SCHLUMOSED

SCHLUMOSED (for sludge , LUMO = light and SEDImentation ) is a measuring system for the separation behavior of sewage sludge .

In biological sewage treatment plants , sewage is cleaned with the help of microorganisms ( sewage sludge ) that are mixed with the sewage. After the cleaning process, which takes place in the aeration tank , the microorganisms have to be separated from the treated wastewater. This takes place in the secondary clarifier, where the sewage sludge settles due to its higher density ( separation ). With the help of the SCHLUMOSED, the separation behavior of the sewage sludge can be characterized online .

Functional diagram of the SCHLUMOSED. A sludge sample in a standing cylinder is penetrated by white light rays at six different heights. The intensity course over time is recorded.

Measuring principle

With the help of an automatic sampling device, sludge from the inlet of the secondary clarifier is transported into the SCHLUMOSED. The sludge then separates in the device over a period of (usually) two hours. During this time, the device is penetrated by white light rays at six different heights (see illustration on the right), which are partially absorbed by the microorganisms suspended in the sludge. The remaining intensity of the light rays is measured and saved as a time series. ${\displaystyle I_{i}(t)}$

In addition, the SCHLUMOSED is calibrated with drinking water before each measurement . The reference values ​​measured here together with the intensity values ​​obtained during the sludge measurement result in the transparency : ${\displaystyle I_{i,ref}}$ ${\displaystyle T_{i}(t)}$

${\displaystyle T_{i}(t)={I_{i}(t) \over I_{i,ref}}}$

Separation diagrams

Separation diagram of a disperse separating sludge

Separation diagram of a sludge separating in association

If the course of the transparency for the six sensors examined is plotted as a function of the separation time, a separation diagram is obtained. The separation diagrams for dispersed sludge and sludge that separates in association differ fundamentally (see pictures on the right).

Characteristic points

If separation occurs in the lattice , a series of characteristic points can be determined for each individual curve in the separation diagram:

Transit time

The transit time ( time of incipient transparency , tiT) is the time at the beginning of a measurement during which the SCHLUMOSED measures the transparency zero (0%). During this time, the concentration of microorganisms in the path of the light beam is so high that the light beam is unable to penetrate the sludge. At the point in time tiT, the sludge level, which is always clearly formed during separation in the association, passes the level of the light beam, and there is a sudden increase in transparency.

Leap in transparency

The jump of transparency (jT) is the transparency value to which the transparency jumps after reaching tiT. It characterizes the particle concentration in the water flowing out of the sludge bed. Since the sludge bed becomes more and more dense over time, the transparency of the outflowing water also increases over time, as more and more particles can be retained by the sludge network.

Transparency peak (peak uf transparency, pT)

The transparency peak results from the decrease in transparency following the jT and indicates how much the particle concentration in the supernatant itself and the particle concentration in the water flowing out of the sludge bed differ.

Final transparency

The final transparency (fT) is the transparency at the end of the measurement after two hours. In the case of separation in the association, the transparency of all six sensors should run the same after reaching the respective transparency peak, so that the final transparencies are also the same.

Daily and weekly courses

The separation behavior of the sewage sludge changes dynamically due to the respective living conditions to which the microorganisms in the sewage treatment plant are exposed. Clear daily and weekly courses can be observed in the course of the measured final transparency. At times of low system load (night hours, weekends), the final transparency increases, while when the system is overloaded, the final transparency decreases so that the system operator should take countermeasures if he wants to avoid the drifting of sludge from the sewage treatment plant.