Areal Biomass Productivity Research Articles

First-order estimates of the costs, input-output energy analysis, and energy returns on investment of conventional and emerging biofuels feedstocks

Here we report on a static, algebraic, spreadsheet-implemented modeling approach to estimate the costs, energy inputs and outputs, and global warming potential of biomass feedstocks. Inputs to the model included literature sourced data for: environmental factors, crop physiological-parameters such as radiation use efficiency and water use efficiency, and crop cost components. Using an energy-input-output life-cycle-assessment approach, we calculated the energy associated with each cost component, allowing an estimate of the total energy required to produce the crop and fuel alongside the energy return on investment. We did this for crop scenarios in the upper Midwest US and Far West US (for algae). Our results suggested that algae are capable of the highest areal biomass production rates of 120 MG/(ha·a), ten times greater than Maize. Algal fuel systems had the highest costs, ranging from 28 to 65 US $/GJ, compared to 17 US $/GJ for Maize ethanol. Algal fuel systems had the lowest energy returns on investment, nearly 0, compared to 25 for Switchgrass to ethanol. The carbon equivalent emissions associated with the production schemes predictions ranged from 40 (Maize) to 180 (algae PBR) CO2eq/GJnet. The promise of low cost fuel and carbon neutrality from algae is demonstrated here to be extremely challenging for fundamental reasons related to the capital-intensive nature of the cultivation system.

Biomass and lipid production from Chlorella vulgaris UTEX 26 cultivated in 2 m3 raceway ponds under semicontinuous mode during the spring season

A Chlorella vulgaris UTEX 26 semicontinuous culture was implemented in 2000 L raceways with M medium during spring season at greenhouse conditions. Areal biomass productivities between 20 and 26 g m−2 d−1 were reached on the third day. The maximal areal lipid productivity obtained was 6.1 g m−2 d−1 and an increment in the saturated fatty acids (SFA) proportion (C14–C18) was favored in comparison with the fatty acids obtained with M medium in photobioreactors of 1 L and photoperiod light:darkness 12:12 h. After the eighth day of the culture or biomass concentrations above 0.25 g L−1, the microalgal cultures were prone to contamination by ciliates and amoebae, due to the sugars excreted by C. vulgaris UTEX 26. The periodical addition of NH4HCO3 to the microalgal culture maintained the ammonium concentration between 25 and 50 mg L−1, which contributed to diminish the contamination risks by protozoa.

Microalgal biodiesel production at outdoor open and polyhouse raceway pond cultivations: A case study with Scenedesmus accuminatus using low-cost farm fertilizer medium

The present study has successfully cultivated a promising microalga Scenedesmus accuminatus at outdoor open and polyhouse raceway ponds using low-cost farm fertilizer medium. The tested microalga was cultivated in both ambient and polyhouse conditions for summer, rainy and winter seasons. Diurnal variation in temperature (26–39 °C), humidity (57–90%), solar intensity (ambient: 44–65, polyhouse: 28–41 k lux), pH of culture suspension (6.5–10.6), and dissolved oxygen (5.5–13.1) were recorded throughout the seasons. Further, of the various culture depth and impeller speed tested, S. accuminatus was found to yield high biomass of 1.2 g L−1 and 1.11 g L−1 under ambient and polyhouse conditions, respectively at 30 cm depth with 65 rpm impeller speed. Keeping this optimal culture depth and impeller speed, the tested microalga was grown in open pond and polyhouse consecutively for two years. Under polyhouse raceway pond, the areal biomass productivity during summer, rainy and winter seasons was estimated to be 10.15, 7.83, 10.38 g m−2 day−1 respectively and correspondingly, the areal lipid productivity was estimated to be 1.05, 0.75, 1.18 g m−2 day−1 respectively. On the other hand, at ambient condition, the areal lipid productivity during summer, rainy and winter seasons was 1.19, 0.42, 1.30 g m−2 day−1 respectively. Thus, annual lipid productivity of S. accuminatus grown under ambient condition was estimated to be 3.094 ton hectare−1year-1, and 3.168 ton hectare−1year-1 under polyhouse raceway pond conditions. Notably, the estimated annual biodiesel yield 2.186 and 2.135 ton hectare−1 year−1 under polyhouse and ambient conditions respectively demonstrates Scenedesmus accuminatus is a potential choice for sustainable biodiesel production.

A new dimension in algal cultivation – 3D printed structures with a range of buoyancies

The free-floating cultivation of macroalgae is a fundamental requirement for the efficient bioremediation of land-based waste streams as this cultivation mode fully utilises the water column available for production, translating to improved areal biomass productivities. To achieve the free-floating cultivation of species grown from propagules and dependent on the attachment to surface structures, we have used 3D printed structures made of polymers with negative, neutral and positive buoyancies to investigate the potential to manipulate the position in the water column for cultivation. Small wheel-shaped structures with internal protected spokes were designed, manufactured and seeded with zoids of Ulva tepida. Their settlement was quantified at different locations of the settlement structure and, although similar across polymer types, approximately 80% less zoids were on the outside of the wheel shaped structures made of polyethylene compared to protected locations 3 days post-seeding. Subsequently, all structures were maintained over 31 days as free-floating cultures under outdoor cultivation in aerated buckets and paddle wheel driven high rate algal ponds (HRAPs). Both negatively and positively buoyant polymers maintained their buoyancies with increasing algal biomass over time in the static test, while the neutrally buoyant polymer showed the highest variation and became exclusively positively buoyant after 14 days of cultivation. Productivities were generally higher and more variable in aerated buckets ranging up to 28.4 ± 1.7 g dw m−2 day−1, than in HRAPs ranging up to 18.9 ± 3.9 g dw m−2 day−1. There was no clear effect of polymer type, and consequently buoyancy, on algal productivity. Similarly, all tested polymers had maximum productivities between 12 and 22 days for cultivation in aerated buckets and 7–17 days in HRAPs. This study highlights the potential to use 3D printing to create settlement structures with a range of buoyancies for land-based cultivation.

Scale-up and large-scale production of Tetraselmis sp. CTP4 (Chlorophyta) for CO2 mitigation: from an agar plate to 100-m3 industrial photobioreactors

Industrial production of novel microalgal isolates is key to improving the current portfolio of available strains that are able to grow in large-scale production systems for different biotechnological applications, including carbon mitigation. In this context, Tetraselmis sp. CTP4 was successfully scaled up from an agar plate to 35- and 100-m3 industrial scale tubular photobioreactors (PBR). Growth was performed semi-continuously for 60 days in the autumn-winter season (17th October – 14th December). Optimisation of tubular PBR operations showed that improved productivities were obtained at a culture velocity of 0.65–1.35 m s−1 and a pH set-point for CO2 injection of 8.0. Highest volumetric (0.08 ± 0.01 g L−1 d−1) and areal (20.3 ± 3.2 g m−2 d−1) biomass productivities were attained in the 100-m3 PBR compared to those of the 35-m3 PBR (0.05 ± 0.02 g L−1 d−1 and 13.5 ± 4.3 g m−2 d−1, respectively). Lipid contents were similar in both PBRs (9–10% of ash free dry weight). CO2 sequestration was followed in the 100-m3 PBR, revealing a mean CO2 mitigation efficiency of 65% and a biomass to carbon ratio of 1.80. Tetraselmis sp. CTP4 is thus a robust candidate for industrial-scale production with promising biomass productivities and photosynthetic efficiencies up to 3.5% of total solar irradiance.

Increasing microalgal lipid productivity for conversion into biodiesel by using a non-energy consuming light guide

Mass cultivation of photosynthetic microalgae combined with mitigation of carbon dioxide (CO2) emissions from industrial off-gases to produce lipids as a biodiesel feedstock can help environmental sustainability. However, traditional open microalgae mass cultivation systems that use sunlight are typically no more than 30 cm deep due to light attenuation and self-shading by the mircroalgae and, therefore, have low CO2 uptake efficiency due to their shallow depth. To address this issue, a non-energy consuming light guide was employed to diffuse light deep into a top-lit, 120 cm deep open gas-lift cultivation system. This gas-lift system has been already shown to increase areal biomass productivity by 60%. Without any increase in supplied light energy, the light guide enhanced light penetration into the bioreactor and resulted in further increases in biomass and lipid productivities per unit area of 33% and 16%, respectively. The factors influencing light and CO2 absorption rates were investigated with a Plackett-Burman experimental design. Mathematical models for predicting biomass and lipid production as well as optimal bioreactor configurations for maximizing lipid production and minimizing production costs were then determined by applying response surface methodology. The optimum configuration of operational parameters identified by the optimization function was then verified in the gas-lift bioreactor equipped with the light guide and resulted in areal biomass productivity of 34.4 gdw/m2day and areal lipid production of 223.9 gLipid/m2.

Model-based feasibility assessment of a deep solar photobioreactor for microalgae culturing

A deep photobioreactor (PBR) based on cone-shaped light guides was conceived to improve the solar light utilization efficiency of microalgae cultures, optimizing light distribution over the culture surface and thus minimizing photoinhibition and photosaturation occurrence. A preliminary model based on local light intensities and local growth rates was developed in order to check its viability. The model was applied to a conceptual PBR unit using irradiance data of Santander (Spain). Areal biomass productivities of 15.17 and 34.57gm−2d−1 were predicted for the most unfavorable and favorable months respectively, both under monthly average cloud cover. These results are, in average, 2.72 times higher than predicted values for an open pond PBR under identical irradiance conditions. A procedure to scale-up the deep PBR in any location was developed. The procedure provides the optimal arrangement of the light guides and its operational parameters as a function of the surface incident light intensity. According to the obtained results, the novel configuration is highly efficient in land use, providing a low surface requirement solution.

Studies on the scale-up of biomass production with Scenedesmus spp. in flat-plate gas-lift photobioreactors.

Microalgae are flagged as next-generation biomass feedstock for sustainable chemicals and fuels, because they actively metabolize the climate gas CO2, do not impact food production, and are not associated with land-use change. Scaling microalgae cultivation processes from lab to pilot scale is key to assessing their economic and ecologic viability. In this work, process performances of two different Scenedesmus species were studied using a 300L flat-plate gas-lift photobioreactor system (14m2 photosynthetically active area) equipped with a customized, broad-spectrum LED illumination system. Scaling up of batch processes from laboratory scale (1.8L, 0.09m2) to the geometrically equivalent pilot scale resulted in reduced volumetric biomass productivities of up to 11% and reduced areal biomass productivities of up to 7.5% at the pilot scale. Since biofilm formation was solely detected at pilot scale, biofilm most likely impaired scalability. Nevertheless, repeated addition of nutrients (BG-11) at pilot scale resulted in a 13.5 gCDW L-1 biomass concentration within a 15day process time with S. obtusiusculus at constant incident-photon flux densities of 1400µmol photons m-2 s-1 and more than 19.5 gCDW L1 after 30 days with Scenedesmus ovalternus SAG 52.80at constant incident-photon flux densities of 750µmol photons m-2 s-1. This resulted in areal biomass productivities of 14 gCDW m-2 day-1 (S. ovalternus) and 19 gCDW m-2 day-1 (S. obtusiusculus), respectively.

Optimization of microalgae-sourced lipids production for biodiesel in a top-lit gas-lift bioreactor using response surface methodology

Microalgae bioreactors that capture industrial carbon dioxide (CO2) emissions to produce lipids for biodiesel are of significant interest. Sun-lit open raceways are generally considered the most economic method for mass cultivation, but the large physical footprint of these shallow systems can limit both industrial site availability and CO2 transfer into the culture medium. To address these issues, a deep top-lit only, gas-lift bioreactor to culture microalgae and capture CO2 was designed and investigated. The results show a three times increase in areal biomass and lipid productivities when compared to traditional raceways used in large-scale microalgae production. Operational factors exerting significant effects on areal biomass and lipid productivities were identified through Plackett-Burman experimental design as gas flow rate, feed gas CO2 content, and dispersion height. By employing response surface methodology, models to predict areal biomass and lipid productivities were derived. The resulting desirability function was then applied to obtain the optimal combination of operational parameters that maximize lipid production per unit area occupied by the bioreactor, whilst keeping biomass production low to reduce downstream processing costs. The optimum operational parameters that fulfill the requirements of the optimization function resulted in areal biomass productivity of 32.1 gdwm−2d−1 and areal lipid production of 198.4 gLipidm−2.

Open thin-layer cascade reactors for saline microalgae production evaluated in a physically simulated Mediterranean summer climate

While microalgae hold the promise for conversion of sunlight and CO2 to a wide variety of products, the economics of algae processes are still debatable. We have designed an open thin-layer cascade photobioreactor for high-cell density cultivation of saline microalgae to advance economic microalgae mass production. Pilot-scale reactors with a surface area of up to 8m2 (cultivation volume 50–140L) were constructed and evaluated using a dynamic climate simulation technology (light, air temperature and humidity) integrating natural sunlight and multi-color LED arrays for a highly realistic reproduction of the sunlight spectrum. Batch processes with Nannochloropsis salina were performed in these reactors in the physically simulated Mediterranean summer climate of Almería, Spain – an ideal location for outdoor microalgae cultivation. Two reactor variants were examined: one with a smooth but expensive rigid channel made of polyethylene sheets, and one with a more uneven but significantly less expensive channel made of pond liner. Maximal intra-day growth rates of 1.9d−1 were observed at a cell density of 1–3gL−1. The maximal cell density of 50gL−1 was obtained within 25days. These high growth rates and cell densities markedly exceed literature data. No difference in growth between the channel variants was observed. This suggests that cost-efficient large-scale thin-layer cascade reactors with inexpensive pond liner channels are feasible. The high cell density allows a reduction of harvesting cost. Optimal process conditions were identified by analyzing the batch and daily economic bioprocess metrics: At a cell density of 17gL−1, an areal biomass productivity of 25gm−2d−1 (volumetric productivity 4gL−1d−1) and a photosynthetic conversion efficiency of 4.6% were observed. The reactor design is discussed in detail to encourage further advancement of thin-layer algal cultivation technology.

Seeding filamentous Ulva tepida on free-floating surfaces: A novel cultivation method

The selection of seaweed species for the integrated cultivation in land-based aquaculture systems is primarily based on the ability to grow in free-floating cultures thereby increasing stocking densities and areal biomass productivity. We assessed a novel approach to enable the free-floating cultivation of seaweed species that are dependent on the attachment to surface structures by seeding zoids of Ulva tepida onto small surfaces which float in the water column. In this study we firstly assessed how the density of settlement surfaces (hereafter referred to as ‘bioballs’) and density of zoids influenced the settlement onto bioballs, and secondly how the stocking density of these seeded bioballs affected the biomass yield in outdoor cultivation over a 35day period. Settlement was not affected by the density of bioballs with zoids settling evenly across bioball treatments. The number of zoids that settled successfully increased with increasing density. However, both seeding factors (density of bioballs and zoids) had a minimal effect on growth rates, yield of biomass per bioball and total biomass harvested, which were primarily affected by stocking density. Low stocking density generally resulted in higher growth rates and yield of biomass per bioball, although the total yield was lower compared to higher stocking densities. Overall, growth rates decreased over time for all stocking densities with a sharp decrease from 27days of outdoor cultivation and onwards due to reproductive events. Our study demonstrates that the rate of biomass production of U. tepida is primarily driven by the stocking density of seeded bioballs, and underlines the importance of short cultivation cycles with harvest prior to reproduction. This novel cultivation method enables the free-floating cultivation of species that normally depend on attachment to fixed surfaces and thereby expands the range of seaweed species for land-based cultivation.

Technical evaluation of photobioreactors for microalgae cultivation

This paper undertakes the description and assessment of various solutions applied for the design of photobioreactors as the type of apparatus, which can provide high output of green algae biomass. The design of such apparatus plays an important role in the context of the concurrent fulfillment of ecological and economic requirements, which are necessary to conduct an efficient and effective technology using cheap and easily accessible resources to produce different goods. Nowadays, algae is seen as one of the most promising sustainable way to produce energy in the future (biofuels, electricity, thermal energy) but technologies of biomass production and processing are still under development particularly to increase biomass and energy output. The cultivation costs in closed systems are still high, limiting their commercial applications to high-valued compounds but they can be reduced by efficient bioreactor designs, which are able to achieve high areal biomass productivities. This paper focuses on the advantages and drawbacks associated with the application of the particular types of bioreactors in algae production, description of their operation parameters and area for practical application, pointing of the constructions (tubular, flat panel, bubble column) that can contribute to improvement the profitability of large-scale production.

Process evaluation of energy requirements for feed production using dairy wastewater for algal cultivation: Theoretical approach

Dairy production is an intensive agricultural practice that elicits many environmental concerns including noxious emissions, potential health risks to nearby human communities and eutrophication of aquatic ecosystems. These environmental impacts can be reduced by using the emissions and dissolved nutrients including nitrogen available in dairy wastewaters to produce algal biomass, which can be recycled for animal feed with higher protein content compared to alfalfa. However, energy demand is a major criterion for selecting an algal biomass cultivation system. Traditionally algae have been cultivated in raceways to minimize energy input, but raceways tend to have lower areal biomass productivity compared to photobioreactors. However, higher productivity may be achievable through growth in innovative designs utilizing gravity to provide reduced cultivation depths and temperature control strategies. The feasibility of animal feed production in raceways is compared to gravity fed production systems for evaluating production cost and direct energy demand. Agricultural style gravity fed production systems have an estimated cultivation energy consumption of 25Whm−2d−1 compared to raceways at 15.4Whm−2d−1. However, these systems can significantly increase areal biomass productivities reducing the energy required for biomass production from 2.01kWhkg−1 to 1.41kWhkg−1. Total cost of energy for biomass cultivation and harvesting, when sedimentation is combined with centrifugation to achieve 25% solid content, is estimated to be $176 and $256 per mton in gravity fed systems and raceways, respectively. This can be compared to $334 and $1407 per mton of biomass when only using centrifugation for processing in gravity fed systems and raceways, respectively.

Improved mixing efficiency and biomass productivity of Ettlia sp. in co-cultivation system with loaches

Maintaining a homogeneous cell suspension has been identified as a key parameter for higher biomass productivity of microalgae cultivation systems. This study proposes an alternative mixing method where microalgae are co-cultivated with loaches to improve the mixing efficiency and microalgal biomass productivity. The highly settleable microalga, Ettlia sp. showed a stable temporal cell concentration at the specified sampling sites when co-cultivated with 10 loaches, whereas it sank to the bottom of a 20L rectangular vessel (20cm deep) within 12h in a water-pump-assisted mixing system. As a consequence of the better mixing efficiency in the co-cultivation system, biomass and lipid productivities of co-cultivation system were 66.9±8.3mg/L/day and 14.7±1.0mg/L/day, respectively, and were about 57.6% and 32.4% higher than the results from the water-pump-assisted mixing system. In addition, when the co-cultivation systems were cultured under various depth conditions (10, 16, 20, 40, 60, 80cm deep) to determine the maximum areal biomass and lipid productivity, the system showed the highest biomass productivity with a depth of around 16–20cm, while the lipid content and productivity were sharply lowered at this depth. The introduction of loaches also altered the microbial community structure of the co-cultivation systems. Therefore, these results suggest that the co-cultivation of loaches can be used as an efficient mixing method, while also introducing new ecological players, the loaches themselves and associated microorganisms, which can improve the sustainability of microalgae cultivation systems.

Growth model for raceway pond cultivation of Desmodesmus sp. MCC34 isolated from a local water body

Biofuel production by microalgae has the advantage of higher biomass productivity over land crops. The selection of potential microalgae depends on the growth in outdoor mass cultivation during different seasons, which can be predicted by a mathematical model. Here, freshwater green algae were isolated from a local water body in Pilani, Rajasthan, India (geographical coordinates: 28°22′N 75°36′E) and characterized by microscopy and ribosomal RNA analysis. The strain was submitted to the Indian Agricultural Research Institute's microbial culture collection (IARI, India) and identified as Desmodesmus sp. MCC34. This strain, along with a fresh water green algae (Chlorella minutissima), two marine green algae species (Dunaliella salina and Dunaliella tertiolecta) and two nitrogen fixing cyanobacteria (Nostoc muscorum and Anabaena doliolum), were screened for lipid productivity and growth kinetics under culture room and raceway pond conditions. Desmodesmus sp. MCC34 showed the highest specific growth rate (0.26 day−1), biomass production (1.9 g L−1) and lipid productivity (103 mg L−1 day−1). The optimal temperature and saturating light intensity for maximal growth of Desmodesmus sp. MCC34 were 35 °C and 75 μmol m−2 s−1 with molar extinction coefficient of 0.22 m2 g−1, respectively. Desmodesmus sp. MCC34 was then subjected to outdoor cultivation in a 20‐m long raceway pond for 18 days during March and November 2013. The areal biomass productivity and volumetric biomass productivity were 13946.23 kg ha−1 year−1 and 56.94 mg L− 1day−1 during the month of March, decreasing to 6262.28 kg ha−1 year−1 and 25.57 mg L− 1day−1 during the month of November. A mathematical model was constructed to explain the relationship between biomass production and growth parameters such as temperature, light intensity and nutrient concentration. The productivity values predicted with the proposed model correspond well with the experimental data, suggesting the validity of the model.

Environmental sustainability analysis of a protein-rich livestock feed ingredient in The Netherlands: Microalgae production versus soybean import

Sustainability in terms of the natural resource demands of protein-rich algal meal for livestock feed applications was examined. In The Netherlands, an integrated microalgal biorefinery delivered the following products: digestate, electricity, heat available for a nearby bio-ethanol facility and algae oil and meal. Pilot scale (500m2) data were used to conduct an exergy analysis (EA), which revealed the process inefficiencies of energy-intensive processes such as drying (44.01%) and inoculum production (54.98%). An attributional life cycle assessment (LCA) using system expansion exposed the high contribution of biomass digestion to the total resource footprint of the biorefinery (72.74%) due to the high daily demand for biomass and electricity consumption of the dosage system. In this study, algal meal was compared with soybean meal, which is the most commonly used protein-rich animal feed ingredient; it is produced in Brazil and transported to The Netherlands. Because algae production is a young, small-scale technology, the resource footprint of the large-scale soy meal production was a factor of 102 lower, mainly as a result of the energy-intensive algae cultivation stages. A sensitivity analysis showed that the resource footprint of algal meal production could be comparable with soy meal when, overall, the areal biomass productivity increases, electricity production is based on more renewable sources (wind) and the energy consumption from mixing and blowing flue gases into the ponds decreases.

Sustainable production of toxin free marine microalgae biomass as fish feed in large scale open system in the Qatari desert

Mass cultivation of microalgae biomass for feed should be cost effective and toxin free. Evaporation loss in Qatar can be as high as 2cm/d. Hence, production of marine microalgae biomass in Qatar would also require mitigating water loss as there was only very limited groundwater reserve. To address these issues, a combination of four growth conditions were applied to a 25,000L raceway pond: locally isolated microalgae strain was selected which could grow in elevated salinity; strain that did not require silica and vitamins; volume of the culture would increase over time keeping denser inoculum in the beginning, and evaporation water loss would be balanced by adding seawater only. A local saline tolerant Nannochloropsis sp. was selected which did not require silica and vitamins. When the above conditions were combined in the pond, average areal biomass productivities reached 20.37g/m2/d, and the culture was not contaminated by any toxic microalgae.

Attached cultivation for improving the biomass productivity of Spirulina platensis

To improve cultivation efficiency for microalgae Spirulina platensis is related to increase its potential use as food source and as an effective alternative for CO2 fixation. The present work attempted to establish a technique, namely attached cultivation, for S. platensis. Laboratory experiments were made firstly to investigate optimal conditions on attached cultivation. The optimal conditions were found: 25gm−2 for initial inoculum density using electrostatic flocking cloth as substrata, light intensity lower than 200μmolm−2s−1, CO2 enriched air flow (0.5%) at a superficial aeration rate of 0.0056ms−1 in a NaHCO3-free Zarrouk medium. An outdoor attached cultivation bench-scale bioreactor was built and a 10d culture of S. platensis was carried out with daily harvesting. A high footprint areal biomass productivity of 60gm−2d−1 was obtained. The nutrition of S. platensis with attached cultivation is identical to that with conventional liquid cultivation.

Antenna size reduction as a strategy to increase biomass productivity: a great potential not yet realized

A major limitation in achieving high photosynthetic efficiency in microalgae mass cultures is the fact that the intensity of direct sunlight greatly exceeds the photosynthetic capacity of the cells. Due to the high pigment content of algal cells, the light absorption rate surpasses the much slower conversion rate to biochemical energy. The excess of light energy is predominantly dissipated as heat, decreasing the light use efficiency of the culture. Algae with a truncated antenna system could substantially increase biomass productivity of mass cultures because oversaturation of the photosystems and concomitant dissipation of light energy are minimized. In this study, we measured the areal biomass productivity of wild-type strain cultures and four promising antenna size mutant cultures of Chlamydomonas reinhardtii. This was performed under simulated mass culture conditions. The strains were cultivated in turbidostat controlled lab-scale panel photobioreactors at an incident light intensity of 1500 μmol photons m−2 s−1. The mutant cultures did not exhibit the expected higher productivity. The greatest mutant culture productivity values were approximate to those of the wild-type productivity of 1.9 g m−2 h−1. The high sensitivity to abrupt light shifts indicated that the mutant cultures experienced reduced fitness and higher susceptibility to photodamage. This can possibly be explained by impaired photoprotection mechanisms induced by the antenna complex alterations, or by unintended side effects of the genetic modifications. Still, if these effects could be eliminated, the principle of antenna size reduction is a promising strategy to increase productivity. Selection criteria for the future creation of antenna size mutants should, therefore, include tolerance to high light conditions.

Characterization of endolithic cyanobacterial strain, Leptolyngbya sp. ISTCY101, for prospective recycling of CO₂ and biodiesel production.

The present investigation evaluates the potential of an endolithic cyanobacterium isolated from marble rock to utilize sodium bicarbonate (NaHCO₃) as carbon source for prospective recycling of CO₂ into biodiesel. Microalgae thriving on marble were cultured and subjected to increasing NaHCO₃ concentration. The most competent isolate was identified and characterized in terms of growth, lipid content and fatty acid profile. A semicontinuous mesh incubator was designed for biofilm development. Isolate ISTCY101 was identified as Leptolyngbya sp. by 16S rRNA sequencing. Leptolyngbya ISTCY101 efficiently used BG-11 (50 mM NaHCO₃) and artificial seawater medium (25 gL(-1) NaCl) with biomass productivity 78.9 and 75.74 mg L(-1)d(-1), respectively. Maximum areal biomass productivity of 2.01 gm(-2)d(-1) was recorded in the mesh incubator, with complete exclusion of centrifugation for harvesting. Lipid content varied from 16% to 21%, consisting predominantly of C16:0, C16:1, C18:0, C18:1 fatty acids (>60%) making promising feedstock for biodiesel production.