Areal Biomass Productivity Research Articles

Potential of microalgae as a sustainable feed ingredient for aquaculture

An increase in fish consumption, combined with a decrease in wild fish harvest, is driving the aquaculture industry at rapid pace. Today, farmed seafood accounts for about half of all global seafood demand for human consumption. As the aquaculture industry continues to grow, so does the market for aquafeed. Currently, some of the feed ingredients are coming from low-value forage fishes (fish meal) and terrestrial plants. The production of fish meal can’t be increased as it would affect the sustainability and ecosystem of the ocean. Similarly, increasing the production of terrestrial plant-based feed leads to deforestation and increased freshwater use. Hence, alternative and environmentally sustainable sources of feed ingredients need to be developed. Microalgae biomasses represent potential feed source ingredients as the cell metabolites of these microorganisms contain a blend of essential amino acids, healthy triglycerides as fat, vitamins, and pigments. In addition to serving as bulk ingredient in aquafeed, their unique array of bioactive compounds can increase the survivability of farmed species, improve coloration and quality of fillet. Microalgae has the highest areal biomass productivities among photosynthetic organisms, including fodder crops, and thus has a high commercial potential. Also, microalgal production has a low water and arable-land footprint, making microalgal-based feed environmentally sustainable. This review paper will explore the potential of producing microalgae biomass as an ingredient of aquaculture feed.

A Review of Energy Consumption in the Acquisition of Bio-Feedstock for Microalgae Biofuel Production

Microalgae biofuel is expected to be an ideal alternative to fossil fuels to mitigate the effects of climate change and the energy crisis. However, the production process of microalgae biofuel is sometimes considered to be energy intensive and uneconomical, which limits its large-scale production. Several cultivation systems are used to acquire feedstock for microalgal biofuels production. The energy consumption of different cultivation systems is different, and the concentration of culture medium (microalgae cells contained in the unit volume of medium) and other properties of microalgae vary with the culture methods, which affects the energy consumption of subsequent processes. This review compared the energy consumption of different cultivation systems, including the open pond system, four types of closed photobioreactor (PBR) systems, and the hybrid cultivation system, and the energy consumption of the subsequent harvesting process. The biomass concentration and areal biomass production of every cultivation system were also analyzed. The results show that the flat-panel PBRs and the column PBRs are both preferred for large-scale biofuel production for high biomass productivity.

Development and validation of a screening system for characterizing and modeling biomass production from cyanobacteria and microalgae: Application to Arthrospira platensis and Haematococcus pluvialis

A miniaturized, small-scale photobioreactor (PBR) known as EOSS2-PBR (Efficient Overproducing Screening System photobioreactor) has been developed to characterize microalgal growth under controlled conditions. As with similar systems, EOSS2-PBR allows the screening of either culture conditions or species performance, but it is also specially designed to provide high levels of light absorption control conditions in the culture volume.First, an experimental characterization was carried on to (i) determine operating conditions to adjust optimal parameters controlling EOSS2-PBR performance, such as thermal behavior of PBR, and (ii) ensure that no limitation other than light occurred to control the system and assure high reliable productivities.EOSS2-PBR performance was then characterized by Arthrospira platensis and Haematococcus pluvialis cultures. By accurately relating growth to light transfer conditions, this facilitates the setting of kinetic growth models, which is illustrated in this work for the cyanobacterium Arthrospira platensis. Besides, continuous cultures of Haematococcus pluvialis were run in both EOSS2-PBR and 1L Airlift flat-panel PBR under the same culture conditions to confirm reliability in the determination of areal biomass productivity. Similar results were obtained in the two PBRs with a variance of less than 5%.

Reducing self-shading effects in Botryococcus braunii cultures: effect of Mg2+ deficiency on optical and biochemical properties, photosynthesis and lipidomic profile

Microalgae biomass exploitation as a carbon–neutral energy source is currently limited by several factors, productivity being one of the most relevant. Due to the high absorption properties of light-harvesting antenna, photosynthetic cells tend to capture an excessive amount of energy that cannot be entirely channeled through the electron transfer chain that ends up dissipated as heat and fluorescence, reducing the overall light use efficiency. Aiming to minimize this hurdle, in this work we studied the effect of decreasing concentrations of Magnesium (Mg2+) on the chlorophyll a content, photosynthetic performance, biomass and lipid production of autotrophic cultures of Botryococcus braunii LB 572. We also performed, for the first time, a comparative lipidomic analysis to identify the influence of limited Mg2+ supply on the lipid profile of this algae. The results indicated that a level of 0.0037 g L−1 MgSO4 caused a significant decline on chlorophyll a content with a concomitant 2.3-fold reduction in the biomass absorption coefficient. In addition, the Mg2+ limitation caused a decrease in the total carbohydrate content and triggered lipid accumulation, achieving levels of up to 53% DCW, whereas the biomass productivity remained similar for all tested conditions. The lipidome analysis revealed that the lowest Mg2+ concentrations also caused a differential lipid profile distribution, with an enrichment of neutral lipids and an increase of structural lipids. In that sense, we showed that Mg2+ limitation represents an alternative optimization approach that not only enhances accumulation of neutral lipids in B. braunii cells but also may potentially lead to a better areal biomass productivity due to the reduction in the cellular light absorption properties of the cells.

Impact of Dropwise Condensation on the Biomass Production Rate in Covered Raceway Ponds

This study investigates the effect of condensed water droplets on the areal biomass productivity of outdoor culture systems with a free surface, protected by a transparent window or cover to prevent contamination and to control the growth conditions. Under solar radiation, evaporation from the culture causes droplets to condense on the interior surface of the cover. To quantify the effect of droplets on the system’s performance, the bidirectional transmittance of a droplet-covered window was predicted using the Monte Carlo ray-tracing method. It was combined with a growth kinetics model of Chlorella vulgaris to predict the temporal evolution of the biomass concentration on 21 June and 23 September in Los Angeles, CA. A droplet contact angle of 30∘ or 90∘ and a surface area coverage of 50% or 90% were considered. Light scattering by the condensed droplets changed the direction of the incident sunlight while reducing the amount of light reaching the culture by up to 37%. The combined effect decreased the daily areal biomass productivity with increasing droplet contact angle and surface area coverage by as much as 18%. Furthermore, the areal biomass productivity of the system was found to scale with the ratio X0/a of the initial biomass concentration X0 and the specific illuminated area a, as previously established for different photobioreactor geometries, but even in the presence of droplets. Finally, for a given day of the year, the optical thickness of the culture that yielded the maximum productivity was independent of the window condition. Thus, the design and operation of such a system should focus on maintaining a small droplet contact angle and surface area coverage and an optimum optical thickness to maximize productivity.

Pilot outdoor cultivation of an extreme alkalihalophilic Trebouxiophyte in a floating photobioreactor using bicarbonate as carbon source

As an alternative carbon supply approach in the microalgae cultivation process, bicarbonate shows many advantages over the conventional method of CO2 sparging and may have great applicability in the future. However, the optimal bicarbonate concentrations for high biomass productivity and carbon utilization efficiency (CUE) are usually different, and a method to simultaneously achieve both of them is lacking. In this study, the CUE and biomass productivity of an isolated alkalihalophilic Trebouxiophyte in bicarbonate-based cultivation condition was investigated. The results showed that CUE decreased as the bicarbonate concentration increased, where the highest CUE of 96.7 ± 0.25% was achieved in a culture with 100 mmol L−1 bicarbonate, while the highest biomass density of 1.40 ± 0.01 g L−1 was produced in a 300 mmol L−1 bicarbonate culture. The bicarbonate concentration of 300 mmol L−1 was selected for a balance between CUE and biomass productivity. Under this concentration, the Trebouxiophyte cultured at high light intensity had higher CUE (46.01 ± 0.65%) and biomass productivity (0.80 g L−1 d−1) than those with 2% CO2. The outdoor cultivation in the floating photobioreactor produced a higher biomass concentration (0.603 g L−1), highest areal biomass productivity (10.1 g m−2 d−1), and CUE (22.61 ± 0.03%) than those in an open pond, which was 0.377 ± 0.01 g L−1, 5.36 g m−2 d−1 and 11.65 ± 0.01%. These results indicated that Trebouxiophyte can be efficiently produced with bicarbonate as the sole carbon source, and provided a good example to select a balanced bicarbonate concentration to simultaneously achieve high biomass productivity and CUE.

Semi-continuous removal of nutrients and biomass production from domestic wastewater in raceway reactors using Chlorella variabilis TH03-bacteria consortia

Abstract Production of algae biomass from wastewaters have been considered as an economical strategy for feasible commercialization of microalgae industry. Technically, large scale cultivation of microalgae in wastewaters should be conducted in semi-continuous and/or continuous modes, in which stable health of algal cultures of previous generations for the use of later generations needs to be ensured. In this regards, this study has investigated stability of growth and pollutant removal capability of Chlorella variabilis TH03-bacteria consortia using domestic wastewater as the sole of nutrient source in raceway ponds. Experiments were performed in semi-continuous mode with the aim of recovering valuable nutrients including carbon, nitrogen and phosphorous from the waste stream to algal biomass. Data revealed that prior domestication of C. variabilis TH03 in unsterilized domestic wastewaters established seed cultures of C. variabilis TH03–bacteria consortia, which enabled to grow effectively in new wastewaters under highly variable conditions. Moreover, once nutrient levels dropped below those required by the national technical regulation on domestic wastewater QCVN 14 : 2008/BTNMT, the replacement of 80% volume of the algal–bacteria culture with new wastewater media was recommended to ensure both culture stability as well as high pollutant treatment capacity of the raceway systems. Under the optimal replacement, biomass concentration and areal biomass productivity of 1.67–1.85 g/L and 11.1–15.3 g/m2 day, respectively, were steadily achieved over 148 days of the outdoor cultivations. Removal efficiencies of nutrients in the form of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorous (TP) removed by the C. variabilis TH03-bacteria consortia in the reactor systems were determined as 64.7–90.7, 85.1–96.8 and 99.7%–100%, respectively. The obtained results are useful for further optimization including design and manage C. variabilis TH03-bacteria consortia based continuous processes in larger scales for the production of high volume and low price biomass, helping to obtain returns from treatment of the waste stream, which is currently considered as a major source of water pollution in Vietnam.

Application of in vitro protein solubility for selection of microalgae biomass as protein ingredient in animal and aquafeed

Microalgae when grown under certain conditions can be rich sources of protein and can complement conventional protein sources like fishmeal and soymeal, in the aquaculture and animal feed industry. In this study, evaluation of four marine microalgae strains (Picochlorum sp., Nannochloris sp., Nannochloropsis sp., and Chlorella sp.) revealed that in vitro protein solubility and digestibility may serve as key indicators in determining the suitability of microalgae as a protein ingredient in feed. The greenhouse areal biomass productivities, protein and lipid concentrations of these strains ranged between 9–17 g m−2 day−1, 30–38% and 22–24%, respectively. Preliminary in vitro assays using undisrupted biomass of Picochlorum sp. revealed that its protein solubility was 47% and 67% less and digestibility was 28% and 22% less compared with fishmeal and de-oiled soy flour (DOSF), respectively. However, disruption of Picochlorum sp. biomass resulted in 2.5- and 1.5-fold increase in protein solubility and digestibility, respectively, as compared with undisrupted biomass. Further in vitro studies indicated that the soluble protein fractions differed significantly among the four experimental microalgae. The highest in vitro protein solubility (%) and soluble protein fractions (g kg−1 biomass) recorded in the four strains were the following: Picochlorum sp. (53%; 176 g kg−1), Nannochloris sp. (57%; 217 g kg−1), Nannochloropsis sp. (71%; 214 g kg−1), and Chlorella sp. (53%; 197 g kg−1). In addition, extracts from all these four strains were tested for the presence of trypsin inhibitors and found that all these strains have significantly lower trypsin inhibiting activity (TIA) compared with DOSF. The methodology presented in this study combines growth, biochemical composition, protein solubility, in vitro protein digestibility, and TIA and thus provides a reliable strategy in selection of microalgae as protein feed ingredient.

Comparison of Areal Productivity of Nannochloropsis oceanica Between Lab-Scale and Industrial-Scale Raceway Pond.

The areal biomass productivities (g-1 m-2 day-1) of Nannochloropsis oceanica between different sizes of way ponds were compared. Sequential batch cultivation using 2-m2, 20-m2, and 200-m2 raceway ponds with an industrial scale 4000-m2 raceway as the main culture was conducted in summer and autumn during 2017 at Whyalla, Australia. Areal productivities of sequential batch cultivation during the same culture period were 8.4g ± 0.9g-1m-1day-1 in the 2-m2 ponds, 9.3g-1m-1day-1 in the 20-m2 ponds, and 8.0g-1m-1day-1 in the 200-m2 ponds respectively. In parallel with the operation of the main 4000-m2 pond, some smaller scale ponds of 2, 20, and 200m2 were operated at the same site under the same conditions. Areal productivity data of dry biomass of Nannochloropsis oceanica in each pond are very similar between industrial 4000-m2 pond and other smaller ponds. In this work, the authors demonstrate that using the growth rate and productivities of Nannochloropsis from smaller scale open ponds with the same depth is valid to estimate for large-scale ponds in excess of 4000m2.

Studies on the Attached Cultivation of Filamentous Oleaginous Microalga Tribonema minus

Attached cultivation is a promising method for microalgal biomass production. Filamentous oleaginous microalga Tribonema minus (hereafter T. minus ) has shown a remarkable potential for biofuel production in terms of its high lipid content. However, the strain has only been cultivated in suspended cultivation systems including open pond and closed photobioreactors. Here, we attempted to study the attached cultivation of T. minus , which might be helpful for its scale-up cultivation and industrial applications. As the results, the optimal conditions for T. minus growth in the attached biofilm are 200 μmol photons m −2 s −1 of light intensity and 5% of CO 2 , and the maximum biomass density of 223 g m −2 has been achieved under the light intensity. The non-woven fabric as substratum was found as the best substratum in thin layer attached bioreactor, on which the average biomass productivity of T. minus is about (9.73 ± 2.19) g m −2 d −1 . Furthermore, two attached bioreactor systems, rotary drum and rotation disc, were designed following the light dilution strategy and introduced into T. minus cultivation. The highest footprint areal biomass productivity of these two systems is 33 and 47.1 g m −2 d −1 , respectively, much higher than that in suspended cultivation system. The results shows that T. minus can be cultured with attached cultivation method to improve its biomass productivity.

A comparative life cycle assessment of microalgae production by CO2 sequestration from flue gas in outdoor raceway ponds under batch and semi-continuous regime

To be a sustainable energy source, a microalgal cultivation model should address important environmental challenges for its large-scale implementation. In this work, the performance of an outdoor raceway pond system was evaluated for biomass production and sequestration of flue gas carbon-dioxide under different conditions. The microalgae growth was influenced by several physio-chemical factors such as temperature, solar irradiance, carbon-dioxide in the incoming feed, cross-contamination etc. Batch microalgal cultivation, without any external carbon supplementation (0.04% CO2, v/v), exhibited lower areal biomass productivity, whereas flue gas (10 ± 2% CO2, v/v) feeding increased dissolved medium carbon concentrations, which improved carbon-dioxide fixation rate. To further improve the system’s performance, semi-continuous regime was adopted that resulted in maximum biomass density of 0.42 g/L and 3.5-fold increase in areal productivity of 11.488 g/m2.s. Next, a “cradle-to-gate” Life Cycle Assessment (LCA) was performed using SimaPro 8.3.0.14 software to identify the potential environmental impacts associated with the production of Chlorella vulgaris biomass (functional unit: 1 kg). Results showed cultivation step to have significant environmental impact (>75%) in terms of GHG emission, energy requirement and other impact categories as estimated by GWP 100 IPCC 2013, CED and ReCiPe Endpoint method. Further, sensitivity analysis assisted in identifying the effect of variables with greatest impact on systems performance in the proposed scenarios; especially with the co-location of cultivation systems and flue gas emitting point sources. The results of attributional LCA revealed that flue gas utilization by microalgae in outdoor raceway ponds has less carbon footprint when a semi-continuous cultivation is carried out and will be more suitable when raceway ponds are co-located with thermal power plants.

Improving membrane photobioreactor performance by reducing light path: operating conditions and key performance indicators

Microalgae cultivation has been receiving increasing interest in wastewater remediation due to their ability to assimilate nutrients present in wastewater streams. In this respect, cultivating microalgae in membrane photobioreactors (MPBRs) allows decoupling the solid retention time (SRT) from the hydraulic retention time (HRT), which enables to increase the nutrient load to the photobioreactors (PBRs) while avoiding the wash out of the microalgae biomass.The reduction of the PBR light path from 25 to 10 cm increased the nitrogen and phosphorus recovery rates, microalgae biomass productivity and photosynthetic efficiency by 150, 103, 194 and 67%, respectively.The areal biomass productivity (aBP) also increased when the light path was reduced, reflecting the better use of light in the 10-cm MPBR plant. The capital and operating operational expenditures (CAPEX and OPEX) of the 10-cm MPBR plant were also reduced by 27 and 49%, respectively.Discharge limits were met when the 10-cm MPBR plant was operated at SRTs of 3–4.5 d and HRTs of 1.25–1.5 d. At these SRT/HRT ranges, the process could be operated without a high fouling propensity with gross permeate flux (J20) of 15 LMH and specific gas demand (SGDp) between 16 and 20 Nm3air·m−3permeate, which highlights the potential of membrane filtration in MPBRs.When the continuous operation of the MPBR plant was evaluated, an optical density of 680 nm (OD680) and soluble chemical oxygen demand (sCOD) were found to be good indicators of microalgae cell and algal organic matter (AOM) concentrations, while dissolved oxygen appeared to be directly related to MPBR performance. Nitrite and nitrate (NOx) concentration and the soluble chemical oxygen demand:volatile suspended solids ratio (sCOD:VSS) were used as indicators of nitrifying bacteria activity and the stress on the culture, respectively. These parameters were inversely related to nitrogen recovery rates and biomass productivity and could thus help to prevent possible culture deterioration.

Simultaneous removal of pollutants and high value biomaterials production by Chlorella variabilis TH03 from domestic wastewater

Cultivation of microalgae in the domestic wastewater is an alternative approach over conventional activated sludge processes for simultaneous pollutants removal and biomaterials production for biorefinery. This study was aimed at growing a Chlorella variabilis TH03 in domestic wastewater using various closed photobioreactors and open-reactor systems for evaluation of the algal growth, pollutants removal efficiency, biomass productivity and characterization of the biomass. Results indicated that the C. variabilis TH03 exhibited an outstanding growth, achieving maximum biomass concentration of 1.52, 1.67, 1.54 and 1.72 g/L, with specific growth rate of 0.32/day, 0.27/day, 0.22/day and 0.34/day in PBR-5-R, PBR-5-S, T-50 and RW-500 reactor systems, respectively. Remarkably, additional supplement of CO2 significantly enhanced areal biomass productivity of C. variabilis TH03 grown in RW-500 from 13.1 to 38.5 g/m2 day. Pollutants in term of COD, total nitrogen and total phosphorous were removed by 74.8–89.8%, 93.8–96.1% and 97.1–99.9%, respectively, during 14–17 days cultivation of the C. variabilis TH03. The fatty acid methyl esters of the algal biomass was determined as 22.55–26.12% with the most abundant fatty acids of C16:0 (26.13–27.67%), C16:3n4 (20.07–22.24%) and C18:3n3 (34.83–36.79%) which were desirable fatty acids for biodiesel and bio-jet fuels synthesis. Moreover, total carbohydrates and proteins in the algal biomass were accumulated up to 31.56–35.23% and 33.67–37.34%, respectively. Our preliminary results demonstrated the cultivation technology of C. variabilis TH03 can sustainably replace the conventional activated sludge technologies for domestic wastewater treatment.

Factors affecting pollutants removal and biomass production capability of Chlorella variabilis TH03 in domestic wastewater

Cultivation of microalgae in wastewaters and co-production of algal biomass have been considered as a sustainable approach for wastewater treatment. To achieve desirable biomass productivity and pollutants removal efficiencies, microalgal strain, cultivation mode and culturing conditions should be optimized. This was firstly aimed at examining growth characteristics of Chlorella variabilis TH03 strain under phototrophic, heterotrophic and mixtrophic cultivations using BG-11 medium as the sole of nutrient source. Secondly, the culturing variables such as aeration rate, percent dilution, N/P ratio and supplemented CO2 concentration were optimized to maximize biomass production and nutrient removal efficiencies of the algal strain in domestic wastewater. Thirdly, growth and nutrient removal capability of C. variabilis TH03 were investigated in an outdoor reactor system using domestic wastewater as a culture medium. Data showed that C. variabilis TH03 grew well under phototrophic and mixtrophic conditions but completely inhibited under heterotrophic conditions. In mixtrophic conditions, optimal aeration rate, percent dilution, N/P ratio and supplemented CO2 concentration achieved for the maximum growth and nutrient removal efficiencies were 0.2 vvm, no dilution, N/P = 15:1 and 15% CO2, respectively. Moreover, C. variabilis TH03 also exhibited an outstanding growth and nutrient removal capability in the outdoor reactor system, reaching areal biomass productivity of 39.5 g/m2∙day. Pollutants including COD, TN and TP were removed at efficiencies of 73.9, 97.1 and 99.8%, respectively. Nutrient levels in the effluent dropped below those required by the national technical regulation on domestic wastewater QCVN 14:2008/BTNM and QCVN 14-MT: 2015/BTNMT. The obtained results are useful for further study in large scale cultivation of C. variabilis TH03 for the production of high volume and low price biomass, helping to obtain returns from treatment of the waste stream, which is currently considered as a major source of water pollution in Vietnam.

Annual outdoor cultivation of the diatom Thalassiosira weissflogii: productivity, limits and perspectives

Diatoms are a promising source of renewable biomass for production of energy and functional ingredients and food products. The eurythermal diatom Thalassiosira weissflogii shows great resistance and robustness, and can be considered a suitable candidate for outdoor cultivation. In this study we investigated the resilience of one strain of this species during one-year outdoor experimentation in inclined tubular photobioreator with a working volume of 40 L. Cells of T. weissflogii overcome temperature and irradiance fluctuations by adapting their growth rate at the different environmental conditions. Calculation of areal biomass productivity based on 30 cultures along the year showed a median value of 3.83 g m−2 day−1 with maximal values of biomass (6.8 g m−2 day−1) and lipids (1.2 g m−2 day−1) reached in February and July, respectively. We observed a decline in biomass productivity with temperature increase, whereas lipid content (10–20% of dry biomass) was not significantly affected by the environmental conditions as far as a high concentration of nutrients was maintained. The outdoor experimentation successfully proved one year-round production of biomass from a single diatom species in closed photobioreactor, making T. weissflogii a suitable candidate for guaranteeing stable annual productive cycles in outdoor plant.

Outdoor cultivation of the green microalga Chlorella vulgaris under stress conditions as a feedstock for biofuel.

The present work investigated the potential of the green alga Chlorella vulgaris to produce high-quality biofuel under culture stress conditions. The cultivation was carried out in a 1000 lopen plate tank system, which provides biomass yields comparable to open pond systems, but with less area needed. Algal biomass and lipid content were measured repeatedly. We compared the two solvent systems n-hexane and hexane/isopropanol (HIP) for extraction efficiency of lipids and applied three different extraction methods Soxhlet, soaking, and soaking followed by Soxhlet (soak-Sox). The combination of the HIP solvent and the soak-Sox provided the highest lipid yield (15.8 ± 0.174). Volumetric biomass and lipid productivity were 0.201gl-1day-1 and 31.71mgl-1day-1, respectively, whereas areal biomass and lipid productivity were 25.73gm-2day-1 and 4.066gm-2day-1, respectively. The fatty acid profile by means of gas chromatography resulted in seven fatty acids from C12 to C18. The most abundant fatty acid methyl esters (FAMES) were palmitic (C16:0), oleic (C18:1), and stearic (C18:0) acids. Lipid synthesis enhanced by optimizing the Kuhl growth medium with replacing nitrate by urea (50% N compared to the original recipe) increased salt content (10g/l NaCl), ferrous sulfate (0.5g/l), and sodium acetate addition (1g/l). With regard to density, kinematic viscosity, gravity, pour point, flash point, and cetane number, the Chlorella-biodiesel comply with ASTM and EN standards thus pointing at the high potential of lipids synthesized by Chlorella as a feedstock for biodiesel production.

Performance evaluation of an outdoor algal biorefinery for sustainable production of biomass, lipid and lutein valorizing flue-gas carbon dioxide and wastewater cocktail

We evaluated wastewater remediation and CO2 utilization potential of Chlorella minutissima from flue gas in a raceway pond, while synthesizing lutein and lipid for potential healthcare and biofuel application. A mix of 20% kitchen waste, 10 g L−1 of poultry litter waste and 5% flue gas was maintained while cultivating the microalga. Complete removal of nitrate, nitrite and ammonium, 85% carbon and 91% phosphorus was observed. An average areal biomass productivity of 4.06 ± 0.12 g m−2 day−1 with a specific growth rate of 0.34 ± 0.03 day−1 was observed within 9 days. Biomass productivity of 6.21 ± 0.16 g m−2 day−1 with a specific growth rate of 0.34 ± 0.03 day−1 was achieved during winter. Furthermore, lipid content with appropriate fatty acid composition 1.04:1 (saturation:unsaturation) increased from 25% to 58%. Additionally, lutein productivity of 1.2 ± 0.08 mgL−1 day−1, while utilizing 80.74 ± 0.07 mg L−1 day−1 of CO2 from 5% flue gas was obtained.

Biophysical model and techno-economic assessment of carbon sequestration by microalgal ponds in Indian coal based power plants

The present study evaluated the carbon dioxide (CO2) sequestration potential of Thalassiosira pseudonana using the influencing key climatic datasets of an Indian coal based power plant through a biophysical energy balance model developed on MATLAB platform with ODE45s solver. The maximum average areal biomass productivity was predicted to be 111.39 kg ha−1d−1 with maximum growth in February, leading to the CO2 capture of 147.03 kg ha−1d−1. Further, techno-economic analysis was performed utilizing the results of the formulated biophysical model to access the process feasibility using SuperPro designer. Results revealed the technical viability and economic feasibility of the process, with the unit production price of 58.41 $ per ton with a reasonable rate of returns and acceptable short payback time of 2.81 years. A yearly carbon credits of 52 M$ could be earned by the company. Sensitivity analysis showed the process to be highly dependent over the raw material prices and facility operation. The integrated site-specific biophysical model and economic analysis are essential to provide reliable realistic estimates of the algal carbon sequestration technology that could drive the energy policies towards sustainable development.

Qualitative biodiesel production from a locally isolated chlorophycean microalga Scenedesmus obliquus (Turpin) Kützing GA 45 under closed raceway pond cultivation

The energy security scenario in the world would remain at high risk until non-conventional, indigenously produced renewable biofuels replace/supplement petroleum-based conventional fossil fuels. In the present study, an indigenously isolated chlorophycean microalga, Scenedesmus obliquus (Turpin) Kützing GA 45, was explored under raceway pond cultivation to assess its potential for production of lipids for qualitative biodiesel purpose. Microalgal cultivation was carried out in closed raceway ponds (14 × 4 × 0.75 m) with a capacity of 40,000 L each. The maximum areal biomass and lipid productivities were recorded to be 13.12 and 1.39 g m−2 day−1 at 30 cm culture depth during winter season followed by summer and rainy seasons. Under biphasic nitrogen starvation strategy, the maximum lipid productivity increased up to 2.29, 1.88, and 2.43 g m−2 day−1, respectively during summer, rainy, and winter seasons. The average lipid productivity was consequently calculated to be 2.2 g m−2 day−1, thus projecting an approximate annual lipid productivity of 7.04 t ha−1 y−1, assuming 10 cultivation cycles per year. Characterization of various fuel properties of the biodiesel produced, were found to be within the specified limits of national and international biodiesel standards, thus signifying the potential of the new isolate S. obliquus GA 45 for qualitative biodiesel production.

Treating anaerobically digested piggery effluent (ADPE) using microalgae in thin layer reactor and raceway pond

The successful cultivation of microalgae on anaerobically treated wastewaters would not only allow for the bioremediation of the waste stream but also the cost effective production of algal biomass. In this study, the growth and bioremediation ability of a microalgal consortium of Chlorella sp. and Scenedesmus sp. for treating anaerobically digested piggery effluent (ADPE) was assessed and compared using a thin layer reactor (TLR) (0.5-cm depth, 350 L) and a conventional raceway pond (15-cm depth, 1500 L) with an initial ammonium concentration of 110 ± 10 mg N-NH4+ L−1. The ammonium removal rate of microalgae grown in the TLR (19.23 mg N-NH4+ L−1 d−1) was 1.4 times higher than that grown in the raceway pond. The ash-free biomass yield (0.84 g L−1) and the average volumetric biomass productivity (60 mg L−1 d−1) of the algal consortium in the TLR were 2.5 and 2 times higher than that achieved in the raceway pond, respectively. However, considering four times higher culture volume in the raceway pond, the average areal biomass productivity in the raceway pond (4.2 g m−2 s−1) was more than two times higher than the productivity achieved in the TLR (1.9 g m−2 s−1). As a result of this, the areal lipid productivity of the microalgae grown in the raceway pond was also 2.7 times higher than that grown in the TLR. Our results indicated that under the operational conditions evaluated in this study and based on areal biomass productivity, raceway pond performed better than the thin layer reactor for treating ADPE.