Biomass productivity and characterization of Tetradesmus obliquus grown in a hybrid photobioreactor.

In this study, the effects of CO2 addition on the growth performance and biochemical composition of the green microalga Tetradesmus obliquus cultured in a hybrid algal production system (HAPS) were investigated. The HAPS combines the characteristics of tubular photobioreactors (towards a better carbon dioxide dissolution coefficient) with thin-layer cascade system (with a higher surface-to-volume ratio). Experimental batches were conducted with and without CO2 addition, and evaluated in terms of productivity and biomass characteristics (elemental composition, protein and lipid contents, pigments and fatty acids profiles). CO2 enrichment positively influenced productivity, and proteins, lipids, pigments and unsaturated fatty acids contents in biomass. The HAPS herein presented contributes to the optimization of microalgae cultures in open systems, since it allows, with a simple adaptation-a transit of the cultivation through a tubular portion where injection and dissolution of CO2 is efficient-to obtain in TLC systems, greater productivity and better-quality biomass.

Techno-economic assessment of microalgae production, harvesting and drying for food, feed, cosmetics, and agriculture.

The objective of this techno-economic analysis is to define the costs for an industrial microalgae production process, comparing different operation strategies (Nannochloropsis oceanica cultivation during the whole year or cultivation of two species, where Phaeodactylum tricornutum and Tisochrysis lutea alternate), production scales (1 and 10 ha), harvesting technologies (centrifugation or ultrafiltration) and drying methods (freeze-drying or spray drying). This study is based on an industrial scale process established in the south of Portugal. The strategy of cultivating N. oceanica all year round is more attractive from an economic perspective, with production costs of 53.32 €/kg DW and a productivity of 27.61 t/y for a scale of 1 ha, a 49.31% lower cost and two-fold productivity than species alternation culture strategy. These results are for biomass harvested by centrifugation (10.65% biomass cost) and freeze-drying (20.15% biomass cost). These costs could be reduced by 7.03% using a combination of ultrafiltration and spray drying, up to 17.99% if expanded to 10 ha and 10.92% if fertilisers were used instead of commercial nutrient solutions. The study shows potentially competitive costs for functional foods, food, and feed additives, specialised aquaculture products (live feed enrichment) and other high value applications (e.g., cosmetics).

The optimization of centrifugal pump driving horizontal tubular photobioreactor for enhancing astaxanthin production using heterotrophic Haematococcus pluvialis.

Haematococcus pluvialis is the prime source of natural astaxanthin for commercial exploitation. The large-scale cultivation of H. pluvialis is one of the key technologies for the development of natural astaxanthin industry. So far, horizontal tubular photobioreactor (HTPBR) circulated by a centrifugal pump has been the main PBR for the large-scale cultivation of H. pluvialis. Shear stress is a negative factor in microalgal cultivation at different scales, particularly for large-scale cultivation. To reduce the adverse impact of shear stress, the tolerance of H. pluvialis to the shear stress during the induction stage was first investigated in this study. H. pluvialis aplanospore was not sensitive to stresses between 19.18 and 27.32 Pa, but was resulted in about 30% cell death under shear stress between 27.32 and 63.84 Pa. Accordingly, two centrifugal pumps with different impellers was selected in 400 L HTPBRs to study the outdoor photoinduction for astaxanthin accumulation. The highest astaxanthin productivity and astaxanthin concentration were obtained in HTPBRs using a centrifugal pump equipped with three unshrouded backward-bladed impellers. The HTPBR was then successfully scaled up to 800 L with a similar performance, showing good scalability.

Comparative life cycle assessment of a mesh ultra-thin layer photobioreactor and a tubular glass photobioreactor for the production of bioactive algae extracts.

This study aimed at the comparison of two different photobioreactors with focus on technology and sustainability. The mesh ultra-thin layer photobioreactor (MUTL-PBR) exhibited around 3-fold biomass based space-time-yield and an around 10-fold specific antioxidant capacity than the traditional reference photobioreactor. Life cycle assessment (LCA) was done under autotrophic conditions in both pilot scale reactors with focus on biomass production and on antioxidant capacity of the biomass, respectively. Biomass production within the reference reactor showed a lower environmental impact in most categories. A significantly higher energy demand for mixing and cooling of the cell suspension within the MUTL-PBR is the major reason for its environmental burden. This relates to high impacts in the categories "non-renewable energy" and "global warming potential" per kg biomass. Comparing algal antioxidant capacity, environmental impact of the MUTL cultivation was 5-10 times lower. This clearly illustrates the potential of MUTL-PBR for sustainable production of bioactive substances.

Nutrients recycling and biomass production from Chlorella pyrenoidosa culture using anaerobic food processing wastewater in a pilot-scale tubular photobioreactor.

Microalgae cultivation in anaerobic food wastewater was a feasible way for high biomass production and nutrients recycling. In this study, Chlorella pyrenoidosa culture on anaerobic food wastewater was processed outdoors using a pilot-scale tubular photobioreactor. The microalgae showed rapid growth in different seasons, achieving high biomass production of 1.83-2.10 g L-1 and specific growth rate of 0.73-1.59 d-1. The biological contamination and dissolved oxygen were controlled at suitable levels for algal growth in the tubular photobioreactor. Lipids content in harvested biomass was 8.1-15.3% of dried weight, and the analysis in fatty acids revealed high quality with long carbon chain length and high saturation. Additionally, algal growth achieved effective pollutants purification from wastewater, removing 42.3-53.8% of CODCr, 82.6-88.7% of TN and 59.7-67.6% of TP. This study gave a successful application for scaled-up microalgae culture in anaerobic food processing wastewater for biodiesel production and wastewater purification.

Strengthening flash light effect with a pond-tubular hybrid photobioreactor to improve microalgal biomass yield.

Poor light utilization efficiency and large occupied area of traditional raceway pond photobioreactors result in low areal microalgal biomass yield in industrial applications. In this study, a pond-tubular hybrid photobioreactor (PTH-PBR) comprising raceway ponds and horizontal tubes was developed to strengthen flash light effect and improve areal microalgal biomass yield. The highest flash cycle frequency (0.63 Hz) of microalgae cells along flow pathway was obtained in the raceway pond of PTH-PBR when shaded area percentage was 20% and ratio of adjacent tube interval to tube diameter was 1, which enhanced microalgal biomass yield by 31.2% than traditional raceway pond. Meanwhile, intracellular chlorophyll content increased by 33.6% and PSII maximum quantum yield (Fv/Fm) increased by 8.1% due to decreased photoinhibition stress. The areal microalgal biomass yield of PTH-PBR was 54.7% higher than that of traditional raceway pond without horizontal tubes.

Innovative development of membrane sparger for carbon dioxide supply in microalgae cultures.

The present study was aimed to develop a membrane sparger (MS) integrated into a tubular photobioreactor to promote the increase of the carbon dioxide (CO2 ) fixation by Spirulina sp. LEB 18 cultures. The use of MS for the CO2 supply in Spirulina cultures resulted not only in the increase of DIC concentrations but also in the highest accumulated DIC concentration in the liquid medium (127.4 mg L-1 d-1 ). The highest values of biomass concentration (1.98 g L-1 ), biomass productivity (131.8 mg L-1 d-1 ), carbon in biomass (47.9% w w-1 ), CO2 fixation rate (231.6 mg L-1 d-1 ), and CO2 use efficiency (80.5% w w-1 ) by Spirulina were verified with MS, compared to the culture with conventional sparger for CO2 supply. Spirulina biomass in both culture conditions had high protein contents varying from 64.9 to 69% (w w-1 ). MS can be considered an innovative system for the supply of carbon for the microalgae cultivation and biomass production. Moreover, the use of membrane system might contribute to increased process efficiency with a reduced cost of biomass production.

Novel photobioreactor design for the culture of Dunaliella tertiolecta - Impact of color in the growth of microalgae.

Microalgae are affected by the amount of light received. This parameter can be controlled by changing the light source and altering the reactor used for their growth. In this study, the effect of different colors of light was analyzed in the growth of Dunaliella tertiolecta, observing that blue lighting systems reached a biomass 10 times superior to the one generated by orange lightning systems. This growth effect was seen in a novel tubular internally illuminated photobioreactor. In this photobioreactor, the blue reactor produced 1.7 times the biomass of the red reactor, with the particularity that the latter showed an oscillating behavior in its growth. From irradiance models, the light dispersion coefficient is higher than the absorption coefficient when using red light. In contrast, with blue light, the value of the scattering coefficient is almost null.

Strengthening mass transfer of carbon dioxide microbubbles dissolver in a horizontal tubular photo-bioreactor for improving microalgae growth.

A CO2 microbubbles dissolver (CMD) was developed to facilitate dissolving inorganic carbon and strengthening mass transfer in a horizontal tubular photo-bioreactor system (HTPBRS), which enhanced microalgae biomass productivity with flue gas containing 15% CO2. The influence of pump power on the bubble formation and mixing effect was found to be more obvious than that of gas flow rate. Ceramic shell aerator was more favorable for reducing bubble diameter and enhancing mass transfer than traditional rubber strip aerator. Bubble formation time decreased by 53.4% and mixing time decreased by 68.9% in response to the increased pump power. When the base area ratio of ceramic shell aerator to dissolver in the HTPBRS increased, bubble formation time decreased by 19.6% and mass transfer coefficient increased by 80.9%. The biomass yield of microalgae Chlorella PY-ZU1 with ceramic shell aerator was 30% higher than that with rubber strip aerator in the HTPBRS.

Growth modeling of the green microalga Scenedesmus obliquus in a hybrid photobioreactor as a practical tool to understand both physical and biochemical phenomena in play during algae cultivation.

In recent years, numerous studies have justified the use of microalgae as a sustainable alternative for the generation of different types of fuels, food supplementation, and cosmetics, as well as bioremediation processes. To improve the cost/benefit ratio of microalgae mass production, many culture systems have been built and upgraded. Mathematical modeling the growth of different species in different systems has become an efficient and practical tool to understand both physical and biochemical phenomena in play during algae cultivation. In addition, growth modeling can guide design changes that lead to process optimization. In the present work, growth of the green microalga Scenedesmus obliquus was modeled in a hybrid photobioreactor that combines the characteristics of tubular photobioreactors (TPB) with thin-layer cascades (TLC). The system showed productivity greater than 8.0 g m-2 day-1 (dry mass) for CO2 -fed cultures, and the model proved to be an accurate representation of experimental data with R2 greater than 0.7 for all cases under variable conditions of temperature and irradiance to determine subsystem efficiency. Growth modeling also allowed growth prediction relative to the operating conditions of TLC, making it useful for estimating the system given other irradiance and temperature conditions, as well as other microalgae species.

Autotrophic and heterotrophic microalgae and cyanobacteria cultivation for food and feed: life cycle assessment.

The lack of protein sources in Europe could be reduced with onsite production of microalgae with autotrophic and heterotrophic systems, owing the confirmation of economic and environmental benefits. This study aimed at the life cycle assessment (LCA) of microalgae and cyanobacteria cultivation (Chlorella vulgaris and Arthrospira platensis) in autotrophic and heterotrophic conditions on a pilot industrial scale (in model conditions of Berlin, Germany) with further biomass processing for food and feed products. The comparison of analysis results with traditional benchmarks (protein concentrates) indicated higher environmental impact of microalgae protein powders. However high-moisture extrusion of heterotrophic cultivated C. vulgaris resulted in more environmentally sustainable product than pork and beef. Further optimization of production with Chlorella pyrenoidosa on hydrolyzed food waste could reduce environmental impact in 4.5 times and create one of the most sustainable sources of proteins.

Microalgal cultivation and hydrodynamic characterization using a novel tubular photobioreactor with helical blade rotors.

Industrial-scale microalgal cultivation for food, feedstocks and biofuel production is limited by several engineering factors, such as cultivation systems. As a closed microalgal growth system, tubular photobioreactors are the most preferred ones in the mass algae production. In this work, microalgal cultivation and hydrodynamic characterization using a novel tubular photobioreactor equipped with helical blade rotors (HBRs) were investigated, with the aid of computational fluid dynamics and cultivation experiments to evaluate the effect of HBRs on the performance of tubular photobioreactor and growth of the Chlorella sp. The results showed that the use of HBRs in tubular photobioreactors would result in swirl flow and increase of radial velocity and circumferential velocity; it also indicated that the HBRs would enable microalgal cells to move forward helically and to be shuttled alternatively between the light zone and the dark zone. This has led to the faster growth rate of Chlorella sp. and no attachment on the tube surface in the tubular photobioreactor during the whole cultivation cycle. In conclusion, the HBRs could improve the performance of tubular photobioreactors and thus impact positively on the cultivation of microalgae cells for biotechnological industry.

Cultivation of shear stress sensitive and tolerant microalgal species in a tubular photobioreactor equipped with a centrifugal pump.

The tolerance to shear stress of Tetraselmis suecica, Isochrysis galbana, Skeletonema costatum, and Chaetoceros muelleri was determined in shear cylinders. The shear tolerance of the microalgae species strongly depends on the strain. I. galbana, S. costatum, and C. muelleri exposed to shear stress between 1.2 and 5.4 Pa resulted in severe cell damage. T. suecica is not sensitive to stresses up to 80 Pa. The possibility to grow these algae in a tubular photobioreactor (PBR) using a centrifugal pump for recirculation of the algae suspension was studied. The shear stresses imposed on the algae in the circulation tubes and at the pressure side of the pump were 0.57 and 1.82 Pa, respectively. The shear stress tolerant T. suecica was successfully cultivated in the PBR. Growth of I. galbana, S. costatum, and C. muelleri in the tubular PBR was not observed, not even at the lowest pumping speed. For the latter shear sensitive strains, the encountered shear stress levels were in the order of magnitude of the determined maximum shear tolerance of the algae. An equation was used to simulate the effect of possible damage of microalgae caused by passages through local high shear zones in centrifugal pumps on the total algae culture in the PBR. This simulation shows that a culture of shear stress sensitive species is bound to collapse after only limited number of passages, confirming the importance of considering shear stress as a process parameter in future design of closed PBRs for microalgal cultivation.

Growth of Tetraselmis suecica in a tubular photobioreactor on wastewater from a fish farm.

Wastewater from a fish farm was remediated in a continuously operated tubular photobioreactor in which Tetraselmis suecica was cultured. The N and P removal efficiencies and the productivity of T. suecica growing on the wastewater were determined. Possibilities to optimize the productivity by adding extra orthophosphate were investigated. At a biomass concentration of 0.5 g L(-1) on only wastewater, the N and P removal efficiencies were 49.4% and 99.0%, respectively. When extra phosphate was dosed to the wastewater, a 95.7% N removal efficiency and a 99.7% P removal efficiency could be reached at a biomass concentration of 1.0 g L(-1). This also resulted in significantly higher average net volumetric productivity ranging from 0.35 g L(-1) d(-1) at a biomass concentration of 0.5 g L(-1) to 0.46 and 0.52 g L(-1) d(-1) at biomass concentrations of 0.75 and 1.0 g L(-1), respectively. This study shows the feasibility of an integrated multi-trophic aquaculture approach where wastewater from the fish farms is used to produce feed for juvenile shellfish at high productivity and constant quality.

Use of mixed culture bacteria for photofermentive hydrogen of dark fermentation effluent.

Hydrogen production (HP) from dark fermentation effluent of starch wastewater via vertical tubular photo-bioreactor was investigated. The reactor was inoculated with mixed culture of bacteria and operated at light intensity of 190 W/m(2). Hydraulic retention time (HRT) and organic loading rate (OLR) was varied between 0.9 to 4.0 h and 3.2 to 16 g COD/l.d., respectively. Increasing the HRT from 0.9 to 2.5 h, significantly (P<0.05) increased HP from 1±0.04 to 3.05±0.19 l/d, respectively. However, minimal increase in HP occurred when increasing the HRT up to 4.0 h. The HP remained unaffected when increasing the OLR from 3.2 to 6.4 g COD/l.d. Further increase in the OLR up to 8.2 and 16 g COD/l.d., resulted in a drop in HP i.e. 0.96 and 0.19 l/d, respectively. Microbial community analysis of the reactor samples showed the presence and dominance of hydrogen producing purple non-sulfur phototrophic (PNS) bacterium, Rhodopseudomonas palustris in the reactor.