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In this work, we introduce a modified rotating biological contactor (RBC) system and demonstrate its feasibility by applying the newly devised process to the biological treatment of artificial waste gas. In the proposed system, the waste gas is introduced to the bioreactor in the spacings between the rotating discs through a hollow shaft, thus allowing for intimate gas-liquid contact. A 91-l modified RBC containing 20 biofilm support discs 40 cm in diameter was used in the experiments. Toluene was used as the model pollutant, and the system was operated under standard operating conditions for more than one year in order to investigate its long-term performance and assess its ability to control the growth of the biofilm. It was demonstrated that the proposed system allows to efficiently control the growth of the biofilm, thus overcoming the clogging problem inherent in most conventional methods for the biological treatment of waste gas. Moreover, the system was shown to exhibit stationary long-term performance for a period of more than one year, hence indicating its feasibility for industrial application.

In the first part of this paper, we introduced a modified rotating biological contactor (RBC) for the biological treatment of waste gas, and demonstrated its feasibility by applying the process to the biodegradation of toluene in a 91-liter reactor containing 20 biofilm support discs with a diameter of 40 cm [1]. We showed that the proposed system allows the unlimited growth of the biofilm to be suppressed, hence eliminating the risk of clogging associated with other biological waste gas treatment systems. Furthermore, we observed stationary long-term performance for more than one year under typical standard operating conditions. In this part of our work, we investigate experimentally the influence of the main process parameters, i.e., gas flow rate, inlet gas concentration, and rotational speed of the biofilm supports on process performance for the same system. Experimental results indicate that the modified RBC system is mass transfer limited for toluene loadings below 150 g/m(3)h, whereas at higher inlet concentrations of the pollutant, it becomes limited by the biodegradation reaction inside the biofilm. Surprisingly, the disc rotational speed is found to have no major effect on process performance for the system under investigation. A time-independent mathematical model of the process is also presented, and predictions are compared with experimental degradation data. In the range of the investigation process parameters, good agreement between the experimental data and simulation results is obtained.