•Microalgae are the agent for carbon biosequestration.•CO2 from flue gas is potential carbon source for microalgae cultivation.•The effect of inhibition derived by toxic pollutants in flue gas ...towards microalgae.•The advantages and disadvantages of microalgae cultivation system.
The unceasing rise of greenhouse gas emission has led to global warming and climate change. Global concern on this phenomenon has put forward the microalgal-based CO2 sequestration aiming to sequester carbon back to the biosphere, ultimately reducing greenhouse effects. Microalgae have recently gained enormous attention worldwide, to be the valuable feedstock for renewable energy production, due to their high growth rates, high lipid productivities and the ability to sequester carbon. The photosynthetic process of microalgae uses atmospheric CO2 and CO2 from flue gases, to synthesize nutrients for their growth. In this review article, we will primarily discuss the efficiency of CO2 biosequestration by microalgae species, factors influencing microalgal biomass productions, microalgal cultivation systems, the potential and limitations of using flue gas for microalgal cultivation as well as the bio-refinery approach of microalgal biomass.
In this paper, we review different types of polymer electrolytes, recent approaches and technological applications of polymer electrolytes. The report first discusses the characteristics, advantages ...and applications for three types of polymer electrolytes: gel polymer electrolytes, solid polymer electrolytes and composite polymer electrolytes. Next, we discuss the features and performance of different polymer hosts based on some important and recently published literature. Recent progress of some approaches used in improving the performance of the polymer electrolytes is highlighted. The last part of the review includes the technological applications of some electrical energy storing/converting devices: electrochemical capacitors, batteries, fuel cells and dye-sensitized solar cells. It is also stressed that the technological advancement in the polymer electrolytes plays a pivotal role in the development of energy storing/converting systems.
•Potential of microalgae biorefinery for producing high value products is assessed.•Conventional processes of microalgae biorefinery are discussed.•Recent technologies on microalgae biorefinery are ...reviewed.•Techno-economic analysis and LCA assessment on microalgal biorefinery are addressed.•Advantages of microalgae biorefinery and derived high-value products are emphasized.
Microalgae have received much interest as a biofuel feedstock in response to the uprising energy crisis, climate change and depletion of natural sources. Development of microalgal biofuels from microalgae does not satisfy the economic feasibility of overwhelming capital investments and operations. Hence, high-value co-products have been produced through the extraction of a fraction of algae to improve the economics of a microalgae biorefinery. Examples of these high-value products are pigments, proteins, lipids, carbohydrates, vitamins and anti-oxidants, with applications in cosmetics, nutritional and pharmaceuticals industries. To promote the sustainability of this process, an innovative microalgae biorefinery structure is implemented through the production of multiple products in the form of high value products and biofuel. This review presents the current challenges in the extraction of high value products from microalgae and its integration in the biorefinery. The economic potential assessment of microalgae biorefinery was evaluated to highlight the feasibility of the process.
In recent years, the production of hydrogen (H2) via dark fermentation has become increasingly popular because it is a sustainable approach to produce clean energy. This review presents an overview ...with a critical analysis of the technical challenges in obtaining high H2 yield through dark fermentation. Particular focus is given to the pretreatment methods that affect H2 production. We observed that heat pretreatment is the most frequently applied and the most effective method of eliminating H2-consuming bacteria (HCB) while preserving H2-producing bacteria (HPB). The pre-dominant HPB species after pretreatment belongs to the genus Clostridium and hence the fermentation conditions are optimized according to their preference for H2 production. Besides, we also reviewed fermentation conditions such as substrate, pH, temperature, oxidation–reduction potential (ORP), types of nutrient and inhibitor substrate, to obtain clearer insight on the influences of critical parameters in H2 production.
•Nanocellulose was successfully isolated from Gelidium elegans red algae.•Nanocellulose possessed of high thermal stability than raw algae biomass.•Nanocellulose having an aspect ratio of 25 with 73% ...crystalline.
Nanocellulose was successfully isolated from Gelidium elegans red algae marine biomass. The red algae fiber was treated in three stages namely alkalization, bleaching treatment and acid hydrolysis treatment. Morphological analysis was performed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). TEM results revealed that the isolated nanocellulose had the average diameter and length of 21.8±11.1nm and of 547.3±23.7nm, respectively. Fourier transform infrared (FTIR) spectroscopy proved that the non-cellulosic polysaccharides components were progressively removed during the chemically treatment, and the final derived materials composed of cellulose parent molecular structure. X-ray diffraction (XRD) study showed that the crystallinity of yielded product had been improved after each successive treatments subjected to the treated fiber. The prepared nano-dimensional cellulose demonstrated a network-like structure with higher crystallinity (73%) than that of untreated fiber (33%), and possessed of good thermal stability which is suitable for nanocomposite material.
•Mixotrophic was found effective than photoautotrophic cultivation condition.•Glycerol exhibited significant growth performance over glucose or urea.•High yields obtained in glucose, urea and ...glycerol supplemented POME.•High pollutant removal efficiencies achieved.•Finding the cheap and effective carbon or nutrients is essential.
Microalgae are a promising feedstock for biofuel generation. Economical and effective mass cultivation is essential for greater feasibility in microalgal-based biofuel full applications. The present study reported on cultivation of Chlorella sorokiniana CY-1 in palm oil mill effluent (POME) under photoautotrophic and mixotrophic cultivation. Enhancement of biomass and lipid productions were carried out by using glucose, urea and glycerol supplementations. Mixotrophic cultivation was more effective than photoautotrophic condition. Glycerol addition exhibited greater microalgae growth performance compared to supplementing glucose or urea. Biomass (1.68 g L−1) and lipid (15.07%) production were highest in POME medium with combinations of 200 mg L−1 urea, glucose and glycerol supplementation. Chlorella sorokiniana CY-1 grown in POME with glucose and glycerol supplementation gave considerably comparable yields as in all supplements-added POME medium. Ideal fatty acids compositions shown in urea and glycerol supplemented-POME medium though lower biomass production obtained. The pollutant remediation efficiencies attained were 63.85% COD, 91.54% TN and 83.25% TP in all supplements-added medium. The estimated net energy ratio was 0.55 and nutrient cost could be reduced up to 76%. Cheap and effective carbon and nutrients supplementation is essential to minimize the economic impact and maximize yields in commercial scale microalgae cultivation for biofuel production and environmental sustainability.
•Unmodified rice starch could be used as a natural coagulant in POME treatment.•Flocs formed by rice starch showed higher settleability as compared to alum.•Combination between rice starch and alum ...reduced both dosages with high TSS removal.•Both coagulants and flocs were characterized by FTIR, TGA and SEM.
The present study investigated the use of starch to replace inorganic coagulants for the treatment of agro-industrial wastewater from palm oil mill, namely palm oil mill effluent (POME). Rice starch was found to be the best starch because it yielded similar total suspended solids (TSS) removal as alum, significantly shortened the settling time and produced flocs with higher resistance towards stronger shear force. The use of rice starch alone in room temperature enabled the removal of TSS up to 84.1% using the recommended values of dosage, initial pH, settling time and slow stirring speed at 2g/L, pH 3, 5min and 10rpm, respectively. Higher TSS removal of 88.4% could still be achieved at lower dosage of rice starch (0.55g/L) only when rice starch was used together with 0.2g/L of alum during the treatment of POME. To gain further insights on the properties of coagulants and flocs produced from the treatment, characterization methods such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were used.
•Chlorella sorokiniana CY-1 outcompeted Chlorella vulgaris ESP-31 to grow in POME.•POME pretreatment using acid and heat improved biomass and lipid yields of CY-1.•CY-1 produced biomass (2.12 g L−1) ...and lipid yields (11.21%) in pretreated POME.•Pollutants removal efficiencies were 62.07% (TN), 47.09% (COD) and 30.77% (TP).
Microalgae cultivation in wastewaters has been identified as the solution for economical microalgae cultivation. This study investigated the feasibility of using POME for Chlorella sp. cultivation to yield biomass and lipids, as it generates massively in Malaysia which ranked world palm oil exporter. The optimal POME concentration and pretreatment strategy were applied to promote biomass and lipid productivities. Chlorella sorokiniana CY-1 attained maximal of 11.21% of lipid content with 2.12 g L−1 of biomass concentration when cultivation in acid-heat pretreated 30% (v/v) POME. This provides relatively higher yield than those reported values on POME. Pretreatment was found effective to enhance biomass productions, as it converts lignin in POME into reducing sugars to serve as the supplement. The pollutants removal efficiencies were 62.07% for TN, 47.09% for COD, and 30.77% for TP. This contributes towards greater feasibility in microalgae cultivation for biofuel productions and as well towards environmental sustainability.
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.
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•Metal oxide is promising support for biofuel synthesis via deoxygenation process.•High oxygen content of biofuel will lead to corrosion and instability.•Al2O3-TiO2 catalyst has drawn the attention in deoxygenation process for biofuel.•Controlled synthesis method can improve the effectiveness of Al2O3-TiO2.
