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The Challenge of Sludge
Sludge is produced during every stage of wastewater treatment and must be further processed and disposed of. Sludge treatment often accounts for 30–50% of a wastewater treatment plant’s total operating costs.
Process Steps
Thickening
The initial step is pre-thickening to increase the solids content to 4–8%. This can be achieved either by gravity or mechanically.
Conditioning
Prior to mechanical dewatering, the sludge is conditioned with a polymer. The correct polymer selection and dosing play a decisive role in the effectiveness of the dewatering process.
Mechanical Dewatering
Various technologies are available at this stage:
- Screw presses: Lowest energy consumption, fully automated
- Centrifuges: High throughput, higher dry solids content
- Chamber filter presses: Maximum dry solids, batch operation
- Belt filter presses: Proven technology, medium dry solids
Disposal Costs
Disposal costs are directly related to the volume of sludge:
- Agricultural utilisation: 15–30 €/t
- Thermal treatment: 40–80 €/t
- Landfill: 80–150 €/t
Each additional percent of dry solids means reduced volume and, consequently, direct cost savings.