Strategy for selection of methods for separation of bioparticles from particle mixtures

The desired product of bioprocesses is often produced in particulate form, either as an inclusion body (IB) or as a crystal. Particle harvesting is then a crucial and attractive form of product recovery. Because the liquid phase often contains other bioparticles, such as cell debris, whole cells, particulate biocatalysts or particulate by-products, the recovery of product particles is a complex process. In most cases, the particulate product is purified using selective solubilization or extraction. However, if selective particle recovery is possible, the already high purity of the particles makes this downstream process more favorable. This work gives an overview of typical bioparticle mixtures that are encountered in industrial biotechnology and the various driving forces that may be used for particle-particle separation, such as the centrifugal force, the magnetic force, the electric force, and forces related to interfaces. By coupling these driving forces to the resisting forces, the limitations of using these driving forces with respect to particle size are calculated. It shows that centrifugation is not a general solution for particle-particle separation in biotechnology because the particle sizes of product and contaminating particles are often very small, thus, causing their settling velocities to be too low for efficient separation by centrifugation. Examples of such separation problems are the recovery of IBs or virus-like particles (VLPs) from (microbial) cell debris. In these cases, separation processes that use electrical forces or fluid-fluid interfaces show to have a large potential for particle-particle separation. These methods are not yet commonly applied for large-scale particle-particle separation in biotechnology and more research is required on the separation techniques and on particle characterization to facilitate successful application of these methods in industry.     

Hydrodynamic behaviors in fermentative hydrogen bioreactors by pressure fluctuation analysis

Three bioreactor configurations were employed in these investigations, which consisted of working volumes of 10, 1.2 and 1.2 L. Power spectrum diagrams of bed pressure fluctuation were used with hydraulic retention times (HRT) and geometric factors to identify the flow regimes in the bioreactors, where HRT varied from 8 to 1 h. It was found that the flow regimes in the bioreactors changed from a dispersed regime to coalesced and slugging regimes, when the biogas production rate (BPR) increased, as a result of decreasing the operating HRT. The flow regime was a dispersed bubble regime when the HRT was higher than 4 h in the bioreactor, whereas when the HRT was 2 h the coalesced bubble phenomena occurred in the bioreactor. A slugging regime was found when the HRT was lower than 1 h in thinner bioreactor.     

Resistance of bioparticles formed of phosphate-accumulating bacteria and zeolite to harsh environmental conditions

Extreme environmental conditions, such as pH fluctuations, high concentrations of toxicants or grazing of protozoa, can potentially be found in wastewater treatment systems. This study was carried out to provide specific evidence on how ‘bioparticles’ can resist these conditions. The term ‘bioparticle’ is used to describe a particle comprising natural zeolitized tuff with a developed biofilm of the phosphate-accumulating bacterial species, Acinetobacter junii, on the surface. The bacteria in the biofilm were protected from the negative influence of extremely low pH, high concentrations of benzalkonium-chloride and grazing by Paramecium caudatum and Euplotes affinis, even under conditions that caused complete eradication of planktonic bacteria. During an incubation of 24?h, the biofilms were maintained and bacteria detached from the bioparticles, thus bioaugmenting the wastewater. The bioparticles provided a safe environment for the survival of bacteria in harsh environmental conditions and could be used for successful bioaugmentation in wastewater treatment plants.