-continuous cultivation based on the following conditions for each cycle (3 days per cycle): 30% (v/v) removal of cultivation medium and 0.04 L/L of chicken compost in cultivation medium of pH 3. The average biomass productivity attained through these conditions was 0.0736 g/L/day, which was higher than batch cultivation (0.0568 g/L/day). Besides, the average total lipid content from each cycle under semi-continuous cultivation was maintained in the range of 25–35 wt%. The success of lipid extraction from the microalgae biomass was evidenced by the result of Fourier Transform Infrared Red (FT-IR) analysis that revealed lower peak intensity of carbon, especially in the range 2809–3012 cm−1 after lipid extraction. It was also worthwhile to mention that the fatty acid methyl ester (FAME) compositions of Chlorella vulgaris consisted mainly of C16:0 and C18:3 that were not significantly altered during the semi-continuous cultivation. Both saturated and unsaturated fatty acids in the harvested biomass accounted for approximately 26.3% and 73.3%, respectively, within 5 cycles of the cultivation.

To suffice the escalating global energy demand, microalgae are deemed as high potential surrogate feedstocks for liquid fuels. The major encumbrance for the commercialization of microalgae cultivation is due to the high costs of nutrients such as carbon, phosphorous, and nitrogen. Meanwhile, the organic-rich anaerobic digestate which is difficult to be purified by conventional techniques is appropriate to be used as a low-cost nutrient source for the economic viability and sustainability of microalgae production. This option is also beneficial in terms of reutilize the organic fraction of solid waste instead of discarded as zero-value waste. Anaerobic digestate is the side product of biogas production during anaerobic digestion process, where optimum nutrients are needed to satisfy the physiological needs to grow microalgae. Besides, the turbidity, competing biological contaminants, ammonia and metal toxicity of the digestate are also potentially contributing to the inhibition of microalgae growth. Thus, this review is aimed to explicate the feasibility of utilizing the anaerobic digestate to cultivate microalgae by evaluating their potential challenges and solutions. The proposed potential solutions (digestate dilution and pre-treatment, microalgae strain selection, extra organics addition, nitrification and desulfurization) corresponding to the state-of-the-art challenges are applicable as future directions of the research.

Hydrothermal carbonization (HTC) provides a promising alternative to valorize food waste digestate (FWD) and avoid disposal issues. Although hydrochar derived from FWD alone had a low calorific content (HHV of 13.9 MJ kg-1), catalytic co-HTC of FWD with wet lignocellulosic biomass (e.g., wet yard waste; YW) and 0.5 M HCl exhibited overall superior attributes in terms of energy recovery (22.7 MJ kg-1), stable and comprehensive combustion behaviour, potential nutrient recovery from process water (2-fold higher N retention and 129-fold higher P extraction), and a high C utilization efficiency (only 2.4% C loss). In contrast, co-HTC with citric acid provided ∼3-fold higher autogenous pressure, resulting in a superior energy content of 25.0 MJ kg-1, but the high C loss (∼74%) compromised the overall environmental benefits. The results of this study established a foundation to fully utilize FWD and YW hydrochar for bioenergy application and resource recovery from the process water.

Combining adsorptive activated carbon and catalytic oxidative cerium oxide, an adsorptive catalyst could be synthesized. Cerium oxide impregnated on activated carbon had been utilized in various gas pollutant removal technologies. In this study, impregnation of cerium oxide and sodium hydroxide on palm shell activated carbon (PSAC) was attempted to produce an adsorbent for H2S removal from biogas produced in palm oil industry. Effects of preparation parameters of CeO2/NaOH/PSAC towards H2S removal were successfully studied. The studied parameters were impregnation time, cerium amount, NaOH concentration, calcination temperature and calcination time. From the study, it was found that every parameter can be optimized because there was a value of the parameter that resulted in a maximum adsorption capacity. The optimum preparation parameters of CeO2/NaOH/PSAC were found to be 1.5 h impregnation time, 5% cerium, 1.0 M NaOH, 400 °C calcination temperature and 3 h calcination time. Selected adsorbents were characterized in order to further understand adsorbent properties and characteristics of the reaction.

Fluctuating market price of fossil fuel and overwhelming emission of greenhouse gases to the atmosphere have resulted in climate change and have been a global concern in this decade. Hence, biodiesel has become an alternative option to fossil diesel as it is renewable and environmentally friendly. Nevertheless, this alternative fuel that is usually derived from terrestrial oil crops will cause shortage in food supply and deforestation if mass production is realized. In recent years, cultivation of aquatic microorganism (particularly microalgae) to produce biodiesel is considered as a practical solution due to their high growth rate and ability to synthesize large quantity of lipid within their cell. However, the development of energy and cost-efficiency of microalgae cultivation system are the main issues in producing renewable microalgae biodiesel. Of late, wastewater or organic compost has been used as the cultivation medium as it can provide sufficient nutrients to sustain microalgae growth. Microalgae cultivation method and system are vitally important as these factors undoubtedly affect the final microalgae biomass and lipid yield. In this review, the cultivation system of microalgae, nutrients demanded for microalgae production, cell harvesting and drying, microalgae oil extraction, and utilization of microalgae biomass for biodiesel production are introduced and discussed. It is anticipated to convey clearer perspectives in upstream and downstream processes in microalgae-derived biodiesel production.

The development of an efficient third-generation L-lactic acid (L-LA) production process from Eucheuma denticulatum extract (EDE) was achieved in this study. Microwave-assisted dilute acid hydrolysis (MADAH) and microwave-assisted hydrothermal hydrolysis (MAHTH) were chosen as the hydrolysis of EDE for the objective of increasing galactose yield. Single-factor optimization of hydrolysis of the EDE was studied, MADAH had high performance in galactose production relative to MAHTH, in which the yield and optimal conditions for both processes were 50.7% (0.1 M H2SO4, 120 °C for 25 min) and 47.8% (0 M H2SO4,160 °C for 35 min), respectively. For fermentation, the optimal L-LA yield was achieved at the inoculum cell density of 4% (w/w) Bacillus coagulans ATCC 7050 with 89.4% and 6% (w/w) Lactobacillus acidophilus LA-14 with 87.6%. In addition, lipid-extracted Chlorella vulgaris residues (CVRs) as co-nutrient supplementation increased the relative abundance of B. coagulans ATCC 7050, thus benefiting L-LA production.

This study aims to produce biochar and sugars from a macroalga Eucheuma denticulatum using dilute sulfuric acid hydrolysis along with microwave-assisted heating. The reactions were operated at sulfuric acid concentrations of 0.1 and 0.2M, reaction temperatures of 150-170°C and a heating time of 10min. Compared to the raw macroalga, biochar qualities were improved with increased carbon content and lower ash and moisture contents. The calorific value of the biochar could be intensified up to 45%, and 39% of energy yield was recovered. Apart from producing biochar, the highest total reducing sugars were 51.47g/L (74.84% yield) along with a low by-product 5-HMF of 0.20g/L, when the biomass was treated under the optimum conditions at 160°C with 0.1M H2SO4. Thus, this study demonstrated that macroalgae could be potentially used as biomass feedstock under microwave-assisted acid hydrolysis for the production of biofuel and value-added products.

Biodiesel by non-edible oils via ultrasonic cavitational technique offers a unique and novel approach towards waste management. This study aims to synthesis biodiesel from two non-edible sources namely; Salvadora alii oil and Thespesia populneoides oil. Transesterification was carried out in the presence of solid base calcium oxide catalyst while using an ultrasonic cavitation (UC) reactor. Parametric optimisation was conducted by central composite design and response surface methodology. Results revealed that optimum condition to obtain maximum yield (≈92 wt %) of Salvadora alii methyl ester was as; molar ratio = 10:1 (alcohol: oil), catalyst amount = 3 wt %, and amplitude = 50% in 30 min of reaction time. Similarly, optimum condition was found satisfactory to render maximum yield (≈88.6 wt %) of Thespesia populenoides methyl ester as molar ratio = 6:1 (alcohol: oil), catalyst amount = 3.5 wt %, and amplitude = 45% in 30 min of reaction time. At obtained optimised values UC was compared with mechanical stirring (MS). UC showed 3 fold higher reaction constants and 3 fold more time efficiency than MS. The superiority of UC over MS can be established. Biomass waste to biofuel can make biodiesel synthesis towards cleaner fuel. These results suggest that combination of non-edible oils and UC technology have the potential to make cleaner process. Most of the fuel properties were met the EN 14214 and ASTM D 6751 standards.

Significant development in conversion technologies to produce bioethanol from microalgae biomass is causing paradigm-shift in energy management. In this study, carbohydrate-rich microalgae, Scenedesmus dimorphus (49% w/w of carbohydrate) is selected with the aim to obtain qualitative correlation between pretreatment and fermentation process. In view of this, separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) were conducted experimentally. The fermentation behavior were investigated for microalgae biomass treated via organosolv, enzymatic and acidic pretreatment. Fermentation process was carried out by ethanologen microbe, Saccharomyces cerevisiae . From the result, it is observed that a combination of two treatment is found to be the most effective in producing fermentable sugar for the subsequent fermentation process. The organosolv treatment which is followed with the SSF process produced a theoretical yield of bioethanol that exceeded 90%. On the other hand, hydrothermal acid-hydrolyzed fermentation produced the bioethanol yield with 80% of its theoretical yield. Enzymatic-hydrolyzed SHF produced 84% of theoretical yield at longer reaction time compared with others. The results were obtained with constant fermentation parameters conducted at pH 5, temperature of 34 °C, and microalgae biomass loading at 18 g/L. Ultimately, the coupling of organosolv-treated biomass with SSF process is found to be the most cost-effective for S. dimorphus biomass as bioethanol feedstock.

Owning to the presence of essential mineral nutrient content in wastewater, cultivation of microalgae using wastewater sources provides an alternative and sustainable solution for biodiesel production. Hence, the potential of using domestic wastewater as nutrient source to cultivate Chlorella vulgaris was presently studied. It was found that the microalgae was favoured to grow in domestic wastewater under the conditions of 0.02 v/v of wastewater, initial pH of 3, and 0.03 v/v of initial amount of microalgae seed with 24 h of continuous illumination. Under these conditions, a high lipid content of 32.7% was embedded within the microalgae biomass. From the analysis of fatty acid methyl ester (FAME) profile, the extracted microalgae lipid was suitable for biodiesel production. The existing growth kinetic models were able to predict the growth of Chlorella vulgaris using the domestic wastewater as nutrients source. The fair model fitting was however limited to contaminant-free conditions, where the growth decays of the microalgae was negligible.

Interest in biodiesel research has escalated over the years due to dwindling fossil fuel reserves. The implementation of a carbon-based solid acid catalyst in biodiesel production eradicates the separation problems associated with homogeneous catalysis. However, its application in the glycerol-free interesterification process for biodiesel production is still rarely being studied in the literature. In this study, novel environmentally benign catalysts were prepared from oil palm empty fruit bunch (OPEFB) derived activated carbon (AC) which is sustainable and low cost via direct sulfonation using concentrated sulfuric acid. The effects of synthesizing variables such as carbonization and sulfonation temperatures with different holding times towards the fatty acid methyl ester (FAME) yield in interesterification reaction with oleic acid and methyl acetate were investigated in detail. It was found that the optimum carbonization temperature and duration together with sulfonation temperature and duration were 600 °C, 3 h, 100 °C and 6 h, respectively. The catalyst possessed an amorphous structure with a high total acid density of 9.0 mmol NaOH g−1 due to the well-developed porous framework structure of the carbon support. Under these optimum conditions, the OPEFB derived solid acid catalyst recorded an excellent catalytic activity of 50.5% methyl oleate yield at 100 °C after 8 h with 50:1 methyl acetate to oleic acid molar ratio and 10 wt% catalyst dosage. The heterogeneous acid catalyst derived from OPEFB had shown promising properties that made them highly suitable for cost-effective and environmental-friendly glycerol-free biodiesel production.

Producción Científica, Relevance of Biotechnology for a sustainable living has increased over the past few decades by addressing the different domains including agriculture, food, health care, livestock management, energy, environment, climate change, waste management and a multitude of other areas. Today, the subject not only encompasses life sciences and engineering, but spans across most of the human activities, affecting and influencing every one. The subject is poised to tackle emerging challenges like rapidly spreading global pandemics by providing solutions in the form of vaccines or drugs, immune boosters and diagnostics. Green processes, renewable clean energy, super foods and nutraceuticals, biodegradable polymers and materials are but a few of the outcomes of development in this field. In wake of the rapid deterioration of land and water resources and environment catalysed by anthropogenic activities, urgent calls have to be made on addressing the issues of solid, liquid and chemical waste management, atmospheric pollution, and moving towards greener manufacturing processes and deriving energy through renewable routes for a sustainable development and improved quality of life. It may not be incorrect to say that the world needs to move towards a sustainable bio-economy for human race to persist on this planet.

Algae biomass comprises variety of biochemicals components such as carbohydrates, lipids and protein, which make them a feasible feedstock for biofuel production. However, high production cost mainly due to algae cultivation remains the main challenge in commercializing algae biofuels. Hence, extraction of other high value-added bioproducts from algae biomass is necessary to enhance the economic feasibility of algae biofuel production. This paper is aims to deliberate the recent developments of conventional technologies for algae biofuels production, such as biochemical and chemical conversion pathways, and extraction of a variety of bioproducts from algae biomass for various potential applications. Besides, life cycle evaluation studies on microalgae biorefinery are presented, focusing on case studies for various cultivation techniques, culture medium, harvesting, and dewatering techniques along with biofuel and bioenergy production pathways. Overall, the algae biorefinery provides new opportunities for valorisation of algae biomass for multiple products synthesis.

The rapid depletion of fossil fuels and ever-increasing environmental pollution have forced humankind to look for a renewable energy source. Microalgae, a renewable biomass source, has been proposed as a promising feedstock to generate biofuels due to their fast growth rate with high lipid content. However, literatures have indicated that sustainable production of microalgae biofuels are only viable with a highly optimized production system. In the present study, a cradle-to-gate approach was used to provide expedient insights on the effect of different cultivation systems and biomass productivity toward life cycle energy (LCEA), carbon balance (LCCO2) and economic (LCC) of microalgae biodiesel production pathways. In addition, a co-production of bioethanol from microalgae residue was proposed in order to improve the economic sustainability of the overall system. The results attained in the present work indicated that traditional microalgae biofuels processing pathways resulted to several shortcomings, such as dehydration and lipid extraction of microalgae biomass required high energy input and contributed nearly 21 to 30% and 39 to 57% of the total energy requirement, respectively. Besides, the microalgae biofuels production system also required a high capital investment, which accounted for 47 to 86% of total production costs that subsequently resulted to poor techno-economic performances. Moreover, current analysis of environmental aspects of microalgae biorefinery had revealed negative CO2 balance in producing microalgae biofuels.

A green approach using hydrogen peroxide (H2O2) to intensify the fuel properties of spent coffee grounds (SCGs) through torrefaction is developed in this study to minimize environmental pollution. Meanwhile, a neural network (NN) is used to minimize bulk density at different combinations of operating conditions to show the accurate and reliable model of NN (R2 = 0.9994). The biochar produced from SCGs torrefied at temperatures of 200–300 °C, duration of 30–60 min, and H2O2 concentrations of 0–100 wt% is examined. The results reveal that the higher heating value (HHV) of biochar increases with rising temperature, duration, or H2O2 concentration, whereas the bulk density has an opposite trend. The HHV, ignition temperature, and bulk density of biochar from torrefaction at 230 °C for 30 min with a 100 wt% H2O2 solution (230-100%-TSCG) are 27.00 MJ∙kg−1, 292 °C, and 120 kg∙m−3, respectively. This HHV accounts for a 29% improvement compared to that of untorrefied SCG. The contact angle (126°), water activity (0.51 aw), and moisture content (7.69%) of the optimized biochar indicate that it has higher resistance against biodegradation, and thereby can be stored longer. Overall, H2O2 is a green treatment additive for SCGs solid fuel. This study has successfully produced biochar with greater HHV and low bulk density at low temperatures. The green additive development can effectively reduce environmental pollutants and upgrade wastes into resources, and achieve “3E”, namely, environmental (non-polluting green additives), energy (biofuel), and circular economy (waste upgrade). In addition, the produced biochar has great potential in the fields of bioadsorbents and soil amendments.

In this work, the effects of various pretreatments’ parameters on kenaf core fibre were analyzed statistically and optimized using Response Surface Methodology based on the total glucose yield. The chemical compositions of the pretreated fibres were examined to discuss the effect of pretreatment on the fibre hydrolysability comprehensively. The results showed that estimation model for each pretreatment of kenaf core fibre were polynomial equations. The optimum conditions for water, acid and alkali pretreatments were 170 °C for 45 min, 120 °C for 90 min in 2.0% H2SO4 solution and 140 °C for 60 min in 3.0% NaOH solution, respectively. Among the three pretreatments, water pretreatment achieved the highest total glucose yield (25.5%), followed by acid (20.0%) and alkali (18.2%) pretreatments. Based on chemical compositions analysis, both water and acid pretreatments were capable of eliminating almost 100% of hemicellulose with negligible removal of lignin while the alkali pretreatment removed both the lignin and hemicellulose more than 60%. This result revealed that the removal of hemicellulose showed greater influential in enhancing the enzymatic accessibility and hence, hydrolysability of kenaf core fibre.

Bioconversion technologies of biomass to bioethanol require intensive energy process due to several pretreatment steps to break down the biomass in order to obtain fermentable sugar for subsequent fermentation. Hence, a feasible approach to the production of bioethanol from lipid-extracted biomass of Scenedesmus dimorphus will be presented in this study in a biorefinery concept. The lipid-extracted biomass was directly subjected to simultaneous saccharification and fermentation thereby avoiding the costly pretreatment, lowering the contamination risk and reducing the complication of high sugar content. The technological challenges for this fermentation process were investigated to identify optimum conditions for amyloglucosidase enzyme activity and Sacchromyces cerevisiae yeast ethanolic fermentation. As a result, the optimum key parameters for the fermentation were identified at an enzyme concentration of 60 units/ml, pH 5, temperature at 36 °C and yeast loading of 3 g/L. At the optimum condition, an overall conversion of more than 90% of the theoretical yield was achieved with maximum bioethanol yield of 0.26 g bioethanol/g lipid-extracted biomass. The direct usage of lipid-extracted biomass into simultaneous saccharification and fermentation with single enzyme ensures the feasibility of the biofuel produced.