A whole plant designed for energy efficiency
The Bocholt sewage treatment plant handles all the wastewater collected in the sewer network from the city of Bocholt, as well as rainwater from street inlets and roof drainage. They use a combination of mechanical, chemical and biological processes to treat the wastewater before it is fed back into the course of the local river after being cleaned.
The plant generates more electricity than it uses, and the surplus is fed into the local power grid.
The modern sewage treatment plant is designed for sustainable and energy efficient operation, and they continue to invest in equipment which improve efficiency. The plant can treat up to 108,000 cubic meters of wastewater every day and the resulting sludge is thickened using centrifuges and then pumped into two digesters for digestion. The sewage gas produced in the digestion process is used in the company’s own combined heat and power plant to generate energy. The sewage treatment plant also uses biomass, photovoltaics and wind energy to generate around 6.3 million kilowatt hours of renewable electricity per year. Because it only consumes 3.3 million kilowatt hours, it generates more electricity than it uses, and the surplus is fed into the local power grid.
Clean water. Clean process. Andreas Wehren and Christian Schaffeldt from the Bocholt wastewater treatment plant discuss how ABB IE5 SynRM motors are helping clean 108,000 cubic meters of wastewater every day, in the most energy efficient and environmentally friendly way.
Investing in efficient technology
Minimizing climate change and improving energy efficiency are central factors when it comes to investments in the Bocholt plant. Andreas Wehren, Operations Manager, Central Sewage Treatment Plant, Mussum, has been there for ten years. He says: “Because of climate change, we want to become more and more energy efficient. When I took over the sewage treatment plant as manager, we still needed almost five million kilowatt hours to operate. Now we need an average of around three million, partly because we have invested a lot in energy-efficient technology. “
We have invested a lot in energy-efficient technology
In 2020, two new investments were required at the plant, in the flocculation filtration system and in back sludge pumping station II. In both cases, the operators decided upon ABB packages, which consist of IE5 SynRM motors and ACS880-31 ultra-low harmonic drives.
An ultra-premium efficiency IE5 synchronous reluctance motor in the flocculation filtration plant (source: ABB).
Ultra-premium efficiency and excellent partial load operation
With this investment, the Bocholt sewage treatment plant will install seven IE5 SynRM motor and drive packages. The IE5 SynRM motors, in particular, will bring a new level of efficiency to their operations. Thanks to their design and the way they operate, the rotor of a SynRM motor does not need windings or magnets, and there is no induction current in the rotor so there are no rotor losses.
Andreas Wehren appreciates the ultra-premium efficiency and the good partial load efficiency of the ABB SynRM motors. “Operation at partial load is important because we have many control processes in the sewage treatment plant, such as for hydraulic adjustment or air volume control. Due to the increasing dry spells, we are now driving more partial load than full load. We used to regulate this with on-off operations. Today, we fine-tune operations with the help of variable speed drives. That’s why we now have at least 50 drives running.”
Andreas Wehren, Operations Manager, emphasizes the importance of saving energy in the new investments (source: ABB).
Four SynRM motor and drive packages for sludge pumping station II
Four of the new ABB packages have already been in use in the reverse sludge pumping station II since October 2020. Andreas Wehren explains: “Sludge pumping station II is one of the most important pumping stations because the sludge that settles out of the treated wastewater in the secondary clarifier has to be constantly returned to the incoming raw water so that the cycle remains closed.”
Before this investment, sludge pumping station II used six pumps. However, the operators have been able to improve both mechanical and electrical efficiency by selecting SynRM motors and improving the impeller geometry in the pumps. This means that now they need only four pumps and the four IE5 SynRM motors.
Employing SynRM motors and improving the impeller geometry in the pumps has improved both mechanical and electrical efficiency.
Better still, the new pumps also require less drive power. In addition, because the motors are controlled by variable speed drives, the return sludge flow can be adapted to the hydraulic load on the sewage treatment plant, which saves even more energy. By using ultra-low harmonic drives they also reduce the risk of disturbances in the power network, keeping the supply voltage stable.
Three SynRM motor and drive packages for flocculation filtration
Three more ABB packages were selected for the flocculation filtration system. Each package consists of an IE5 SynRM motor with 55 kilowatts of power and an ACS880-31 drive. The ABB motors drive the pumps, which lift the wastewater around five meters so that it can be completely filtered in the flocculation filtration. The first package was installed in September 2020 and the remaining two will be installed in early 2021.
Initiated with the National Climate Protection Initiative, the Federal Environment Ministry supports projects that make a contribution to reducing greenhouse gas emissions
Ministry support for energy efficient technology
The investments at the Bocholt sewage treatment plant are funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety. Initiated with the National Climate Protection Initiative, the Federal Environment Ministry supports projects that make a contribution to reducing greenhouse gas emissions.