Asset Publisher Asset Publisher

The Concept of Energy Re-Use


Anaerobic Sludge Digestion for Recovery of Energy from organic matter.

The challenge in terms of sustainability:

The sustainable management of limited resources

The initial situation:

  • High global energy demand
  • Scarcity of clean water resources
  • Increase of costs associated with traditional sources of clean water (e.g. seawater desalination)

Economic situation:
The economic significance and environmental benefits of integrating the Anaerobic Sludge Digestion Technology as a core process step in municipal wastewater treatment have become more than obvious during the last years.

The solution:

Passavant-Roediger Sequential Gas Lance Mixing System

Main benefits of Anaerobic Sludge Digestion:

  • Reduction of Sludge Quantity (total mass balance reduction 20 %)
  • Odour Reduction
  • Biogas Production & Utilization
  • Reduction of Greenhouse Gases

Digester performance depends on the digester shape and mixing system. Poor digester mixing is the most common reason for poor performance.
Thus Passavant-Roediger has developed the Sequential Gas Lance Mixing System for the injection of digester gas, based on the expert experience gained from the installation of more than 1,500 digestion tanks worldwide.


  • Gas is injected shortly above the digester bottom via flexible insert lances
  • Scum layers are broken up by high turbulence. Scum is mixed into the sludge and gas production increased
  • Gas mixing systems operate independent of the sludge level, while draft tubes and pump mixing to the top depend on constant level
    —> low sludge level can be necessary in case of heavy foaming
  • Gas mixing raises gas production by releasing small gas bubbles from solids
  • The entire compression energy is released within the digester, pipe friction losses are negligible
  • With 25 to 50 Wh/(m³∙d) power consumption of gas mixing is very low (low OPEX)

The sustainable strengths:

Main advantage:

  • Continuous operation of the mixing system not required à considerable reduction of operation costs
  • Saving of Energy


  • Prevention of deposit formations, even in case of shallow digester bottoms
  • Low-cost digesters with flat bottom can be completely mixed with the hanging lance system
  • Maintenance works at the mixing system always possible, even during operation of the plant
  • No necessity to empty the digester at regular intervals

Further Benefits:

  • Reduction of the sludge volume, thus requiring smaller aggregates/plants/equipment
  • Fewer chemical substances needed for conditioning
    —> reduction of disposal expenses
  • Elimination of difficulty to dispose of grease trap residues and simultaneous fermentation in the digester
  • Production of biogas (can in many cases be used for self-sufficient plant operation)
  • In conjunction with a pasteurization stage, the sludge can be safely disinfected
    —> hygienically-safe Sludge Re-Use

Brief profile of the company:

Name: Passavant-Roediger GmbH
Headquarters: Hanau
Year established: 1842
Employees: 95
Solutions: Water, Wastewater, Sludge & Waste Treatment Plants as well as related Products & Services (Manufacturing Facilities, Operation & Maintenance, After Sales Service)

Internationality: Subsidiaries/Offices in Algeria, Bulgaria, China, Hungary, Romania, Turkey, U.A.E., Jordan, etc.