Why choose mixed media over dual media?
In certain situations, it is desirable to employ a third media layer in order to create a greater difference between the smallest size particle in the bottom of the bed and the particle size at the top of the bed. In order to accomplish this, a higher density material is required. Properly sized and proportioned, these mixed media beds are known to result in added protection from breakthrough of certain pathogens like Giardia cysts. The benefits of such beds are mostly realized on cold, low turbidity waters. In this application they are capable of higher flow rates, and longer runs with acceptable head loss development characteristics. Frequently, warmer waters with higher turbidities, and higher flow rates result in undesirably high head loss development. In these cases mixed media is normally not employed. In other cases such as high turbidity water, with minimal driving head available, the benefits of mixed media cannot be realized, and thus the cost is not justified.
