MBBR media retention keeps every carrier inside the reactor where it belongs. However, many plants lose carriers through outlet pipes, weirs and pumps. In fact, even a slow leak cuts treatment capacity month after month. Therefore, screen design deserves as much attention as the media itself.

Why MBBR Media Retention Fails

Carriers escape for simple reasons. For example, a slot may sit wider than the carrier itself. Similarly, weak mixing pushes media into one corner. As a result, the screen blinds and the water level climbs.

Blinding causes most media losses. Rags, hair and fibres wrap around the bars. Consequently, flow slows down and the tank spills toward the outlet. Cracked welds and shrunken gaskets create the same leak path.

Even a 5% loss trims the biofilm surface area. In practice, that gap shows up as higher ammonia in the effluent.

Screen Types That Hold Media in Place

Plants use four main screen styles. Each one suits a different tank layout.

• Wedge wire screens – angled bars shed solids well and resist blinding.
• Perforated plates – cheap and simple, yet they clog faster.
• Cylindrical sieves – a large open area in a small footprint.
• Mesh panels – a good fit for small package plants.

Wedge wire remains the safest choice for most reactors. Moreover, it handles high flow without a big head loss. For instance, a narrow channel favours a flat wall screen. Round tanks, however, suit cylindrical sieves better.

Sizing MBBR Media Retention Screens

Screen area drives the whole design. Engineers normally keep the approach velocity under 0.1 m/s. Otherwise, carriers press against the bars and stay stuck there. In addition, the slot width should measure about half the carrier height.

A 25 mm carrier, for example, pairs well with a 10 mm slot. Wide slots let broken pieces slip through. Narrow slots blind quickly and therefore raise the cleaning workload.

Aeration Keeps the Screen Face Clean

Air does more than feed the biofilm. It also sweeps carriers away from the screen. Therefore, many designers add an air scour header below each screen. In short, moving water keeps the openings open.

Flow peaks deserve the same attention. For example, storm flow can double the velocity across the screen. Additionally, a bypass channel protects the reactor during these peaks.

Simple Checks That Prevent Media Loss

Operators catch most problems early with a short routine.

• Measure the level difference across the screen each shift.
• Look for stray carriers in the outlet chamber.
• Inspect welds, gaskets and frame bolts every month.
• Record the media volume once a year.

Our MBBR troubleshooting guide covers related process faults in more detail. Moreover, the US EPA NPDES program publishes useful guidance on treatment plant performance.

Get the Retention Design Right

Strong MBBR media retention protects your investment for decades. Oxy-Tech supplies carriers and screen guidance together. As a result, your reactor keeps its full media load and its full capacity. Contact our team for a quick sizing review.