By Senjie Engineering Team · Last updated: 2026-07-27
TL;DR: Tannery wastewater treatment precipitates chromium as chromium hydroxide (raising pH to roughly 8.5) and clarifies it by settling or dissolved air flotation before a filter press dewaters the resulting sludge. Mechanical dewatering by filter press typically produces a cake at 30–45% solids (roughly 55–70% moisture), compared with 85–95% water in the raw settled sludge. This guide covers press type, filter cloth choice, chrome recovery, and how tannery clusters in South Asia and Latin America size their equipment.
Why does a tannery need a filter press?
Chrome tanning liquors contain dissolved trivalent chromium (Cr3+) along with high organic load (fat, protein, and hide fragments), giving tannery wastewater a high COD and BOD alongside heavy-metal content. Raising effluent pH to about 8.5 precipitates the chromium as chromium hydroxide, which is then clarified (commonly by settling tanks or dissolved air flotation) and pumped as a thin sludge to a filter press. The press compacts this sludge into a solid, transportable cake and returns clear filtrate to the treatment line.
How much moisture is left in tannery filter press cake?
Sludge arriving at the press from settling or DAF units is typically 85–95% water. Mechanical dewatering by filter press (or belt/centrifuge, though filter press is most common for chrome sludge) commonly brings this down to 30–45% solids by weight, i.e. roughly 55–70% moisture in the cake. Adding membrane (diaphragm) squeeze plates pushes solids content toward the higher end of that range and shortens the time cake sits under pressure.
Chamber, membrane, or plate-and-frame: which suits chrome sludge?
| Factor | Recessed Chamber Press | Membrane (Diaphragm) Press |
|---|---|---|
| Typical cake solids, chrome sludge | ~30–38% | ~38–45% (higher, drier) |
| Feed pressure | 0.6–1.0 MPa | 0.6–1.0 MPa feed + membrane squeeze |
| Best fit | Smaller tanneries, lower daily wastewater volume | Larger clusters, high disposal cost, chrome recovery focus |
| Upfront cost | Lower | 15–30% higher for equal plate area |
Larger tannery estates and export-grade processors more often choose membrane presses because drier cake means lower hauling weight and, where chrome recovery is practiced, a more concentrated cake to redissolve.
Can the filter cake be recycled instead of landfilled?
Yes — in many tanneries the chromium-rich cake is redissolved with sulfuric acid to regenerate a basic chromium sulfate tanning liquor, which is reused in the tanning drum. This chrome-recovery route reduces both raw chemical purchase cost and the volume of hazardous waste sent to landfill, but it requires the cake to be reasonably pure chromium hydroxide (minimal co-precipitated organics), which depends on how well upstream screening and primary clarification remove fats and hide fragments before chrome precipitation.
What filter cloth handles chrome sludge without clogging?
Chromium hydroxide precipitate is a fine, gelatinous floc that blinds coarse cloth quickly. Woven polypropylene (PP) monofilament cloth, generally in a fine micron rating similar to other chemical-sludge duty, resists the wide pH swings of tannery process water (tanning and liming stages both produce extreme pH effluent) better than natural fibers. Expect cloth life to run shorter than in mineral dewatering because of the fine, sticky nature of chrome floc; plan on periodic acid or alkaline cloth washing to maintain flow rate between full replacements.
How much does a tannery filter press cost?
As with other wastewater applications, price is driven mainly by plate size, plate count, and automation level rather than the tannery application itself. Manually operated chamber presses for smaller tanneries sit at the lower end of the industrial filter press price range; PLC-controlled membrane presses with automatic plate shifting sit at the higher end, and are more common at large tannery estates in South Asia and Brazil that run multiple shifts. Get a quotation based on your actual daily wastewater flow and settled-sludge yield rather than hide throughput alone.
Why buy a tannery wastewater filter press from a China-based manufacturer?
Senjie is a China-based manufacturer of filter presses and filter press cloth, supplying chamber, plate-and-frame, and membrane presses matched with PP filter cloth engineered for chemical and heavy-metal sludge duty. Because press and cloth are sourced from the same manufacturer, plate seal dimensions and cloth micron rating are matched from the start — reducing leak and blinding issues common when equipment and consumables come from different suppliers. Export documentation, spare plate/cloth kits, and installation guidance are available for tannery buyers in South Asia, Africa, and Latin America.
Frequently Asked Questions
What pH is chromium precipitated at before filter pressing?
Chromium hydroxide precipitation is typically carried out at approximately pH 8.5, which minimizes chromium solubility and converts dissolved Cr3+ into a filterable solid.
What cake dryness should a tannery expect from a filter press?
Mechanical dewatering by filter press typically achieves 30–45% solids by weight (roughly 55–70% moisture), compared with 85–95% water in the raw settled sludge feeding the press.
Can the chrome-rich filter cake be reused?
Yes, many tanneries redissolve the cake with sulfuric acid to regenerate tanning liquor for reuse, reducing both chemical cost and hazardous waste volume, provided the cake is reasonably free of co-precipitated organics.
Does tannery wastewater need special filter cloth?
Yes — fine, gelatinous chromium hydroxide floc blinds coarse cloth quickly, so PP monofilament cloth resistant to wide pH swings is the standard choice, with shorter replacement intervals than mineral-sludge applications.
Is a membrane filter press worth it for a tannery?
It’s generally worth the premium for larger tannery estates or where chrome recovery is practiced, since the drier cake reduces hauling weight and yields a more concentrated feed for chrome regeneration.
Get a Sizing Recommendation
Share your daily wastewater flow and settled-sludge yield with our engineers for a plate size and press-type recommendation. See our Filter Press: Types, Specs & Cost Guide, our Plate & Frame vs Chamber vs Membrane comparison, and our Filter Press Cloth: Material & Selection Guide. Related equipment: Chamber Filter Press, Membrane Filter Press, Wastewater Filter Press, and Filter Press Cloth.
Reference: U.S. EPA — Industrial Wastewater Treatment.