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Biological processing compartment
The second stage of the MBT process is the Biological Compartment which can
include:
Composting compartment
Anaerobic digestion compartment
Biodrying compartment
The first two processes are described at the beginning of this report. In the last
process (Biodrying) the waste material undergoes a period of rapid heating
through the action of aerobic microbes. During this partial composting stage
the heat generated by the microbes result in rapid drying of the waste. These
systems are often configured to produce a refuse-derived fuel where a dry, light
material is advantageous for later transport combustion. (Wastesum.,2010)
In some of the systems, both Anaerobic digestion <strong>and</strong> Composting
compartments exist <strong>and</strong> the combination of both gives the <strong>best</strong> results as for
the treatment process.
Products of the MBT facility:
The products of the Mechanical Biological Treatment technology are:
Recyclable materials such as metals, paper, plastics, glass etc.
Unusable materials (inert materials) prepared for their safe final disposal
to sanitary l<strong>and</strong>fill
Biogas (in the case of the anaerobic digestion)
Organic stabilized end product
High calorific fraction (refuse derived fuel – RDF)
4.7.3. Environmental Impacts from MBT Plants
Carbon Dioxide <strong>and</strong> Methane
The CO2 emissions from these types of plants come from biogenic materials.
The quantity of this greenhouse gas depends on the stages of the whole
process. Another parameter is how pure the final product has become after the
mechanical sorting process. Finally several factors that have to do with the
waste treatment process affect CO2 concentration in the environment.
Ammonia NH3
Ammonia is produced in many stages of these waste treatment plants. The
concentration is analogical to the waste type <strong>and</strong> the contamination of it from
many different chemical substances (materials that could not be separated
during the process).
An additional problem is represented by the partial oxidation of NH3 to N2O,
which is linked to the damaging of filters. This is also a potent greenhouse gas,
so the minimization of this secondary emission is also of relevance. Another