Areal Biomass Productivity Research Articles

Microalgae Versus Land Crops as Feedstock for Biodiesel: Productivity, Quality, and Standard Compliance

Despite certain environmental advantages over fossil diesel, land crop-derived biodiesels may not satisfy the increasing worldwide demand for transportation fuels. As an abundant photosynthesizer, algae could be an adequate surrogate for biodiesel production. Nevertheless, high production costs, scarce selected species, and inaccurate assumptions about production yields represent industrial uncertainties. In this study, a reliable approach to analyzing algal biodiesel production has been developed based on species-to-species variations in oil productivity and quality. This approach compares biodiesels from Chlorophyta strains with land crop feedstock according to (i) potential yields, (ii) oil quality, and (iii) compliance with biodiesel quality standards. Algal yields were assessed by (i) extrapolating the strain-specific laboratory results to commercial-scale growth systems; (ii) converting volumetric to areal biomass productivity; and (iii) estimating oil yields for each strain, as the product of their projected areal biomass productivity for each growth system, and the oil percentage in biomass as determined in the laboratory. Biodiesel fuel properties were estimated by using fatty acid methyl ester profile predictive models. The Chlorophyta strains in this study provided annual oil yields that were generally higher than those of land crops by one order of magnitude. Six strains yielding more than 40 mg oil l−1 day−1 were identified as adequate for sustaining biodiesel production. Trebouxiophyceae algae were the most productive. Critical biodiesel parameters from both feedstock types suggest that most microalgae-derived biodiesels meet international fuel quality standards with better values than those of land crops. Because some of the highly productive feedstock does not simultaneously meet all the standards for a high quality biodiesel, optimization solutions are discussed.

The effect of harvesting on biomass production and nutrient removal in phototrophic biofilm reactors for effluent polishing

An increasing number of wastewater treatment plants require post-treatment to remove residual nitrogen and phosphorus. This study investigated various harvesting regimes that would achieve consistent low effluent concentrations of nitrogen and phosphorus in a phototrophic biofilm reactor. Experiments were performed in a vertical biofilm reactor under continuous artificial lighting and employing artificial wastewater. Under similar conditions, experiments were performed in near-horizontal flow lanes with biofilms of variable thickness. It was possible to maintain low nitrogen and phosphorus concentrations in the effluent of the vertical biofilm reactor by regularly harvesting half of the biofilm. The average areal biomass production rate achieved a 7 g dry weight m−2 day−1 for all different harvesting frequencies tested (every 2, 4, or 7 days), corresponding to the different biofilm thicknesses. Apparently, the biomass productivity is similar for a wide range of biofilm thicknesses. The biofilm could not be maintained for more than 2 weeks as, after this period, it spontaneously detached from the carrier material. Contrary to the expectations, the biomass production doubled when the biofilm thickness was increased from 130 μm to 2 mm. This increased production was explained by the lower density and looser structure of the 2 mm biofilm. It was concluded that, concerning biomass production and labor requirement, the optimum harvesting frequency is once per week.

Nutrient Removal and Biomass Production in an Outdoor Pilot-Scale Phototrophic Biofilm Reactor for Effluent Polishing

An innovative pilot-scale phototrophic biofilm reactor was evaluated over a 5-month period to determine its capacity to remove nitrogen and phosphorus from Dutch municipal wastewater effluents. The areal biomass production rate ranged between 2.7 and 4.5 g dry weight/m(2)/day. The areal nitrogen and phosphorus removal rates averaged 0.13 g N/m(2)/day and 0.023 g P/m(2)/day, which are low compared to removal rates achieved in laboratory biofilm reactors. Nutrient removal increased during the day, decreased with decreasing light intensity and no removal occurred during the night. Additional carbon dioxide supply was not requisite as the wastewater was comprised of enough inorganic carbon to sustain microalgal growth. The study was not conclusive for the limiting factor that caused the low nutrient removal rate, possibly the process was limited by light and temperature, in combination with pH increases above pH 9 during the daytime. This pilot-scale study demonstrated that the proposed phototrophic biofilm reactor is not a viable post-treatment of municipal wastewater effluents under Dutch climate conditions. However, the reactor performance may be improved when controlling the pH and the temperatures in the morning. With these adaptations, a phototrophic biofilm reactor could be feasible at lower latitudes with higher irradiance levels.

Scenario analysis of large scale algae production in tubular photobioreactors

Microalgae productivity in tubular photobioreactors depends on algae species, location, tube diameter, biomass concentration, distance between tubes and for vertically stacked systems, the number of horizontal tubes per stack. A simulation model for horizontal and vertically stacked horizontal tubular reactors was made to quantify the effect of these decision variables on production yield. The model uses reactor dimensions, dynamic sunlight patterns over the day and year, and growth characteristics of algae species as inputs. Scenario studies were done to study the effect of decision variables on reactor performance in The Netherlands, France and Algeria. Results indicate that the areal biomass productivity in vertically stacked photobioreactors is 25–70% higher than in plain horizontal systems. Reactor design is location specific because light conditions differ. In The Netherlands, the best horizontal distance between tubes is 0.05m for horizontal and 0.25m for vertical systems. For France and Algeria, the best horizontal distance between vertical systems is 0.20m and 0.15m respectively. System performance can be improved further by using light reflection materials on the ground surface. Improving the transparency properties of tube material does not significantly affect areal productivity.

Growth Rate and Biomass Productivity of Chlorella as Affected by Culture Depth and Cell Density in an Open Circular Photobioreactor

The effects of culture depth (2-10 cm) and cell density on the growth rate and biomass productivity of Chlorella sp. XQ-200419 were investigated through the use of a selfdesigned open circular pond photobioreactor-imitation system. With increases in culture depths from 2 to 10 cm, the growth rate decreased significantly from 1.08 /d to 0.39 /d. However, the biomass productivity only increased slightly from 8.41 to 11.22 g/m2/d. The biomass productivity (11.08 g/m2/d) achieved in 4 cm culture with an initial OD540 of 0.95 was similar to that achieved in 10 cm culture with an initial OD540 of 0.5. In addition, the duration of maximal areal productivity at a 4 cm depth was prolonged from 1 to 4 days, a finding that was also similar to that of the culture at a 10 cm depth. In both cases, the initial areal biomass densities were identical. Based on these results and previous studies, it can be concluded that the influence of culture depth and cell density on areal biomass productivity is actually due to different areal biomass densities. Under suitable conditions, there are a range of optimal biomass densities, and areal biomass productivity reaches its maximum when the biomass density is within these optimal ranges. Otherwise, biomass productivity will decrease. Therefore, a key factor for high biomass productivity is to maintain an optimal biomass density.

Synchronization of fluid-dynamics related and physiological time scales and algal biomass production in thin flat-plate bioreactors

Experiments on ultrahigh density unicellular algae cultures in thin flat-plate bioreactors (thickness ≤2 cm) indicate that: i) Optimal areal biomass production rates are significantly higher than in traditional ponds or raceways, ii) productivity grows for radiation levels substantially higher than one sun; saturation emerging, possibly, at intensities of about four suns, and iii) optimal volumetric and areal production rates as well as culture densities increase as reactor thickness is reduced. The observations are reproduced within the framework of a simple model, which takes into account the random motion of cells across the reactor thickness, and the competing effects of two physiologically significant time scales. These are TR, the time that elapses from the moment a reaction center has collected the number of photons required for one photosynthetic cycle until it is available again for exploiting impinging photons (1–10 ms), and TW, an average of the decay time characteristic of photon loss processes (several ms to several tens of ms).

A Comparison ofNannochloropsis salinaGrowth Performance in Two Outdoor Pond Designs: Conventional Raceways versus the ARID Pond with Superior Temperature Management

The present study examines how climatic conditions and pond design affect the growth performance of microalgae. From January to April of 2011, outdoor batch cultures ofNannochloropsis salinawere grown in three replicate 780 L conventional raceways, as well as in an experimental 7500 L algae raceway integrated design (ARID) pond. The ARID culture system utilizes a series of 8–20 cm deep basins and a 1.5 m deep canal to enhance light exposure and mitigate temperature variations and extremes. The ARID culture reached the stationary phase 27 days earlier than the conventional raceways, which can be attributed to its superior temperature management and shallower basins. On a night when the air temperature dropped to −9°C, the water temperature was 18°C higher in the ARID pond than in the conventional raceways. Lipid and fatty acid content ranged from 16 to 25% and from 5 to15%, respectively, as a percentage of AFDW. Palmitic, palmitoleic, and eicosapentaenoic acids comprised the majority of fatty acids. While the ARID culture system achieved nearly double the volumetric productivity relative to the conventional raceways (0.023 versus 0.013 g L−1day−1), areal biomass productivities were of similar magnitude in both pond systems (3.47 versus 3.34 g m−2day−1), suggesting that the ARID pond design has to be further optimized, most likely by increasing the culture depth or operating at higher cell densities while maintaining adequate mixing.

Microalgae biomass and lipid production potential, and mechanical stress compliance

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.

Biomass and bioenergy production potential of microalgae consortium in open and closed bioreactors using untreated carpet industry effluent as growth medium

Improved wastewater management with beneficial utilization will result in enhanced sustainability and enormous cost savings in industries. Algae cultivation systems viz. raceway ponds, vertical tank reactors (VTR) and polybags were evaluated for mass production of algal consortium using carpet industry (CI) untreated wastewater. Overall areal biomass productivity of polybags (21.1gm−2d−1) was the best followed by VTR (8.1gm−2d−1) and raceways (5.9gm−2d−1). An estimated biomass productivity of 51 and 77tonsha−1year−1 can be achieved using 20 and 30L capacity polybags, respectively with triple row arrangement. Biomass obtained from algal consortium was rich in proteins (∼53.8%) and low in carbohydrates (∼15.7%) and lipids (∼5.3%). Consortium cultivated in polybags has the potential to produce 12,128m3 of biomethane ha−1year−1. To be economically viable, the capital expenditure for polybag reactors needs to be reduced to $10m−2 for bioenergy/biofuel production.

Production potential of aquatic plants in systems mixing floating and submerged macrophytes

1. To investigate whether the areal production of aquatic plant systems can be increased by growing floating and submerged plants together, the floating fern Azolla filiculoides was grown at six densities and two nutrient availabilities in the presence and absence of the submerged macrophyte Elodea canadensis.2. High nutrient availability did not affect the total areal biomass production, but raised the internal N concentration of Azolla and Elodea by 34% and 152%, respectively, and the internal P concentration by 50% and 378%.3. High Azolla density reduced Elodea production, whereas Elodea did not affect the production of Azolla. A maximal total production of 4.0 g DW m−2 day−1 was obtained at an Azolla density at and above full surface cover, when Elodea contribute with less than 10% to the total. This contribution did not raise the combined production of Azolla and Elodea significantly above the production of Azolla grown alone. Thus, maximum production was not enhanced by growing floating and submerged macrophytes together.