Continuous harvesting of microalgae by new microfluidic technology for particle separation

Technologies for harvesting the microalgae for industrial applications: Current trends and perspectives

Microalgae are emerging as a promising source for augmenting the supply of essential products to meet global demands in an environmentally sustainable manner. Despite the potential benefits of microalgae in industry, the high energy consumption for harvesting remains a significant obstacle. This review offers a comprehensive overview of microalgae harvesting technologies and their industrial applications, with particular emphasis on the latest advances in flocculation techniques. These cutting-edge methods have been applied to biodiesel production, food and nutraceutical processing, and wastewater treatment. Large-scale harvesting is still severely impeded by the high cost despite progress has been made in laboratory studies. In the future, cost-effective microalgal harvesting will rely on efficient resource utilization, including the use of waste materials and the reuse of media and flocculants. Additionally, precise regulation of biological metabolism will be necessary to overcome algal species-related limitations through the development of extracellular polymeric substance-induced flocculation technology.

Lab on a chip for a low-carbon future

Transitioning our society to a sustainable future, with low or net-zero carbon emissions to the atmosphere, will require a wide-spread transformation of energy and environmental technologies. In this perspective article, we describe how lab-on-a-chip (LoC) systems can help address this challenge by providing insight into the fundamental physical and geochemical processes underlying new technologies critical to this transition, and developing the new processes and materials required. We focus on six areas: (I) subsurface carbon sequestration, (II) subsurface hydrogen storage, (III) geothermal energy extraction, (IV) bioenergy, (V) recovering critical materials, and (VI) water filtration and remediation. We hope to engage the LoC community in the many opportunities within the transition ahead, and highlight the potential of LoC approaches to the broader community of researchers, industry experts, and policy makers working toward a low-carbon future.

Enhancement of microalgae growth using magnetic artificial cilia

Microalgae have shown great potential as a source of biofuels, food, and other bioproducts. More recently, microfluidic devices have been employed in microalgae-related studies. However, at small fluid volumes, the options for controlling flow conditions are more limited and mixing becomes largely reliant on diffusion. In this study, we fabricated magnetic artificial cilia (MAC) and implemented them in millimeter scale culture wells and conducted growth experiments with Scenedesmus subspicatus while actuating the MAC in a rotating magnetic field to create flow and mixing. In addition, surface of MAC was made hydrophilic using plasma treatment and its effect on growth was compared with untreated, hydrophobic MAC. The experiments showed that the growth was enhanced by ten and two times with hydrophobic and hydrophilic MAC, respectively, compared with control groups which contain no MAC. This technique can be used to investigate mixing and flow in small sample volumes, and the enhancement in growth can be beneficial for the throughput of screening studies. Moreover, the methods used for creating and controlling MAC can be easily adopted in labs without microfabrication infrastructures, and they can be mastered by people with little prior experience in microfluidics.

Public-Health-Driven Microfluidic Technologies: From Separation to Detection

Separation and detection are ubiquitous in our daily life and they are two of the most important steps toward practical biomedical diagnostics and industrial applications. A deep understanding of working principles and examples of separation and detection enables a plethora of applications from blood test and air/water quality monitoring to food safety and biosecurity; none of which are irrelevant to public health. Microfluidics can separate and detect various particles/aerosols as well as cells/viruses in a cost-effective and easy-to-operate manner. There are a number of papers reviewing microfluidic separation and detection, but to the best of our knowledge, the two topics are normally reviewed separately. In fact, these two themes are closely related with each other from the perspectives of public health: understanding separation or sorting technique will lead to the development of new detection methods, thereby providing new paths to guide the separation routes. Therefore, the purpose of this review paper is two-fold: reporting the latest developments in the application of microfluidics for separation and outlining the emerging research in microfluidic detection. The dominating microfluidics-based passive separation methods and detection methods are discussed, along with the future perspectives and challenges being discussed. Our work inspires novel development of separation and detection methods for the benefits of public health.

Effect of pluronic block polymers and N-acetylcysteine culture media additives on growth rate and fatty acid composition of six marine microalgae species

Abstract

The efficiency of microalgal biomass production is a determining factor for the economic competitiveness of microalgae-based industries. N-acetylcysteine (NAC) and pluronic block polymers are two compounds of interest as novel culture media constituents because of their respective protective properties against oxidative stress and shear-stress-induced cell damage. Here we quantify the effect of NAC and two pluronic (F127 and F68) culture media additives upon the culture productivity of six marine microalgal species of relevance to the aquaculture industry (four diatoms-Chaetoceros calcitrans, Chaetoceros muelleri, Skeletonema costatum, and Thalassiosira pseudonana; two haptophytes-Tisochrysis lutea and Pavlova salina). Algal culture performance in response to the addition of NAC and pluronic, singly or combined, is dosage- and species-dependent. Combined NAC and pluronic F127 algal culture media additives resulted in specific growth rate increases of 38%, 16%, and 24% for C. calcitrans, C. muelleri, and P. salina, respectively. Enhanced culture productivity for strains belonging to the genus Chaetoceros was paired with an ~27% increase in stationary-phase cell density. For some of the species examined, culture media enrichments with NAC and pluronic resulted in increased omega-3-fatty acid content of the algal biomass. Larval development (i.e., growth and survival) of the Pacific oyster (Crassostrea gigas) was not changed when fed a mixture of microalgae grown in NAC- and F127-supplemented culture medium. Based upon these results, we propose that culture media enrichment with NAC and pluronic F127 is an effective and easily adopted approach to increase algal productivity and enhance the nutritional quality of marine microalgal strains commonly cultured for live-feed applications in aquaculture.

Key points

• Single and combined NAC and pluronic F127 culture media supplementation significantly enhanced the productivity of Chaetoceros calcitrans and Chaetoceros muelleri cultures.

• Culture media enrichments with NAC and F127 can increase omega-3-fatty acid content of algal biomass.

• Microalgae grown in NAC- and pluronic F127-supplemented culture media are suitable for live-feed applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11147-8.

Microfluidics for microalgal biotechnology

Microalgae have expanded their roles as renewable and sustainable feedstocks for biofuel, smart nutrition, biopharmaceutical, cosmeceutical, biosensing, and space technologies. They accumulate valuable biochemical compounds from protein, carbohydrate, and lipid groups, including pigments and carotenoids. Microalgal biomass, which can be adopted for multivalorization under biorefinery settings, allows not only the production of various biofuels but also other value-added biotechnological products. However, state-of-the-art technologies are required to optimize yield, quality, and the economical aspects of both upstream and downstream processes. As such, the need to use microfluidic-based devices for both fundamental research and industrial applications of microalgae, arises due to their microscale sizes and dilute cultures. Microfluidics-based devices are superior to their competitors through their ability to perform multiple functions such as sorting and analyzing small amounts of samples (nanoliter to picoliter) with higher sensitivities. Here, we review emerging applications of microfluidic technologies on microalgal processes in cell sorting, cultivation, harvesting, and applications in biofuels, biosensing, drug delivery, and nutrition.

Clog-Free Trilobite Filtration: Tunable Flow Setup and Velocity Measurements

The ability to separate and filter out microscopic objects lies at the core of many biomedical applications. However, a persistent problem is clogging, as biomaterials stick to the internal chip surface and limit device efficiency and liability. Here, we review an alternative technique that could solve these clogging issues. By leveraging tunable flow fields and particle inertia around special trilobite-shaped filtration units, we perform filtration of plastic beads by size and we demonstrate sorting of live cells. The separation and filtration are performed completely without signs of clogging. However, a clog-free operation relies on a controlled flow configuration to steer the particles and cells away from the filter structures. In this paper, we describe the tunable flow system for such an operation and we describe an optical setup enabling hydrodynamical interactions between particles and cells with the flow fields and direct interactions with the filter structures to be characterized. The optical setup is capable of measuring particle and flow velocities (by Particle Tracking Velocimetry (PTV), Micro Particle Image Velocimetry (μPIV), and streakline visualization) in meters per second necessary to avoid clogging. However, accurate measurements rely on strict calibration and validation procedures to be followed, and we devote a substantial portion of our paper to laying out such procedures. A comparison between μPIV data and a known flow profile is particularly valuable for assessing measurement accuracy, and this important validation has not been previously published by us. The detail level in our description of the flow configuration and optical system is sufficient to replicate the experiments. In the last part of the paper, we review an assessment of the device performance when handling rigid spheres and live cells. We deconvolute the influences of cell shape from effects of size and find that the shape has only a weak influence on device performance.

Sheathless separation of microalgae from bacteria using a simple straight channel based on viscoelastic microfluidics

Microalgae cells have been recognized as a promising sustainable resource to meet worldwide growing demands for renewable energy, food, livestock feed, water, cosmetics, pharmaceuticals, and materials. In order to ensure high-efficiency and high-quality production of biomass, biofuel, or bio-based products, purification procedures prior to the storage and cultivation of the microalgae from contaminated bacteria are of great importance. The present work proposed and developed a simple, sheathless, and efficient method to separate microalgae Chlorella from bacteria Bacillus Subtilis in a straight channel using the viscoelasticity of the medium. Microalgae and bacteria migrate to different lateral positions closer to the channel centre and channel walls respectively. Fluorescent microparticles with 1 μm and 5 μm diameters were first used to mimic the behaviours of bacteria and microalgae to optimize the separating conditions. Subsequently, size-based separation in Newtonian fluid and in viscoelastic fluid in straight channels with different aspect ratios was compared and demonstrated. Under the optimal condition, the removal ratio for 1 μm microparticles and separation efficiency for 5 μm particles can reach up to 98.28% and 93.85% respectively. For bacteria and microalgae cells separation, the removal ratio for bacteria and separation efficiency for microalgae cells is 92.69% and 100% respectively. This work demonstrated the continuous and sheathless separation of microalgae from bacteria for the first time by viscoelastic microfluidics. This technique can also be applied as an efficient and user-friendly method to separate mammalian cells or other kinds of cells.

Microfluidic technology for plankton research

Plankton produces numerous chemical compounds used in cosmetics and functional foods. They also play a key role in the carbon budget on the Earth. In a context of global change, it becomes important to understand the physiological response of these microorganisms to changing environmental conditions. Their adaptations and the response to specific environmental conditions are often restricted to a few active cells or individuals in large populations. Using analytical capabilities at the subnanoliter scale, microfluidic technology has also demonstrated a high potential in biological assays. Here, we review recent advances in microfluidic technologies to overcome the current challenges in high content analysis both at population and the single cell level.

Selective separation of microalgae cells using inertial microfluidics

Microalgae represent the most promising new source of biomass for the world's growing demands. However, the biomass productivity and quality is significantly decreased by the presence of bacteria or other invading microalgae species in the cultures. We therefore report a low-cost spiral-microchannel that can effectively separate and purify Tetraselmis suecica (lipid-rich microalgae) cultures from Phaeodactylum tricornutum (invasive diatom). Fluorescent polystyrene-microbeads of 6 μm and 10 μm diameters were first used as surrogate particles to optimize the microchannel design by mimicking the microalgae cell behaviour. Using the optimum flowrate, up to 95% of the P. tricornutum cells were separated from the culture without affecting the cell viability. This study shows, for the first time, the potential of inertial microfluidics to sort microalgae species with minimal size difference. Additionally, this approach can also be applied as a pre-sorting technique for water quality analysis.

A New Microfluidic Device for Classification of Microalgae Cells Based on Simultaneous Analysis of Chlorophyll Fluorescence, Side Light Scattering, Resistance Pulse Sensing

Fast on-site monitoring of foreign microalgae species carried by ship ballast water has drawn more and more attention. In this paper, we presented a new method and a compact device of classification of microalgae cells by simultaneous detection of three kinds of signals of single microalgae cells in a disposable microfluidic chip. The microfluidic classification device has advantages of fast detection, low cost, and portability. The species of a single microalgae cell can be identified by simultaneous detection of three signals of chlorophyll fluorescence (CF), side light scattering (SLS), and resistance pulse sensing (RPS) of the microalgae cell. These three signals represent the different characteristics of a microalgae cell. A compact device was designed to detect these three signals of a microalgae cell simultaneously. In order to demonstrate the performance of the developed system, the comparison experiments of the mixed samples of three different species of microalgae cells between the developed system and a commercial flow cytometer were conducted. The results show that three kinds of microalgae cells can be distinguished clearly by our developed system and the commercial flow cytometer and both results have good agreement.