VOCS IN FIXED-FILM PROCESSES .2. MODEL STUDIES

Models incorporating liquid-gas mass-transfer and biofilm mass-transfe r resistances were developed for trickling filters (TF) and rotating b iological contractors (RBC). Biodegradation and volatilization coeffic ients were estimated from the previously described pilot-scale studies . The volatilization coefficients of a given compound in the TF and RB C were generally constant across the experimental conditions investiga ted, While biodegradation-rate coefficients were constant in the TF ac ross experimental conditions, in the RBC the biodegradation-rate coeff icients appeared to be greatest under conditions of low loading and hi gh disc rotation speed and lowest under conditions of high loading and low disk rotational speed, The biofilm was completely penetrated by m ost of the contaminants and diffusional resistance did not limit the r ate of biodegradation of any of the compounds. In the RBC, diffusion i n the biofilm appeared to be limiting the biodegradation of toluene, o -xylene, and 1,3,5-trimethylbenzene. The ratio of gas- and liquid-phas e mass-transfer coefficients ranged from 91.4 for the TF to 5.6 for th e RBC. Due to the relatively wide confidence intervals associated with these estimates, the values could not be statistically differentiated , however, the results suggest a significant contribution of gas-phase resistance to mass transfer in some cases.