Understanding the salinity effect on cationic polymers in inducing flocculation of the microalga Neochloris oleoabundans.

A mechanistic study was performed to evaluate the effect of salinity on cationic polymeric flocculants, that are used for the harvesting of microalgae. The polyacrylamide Synthofloc 5080H and the polysaccharide Chitosan were employed for the flocculation of Neochloris oleoabundans. In seawater conditions, a maximum biomass recovery of 66% was obtained with a dosage of 90mg/L Chitosan. This recovery was approximately 25% lower compared to Synthofloc 5080H reaching recoveries greater than 90% with dosages of 30mg/L. Although different recoveries were obtained with both flocculants, the polymers exhibit a similar apparent polymer length, as was evaluated from viscosity measurements. While both flocculants exhibit similar polymer lengths in increasing salinity, the zeta potential differs. This indicates that polymeric charge dominates flocculation. With increased salinity, the effectivity of cationic polymeric flocculants decreases due to a reduction in cationic charge. This mechanism was confirmed through a SEM analysis and additional experiments using flocculants with various charge densities.

Dosage effect of cationic polymers on the flocculation efficiency of the marine microalga Neochloris oleoabundans.

A mechanistic mathematical model was developed to predict the performance of cationic polymers for flocculating salt water cultivated microalgae. The model was validated on experiments carried out with Neochloris oleoabundans and three different commercial flocculants (Zetag 7557®, Synthofloc 5080H® and SNF H536®). For a wide range of biomass concentrations (0.49-1.37 g L(-1)) and flocculant dosages (0-150 mg L(-1)) the model simulations predicted well the optimal flocculant-to-biomass ratio between 43 and 109 mgflocculant/gbiomass. At optimum conditions biomass recoveries varied between 88% and 99%. The cost of the usage of commercial available flocculants is estimated to range between 0.15$/kgbiomass and 0.49$/kgbiomass.

Immobilized salt-tolerant yeasts: application of a new polyethylene-oxide support in a continuous stirred-tank reactor for flavour production.

Immobilization of salt-tolerant yeasts considerably decreases the total time required for the flavour development in soy-sauce processes. For immobilization of cells, alginate gel is mostly used as support material. However, alginate is not very suitable for use in soy-sauce processes because alginate is sensitive to abrasion and chemically unstable towards the high salt content of the soy-sauce medium. In contrast, a newly developed polyethylene-oxide gel seems to be more suitable, but this gel has not been used so far for flavour production in a bioreactor with a high salt content. Therefore, this gel was applied with immobilized salt-tolerant yeasts in a continuous stirred-tank reactor, containing more than 12.5% (w/v) salt. In this reactor, the polyethylene-oxide gel particles did not show any abrasion for several days, while alginate gel beads were already destroyed within 1 day. In addition, the polyethylene-oxide gel particles with immobilized salt-tolerant yeasts Candida versatilis and Zygosaccharomyces rouxii showed a good flavour production. From this work, it was concluded that the application of polyethylene-oxide gel in long-term soy-sauce processes is attractive in the case the sticking together of polyethylene-oxide gel particles can be controlled.

Immobilized soy-sauce yeasts: development and characterization of a new polyethylene-oxide support.

Entrapment of cells in alginate gel is a widely used mild immobilization procedure. However, alginate gel is not very suitable for use in long-term continuous soy-sauce processes because alginate is sensitive to abrasion and chemically unstable towards the high salt content of soy-sauce medium. Therefore, a chemically crosslinked polyethylene-oxide gel was used instead. The disadvantage of this gel was that due to the crosslinking reaction, the viability of the cells after immobilization was poor. For this reason, a new mild procedure for immobilizing soy-sauce yeasts in polyethylene-oxide gel was developed, resulting in high survival percentages of the soy-sauce yeasts Zygosaccharomyces rouxii and Candida versatilis. This newly developed polyethylene-oxide gel, unlike alginate gel, appeared not to be sensitive to abrasion, even in the presence of high salt concentrations. Therefore, we concluded that this newly developed polyethylene-oxide gel is more suitable than alginate gel for use as immobilization material in long-term processes with a high salt content, like soy-sauce processes.

Mechanism behind autoflocculation of unicellular green microalgae Ettlia texensis.

The oleaginous Ettlia texensis is an autoflocculating green microalga that can be used for bio-flocculation of other microalgae species to facilitate harvesting. In this study the mechanism behind autoflocculation of E. texensis was revealed by scanning electron microscopy (SEM) analysis and by characterisation of the cell surface properties. SEM analysis and measurement of extracellular polymeric substances (EPS) showed that autoflocculation of E. texensis is due to the EPS containing mainly glycoproteins patched to the cell surface. Despite the presence of charged groups on the cell surface, they do not seem to attribute to autoflocculation of E. texensis. During bio-flocculation of E. texensis with Chlorella vulgaris EPS structures between both microalgal species were observed. EPS thus not only play a predominant role in autoflocculation of E. texensis but also in bio-flocculation when using this microalga to harvest others.

Cationic polymers for successful flocculation of marine microalgae.

Flocculation of microalgae is a promising technique to reduce the costs and energy required for harvesting microalgae. Harvesting marine microalgae requires suitable flocculants to induce the flocculation under marine conditions. This study demonstrates that cationic polymeric flocculants can be used to harvest marine microalgae. Different organic flocculants were tested to flocculate Phaeodactylum tricornutum and Neochloris oleoabundans grown under marine conditions. Addition of 10 ppm of the commercial available flocculants Zetag 7557 and Synthofloc 5080H to P. tricornutum showed a recovery of, respectively, 98% ± 2.0 and 94% ± 2.9 after flocculation followed by 2h sedimentation. Using the same flocculants and dosage for harvesting N. oleoabundans resulted in a recovery of 52% ± 1.5 and 36% ± 11.3. This study shows that cationic polymeric flocculants are a viable option to pre-concentrate marine cultivated microalgae via flocculation prior to further dewatering.

Effect of growth phase on harvesting characteristics, autoflocculation and lipid content of Ettlia texensis for microalgal biodiesel production.

The effect of growth phase on the recovery of the autoflocculating microalgae Ettlia texensis was studied. In the stationary phase, 90% recovery was achieved after 3h settling. Scanning electron microscopic pictures revealed that extracellular polymeric substances (EPS) on the cell surface were involved in autoflocculation. During the stationary phase an increase of the protein fraction in the EPS was observed while the total fatty acids content increased. The autoflocculating properties of E. texensis combined with favourite fatty acid content and composition make this microalgae an excellent candidate for biodiesel production if harvested at the end of the stationary phase.

Effect of natural and chimeric haemagglutinin genes on influenza A virus replication in baby hamster kidney cells.

Baby hamster kidney (BHK21) cells are used to produce vaccines against various viral veterinary diseases, including rabies and foot-and-mouth-disease. Although particular influenza virus strains replicate efficiently in BHK21 cells the general use of these cells for influenza vaccine production is prohibited by the poor replication of most strains, including model strain A/PR/8/34 [H1N1] (PR8). We now show that in contrast to PR8, the related strain A/WSN/33 [H1N1] (WSN) replicates efficiently in BHK21 cells. This difference is determined by the haemagglutinin (HA) protein since reciprocal reassortant viruses with swapped HAs behave similarly with respect to growth on BHK21 cells as the parental virus from which their HA gene is derived. The ability or inability of six other influenza virus strains to grow on BHK21 cells appears to be similarly dependent on the nature of the HA gene since reassortant PR8 viruses containing the HA of these strains grow to similar titres as the parental virus from which the HA gene was derived. However, the growth to low titres of a seventh influenza strain was not due to the nature of the HA gene since a reassortant PR8 virus containing this HA grew efficiently on BHK21 cells. Taken together, these results suggest that the HA gene often primarily determines influenza replication efficiency on BHK21 cells but that in some strains other genes are also involved. High virus titres could be obtained with reassortant PR8 strains that contained a chimeric HA consisting of the HA1 domain of PR8 and the HA2 domain of WSN. HA1 contains most antigenic sites and is therefore important for vaccine efficacy. This method of producing the HA1 domain as fusion to a heterologous HA2 domain could possibly also be used for the production of HA1 domains of other viruses to enable the use of BHK21 cells as a generic platform for veterinary influenza vaccine production.

Rheological properties and mechanical stability of new gel-entrapment systems applied in bioreactors.

The mechanical stability of gels applied for entrapment and retention of biocatalysts in bioreactors is of crucial importance for successful scale-up applications. Gel abrasion in agitated reactors will depend on liquid shear, bubble shear, and wall shear, as well as collisions between the gel particles. As a simplified standardized model system, abrasion of gel beads was studied in 1-m-high bubble columns with controlled aeration, and quantified by measuring the loss of gel material into solution. Gel beads were also taken out to measure stress-strain response during controlled compression. More general rheological properties of different gels were studied by applying a variety of regimes of controlled compression of standardized gel cylinders: Gel strength was measured by recording the fracture properties and the Young's modulus. Viscoelastic properties were revealed by recording creep during compression as well as recovery after compression. Oscillation tests up to 1000 cyclic compressions were applied to compare the fatigue of different gels. Results obtained for Ca-alginate gels, gels of chemically modified polyvinyl alcohol with stilbazolium groups (PVA-SbQ) as well as mixed gels of Ca-alginate and PVA-SbQ are compared with previously published data for kappa-carrageenan, agar, and polyethylene glycol (PEG) gels. It is concluded that material fatigue rather than mechanical properties such as stiffness or fracture stress should be considered when selecting a suitable gel material on the basis of abrasion resistance. The very soft and superelastic PVA-SbQ gel showed no significant fatigue in mechanical tests and no abrasion was detected in the standardized model system used. Ca-alginate gels, however, showed severe irreversible changes due to fatigue at oscillating loads and creep at constant load. Due to their similarities with kappa-carrageenan gels in mechanical tests, it is likely that Ca-alginate would also be sensitive to abrasion. Mixed gels of Ca-alginate and PVA-SbQ represent a complex system with intermediate properties, showing significant fatigue and creep, but elastic properties from the PVA-SbQ gel make it less sensitive than the pure Ca-alginate gel.

Simultaneous nitrification and denitrification using immobilized microorganisms.

Nitrogen removal from wastewaters is a multiple step process in which nitrification is often a problem due to the slow growth rates of the nitrifying bacteria. By immobilization of these bacteria, nitrification can be efficiently accomplished in compact reactors. In this paper, the possibilities of integrated nitrification and denitrification within a single reactor system are evaluated. Two main systems are studied: a) Nitrosamines europaea and Pseudomonas denitrificans co-immobilized in a a gel bead and operated in an air-lift reactor; b) the same bacteria separately immobilized and operated in different compartments of a multiple gas-lift reactor.