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Wissenschaftliche Begleitung einer Biogasanlage

> current research work

Low Temperature Conversion (LTC) of Biomass for resource recovery

Background information:

Sewage sludge recycling / Situation


Yearly, in Germany about 10 Megatons of sewage sludge accumulates with a dry matter content of 30%. 

The resulting volume approximately corresponds to 3.5 times the volume of the pyramid of Giseh.

Where does all the sewage sludge go? Notice: Since June 2005 the land filling of sewage sludge is forbidden!

Recycling of sewage sludge in Germany (2002)

In comparision to 2002, use of sewage sludge in agriculture (green) is increasingly shifting to thermal treatment (red) and alternative methods (blue), such as gasification or low temperature conversion.


Sewage sludge treatment 

by Low Temperature Conversion (LTC)




Low Temperature Conversion (LTC) was developed by the research group of Prof. Dr. Ernst Bayer (+ 31.01 2002) at the University of Tübingen in the eighties. Using a BP-grant for renewable energies, he experimentally simulated the principle of the formation of petroleum and coal from biomass in the laboratory. 

Indeed, in 1906, the thermal decomposition of organic material (wood, saccharide, bones, blood) under anaerobic conditions was already known as so-called “dry distillation”. The “dry distillation” was technically used for the production of coal to bleach treacles and phosphorous from animal coal.

LTC operation

During LTC the thermo-catalytic process of conversion takes place anaerobically, under normal pressure and temperatures between 380-450°C. The gaseous product condensates to ‘crude oil’, reaction water and salts after cooling. A small part exhausts as non condensable gases (hydrogen, methane, ethane, propane). A hard organic solid remains in the reactor, containing all non-volatile substances (including most of the heavy metals).

Looking beyond the petroleum frontier:

In times of increasing oil prices, production of hydrocarbons from biomass may be regarded as a source of alternative fuels from renewable organic material. For this reason, we investigate a variety of substrates such as animal meal, rapeseed, animal fat and other organic residues such as PE or PP.

Basic principle of LTC exemplified by sewage sludge

LTC = removal of functional groups (carbonyl groups, OH, OS, Cl) from organic molecules.

Chemical Equation

Bacterial biomass contains up to 28-30% lipids, about 50% proteins and 5-30% polysaccharides. The following equations describe the schematical process during the LTC conversion:




Equations show that hydrocarbons are mainly formed from fats (lipids) and proteins.

In LTC, mother nature's hydrocarbon chains remain basically intact. Only carbon dioxide or ammonia is removed. This is a catalytic process. By contrast, in a pyrolytic process, the splitting of C-C-bounds occurs. Thus, LTC should not be confused with pyrolysis.

Production of oil and coal in the laboratory

The following figure demonstrates the flow diagram of the test plant. The conversion of the substrate occurs in an electrically heated furnace (10 kW). Under anaerobic conditions, the furnace is heated up to 400°C for 3 hours to react about 300 – 1000g of substrate.

Schematic flow chart of the LTC operation (NCG: non condensable gases)


Picture gallery "Laboratory"

Substrates for LTC

  • microbial biomass
    • dried sewage sludge

  • animal biomass (waste of slaughter houses)
    • animal meal & MBM

    • animal fat

  • vegetable biomass / residues of the production of biodiesel
    • Solid residues from rapeseed extraction
    • Residues from biodiesel manufacturing

  •  plastics (especially PP and PE)

for further information please click here
(Direction: Dorina Benz and Martin Kosa, University of Applied Sciences Gießen-Friedberg, course of studies Technical Compiliation & Multimedia based Documentation)

 Pilot plant

Based on the laboratory results, a pilot plant was built. The project was supported by the foundation Deutschen Bundesstiftung Umwelt, Osnabrück.  Project partners have been the Fa. Werkstoff und Funktion Grimmel Wassertechnik, Ober-Mörlen and the firm Rünagel Elektrotechnik, Viereth-Trunstadt.  The pilot plant was successfully tested at the sewage treatment plant Füssen

a: substrates house b: input screw c: internal circulation of packed bed e:condenser f: oil trap

The reactor has an internal loop. This enables the realization of different retention times.

Picture Gallery "Pilotanlage"

Use of products


  • In-house utilization at sewage treatment plants as a substitute for heating oil in the form of an isolated application 


  • Usage of the coal for drying the sewage sludge at the STP
  • Application as filter instead of much more expensive activated‑carbon filters (provided that the amount of inorganic components is marginal)
  • Transfer to cement- or brick-industry; a high content of phosphorous can cause a limitation
  • In case of high phosphorous content, the coal is an attractive source of mineral fertilizer, e.g. for sod, landscaping etc.

Dioxines (PCDD/F)

The LTC causes a dehalogenation of the dioxines (PCDD/F). 


An eco-efficiency-analysis of sewage sludge disposal through LTC was undertaken, comparing it to coincineration in a coal-fired cogeneration plant.  The study shows that under the conditions used at the sewage treatment plant in Füssen, coincineration offers greater economic and ecological benefits. If the costs for the utilisation of the coal-containing residues, however, is free of charge, a comparison of total costs and ecological balances show that LTC, fitted with an exhaust gas heating system, is economically more efficient than coincineration.  A LTC plant with an electrical heating system is not appropriate for technical-scale LTC because of its high energy requirements, neither from a financial nor an ecological point of view. 

Public relations

Presentation of the DBU supported project at several local traide fairs, e. g. ACHEMA in May 2003 / 2006 and  IFAT 2005.

Diverse lectures:
-    VDI-Wissensforum „Klärschlamm, Tiermehl, Gülle, Biogene Abfälle“ in Dortmund, 10/2003
-    German-Brazilian Environmental Symposium at the University Tübingen 07/2004
-     Anaerobic Digestion, Montreal, 09/2004
-    German-Brazilian Technical Discussion Biodiesel12/2004 at FAL in Braunschweig
-    Public Informative Meeting on LTC in Füssen 06/2004
-    International Congress Environmental Science and Technology, New Orleans, 01/2005
-    German-Brazilian Symposium 09/2005 in Santa Maria, Brazil.

-    Second International Congress Environmental Science and Technology, Houston, 08/2006

Newspapers, radio and TV reports about the LTC activites at the laboratory of waste management. (Filmlets: "Heute NTK 15.06.2004" , HR-filmlet , "TV Allgäu"  "TV Bodensee".

For further information, please contact: 


LTC of  animal fat

Currently, the laboratory of waste management is intensifying its research in the thermocatalytic cracking of animal fat. The objective is the development of a small-scale reactor with continuous operation.

Contrary to sewage sludge, animal fat contains no in-situ catalsyts. Therefore, it is necessary to conduct the gas phase over an external catalyst.  

 With the thermocatalytic conversion of fat, about 90% aliphatic hydrocarbons (Hu > 40MJ/kg) and a lower fraction (< 10%) of olefins and aromatic compounds are produced.

According to these results, a patent application was filed for fuel production from animal fat.

A schematic flow chart of the catalysis of animal fat:

The high-quality characteristics of the LTC product qualify oil from animal fat as a competitive fuel. The table below shows a comparison of light fuel oil with an 1:1 mixture of light fuel oil and oil from animal fat, as well as pure oil from animal fat.

Picture gallery "animal fat"

1.) Formula for transesterification from fat to methyl ester of fatty acid

2.) Concerted transformation of fatty acids in aliphatic hydrocarbons by LTC