Abaynesh Yihdego Gebreyohannes

Pectinases immobilization on magnetic nanoparticles and their anti-fouling performance in a biocatalytic membrane reactor

Enzyme immobilization on commercial superparamagnetic nanoparticles (NPSP) was performed using covalent bonding. The biofunctionalized NPSP was then immobilized on the surface of the membrane using an external magnetic field to form a magneto-responsive biocatalytic membrane reactor (BMRSP). The magnetically formed smart nanolayer can be easily re-dispersed and recovered from the membrane when the enzyme is deactivated or whenever cleaning is required due to substrate over-accumulation. The system was used to hydrolyze pectin contained in different streams. Results are supported with complementary data from hydrodynamic, kinetic and morphological characterization in a flow-through reactive filtration. Wavelength-dispersive X-ray spectroscopy (WDS) elemental mapping revealed that the NPSP are uniformly dispersed on the surface of the membrane forming a thin biocatalytic layer. Both results of hydrodynamic studies and SEM micrographs of the membrane with the enzyme layer under various operating conditions, show that the immobilized enzyme effectively reduced membrane–foulant interaction. Comparison of filtration data using this commercial NPSP reveals good agreement with our previously used home-made NPSP. This implies that the scaling-up and commercialization of the developed BMRSP can be straightforward.

Phosphotriesterase-Magnetic Nanoparticle Bioconjugates with Improved Enzyme Activity in a Biocatalytic Membrane Reactor

The need to find alternative bioremediation solutions for organophosphate degradation pushed the research to develop technologies based on organophosphate degrading enzymes, such as phosphotriesterase. The use of free phosphotriesterase poses limits in terms of enzyme reuse, stability, and process development. The heterogenization of enzyme on a support and their use in bioreactors implemented by membranes seems a suitable strategy, thanks to the ability of membranes to compartmentalize, to govern mass transfer, and to provide a microenvironment with tuned physicochemical and structural properties. Usually, hydrophilic membranes are used since they easily guarantee the presence of water molecules needed for the enzyme catalytic activity. However, hydrophobic materials exhibit a larger shelf life and are preferred for the construction of filters and masks. Therefore, in this work, hydrophobic polyvinylidene fluoride (PVDF) porous membranes were used to develop biocatalytic membrane reactors (BMR). The phosphotriesterase-like lactonase (PLL) enzyme ( SsoPox triple mutant from S. solfataricus) endowed with thermostable phosphotriesterase activity was used as model biocatalyst. The enzyme was covalently bound directly to the PVDF hydrophobic membrane or it was bound to magnetic nanoparticles and then positioned on the hydrophobic membrane surface by means of an external magnetic field. Investigation of kinetic properties of the two BMRs and the influence of immobilized enzyme amount revealed that the performance of the BMR was mostly dependent on the amount of enzyme and its distribution on the immobilization support. Magnetic nanocomposite mediated immobilization showed a much better performance, with an observed specific activity higher than 90% compared to grafting of the enzyme on the membrane. Even though the present work focused on phosphotriesterase, it can be easily translated to other classes of enzymes and related applications.

Municipal Wastewater Treatment by Membrane Bioreactors

While the population and therefore the demand for water keep increasing alarmingly, the type and quantity of water source remains the same. This leads the world to water scarcity. In this chapter, the need for wastewater recycling and stringent rules to control water pollution, instigated by water scarcity, is identified as the main driving force for the current and future increase in the use of advanced wastewater treatment systems. The types and sources of wastewater, water pollution, and pollutants along with the available treatment technologies are described. The need to continue to develop new strategies for water management is recommended. In most scenarios water reuse and/or recycling are deemed to be financially feasible approaches and hence are discussed as vital in this chapter. Municipal wastewater represents a large volume of wastewater released from different sources. The wastewater is rich in organic and inorganic compounds with high biodegradability. This chapter discusses Membrane Bioreactor (MBR) process with a special focus on biomass-based MBRs and its suitability for municipal wastewater treatment/reclamation in comparison with the existing conventional treatment technologies. Selected groups of microbes isolated and described in the literature as efficient for use in MBR systems are highlighted. The effort, desire, and market trends on MBR for municipal/domestic wastewater treatment and valorization are commentated by reviewing a wide range of projects funded by EU and other reports. It is also noted that, although there is progressive development and significant rise in the use of MBRs, severe membrane fouling and presence and retention of emerging micropollutants limited its further success. Remark is given to the importance of integrating MBR with emerging membrane operations and the simultaneous use of enzyme membrane reactors and mixed community of microbes to reclaim municipal wastewater with a desirable quality.