MBBR carriers are almost always made from a durable, chemically resistant polymer — most commonly high-density polyethylene (HDPE) — with a density close to that of water so they can be fluidised with modest energy. The material must survive years of continuous abrasion, aeration and exposure to wastewater without degrading.
Why polyethylene dominates
Polyethylene combines low cost, good chemical resistance and a density that can be tuned to sit just below that of water, so carriers stay suspended when aerated and settle gently when aeration stops. Its toughness matters because carriers collide millions of times over their life; a brittle or soft material would shed fragments or deform, changing the fill ratio and clogging screens. Some carriers use other polymers or additives for specific chemistries, but the core requirements — near-neutral buoyancy, abrasion resistance and chemical stability — are the same.
Density is deliberately set close to 0.95–0.98 relative to water for typical carriers so that only gentle circulation is needed. Carriers that are too light float and are hard to distribute; carriers that are too heavy demand excessive aeration to keep moving. The exact material grade and density are specified by the manufacturer and should be confirmed per project, especially for aggressive industrial effluents.
Material properties that matter
The indicative properties below illustrate the selection logic. Actual grades and figures must be taken from the supplier and confirmed per project.
Carrier material considerations (indicative — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Typical polymer | HDPE | — | Chemically resistant, tough and cost-effective. |
| Relative density | ~0.95–0.98 | to water | Near-neutral buoyancy for easy fluidisation. |
| Key requirement | Abrasion resistance | — | Survives continuous carrier collisions. |
| Industrial effluents | Check compatibility | — | Aggressive chemistries may need special grades. |
Frequently Asked Questions
What are MBBR carriers made of?
Why is carrier density important?
Do carriers degrade over time?
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