Modeling the effect of immobilization of microorganisms on the rate of biodegradation of phenol under inhibitory conditions

The main objective of this research is to model the effect of biodegradation process of phenol at high initial concentrations using a well known immobilization technique of the biomass. This work focused on testing the effect of activated carbon and clay while considering the diffusive internal mass transfer limitations. Biodegradation of phenol was performed by using enriched microorganisms from a compost of agricultural wastes. The average phenol biodegradation rate (uptake) of free biomass system was 235.3 mg g−1 h−1 at initial concentration range of 212–260 mg/L. However, the values for the systems of immobilized biomass in alginate and activated carbon (1 mm), alginate, activated carbon (4 mm), alginate, activated carbon and clay (1 mm) and alginate, activated carbon and clay (4 mm) were 64.9, 27.6, 27.5, and 8 mg g−1 h−1 respectively. The effective diffusion factors in different matrix were obtained using an intra-particle diffusion-based mathematical model. Diffusion limitation was observed when the matrix contained clay in addition to activated carbon. The diffusion coefficient was decreased from 1.6 × 10−8 to 1.2 × 10−9 cm2/s when clay was added to the matrix of 1 mm of alginate and activated carbon. Also, slight differences between the diffusion factors were observed for larger beads. The combination of clay and AC contributes to better mineralization of phenol at high concentrations. This could be attributed to the synergism of both additives.