The performance of a single tube extractive membrane bioreactor (STEMB) exposed to an alternating sequence of toluene (TOL) and dichloromethane (DCM) was investigated. These compounds are two of the most commonly used solvents in the chemical and pharmaceutical industries, and so were used to simulate the scenario of sequentially alternating pollutants. Undefined microbial cultures were used. During experiments, no TOL accumulation was detected in the STEMB. It may be possible that a commensal microbial relationship developed in the system, which maintained the microbial culture responsible for TOL degradation active throughout experiments. On the other hand, accumulation of DCM was detected whenever this compound was introduced. These accumulations resulted in a transient decrease in the removal efficiency of the STEMB. The influence of the membrane-attached biofilm in decreasing DCM discharges was shown. Investigations into the use of an additional carbon source to improve the system response were carried out during critical periods of operation, eg start-up and starvation periods. This strategy proved a successful tool in reducing DCM discharges.