Effect of temperature and moisture on high pressure lipid/oil extraction from microalgae

Commercially viable carbon–neutral biodiesel production from microalgae has potential for replacing depleting petroleum diesel. The process of biodiesel production from microalgae involves harvesting, drying and extraction of lipids which are energy- and cost-intensive processes. The development of effective large-scale lipid extraction processes which overcome the complexity of microalgae cell structure is considered one of the most vital requirements for commercial production. Thus the aim of this work was to investigate suitable extraction methods with optimised conditions to progress opportunities for sustainable microalgal biodiesel production. In this study, the green microalgal species consortium, Tarong polyculture was used to investigate lipid extraction with hexane (solvent) under high pressure and variable temperature and biomass moisture conditions using an Accelerated Solvent Extraction (ASE) method. The performance of high pressure solvent extraction was examined over a range of different process and sample conditions (dry biomass to water ratios (DBWRs): 100%, 75%, 50% and 25% and temperatures from 70 to 120 ºC, process time 5–15 min). Maximum total lipid yields were achieved at 50% and 75% sample dryness at temperatures of 90–120 ºC. We show that individual fatty acids (Palmitic acid C16:0; Stearic acid C18:0; Oleic acid C18:1; Linolenic acid C18:3) extraction optima are influenced by temperature and sample dryness, consequently affecting microalgal biodiesel quality parameters. Higher heating values and kinematic viscosity were compliant with biodiesel quality standards under all extraction conditions used. Our results indicate that biodiesel quality can be positively manipulated by selecting process extraction conditions that favour extraction of saturated and mono-unsaturated fatty acids over optimal extraction conditions for polyunsaturated fatty acids, yielding positive effects on cetane number and iodine values. Exceeding biodiesel standards for these two parameters opens blending opportunities with biodiesels that fall outside the minimal cetane and maximal iodine values.

Combustion analysis of microalgae methyl ester in a common rail direct injection diesel engine

In this study, the biodiesel properties and effects of blends of oil methyl ester petroleum diesel on a CI direct injection diesel engine is investigated. Blends were obtained from the marine dinoflagellate Crypthecodinium cohnii and waste cooking oil. The experiment was conducted using a four-cylinder, turbo-charged common rail direct injection diesel engine at four loads (25%, 50%, 75% and 100%). Three blends (10%, 20% and 50%) of microalgae oil methyl ester and a 20% blend of waste cooking oil methyl ester were compared to petroleum diesel. To establish suitability of the fuels for a CI engine, the effects of the three microalgae fuel blends at different engine loads were assessed by measuring engine performance, i.e. mean effective pressure (IMEP), brake mean effective pressure (BMEP), in cylinder pressure, maximum pressure rise rate, brake-specific fuel consumption (BSFC), brake thermal efficiency (BTE), heat release rate and gaseous emissions (NO, NOx,and unburned hydrocarbons (UHC)). Results were then compared to engine performance characteristics for operation with a 20% waste cooking oil/petroleum diesel blend and petroleum diesel. In addition, physical and chemical properties of the fuels were measured. Use of microalgae methyl ester reduced the instantaneous cylinder pressure and engine output torque, when compared to that of petroleum diesel, by a maximum of 4.5% at 50% blend at full throttle. The lower calorific value of the microalgae oil methyl ester blends increased the BSFC, which ultimately reduced the BTE by up to 4% at higher loads. Minor reductions of IMEP and BMEP were recorded for both the microalgae and the waste cooking oil methyl ester blends at low loads, with a maximum of 7% reduction at 75% load compared to petroleum diesel. Furthermore, compared to petroleum diesel, gaseous emissions of NO and NOx, increased for operations with biodiesel blends. At full load, NO and NOx emissions increased by 22% when 50% microalgae blends were used. Petroleum diesel and a 20% blend of waste cooking oil methyl ester had emissions of UHC that were similar, but those of microalgae oil methyl ester/petroleum diesel blends were reduced by at least 50% for all blends and engine conditions. The tested microalgae methyl esters contain some long-chain, polyunsaturated fatty acid methyl esters (FAMEs) (C22:5 and C22:6) not commonly found in terrestrial-crop-derived biodiesels yet all fuel properties were satisfied or were very close to the ASTM 6751-12 and EN14214 standards. Therefore, Crypthecodinium cohnii- derived microalgae biodiesel/petroleum blends of up to 50% are projected to meet all fuel property standards and, engine performance and emission results from this study clearly show its suitability for regular use in diesel engines.

Microalgae: An alternative source of biodiesel for the compression ignition (CI) engine

This thesis is a comprehensive study of microalgae biodiesel for the compression ignition engine. It examines microalgae growing conditions, the extraction process and physiochemical properties with a wide range of microalgae species. It also evaluates microalgae biodiesel with regards to engine performance and emission characteristics and explains the difficulties and potentiality of microalgae as a biodiesel. In doing so, an extensive analysis of different extraction methods and engine testing was conducted and a comprehensive study on microalgae biodiesel is presented.

Technoeconomic analysis of an integrated microalgae photobioreactor, biodiesel and biogas production facility

As fossil fuel prices increase and environmental concerns gain prominence, the development of alternative fuels from biomass has become more important. Biodiesel produced from microalgae is becoming an attractive alternative to share the role of petroleum. Currently it appears that the production of microalgal biodiesel is not economically viable in current environment because it costs more than conventional fuels. Therefore, a new concept is introduced in this article as an option to reduce the total production cost of microalgal biodiesel. The integration of biodiesel production system with methane production via anaerobic digestion is proved in improving the economics and sustainability of overall biodiesel stages. Anaerobic digestion of microalgae produces methane and further be converted to generate electricity. The generated electricity can surrogate the consumption of energy that require in microalgal cultivation, dewatering, extraction and transesterification process. From theoretical calculations, the electricity generated from methane is able to power all of the biodiesel production stages and will substantially reduce the cost of biodiesel production (33% reduction). The carbon emissions of biodiesel production systems are also reduced by approximately 75% when utilizing biogas electricity compared to when the electricity is otherwise purchased from the Victorian grid. The overall findings from this study indicate that the approach of digesting microalgal waste to produce biogas will make the production of biodiesel from algae more viable by reducing the overall cost of production per unit of biodiesel and hence enable biodiesel to be more competitive with existing fuels.

Bioprocess engineering of microalgae to produce a variety of consumer products

Microalgae biotechnology has recently emerged into the lime light owing to numerous consumer products that can be harnessed from microalgae. Product portfolio stretches from straightforward biomass production for food and animal feed to valuable products extracted from microalgal biomass, including triglycerides which can be converted into biodiesel. For most of these applications, the production process is moderately economically viable and the market is developing. Considering the enormous biodiversity of microalgae and recent developments in genetic and metabolic engineering, this group of organisms represents one of the most promising sources for new products and applications. With the development of detailed culture and screening techniques, microalgal biotechnology can meet the high demands of food, energy and pharmaceutical industries. This review article discusses the technology and production platforms for development and creation of different valuable consumer products from microalgal biomass.

Measuring the regional availability of biomass for biofuels and the potential for microalgae

Biomass is an important energy resource for producing bioenergy and growing the global economy whilst minimising greenhouse gas emissions. Many countries, like Australia have a huge amount of biomass with the potential for bioenergy, but non-edible feedstock resources are significantly under-exploited. Hence it is essential to map the availability of these feedstocks to identify the most appropriate bioenergy solution for each region and develop supply chains for biorefineries. Using Australia as a case study,we present the spatial availability and opportunities for second and third generation feedstocks. Considerations included current land use, the presence of existing biomass industries and climatic conditions. Detailed information on the regional availability of biomass was collected from government statistics, technical reports and energy assessments as well as from academic literature. Second generation biofuels have the largest opportunity in New South Wales, Queensland and Victoria (NSW, QLD and VIC) and the regions with the highest potential for microalgae are Western Australia and Northern Territory (WA, NT), based on land use opportunity cost and climate. The approach can be used in other countries with a similar climate. More research is needed to overcome key technical and economic hurdles.

The gut microbial community of midas cichlid fish in repeatedly evolved limnetic-benthic species pairs

Gut bacterial communities are now known to influence a range of fitness related aspects of organisms. But how different the microbial community is in closely related species, and if these differences can be interpreted as adaptive is still unclear. In this study we compared microbial communities in two sets of closely related sympatric crater lake cichlid fish species pairs that show similar adaptations along the limnetic-benthic axis. The gut microbial community composition differs in the species pair inhabiting the older of two crater lakes. One major difference, relative to other fish, is that in these cichlids that live in hypersaline crater lakes, the microbial community is largely made up of Oceanospirillales (52.28%) which are halotolerant or halophilic bacteria. This analysis opens up further avenues to identify candidate symbiotic or co-evolved bacteria playing a role in adaptation to similar diets and life-styles or even have a role in speciation. Future functional and phylosymbiotic analyses might help to address these issues.

Method for comparing the capture efficiency of benthic sampling devices

Traditional comparisons between the capture efficiency of sampling devices have generally looked at the absolute differences between devices. We recommend that the signal-to-noise ratio be used when comparing the capture efficiency of benthic sampling devices. Using the signal-to-noise ratio rather than the absolute difference has the advantages that the variance is taken into account when determining how important the difference is, the hypothesis and minimum detectable difference can be made identical for all taxa, it is independent of the units used for measurement, and the sample-size calculation is independent of the variance. This new technique is illustrated by comparing the capture efficiency of a 0.05 m(2) van Veen grab and an airlift suction device, using samples taken from Heron and One Tree lagoons, Australia.

Mapping and characterisation of the inter-reefal benthic assemblages of the Torres Strait

A comprehensive survey of the benthic assemblages of the Torres Strait was conducted in order to provide critical baseline information for regional marine planning, assessing the environmental sustainability of fisheries and understanding the ecosystems of the region. Over 150 sites throughout the region were sampled with a modified prawn trawl, towed underwater video, pipe dredge and epibenthic sled. This manuscript provides a broad overview of the activities undertaken and data collected. Two thousand three hundred and seventy-two different nominal species were sampled by the trawl and sled, only 728 by both gears. The towed video was not able to provide the same level of taxonomic resolution of epibenthic taxa, but was particularly useful in areas where the seabed was too rough to be sampled. Data from the trawl, sled and video were combined to characterise the epibenthic assemblages of the region. Data from the towed video was also used to provide a characterisation of the inter-reefal benthic habitats, which was then analysed in combination with physical covariate data to examine relationships between the two. Levels of mud and gravel in the sediments, trawling effort and seabed current stress were the covariates most significantly correlated with the nature of the seabed habitats.

Economic analyses and policy implications for microalgae biofuels in Australia

The benefits of microalgae biofuels over first and second generation counterparts suggest it has potential as a major biofuel feedstock in Australia. However, the high costs of cultivation and processing has been a major drawback for investors and policymakers. This presentation outlines the economic potential for microalgae biofuels: firstly, through production of microalgae co-products (e.g feed and fertiliser); and secondly, deriving what consumers are willing to pay for microalgae biofuels based on external benefits. These findings will assist decision-makers in both private and public sectors and inform policy development with respect to microalgae as a feedstock for biofuels and other products. This study adds an economics perspective to the current technical literature which has been dominated by biochemical, engineering and financial valuation studies.

Profiling of carotenoids and antioxidant capacity of microalgae from subtropical coastal and brackish waters

Carotenoids are associated with various health benefits, such as prevention of age-related macular degeneration, cataract, certain cancers, rheumatoid arthritis, muscular dystrophy and cardiovascular problems. As microalgae contain considerable amounts of carotenoids, there is a need to find species with high carotenoid content. Out of hundreds of Australian isolates, twelve microalgal species were screened for carotenoid profiles, carotenoid productivity, and in vitro antioxidant capacity (total phenolic content (TPC) and ORAC). The top four carotenoid producers at 4.68-6.88 mg/g dry weight (DW) were Dunaliella salina, Tetraselmis suecica, Isochrysis galbana, and Pavlova salina. TPC was low, with D. salina possessing the highest TPC (1.54 mg Gallic Acid Equivalents/g DW) and ORAC (577 μmol Trolox Equivalents/g DW). Results indicate that T. suecica, D. salina, P. salina and I. galbana could be further developed for commercial carotenoid production.

The distribution and abundance of electrosensory pores in two benthic sharks: a comparison of the wobbegong shark, Orectolobus maculatus, and the angel shark, Squatina australis

Electroreception is an ancient sense found in many aquatic animals, including sharks, which may be used in the detection of prey, predators and mates. Wobbegong sharks (Orectolobidae) and angel sharks (Squatinidae) represent two distantly related families that have independently evolved a similar dorso-ventrally compressed body form to complement their benthic ambush feeding strategy. Consequently, these groups represent useful models in which to investigate the specific morphological and physiological adaptations that are driven by the adoption of a benthic lifestyle. In this study, we compared the distribution and abundance of electrosensory pores in the spotted wobbegong shark (Orectolobus maculatus) with the Australian angel shark (Squatina australis) to determine whether both species display a similar pattern of clustering of sub-dermal electroreceptors and to further understand the functional importance of electroreception in the feeding behaviour of these benthic sharks. Orectolobus maculatus has a more complex electrosensory system than S. australis, with a higher abundance of pores and an additional cluster of electroreceptors positioned in the snout (the superficial ophthalmic cluster). Interestingly, both species possess a cluster of pores (the hyoid cluster, positioned slightly posterior to the first gill slit) more commonly found in rays, but which may be present in all benthic elasmobranchs to assist in the detection of approaching predators.

Benthic-pelagic coupling in the northern Baltic Sea: importance of bioturbation and benthic predation

Benthic-pelagic coupling describes processes that operate across and between the seafloor and open-water ecosystems. In soft-sediment communities, bioturbation by sediment-dwelling and epibenthic organisms may strongly shape habitat characteristics and influence processes, e.g. biogeochemical cycling, which supplies bioavailable nutrients to pelagic primary producers. In addition, benthic fauna may mediate benthic-pelagic coupling by affecting the survival and hatching of zooplankton dormant eggs in the sediment. In the shallow waters and seasonally fluctuating environment of the Baltic Sea, emergence from the seafloor essentially contributes to the dynamics of zooplankton pelagic populations. In this thesis, I examine how benthic organisms with different functional traits affect the link between the benthic and pelagic systems in the northern Baltic Sea. By means of experimental laboratory studies, the effects of sediment-dwelling (Monoporeia affinis, Macoma balthica and Marenzelleria spp.) and nectobenthic (Mysis spp.) taxa on the survival and hatching of zooplankton benthic eggs and on benthic nutrient fluxes and sediment structure were investigated. In the predation studies, the nectobenthic mysids Mysis spp. preyed upon benthic eggs of the cladoceran Bosmina longispina maritima (syn. B. coregoni maritima), both in pelagic and benthic environments. Of the sediment-dwelling species, the amphipod M. affinis and the bivalve M. balthica reduced the number of cladoceran eggs in the sediment, whereas the polychaetes Marenzelleria spp. had no effects on cladoceran eggs. Both M. balthica and M. affinis also increased the mortality rates of benthic eggs of copepods and rotifers. It was estimated that zooplankton eggs provide an additional carbon source for food-limited benthic communities. The results indicate that predation pressure on zooplankton benthic eggs may be strong, but varies widely depending on the season and the functional characteristics of the macrofauna. Macoma balthica buried cladoceran eggs and a fluorescent tracer from the sediment surface to a depth of 3 4 cm, indicating efficient sediment mixing. In contrast, the other taxa had fewer effects on particle distributions. In addition to organic matter mineralization, particle mixing is crucial to the success of benthic recruitment of zooplankton, since only eggs close to the sediment surface may hatch. Macoma balthica and M. affinis altered the patterns of zooplankton emergence from the sediment. In general, the highest emergence rates were observed in the absence of macroscopic fauna, and M. balthica exerted a stronger suppressive effect than M. affinis. Moreover, copepods were less severely affected than cladocerans, while only one species (Temora longicornis) clearly benefited from the presence of the macrofauna. These differences probably result from species-specific differences in the resistance of eggs to disturbances. The results show that benthic fauna may considerably alter the patterns of zooplankton emergence from the seafloor, thereby shaping zooplankton pelagic populations. The semi-motile M. balthica and Marenzelleria spp. increased the fluxes of phosphate and ammonium from the sediment to the water, whereas the motile M. affinis and Mysis mixta had a contrasting effect. In the eutrophied Baltic Sea, efficient internal cycling of bioavailable nutrients forms a strong feedback inhibiting the recovery of the ecosystem. Based on the results, a change in species dominance from the two motile taxa, susceptible to oxygen deficiency, to the more tolerant semi-motile taxa provides additional feedback, strengthening internal nutrient cycling and accelerating eutrophication, with deteriorating near-bottom oxygen conditions and changes in the benthic communities. In shallow-water ecosystems, benthic nutrient regeneration plays a key role in determining the overall productivity of the ecosystem. In addition, the results of this study show that the communities in the benthos may essentially contribute to the structure of those in the plankton.