Modernisation of over 10 systems with Schreiber counterflow ventilation
Schreiber countercurrent aeration systems are characterised by a rotating scraper in the aeration tank, on which part or all of the aeration equipment is mounted. The scraper moves through the tank at high speed and thus simultaneously ensures circulation. The oxygen input and nitrification/denitrification in such systems are originally controlled by the Schreiber-specific O2 minimiser.
The Schreiber counterflow ventilation concept was innovative at the time and showed good cleaning results and operational stability. One weak point was always the central swivel joint with the central air feed-through. In addition, the number of aerators was limited by design if they were only attached to the scraper. The concept of counterflow ventilation is now outdated and no longer meets the requirements placed on the energy efficiency of ventilation systems in particular. Even the O2 minimiser does not deliver the control technology results that can be expected today.
From an operational point of view, it is particularly problematic that longer downtimes can occur in the event of damage to the central swivel joint or the seal, as this special spare part is no longer available directly from the manufacturer. It has to be procured from other suppliers at great expense and with long waiting times.
BITControl has now redesigned and retrofitted a number of activated sludge plants that were equipped with Schreiber counterflow aeration. The implemented concepts and results are described here.
Modernisation of Rheinböllen wastewater treatment plant
The Rheinböllen wastewater treatment plant has been equipped with a modern AQUA PROVI process control system and a powerful AQUA LOGIC fuzzy control system since 2004. When the process control system was installed, great importance was attached to recording the power consumption of the most important consumers. As a result, we were able to precisely record the energy savings after the plant was converted. In particular, we can also monitor ongoing operation.
Before modernisation
The Rheinböllen wastewater treatment plant has two aeration tanks with counterflow aeration and a secondary clarifier. The aeration tanks had a parallel flow.
Modernisation steps
In a first step, the two aeration tanks were switched from parallel to series operation. This led directly to the Nges discharge values being halved. The series connection had a stabilising effect on the process, as the main degradation takes place in the first tank. Only secondary purification takes place in the second tank. This accelerates the material conversion and peaks are broken down more quickly.
In the second step, the aeration system was rebuilt. The aerator bridge was decommissioned and surface aeration was installed in the two aeration tanks. Circulation in the denitrification phase is achieved by shock aeration. Load shocks were programmed to maintain the properties of the aerators.
Energy consumption was significantly reduced following the renovation:
The electricity consumption of the blowers initially fell from approx. 600 kWh/d to 300 kWh/d and has since risen again to approx. 380 kWh/d. On the one hand, the graph shows the significant energy savings. However, it also shows that ongoing operation must be constantly monitored and readjusted even after optimisation.
Modernisation of Alsenz wastewater treatment plant
The Alsenz wastewater treatment plant has a similar structure to the Rheinböllen wastewater treatment plant. The conversion was carried out in a similar way. Here, nitrate and ammonium measurement are installed for control purposes and phosphate measurement for phosphate precipitation.
This system is currently in the running-in phase. The control system has not yet been adjusted. However, savings are already clearly recognisable.
Modernisation of Waxweiler wastewater treatment plant
The aeration system at the Waxweiler wastewater treatment plant was also replaced and considerable savings achieved.
