The academic literature presents various bacterial cell encapsulation methods and their impact on the viability of microbial cells after recovery. The major encapsulation method categories are micro-encapsulation and macro-encapsulation procedures.

Both approaches (micro-encapsulation and macro-encapsulation) aim to immobilize the microbial cell within a porous solid or semi-solid matrix, in order to protect the cell from the hostile environment and avoid biomass loss by a constant outflow rate. The only difference between these methods is the particle size. Micro-encapsulation formulations produce beads with diameters of 1-1000 µm (1 mm), while macro-encapsulation produces particles with a diameter of up to 5 mm. Immobilization may result in changes in the various physico-chemical properties of the microenvironment of the microbial cells, such as the presence of ionic charges, reduced water, altered osmotic pressure, high temperature, space limitation and modified surface tension. These changes can affect the physiology and function of the immobilized cell system. Cell physiology was found to be significantly altered after confinement within the microspheres. Changes in cell physiology and microenvironment conditions probably affect the metabolic activity, proliferation rate and survival of the immobilized bacterial culture.

 

The SBP technology has created a new encapsulation category type under the term ‘large particle encasing a confined environment’ for the encapsulated bacterial culture. This technology is patent-protected and is defined as a novel encapsulation method. The SBP technology provides the following innovative aspects:

  1. Particle size: Large particles (2.5 cm long) that are stable in the presence of intensive shear forces for a period of months. This physical dimension of the SBP capsule also enables on-site control of the implemented biomass by using perforated cages encasing the capsules. This prevents the escape of SBP capsules due to a continuous outflow rate, as demonstrated in various types of wastewater treatment plants. 
    Micro-encapsulated and macro-encapsulated formulations produce beads with diameters of 1-5000 µm (5 mm). Most stable encapsulated formulations are in the size range of less than 500 µm. These small particles create operational difficulties in wastewater treatment, such as on-site control and removal or exchange of these particles from the water. Moreover, lower stability and viability in wastewater environments (i.e., WWTP bioreactor) over time are observed.
  2. SBP particle creates a confined environment: The SBP capsules encase an internal water body that is connected to the host aquatic medium by water channeling, thereby allowing the creation of a confined medium for the internal bacterial culture. The SBP technology does not immobilize the microorganism cells. The novelty of this technology is that it creates a protective aquatic environment for the exogenous microorganism cells within the SBP capsule, without the need to immobilize the bacterial culture. The protective strategy that the SBP technology presents is the use of a constructed microfiltration membrane, instead of integrating the bacterial culture into a perforated biological or/and chemical matrix. The bacterial cells are not immobilized to a polymer or to any other chemical. Rather, they are suspended within the internal aquatic medium of the SBP capsule. The use of a protected suspended bacterial cell culture is assumed to preserve the normal cell physiology and activity and enables the achievement of a high biodegradation rate which is a critical factor in wastewater treatment plants that must meet  limited digestion time specifications (hydraulic retention time-HRT).
  3. High encapsulated biomass concentration: The SBP technology provides an aquatic microenvironment that allows free diffusion of nutrients and oxygen to the bacterial cell culture. The confined aquatic medium within the SBP capsule provides a sufficiently large aquatic volume for bacterial prosperity, such that at any given moment, the biomass will contain bacteria that are found in the various lifecycle stages, similarly to natural growth states and activity. Moreover, the SBP encapsulation technology presents a high biodegradation rate which is probably associated with the presence of the confined aquatic medium and the micro-filtration membrane structure and activity.
    It is important to acknowledge that other published encapsulated formulations pack the bacterial cells within or attached to a polymer. This forms a limited and restricted aquatic medium surrounding the immobilized bacterial cells. The immobilized state creates a physical and physiological limitation on the viability of nutrients to the bacterial cell and on cellular waste disposal. Those limitations have a significant effect on bacterial prosperity (cell divisions) and survival over time. Moreover, it reduces the biodegradation rate generated by the immobilized bacterial cells. 
  4. Rapid biodegradation rate: Rapid trafficking of molecules across the SBP membrane enables a fast biodegradation rate mechanism synchronized to DWWTPs hydraulic retention time (HRT). This allows implementation of the SBP technology within DWWTP bioreactors. The SBP membrane contains two dimensions of molecule-penetration mechanisms: fast path by funnel-like pores (large molecules and colloidal particles as well as small molecules) and slower diffusion through the nano-mesh structure, due to the concentration gradient which enables the flow of small molecules. Both flow paths allow the achievement of a relatively high biodegradation rate. When the bacteria consume the contaminant and mineralize it into carbon dioxide, the internal medium concentration of the contaminant decreases and fresh contaminant molecules from the outer medium spontaneously diffuse into the internal medium of the SBP capsules. It is therefore not necessary to bring the contaminants into the SBP capsules. They will automatically flow into the capsule according to the basic physical law of diffusion.

  

References

Microencapsulation of microbial cells, Sweta Rathore, Parind Mahendrakumar Desai, Celine Valeria Liew, Lai Wah Chan, Paul Wan Sia Heng, Journal of Food Engineering (2013), Vol.116, pages: 369-381.

Is bioaugmentation a feasible strategy for pollutant removal and site remediation? El Fantroussi, S. & Agathos, S. N. Current Opinion in Microbiology (2005), Vol. 8 (3), 268–275.

Microencapsulation of microbial cells. Rathore, S., Desai, P. M., Liew, C. V., Chan, L. W. & Heng, P. W. S. Journal of Food Engineering (2013) Vol. 116, 381–369.

Bioaugmentation: a coming of age. Rittmann, B. E. & Whiteman, R. Biotechnology (1994) Vol.1, 12 –16.

Patent application number PCT/IL2010/000256 (publication number WO2010/122545) Menashe, O. (2010).

The potential of autochthonous microbial culture encapsulation in a con?ned environment for phenol biodegradation. Azaizeh H, Kurzbaum E, Said O, Jaradat H, Menashe O. Environ Sci Pollut Res.(2015) Vol.22:15179– 15187.

Small-bioreactor platform technology as a municipal wastewater additive treatment. Menashe O and Kurzbaum E. Water Sci Technol (2014) Vol.22: 504–510