RotaCut and BioCrack: Optimizing gas yield and operation of the digestion tower

Case Study - Weißenthurm municipal plant

Our wastewater treatment plant is equipped to handle 50,000 PE. About two thirds of the wastewater treated here is municipal, while about one third is industrial. The plant has two serial digestion towers with nominal volumes of 2,200 m³ and 500 m³, respectively. On average, they are fed with 100 m³ of sludge per day, approx. 80% is primary sludge and 20% is surplus sludge.

Although we have a very good climber screen, we have repeatedly had problems with fibrous matter. Anyway we had not observed any floating layers in the digestion tower for 10 years. But one day we did notice a floating layer during a routine check and estimated that it was about 30 cm. While removing it, we discovered that it was actually 1-2 m thick. Six months later, we noticed that another floating layer was forming. To prevent layer formation, we planned to install a macerator as part of the digestion tower circulation and feeding mechanism.

A new CHP (124 kW) had been installed two years previously, but it was not yet operating at capacity. This is why we had been considering a disintegration system from the outset and we planned to install one at this point as part of the conversion work. We looked into how they had worked at other wastewater treatment plants and learned that because of their high operating costs the overall result often did not meet expectations; ultimately, their use seemed unprofitable. While attempting to identify alternative methods, we discovered the BioCrack electrokinetic disintegration system; we installed 3 modules along with a rotary lobe pump and a RotaCut macerator to feed and circulate the large digestion tower.

The system has now been running for 8 months, both treating the primary and surplus sludge before it enters the digestion tower and treating it inside the digestion tower during the circulation process. We have not observed even the beginnings of a floating layer since. We have also found a few foreign bodies in the RotaCut. Gas yield increased over the previous year by 8.22%. Considering the BioCrack system's low power consumption of 0.1 kWh, this is a significant improvement for our treatment plant. Moreover, the sludge now has better settling characteristics and sludge dewatering is easier. The decanter now runs more evenly and is easier to use, consumes less energy and requires less flocculent.