What is it?
In a biological trickle-bed reactor, an aqueous phase is continuously circulated through a bed of inert material. This packing can consist of irregular bulk material, such as rings, saddles, etc. or of structured packing. When selecting the packing material, it is necessary in every single case to ensure that, even in the event of an anticipated excess sludge formation, the reactor will not become choked in the long term.
The surface properties should be such that the biofilm adheres to it firmly. The pollutants in the waste gas and the oxygen are absorbed by the water phase and transported to the biofilm, where the biological transformation takes place. The quality of the mass transfer from the gas to the liquid phase and the elimination performance of the reactor essentially depend on the wetted surface area of the packing. In order to achieve optimum elimination results, i.e. to maximise the wetted surface area, the liquid phase should be distributed uniformly over the surface of the biofilm.
The immobilisation of the biomass and the formation of the biofilm are generally a naturally controlled process which starts after inoculation of the water phase. The continuously circulating liquid phase takes on the function of supplying the microbe population with the necessary nutrients. At the same time, excess activated sludge and reaction products which can also be inhibitors, e.g. hydrogen chloride during the degradation of dichloromethane, are washed out of the reactor. In the liquid phase, the essential conditions such as pH, nutrients and salt accumulation need to be controlled.
Design, maintenance and efficiency
Table 1 shows application limits and restrictions associated with biotrickling (adapted from EIPPCB, 2016, Table 3.191).
Table 1. Application limits and restrictions associated with biotrickling.
|Gas flow (Nm3/h)
|Pressure drop (mbar)
|Concentration of microorganisms
|> 15 g/l dry matter
|Odour concentration (ouE/m3)