Research project OptDigest started at ARA Unteres Pustertal

The production of biogas at wastewater treatment plants is essentially a very effective and environmentally friendly way of providing a renewable energy source. An unsolved problem in this context is the occurrence of foam in the digestion towers. The foam leads to major technical problems (overflowing of the reactors), dangerous situations (penetration into gas pipes) and always also to a significant reduction of the possible biogas production. In the present project, first the state of knowledge shall be defined by studying the technical literature and interviewing the wastewater treatment plant operators in South Tyrol. In a further work package, possible substances responsible for the foam in the excess sludge or in the fermentation substrate are to be investigated. A monitoring and early warning system for wastewater treatment plants will be developed by determining the relevant substances in the fermentation substrate and by developing an adapted foam test. Subsequently, the thermal pre-treatment of the excess sludge and its effect on relevant constituents and foam formation will be investigated in a laboratory plant. Finally, a mobile pilot plant for the thermal pre-treatment of excess sludge will be designed and built. This test plant will be used at wastewater treatment plants of the Pustertal AG with relevant foam problems in the digestion tower (e.g. ARA Unteres Pustertal) in order to be able to investigate this type of foam prevention on a full scale and to optimize the process of thermal pretreatment.

A mobile pilot plant for the pretreatment of the excess sludge was planned by the partner company
Atzwanger AG and STUGA KG, a partner company. The technical-university support was provided by BioTreaT GmbH, a spin-off company of the University of Innsbruck. The plant was designed in such a way that for medium-sized wastewater treatment plants (up to max.100,000 EWCSB120) the entire thickened excess sludge can be pre-treated. The plant is used after
completion on wastewater treatment plants with foaming problems or plants with unsatisfactory biogas production or digested sludge dewatering. During the study period, all relevant operating parameters of the wastewater treatment plant are recorded and the foaming behavior is closely observed or analyzed. In addition, biogas production and sludge dewatering are monitored.

Since the problem of possible odor development was already feared in advance, the general extent of odor development was first minimized by process engineering adjustments and the test plant was coupled with the air scrubbing plant of the Lower Puster Valley WWTP.

Unfortunately, it turned out during operation that the odor development is partly higher than expected in the planning.
The air washing plant of the ARA Unteres Pustertal sometimes reaches the limits of its capacity, so that there have already been inquiries about the odor development.

Those responsible take the problem seriously and are constantly working to exhaust all possibilities for mitigating the problem, so that the research project can run without problems until its planned completion before winter.

If odor nuisance should occur again, especially at night, we ask for feedback to the ARA Unteres Pustertal under telephone 0472 886685.