Life-cycle analysis on biodiesel production from microalgae: Water footprint and nutrients balance

This research examines the life-cycle water and nutrients usage of microalgae-based biodiesel production. The influence of water types, operation with and without recycling, algal species, geographic distributions are analyzed. The results confirm the competitiveness of microalgae-based biofuels and highlight the necessity of recycling harvested water and using sea/wastewater as water source. To generate 1 kg biodiesel, 3726 kg water, 0.33 kg nitrogen, and 0.71 kg phosphate are required if freshwater used without recycling. Recycling harvest water reduces the water and nutrients usage by 84% and 55%. Using sea/wastewater decreases 90% water requirement and eliminates the need of all the nutrients except phosphate. The variation in microalgae species and geographic distribution are analyzed to reflect microalgae biofuel development in the US. The impacts of current federal and state renewable energy programs are also discussed to suggest suitable microalgae biofuel implementation pathways and identify potential bottlenecks.     

Modeling anaerobic digestion of microalgae using ADM1

The coupling between a microalgal pond and an anaerobic digester is a promising alternative for sustainable energy production by transforming carbon dioxide into methane using solar energy. In this paper, we demonstrate the ability of the original ADM1 model and a modified version (based on Contois kinetics for the hydrolysis steps) to represent microalgae anaerobic digestion. Simulations were compared to experimental data of an anaerobic digester fed with Chlorella vulgaris. The modified ADM1 fits adequately the data for the considered 140 day experiment encompassing a variety of influent load and flow rates. It turns out to be a reliable predictive tool for optimising the coupling of microalgae with anaerobic digestion processes.     

Two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production

A two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production was studied, wherein high density heterotrophic cultures of Chlorellasorokiniana serve as seed for subsequent phototrophic growth. The data showed growth rate, cell density and productivity of heterotrophic C.sorokiniana were 3.0, 3.3 and 7.4 times higher than phototrophic counterpart, respectively. Hetero- and phototrophic algal seeds had similar biomass/lipid production and fatty acid profile when inoculated into phototrophic culture system. To expand the application, food waste and wastewater were tested as feedstock for heterotrophic growth, and supported cell growth successfully. These results demonstrated the advantages of using heterotrophic algae cells as seeds for open algae culture system. Additionally, high inoculation rate of heterotrophic algal seed can be utilized as an effective method for contamination control. This two-stage heterotrophic phototrophic process is promising to provide a more efficient way for large scale production of algal biomass and biofuels.     

Differential regulation of fatty acid biosynthesis in two Chlorella species in response to nitrate treatments and the potential of binary blending microalgae oils for biodiesel application

This study was undertaken to investigate the effects of different nitrate concentrations in culture medium on oil content and fatty acid composition of Chlorella vulgaris (UMT-M1) and Chlorella sorokiniana (KS-MB2). Results showed that both species produced significant higher (p<0.05) oil content at nitrate ranging from 0.18 to 0.66 mM with C. vulgaris produced 10.20-11.34% dw, while C. sorokiniana produced 15.44-17.32% dw. The major fatty acids detected include C16:0, C18:0, C18:1, C18:2 and C18:3. It is interesting to note that both species displayed differentially regulated fatty acid accumulation patterns in response to nitrate treatments at early stationary growth phase. Their potential use for biodiesel application could be enhanced by exploring the concept of binary blending of the two microalgae oils using developed mathematical equations to calculate the oil mass blending ratio and simultaneously estimated the weight percentage (wt.%) of desirable fatty acid compositions.     

Microwave-assisted pyrolysis of microalgae for biofuel production

The pyrolysis of Chlorella sp. was carried out in a microwave oven with char as microwave reception enhancer. The results indicated that the maximum bio-oil yield of 28.6% was achieved under the microwave power of 750 W. The bio-oil properties were characterized with elemental, GC-MS, GPC, FTIR, and thermogravimetric analysis. The algal bio-oil had a density of 0.98 kg/L, a viscosity of 61.2 cSt, and a higher heating value (HHV) of 30.7 MJ/kg. The GC-MS results showed that the bio-oils were mainly composed of aliphatic hydrocarbons, aromatic hydrocarbons, phenols, long chain fatty acids and nitrogenated compounds, among which aliphatic and aromatic hydrocarbons (account for 22.18% of the total GC-MS spectrum area) are highly desirable compounds as those in crude oil, gasoline and diesel. The results in this study indicate that fast growing algae are a promising source of feedstock for advanced renewable fuel production via microwave-assisted pyrolysis (MAP).     

Biodegradation of p-nitrophenol by microalgae

A study was made on the use of a mixed microalgal consortium to degrade p-nitrophenol. The consortium was obtained from a microbial community in a waste container fed with the remains and by-products of medium culture containing substituted aromatic pollutants (nitrophenols, chlorophenols, fluorobenzene). After selective enrichment with p-nitrophenol (p-NP), followed by an antibiotic treatment, an axenic microalgal consortium was recovered, which was able to degrade p-nitrophenol. At a concentration of 50 mg L^–1, total degradation occurred within 5 days. Two species, Chlorella vulgaris var. vulgaris f. minuscula and Coenochloris pyrenoidosa, were isolated from the microalgal consortium. The species were able to accomplish p-NP biodegradation when cultured separately, although Coenochloris pyrenoidosa was more efficient, achieving the same degradation rate as the original axenic microalgal consortium. When Coenochloris pyrenoidosa was associated with Chlorella vulgaris in a 3:1 ratio, complete removal of the nitro-aromatic compound occurred within three days. This is apparently the first report on the degradation of a nitro-aromatic compound by microalgae.     

Life cycle assessment of biogas infrastructure options on a regional scale

A life cycle assessment has been completed of potential biogas infrastructures on a regional scale. Centralised and distributed infrastructures were considered along with biogas end uses of Combined Heat and Power (CHP) and injection to the gas grid for either transport fuel or domestic heating end uses. Damage orientated (endpoint) life cycle impact assessment method identified that CHP with 80% heat utilisation had the least environmental impact, followed by transport fuel use. Utilisation for domestic heating purposes via the gas grid was found to perform less well. A 32% difference in transportation requirement between the centralised and distributed infrastructures was found to have a relatively small effect on the overall environmental impact. Global warming impacts were significantly affected by changes in methane emissions at upgrading stage, highlighting the importance of minimising operational losses.     

Optimization of the biomass production of oil algae Chlorella minutissima UTEX2341

High production cost is a major obstacle to the extensive use of microalgae biodiesel. To cut the cost and achieve higher biomass productivity, Chlorella minutissima UTEX2341 was cultured under photoheterotrophic conditions. With the carbon, nitrogen and phosphorus concentration of 26.37, 2.61 and 0.03 g L?1 d?1 respectively, a maximum biomass productivity of 1.78 g L?1 d?1 was obtained, which was 59 times more than that cultured under autotrophic condition. The lipid productivity reached 0.29 g L?1 d?1, which was 11.9 times higher than the highest value reported by Oh et al. (2010). The conversion rate of microalgae lipids to FAME was found to be elevated from 45.65% to 62.97% and the FAME productivity increased from 1.16 to 180.68 mg L?1 d?1 after the optimization. 94% of the fatty acid of C. minutissima UTEX2341 was found to be composed of palmitic, oleic, linoleic and γ linoleic and the unsaturated fatty acids were the main parts (79.42%).     

Studies on the incorporation of CO2 into starch by Chlorella vulgaris

Chlorella vulgaris was grown photosynthetically in batch culture under nitrogen sufficiency or nitrogen limitation. The starch content of the cells was measured as the amount of glucose released by enzymic hydrolysis of partially purified starch. Nitrogen sufficient algae contained approximately 20% of their dry weight as starch, whereas in nitrogen limited cells starch comprised up to 55% of the cellular dry weight. Starch production was pH dependent; optimal production of starch was achieved between pH 7.5 and 8.0. Optimal growth of C. vulgaris occurred at pH 7.0. Carbon yield experiments showed that for every gram of carbon consumed 0.5 g of starch (glucose) could be recovered. author for correspondence     

Techno-economical study of ethanol and biogas from spruce wood by NMMO-pretreatment and rapid fermentation and digestion

Given that N-methylmorpholine-N-oxide (NMMO) is a promising alternative for the pretreatment of lignocelluloses, a novel process for ethanol and biogas production from wood was developed. The solvent, NMMO, is concentrated by multistage evaporation, and the wood is pretreated with the concentrated NMMO. Thereafter, ethanol is produced by the non-isothermal simultaneous saccharification and fermentation (NSSF) method, which is a rapid and efficient process. The wastewater is treated by upflow anaerobic sludge blanket (UASB) digester for rapid production of biogas. The process was simulated by Aspen plus®. Using mechanical vapor recompression for evaporators in the pretreatment and multi-pressure distillation columns, the energy requirements for the process were minimized. The economical feasibility of the developed biorefinery for five different plant capacities was studied by Aspen Icarus Process Evaluator. The base case was designed to utilize 200,000 tons of spruce wood per year and required M€ 58.3 as the total capital investment, while the production cost of ethanol is calculated to be €/l 0.44.     

Vertical tubular photobioreactor for semicontinuous culture of Cyanobium sp

We evaluated the kinetic culture characteristics of the microalgae Cyanobium sp. grown in vertical tubular photobioreactor in semicontinuous mode. Cultivation was carried out in vertical tubular photobioreactor for 2 L, in 57 d, at 30 °C, 3200 Lux, and 12 h light/dark photoperiod. The maximum specific growth rate was found as 0.127 d⁻¹, when the culture had blend concentration of 1.0 g L⁻¹, renewal rate of 50%, and sodium bicarbonate concentration of 1.0 g L⁻¹. The maximum values of productivity (0.071 g L⁻¹ d⁻¹) and number of cycles (10) were observed in blend concentration of 1.0 g L⁻¹, renewal rate of 30%, and bicarbonate concentration of 1.0 g L⁻¹. The results showed the potential of semicontinuous cultivation of Cyanobium sp. in closed tubular bioreactor, combining factors such as blend concentration, renewal rate, and sodium bicarbonate concentration.     

Removal of inorganic ions from wastewaters by immobilized microalgae

Anabaena doliolum and Chlorella vulgaris immobilized on chitosan were more efficient at removing NO₃ ^–, NO₂ ^p–, PO₄ ^3– and CR₂O₇ ^2– from wastewaters than cells immobilized on agar, alginate, carrageenan or even free cells. Carrageenan-immobilized cells, however, were better at removing NH₄ ⁺ and Ni²⁺. The PO₄ ^3– uptake capacity was significantly increased in cells starved of PO₄ ^3– for 24 h. Agar-immobilized cells, though having good metal and nutrient uptake efficiency, had only a slow growth rate. Chitosan is recommended as an algal support for wastewater detoxification.The authors are with the Laboratory of Algal Biology, Department of Botany, Banaras Hindu University, Varanasi-221005, India     

Assessment of carotenoid production by Dunaliella salina in different culture systems and operation regimes

The effect of operation regime and culture system on carotenoid productivity by the halotolerant alga Dunaliella salina has been analyzed. Operation strategies tested included batch and semi continuous regime, as well as a two-stage approach run simultaneously in both, open tanks and closed reactor. The best results were obtained with the closed tubular photobioreactor. The highest carotenoid production (328.8 mg carotenoid l⁻¹ culture per month) was achieved with this culture system operated following the two-stage strategy. Also, closed tubular photobioreactor provided the highest carotenoid contents (10% of dry weight) in Dunaliella biomass and β-carotene abundance (90% of total carotenoids) as well as the highest 9-cis to all-trans β-carotene isomer ratio (1.5 at sunrise).     

Comments on 'Anaerobic digestion of microalgae as a necessary step to make microalgal biodiesel sustainable'

A recent review paper considers the potential of algal biomass as a source of liquid and gaseous biofuels, but there are a number of issues concerning the results and conclusions presented. These include the biomass energy values, which in some cases are unusually high; and the apparent production of more energy from processed biomass than is present in the original material. The main causes for these discrepancies include the choice of empirical formula for protein; confusion between values calculated on a total or volatile solids basis; and the lack of a mass balance approach. The choice of protein formula also affects predicted concentrations of ammonia in the digester. These and other minor errors contribute to some potentially misleading conclusions which could affect subsequent interpretations of the overall process feasibility.     

起始生物量比对3种海洋微藻种间竞争的影响

为深入了解饵料微藻与赤潮微藻间的种间竞争关系,通过微藻共培养的方法,研究了起始生物量比(1:4、1:1和4:1)对3种海洋微藻(塔玛亚历山大藻、蛋白核小球藻和湛江等鞭金藻)两两之间种间竞争的影响,并对其作用机制进行了探讨。结果表明:①3种海洋微藻表现出种间竞争的相互抑制效应;②在与塔玛亚历山大藻(简称A)的种间竞争中,蛋白核小球藻(简称C)和湛江等鞭金藻(简称I)均在竞争中占优势,蛋白核小球藻随自身起始生物量比的提高,其竞争优势越加明显,湛江等鞭金藻在A:I=1:1时竞争优势最为明显;在蛋白核小球藻和湛江等鞭金藻的种间竞争中,当C:I=1:4时,湛江等鞭金藻在竞争中占优势,C:I=1:1时,初期湛江等鞭金藻占竞争优势,随蛋白核小球藻的迅速生长,后期蛋白核小球藻占竞争优势,C:I=4:1时,蛋白核小球藻占绝对竞争优势;③由种间竞争抑制参数比较得出:3种微藻的种间竞争强弱依次为蛋白核小球藻>湛江等鞭金藻>塔玛亚历山大藻。蛋白核小球藻和湛江等鞭金藻在起始比例C:I=1:1时,可共培养利用,在海产经济动物育苗中可对其进行适时采收投喂;两种饵料藻对塔玛亚历山大藻具有明显的抑制作用,可为开发利用饵料藻进行赤潮生物防控提供一定的科学依据。     

Anaerobic digestion of microalgae as a necessary step to make microalgal biodiesel sustainable

The potential of microalgae as a source of biofuels and as a technological solution for CO₂ fixation is subject to intense academic and industrial research. In the perspective of setting up massive cultures, the management of large quantities of residual biomass and the high amounts of fertilizers must be considered. Anaerobic digestion is a key process that can solve this waste issue as well as the economical and energetic balance of such a promising technology. Indeed, the conversion of algal biomass after lipid extraction into methane is a process that can recover more energy than the energy from the cell lipids. Three main bottlenecks are identified to digest microalgae. First, the biodegradability of microalgae can be low depending on both the biochemical composition and the nature of the cell wall. Then, the high cellular protein content results in ammonia release which can lead to potential toxicity. Finally, the presence of sodium for marine species can also affect the digester performance. Physico-chemical pretreatment, co-digestion, or control of gross composition are strategies that can significantly and efficiently increase the conversion yield of the algal organic matter into methane. When the cell lipid content does not exceed 40%, anaerobic digestion of the whole biomass appears to be the optimal strategy on an energy balance basis, for the energetic recovery of cell biomass. Lastly, the ability of these CO₂ consuming microalgae to purify biogas and concentrate methane is discussed.     

Using chlorophyll fluorescence to monitor yields of microalgal production

A monitoring system for microalgal production was developed over a 12:12-h light:dark cycle at a steady state of growth to test the feasibility of estimating carbon production using the fluorescence method. An empirical linear relationship between the electron transport rate, based on the fluorescence method, and carbon assimilation, based on the conventional carbon method, was successfully obtained. The results demonstrate the relevance of the electron transport rate in determining carbon production of microalgae under steady-state growth conditions.