Suspension of plastic media in activated sludge tanks


The paper at hand will present an alternative solution to the common approach, which firstly reduces the number of individual mixers required in such processes and secondly relies on a sound design basis.

Moving Bed Reactor (MBR) processes have gained general acceptance over the past years.

These processes rely on plastic carriers that allow the biologically active sludge to attach to and grow in them. This results in a higher sludge  Concentration in the activated sludge tanks and in higher purification capacities.  There are various types of media from different manufacturers available on the market, which vary in shape and material. The density is normally slightly lighter than water so, in normal conditions, the carriers will float. Typical volume concentrations of carriers are 40 to 60 %.

The mixing task can be defined as the suspension and homogenization of floating particles in activated sludge. The most common approach to fulfill this mixing task in the field is to install a series of submersed mixers and introduce high energy densities in order to suspend the large amounts of carrier media needed. This leads to higher investment and operation costs together with a difficult design and layout, especially, because the arrangement of the mixers is a challenging task. Moreover, an ensemble of multiple mixers increases the susceptibility for malfunction.