of Municipal MBR Applications“
Wissenschaftlicher Fachtext (Wasser
Auftraggeber aqua system consult.
Übersetzung Englisch - Deutsch
In Germany, screens and sieves are defined
by taking into consideration different aspects of construction as
well as parameters like gap size, construction and gap geometry
(DIN 2002). According to DIN 2002 screens have gaps of 2 mm or bigger,
whereas sieves are characterized as having gaps below 2 mm. Today
three different gap geometries, slit, hole and mesh, are available
as can be seen from figure 1.
Figure 1 also indicates the direction of flow, which is necessary for slits to distinguish between horizontal and vertical slits. However, in most cases flow is not perpendicular to the screen or sieve plane, especially rotating drum sieves do not have a uniform flow condition through the device. In this paper
rotating drum slit sieves and screens are referred to as horizontal slit devices.
Pre-treatment of wastewater prior to treatment in a MBR system is essential and crucial for the MBR process. There is
still an ongoing discussion on how to design the optimal pre-treatment system. This is mainly due to the fact that there is very poor knowledge about the capabilities of different pre-treatment units – mainly sieves – to modify the raw
wastewater in a way that avoids braid formation in the MBR tanks. Until today only the parameter of nominal gap size is regarded. In the future it will be necessary to discuss removal efficiency instead of gap size alone.
Of course, concerning efficiency geometry plays an important role as well as operational considerations.
The removal efficiency up to now is determined by using the parameter suspended solids (SS). In the future, this parameter which is not the core of the problem should be replaced by another parameter that characterizes different wastewaters in regards to their ability and likeliness
of forming braids. At DESEE work is ongoing to find a suitable method to describe the braid formation capacity BFC, which would allow us to quantify the efficiency of different pre-treatment systems regarding braid formation in a truly result oriented way.