Cultivation of microalgae on artificial light comes at a cost

Microalgae are potential producers of bulk food and feed compounds, chemicals, and biofuels. To produce these bulk products competitively, it is important to keep costs of raw material low. Light energy can be provided by sun or lamps. Sunlight is free and abundant. Disadvantages of sunlight, however, include day/night cycles, changes in weather conditions, and seasonal changes. These fluctuations in irradiance can be prevented by applying artificial lighting. Artificial lighting will not only increase productivity but will also increase costs associated with microalgae cultivation. This cost increase is recognized, but a detailed quantitative evaluation was still missing. The costs and energy balance related to microalgae cultivation employing artificial light was evaluatedwith a literature study. We calculated that current application of artificial light will increase production costs by 25.3 $ per kilogram of dry-weight biomass. From these calculations, it was determined that 4% to 6% of energy from electric input is fixed as chemical energy in microalgae biomass. Energy loss and increased production cost may be acceptable in the production of high value products, but in general they should be avoided. Microalgae cultivation programs should therefore focus on employing sunlight

Optimizing Carbon Dioxide Utilization for Microalgae Biofilm Cultivation

The loss of carbon dioxide (CO2) to the environmentduring microalgae cultivation is undesirable for both environmentaland economic reasons. In this study, a phototrophic biofilm growthmodel was developed and validated with the objective to maximizeboth CO2 utilization efficiency and production of microalgae inbiofilms. The model was validated in growth experiments with CO2as the limiting substrate. The CO2 utilization and biomassproductivity were maximized by changing the gas flow rate, thenumber of biofilm reactors in series and gas composition. Based onsimulations, the maximum CO2 utilization efficiency that wasreached was 96% based on a process employing flue gas. Thecorresponding drop in productivity was only 2% in comparison tothe non-CO2 limited reference situation. In order to achieve this, 25biofilm reactors units, or more,must be operated in series. Based onthese results, it was concluded that concentrated CO2 streams andplug flow behavior of the gaseous phase over the biofilm surface areessential for high productivity and CO2 utilization efficiency

Biofilm growth of Chlorella sorokiniana in a rotating biological contactor based photobioreactor

Microalgae biofilms could be used as a production platform for microalgae biomass. In this study, a photobioreactor design based on a rotating biological contactor (RBC) was used as a production platform for microalgae biomass cultivated in biofilm. In the photobioreactor, referred to as Algadisk, microalgae grow in biofilm on vertical rotating disks partially submerged in a growth medium. The objective is to evaluate the potential of the Algadisk photobioreactor with respect to the effects of disk roughness, disk rotation speed and CO2 concentration. These objectives where evaluated in relationship to productivity, photosynthetic efficiency, and long-term cultivation stability in a lab-scale Algadisk system. Although the lab-scale Algadisk system is used, operation parameters evaluated are relevant for scale-up. Chlorella Sorokiniana was used as model microalgae. In the lab-scale Algadisk reactor, productivity of 20.1¿±¿0.7¿g per m2 disk surface per day and a biomass yield on light of 0.9¿±¿0.04¿g dry weight biomass per mol photons were obtained. Different disk rotation speeds did demonstrate minimal effects on biofilm growth and on the diffusion of substrate into the biofilm. CO2 limitation, however, drastically reduced productivity to 2–4¿g per m2 disk surface per day. Productivity could be maintained over a period of 21 weeks without re-inoculation of the Algadisk. Productivity decreased under extreme conditions such as pH 9–10, temperature above 40°C, and with low CO2 concentrations. Maximal productivity, however, was promptly recovered when optimal cultivation conditions were reinstated. These results exhibit an apparent opportunity to employ the Algadisk photobioreactor at large scale for microalgae biomass production if diffusion does not limit the CO2 supply. Biotechnol. Bioeng. 2014;111: 2436–2445. © 2014 Wiley Periodicals, Inc

Study of the feasibility of separation of carrier ampholytes from peptides by hydrophobic interaction chromatography on octyl-sepharose

The merits of hydrophobic interaction chromatography on octyl-Sepharose as a method for the separation of carrier ampholytes from peptides have been investigated. K values for the association of octyl groups with small model peptides and with carrier ampholytes in aqueous sodium chloride-containing phosphate buffers were determined as a function of ionic strength and pH. A separation of a somatomedin-containing peptide mixture into seven fractions by hydrophobic interaction chromatography on octyl-Sepharose is shown