The main objective of this work was to investigate the removal of aqueous phenol using immobilized enzymes in both bench scale and pilot scale three-phase fluidized bed reactors. The enzyme used in this application was a fungal tyrosinase [E.C. 1.14.18.1] immobilized in a system of chitosan and alginate. The immobilization matrix consisted of a chitosan matrix cross-linked with glutaraldehyde with an aliginate-filled pore space. This support matrix showed superior mechanical properties along with retaining the unique adsorptive characteristics of the chitosan. Adsorption of the o-quinone product by the chitosan reduced tyrosinase inactivation that is normally observed for this enzyme under these conditions. This approach allowed reuse of the enzyme in repeated batch applications. For the bench scale reactor (1.2-l capacity) more than 92% of the phenol could be removed from the feed water using an immobilized enzyme volume of 18.5% and a residence time of the liquid phase of 150 min. Removal rates decreased with subsequent batch runs. For the pilot scale fluidized bed (60 l), 60% phenol removal was observed with an immobilized enzyme volume of 5% and a residence time of the liquid phase of 7 h. Removal decreased to 45% with a repeat batch run with the same immobilized enzyme.
The emerging accumulation of microplastics (MPs) in global waters is of increasing concern and it is posing great health risks to both humans and aquatic species, yet suitable technologies to remove MPs are lacking. The objective of this study was to investigate activated sludge as a source of promising biocatalysts for the removal of MPs in water. Bacterial communities in activated sludge were first screened for their potential to degrade hydrolyzable plastics from polyethylene terephthalate (PET) pre-treated at 100 C for 1 hour. The consortium grew on a mineral medium with PET MPs as the sole carbon and energy source. To further assess its degrading potential, the consortium was put through a standardized CO 2 evolution test at a temperature of 30 C, pH 7-7.5, reactor residence time 168 days, and PET concentration of 2.63 g/L. The biodegradation extent was further validated through assessment of morphological/structural changes on the PET by means of SEM, DSC, FTIR, and viscometry analyses. Upon incubation, the consortium degraded 17% of PET. The molecular weight remained unchanged, reflecting a degradation via surface erosion. Furthermore, the biodegradation was significantly enhanced at high oxygen flow rates. Two bacterial strains within the consortium were isolated and identified as Bacillus cereus SEHD031MH and Agromyces mediolanus PNP3. Both strains thrived when individually cultured with PET while only B. cereus showed enzymatic activity during a clear-zone test. The examined bacterial strains possess a promising PET-degrading activity that can be further investigated and applied to the elimination of MPs water/wastewater through innovative and effective technologies.
The plug flow model (PFM), overwhelmingly used to describe mass transfer in bubble columns and three‐phase fluidized beds, has never been critically tested. This study analyzes the PFM single parameter, KLa, to quantify mass transfer in the forementioned systems.
Particular attention is paid to the mass transfer features of the zone near the distributor (grid zone) largely ignored until now. This study, carried out under the largest gas and liquid flow rates ever published, for similar types of systems, indicates the presence of two well defined mass transfer zones. These features invalidate, for design purposes, the use of the PFM. However, it still can be used as a qualitative mass transfer indicator. This has permitted a comparison between the mass transfer efficiency of bubble columns and three‐phase fluidized beds with the conclusion that three‐phase fluidized bed of 0.5 cm particles can compete successfully with bubble columns.
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