Phenol and 4-chlorophenol biodegradation by yeast Candida tropicalis in a fluidized bed reactor

The objective of this work was to evaluate (i) the hydrodynamics and oxygen transfer characteristics of a fluidized bed reactor (FBR) and (ii) their performance in the continuous biodegradation of a phenol (Phe) and 4-chlorophenol (4-CP)-containing influent when the FBR was loaded with Candida tropicalis yeast immobilized onto granular activated carbon (GAC) particles. The first part was carried out in terms of the behavior of mixing time (t_m95), bubble diameter (d_B), gas hold-up (ε_G), gas-liquid interfacial area (a′) and oxygen transfer coefficient (k_La) in biphasic (gas-liquid) and triphasic (gas-liquid-carbon) systems, both batch-wise operated in pseudohomogeneous regime at superficial gas flow rates U_G below 1.72 cm s^-1. Mixing time was determined using a tracer technique, ε_G was measured by the volume expansion method; (d_B) was determined by the procedure reported by Poulsen and Iversen and k_La was determined by a transient gassing-in technique. It was found that hydrodynamic variables were severely influenced by GAC particles. The d_B values were smaller in triphasic than in biphasic system, with the consequent increase in the ε_G, a′ and k_La values. The removal efficiencies of both Phe and 4-CP in the bioreactor challenged at increasing volumetric loading rate of pollutants were determined in the second part of the study. Phe and 4-CP was determined by HPLC. Immobilized biomass on GAC was estimated from their total nitrogen content. Regarding continuous biodegradation experiments, the FBR was capable of efficiently removing Phe at volumetric loading rates as high as 60 mg Phe L^-1 h^-1 when it was fed as the sole carbon source. Beyond this point, removal efficiencies drastically decreased. When operated with a feed consisting of a mixture of Phe and 4-CP, the FBR was able to remove more than 98% of 4-CP in the range of volumetric loading rates of 4.1 mg 4-CP L^-1 h^-1 and 55 mg Phe L^-1 h^-1 with no apparent deterioration of bioreactor performance.