Fixed Bed Sewage Treatment Plants
Basically, the sewage treatment plant includes several treatment phases which are installed in different tanks or chambers of a tank. The biology of the sewage treatment plant works according to the submersed fixed bed.
Functional principle of the ClearFox® sewage treatment plants fixed bed technology
The ClearFox fixed bed plants are durable, easy-to-handle solutions for complex cases of application. Up to now, in situations where the wastewater production was fluctuating over time or in terms of content, it has been required to continuously measure the control parameters such as sludge content (via the dried matter measurement) in order to optimise operation. The sewage treatment plant, however, should be regulated automatically over a wide range and be adjustable with simple variables. This is only possible in a biology with fixed sedentary medium (fixed bed), since the consistency and volume of the submersed sludge is of minor importance.
Technology and functional principle – Fixed bed reactor
In order to prevent overdesign of the biology, a consistent filling (buffering) in 24h-compensation is carried out especially for plants with intermittent filling.
For gastronomy establishments, the wastewaters from the kitchen are collected separately and passed through a grease separator or other technically suited systems (flotation).
Via an inlet channel, the wastewater reaches the first tank (chamber) of the sewage treatment plant.
It includes the first (calculated) part of the pre-chamber. The following, second tank includes the rest of the pre-chamber and the required buffer tank. It absorbs the hydraulic fluctuations. Pre-chamber and buffer are arranged either above or next to each other. The sludge storage can be arranged separately or be integrated into the pre-chamber.
A filling pump (compressed air or electrically operated) fills the biological stage consistently (24h compensation). This way, it can be ensured that the most favourable operation point can be set even for fluctuating loads at a later stage.
Standard plants fill the tank via gravity, i.e. without buffer pump.
Fixed bed material forms a biofilm
After the working-in time, a biofilm (colonisation of micro-organisms) is created on the fixed bed material. This transforms organic contaminants contained in the wastewater into settleable and mineral solids. This is mainly done by aerophile organisms. The aeration system under the fixed bed material supplies the organisms with sufficient air. In addition, the rising air creates a current which causes a complete (horizontal and vertical) blending of the tank contents due to the geometry of the inserted fixed bed material (characteristic of an entirely blended cylinder).
Downstream of the fixed bed reactor, the wastewater flows with gravitation to the secondary sedimentation where secondary sludge and supernatant water are separated.
The sludge return pipe can optionally be used for denitrification. The produced sludge can deposit in the secondary sedimentation chamber and is returned with a submersible motor pump or an airlift-pump (secondary pump) back into the sludge storage or the pre-chamber.
Specific fixed-bed substrate
The fixed bed substrate is produced from UV-stabilised polyethylene which is not porous, not squeezable and not biologically degradable in the forseeable future. It has a specific surface (depending on the plant type) of 100-200m2/m3. It has no toxic or recognisable chemical-physical effect on the biological degradation process. The fixed-bed consists of continuous tube-like stable individual elements (net pipes) which run in vertical direction, are permeable on the sides and are welded together on the top ends to form rectangular blocks. Due to its net-like structure, the material can also be blended through in horizontal direction.
Due to the small installation height, the arrangement of the pipes in the blocks must ensure a three-dimensional flow through the fixed bed material. Sufficient stability and rigidity in the face of static and dynamic loads are assured for the entire fixed bed. The individual blocks are fixed with suitable supporting, spacing and holding structures in the tank.