CO2 conversion by microalgae and waste valorization

CO2 utilization by microalgae for the production of valuable bio-based products including renewable fuels and nutraceuticals is one of the key strategic areas of the RICH Center. Detailed characterization is at the heart of the conversion processes because characterization guarantees high process performance efficiencies and product yields. The center is equipped with facilities for observing the microscale structure of microalgae and characterizing the carbohydrate, lipid, protein, and pigment contents of microalgae before extraction. Facilities for downstream processes such as centrifugation for harvesting, freeze drying for dewatering, and controlled/incubated shaking system for lipid/pigment extraction and transesterification are available. The center has a supercritical CO2 system for a more sustainable microalgal conversion to ensure low toxicity, easy product recovery, and operation at low temperatures.

The center is also equipped with tools for waste valorization. Tools for emerging trends in this area such as protein hydrolysate extraction from fish wastes, microalgal cultivation using food waste effluent, and oil spill sorption and recovery are available. The center also has pyrolysis and fermentation units for direct conversion of biomass and food wastes into biogas, bio-oil, biochar, and fermentation products. Food wastes and oil spill contribute considerably to global CO2 emissions.

Some of the facilities and tools in the center for CO2 conversion by microalgae and waste valorization are listed as follows.

  • EVOS XL Cell Imaging Systems: Imaging live and fixed cells and culture determinations (density and growth).
  • Pyrolysis unit: A horizontal tubular quartz reactor fixed inside an encapsulating furnace with digital temperature and inert gas flow rate controls.
  • Bioreactor Fermentation unit: Acidogenesis of food wastes into volatile fatty acids. Equipped with temperature-, pressure-, pH-, agitation- and air flow rate-control.
  • Lab Companion Incubated Shaker IST-3075 system: Temperature-controlled shaking. Cultivation of microalgae, downstream unit processes, fish waste hydrolysis, and crude oil sorption/herding/dispersion. Measurement of protein, carbohydrate, and lipid content through standard protocols such as Hartree-Lowry method, Phenol-Sulfuric Acid method, and Bligh and Dyer Method.
  • OHAUS High Speed Centrifuge and TOPT-10A LCD display Freeze Dryer: Harvesting and dewatering of microalgae. Food waste protein drying after isolation or hydrolysis.
  • Supercritical CO2 system: Lipid and carotenoid extraction, possible combined extraction-reaction process.

The supercritical CO2 system is also in used for other applications, including the synthesis of advanced materials.

The center also uses facilities in the Core Labs, including:

  • FEI Quanta250 ESEM and FEI Nova Nano SEM 30 Series: The morphological characteristics of microalgae and oil sorbent samples are obtained using these microscopes.
  • Witec Alpha 300R Raman Spectrometer: Raman signals with visible laser at a wavelength of 532 nm. The molecular arrangements in the chemical structures of protein wastes, oil sorbent and microalgae samples are compared using Raman spectroscopy.
  • Bruker Vertex 80v FT-IR Spectrometer: Characterization of the functional groups in biomass samples.
  • XRD PANalytical Empyrean: Assessing the crystallinity or otherwise (aromaticity or amorphousness) of biomass samples.
  • NETZSCH High Temperature TGA: Batch pyrolysis or thermal analysis of sorbents and microalgae