The UPM Nordland Papier fine paper factory in Dörpen is the largest of its kind in Europe, producing up to 1.4 million tons of uncoated and coated paper every year with four machines. The company is part of UPM Paper ENA (Europe and North America), a worldwide leading manufacturer of graphic papers, with its head office in Germany and production facilities in Finland, the UK, France, Austria and the U.S.A.Accumulating waste water is treated in a sewage plant, which first works mechanically and then biologically with a maximum capacity of 650 m3/h and it is then fed into the River Ems as“fully purified water”.
Double-stage biological waste water treatment
Since 1968, packaged units made by AERZEN have been in operation here. At that time, the first positive displacement blowers were installed in the fresh water sector. In 2009, two further Delta Blower packaged units were supplied for waste water treatment in the sector of the aeration basins. Since 2012, two rotary lobe compressors of the new Delta Hybrid series have been supplying oxygen for the new moving bed reactor.
The “moving bed” comprises plastic bodies with a size of about five centimetres, floating freely in the waste water and offering an ideal growth surface to micro- organisms, which prefer packed beds. To encourage the multiplication of these bacteria, oxygen, which is generated by the two Delta Hybrid machines, each with a drive capacity of 250 kW, is fed into the reservoir via vents. The two units, one of which covers the operational requirements, and the other kept as redundancy, have been designed for a maximum pressure of 1,500 mbar. They are run depending on demand via the integrated AERZEN AERtronic control system and frequency converter, and supply the reactor basins, which have a height of 12 metres, with a constant maximum pressure of 1,400 mbar.
In the subsequent second treatment stage, the activated sludge stage, the waste water first of all passes through a circular above- ground aeration basin, which is supplied with oxygen by two speed-controlled AERZEN Delta Blowers operated in parallel. In the following three aeration basins, surface aerators are used at the water surface. Afterwards, the waste water passes through a degassing basin and four secondary settling tanks working in parallel. Prior to being fed into the River Ems, an additional clear water filter retains the finest residual contaminants. Due to the multistage treatment of the purified waste water a BOD decomposition of 98 per cent is achieved.
The new Delta Hybrid packages have been designed for all application cases where air and neutral gases are conveyed up to 1.5 bar. Initially, the series only comprised packaged units in the performance range from 600 to 5,900 m3/h. With further development work, AERZEN has increased the performance range to a maximum 9,000 m3/h. These new machines are not only easy to use and to maintain, are robust and have a long service life, but they also reduce energy consumption by 15 per cent compared with conventional compressors.
“So it is not surprising that in spite of nationwide requests for quotations for new investments in the field of compressed air generation in our sewage plant, we have again and again decided on the packaged units made by AERZEN”, says Dipl.-Ing. Hartmut Wagener, operating engineer in the field of public utility.