Experimental and numerical study of steady state stability in a toluene biodegrading biofilter.

Different steady states in a toluene biodegrading biofilter were explored experimentally and numerically. Experimental results showed that a gradual increase of the toluene inlet concentration over several weeks leads to a consistently low exit concentration, with a drastic increase at an inlet concentration change from 7.7 to 8.5 g m-3, indicating an alteration in steady state. A significant and sudden drop in the removal efficiency from 88 to 46% was observed. A model that includes nitrogen and biomass dynamics predicted results matching the experimental biofilter performance well, but the timing of the concentration jump was not reproduced exactly. A model that assumes a gradual increase of toluene inlet concentration of 0.272 g m-3 per day, accurately reproduced the experimental relationship between inlet and outlet concentration. Although there was variation between experimental and simulated results, a clear confirmation of the jump from one steady state to another was found.