Results of carbon removal with a HUBER Drum Screen LIQUID
The results of the tests carried out on two sewage treatment plants are presented in the following. The design size of the sewage treatment plants is 17,000 PE and 28,500 PE. On both plants, the HUBER Drum Screen LIQUID was operated for approximately five weeks, with different throughputs of up to 35 l/s. Both plants have installed a 6 mm preliminary screen and a conventional grit trap. The wastewater was taken from the channel downstream of the grit trap and pumped to the HUBER Drum Screen LIQUID. Figure 6 shows the HUBER Drum Screen LIQUID in compact design with (optional) downstream mechanical screenings thickening which is performed by a HUBER Wash Press WAP® liquid installed in a tank.
Samples marked "2-h" are two-hour random samples (composite samples) taken during the day, while samples marked "10 h" are ten-hour composite samples taken during the night. Additionally, time-proportional 24-hour daily mixed samples were taken and analysed.
The figure on the right show that an average total COD reduction of 51-57% and AFS reduction of 71-72% could be achieved on both sewage treatment plants with the use of a HUBER Drum Screen LIQUID. These results were achieved without adding polymer. The separation capacity of conventional primary settlement tanks with material residence times of 0.5 to 1 h is 25% COD reduction and 50% AFS reduction according to ATV A 131.
Sewage treatment plant 1 with 28,500 PE had a rate of external water of approximately 75%. This background explains the significantly reduced concentrations of AFS and COD in the inflow. Despite of the high rate of external water, more than 90% of all measurements showed a COD elimination of more than 50%. The low AFS concentrations could also be reduced by on average 72%.
On sewage treatment plant 2 with 17,000 PE, the inlet concentrations of > 600 mg/l COD are high compared to plant 1. The reduction achieved on this plant was 71% on average for AFS and 51% for COD.
These excellent outcomes result from the special functional principle of the HUBER Drum Screen LIQUID. The screen is equipped with a fine 0.1-0.3 mm stainless steel mesh. Due to these small apertures the screen retains even finer particles which could not be removed by primary sedimentation. Through screening alone, the HUBER Drum Screen LIQUID achieves results comparable to a conventional primary settlement tank. Due to the additional effect of deep bed filtration, however, the fine screen is able to remove much more COD and AFS from the wastewater flow than a conventional primary settlement tank. Deep bed filtration is enabled by the filter carpet that is formed inside the drum by the separated solidst.
Contrary to a primary settlement tank, it is possible to specifically influence AFS and COD removal efficiency of the drum screen by changing the mesh aperture of the screen.