Effect of dilution rate on dynamic and steady-state biofilm characteristics during phenol biodegradation by immobilized Pseudomonas desmolyticum cells in a pulsed plate bioreactor

Continuous pulsed plate bioreactor (PPBR) was used for phenol biodegradation. Pseudomonas desmolyticum cells immobilized on granular activated carbon was used. Dynamic and steady state biofilm characteristics depend on dilution rate (DR). Lower DR favour phenol degradation and uniform, thick biofilm formation. Exo polymeric substance production in biofilm are favoured at lower dilution rates. Pulsed plate bioreactor (PPBR) is a biofilm reactor which has been proven to be very efficient in phenol biodegradation. The present paper reports the studies on the effect of dilution rate on the physical, chemical and morphological characteristics of biofilms formed by the cells of Pseudomonas desmolyticum on granular activated carbon (GAC) in PPBR during biodegradation of phenol. The percentage degradation of phenol decreased from 99% to 73% with an increase in dilution rate from 0.33 h?1 to 0.99 h?1 showing that residence time in the reactor governs the phenol removal efficiency rather than the external mass transfer limitations. Lower dilution rates favor higher production of biomass, extracellular polymeric substances (EPS) as well as the protein, carbohydrate and humic substances content of EPS. Increase in dilution rate leads to decrease in biofilm thickness, biofilm dry density, and attached dry biomass, transforming the biofilm from dense, smooth compact structure to a rough and patchy structure. Thus, the performance of PPBR in terms of dynamic and steady-state biofilm characteristics associated with phenol biodegradation is a strong function of dilution rate. Operation of PPBR at lower dilution rates is recommended for continuous biologic treatment of wastewaters for phenol removal.