Magnetically modified microalgae and their applications.

The majority of algal cells can interact with a wide range of nano- and microparticles. Upon interaction the modified cells usually maintain their viability and the presence of foreign material on their surfaces or in protoplasm can provide additional functionalities. Magnetic modification and labeling of microalgal biomass ensures a wide spectrum of biotechnological, bioanalytical and environmental applications. Different aspects of microalgal cell magnetic modification are covered in the review, followed by successful applications of magnetic algae. Modified cells can be employed during their harvesting and removal, applied in toxicity microscreening devices and also as efficient adsorbents of different types of xenobiotics.

Harvesting freshwater Chlorella vulgaris with flocculant derived from spent brewer's yeast.

One of the key bottlenecks of the economically viable production of low added value microalgal products (food supplements, feed, biofuels) is the harvesting of cells from diluted culture medium. The main goals of this work were to prepare a novel flocculation agent based on spent brewer's yeast, a brewery by-product, and to test its harvesting efficiency on freshwater Chlorella vulgaris in different environments. The yeast was first autolyzed/hydrolyzed and subsequently chemically modified with 2-chloro-N,N-diethylethylamine hydrochloride (DEAE). Second, optimal dosage of modified spent yeast (MSY) flocculant for harvesting C. vulgaris was determined in culture media of various compositions. It was found that the absence of phosphorus ions decreased (0.4 mg MSY/g biomass), while the presence of algogenic organic matter (AOM) increased (51 mg MSY/g biomass) the required dosage of flocculant as compared to complete mineral medium with phosphorus and without AOM (12 mg MSY/g biomass).

Physicochemical approach to freshwater microalgae harvesting with magnetic particles.

Magnetic harvesting of microalgal biomass provides an attractive alternative to conventional methods. The approach to this issue has so far been pragmatic, focused mainly on finding cheap magnetic agents in combination with harvestable microalgae species. The aim of this work was to study experimentally and theoretically the mechanisms leading to cell-magnetic agent attachment/detachment using real experiments and predictions made by colloidal adhesion (XDLVO) model. Two types of well defined magnetic beads (MBs) carrying ion exchange functional groups (DEAE - diethylaminoethyl and PEI - polyethylenimine) were studied in connection with microalgae (Chlorella vulgaris). Optimal harvesting efficiencies (>90%) were found for DEAE and PEI MBs, while efficient detachment was achieved only for DEAE MBs (>90%). These findings were in accordance with the predictions by XDLVO model. Simultaneously there was found a discrepancy between the XDLVO prediction and the poor detachment of PEI MBs from microalgal surface. This can be ascribed to an additional interaction (probably covalent bonds) between PEI and algal surface, which the XDLVO model is unable to capture given by its non-covalent nature.

Harvesting microalgae with microwave synthesized magnetic microparticles.

To make magnetic harvesting a more viable option, a suspension of inexpensive iron oxide magnetic microparticles (IOMMs) prepared by microwave treatment is presented as a new agent for separating Chlorella vulgaris from a highly diluted suspension. Separation efficiencies were tested under various conditions (model environment, cultivation media, different pH), revealing not only a dependency on the pH and amount of IOMMs, but also the influence of the ions present in the culture medium. Phosphorus ions were identified as the medium component interfering with algae-IOMMs interactions that are essential for magnetic cell separations in the culture medium. Phosphorus limited C. vulgaris cells were magnetically separated from the medium at separation efficiencies of over 95% at a 3:1 mass ratio of IOMMs to microalgae. A rapid and complete demagnetization of harvested algae was achieved by acidic treatment (10vol.% H(2)SO(4)) at 40°C under the influence of ultrasound.