Evan Stephens - Academia.edu (original) (raw)

Papers by Evan Stephens

Single cell green algae (microalgae) are rapidly emerging as a platform for the production of sus... more Single cell green algae (microalgae) are rapidly emerging as a platform for the production of sustainable fuels. Solar-driven H2 production from H2O theoretically provides the highest-efficiency route to fuel production in microalgae. This is because the H2-producing hydrogenase (HYDA) is directly coupled to the photosynthetic electron transport chain, thereby eliminating downstream energetic losses associated with the synthesis of carbohydrate and oils (feedstocks for methane, ethanol and oil-based fuels). Here we report the simultaneous knock-down of three light-harvesting complex proteins (LHCMB1, 2 and 3) in the high H2-producing Chlamydomonas reinhardtii mutant Stm6Glc4 using an RNAi triple knock-down strategy. The resultant Stm6Glc4L01 mutant exhibited a light green phenotype, reduced expression of LHCBM1 (20.6% 60.27%), LHCBM2 (81.2 % 60.037%) and LHCBM3 (41.4 % 60.05%) compared to 100 % control levels, and improved light to H2 (180%) and biomass (165%) conversion efficiencie...

Grünberger A, Stephens E, Hankamer B. Media optimization for the microalgae Chamydomonas reinhard... more Grünberger A, Stephens E, Hankamer B. Media optimization for the microalgae Chamydomonas reinhardtii Stm6 using statistical design. Presented at the IMB Summer Symposium: A systems Biology approach to biofuel production: From light capture to biodiesel production, Brisbane, Australia

Microbiology Australia, 2009

The development of carbon neutral fuels for the future is one of the most urgent challenges facin... more The development of carbon neutral fuels for the future is one of the most urgent challenges facing our society for three reasons ? to minimise the effects of climate change, to protect against fuel price shocks and to provide a secure basis for economic growth.

Algal Research, 2016

Efficient photosynthetic biomass production in a high rate pond (HRP) or a photobioreactor (PBR) ... more Efficient photosynthetic biomass production in a high rate pond (HRP) or a photobioreactor (PBR) represents the first step of microalgae platforms for the production of renewable fuels, animal feeds and a diverse range of high value products. This study analyses the interplay between solar energy input, ambient temperature and system surface area to volume (SA:V) ratio in terms of photosynthetic performance (yield, areal and volumetric productivity, photon conversion efficiency). Ten pilot scale trials were conducted under subtropical conditions using 2 microalgae strains (Chlorella sorokiniana and Chlorella sp.) in 5 different cultivation system geometries: HRPs, flat panel PBRs (0.75 m and 1.5 m high) and tubular PBRs (0.74 m and 1.49 m high). The evaluation of culture temperature and biomass productivity response to solar irradiance in the five production systems suggests that the optimal SA:V ratio range lies between 43-73 m 2 m −3 for C. sorokiniana in non-cooled systems regardless of system geometry under the conditions tested. The overall photosynthetic performance at higher SA:V ratios was improved for Chlorella sp. using temperature regulation. The highest observed daily photon conversion efficiency (PCE) was 4.44% (based on illuminated PBR surface area and total solar spectrum) in the high flat panel PBR using C. sorokiniana (40.8 g m −2 d −1 , 0.23 g L −1 d −1). The highest achieved mean PCE (based on illuminated PBR surface area and total solar spectrum) was 2.5% in the low tubular PBR with Chlorella sp. (24.9 g m −2 d −1 , 0.43 g L −1 d −1). The trial data provides important design principles to help fast track systems optimisation for near optimal subtropical conditions.

Biofuels, Bioproducts and Biorefining, 2013

Technoeconomic analysis of renewable aviation fuels has not been widely considered, despite the i... more Technoeconomic analysis of renewable aviation fuels has not been widely considered, despite the increasing global attention that the fi eld has received. We present three process models for production of aviation-fuel from microalgae, Pongamia pinnata seeds and sugarcane molasses. The models and assumptions have been deposited on a wiki (http://qsafi .aibn.uq.edu.au) and are open and accessible to the community. Based on currently available long-term reputable technological data, this analysis indicates that the biorefi neries processing the microalgae,

Biorefinery, 2018

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Nature Biotechnology, 2010

Biomass and Bioenergy

Abstract The removal of nitrogen (N) and sulphur (S) from biocrude oil produced using hydrotherma... more Abstract The removal of nitrogen (N) and sulphur (S) from biocrude oil produced using hydrothermal liquefaction (HTL), is important for the production of high quality renewable fuels. Here the effect of co-liquefaction of bagasse and algae was analysed. Algae (Chlorella vulgaris and Cyanobacteria) were mixed with bagasse (1:1) subjected to HTL at 250–350 °C for 10–60 min. Higher HTL temperatures had a positive effect in increasing the biocrude yield and slightly reduced N content; S did not show a consistent trend. Most of the nitrogen (~66%) and sulphur (~80%) were recovered in the aqueous phase rather than in the biocrude phase, opening the opportunity to recycle these nutrients for algae cultivation. Co-liquefying bagasse with algae improved the biocrude yield (54 wt%) compared to pure Cyanobacteria (47.5 wt%). It also reduced N content from 7 wt% (Cyanobacteria biocrude) to 4.2 wt% (Cyanobacteria: Bagasse) and S from 0.7 wt% to 0.4 wt%. Principal Component Analysis (PCA) analysis identified that biocrude yield is positively correlated with the initial lipid content and anti-correlated with the carbohydrates fraction. Biocrude N content is closely related to the initial amount of proteins in the algae. The Preference Ranking Organization METHod for Enrichment of Evaluations and its descriptive complement Geometrical Analysis for Interactive Aid (PROMETHEE and GAIA) analysis ranked the co-liquefaction of Chlorella vulgaris and bagasse (1:1) at 350 °C and 60 min as one of the best overall combination in terms of biocrude yield, N and S content.

Separation and Purification Technology

Energies, 2017

As a biofuel feedstock, microalgae has good scalability and potential to supply a significant pro... more As a biofuel feedstock, microalgae has good scalability and potential to supply a significant proportion of world energy compared to most types of biofuel feedstock. Hydrothermal liquefaction (HTL) is well-suited to wet biomass (such as microalgae) as it greatly reduces the energy requirements associated with dewatering and drying. This article presents experimental analyses of chemical and physical properties of bio-crude oil produced via HTL using a high growth-rate microalga Scenedesmus sp. in a large batch reactor. The overarching goal was to investigate the suitability of microalgae HTL bio-crude produced in a large batch reactor for direct application in marine diesel engines. To this end we characterized the chemical and physical properties of the bio-crudes produced. HTL literature mostly reports work using very small batch reactors which are preferred by researchers, so there are few experimental and parametric measurements for bio-crude physical properties, such as viscosity and density. In the course of this study, a difference between traditionally calculated values and measured values was noted. In the parametric study, the bio-crude viscosity was significantly closer to regular diesel and biodiesel standards than transesterified (FAME) microalgae biodiesel. Under optimised conditions, HTL bio-crude's high density (0.97-1.04 kg•L −1) and its high viscosity (70.77-73.89 mm 2 •s −1) had enough similarity to marine heavy fuels. although the measured higher heating value, HHV, was lower (29.8 MJ•kg −1). The reaction temperature was explored in the range 280-350 • C and bio-crude oil yield and HHV reached their maxima at the highest temperature. Slurry concentration was explored between 15% and 30% at this temperature and the best HHV, O:C, and N:C were found to occur at 25%. Two solvents (dichloromethane and n-hexane) were used to recover the bio-crude oil, affecting the yield and chemical composition of the bio-crude.

Journal of Petroleum & Environmental Biotechnology, 2013

Resource limitation is an escalating concern given human expansion and development. Algae are inc... more Resource limitation is an escalating concern given human expansion and development. Algae are increasingly recognised as a promising bioresource and the range of cultivated species and their products is expanding. Compared to terrestrial crops, microalgae are very biodiverse and offer considerable versatility for a range of biotechnological applications including the production of animal feeds, fuels, high value products and waste-water treatment. Despite their versatility and capacity for high biomass productivity on non-arable land, attempts to harness microalgae for necessity of identifying 'suitable' land with proximal resource and infrastructure availability and the need for process and strain optimisation. Microalgae represent a relatively unexplored bioresource both for native and engineered maintenance of motherstocks, (3) rapid strain characterisation and correct matching of strains to applications, (4) ensuring productive and stable cultivation at scale, and (5) ongoing strain development (breeding, adaptation and ongoing strain development and biotechnological applications.

Current Biotechnology, 2016

BACKGROUND: Hydrogen is a clean, versatile fuel and energy carrier which can be produced by a ran... more BACKGROUND: Hydrogen is a clean, versatile fuel and energy carrier which can be produced by a range of renewable technologies for combustion, use in fuel cells, or as a manufacturing feedstock. Despite its attraction and significant technological innovation, commercial feasibility of photobiological hydrogen processes is far from demonstrated. OBJECTIVE: This review examines direct photobiological biohydrogen systems, with a particular focus on the main obstacles that must be overcome to deliver commercially viable, net energy positive systems. As part of this process the interactions between future photobiological biohydrogen systems and other parts of a renewable energy economy are examined to analyse potential technology integration paths. RESULTS: The primary driver for renewably produced hydrogen is the potential for CO 2 emissions reductions. Renewable hydrogen is largely solar driven, either directly (e.g. natural photosynthesis, or bio-inspired devices) or indirectly (e.g. fermentation, electrical hydrolysis). A significant market for hydrogen already exists and is supported by extensive infrastructure providing significant opportunities for emerging renewable hydrogen streams. Several key physiological obstacles to efficient photobiohydrogen production have already been overcome, with oxygen tolerance as the most significant remaining problem. CONCLUSIONS: A much deeper understanding of photosynthetic biology is required before existing knowledge can be integrated with real world systems. Cross-fertilisation between engineering and biology represents the best path forward for implementation as a robust biotechnology.