Poly-ß-hydroxybutyrate production by Synechocystis MT_a24 in a raceway pond using urban wastewater.

Poly-ß-hydroxybutyrate (PHB) is a potential source of biodegradable plastics that are environmentally friendly due to their complete degradation to water and carbon dioxide. This study aimed to investigate PHB production in the cyanobacterium Synechocystis sp. PCC6714 MT_a24 in an outdoor bioreactor using urban wastewater as a sole nutrient source. The culture was grown in a thin-layer raceway pond with a working volume of 100 L, reaching a biomass density of up to 3.5 g L-1 of cell dry weight (CDW). The maximum PHB content was found under nutrient-limiting conditions in the late stationary phase, reaching 23.7 ± 2.2% PHB per CDW. These data are one of the highest reported for photosynthetic production of PHB by cyanobacteria, moreover using urban wastewater in pilot-scale cultivation which multiplies the potential of sustainable cultivation approaches. Contamination by grazers (Poterioochromonas malhamensis) was managed by culturing Synechocystis in a highly alkaline environment (pH about 10.5) which did not significantly affect the culture growth. Furthermore, the strain MT_a24 showed significant wastewater nutrient remediation removing about 72% of nitrogen and 67% of phosphorus. These trials demonstrate that the photosynthetic production of PHB by Synechocystis sp. PCC6714 MT_a24 in the outdoor thin-layer bioreactor using urban wastewater and ambient carbon dioxide. It shows a promising approach for the cost-effective and sustainable production of biodegradable carbon-negative plastics. KEY POINTS: • High PHB production by cyanobacteria in outdoor raceway pond • Urban wastewater used as a sole source of nutrients for phototrophic growth • Potential for cost-effective and sustainable production of biodegradable plastics.

Improving light availability and creating high-frequency light-dark cycles in raceway ponds through vortex-induced vibrations for microalgae cultivation: a fluid dynamic study.

Limited light availability due to insufficient vertical mixing strongly reduces the applicability of raceway ponds (RWPs). To overcome this and create light-dark (L/D) cycles for enhanced biomass production through improved vertical mixing, vortex-induced vibration (VIV) system was implemented by the authors in a previous study to an existing pilot-scale RWP. In this study, experimental characterization of fluid dynamics for VIV-implemented RWP is carried out. Particle image velocimetry (PIV) technique is applied to visualize the flow. The extents of the vertical mixing due to VIV and the characteristics of L/D cycles were examined by tracking selected particles. Pond depth was hypothetically divided into three zones, namely dark, light Iimited and light saturated for detailed analysis of cell trajectories. It has been observed that VIV cylinder oscillation can efficiently facilitate the transfer of cells from light-limited to light-saturated zones. Among the cells that were tracked, 44% initially at dark zone entered the light-limited zone and 100% of initially at light-limited zone entered the light-saturated zone. 33% of all tracked cells experienced high-frequency L/D cycles with an average frequency of 35.69 s-1 and 0.49 light fraction. The impact of VIV was not discernible in the deeper sections of the pond, due to constrained oscillation amplitudes. Our findings suggest that the approximately 20% increase in biomass production reported in our previous study can be attributed to the synergistic effects of enhanced L/D cycle frequencies and improved light availability resulting from the transfer of cells from dark to light-limited zones. To further enhance the effectiveness of VIV, design improvements were developed. It was concluded that light availability could be significantly improved with the presented method for more effective use of RWPs.

Microalgae-mediated biofixation as an innovative technology for flue gases towards carbon neutrality: A comprehensive review.

Microalgae-mediated industrial flue gas biofixation has been widely discussed as a clean alternative for greenhouse gas mitigation. Through photosynthetic processes, microalgae can fix carbon dioxide (CO2) and other compounds and can also be exploited to obtain high value-added products in a circular economy. One of the major limitations of this bioprocess is the high concentrations of CO2, sulfur oxides (SOx), and nitrogen oxides (NOx) in flue gases, according to the origin of the fuel, that can inhibit photosynthesis and reduce the process efficiency. To overcome these limitations, researchers have recently developed new technologies and enhanced process configurations, thereby increased productivity and CO2 removal rates. Overall, CO2 biofixation rates from flue gases by microalgae ranged from 72 mg L-1 d -1 to over 435 mg L-1 d-1, which were directly influenced by different factors, mainly the microalgae species and photobioreactor. Additionally, mixotrophic culture have shown potential in improving microalgae productivity. Progress in developing new reactor configurations, with pilot-scale implementations was observed, resulting in an increase in patents related to the subject and in the implementation of companies using combustion gases in microalgae culture. Advancements in microalgae-based green technologies for environmental impact mitigation have led to more efficient biotechnological processes and opened large-scale possibilities.

Real-Time Sensor Data Profile-Based Deep Learning Method Applied to Open Raceway Pond Microalgal Productivity Prediction.

Microalgal biotechnology holds the potential for renewable biofuels, bioproducts, and carbon capture applications due to unparalleled photosynthetic efficiency and diversity. Outdoor open raceway pond (ORP) cultivation enables utilization of sunlight and atmospheric carbon dioxide to drive microalgal biomass synthesis for production of bioproducts including biofuels; however, environmental conditions are highly dynamic and fluctuate both diurnally and seasonally, making ORP productivity prediction challenging without time-intensive physical measurements and location-specific calibrations. Here, for the first time, we present an image-based deep learning method for the prediction of ORP productivity. Our method is based on parameter profile plot images of sensor parameters, including pH, dissolved oxygen, temperature, photosynthetically active radiation, and total dissolved solids. These parameters can be remotely monitored without physical interaction with ORPs. We apply the model to data we generated during the Unified Field Studies of the Algae Testbed Public-Private-Partnership (ATP3 UFS), the largest publicly available ORP data set to date, which includes millions of sensor records and 598 productivities from 32 ORPs operated in 5 states in the United States. We demonstrate that this approach significantly outperforms an average value based traditional machine learning method (R2 = 0.77 ≫ R2 = 0.39) without considering bioprocess parameters (e.g., biomass density, hydraulic retention time, and nutrient concentrations). We then evaluate the sensitivity of image and monitoring data resolutions and input parameter variations. Our results demonstrate ORP productivity can be effectively predicted from remote monitoring data, providing an inexpensive tool for microalgal production and operational forecasting.

Assessment of Eicosapentaenoic Acid (EPA) Production from Filamentous Microalga Tribonema aequale: From Laboratory to Pilot-Scale Study.

It has long been explored to use EPA-rich unicellular microalgae as a fish oil alternative for production of the high-value omega-3 fatty acid eicosapentaenoic acid (EPA, 20:5, n-3). However, none of the efforts have ever reached commercial success. This study reported a filamentous yellow-green microalga Tribonema aequale that possesses the ability to grow rapidly and synthesize significant amounts of EPA. A series of studies were conducted in a glass column photobioreactor under laboratory culture conditions and in pilot-scale open raceway ponds outdoors. The emphasis was placed on the specific nutrient requirements and the key operational parameters in raceway ponds such as culture depth and mixing regimes. When optimized, T. aequale cells contained 2.9% of EPA (w/w) and reached a very high biomass concentration of 9.8 g L-1 in the glass column photobioreactor. The cellular EPA content was increased further to 3.5% and the areal biomass and EPA productivities of 16.2 g m-2 d-1 and 542.5 mg m-2 d-1, respectively, were obtained from the outdoor pilot-scale open raceway ponds, which were the record high figures reported thus far from microalgae-based EPA production. It was also observed that T. aequale was highly resistant to microbial contamination and easy for harvesting and dewatering, which provide two additional competitive advantages of this filamentous microalga over the unicellular counterparts for potential commercial production of EPA and other derived co-products.

Indirect regulation of temperature in raceway reactors by optimal management of culture depth.

Temperature and irradiance are the two most relevant factors determining the performance of microalgae cultures in open raceway reactors. Moreover, inadequate temperature strongly reduces the biomass productivity in these systems even if enough sunlight is available. Controlling the temperature in large open raceway reactors is considered unaffordable because of the large amount of energy required. This study presents an indirect method for temperature regulation in microalgae raceway reactors by optimizing the culture depth. First, the effect of the culture depth on the raceway temperature is analyzed for different seasons of the year. Afterward, a simulation study is presented where the proposed control approach is compared to the normal operation mode with constant volume in the reactor. This study is also extended to industrial scale. Relevant improvements on the temperature factor and biomass production are presented. The developed knowledge allows the improvement of the performance in open raceway reactors up to 12% without involving additional energy and costs, being a suitable solution for large industrial reactors that until now have no options for controlling the temperature.

A new model to analyze the temperature effect on the microalgae performance at large scale raceway reactors.

In this study a simplified temperature model for raceway reactors is developed, allowing to determine the temperature of the microalgae culture as a function of reactor design and environmental conditions. The model considers the major phenomena taking place in raceway reactors, especially heat absorption by radiation and heat losses by evaporation among others. The characteristic parameters of the model have been calibrated using genetic algorithms, next being validated with a long set of more than 50 days covering different weather conditions. It is worth to highlight the use of the developed model as a tool to analyze the influence of the temperature on the performance of microalgae cultures at large scale. As example, the annual variation of the performance of up to five different microalgae strains has been determined by computing the temperature index, thus the normalized value of performance of whatever microalgae at the real temperature with respect to that achievable at optimal temperature can be established. Results confirm that only strains tolerant to wide ranges of temperature can be efficiently produced all the year around in large scale outdoor raceway reactors without additional temperature control systems.

Year-Round Cultivation of Tetraselmis sp. for Essential Lipid Production in a Semi-Open Raceway System.

There is increasing demand for essential fatty acids (EFAs) from non-fish sources such as microalgae, which are considered a renewable and sustainable biomass. The open raceway system (ORS) is an affordable system for microalgae biomass cultivation for industrial applications. However, seasonal variations in weather can affect biomass productivity and the quality of microalgal biomass. The aim of this study was to determine the feasibility of year-round Tetraselmis sp. cultivation in a semi-ORS in Korea for biomass and bioactive lipid production. To maximize biomass productivity of Tetraselmis sp., f medium was selected because it resulted in a significantly higher biomass productivity (1.64 ± 0.03 g/L) and lower omega-6/omega-3 ratio (0.52/1) under laboratory conditions than f/2 medium (0.70/1). Then, we used climatic data-based building information modeling technology to construct a pilot plant of six semi-ORSs for controlling culture conditions, each with a culture volume of 40,000 L. Over 1 year, there were no significant variations in monthly biomass productivity, fatty acid composition, or the omega-6/omega-3 ratio; however, the lipid content correlated significantly with photosynthetic photon flux density. During year-round cultivation from November 2014 to October 2017, areal productivity was gradually increased by increasing medium salinity and injecting CO2 gas into the culture medium. Productivity peaked at 44.01 g/m2/d in October 2017. Throughout the trials, there were no significant differences in average lipid content, which was 14.88 ± 1.26%, 14.73 ± 2.44%, 12.81 ± 2.82%, and 13.63 ± 3.42% in 2014, 2015, 2016, and 2017, respectively. Our results demonstrated that high biomass productivity and constant lipid content can be sustainably maintained under Korean climate conditions.

Magnetic field as promoter of growth in outdoor and indoor assays of Chlorella fusca.

This study aimed to evaluate the influence of a magnetic field (MF) intensity of 25 mT on Chlorella fusca cultivation in outdoor and indoor conditions, and evaluate the changes in the macromolecules, pigment content and protein profile. C. fusca was cultivated for 15 d in raceway photobioreactor. MF was applied for 24 h d-1 and 1 h d-1. In outdoor cultivation, MF applied for 24 h d-1 increased 23% in the biomass concentration, while indoor assays resulted in an increase in both modes, with biomass production increasing between 70 and 85%. Biomass composition was altered when MF was applied for 1 h d-1 in indoor assays; the highest protein content was achieved (32.7%). Nitrate consumption was higher in outdoor assays, while MF application did not alter the protein profile. The results showed that combining the outdoor conditions with MF is advantageous, as higher biomass concentration can be achieved with lower energy expenditure.

Stocking density alters growth performance, serum biochemistry, digestive enzymes, immune response, and muscle quality of largemouth bass (Micropterus salmoides) in in-pond raceway system.

The effects of stocking density on growth performance, serum biochemistry, digestive enzymes, immune response, and muscle quality of largemouth bass (Micropterus salmoides) reared in nine in-pond raceway systems (IPRS, 22.0 m × 5.0 m × 2.0 m) were studied. M. salmoides with initial an body weight of 8.25 ± 0.51 g and body length of 6.99 ± 0.44 cm were reared at an initial stocking density of 90.91 ind./m3 (low stocking density, LSD), 113.63 ind./m3 (middle stocking density, MSD), and 136.36 ind./m3 (high stocking density, HSD) with triplication. After 300 days of culture, MSD recorded the highest final body weight, weight gain, specific growth rate, and yield, but the food conversion ratio in MSD was the lowest. The viscerosomatic index in LSD was significantly higher than other groups. The fish serum reared at HSD showed significantly lower total protein, higher total cholesterol, triglyceride, total bilirubin, glucose content, alanine transaminase, and aspartate transaminase activity. Significantly lower intestinal amylase, lipase, trypsin activities, hepatic superoxide dismutase (SOD) and catalase (CAT) activities, and higher malondialdehyde content were detected in HSD compared to others. The content of crude lipid, saturated fatty acid decreased, and total essential amino acid, delicious amino acid, and polyunsaturated fatty acid increased in muscle with stocking density increase. No significant difference was observed in muscle texture. Profitability analysis indicated the benefit-to-cost ratio varied between 1.10 and 1.68, of which MSD was significantly higher than others. The optimal stocking density for M. salmoides should be 113.63 ind./m3 in an IPRS farm.

Application of computational fluid dynamics (CFD) on the raceway design for the cultivation of microalgae: a review.

Microalgae are a potential solution to supersede fossil fuels and produce renewable energy. The major obstacle to the commercialization of microalgae-based biofuels is the high production cost, including nutritional requirements, photobioreactor design, and downstream processes. As for the photobioreactor design, open ponds have been adopted by major commercial plants for their economic advantages. Raceway is a popular type among open ponds. Nevertheless, the fluid dynamics of the raceway operation is quite complex. Software simulation based on Computational Fluid Dynamics is an upcoming strategy for optimizing raceway design. The optimization intends to affect light penetration, particle distribution, mass transfer, and biological kinetics. This review discusses how this strategy can be helpful to design a highly productive raceway pond-based microalgal culture system.

Removal of contaminants of emerging concern by continuous flow solar photo-Fenton process at neutral pH in open reactors.

For the first time, the operational feasibility of the solar photo-Fenton process at neutral pH in continuous flow has been tested for three consecutive days. The aim of the treatment was to remove of contaminants of emerging concern (CECs) from wastewater treatment plant secondary effluents. To this end, a 5 cm-deep raceway pond reactor was run in continuous flow mode and the degradation of the CECs present in real secondary effluents was monitored at their natural concentrations. To keep dissolved iron at neutral pH, ethylenediamine-N,N'-disuccinic acid (EDDS) was used to form the complex Fe(III):EDDS as an iron source for the photo-Fenton reactions. At pilot scale the effects of the Fe(III):EDDS molar ratio (1:1 and 1:2) and hydraulic residence time (HRT) (20 and 40 min) on CEC removal were studied. The best operating condition was 20 min of HRT, giving rise to a treatment capacity of 900 L m-2 d-1 with CEC removal percentages of around 60%. The reactant concentrations were 0.1 mM Fe(III):EDDS at a 1:1 M ratio and 0.88 mM H2O2. Under these operating conditions, the short-term stability of the process was also demonstrated, thus pointing out the potential of this solar technology as a tertiary treatment.

Optimum feeding frequency of juvenile largemouth bass (Micropterus salmoides) reared in in-pond raceway recirculating culture system.

This study was conducted to determine the effects of feeding frequency on the growth, serum biochemical parameters, antioxidant status and hepatic growth hormone (GH), insulin-like growth factor I (IGF-I), lipoprotein lipase (LPL) and hepatic lipase (HL) gene expression levels of juvenile largemouth bass (Micropterus salmoides) reared in an in-pond raceway recirculating culture system (IPRS). Fish (initial body weight 5.0 ± 0.4 g) were hand-fed with a commercial diet under one of three different feeding frequency treatments (2, 3 or 4 meals/day) for 120 days. The results indicated that no significant differences were observed in the final body weight, weight gain and specific growth rate of fish fed different feeding frequencies on 30 days and 60 days (P > 0.05). Fish fed 2 times/day had higher growth than that fed 4 times/day on 90 days but had higher growth than those fed 3 and 4 times/day on 120 days. No significant differences were found in serum alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP) activities, total protein (TP), lysozyme and triglyceride (TG) content, hepatic total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX) activities and malondialdehyde (MDA) content among fish fed different feeding frequency (P > 0.05). Serum glucose (Glu) content and catalase (CAT) activity decreased, while total cholesterol (TC) content increased with increasing feeding frequency. Fish fed 2 times/day had higher hepatic total superoxide dismutase (T-SOD) than that fed 4 times/day on 60 days, 90 days and 120 days (P < 0.05). Fish fed 2 times/day had higher IGF-1 gene mRNA expression on 30 days, 60 days and 120 days (P < 0.05), while no significant difference on 90 days. No significant difference was found in GH gene mRNA expression on 30 days and 60 days, while fish fed 4 times/day had lower values than that fed 2 times/day on 90 days and 120 days (P < 0.05). Fish fed 2 times/day had significantly higher LPL mRNA expression level than that fed 4 times/day on 60 days and 90 days and had significantly higher HL mRNA expression level on 60 days, 90 days and 120 days (P < 0.05). Based on growth, physiology, hepatic gene expression levels, labour costs and intensity, the optimal feeding frequency of largemouth bass (average body weight 5.0 ± 0.4 g) reared in IPRS is 2 times/day. These data are very necessary for the optimizing of culture conditions and feeding management strategy in IPRS culture operations.

Optimization of a raceway pond system for wastewater treatment: a review.

Microalgae are photosynthetic microorganisms with potential for biofuel production, CO2 mitigation and wastewater treatment; indeed they have the capacity to assimilate pollutants in wastewaters. Light supply and distribution among the microalgae culture is one of the major challenges of photo-bioreactor design, with many studies focusing on microalgae culture systems such as raceway ponds (RWP), widely used and cost-effective systems for algal biomass production. This review focuses on possible improvements of the RWP design in order to achieve optimal microalgal growth conditions and high biomass productivities, to minimize energy consumption and to lower the capital costs of the pond. The improvement strategy is based on three aspects: (1) hydrodynamic characteristics of the raceway pond, (2) evaluation of hydrodynamic and mass transfer capacities of the pond and (3) design of the RWP. Finally, a possible optimal design for the RWP is discussed in the context of wastewater treatment.

The effects of crowding stress on the growth, physiological response, and gene expression of the Nrf2-Keap1 signaling pathway in blunt snout bream (Megalobrama amblycephala) reared under in-pond raceway conditions.

We evaluated the effects of high density stress on growth performance, antioxidant parameters, and Nrf2 pathway signaling molecules after different lengths of exposure (30, 60, or 90 days) of Megalobrama amblycephala to in-pond raceway aquaculture systems (IPRS). M. amblycephala (average initial weight 2.33 ±â€¯0.15 g) were reared at two different initial densities (low density group [LD] had 534 fish/m3 and high density group [HD] had 1073 fish/m3) for 90 days. The growth performance was adversely influenced by the high stocking density. The HD group had elevated white blood cell counts, hemoglobin content, and hematocrit on days 60 and 90. The mRNA levels of NOX2 on days 60 and 90, Nrf2 on days 30, 60, and 90, Keap1 on day 30, Bach1 on days 30 and 60, SOD on day 30, and CAT on day 30 were significantly higher in the HD group than in the LD group. Similarly, higher trends were observed in the enzymatic activities of SOD on day 60, CAT on days 60 and 90, and GPx on day 60 in the HD group, compared to the LD group. Furthermore, HD bream showed an increased MDA content on days 60 and 90 compared to that of the LD group. This study demonstrates that high density-induced antioxidant defenses were involved in modifications to the enzymatic and transcriptional regulation of Nrf2-Keap1 signaling molecules and that M. amblycephala growth was reduced in a crowded IPRS.

Phycoremediation of paddy-soaked wastewater by indigenous microalgae in open and closed culture system.

Phycoremediation; biotransformation of nutrients and or pollutants by microalgae, supports sustainable wastewater treatment, coupled with biomass production, resulting in enhanced cost savings, waste minimization, and energy conservation. A major challenge in this technique involves cultivation system to be adopted, mode of treatment and harvesting methods. Three different algal cultivation systems; polybags (PB), photobioreactors (PBR) and race way ponds (RWP) were employed for culturing an indigenous microalga, Scenedesmus obliquus in rice mill paddy-soaked wastewater (PSW). The maximum biomass productivity (BP) of 340 ±â€¯2 mg/L/d was observed in PBR with an ammonical nitrogen (NH3-N) removal (RN) of 96.12 ±â€¯0.21% and the phosphates (PO4-P) removal (RP) of 97.58 ±â€¯0.18%. Highest lipids (L)∼12% (% biomass), protein (P)∼40% and carbohydrates (C)∼20%) were gained in PBR culture system, followed by RWP and PB.

Microalgae grow on source separated human urine in Nordic climate: Outdoor pilot-scale cultivation.

Human urine contributes approximately 80% of nitrogen and 50% of phosphorous in urban wastewaters while having a volume of only 1-1.5 L/d per capita compared to 150-200 L/d per capita of wastewater generated. There is interest to study source separation of urine and search methods to recover the nutrients form the urine. In this study, the objective was to use the nutrients in source separated urine for outdoor cultivation of microalgae in Nordic climate. A freshwater green microalga Scenedesmus acuminatus was grown in different dilutions (1:20 and 1:15) of source separated human urine, in a semi-continuously operated outdoor raceway pond with a liquid volume of 2000 L, at hydraulic retention time of 15 d. The microalgae could remove 52% nitrogen and 38% phosphorus even at culture temperatures as low as 5 °C, while obtaining a biomass density of 0.34 g VSS/L. Harvested microalgal biomass could be used to produce methane with a yield of 285 L CH4/kg volatile solids.

Utilization of centrate for the outdoor production of marine microalgae at the pilot-scale in raceway photobioreactors.

In this study, the outdoor production of marine microalgae in raceway photobioreactors was investigated, modifying the centrate percentage in the culture medium (20, 30, 40 and 50%) and using two different dilution rates (0.2 day-1 and 0.3 day-1). The data obtained showed that microalgae are capable of producing biomass in addition to recovering the nutrients contained in the centrate. The best results for biomass productivity and light efficiency were obtained when the centrate was set at 20% with a dilution rate of 0.3 day-1. The biomass productivity was 32.42 g m-2·day-1 while the photosynthetic efficiency was 0.74 gbiomass·E-1 (3.66%). Regarding the nutrients, nitrogen (the majority being in the form of ammonium [NH4+]) and phosphorus were only fixed into biomass when optimal conditions were set; if this was not the case, they were lost to stripping or precipitation. The maximal nutrient removal capacities under the optimal conditions were 28.72 mgN·l-1·day-1 and 3.99 mgP·l-1·day-1. Population changes were determined by the dilution rate set whilst the centrate percentage had little effect. Four strains were present in the culture, Nannochloropsis g. being the main one. Biochemical changes did not vary greatly between the conditions set for the culture, with a composition rich in proteins and carbohydrates being observed. One can conclude that to produce marine microalgal biomass for a range of potential commodities such as feed, biofertilizers and biofuels, it is possible to use centrate from anaerobic digestion as the sole nutrient source, as a way of reducing costs.

Design and analysis of flow velocity distribution inside a raceway pond using computational fluid dynamics.

Open raceway ponds are widely adopted for cultivating microalgae on a large scale. Working depth of the raceway pond is the major component to be analysed for increasing the volume to surface area ratio. The working depth is limited up to 5-15 cm in conventional ponds but in this analysis working depth of raceway pond is considered as 25 cm. In this work, positioning of the paddle wheel is analysed and corresponding Vertical Mixing Index are calculated using CFD. Flow pattern along the length of the raceway pond, at three different paddle wheel speeds are analysed for L/W ratio of 6, 8 and 10, respectively. Effect of clearance (C) between rotor blade tip and bottom surface is also analysed by taking four clearance conditions i.e. C = 2, 5, 10 and 15. Moving reference frame method of Fluent is used for the modeling of six blade paddle wheel and realizable k-ε model is used for capturing turbulence characteristics. Overall objective of this work is to analyse the required geometry for maintaining a minimum flow velocity to avoid settling of algae corresponding to 25 cm working depth. Geometry given in [13] is designed using ANSYS Design modular and CFD results are generated using ANSYS FLUENT for the purpose of validation. Good agreement of results is observed between CFD and experimental Particle image velocimetry results with the deviation of 7.23%.

The use of natural infochemicals for sustainable and efficient harvesting of the microalgae Scenedesmus spp. for biotechnology: insights from a meta-analysis.

Open raceway ponds are regarded as the most economically viable option for large-scale cultivation of microalgae for low to mid-value bio-products, such as biodiesel. However, improvements are required including reducing the costs associated with harvesting biomass. There is now a growing interest in exploiting natural ecological processes within biotechnology. We review how chemical cues produced by algal grazers induce colony formation in algal cells, which subsequently leads to their sedimentation. A statistical meta-analysis of more than 80 studies reveals that Daphnia grazers can induce high levels of colony formation and sedimentation in Scenedesmus obliquus and that these natural, infochemical induced sedimentation rates are comparable to using commercial chemical equivalents. These data suggest that natural ecological interactions can be co-opted in biotechnology as part of a promising, low energy and clean harvesting method for use in large raceway systems.