Photosynthetic conversion of carbon dioxide from cement production to microalgae biomass.

Production of microalgae is a potential technology for capturing and recycling carbon dioxide from cement kiln emissions. In this study, a process of selecting a suitable strain that would effectively utilize carbon dioxide and generate biomass was investigated. A down-selection screening method was applied to 28 strains isolated from the area surrounding a commercial cement plant. In laboratory-scale (1 L) continuous-mode chemostats, observed productivity was > 0.9 g L-1 d-1 for most strains studied. Chlorella sorokiniana (strain SMC-14M) appeared to be the most tolerant to cement kiln gas emissions in situ, delivered under control of a pH-stat system, and was down-selected to further investigate growth and biomass production at large-scale (1000 L) cultivation. Results demonstrated little variability in lipid, crude protein, and carbohydrate composition throughout growth between kiln-gas grown algal biomass and biomass produced with laboratory grade CO2. The growth rate at which the maximum quantity of CO2 from the emissions is recycled also produced the maximum amount of the targeted biomass components to increase commercial value of the biomass. An accumulation of some heavy metals throughout its growth demonstrates the necessity to monitor the biomass cultivated with industrial flue gases and to carefully consider the potential applications for this biomass; despite its other attractive nutritional properties. KEY POINTS: • Studied high biomass producing algal strains grown on CO2 from cement flue gas. • Chlorella sorokiniana SMC-14M grew well at large scale, in situ on cement flue gas. • Demonstrated the resulting commercial potential of the cultured algal biomass.

Screening of two freshwater green microalgae in pulp and paper mill wastewater effluents in Nova Scotia, Canada.

In recent years, the use of microalgae as feedstock for many marketable products, such as animal/aqua feeds, bioplastics and fertilizers, has gained renewed interest due to their fast growth potential coupled with relatively high lipid, carbohydrate and nutrient content. An algal biorefinery at an industrial site has the potential to sustainably and profitably convert carbon dioxide emissions into microalgal biomass and concomitantly reduce nitrogen and phosphorus from wastewaters. Industrial wastewaters are a potential alternative to traditional media used for large-scale microalgal cultivation. Pulp and paper mills are major consumers of water resources and discharge a huge amount of water to nearby lakes or rivers. This study investigated whether pulp and paper mill waste water is suitable for microalgal cultivation with the aim of achieving significant biomass production. Six different process waters from one Canadian pulp and paper mill were tested with two freshwater green microalgae. All of these waters were unable to support growth of microalgae due to inadequate nutrient concentrations, colour, turbidity and possible toxicity issues.

Integration of microalgae cultivation with industrial waste remediation for biofuel and bioenergy production: opportunities and limitations.

There is currently a renewed interest in developing microalgae as a source of renewable energy and fuel. Microalgae hold great potential as a source of biomass for the production of energy and fungible liquid transportation fuels. However, the technologies required for large-scale cultivation, processing, and conversion of microalgal biomass to energy products are underdeveloped. Microalgae offer several advantages over traditional 'first-generation' biofuels crops like corn: these include superior biomass productivity, the ability to grow on poor-quality land unsuitable for agriculture, and the potential for sustainable growth by extracting macro- and micronutrients from wastewater and industrial flue-stack emissions. Integrating microalgal cultivation with municipal wastewater treatment and industrial CO(2) emissions from coal-fired power plants is a potential strategy to produce large quantities of biomass, and represents an opportunity to develop, test, and optimize the necessary technologies to make microalgal biofuels more cost-effective and efficient. However, many constraints on the eventual deployment of this technology must be taken into consideration and mitigating strategies developed before large scale microalgal cultivation can become a reality. As a strategy for CO(2) biomitigation from industrial point source emitters, microalgal cultivation can be limited by the availability of land, light, and other nutrients like N and P. Effective removal of N and P from municipal wastewater is limited by the processing capacity of available microalgal cultivation systems. Strategies to mitigate against the constraints are discussed.

Evidence for the occurrence of photorespiration in synurophyte algae.

The fluxes of CO(2) and oxygen during photosynthesis by cell suspensions of Tessellaria volvocina and Mallomonas papillosa were monitored mass spectrometrically. There was no rapid uptake of CO(2,) only a slow drawdown to compensation concentrations of 26 µM for T. volvocina and 18 µM for M. papillosa, when O(2) evolution ceased, indicating a lack of active bicarbonate uptake by the cells. Darkening of the cells after a period of photosynthesis did not cause rapid release of CO(2), indicating the absence of an intracellular inorganic carbon pool. However, upon darkening a brief burst of CO(2) was observed similar to the post-illumination burst characteristic of C(3) higher plants. Treatment of the cells of both species with the membrane-permeable carbonic anhydrase inhibitor ethoxyzolamide had no adverse effect on photosynthetic rate, but stimulated the dark CO(2) burst indicating the dark oxidation of a compound formed in the light. In the absence of any active accumulation of inorganic carbon photosynthesis in these species should be inhibited by O(2). This was investigated in four synurophyte species T. volvocina, M. papillosa, Synura petersenii, and Synura uvella: photosynthetic O(2) evolution rates in all four algae, measured by O(2) electrode, were significantly higher (40-50%) in media at low O(2) (4%) than in air-equilibrated (21% O(2)) media, indicating an O(2) inhibition of photosynthesis (Warburg effect) and thus the occurrence of photorespiration in these species.

Estimation of psychomotor delay from the Fitts' law coefficients.

An intrinsic property of human motor behavior is a trade-off between speed and accuracy. This is classically described by Fitts' law, a model derived by assuming that the human body has a limited capacity to transmit information in organizing motor behavior. However, Fitts' law can also be realized as an emergent property of movements generated by delayed feedback. In this article, we describe the relationship between the Fitts' law coefficients and the physiological parameters of the underlying delayed feedback circuit: the relaxation rate or time constant, and the psychomotor delay of the feedback process. This relationship is then used to estimate the motor circuit delay of several tasks for which Fitts' law data are available in the literature. We consistently estimate the delay to be between 0 and 112 ms. A further consequence of this model is that not all combinations of slope and Y-intercept in Fitts' law are possible when movements are generated by delayed feedback. In fact, it is only possible for an observed speed-accuracy trade-off to be generated by delayed feedback if the Fitts' law coefficients satisfy -0.482 < or = a/b < or = 3.343 [bits] where b represents the slope in bits per second and a represents the Y-intercept in seconds. If we assume human movement is generated by delayed feedback, then the Fitts' law coefficients should always be restricted to this range of values.

PHOTOSYNTHETIC INORGANIC CARBON ACQUISITION IN AN ACID-TOLERANT, FREE-LIVING SPECIES OF COCCOMYXA (CHLOROPHYTA)(1).

The processes of CO2 acquisition were characterized for the acid-tolerant, free-living chlorophyte alga, CPCC 508. rDNA data indicate an affiliation to the genus Coccomyxa, but distinct from other known members of the genus. The alga grows over a wide range of pH from 3.0 to 9.0. External carbonic anhydrase (CA) was detected in cells grown above pH 5, with the activity increasing marginally from pH 7 to 9, but most of the CA activity was internal. The capacity for HCO3 (-) uptake of cells treated with the CA inhibitor acetazolamide (AZA), was investigated by comparing the calculated rate of uncatalyzed CO2 formation with the rate of photosynthesis. Active bicarbonate transport occurred in cells grown in media above pH 7.0. Monitoring CO2 uptake and O2 evolution by membrane-inlet mass spectrometry demonstrated that air-grown cells reduced the CO2 concentration in the medium to an equilibrium concentration of 15 µM, but AZA-treated cells caused a drop in extracellular CO2 concentration to a compensation concentration of 27 µM at pH 8.0. CO2 -pulsing experiments with cells in the light indicated that the cells do not actively take up CO2 . An internal pool of unfixed inorganic carbon was not detected at the CO2 compensation concentration, probably because of the lack of active CO2 uptake, but was detectable at times before compensation point was reached. These results indicate that this free-living Coccomyxa possesses a CO2 -concentrating mechanism (CCM) due to an active bicarbonate-uptake system, unlike the Coccomyxa sp. occurring in symbiotic association with lichens.

Performance limitations from delay in human and mechanical motor control.

We discuss natural limitations on motor performance caused by the time delay required for feedback signals to propagate within the human body or mechanical control systems. By considering a very simple delayed linear servomechanism model, we show there exists a best possible speed-accuracy trade-off similar to Fitts' law that cannot be exceeded when delay is present. This is strictly a delay effect and does not occur for the ideal case of instantaneous feedback. We then examine the performance of the vector integration to endpoint (VITE) circuit as a model of human movement and show that when this circuit is generalized to include delayed feedback the performance may not exceed that of the servomechanism with an equal delay. We suggest the existence of such a limitation may be a ubiquitous consequence of delay in motor control with the implication that the index of performance in Fitts' law cannot arbitrarily large.

Inorganic carbon acquisition in some synurophyte algae.

Some characteristics of photosynthesis of three synurophyte algae, Synura petersenii, Synura uvella and Tessellaria volvocina were investigated to determine the mechanism of inorganic carbon (C(i)) uptake. All three species were found to have no external carbonic anhydrase, no capacity for direct bicarbonate uptake and a low whole-cell affinity for C(i). The internal pH of S. petersenii determined using (14)C-benzoic acid and [2-(14)C]-5,5-dimethyloxazolidine-2,4-dione was pH 7.0-7.5, over an external pH range of 5.0-7.5. Thus, the pH difference between the cell interior of S. petersenii and the external medium was large enough, over the alga's growth range, to allow the accumulation of C(i) by the diffusive uptake of CO(2). Monitoring O(2) evolution and CO(2) uptake by suspensions of S. petersenii at pH 7.0 by mass spectrometry did not indicate a rapid uptake of CO(2), and the final CO(2) compensation concentration reached was 24 +/- 0.7 microM. Furthermore, when the cells were darkened, a brief burst of CO(2) occurred before a steady rate of dark respiration was established, suggesting a loss of CO(2) by photorespiration. An examination of the kinetics of ribulose-1,5-bisphosphate carboxylase/oxygenase in homogenates of cells of S. petersenii, S. uvella and Mallomonas papillosa showed that values of the K(m) (CO(2)) were 28.4, 41.8 and 18.2 microM, respectively. These species lack the characteristics of cells with a CO(2)-concentrating mechanism because the cell affinity for C(i) appears to be determined by the relatively high CO(2) affinity of the Rubisco of these algae.

Fifty years later: A neurodynamic explanation of Fitts' law.

An intrinsic property of human motor behaviour is a trade-off between speed and accuracy. This is classically described by Fitts' law, a model derived by assuming the human body has a limited capacity to transmit information in organizing motor behaviour. Here, we propose an alternative foundation, based on the neurodynamics of the motor circuit, wherein Fitts' law is an approximation to a more general relationship. In this formulation, widely observed inconsistencies with experimental data are a consequence of psychomotor delay. The methodology developed additionally provides a method to estimate the delay within the motor circuit from the speed-accuracy trade-off alone.

The diversity of inorganic carbon acquisition mechanisms in eukaryotic microalgae.

Eukaryotic microalgae have developed CO2concentrating mechanisms to maximise the concentration of CO2 at the active site of Rubisco in response to the low CO2 concentrations in the external aquatic medium. In these organisms, the modes of inorganic carbon (Ci) uptake are diverse, ranging from diffusive CO2 uptake to the active transport of HCO3 -and CO2 and many have an external carbonic anhydrase to facilitate HCO3- use. There is unequivocal evidence for the mechanisms of Ci uptake in only about 25 species of microalgae of the chlorophyte, haptophyte, rhodophyte, diatom, and eustigmatophyte groups. Most of these species take up both CO2 and HCO3-, but the rates of uptake of each of these substrates varies with the algal species. A few species take up only one of the two forms of Ci, an adaptation that is not necessarily correlated with their ecological distribution. Evidence is presented for the active uptake of HCO3- and CO2 in two marine haptophytes,Isochrysis galbana Parke and Dicrateria inornata Parke, and for active transport of CO2 but lack of HCO3- uptake in two marine dinoflagellates, Amphidinium carteraeHulburt and Heterocapsa oceanica Stein.