Aerotherm

• The equipment consists of an aerothermal reactor and a heat exchanger.
• It operates with undewatered sludge containing 4 to 6% dry solids.
• The raw sludge is preheated in a sludge-to-sludge heat exchanger utilizing heat recovery.
• Before entering the mesophilic digestion tank, the sludge is cooled in a heat exchanger.
• In the digestion tank, energy-rich biogas is produced.
• By burning the biogas in a cogeneration unit, it is possible to generate electricity and heat.
• Overall, more than 50% of the organic matter in the sludge is degraded, with 5 to 10% of this occurring in the aerobic stage.
• The temperature achieved in the reactor ensures the devitalization of pathogenic microorganisms given a certain retention time.
• The equipment can operate as a single-stage system without biogas production.
• It can also operate as a dual system, where the preliminary stage produces biogas for the mesophilic process.

When applying the aerothermal stabilization and hygienization method, the thermal energy for heating is obtained from the exothermic reaction in the aerobic reactor, where 5 to 10% of the organic matter in the sludge is decomposed. Another source of energy to cover heat losses is hot water (80/72 °C) supplied to the reactor’s heating jacket from a gas or other boiler, or from a cogeneration unit (if installed). Stabilization is completed in the anaerobic stage (before entering, the sludge is cooled in a heat exchanger), where almost all remaining organic matter is converted into energy-rich biogas.

The advantage of this dual technology is significantly lower capacity requirements for the mesophilic digestion tanks, which also no longer need to be heated, and the low hydrogen sulfide content in the biogas, which usually no longer requires desulfurization before combustion.

In cases where biogas production is not considered, the installation of mesophilic digestion tanks is omitted. The entire stabilization process by degradation of the organic sludge component as well as hygienization occurs only in a single stage in the aerothermal reactor with an extended retention time.

A temperature above 60 °C in the aerobic reactor guarantees the devitalization of pathogenic microorganisms (including salmonella), eggs of human and animal parasites, and seeds of plant weeds contained in the sludge, even with just a few hours of retention.

Advantages of the AEROTHERM Method

• The equipment has been operationally verified, including a proven sludge/sludge heat exchanger resistant to fouling, and is capable of flexibly responding to changes in the amount of incoming sludge.
• The sludge treated in the reactor is not only hygienized during the process but also physically and enzymatically prepared for further processing (biogas production, thickening).
• For smaller wastewater treatment plants (WWTPs), AEROTHERM can perform sludge stabilization and hygienization even without biogas production.
• The external energy consumption is low, and with biogas production, the overall energy balance is even positive.
• Reduction of dry solids content in the sludge by more than 50% lowers the requirements for storage space and reduces sludge transportation costs from WWTPs.
• Waste air from the process is deodorized in an odor filter before being released into the atmosphere.
• The process is electronically controlled and does not require continuous supervision.

Energy Demand

• Energy for heating the sludge is partially obtained from the exothermic reaction in the reactor.
• Heat losses are covered by hot water supplied to the reactor’s heating jacket.
• With biogas production, the equipment is almost energy self-sufficient throughout the year.

Selected References

The AEROTHERM method is successfully operated at over a hundred WWTPs in Western Europe. In the Czech Republic, the first reference plant was commissioned in 1996 at the Bystřice pod Hostýnem WWTP.

Selected Applications

• WWTP Bystřice pod Hostýnem, Czech Republic
• WWTP Schwab München, Germany
• WWTP Guldenfingen, Germany
• WWTP Dillingen, Germany
• WWTP Mittleres Emmental, Switzerland
• WWTP Třebíč, Czech Republic – pilot operation

Microbiological Quality of Sludge from the Třebíč WWTP Before and After Treatment

*According to Decree No. 382/2001 Coll. for Category I sludge
CFU… Colony Forming Units

Performance range of AEROTHERM according to the amount of processed sludge

Technological diagram