The effects of medium salinity on the delivery of carbon dioxide to microalgae from capture solvents using a polymeric membrane system

Efficient provision of carbon dioxide to microalgae is one of the major challenges to cost-effective large-scale cultivation. Previously, we have demonstrated the effectiveness of a novel membrane system in delivering CO2 to a marine strain of Chlorella sp. from CO2-loaded solvents. In this approach, the solvent is pumped through a non-porous hollow fibre membrane immersed in a microalgae medium, allowing passive transfer of CO2 that is utilised by the microalgae to enhance their growth, while simultaneously regenerating the solvent. In this article, we compare the growth of both fresh water and marine strains of algae using this membrane delivery system. While the fresh water medium has less pH buffering capacity and can dissolve less CO2, it proves similarly effective in delivering CO2 to the growing algae. Both the freshwater and marine species of Chlorella have slightly higher growth rates than the other species tested—Dunaliella tertiolecta and Haematococcus pluvialis. However, due to the lower osmotic pressure of the fresh water medium, more water is drawn through the membrane into the solvent than when the salt water medium is used. In conclusion, while CO2 delivery through the membrane system is effective for both salt and fresh water media, better performance is obtained for the salt water medium

Ultrasonic encapsulation - A review

Encapsulation of materials in particles dispersed in water has many applications in nutritional foods, imaging, energy production and therapeutic/diagnostic medicine. Ultrasonic technology has been proven effective at creating encapsulating particles and droplets with specific physical and functional properties. Examples include highly stable emulsions, functional polymeric particles with environmental sensitivity, and microspheres for encapsulating drugs for targeted delivery. This article provides an overview of the primary mechanisms arising from ultrasonics responsible for the formation of these materials, highlighting examples that show promise particularly in the development of foods and bioproducts

Enhanced CO2 bio-utilization with a liquid-liquid membrane contactor in a bench-scale microalgae raceway pond

Microalgae are able to absorb CO2 generated from sources such as flue gas to produce biomass with high lipid content. In this research, an immersed liquid-liquid membrane contactor was investigated to deliver CO2 captured by a chemical solvent to the microalgae culture via semipermeable membranes. Experiments showed that the CO2 mass transfer could be facilitated by using a thinner membrane support layer, or avoiding a support altogether, as the support was liquid filled which reduced the mass transfer coefficient. In order to better condition the culture media, the solvent flow was controlled by pH feedback. This scenario showed comparable biomass productivity (0.10 g L-1 d-1) to the conventional direct bubbling method, but with a lower energy cost and higher CO2 utilization efficiency. Further, a pond liner was formed from flat sheet membranes as a more effective alternative to a hollow fiber arrangement. The optimized system achieved a CO2 utilization efficiency of up to 90% compared to 47% with the uncontrolled hollow fiber membrane system and 11% for air sparging, thereby reducing the CO2 released to the atmosphere

Critical review of strategies for CO2 delivery to large-scale microalgae cultures

Microalgae have great, yet relatively untapped potential as a highly productive crop for the production of animal and aquaculture feed, biofuels, and nutraceutical products. Compared to conventional terrestrial crops they have a very fast growth rate and can be produced on non-arable land. During microalgae cultivation, carbon dioxide (CO2) is supplied as the carbon source for photosynthesising microalgae. There are a number of potential CO2 supplies including air, flue gas and purified CO2. In addition, several strategies have been applied to the delivery of CO2 to microalgae production systems, including directly bubbling CO2-rich gas, microbubbles, porous membrane spargers and non-porous membrane contactors. This article provides a comparative analysis of the different CO2 supply and delivery strategies and how they relate to each other

A study of the effectiveness and energy efficiency of ultrasonic emulsification

Three essential experimental parameters in the ultrasonic emulsification process, namely sonication time, acoustic amplitude and processing volume, were individually investigated, theoretically and experimentally, and correlated to the emulsion droplet sizes produced. The results showed that with a decrease in droplet size, two kinetic regions can be separately correlated prior to reaching a steady state droplet size: a fast size reduction region and a steady state transition region. In the fast size reduction region, the power input and sonication time could be correlated to the volume-mean diameter by a power-law relationship, with separate power-law indices of −1.4 and −1.1, respectively. A proportional relationship was found between droplet size and processing volume. The effectiveness and energy efficiency of droplet size reduction was compared between ultrasound and high-pressure homogenisation (HPH) based on both the effective power delivered to the emulsion and the total electric power consumed. Sonication could produce emulsions across a broad range of sizes, while high-pressure homogenisation was able to produce emulsions at the smaller end of the range. For ultrasonication, the energy efficiency was higher at increased power inputs due to more effective droplet breakage at high ultrasound intensities. For HPH the consumed energy efficiency was improved by operating at higher pressures for fewer passes. At the laboratory scale, the ultrasound system required less electrical power than HPH to produce an emulsion of comparable droplet size. The energy efficiency of HPH is greatly improved at large scale, which may also be true for larger scale ultrasonic reactors

The inhibitory roles of native whey protein on the rennet gelation of bovine milk

Rennet gelation is used to produce many types of cheese. The effect of native whey protein on rennet gelation kinetics was investigated. Milks with a wide range of whey protein:casein (WP:CN) ratios (with standardised casein concentrations) were made from powders produced by microfiltration. Measurements of casein macro peptide release showed that native whey protein inhibited the enzymatic action of chymosin, which delayed the onset and reduced the subsequent rate of gelation. Experiments in which increased chymosin concentrations compensated for the inhibition, demonstrated that other factors also contributed to the reduced gelation rate. Neither an increase in viscosity nor a reduction in soluble calcium was responsible, leading to the conclusion that in addition to inhibiting chymosin, native whey proteins present a physical barrier to para-casein aggregation. This study demonstrates and explains how casein-enriched retentates from microfiltration gel faster than regular cheese milk that contains higher amounts of native whey protein

Energy evaluation of algal cell disruption by high pressure homogenisation

The energy consumption of high pressure homogenisation (HPH) was analysed to determine the feasibility of rupturing algal cells for biodiesel production. Experimentally, the processing capacity (i.e. flow rate), power draw and cell disruption efficiency of HPH were independent of feed concentration (for Nannochloropsis sp. up to 25% w/w solids). Depending on the homogenisation pressure (60–150 MPa), the solids concentration (0.25–25% w/w), and triacylglyceride (TAG) content of the harvested algal biomass (10–30%), the energy consumed by HPH represented between 6% and 110-times the energy density of the resulting biodiesel. Provided the right species (weak cell wall and high TAG content) is selected and the biomass is processed at a sufficiently high solids concentration, HPH can consume a small fraction of the energy content of the biodiesel produced. This study demonstrates the feasibility of process-scale algal cell disruption by HPH based on its energy requirement

Ultrasonic pretreatment of food waste to accelerate enzymatic hydrolysis for glucose production

Recovering valuable materials from food waste by applying the concept of a bio-refinery is attracting considerable interest. To this effect, we investigated the possibility of enhancing the enzymatic hydrolysis of food waste using ultrasonic technology. The effect of pre-treating blended food waste with high-intensity ultrasound (20 kHz) on subsequent hydrolysis by glucoamylase was investigated as a function of sonication time and temperature. Particle sizing by laser diffraction, and imaging via scanning electronic microscopy showed that ultrasonic pre-treatment could reduce the particle size of the blended food waste significantly, resulting in a better interaction with the enzyme. As a consequence, the glucose yield of enzymatic hydrolysis was ∼10% higher for food waste pre-sonicated using the most intensive ultrasonication conditions studied (5 min sonication at a power of 0.8 W/mL at 20 °C) than for the untreated control. In addition, the time required to achieve high yields of glucose could be more than halved using ultrasonic pre-treatment. This could enable the hydrolysis reactor size or the enzyme usage to be reduced by more than 50%. Therefore, an ultrasound-assisted bioconversion process from food waste into a value-added product has been demonstrated