Energy-efficient sludge treatment at winery

Wine harvesting season can be challenging for wastewater treatment plants. This was the case in the wine-growing community of Edenkoben in the Palatinate region of Germany. When the grapes were processed, the effluent load rose steeply — by a factor of 17. High-load anaerobic digestion provided a flexible solution that cut power consumption by 20%, generated over half of the required electricity on-site and reduced sewage sludge volumes.

The increase in the effluent load also pushes up the plant’s power consumption, which can surge to three times the normal level at harvesting time. Small-scale wastewater plants use a technique known as aerobic stabilisation to prevent the sludge produced during wastewater treatment from developing unpleasant odours. This involves prolonged aeration to stabilise the sludge. The downside is that the aeration system consumes a lot of energy.

Edenkoben’s wastewater treatment plant has operated far more efficiently since the introduction of the high-load anaerobic digestion, a process developed by researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart.

“We converted the plant to a process based on high-load anaerobic digestion with the help of colleagues from several engineering companies. The new process implemented in Edenkoben has numerous advantages. First, it generates energy instead of merely consuming it. Second, it reduces the quantity of sludge that would otherwise have to be disposed of at great cost,” explained Fraunhofer IGB scientist Dr Werner Sternad.

Energy consumption is 20% lower because the process doesn’t require a power-hungry aeration system. Of the power actually consumed, 50% or more is generated from sewage gas on-site in two cogeneration units. This means that less than half of the electricity the wastewater plant needs is bought in. Sludge disposal is another area in which it has been possible to slash costs. In the past, the sludge had to be dewatered on a daily basis. Anaerobic digestion produces so little sludge that now the filter press runs only twice a week, except during the wine harvest.

One of the researchers’ main priorities was to design a solution for Edenkoben adapted to the local situation, namely wide seasonal variations in the effluent load. “We installed two digestion tanks, which can be operated in parallel during the wine harvest, or in series at other times of the year. This makes it possible to adapt the process flow to the volume of sludge produced and optimise sludge treatment,” Sternad said.

The new plant entered service in early 2016. When operating in series mode, it is processing approximately 40 m³ per day. During the wine harvest, however, it can now go up to 130 m³.

The two-stage high-load anaerobic digestion system in Edenkoben allows the wastewater treatment plant to cope with a higher effluent load during the wine harvest. © Photo Verbandsgemeindewerke Edenkoben