A membrane bioreactor for the simultaneous treatment of acetone, toluene, limonene and hexane at trace level concentrations

The performance of a flat-membrane biofilm reactor (MBR) for the removal of acetone, toluene, limonene and hexane at concentrations ranging from 1.3 to 3.2 mg m−3 was investigated at different gas residence times (GRT): 60, 30, 15 and 7 s. A preliminary abiotic test was conducted to assess the mass transport of the selected volatile organic compounds (VOCs) through the membrane. A reduced transport of limonene and hexane was observed with water present over the dense side of the membrane. The presence of a biofilm attached on the dense side of the membrane following bioreactor inoculation significantly increased VOC transport. High acetone and toluene removals (>93%) were recorded in the MBR regardless of the GRT. To remediate the low hexane removal performance (RE < 24%) recorded at the initial stages of the process, a re-inoculation of the membrane with a hexane-degrading consortium embedded in silicon oil was performed. Although hexane removal did not exceed 27%, this re-inoculation increased limonene removals up to 90% at a GRT of 7 s. The absence of inhibition of hexane biodegradation by substrate competition confirmed that hexane removal in the MBR was indeed limited by the mass transfer through the membrane. Despite the low carbon source spectrum and load, the microbiological analysis of the communities present in the MBR showed high species richness (Shannon–Wiener indices of 3.2–3.5) and a high pair-wise similarity (84–97%) between the suspended and the attached biomass.

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► Membrane bioreactors are an efficient technology for the treatment of soluble VOCs.
► High removals were obtained for acetone, toluene and limonene at GRTs of 7 s.
► Microbial activity mediated higher concentration gradients over the membrane.
► Selection of membrane material is a key design criterion to achieve high removals.
► A high microbial biodiversity was observed despite the limited carbon source.