Separation Properties of Activated Sludges

In waste water treatment plants of the aerated type the biosludge is separated from the cleaned water in the secondary settling tank. It was found that a secondary settling tank produces a turbid effluent when the sludge separates in the dispersed regime; the effluent is however much clearer when the crosslinked regime prevails, irrespective of the size and design of the secondary settling tank. Which regime prevails depends on concentration and type of suspended solids AND on the living conditions of the biocenosis. One and the same sludge can reverse the separation regime within hours and that repeatedly. As yet we only know that a high (low) load of the waste water treatment plant can lead to dispersed (crosslinked) separation.

A sludge that behaves in the crosslinked regime will in the 1000 ml cylinder form a sharp sludge interface with the supernatant above it, showing a 2-3 mm wide, more transparent layer, above the interface. The interface and the more transparent layer can be measured with the SCHLUMOSED.

While the sludge settles, water flows up trough the interface. The interface must thus have a certain strength, otherwise small flocs would be torn off the interface. That the interface does indeed exhibit such strength was proven with the STRENGTH TESTER.

The strength of the sludge interface may depend on the number of filamentous microbes; however, it is unlikely that the filamentous microbes have the ability to change the regime from crosslinked to dispersed and vice versa when the living conditions change.

The following questions will be investigated:

a.) Which parameters of plant design or plant operation lead to a change of regime and influence the strength of the sludge interface ?

b.) Which microbes have the ability to induce a change of regime and which means do they use ?