Although it is normally included in the same group, the bioscrubber (Figure 4.4) is not itself truly a biological treatment system, but rather a highly efficient method of removing odour components by dissolving them. Unsurprisingly, then, it is most appropriate for hydrophilic compounds like acetone or methanol.
The gas to be treated passes through a fine water spray generated as a mist or curtain within the body of the bioscrubber vessel. The contaminant is absorbed into the water, which subsequently pools to form a reservoir at the bottom. The contaminant solution is then removed to a secondary bioreactor where the actual process of biodegradation takes place. In practice, activated sludge systems are often used in this role.
As in the preceding case, process control can be achieved by monitoring the water phase and adding nutrients, buffers or fresh water as appropriate.