#Product Trends
Sewage Treatment Plant Lingen/Ems
New Dewatering Equipment
Lingen/Ems sewage treatment plant
The Lingen sewage treatment plant (STP) purifies a wastewater volume of approx. 14,000 m³ each day. The facility is designed for an inhabitant figure of 195,000, and the current load currently stands at an inhabitant figure of 110,000, with about 50,000 inhabitants coming from industry and trade. The significant wastewater producers include a manufacturer of polyacrylic fibres, a minced meat factory, a manufacturer of bathroom and office products, as well as a chemical plant. In addition, the wastewater from a neighbouring community is also purified in Lingen.
At present only the "Plus Energy Sewage Treatment Plant with Phosphorus Recovery" project funded by the German Federal Environmental Agency (funding priority: energy-efficient wastewater disposal plants).
The objective here is to convert the Lingen/Ems sewage treatment plant from one of the largest energy consumers in the community into a "positive energy ratio treatment plant". At this stage it can already be regarded as a showcase plant. It means that it will be possible in future to generate surpluses of electricity and heat via the plant's operations.
The target status of the plant is to be achieved by means of a number of individual objectives such as phosphate recovery, increased electricity generation via thermal sludge disintegration as well as reduced chemical consumption and sewage sludge levels.
The thermal sewage sludge disintegration process functions using the LysoTherm® system which is based on the indirect heating of the sludge using thermal oil. The heat required for this is provided by the two new CHPs. The sludge can be more easily degraded anaerobically by the thermal sludge disintegration, in turn leading to increased digester gas yields. A further step in this overall concept was what is known as the LysoGest® process in which primary and thermally disintegrated (hydrolysed) excess activated sludge is digested in separate digesters. This process makes it possible to concentrate the nutrients, especially phosphorus.
During the long-term testing of the individual process steps, the transformation in the dewatering properties of the individual sludges was also included in the scientific evaluations.
Changing from bag filter presses to decanters optimises dewatering
Prior to the tests, the sludge was dewatered from the digestion tanks via two bag filter presses. During the tests it was found that using these presses produced only a small increase in the dry matter content (TR) in the dewatered sewage sludge at around 27% (without MAP precipitation). However, a significant increase in polymer consumption to up to 26kg WS/t TR was also registered. The consumption of iron salt solution used for dewatering also increased by about 15%.
As sufficient experience had already been gained with the bag presses, plans were set to test a further dewatering unit across an extended period with support from the Lingen/Ems sewerage plant (Mr Hüer, Mr Bohlin), the Technical University of Darmstadt responsible for the sampling processes for the tests, from Dr. Kopp – Sewerage Plant Consultant, and the firm Pollution Control Service GmbH (Mr Ewert).
As with Hiller GmbH all scroll drive types (DecaDrive, FSG–Drive, Hydraulic) are manufactured in-house, and can be used at any time as required, the decision was made in favour of centrifuge technology.
The long-term tests were conducted in the period from 07-07-14 to 24-07-14 using a Hiller DP573 high-performance centrifuge with four-valve gear unit.
The following sludge compositions were tested:
• Mixed sludge consisting of hydrolysed, fully digested and excess activated sludge subjected to MAP digestion, as well as fully digested primary sludge
• Mixed sludge consisting of hydrolysed, fully digested excess activated sludge without MAP precipitation and fully digested primary sludge
• Hydrolysed, digested and excess activated sludge subjected to MAP precipitation
• Hydrolysed, digested and excess activated sludge subjected to MAP precipitation, 50% increase in MgCl2 addition
• Hydrolysed, digested excess activated sludge without MAP precipitation
• Fully digested primary sludge
The results of the tests showed that, depending on the sludge composition, the flocculant consumption could be reduced by up to 45% in comparison to the bag presses, and that in some cases iron solution was not required at all. Using a decanting centrifuge, a 3% higher output could be achieved when processing excess activated sludge, and with mixed sludge with MAP precipitation, TR values of 33% were achieved using the bag filter press and the centrifuge.
Using Hiller separation technology permitted the separate dewatering of individual sludges that could not previously be separately dewatered. This relates in particular to the hydrolysed and fully digested excess activated sludge that could ALWAYS be dewatered using the centrifuge, regardless of the prior sludge treatment.
The dewatering tests using the Hiller high-performance centrifuge at Lingen STP have shown that sludge dewatering on the sewage treatment plant can be conducted more economically by using the Hiller centrifuge under comparable conditions.
A DP664, a latest series centrifuge with four-valve gear unit, optimised bowl drive as well as an aerodynamic rotor design was installed at the Lingen STP. Taken overall, these positive characteristics mean that the requirements of the DWA-M 381 with regard to the required energy consumption are easily met.
Figure: The new decanter in use at the Lingen STP ensures higher discharge levels
Conclusion: The operational experience gained so far with the selected Hiller high-performance centrifuge reflects the positive results from the tests conducted in advance. The result will be further improved in future by optimising the centrifuge, the amount and type of flocculant and the dosing of iron or other digestion agents required.
The thermally disintegrated, fully digested sludge dewatered by the centrifuge is produced with a crumbly structure which can then be allowed to dry easily. The project at the Lingen/Ems sewage treatment plant was a complete success and can truly be called a showcase project.
