Wet Algal Biomass Research Articles

Hydrothermal extraction of ulvans from Ulva spp. in a biorefinery approach

A simple cascade process based on the hydrothermal fractionation of Ulva spp. biomass was proposed. Considering the overall extraction yields (50 %), ulvan recovery (23 %), and ulvan composition, structural, mechanical and cytotoxic properties, the selected optimal final heating temperature was 160 °C. Ethanol precipitation provided the highest ulvan recovery yields but choline chloride precipitated ulvans showed stronger mechanical properties, G´ moduli 1.5·104 Pa and 3·104 Pa for ethanol and for choline chloride, respectively. Both products were safe on NCTC 929 mouse fibroblasts and after a cooling stage, formed films without requiring any additives. From the ulvan-free liquid fraction, one product with 43 % (wt, d.b.) phenolics and moderate antiradical properties and a byproduct containing nutrients and minerals were separated. The methane potential of the corresponding residual solids was influenced by the hydrothermal heating temperature and was doubled compared to than for the untreated seaweed biomass (60 mL/g VS). This scheme could be also applied to the wet algal biomass, in a chemical free alternative to provide ready to use ulvan biopolymers, bioactives, nutrients, salts and biogas, conforming a biorefinery approach.

Aqueous phase recycling: impact on microalgal lipid accumulation and biomass quality.

The potential success of microalgal biofuels greatly depends on the sustainability of the chosen pathway to produce them. Hydrothermal liquefaction (HTL) is a promising route to convert wet algal biomass into biocrude. Recycling the resulting HTL aqueous phase (AP) aims not only to recover nutrients from this effluent but also to use it as a substrate to close the photosynthetic loop and produce algal biomass again and process this biomass again into new biocrude. With that purpose, the response to AP recycling of five Chlorellaceae strains was monitored over five cultivation cycles. After four successive cycles of dynamic growth under nutrient-replete conditions, the microalgae were cultivated for a prolonged fifth cycle of 18 days in order to assess the impact of the AP on lipid and biomass accumulation under nutrient-limited conditions. Using AP as a substrate reduced the demand for external sources of N, S, and P while producing a significant amount of biomass (2.95-4.27 g/L) among the strains, with a lipid content ranging from 16 to 36%. However, the presence of the AP resulted in biomass with suboptimal properties, as it slowed down the accumulation of lipids and thus reduced the overall energy content of the biomass in all strains. Although Chlorella vulgaris NIES 227 did not have the best growth on AP, it did maintain the best lipid productivity of all the tested strains. Understanding the impact of AP on microalgal cultivation is essential for further optimizing biofuel production via the HTL process.

Nitrogen dynamics and biological processes in soil amended with microalgae grown in abattoir digestate to recover nutrients

The use of microalgae for nutrient recovery from wastewater and subsequent conversion of the harvested biomass into fertilizers offers a sustainable approach towards creating a circular economy. Nonetheless, the process of drying the harvested microalgae represents an additional cost, and its impact on soil nutrient cycling compared to wet algal biomass is not thoroughly understood. To investigate this, a 56-day soil incubation experiment was conducted to compare the effects of wet and dried Scenedesmus sp. microalgae on soil chemistry, microbial biomass, CO2 respiration, and bacterial community diversity. The experiment also included control treatments with glucose, glucose + ammonium nitrate, and no fertilizer addition. The Illumina Mi-Seq platform was used to profile the bacterial community and in-silico analysis was performed to assess the functional genes involved in N and C cycling processes. The maximum CO2 respiration and microbial biomass carbon (MBC) concentration of dried microalgae treatment were 17% and 38% higher than those of paste microalgae treatment, respectively. NH4+ and NO3− released slowly and through decomposition of microalgae by soil microorganisms as compared to synthetic fertilizer control. The results indicate that heterotrophic nitrification may contribute to nitrate production for both microalgae amendments, as evidenced by low amoA gene abundance and a decrease in ammonium with an increase in nitrate concentration. Additionally, dissimilatory nitrate reduction to ammonium (DNRA) may be contributing to ammonium production in the wet microalgae amendment, as indicated by an increase in nrfA gene and ammonium concentration. This is a significant finding because DNRA leads to N retention in agricultural soils instead of N loss via nitrification and denitrification. Thus, further processing the microalgae through drying or dewetting may not be favorable for fertilizer production as the wet microalgae appeared to promote DNRA and N retention.

Enzymatic cell disruption followed by application of imposed potential for enhanced lipid extraction from wet algal biomass employing photosynthetic microbial fuel cell

Solvent-free algal cell lysis using fungal enzyme for enhanced lipid recovery diminishes per unit production cost of algal biodiesel. In this investigation, a triple chamber photosynthetic microbial fuel cell (PMFC) was fabricated, where positive potential was imposed in the extraction chamber to draw the negatively charged lipid ions from the cathodic chamber. Under optimum imposed potential of + 3.0 V (vs standard hydrogen electrode) and with 3.5% (v/v) dosage of fungal enzyme in to the algal consortium of cathodic chamber, a maximum of 79.0% of lipid was recovered. Additionally, enzyme-assisted de-oiled algal biomass was applied in the anodic chamber to function as substrate and mediator for exo-electrogens, and the maximum power density of 10.0 W/m3 with 82.4% removal of chemical oxygen demand was achieved while treating synthetic wastewater. Therefore, this cost-effective exploration demonstrated successful bioelectricity production and concomitant wastewater treatment with solvent-free direct lipid recovery from wet algal biomass through PMFC.

Effects of water recirculation on microalgae assemblage and corresponding sustainability of the photobioreactor cultivation system

An algae photobioreactor (APB) was used to determine the effect of water recirculation on the growth of algal assemblage. CO2 in the flue gas from a power plant was the carbon source. Boiler water was used as the source water. The results showed that microalgae cultivation under recirculation conditions was stable over a period of four months. Biomass productivities during the 1st through 4th months of recirculation (0.26, 0.23, 0.20, and 0.18 g L−1 d−1, respectively) were not significantly different than freshwater (0.22 g L −1 d −1). Furthermore, the relationship between eukaryotic and bacterial domains in the assemblage remained consistent throughout the four months of recirculation (80.7, 87.1, 83.1, and 82.1%, respectively, and 19.2, 12.8, 16.9, and 17.8%, respectively). This was not significantly different than the abundance of each domain in the control freshwater cultivation (83.7% eukaryotic and 16.2% bacterial). A 1 m3 photobioreactor was then envisioned for a mass, energy, and exergy analysis to evaluate the water recirculation on sustainability of the culture system. The mass balance analysis concluded that 98% reduction in water usage, 25% reduction in nitrogen, and 12.5% reduction in phosphorus could be achieved during cultivation operating under recirculation for one year, while maintaining biomass productivity of 1.2 kg wet algal biomass and sequestration of 0.4 kg CO2 per day. The exergy balance analysis concluded that without considering solar irradiation, the culture with water recirculation greatly enhanced the rational exergy efficiency, which represents a more sustainable cultivation system for CO2 capture and utilization.

Feasibility of Utilizing Wastewaters for Large-Scale Microalgal Cultivation and Biofuel Productions Using Hydrothermal Liquefaction Technique: A Comprehensive Review.

The two major bottlenecks faced during microalgal biofuel production are, (a) higher medium cost for algal cultivation, and (b) cost-intensive and time consuming oil extraction techniques. In an effort to address these issues in the large scale set-ups, this comprehensive review article has been systematically designed and drafted to critically analyze the recent scientific reports that demonstrate the feasibility of microalgae cultivation using wastewaters in outdoor raceway ponds in the first part of the manuscript. The second part describes the possibility of bio-crude oil production directly from wet algal biomass, bypassing the energy intensive and time consuming processes like dewatering, drying and solvents utilization for biodiesel production. It is already known that microalgal drying can alone account for ∼30% of the total production costs of algal biomass to biodiesel. Therefore, this article focuses on bio-crude oil production using the hydrothermal liquefaction (HTL) process that converts the wet microalgal biomass directly to bio-crude in a rapid time period. The main product of the process, i.e., bio-crude oil comprises of C16-C20 hydrocarbons with a reported yield of 50–65 (wt%). Besides elucidating the unique advantages of the HTL technique for the large scale biomass processing, this review article also highlights the major challenges of HTL process such as update, and purification of HTL derived bio-crude oil with special emphasis on deoxygenation, and denitrogenation problems. This state of art review article is a pragmatic analysis of several published reports related to algal crude-oil production using HTL technique and a guide towards a new approach through collaboration of industrial wastewater bioremediation with rapid one-step bio-crude oil production from chlorophycean microalgae.

PHYSICAL PRETREATMENT OF ULVA FASCIATA FOR ENHANCINGBIODIESEL PRODUCTION AND QUALITY

The green algae Ulva faciata was subjected to different physical pretreatments comprising thermal and mechanical techniques at different experimental conditions to state the most appropriate method of cell disruption for increasing the quantity of the extracted lipid and hence improve the quality of the produced biodiesel with low cost. Thermal pretreatment was autoclaving of either wet or dry algal biomass, while mechanical pretreatments include microwave and ultrasonication at different time intervals. The control was the alga without pretreatment extracted at optimum conditions: 60 min, 55oC, shaking speed at 250 rpm, < 0.16 mm particle size with 25:1 v/w solvent to solid ratio. The results showed that the quantity of extracted lipids in case of using all physical pretreatments increased the Total fatty acids yield significantly by about 2-folds of the control for wet algae in hydrothermal treatment with optimum time of treatment 40 minutes, and 1.4 folds for dry algae in thermal pretreatment of the dried alga for 60minutes autoclaving period. The sharp increase by 2.2 folds of extracted lipids was recorded by microwave pretreatment for radiation period (5 min), while ultrasonication showed 2.1-fold increase in lipid yield at 15minutes ultrasound exposure time. Concerning the physical properties of the produced biodiesel after all physical pretreatments, the results indicated that the produced biodiesel had very high quality as all its properties are almost complied with the ASTM D6751 and EN14214 standards. These results were confirmed statistically where all physical pretreatments had high significant effect on fatty acids yield and Biodiesel properties.

A parametric study through the modelling of hydrothermal gasification for hydrogen production from algal biomass

AbstractHydrothermal gasification (HTG) is applicable to high moisture content biomass feedstock such as wet microalgae. The key interests of this thermochemical processing are its ability to use whole algae instead of simply lipid extracts and to use a wide range of algal feedstocks. It employs water in the form of a reaction medium to disintegrate biomass into hydrogen gas. The products' composition and yields are a function of process parameters, namely feed concentration, pressure, and temperature. There is very limited literature available on model development to understand the impacts of various input parameters on the products of HTG. This study presents development of a detailed process model for HTG and the illustration of process parameters on the gas product yields. The approach includes developing the system model, identifying the key process parameters in the reactor setup that affect syngas yield, and understanding the overall process in terms of final product yield. A simulation of hydrothermal gasification based on thermodynamic equilibrium is studied. Based on the developed process model about 52.1 t/day of hydrogen can be produced from 500 t/day of wet algal biomass. This shows the potential of large‐scale hydrogen production through this process for hydrogen economy. The results from this study could be used by the gas processing industry and policymakers to determine the most feasible means of converting biomass‐based resources into gaseous fuels.

Outdoor cultivation of Chlorella pyrenoidosa in paddy-soaked wastewater and a feasibility study on biodiesel production from wet algal biomass through in-situ transesterification

Sustainable resources management, incorporating energy markets and resources such as electricity, fossil fuels, renewable and sustainable energy capital is essential for society to understand production and conversion of various forms of energy, their current as well as future supply. Waste-to-energy (WTE) or energy-from-waste (EFW) is a well-identified transitional technology which could prevent complete depletion of renewable resources. In our present study, the selected microalgae (Chlorella pyrenoidosa) was cultured in paddy-soaked wastewater (PWW) using outdoor raceway ponds of 50 L capacity where biotransformation of nutrients (NH3–N removal: 75.89 ± 0.69%; PO4–P removal: 73.71 ± 0.75%; yield co-efficient YN: 6.12 mg biomass/mg of N; YP: 7.77 mg biomass/mg P) has occurred with better growth and biochemical composition (dry biomass weight: 1.56 ± 0.11 g/L; chlorophyll: 15.57 ± 0.14 mg/L; specific growth rate (SGR): 0.42/d; lipids: 27.47 ± 1.41% biomass; carbohydrates: 23.77 ± 1.00% and protein: 46.12 ± 3.55%). Further, the obtained algal lipid was identified for a wide range of fatty acid methyl esters (FAME) and consequently brought forward to in-situ single-step transesterification by optimizing reaction conditions. Central composite design (CCD) of response surface methodology (RSM) has given optimized conditions of sample amount: 2 g (wet); methanol sulphuric acid volume: 3 mL; and hexane volume: 4 mL, under the reaction temperature of 90 °C for maximum biodiesel conversion (46.54% of algal lipids). The outcome of our current research may add value to the application and development of WTE technology for sustainable energy conservation.

Nutrient recycle from algae hydrothermal liquefaction aqueous phase through a novel selective remediation approach

Algae have received increasing interest in the past several decades as a biofuel feedstock source. However, sustainable nutrient supply has presented algal biofuels with a major obstacle in the value chain. At a scale where algal biofuels would meet a significant portion of transportation fuel needs, the demand for nutrients, specifically nitrogen and phosphorus, would exceed current global agricultural production. One downstream conversion pathway, hydrothermal liquefaction (HTL), produces bio-crude oils from wet algal biomass with a waste aqueous phase (HTL-AP), containing a significant amount of carbon and nitrogen. While this stream is rich in organic content and nutrients, it also contains toxic components, which include heterocyclic nitrogen compounds and phenolic compounds. Thus, the recyclability and potential toxicity of HTL-AP need to be studied in detail. The feasibility of utilizing nutrients available in HTL-AP was experimentally determined for Chlorella vulgaris and Desmodesmus armatus monocultures. Our work focused on determining the tolerance of these algae species toward HTL-AP toxicity through varying dilutions. Nitrogen replacement in the growth media was varied from a low of 18% to a high of 141% across both species. The most notable of these results show that addition of a 100× dilution (35% nitrogen replacement) of untreated HTL-AP decreased growth in C. vulgaris by 47 ± 7% with respect to a control medium. Adsorption treatments, including activated carbon and various resins, were introduced to remediate the HTL-AP toxic effects. Treatment of the HTL-AP portion with an ion-exchange resin, Dowex 50WX8, supported C. vulgaris growth at a 100× dilution (35% nitrogen replacement) with no statistical change compared to the control. An in-depth molecular profiling demonstrated for the first time the selective removal of high‑nitrogen containing components by resin treatment. This work provides a foundation for studying the toxic components of HTL-AP and possible mechanisms by which treatments can remove these components.

Impact on performance and emissions of the aspiration of algal biomass suspensions in the intake air of a direct injection diesel engine

Recently, the production of sustainable biofuels from algal biomass has gained significant attention and been investigated as a potential replacement of fossil fuel. However, existing downstream processes for producing biodiesel from algae cells are complex, highly energy-intensive, and have high economic and environmental cost. Therefore, this work introduces an alternative and novel method of utilizing the energy content of microalgae that precludes lipid extraction by aspirating wet algal biomass suspensions directly into the intake air of an internal combustion engine.For all engine experiments, powdered algae cells were prepared as slurries at different biomass concentrations. The impacts of (i) varying the biomass concentration with constant suspension injection flowrate into the engine intake and (ii) varying suspension injection flowrate with constant biomass concentration were investigated.A correlation between engine work produced during combustion and algal biomass aspiration was found. At constant flowrate and greater than 5% biomass concentrations, an increase of energy release during combustion from the aspirated algae could be observed. However, the aspiration of low concentration biomass suspension produced a negative impact on engine performance relative to water-only aspiration. The engine exhaust gas of nitrogen oxides (NOx) was reduced for all algae suspension tests relative to diesel-only combustion. However, the carbon monoxide (CO) emission level was much higher relative to diesel-only tests at high biomass concentrations and injection flowrate.These findings demonstrate the possibility of utilising the energy content of algal biomass in combustion without lipid extraction, with added benefits of reducing NOx emissions.

Evaluation and optimization of feedstock quality for direct conversion of microalga Chlorella sp. FC2 IITG into biodiesel via supercritical methanol transesterification

The study reports evaluation of feedstock quality for direct conversion of microalga Chlorella sp. FC2 IITG into biodiesel via supercritical methanol transesterification (SCMT). Characterization of biomass feedstock quality on fatty acid methyl esters (FAME) yield was performed based on two key parameters: intracellular lipid content and water content of the biomass. Statistical optimization of transesterification parameters, e.g., lipid content, water content of biomass, and methanol loading, predicted the optimum values of 52% (w/w), 5.75 mL g−1, and 115 mL g−1, respectively, with maximum FAME yield of 96.9%. This improved FAME yield was achieved with much lower methanol loading and higher water content per gram of biomass and hence offers elevated economic feasibility via minimizing the utilization of alcohol and enabling direct conversion of wet algal biomass into biodiesel. FAME produced via SCMT satisfied most of the biodiesel properties as per ASTM and European standards thereby referring to good quality biodiesel.

Density of benthic macroalgae in the intertidal zone varies with surf zone hydrodynamics

ABSTRACTSurf zone hydrodynamics influence subsidies (larval settlers and phytoplankton food) to the intertidal zone; subsidies have been observed to be much higher at more dissipative shores compared to reflective shores. Benthic macroalgal populations may be favoured at more reflective surf zones due to slower water exchange with the coastal ocean, facilitating retention of spores. In addition, larval invertebrate settlers are far less abundant at more reflective surf zones, and benthic macroalgae may experience lower competition from sessile invertebrates for space. We used surf zone width as an indictor of surf zone hydrodynamics; surf zones are wider at more dissipative surf zones compared to reflective surf zones. We tested the hypothesis that as surf zone width increases, macroalgal density would decrease. We used aerial near-infrared and visible light images to calculate the normalised difference vegetation index (NDVI) at eight intertidal sites along the Oregon coast and compared NDVI with algal biomass (dry and wet weight per square metre) at each specific location; linear regressions between NDVI and dry and wet algal biomass were significant (P < 0.01); NDVI was an accurate indicator of macroalgal density. Surf zone width was measured using Google Earth images. NDVI and dry and wet algal biomass were significantly lower at wider surf zones (P < 0.01). Although the mechanism underlying this relationship is unknown, the intertidal macroalgal community clearly varied with surf zone hydrodynamics as indicated by surf zone width.

Review on direct transesterification method using recent technologies

Nowadays the research is focused on microalgae oil for biodiesel production because of high yield as compared to vegetable plant oil and it fixes carbon dioxide from atmosphere. It is a third-generation biofuel that can easily replace diesel which will deplete in couple of decades and can be used in diesel engine without any modification simultaneously cutting down the engine emissions. The biodiesel production from microalgae is a complex process which includes harvesting, drying, cell disruption, lipid extraction and biodiesel production. However, using direct in-situ transesterification these steps are reduced, and biodiesel production get simplified. Here in this wet algal biomass directly transesterified using alcohol, catalyst and solvents thus eliminating the drying and oil extraction process. This paper reviews the different methods used for direct transesterification in order to reduce the cost of production and increase the biodiesel yield. For cell different techniques are studied and analyzed the best technique from literature review.

Fermentative hydrogen production from microalgal biomass by a single strain of bacterium Enterobacter aerogenes – Effect of operational conditions and fermentation kinetics

Abstract Biohydrogen production through dark fermentation is a promising technology for generating renewable energy, while using microalgal biomass as a third generation feedstock can further increase the sustainability of the process. In the present study, Scenedesmus obliquus was used as model microalga substrate for studying the impact of operational parameters in batch dark fermentation trials using a strain of Enterobacter aerogenes bacteria. (i) The initial gas-liquid ratio in the bioreactor (from 1.3 to 8.2) was tested, resulting in higher bioH2 yields for ratios above 5. (ii) Different bacterial growth, inoculation procedures and fermentation media were tested in combined experiments. The best conditions were chosen by maximising bioH2 yield and minimising production time and costs. (iii) The autoclave sterilization effect on sugar extraction and bioH2 yield was tested for different microalga concentrations (2.5–50 g/L) with best results attained for 2.5 g/L (81.2% extraction yield, 40.9 mL H2/g alga). For the best operational conditions, fermentation kinetics were monitored and adjusted to the Modified Gompertz model, with t95 (time required for bioH2 production to attain 95% of the maximum yield) below 4.5 h. The maximum hydrogen production was higher when using wet algal biomass enabling the energy consuming biomass drying step to be skipped.

Selective extraction of neutral lipid from wet algae paste and subsequently hydroconversion into renewable jet fuel

Abstract Wet algae paste, after harvested, was converted into renewable jet fuel through selective extraction and subsequent hydroconversion without further purification. A fractional extraction method based on ethanol and hexane starting from wet algae was firstly designed and investigated. The oil recovery was as high as 90 wt% of lipid after three extraction cycles. Such a method results in fractional extraction of polar lipid and neutral lipid separately from wet algal biomass. The obtained neutral lipid rich fraction has very low metal content, in which the Ca, Mg, and Cu contents are 2, 0, and 3 mg/kg, respectively. It can be converted into jet fuel range paraffin by one-step hydrocracking over Pt/Meso-ZSM-5 catalyst directly. The freeze point, flash point, and energy density of the obtained jet fuel are −57 °C, 42 °C, and 45 MJ/kg, respectively, which satisfies the ASTM 7566 standard and can be used as high quality jet fuel blend.

Supercritical water upgrading of water-insoluble and water-soluble biocrudes from hydrothermal liquefaction of Nannochloropsis microalgae

Treatment of wet algal biomass in hot compressed water produces crude bio-oil that spontaneously separates from the aqueous phase upon cooling. Additional bio-oil (water-soluble biocrude) can be obtained via solvent extraction of the aqueous phase coproduct. The present study is the first to examine the supercritical water upgrading (both with and without catalysts) of these two biocrude types independently. Of the catalysts tested, Pt/C had the best effect on upgrading the water-insoluble biocrude from algae liquefaction. It provided the highest C (80.9wt%) and H content (10.6wt%) and heating value (41.6MJ/kg), and the lowest N (2.47wt%), S (0.26wt%), and O contents (4.80wt%). The use of process water from liquefaction for supercritical water upgrading leads to higher quality upgraded oils. Hydrothermal upgrading of the water-soluble biocrude from algae liquefaction significantly improved its quality as the C content increased from 61.0 to 75.1wt%, heating value increased from 29.3 to 35.4MJ/kg, and the combined N, S and O content decreased from 30wt% to 16wt%. The material produced by upgrading the water-soluble biocrude from algae HTL contained aromatic hydrocarbons.

Sequential Hydrothermal Liquefaction characterization and nutrient recovery assessment

Hydrothermal Liquefaction (HTL) has been considered as an effective process for converting wet algal biomass to biocrude. A major limitation of HTL however, is its inability to harvest high value-added byproducts or recover nutrients. Sequential Hydrothermal Liquefaction (SEQHTL) was recently developed to overcome this limitation to allow the simultaneous extraction of co-products and biocrude production. In this study, the performance for SEQHTL treating different algal species was assessed in terms of process versatility, biocrude production and nutrient recovery. The impact of feedstock and relevant feed stream thermophysical properties was evaluated. The biocrudes produced had moderately low oxygen content (<14%), reduced nitrogen content (<8%), very low sulfur (<1.4%), and HHV ranging from 33 to 37MJ/kg. Galdieria sulphuraria produced less crude (~20wt%) as well as less char (~11wt%). The Chlorella sp. had higher crude yields (~30wt%) and superior nutrient recovery in aqueous effluents, ranging from 2640 to 3600mg/L of phosphorous and from 2100 to 3700mg/L of total nitrogen. The results also show non-Newtonian shear thinning and increasing effective viscosity at higher solid loadings. Although SEQHTL proved more suitable for algae with moderate to high lipid content, its versatility and mild reaction conditions allow for the harvesting significant quantities of water-soluble nutrients. These findings compare favorably to HTL studies and suggest that these compounds can be recovered for either recycle or producing other value-added co-products.

Cultivation of Nannochloropsis oculata in centrate and conversion of its lipids to biodiesel in a low-cost microwave reactor

ABSTRACTIn the present study, 100% centrate (wastewater generated in the sludge centrifuge of a municipal wastewater treatment plant) was used for the cultivation of microalga Nannochloropsis oculata in a lab scale externally illuminated photobioreactor. Cells were harvested at the end of the exponential phase and the resulting wet algal biomass (80 wt % moisture) was subjected to direct saponification in a low-cost microwave reactor using ethanolic KOH to convert the algal lipids to soap. The soap was separated from other unsaponifiable matter by precipitation using saturated KCl and subjected to simultaneous acidulation and esterification to form biodiesel of high purity (97.04% FAME in final biodiesel). Optimum values of esterification of fatty acids in microwave reactor were: microwave power-450 W, molar ratio of methanol to fatty acids -80:1, concentration of sulphuric acid-2.5 wt %, reaction time-11 min and reaction temperature-60 °C. Kinetics studies of esterification conducted under these conditions revealed that the rate constant was high (0.452 min−1). The final yield of biodiesel was 97.11%. Cetane number and oxidation stability index of biodiesel were evaluated to be 59.349 and 3.298 h respectively. Removal rates of Chemical oxygen demand (COD), total nitrogen and total phosphorous were 82.65%, 62.25% and 52.65% respectively.

Progress on lipid extraction from wet algal biomass for biodiesel production.

SummaryLipid recovery and purification from microalgal cells continues to be a significant bottleneck in biodiesel production due to high costs involved and a high energy demand. Therefore, there is a considerable necessity to develop an extraction method which meets the essential requirements of being safe, cost‐effective, robust, efficient, selective, environmentally friendly, feasible for large‐scale production and free of product contamination. The use of wet concentrated algal biomass as a feedstock for oil extraction is especially desirable as it would avoid the requirement for further concentration and/or drying. This would save considerable costs and circumvent at least two lengthy processes during algae‐based oil production. This article provides an overview on recent progress that has been made on the extraction of lipids from wet algal biomass. The biggest contributing factors appear to be the composition of algal cell walls, pre‐treatments of biomass and the use of solvents (e.g. a solvent mixture or solvent‐free lipid extraction). We compare recently developed wet extraction processes for oleaginous microalgae and make recommendations towards future research to improve lipid extraction from wet algal biomass.