The Society for Graduate and Professional  Engineers


Recycling the Future

Biological Waste   Bins for Germany !

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Biological Waste Plant in Germany

Report by the Executive Director on a visit to a Biogas Plant for Biological Waste in Germany.


The integrated methanation and compost process (IMC-process) in an innovative, two-stage process for producing refined fermentation gas and a low-toxic, high-quality biological compost.  The special characteristics of this novel aerobic/anaerobic process means that flow time can be minimized and the compost quality significantly improved.

The IMC is constructed in a modular design, so that further modules can easily be added to the existing systems when the processing volume increases.  One special feature of the IMC-process is aerobic hydrolysis and acidification, with a subsequent separation of solids and liquids.  Because only the pressed water is subject to anaerobic treatment, the solids will always remain aerobic.  This means that no unpleasant odours will be emitted, as is often unavoidable with anaerobic treatment of solids.  Subsequent rotting in open areas can therefore be undertaken without any complications.


The IMC-process is also characterised by a decomposition of heavy metals and salt in fresh compost.   During aerobic hydrolysis and acidification, the temperature will rise to approximately 60C (auto-thermal process).  This high temperature and the low pH value of 4-4.5 in the acidification phase, will ensure hygienically safe solids.

The IMC-Process

The biological waste arriving in the plant is sieved off, purified of all iron metals by means of a magnetic separator and conducted to the first stage - the aerobic reactor.  There it is mixed with water.  The solids remain in the reactor for three days.  Every 24 hours they are withdrawn and the water pressed off, before the solids are again returned to the reactor and mixed with circuit water.  After three days, the solid matter is conducted to the post-rotting phase as fresh compost.  The pressed-off water, organically highly-enriched, then reaches the anaerobic level.  The dissolved organic material is decomposed to form valuable biogas.  The waste water is only slightly organically polluted and can be clarified in a water-treatment plant and re-used as circuit water.


Biogas plant for waste foodstuffs

Waste from foodstuffs arises in production, in food processing and, in food merchandising, in large kitchens and in households.  The volumes involved are considerable.  They have to be sorted into categories and disposed of in a way that is not harmful to the environment.

Biogas plants for disposal of wastes from foodstuffs allows two important tasks of environment protection to be solved at the same time :

  • Creation of conditions for an environment-friendly waste disposal system.

  • Use of energy as a regenerative energy source

A biogas plant for disposal of waste foodstuffs can, according to the quantities that need to be processed and the operation location, be adapted as a mobile container unit or stationary treatment plant.  The system can be used both as a complete plant with an anaerobic section or as a co-fermentation plant for use in, for instance, a sewage treatment plant.

The waste foodstuffs can be supplied to the plant in waste containers and brought into the processing system.  The material is broken down to manageable sizes and conducted to a storage container.  When the storage container is full, the material is broken down further by means of a fine-grinder of the model Gorator, until a grain size less than 3 mm is obtained.  The material is then pumped into the first stage, the aerobic hydrolysis and acidification process.

The hydrolysis container can hold a full daily batch.  It is mixed thoroughly by means of a stirring apparatus.  Heat is applied and the temperature is raised to approx 55C.  Hydrolysis and acidification lead to a pH value of between 4 and 5 after a very brief period.  The temperature factor and lower pH value will ensure that the material is hygienically safe at all times.

The anaerobic reactor is charged continuously from a buffer container.  The material to be fermented stays in the anaerobic reactor for a period of  ten days.  After this time, approx 90-95% of the organic dry substance will have been decomposed.

The waste water emanating from the anaerobic reactor is cleaned in a water clarification unit and can then be discharged into the sewage channels.  The generated biogas can, for instance, be converted into energy in a block-type thermal power station. 

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Waste disposal Containers

As I was leaving Hanover airport in Germany, my attention was caught by a colourful group of BINS, centered around an ashtray.  The bins had a plastic liner and enabled members of the public to sort their waste disposal, even at an airport.

German airport police were intrigued by me taking a photograph of waste disposal containers.  I asked them if they have to enforce this kind of discipline and the answer was no -  as members of the public living in Germany would not dispose of waste in any other way.




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Last modified: 08/03/2016