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The sludge can be placed directly after dewatering without intermediate storage.
Turning
Full-surface turning enables optimum evaporation and consistently avoids the development of anaerobic zones.
Displacing
The sludge is automatically transported through the drying hall.
Accumulation
The dried granules can be accumulated in the drying hall up to a height of 80cm and thus temporarily stored until removal.
Clearing
At the end of the hall, the dried sewage sludge is discharged e.g. into a storage bunker or a conveyor.
WendeWolf®
The WendeWolf, a turning and conveying machine, is the heart of the solar dryer. The machine essentially consists of a moving steel bridge, a height-adjustable turning drum and controls for the machines and the hall climate.
The drum is driven and rotated by frequency-controlled drive motors. The drive motors allow a rapid traverse speed of 8 m/min and a working speed of between 0.8 and 2.0 m/min. The turning drum rotates at a speed of approx. 2.5 m/s during turning. The operating speed is reduced under heavy load.
The serrated metal combs of the drum turn the sludge to be dried over the entire width of the bed at an adjustable depth and transport the sludge from the feed opening through the hall to the clearing opening. The sludge can be turned and moved in both directions, there is no preferred direction. The drum movement also makes it possible to remove larger heaps that occur when tipping the filter cake from skips or with wheel loaders.
Furthermore, the turning machine distributes the sludge in the hall and the dried granulate can be piled up to a height of 80 cm at the end of the hall. The drying area itself does not need to be entered or driven on.
The height of the drum is adjusted using a spindle drive.
The roller stroke is over 750 mm.
Example: WendeWolf SW-12 | Values |
---|---|
Diameter of the turning drum | 1,0 m |
Length | 4,3 m |
Total width | 11,7 m |
Weight | 4100 kg |
Clearance height | 2,6 m |
Lane distance | 11,3 m |
Protection class of the motors | IP66 |
Total connected load | 15 kW |
Tension | 400 V |
Frequency | 50 Hz |
Drum speed | 30-60 rpm |
Fast gear | 8.0 m/min |
Operation | 0.8-2.0 m/min |

Electrical engineering
The connected load of the turning machine is approx. 14 kW, the connected loads for the circulating air fans (whirlers) are approx. 0.6 – 0.7 kW per 100 m² drying area.
A separate Internet connection must be provided on site for remote monitoring of the system and for transferring software updates.
Drying hall (greenhouse)
These are commercially available greenhouse constructions that are slightly adapted to the requirements of a drying hall.
The basic construction is sufficiently protected against corrosion with hot-dip galvanized steel.
Various materials can be used for the roof and wall cladding, whereby the materials used should have a transparency of 85% or more.
The following materials can be used for the covering:
Greenhouse films
Polyethylene films (UV-5) as single films, inflatable double films or air bubble films commonly used in greenhouse construction
ETFE (f-clean) as single film or inflatable double film
Roof panels
Polycarbonate or PVC sheets in single or double bar design.
Glass – single or double glazing
The choice of roofing and the dimensioning of the supporting structure, the roofing and the side walls must take into account the local conditions (wind load / snow load).
It has been shown that although glass has excellent transparency, the supporting structure must be more complex than with plastic roofing.
Weight comparison covering | Values |
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4 mm glass | approx. 10.0 kg/m² |
Double-skin sheets | approx. 1.5 kg/m² |
inflatable double foil | approx. 0.7 kg/m² |
Furthermore, good thermal insulation of the roofing is an advantage; poorly insulated roofs fog up more easily. This leads to a lower radiation input and thus to less evaporation.
The WendeWolf® requires a free clearance height of approx. 2.2 meters above the ground in the area of the roadway, the side walls must be designed accordingly high.
A height of approx. 2.5 meters should be selected as a clear passage through the hall.
Civil engineering and side walls
An asphalted surface as used for road construction is suitable for the hall floor; a reinforced concrete slab can be dispensed with. The side boundary walls, which also serve as a roadway for the WendeWolf®, can be constructed using precast concrete elements or poured on site using traditional concrete construction methods.
The plinth height incl. The running rail should be approx. 0.85 m, the support surface for the machine must be 0.20 meters. The clear width between the boundary walls is 11.3 m, but the machine technology can also be adapted to other widths.
The local requirements and regulations must be observed.
Frequently asked questions
The WendeWolf® process is designed for medium-sized wastewater treatment plants. The projects we have realized are between 5,000 and 500,000 population equivalents with a drying area of 500 to 12,500m². The sludge quantities per year in these plants are approx. 400 – 32,850 tons (mechanically dewatered). The system has a modular structure, the size of a single hall is 12 x 120 meters, i.e. 1,440 m².
Additional halls can be erected if this becomes necessary due to the quantities of sludge produced.
The evaporation rate decreases as soon as a degree of dryness of around 65% dry matter is reached. If you only charge by weight, drying above around 65% dry matter is generally no longer worthwhile. Example: Feeding the filter cake into the dryer with 25% dry matter. Each ton contains 750 kg of water and 250 kg of solids. If dried to 65%, the remaining quantity is 250/0.65 = 384 kg, of which 250 kg is solids and 134 kg is water. This means that 616 kg or 82% of the original water content of 750 kg has already evaporated. If it is desired to dry to 85%, the remaining quantity is 250/0.85 = 294 kg, of which 44 kg is water.
With the necessary access and exit routes, approx. 1.5 m² per ton of delivered sludge should be provided. On the one hand, we dimension according to the delivered dry matter content and the desired degree of drying and, on the other hand, according to the stack volume between the possible discharge times.
The investment costs are divided roughly equally between civil engineering work, hall construction and machine technology. The investment costs per annual tonne of filter cake vary between 400 and 500 €/t.