AEROBIC DEGRADATION OF TOLUENE IN A CLOSED CHEMOSTAT WITH AND WITHOUTA HEAD SPACE OUTLET

The present paper describes the continuous aerobic cultivation of a Ps eudomonas strain with toluene as the substrate in a closed chemostat w ith oxygen or air as the gas phase. Due to the constant supply of a ni trogen-saturated aqueous medium, nitrogen passes from the liquid phase of the chemostat into the gas phase (head space). This results in an increasing nitrogen content (asymptotic approach to 100%). The concomi tant decrease in the partial pressure of the oxygen in the gas phase f inally leads to an oxygen limitation for the bacteria in the medium an d an incomplete toluene degradation. The critical nitrogen content of the gas phase at which oxygen limitation begins depends on the toluene concentration in the incoming medium. However, when the gas is contin uously removed from the head space, the nitrogen content reaches a ste ady-state value of less than 100%, depending on the flow rate of the o utgoing gas. The oxygen limitation and the associated incomplete tolue ne degradation can be prevented in this way. The method of gas removal from the head space to avoid oxygen limitation is also applicable whe n the reactor is supplied with air instead of oxygen. Waste waters con taminated with highly volatile pollutants can thus be biologically dec ontaminated under aerobic conditions, without shifting the pollution p roblem from the liquid to the gas phase.