What you should know: Everything about wastewater treatment and small sewage treatment plants (3)

Trickling Filter Systems

Trickling filter treatment plants have a long tradition and have been known for around 30 years. #Container sizes und #installation depths are relatively high compared to most other systems. The technical equipment consists of 2-3 pumps and 1-2 float switches. Trickling filter systems are among the systems that build up a biofilm for biological purification. The #cleaning performance is usually limited to#effluent class C (#carbon reduction).

Special System Features
In a #trickling filter system the wastewater is biologically cleaned by #microorganisms. The #trickling filter bzw. #biofilm carrier usually consists of a layer of coarse-grained granules made of plastic or lava slag. This filling lies on a grid, has a minimum filling height of 1.50 m and is not submerged, but is trickled through by the water. The bacteria that are needed to clean the waste water multiply on these trickling filters.
The wastewater from the #Primary treatment (#septic tank) reaches the surface of the trickling filter evenly via a drip channel. For better distribution on the surface, the water is applied in surges. This is usually done via a tipping channel, which empties the contents into the drip channel in a surge when it is filled with water. Finally, the water is collected below the trickling filter and pumped into a secondary settling tank.
Part of the water from the secondary clarifier is finally pumped back into the primary clarifier and the cycle begins again. Since the pump is located at the bottom of the secondary clarification tank, the biosludge removed here is conveyed to the primary clarification at the same time, while the excess water flows out of the secondary clarification tank as treated wastewater. Some systems now pump part of the drained water back onto the surface of the filling via a spray device.

What should be given special attention?

• Care must be taken to ensure that no coarse matter and sludge from the preliminary treatment get onto the trickling filter. Silting occurs when puddles form on the surface of the trickling filter. Since the biomass biomass has to be supplied with oxygen from the air, silting up can lead to putrefaction and the death of the biomass.
• The optimal distribution of the waste water on the surface is of particular importance, since the survival of the biological growth on the filling material depends on an even supply of nutrients. In order to ensure that the biofilm is supplied with atmospheric oxygen, natural ventilation must be ensured in all areas.
• Sludge can accumulate on the bottom of the trickling filter, which must be removed by the maintenance service if necessary.

What do controls look like?

• The operator should check the function of the tipping device monthly and pay attention to any #solids drift from the preliminary treatment.
• The statutory controls must be carried out.

Submerged Fixed-bed Plants

With submerged #fixed-bed systems , the #Biofilm is constantly submerged in the water. The required compressed air is generated with a compressor and passed through the #fixed bed (#growing body) durch das #membrane aerators .
The air compressor is installed in the building or in an outdoor cabinet.
The cleaning performance is usually limited to discharge class C (carbon degradation).

Special system features
Grid-like tubes or lamellar plastic blocks are used as growth bodies, on the surfaces of which the biofilm forms. The amount of biofilm depends on the size of the vegetation area. This in turn determines the volume of the container. A reduction in the required container volume due to larger growth areas requires a reduction in the interstices of the growth body. Therefore, when selecting the growth bodies, care must be taken to ensure that the gaps are not too small, as the biofilm can easily overgrow these gaps.
The #wastewater is fed into the #Bioreaktor via a primary treatment (#settlement pit ) in a free gradient. The membrane aerators are arranged under the block of the growth body in the bioreactor. The compressed air flows through the growth bodies and at the same time takes some of the water up with it. The biofilm is thus supplied with nutrients and atmospheric oxygen. The water flows down the side of the block, creating a water roller. The air flow also ensures that the biomass cannot clog the cavities. The cleaned #Water water goes into the secondary clarifier, in which the dead biomass is retained. An air-driven #mammothpump ensures that this sludge is conveyed to the preliminary treatment.

What should be given special attention?

• Care must be taken to ensure that no coarse matter from the preliminary clarification enters the bioreactor. Coarse matter clogs the cavities in the growth body over time. The water roller can no longer build up and the growth body becomes completely silted up. The biofilm breaks down and the system is no longer functional. In order to restore the function, the #fixed bed usually has to be removed, cleaned and reinstalled. The cost of this work is very high.
• If the ventilation system is too small or if the system is temporarily shut down, the cavities can become overgrown with biomass. Complex cleaning is also required here.

What do controls look like?

• The operator should ensure that no solids escape from the preliminary treatment. The proper flow through the fixed bed must also be checked. This can be judged by the change in the bubble pattern. Inadequate flow can be caused by solids from the primary clarification, aging of the membrane diffusers and wear and tear on the compressor.
• The statutory controls must be carried out.

Vortex Floating Bed Systems

The biofilm in this system is constantly submerged, but not permanently installed, as is the case with the submerged fixed bed. A plastic material is used as the growth body, the specific weight of which corresponds approximately to that of water. The required compressed air is generated with an air compressor and fed into the bioreactor via perforated membrane diffusers.
The compressor is installed in a building or in an outdoor cabinet.
The cleaning performance is usually limited to effluent class C (carbon degradation).

Special system features
The growth bodies have a spherical or cylindrical shape with a diameter of 1-2 cm. The growth bodies have a lamellar structure on which the biofilm forms on the inner surfaces. The growth bodies are kept in suspension by the pressure aeration and at the same time supplied with nutrients from the waste water and, by the pressure aeration, with atmospheric oxygen.
The waste water is fed into the bioreactor via a preliminary treatment (settlement pit) in a free gradient and treated there.
The cleaned water enters the secondary clarifier, in which sludge particles from the bioreactor are retained. An air-driven mammoth pump ensures that this sludge is conveyed to the preliminary treatment.

What should be given special attention?
Since the #floating bed bed can move freely in the water, inlets and outlets must be provided with a grid. The bioreactor must be completely covered with a net so that the floating bed does not drift if the plant is flooded due to backwater.

What do controls look like?

• During #sludge disposal, the network or the grids on inlets and outlets can be damaged.
• The change in the bubble pattern can be used to assess whether there is a defect in the compressor or the membrane diffuser. Inadequate ventilation can be caused by aging of the membrane diffusers and wear and tear on the compressor.
• The statutory controls must be carried out.

There are other common processes and system types in the next part of our series, before the fifth and final part deals with the processes and systems that are state of the art in the era of water and climate protection. So stay tuned - it's worth it!