Ask two suppliers which media your plant needs and you can get two different answers, because the honest one is that it depends on what you are trying to take out of the water. Suspended dirt, dissolved organic load, ammonia, and toxic industrial compounds each come out by a different mechanism, and each mechanism has its own media. Get the match right and the plant is smaller, cheaper to run and more stable; get it wrong and you are paying for capacity you never use. This guide sets out how we, as a media manufacturer, help plants pick the right biofilm carriers, settling media and filter media — and put them in the right order.
Start with the contaminant, not the media
The first job is to name the problem. Only then do you choose a product. Is the pollutant suspended or dissolved? Organic or inorganic? Biodegradable or not? Each answer points to a removal mechanism — sedimentation and straining for solids, biology for degradable organics and nutrients, chemical oxidation for the refractory stuff, adsorption for specific dissolved species — and the mechanism, in turn, points to the media. The table below is the shortcut we use to get from a water analysis to a media shortlist.
| What you need to remove | Removal mechanism | Media |
|---|---|---|
| Suspended solids, turbidity, flocs | Sedimentation, then filtration | Tube settlers and inclined settlers; sand and ceramic sand filter media |
| Dissolved organics, BOD/COD, ammonia (nitrify), nitrate (denitrify) | Biological — bacteria grown on a surface | MBBR biofilm carriers (K1-type), bio balls and rings |
| Refractory, toxic or coloured organics that biology cannot break down | Chemical — advanced / catalytic oxidation | Iron-carbon micro-electrolysis filler |
| Specific dissolved species (odour, some metals, ammonia spikes) | Adsorption / ion exchange | Activated carbon, zeolite adsorbent media |
Most real plants need more than one of these, because a typical wastewater carries several of these problems at once. That is why media selection is really about building a train, which we come back to at the end.
Biological media: MBBR and biofilm carriers
When the load is dissolved and biodegradable — the organic strength measured as BOD or COD, plus ammonia and nitrate — the work is done by bacteria, and the media’s only job is to give those bacteria a large, protected surface to live on. That is what an MBBR biofilm carrier is: a small plastic (usually HDPE) piece, shaped with a sheltered internal surface, that floats and tumbles freely in the aerated tank. Biomass grows as a film on the carriers instead of drifting as loose sludge, so the tank holds far more active bacteria, rides out shock loads, and does not depend on a clarifier returning sludge to keep going.
Three numbers decide which carrier to buy. Specific surface area (m²/m³) is the biofilm area per unit of media, and it sets how much treatment each cubic metre of carrier delivers; what matters is the protected area the biofilm actually keeps, not just the headline figure. Fill ratio — the share of the tank filled with carriers — usually runs from about 30 to 70 percent, higher for strong industrial loads and lower for municipal, with room always left for the carriers to move. And density is set just below water so the carriers suspend and circulate on ordinary aeration. Pick the surface area from the load, the fill ratio from the strength of the wastewater, and confirm the carrier moves freely without dead zones. K1-type media suit BOD removal and nitrification; other shapes and larger bio balls fit specific movement or handling needs.
Settling media: tube settlers and inclined settlers
Once biology or coagulation has done its work, the solids have to be dropped out of the water, and that is sedimentation. A plain tank settles slowly because a particle has to fall its whole depth. Inclined settling media fix that with shallow settling: pack the tank with channels tilted at around 60 degrees, and a particle only has to sink a short way to a wall, where it lands and slides back to the sludge while clear water rises past. The trick shortens the settling distance by most of the tank depth and multiplies the effective settling area many times over, so the same tank handles a far higher flow, or a much smaller tank does the job.
Two design points keep it working. The upflow velocity is kept low, and the flow inside the channels is kept laminar, so the settled floc is not torn back up into the water. Beyond that the choice is between honeycomb tube settlers and inclined plates, and it comes down to flow and solids.
| Point | Tube settler (honeycomb) | Inclined plate (lamella) |
|---|---|---|
| Structure | Enclosed hexagonal tubes, set near 60° | Flat inclined plates, about 55–65° |
| Best for | Smaller or moderate flows, cleaner water, lowest first cost | Larger flows and higher or variable solids loads |
| Solids handling | Lower — tubes can foul when solids run high | Higher — open plates discharge sludge well |
| Material and handling | Plastic (PP or PVC), light, quick to install | Often steel; heavier and more capital |
| Footprint cut vs a plain tank | Large — many times the settling area | Very large — up to around 80–90% |
As a rule, tube settler media are the compact, low-cost pick for cleaner water and small to moderate flows; inclined plates earn their extra cost on large flows and heavy or swinging solids.
Filter media: sand and ceramic sand
Filtration is the polishing step that strains out the fine solids sedimentation leaves behind, giving a genuinely clear effluent — and it is the front-line step in drinking-water and process-water plants. Water passes down through a bed of graded granules, and the particles are trapped in the pores between grains; when the bed loads up, it is backwashed clean and used again for years. Silica sand is the long-standing, low-cost choice for turbidity removal, and it works well when it is properly graded and backwashed. Ceramic sand filter media is the step up: fired from kaolin, its grains are angular and porous rather than smooth, so the bed holds far more dirt before it needs washing, intercepts fine solids more strongly, and resists acids, alkalis and wear. Where the water is difficult, or long runs and durability matter, the ceramic pays for itself. Grain size follows the duty — finer grades for sharper clarification, coarser for pressure-drop control and dirt-holding.
Advanced-oxidation media: iron-carbon for the hard stuff
Some industrial wastewaters — from dyeing, plating, chemical and pharmaceutical works — carry organics that are toxic or simply indigestible to bacteria, and no amount of biological media will treat them directly. Here the media that helps is iron-carbon micro-electrolysis filler. Each pellet fuses iron and carbon; immersed in the wastewater the two set up countless tiny galvanic cells that drive an oxidation reaction with no external power, tearing the refractory molecules apart. The point of it is to sit ahead of the biological stage: it knocks down the COD, fades the colour, and raises the biodegradability of the water so that a normal MBBR or activated-sludge stage downstream can finish a stream it could not otherwise touch. Treat it as the key that makes an impossible wastewater treatable, not as a stand-alone answer.
Putting it together: the media train
Real plants stack these media in sequence, and the order matters as much as the media themselves — chemical pretreatment before biology, biology before settling, settling before filtration. A common arrangement for a difficult industrial effluent looks like this:
| Stage | Job | Media |
|---|---|---|
| 1. Pretreatment (only if the water is refractory or toxic) | Break down hard-to-degrade organics and lift biodegradability | Iron-carbon micro-electrolysis filler |
| 2. Biological | Remove BOD and COD; nitrify ammonia and denitrify nitrate | MBBR biofilm carriers |
| 3. Clarification | Settle the biomass and flocs out of the water | Tube settlers / inclined settlers |
| 4. Filtration (polishing) | Strain the last fine solids for a clear effluent | Ceramic sand / sand filter media |
A municipal or lightly loaded plant often skips the iron-carbon stage and runs biology, clarification and filtration. The discipline is the same either way: match each stage’s media to the contaminant it is there to remove, and let each stage hand cleaner water to the next.
A short workflow keeps selection honest:
- Analyse the water: flow, suspended solids, BOD and COD, ammonia and nitrate, and anything toxic or refractory.
- Name the mechanisms you need: sedimentation, filtration, biological, oxidation, adsorption.
- Choose the media for each mechanism, using surface area and fill ratio for carriers, and grain size for filters.
- Sequence the stages: pretreat, then treat biologically, then clarify, then polish.
- Size each stage to the flow and load, leaving margin for shocks.
- Confirm the design and the media with the supplier before you build.
Talk to us before you specify
Rongjian manufactures the media that fills these plants — MBBR biofilm carriers and bio balls, tube settler media, sand and ceramic sand filter media, and iron-carbon micro-electrolysis filler. We supply municipal and industrial water plants across many countries, and we would rather help you match the media to your water than sell you a tankful that under-performs. Send us a water analysis and your target — the flow, the load and the effluent standard — and we will recommend the media for each stage, the fill ratio and grain sizes, and the order to run them in. Reach out through the enquiry form or contact your Rongjian representative for a selection review or a quotation.
Frequently asked questions
What is the difference between MBBR media and activated sludge?
Activated sludge grows bacteria as loose flocs floating in the tank, which then have to be settled out and pumped back to keep the population up. MBBR grows the bacteria fixed on plastic carriers instead, so there is no sludge return, the biomass cannot wash out, and the process copes far better with shock loads. An MBBR also holds more biomass per cubic metre, so the tank can be smaller, and carriers can be added to uprate an existing activated-sludge tank.
How do I choose the MBBR surface area and fill ratio?
Start from the load. Take the surface area you need from the BOD or COD to be removed, and choose a carrier whose protected surface area covers it. Then set the fill ratio — usually 30 to 70 percent — from the strength of the wastewater, higher for strong industrial effluent and lower for municipal, always leaving room for the carriers to circulate freely. Confirm the media suspend and move on your aeration without dead zones.
Tube settlers or a lamella clarifier — which should I use?
Both use inclined shallow settling, so the choice is about flow and solids. Tube settlers are compact, plastic and low-cost, and suit cleaner water at small to moderate flows. Inclined plate (lamella) settlers cost more but handle larger flows and heavier or variable solids loads, and cut footprint the most, so they are the pick for big industrial clarifiers.
What filter media removes suspended solids from water?
Granular filter media in a backwashable bed. Silica sand is the standard, low-cost choice for turbidity when it is properly graded and backwashed. Ceramic sand filter media is the upgrade: its angular, porous grains hold more dirt, filter finer, and resist acids and wear, which gives longer runs and a longer life in demanding or corrosive water.
How do you treat wastewater that biology cannot break down?
Put a chemical stage in front of the biology. Iron-carbon micro-electrolysis filler drives an advanced-oxidation reaction that breaks refractory and toxic organics into smaller pieces, cuts the COD and colour, and raises the biodegradability of the water. Once it has passed through the iron-carbon bed, a normal biological stage can finish a stream that would otherwise poison or pass straight through it.
In what order should the media be arranged?
Follow the treatment train: chemical pretreatment first if the water is refractory or toxic, then biological treatment for BOD, COD and nutrients, then clarification to settle the solids, then filtration to polish. Each stage hands cleaner water to the next, and skipping the order — filtering before you have settled, for instance — just clogs the later stages faster.
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Rongjian
Process Media Manufacturer Since 2010
Rongjian produces tower packing, molecular sieves, ceramic grinding media and other process media from our Pingxiang production base. We supply to industrial projects in over 100 countries.
