• Energy Research

Rapid climate change and forecasted damage from fossil fuel combustion, forced researchers to investigate renewable and clean energy sources for the sustainable development of societies throughout the world. Biomass-based energy is one of the most important renewable energy sources for meeting daily energy needs, which are gaining in popularity daily. Gasification-based bioenergy production is an effective way to replace fossil fuels and reduce CO2 emissions. Even though biomass gasification has been studied extensively, there is still much opportunity for improvement in terms of high-quality syngas generation (high H2/CO ratio) and reduced tar formation. Furthermore, the presence of tar has a considerable impact on syngas quality. Downdraft gasifiers have recently shown a significant potential for producing high-quality syngas with lower tar concentrations. This article presents a comprehensive review on the advancement in biomass downdraft gasification technologies for high-quality synthesis gas. In addition, factors affecting syngas production and composition e.g., equivalency ratio, temperature, particle size, and gasification medium on synthesis gas generation are also comprehensively studied. The up-gradation and various applications of synthesis gas are also discussed in brief in this review article.

This study was conducted to investigate the feasibility of microalgal biomass production and nutrient removal from recirculating aquaculture systems (RAS) water (RASW) with low phosphate concentration. For this purpose, Nannochloropsis oculata, Pavlova gyrans, Tetraselmis suecica, Phaeodactylum tricornutum, and their consortium were cultivated in RASW and RASW supplemented with vitamins (+V). Among them, N. oculata showed the maximum biomass production of 0.4 g/L in RASW. Vitamins supplementation significantly increased the growth of T. suecica from 0.16 g/L in RASW to 0.33 g/L in RASW + V. Additionally, T. suecica showed the highest nitrate (NO3-N) removal efficiency of 80.88 ± 2.08 % in RASW and 83.82 ± 2.08 % in RASW + V. Accordingly, T. suecica was selected for scaling up study of microalgal cultivation in RASW and RASW supplemented with nitrate (RASW + N) in 4-L airlift photobioreactors. Nitrate supplementation enhanced the growth of T. suecica up to 2.2-fold (day 15). The fatty acid nutritional indices in T. suecica cultivated in RASW and RASW + N showed optimal polyunsaturated fatty acids (PUFAs)/saturated fatty acid (SFAs), omega-6 fatty acid (n-6)/omega-3 fatty acid (n-3), indices of atherogenicity (IA), and thrombogenicity (IT)). Overall, the findings of this study revealed that despite low phosphate concentration, marine microalgae can grow in RASW and relatively reduce the concentration of nitrate. Furthermore, the microalgal biomass cultivated in RASW consisting of pigments and optimal fatty acid nutritional profile can be used as fish feed, thus contributing to a circular bioeconomy.

Abstract Biodiesel, as one of the best alternative fuels, has a number of advantages over petro diesel, such as originating from a renewable and domestic feedstock which reduces the net production cost of biodiesel. In the recent years, biodiesel has received increasing interest due to energy crisis worldwide along with exhausting reserves and the shortage of oil supplies. The major problem behind the use of vegetable oil for biodiesel production is sustainability because it directly competes with human food. To combat this problem, the other renewable sources have been developed as microbial oils have similarity to vegetable oils and extensively used for biodiesel production. Oleaginous yeasts have recently been suggested as microscopic biofactories and alternative lipid producer to vegetable oil for a more sustainable biodiesel industry. It is a potential novel technology where non-edible lignocellulosic biomasses are exploited as raw materials for biodiesel production from oleaginous yeasts which drop net greenhouse gas emissions by substituting the practice of fossil fuels and would convey benefits to rural economies and national energy security. The usage of oleaginous yeasts have many advantages over other renewable sources like faster growth rate, shorter life cycle, easier scale-up, with no effects from the season and climate variation, and can serve as the excellent oil accumulating renewable feedstocks which are non-competitive to food resources and do not require arable land. Non-edible lignocellulosic biomass, consists of three different types of natural polymers, namely cellulose, hemicellulose, and lignin, is the most abundant renewable bioresource in the biosphere. The production of fermentable sugars from hydrolysates of various non-edible lignocellulosic biomass, either by physical, chemical or enzymatic hydrolysis has been utilized as feedstock in bioethanol or biodiesel production, extensively. During hydrolysis generation of non-carbohydrate compounds, such as 5- hydroxymethylfurfural (HMF), furfural acetic acid and phenolic compounds have various effects on the growth of microorganisms, their metabolism, as well as on final products, presenting a key challenge in the biological conversion of biomasses.

Lutein, a bioactive xanthophyll, has recently attracted significant attention for numerous health benefits, e.g., protection of eye health, macular degeneration, and acute and chronic syndromes etc. Microalgae have emerged as the best platform for high-value lutein production with high productivity, lutein content, and scale-up potential. Algal lutein possesses numerous bioactivities, hence widely used in pharmaceuticals, nutraceuticals, aquaculture, cosmetics, etc. This review highlights advances in upstream lutein production enhancement and feasible downstream extraction and cell disruption techniques for a large-scale lutein biorefinery. Besides bioprocess-related advances, possible solutions for existing production challenges in microalgae-based lutein biorefinery, market potential, and emerging commercial scopes of lutein and its potential health applications are also discussed. The key enzymes involved in the lutein biosynthesizing Methyl-Erythritol-phosphate (MEP) pathway have been briefly described. This review provides a comprehensive updates on lutein research advancements covering scalable upstream and downstream production strategies and potential applications for researchers and industrialists.

The importance of expanding our knowledge on microorganisms derived from extreme environments stems from the development of novel and sustainable technologies for our health, food, and environment. Microalgae and cyanobacteria represent a group of diverse microorganisms that inhabit a wide range of environments, are capable of oxygenic photosynthesis, and form a thick microbial mat even at extreme environments. Studies of thermophilic microorganisms have shown a considerable biotechnological potential due to their optimum growth and metabolisms at high temperatures (≥50 °C), which is supported by their thermostable enzymes. Microalgal and cyanobacterial communities present in high-temperature ecosystems account for a large part of the total ecosystem biomass and productivity, and can be exploited to generate several value-added products of agricultural, pharmaceutical, nutraceutical, and industrial relevance. This review provides an overview on the current status of biotechnological applications of thermophilic microalgae and cyanobacteria, with an outlook on the challenges and future prospects.

The aim of this work is remediation of dairy wastewater (DWW) for biodiesel feedstock production using poly-microalgae cultures of four microalgae namely Chlorella minutissima (C. minutissima), Scenedesmus abundans (S. abundans), Nostoc muscorum (N. muscorum) and Spirulina sp. The poly-microalgae cultures were prepared as C. minutissima + N. muscorum (CN), C. minutissima + N. muscorum + Spirulina sp. (CNSS) and S. abundans + N. muscorum + Spirulina sp. (SNSS). Poly-microalgae culture CNSS cultivated on 70% DWW achieved 75.16, 61.37, 58.76, 84.48 and 84.58%, removals of biological oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and suspended solids (SS), respectively, at 12:12 h photoperiod that resulted into total biomass and lipid yield of 3.47 ± 0.07 g/L and 496.32± 0.065 mg/L. However, maximum biomass and lipid yields of 5.76 ± 0.06 and 1152.37 ± 0.065 mg/L were achieved by poly-microalgae culture CNSS cultivated on 70% DWW + 10 g/L of glucose at 18:6 h photoperiod. Fatty acid methyl ester (FAME) analysis shown presence of C14:0 (myristic acid) C16:0 (palmitic acid), C16:1 (palmitoleic acid), C18:0 (stearic acid), C18:2 (linoleic acid) and C18:3 (linolenic acid), it indicates that the lipids produced from poly-microalgae cultures are suitable for biodiesel production. Thus, poly-microalgae cultures could be more efficient than mono-microalgae cultures in the remediation of DWW and for biodiesel feedstock production.

Plastics usage is rising daily because of increased population, modernization, and industrialization, which produces a lot of plastic garbage. Due to their various chemical structures, long chain polymeric compositions, and thermal/decomposition behavior, it is challenging to recycle these plastic wastes into hydrocarbon fuels. In the current work, domestic plastic waste was pyrolyzed at 473 to 973 K in a fixed bed reactor and compared with the three virgin plastics LDPE (low-density polyethylene), HDPE (high-density polyethylene), and PP (polypropylene), as well as a mixture of the three (virgin mixed plastics). The pyrolysis results showed that maximum liquid hydrocarbons obtained from HDPE, LDPE, PP, mixed plastic, and domestic waste were 64.6 wt.%, 62.2 wt.%, 63.1 wt.%, 68.6 wt.%, and 64.6 wt.% at 773 K, respectively. The composition of liquid fuels was characterized using FTIR and GC-MS, which showed a wide spectrum of hydrocarbons in the C8–C20 range. Furthermore, liquid fuel characteristics such as density, viscosity, fire and flash point, pour point, and calorific value were examined using ASTM standards, and the results were found to be satisfactory. This study provides an innovative method for recycling waste plastics into economical hydrocarbon fuel for use in transportation.

Upgrading carbon-negative microalgal biomass to biofuels and value-added products presents a three-pronged solution for waste treatment, carbon capture, and economically viable bioenergy production. Acidogenesis and methanogenesis are versatile processes at the core of anaerobic digestion systems, facilitating the conversion of diverse biogenic substrates into energy and a wide range of biobased products. The present study was conducted to integrate acidogenesis and methanogenesis for coproduction of biohydrogen, biomethane, and volatile fatty acids from Nordic phytoplankton consortia. For this purpose, microalgal consortia was cultivated in a raceway pond equipped with high surface area structures. Harvested microalgal biomass was subjected to thermoalkaline (2% NaOH solution at 121 °C) and enzymatic (cellulase) pretreatments. The hydrolysates of the pretreated biomass were inoculated with thermally treated sludge for acidogenic fermentation and with mixture of untreated sludge and cow dung (1:1 v/v ratio) for anerobic digestion. The acidogenic process produced a significant amount of biohydrogen (maximum 164.8 mL bioH2/VSload) along with volatile fatty acids (maximum 7.9 g COD/L), while methanogenesis resulted in biomethane production of maximum 210.7 mL bioCH4/VSload, accompanied by an ammonium recovery of 1278 mg NH4+/L. These maximum yields were all achieved by enzymatic pretreatment of the biomass fraction harvested from high surface area brush head structures inserted in the raceway pond. These results have important implications for designing phytoplankton cultivation systems and upstream pathways to optimize energy production from carbon-negative phytoplankton biomass. Validerad;2024;Nivå 2;2024-03-28 (hanlid);Funder: Tekniikan Edistämissäätiö (8883);Full text license: CC BY