MBBR Biofilm Carrier Media

MBBR biofilm carrier media are the small plastic pieces that do the biological work in a moving bed biofilm reactor, one of the common ways to treat sewage and industrial wastewater. The idea is simple. The bacteria that break down the pollutants in wastewater need a surface to grow on. In an MBBR, that surface is provided by thousands of these little HDPE carriers, which are poured loose into the aeration tank rather than fixed in place. The air blown into the tank both feeds the bacteria with oxygen and keeps the carriers in constant, gentle motion, tumbling through the water. A film of bacteria, the biofilm, grows on each carrier, and as the carrier tumbles that film is repeatedly brought into contact with the dirty water, so the bacteria continuously consume the organic matter and convert the ammonia. Because the carriers are always moving and always covered in active biofilm, a large amount of treatment is packed into the tank. Clean the pollutants off with the biofilm, keep it moving with air, and the wastewater comes out treated.

The K1 shape is built around one problem: keeping the biofilm safe. A carrier that is just a smooth bead would grow biofilm on its outside, but as the carriers tumble and knock against each other and the tank walls, that exposed film would be scraped straight off. The K1 design solves this by putting the growing surface on the inside. Each carrier is a short tube with a cross of walls dividing its interior into cells, and a set of fins around the outside. The bacteria grow in the sheltered cells inside the cross, where nothing can rub against them; the outer fins take the knocks and also stop two carriers sitting flush against each other and sealing their openings. The result is a large, protected area, over 900 square metres of surface in each cubic metre of media, that stays covered in healthy biofilm even in a vigorously mixed tank. The open cross also lets water flow right through the carrier, so the biofilm inside is constantly fed. It is a lot of working surface, kept where the tumbling cannot strip it.

The main thing you set is the fill ratio, how much of the tank volume you fill with carriers, and it runs from about 15 up to 70 percent, chosen from the pollutant load: a lightly loaded or upgraded tank needs fewer carriers, a heavily loaded one more, but a ceiling is left so the carriers have room to move freely. The other numbers describe the media itself. The surface area is over 900 square metres per cubic metre, which is the biofilm area you are buying. The density is set just below that of water, so the carriers float low and suspend easily rather than sinking or bobbing on top, and they move on ordinary aeration. A fresh batch grows its biofilm and comes fully into service in about 5 to 15 days. It works in water up to about 65 degrees, and the carriers are made in several small sizes, roughly 10 to 25 millimetres. Tell us your tank volume and load and we will work out the fill and the quantity.

Conventional activated sludge grows its bacteria as loose flocs floating free in the tank, which then have to be settled out in a clarifier and pumped back to the tank to keep the population up. MBBR grows the bacteria fixed on the carriers instead, and that changes several things for the better. There is no sludge to return, so the pumping and the clarifier-to-tank recycle disappear. The biomass cannot wash out of the tank, because it is held on the carriers, so the process copes far better with sudden high loads or toxic shocks and recovers quickly. It holds much more biomass per cubic metre, so the tank can be smaller, or an existing overloaded tank can simply have carriers added to boost its capacity without being enlarged, a very common upgrade. And there is no fixed bed to clog and backwash. The trade is the cost of the carriers and the need for a screen to keep them in the tank. For most new plants and for uprating old ones, those are easy trades. Send us your flow and load and we will size the media.