Validation of Monod Model for the Removal of Styrene from Waste Gas Stream

Abstract

In the past decades biofiltration used to as a promising choice to other conventional volatile organic compounds control technologies actually for low inlet concentration and higher gas stream flow rates. The objective of this research was to investigate the kinetic behavior of the biofiltration process for the removal of styrene. The biodegradation kinetics of styrene estimated with measuring the removal rates along the biofilter column operating under continuous conditions. Experiments were conducted in a laboratory-scale three segment biofilter with a mixture of sieved compost and inert plastic chips as the filter material. Thickened activated sludge was used to improve the microbial density of the bed material. The reaction order rate constants obtained from continuous experiment and were used as the specific growth rate in the Monod kinetics. The half saturation constant on the Monod kinetic expression was then estimated by fitting the experimental results on the removals of low concentrations of styrene over the entire biofilter. As results indicate, at higher loadings such as 75 and 45 g m(-3) h(-1), the measured concentration profiles show a liner dependence on the bed height in the biofilter. This is the condition of reaction limitation for a reaction with zero-order kinetics. From the experimental data, maximum elimination capacity (EC(max)) was estimated to be 44, 40 and 26 g m(-3) h(-1) at empty bed retention times (EBRTs) of 120, 60 and 30 s, respectively. However at the lower loadings, the measured concentration profile of biofilter is exponential incline which is the condition of both reaction and diffusion limitations for a reaction with zero order kinetics. Eventually and without respect to the EBRT, the best performance of biofilter was obtained at inlet concentrations of lower than 0.5 g m(-3) and styrene outlet concentrations were negligible. The significant influence of EBRT on the styrene removal rate can also be explained based on the fact that the removal rate is concentration dependent and whenever the biodegradation kinetics of styrene was a zero order with reaction limitation and EBRT would have had no influence on the overall removal rate of styrene in the biofilter. At all EBRTs, the experimental results obtained for the removal capacity of the biofilter matched the Monod model predictions. The removal rate of styrene did not increase with increasing the loading rate and the Monod expression to approach zero order kinetics at higher styrene concentrations. Also, the zero order was always concentration dependent and, therefore, could not predict the experimental results at higher concentrations where the process became independent of styrene concentration.