This brings us to how much media is required, what media materials are suitable, and where should it be purchased.
Here are my quick bullet points on MBBR media:
- Media provides growth surfaces for the microbes. The media needs to be near neutral buoyancy and composed of stable material (usually polyethylene or polypropylene).
- Loading rates are based on surface area per cubic meter volume. So you want media with higher surface areas per cubic meter. You should also be aware that clogging can be a problem if the media has "too much" surface area. Ask the manufacturer their experiences with various options.
- Normally the media has 85% open space for water and microbial growth. Less plastic means more volume for treatment. But the plastic must be robust enough to handle biofilm weight, friction, and degradation from UV radiation/chemicals.
- For true MBBR systems the media is added to approximately 66% volume. Again, system specific issues may require changes in media volumes added.
- Media lifespan - while long lived, media will eventually need to be replaced. Ten years is an often quoted number.
- Media size - can it washout if screen failure occurs. (Larger media would be more likely to be contained in a clarifier).