Improving separation efficiency of sand traps with claw compressors
Wastewater Treatment Facility
Wastewater treatment facility Poppenweiler The Poppenweiler wastewater treatment facility has a population equivalent (PE) of 31,000 and is part of the in-house operation activities of the Ludwigsburg municipal drainage service, which also includes sewage treatment plants in the districts of Eglosheim (18,500 PE) and Hoheneck (167,000 PE). The wastewater treatment facility was commissioned in 1976 and was radically expanded and modernized from 1994 to 1996. The reasons for this were that the old wastewater treatment facility was no longer able to meet the purification performance requirements, primarily with regard to the breakdown of nitrogen and phosphorus. In addition, the communities of Affalterbach and Marbach-Siegelhausen were also connected to the Poppenweiler wastewater treatment facility. Today, the 31,000 PE, size class 4 wastewater treatment facility covers a settlement area of 342 hectares.
They wanted to change the turbulent kinetic energy caused by the rolling speed in the wastewater by changing the air volume flow. So they wanted to use the flow velocity to influence the vertical circulation of the wastewater caused by aeration and its forward motion.
Busch overpressure solution and its benefits for the customerThe already installed rotary lobe blower was not adjustable and thus provided a constant volume flow at an overpressure of 0.5 bar. At that point, Walter Eichinger contacted the company Dr.-Ing. K. Busch GmbH. The company recommended installing a Mink claw compressor (Fig. 2) with an external variable speed drive. This compressor also provides constant overpressure of 0.5 bar, but the volume flow can be adjusted with a frequency converter so that it can be precisely adjusted for the requirements in the existing sand trap. Using the operating principle of the claw compressor, it can be adjusted within a large range from 20 to 60 Hertz without affecting the generated overpressure.
Fig. 2: Mink claw compressor for aerating the sand trap. Source: Busch Vacuum Solutions.
Now this solution introduces the exact amount of air needed with several nozzles, which are attached along the entire length of the sand trap (Fig. 3) at a depth of 2.90 metres. The rolling movement that they cause in the wastewater is now regulated by its circulation velocity in such a way that sand and other mineral materials settle in the tank’s sand trap channel. At the same time, the organic materials remain suspended and exit the sand trap to the aeration tanks via the primary clarifier, where they are needed for denitrification. Rolling movement that is too weak due to insufficient aeration may lead to unwanted deposits of organic materials in the form of sludge at the bottom of the tank and in the sand trap channel. Separation of oils, greases and other suspended materials was also improved so they swim at the top of the grease trap and can be skimmed.
Fig. 3: Cross-sectional drawing of the sand trap. Source: Busch Vacuum Solutions.
And Walter Eichinger also noticed a further advantage from the new Mink claw compressor: compared to the previous rotary lobe blower, the claw compressor is more energy-efficient and is equipped with an IE3 energy-saving motor, which translates to energy savings of approximately 33%. Maintenance is limited to an annual oil change, which is performed by a Busch service technician.