Introduction: Why Multi-Media Filters Need Smart Layering
In industrial and municipal water treatment, multi-media filters are a reliable and efficient solution for removing suspended solids, turbidity, and particulate matter. These filters don’t rely on just one type of media but several, layered by density and size.
Among the most important of these is anthracite, which often forms the topmost layer in the filter bed.
This blog explains why anthracite is essential, its properties, and how it enhances overall filter performance.
What Is Anthracite?
Anthracite is a hard, naturally occurring coal with:
High carbon content (90–95%)
Low volatile impurities
High specific gravity (~1.6–1.7)
Angular to sub-angular particle structure
In water treatment, anthracite is crushed and graded to specific sizes (commonly 0.8–1.4 mm or 1.4–2.5 mm) and used as a coarse filtration media.
The Function of Anthracite in Multi-Media Filters
1. Top Layer for Coarse Particle Removal
Anthracite sits at the top of the filter bed, where incoming raw water first enters. Its primary function is to trap large suspended solids, reducing the load on lower layers like sand and garnet.
2. Protects Finer Media Below
By catching debris early, anthracite prevents:
Premature clogging of finer media layers
Uneven flow paths (channeling)
Media cementation or hardening
3. Promotes Deep Bed Filtration
Its relatively low density compared to sand and garnet allows for layered filtration—water travels deeper through the bed, ensuring more contact time and higher removal efficiency.
4. Extends Backwash Interval
With better particle distribution and fewer blockages, anthracite helps reduce the frequency of backwash, saving water and energy.
Properties That Make Anthracite Ideal for Filtration
| Property | Benefit |
|---|---|
| High carbon content | Chemically stable and durable |
| Low friability | Long-lasting, resists breakdown |
| Angular shape | Effective particle retention |
| Low density (1.6–1.7) | Floats above sand and garnet naturally |
| High void ratio | Better flow distribution |
Recommended Multi-Media Filter Configuration with Anthracite
| Layer | Media | Size (mm) | Thickness |
|---|---|---|---|
| Top | Anthracite | 0.8–1.4 | 300 mm |
| Middle | Filter Sand/Purozite | 0.6–1.0 | 300 mm |
| Bottom | Garnet | 0.3–0.6 | 150 mm |
| Support | Graded Gravel | 2–6 | 100 mm |
Real-World Performance: Industrial RO Pre-Treatment
A commercial RO plant using anthracite in a multi-layer setup observed:
Turbidity drop: From 8.2 NTU to 0.6 NTU
TSS removal: From 85 ppm to <5 ppm
Backwash frequency: Reduced from every 3 days to every 7–10 days
Improved membrane life: From 12 months to 22+ months
Maintenance and Media Life
Backwash frequency: Every 5–10 days depending on load
Expected lifespan: 3–5 years with proper maintenance
Cleaning: Occasional high-flow backwash is sufficient
Check for: Media degradation, color change, and loss of performance
Why Choose Starke Anthracite?
Starke provides high-quality, pre-washed anthracite media for multi-media filtration systems:
✅ Uniform particle size
✅ AWWA B100 compliant
✅ Washed, dried, and dust-free
✅ Long lifespan, stable performance
✅ Available in 25 kg bags and 1-ton jumbo bags
Also available in custom mesh sizes based on flow rate and application.
Frequently Asked Questions
Q1. Can anthracite be used as a single-layer media?
It can, but performance is limited. It works best when layered with finer media like sand or garnet.
Q2. Is anthracite safe for drinking water filtration?
Yes, if certified and properly graded. Starke anthracite is used in municipal and RO pre-treatment plants.
Q3. Does anthracite remove chlorine or organics?
No. It removes particulates. Use activated carbon for organics or chlorine.
Q4. Can I replace sand with anthracite?
No. Anthracite complements sand but doesn’t offer the same filtration depth alone.
Ready to improve your filter performance with anthracite?
Get expert help and high-purity media from Starke today.
Email: info@starkefiltermedia.com
Website: www.starkefiltermedia.com