Method

In the present project, the impurities from the digested sludge are separated through mechanical treatment. Hydrocyclones are a promising device for the separation of impurities, as they require little effort regarding maintenance and wear prevention. In the hydrocyclone, the centrifugal forces are used to separate solid particles from the suspension. The solids are separated into the underflow of the cyclone while the clean liquid runs off through the overflow.
There are no generally valid calculation models for the design of the hydrocyclone. Therefore, empirically determined principles are used for the performance estimations (separation efficiency and pressure loss). The disadvantage of the empirical principles is their limited validity within the investigated framework conditions. Scientific literature does not provide suitable empirical equations for the separation of particles from fermentation sludges. Moreover, sufficient design criteria for the hydrocyclones in this application are not available.

The present project investigates the separation on laboratory scale using model liquids and model particles on the basis of rheology and particle size distribution analysis. Empirical optimization studies for the geometry and operating parameters as well as flow profile measurements using Particle Image Velocimetry (PIV) are carried out at a test rig. In an optimization study, the highest possible separation efficiency is to be achieved with the lowest possible pressure loss (energy consumption). The cyclone geometry determined on laboratory scale is transferred to a hydrocyclone on a large scale, and is installed and evaluated at a waste water treatment plant.