Fixed bed process
The fixed-bed process ( English moving bed or English Submerged Fixed Bed ) is a purification of a treatment system comprising (settle on the bacteria cultures) by aeration of carrier material the effluent obtained. In contrast to this is the much more common activated sludge process , in which the active microorganisms do not settle firmly on the carrier material, but are added to the wastewater as a suspension .
Basics
In the fixed bed process, a clearly defined amount of growth bodies is either kept in suspension (moving bed) or installed as a grid over the aerators (fixed bed). In a few days, microorganisms and microorganisms settle on it. The oxygen entry is controlled by a compressor that distributes the atmospheric oxygen either via membrane aerators (fine-bubble entry) or nozzle pipes (medium-bubble entry) under the fixed bed area.
Compared to membrane aerators, nozzle pipes have the advantage of not clogging or silting up and, thanks to their medium-bubble entry, they fill the entire surface of the fixed bed. In addition, the compressed air siphon effect ensures that excess sludge is detached and the water body is mixed.
The advantage of the fixed bed process compared to the activated sludge process is a significantly more efficient cleaning, which takes up a much smaller volume with a comparable cleaning performance. The disadvantage is a higher technical effort and energy requirement.
Process variants
There are different process variants. In an aeration tank , for example, there is a floating fixed bed, which is formed from individual, honeycomb-shaped (impact-resistant polystyrene ) or other, often cylindrical or spherical lattice bodies with lamellas inside.
Other methods (e.g. 3KPLUS) use permanently installed grid systems that cannot sink and carry large amounts of growth. A biologically active film of biomass ( biofilm ) is created on all surfaces of the float or grid . With higher loads, this takes on a furry structure that can be several centimeters thick. The growth is mostly stabilized by thread bacteria.
The microorganisms living in the growth absorb the dissolved and undissolved pollutants contained in the wastewater and oxidize them to water, carbon dioxide and salts. They multiply and maintain a certain biofilm thickness in interaction with the flow, so that sufficient microorganisms are always present. The growth of these biologically active films is thus self-regulating, which is an advantage over the activation processes. The higher energy consumption compared to processes with suspended biomass can be disadvantageous.