Adequate model complexity for scenario analysis of VOC stripping in a trickling filter

Two models describing the stripping of volatile organic contaminants (VOCs) in an industrial trickling filter system are developed. The aim of the mod els is to investigate the effect of different operating conditions (VOC loa ds and air flow rates) on the efficiency of VOC stripping and tile resultin g concentrations in the gas and liquid phases. The first model uses the sam e principles as the steady-state non-equilibrium activated sludge model Sim ple Treat, in combination with an existing biofilm model. The second model is a simple mass balance based model only incorporating air and liquid and thus neglecting biofilm effects. In a first approach, the first model was incorporated in a five-layer hydro dynamic model of the trickling filter, using the carrier material design sp ecifications for porosity, water hold-up and specific surface area. A trace r test with lithium was used to validate this approach, and the gas mixing in the filters was studied using continuous CO2 and O-2 measurements. With the tracer test results, the biodegradation model was adapted, and it becam e clear that biodegradation and adsorption to solids can be neglected. On t his basis, a simple dynamic mass balance model was built. Simulations with this model reveal that changing the air flow rate in the trickling filter s ystem has little effect on the VOC stripping efficiency at steady state. Ho wever, immediately after an air flow rate change, quite high flux and conce ntration peaks of VOCs can be expected. These phenomena are of major import ance for the design of an off-gas treatment facility.