RakeMax® Screens successful on big STPs in Northern Germany

HUBER Multi-Rake Bar Screen RakeMax® on the plant of Hetlingen

The RakeMax® screens installed on STP Hetlingen in the North Western periphery of Hamburg and in the pumping station Süd Wilhelmshaven give proof of the reliability and robustness of the HUBER RakeMax® Multi-Rake Bar Screen. The area of the sewage board AZV Südholstein is one of the boom areas in the greater Hamburg region.

On WWTW Hetlingen about 30 million m³ wastewater are treated per year, a great contribution to the pollution control of the river Elbe. Since 1965 when the plant and interceptor were built, the wastewater from the North West of Hamburg and the neighbouring districts have been treated there, in total of 600,000 residents on an area bigger than 800 km². Through all these years the treatment technology has steadily been updated to keep pace with the increasing requirements of modern wastewater treatment. It was in 2008 when the plant operators for the first time thought about to modernize the preliminary treatment stage. It was an important point for them that the installation of new screens should not interfere with the overall STW operation. The three-line system of inlet screens consisted of a coarse screen (40 mm bar spacing) and downstream fine screen (20 mm bar spacing) for each channel. After the operators had spoken with us, they decided in 2008 to test the efficiency of a HUBER RakeMax® screen with 10 mm bar spacing in one of the channels. As the results of the test phase were very positive, the customer kept the screen and ordered the same type of screen also for the two other channels. The new screens do not need an additional preceding coarse screen. The reliability of the HUBER RakeMax® screen is among other factors due to the screen rack design with its special profile bars which have the effect that the hydraulic loss is very low. As a result, the hydraulic throughput capacity is increased compared to conventional flat steel profile or trapezoidal profile bars. This bar shape furthermore prevents jamming of solid material, such as gravel. The solids contained on the screen rack form a filter surface so that even finer particles are removed from the wastewater when the rack is blinded with solids.

A similar installation example is the RakeMax® screen installed in the pumping station Süd Wilhelmshaven. The wastewater of the city of Wilhelmshaven is treated with a combined sewer system. The combined sewage flows into the pumping station Süd. The catchment area of this pumping station consists of a sewered area of about 530 ha, of which about 270 ha generate runoff. The pumping station Süd consists of pumping station 1 and pumping station 2. Pumping station 1 delivers the dry weather flow from about 27,000 residents and the majority of the precipitation flow to the central sewage treatment works. The combined sewage overflow caused by heavy rainfalls is delivered into the nearby receiving water body by pumping station 2. The maximum delivery of the overflow pumps is about 46,000 m³/h. The plant operators installed a sewer network control system to limit the load on the waters. The precipitation development and runoff generation in the sewer network are permanently monitored to ensure the available storage space is optimally used. To achieve an additional load reduction, it was decided to replace the 20 mm coarse screens with 6 mm fine screens. At the beginning of 2009, they invited to tender for the replacement fine screens with the purpose to achieve a significant reduction of unhygienic coarse material, solids and fibres discharged to the receiving water course with combined sewage overflows. In April 2009, HUBER received the order and used some dry weather phases to dismount the old screens and install the new plant components. Two of the channels of the three-line system were equipped with a 6 mm HUBER RakeMax® screen each, which offers the advantages of the special bar shape as described above. The coarse screen installed in the third channel has been kept as stand-by unit for emergencies. Another special technical feature of the new RakeMax® screens is their hydraulic liftability. The screen can very quickly move upwards out of the channel. This is especially beneficial where no emergency bypass is available and the channel cross section (and thus flow-through) must temporarily be freed in case of a failure.

These two application examples show that the RakeMax® screen, due to its versatility and flexibility, can easily be integrated in systems with given hydraulic and constructional conditions.

In short: With this screen type, solutions can be provided for virtually any application, even and especially with given hydraulic and constructional conditions.