How the calculation works
- Dry solids per day = sludge volume × sludge density × dry solids content. 20 m³ of sludge at 3 % holds about 610 kg of dry solids.
- Filter cake per day = dry solids ÷ dry solids content of the cake. At 30 % that is about 2.0 t of cake.
- Cake volume = cake mass ÷ cake density.
- Chamber volume per cycle = cake volume per day ÷ cycles per day.
- Chambers: one chamber holds roughly 0.9 × plate side² × cake thickness – about 17 L for an 800 mm plate with 30 mm cake.
Typical values
| Sludge | Dry solids in the feed | Dry solids in the cake |
|---|---|---|
| Municipal sewage sludge, conditioned | 2–5 % | 25–35 % |
| Metal hydroxide sludge | 1–4 % | 25–40 % |
| Waterworks sludge | 1–5 % | 25–40 % |
| Mineral and gravel-wash sludge | 10–40 % | 60–80 % |
Limits of this calculator
The cake dryness and the cycle time depend on the sludge and its conditioning and should be confirmed by a filtration test. The number of cycles per day follows from the filling, pressing and discharge times; two to four cycles are usual for sewage sludge. Our filter presses and feed pumps are sized from your sludge data.
Frequently asked questions
How do I calculate the size of a filter press?
Work out the dry solids per day, convert them into cake volume using the cake dryness and density, and divide by the number of cycles per day. The result is the chamber volume the press needs.
How many cycles per day can a filter press run?
Typically two to four cycles per day for sewage and hydroxide sludge, and more for fast-filtering mineral sludge. A cycle includes filling, pressing, opening and cake discharge.
What cake thickness should I choose?
30–32 mm is the standard for most sludges. Thinner cakes of 25 mm shorten the cycle for sludge that filters slowly; 40–50 mm suits fast-filtering mineral sludge.