19    INVESTIGATION OF SOLID WASTE DRYING BY
AEROBIC BIOLOGICAL TREATMENT
Joachim Brummack, Dr.-Ing.
Bernhard Gemende, Dr.-Ing., speaker
Peter Loetzsch, Professor Dr.-Ing. habil.
Silke Paar, Dipl.-Ing.
Dresden University of Technology,
Process and Environmental Engineering Institute
ABSTRACT
The application of biological prior to thermal treatment of municipal solid waste is very
promising to facilitate separation of inert materials and homogenization of municipal solid
waste. In addition, a remarkable energetic effect can be achieved. By using the biological treatment as a drying step, the input water content for a subsequent incineration could be considerably reduced and optimized. Corresponding pilot-scale tests in fixed bed and rotary reactors are
presented. The experimental results are checked by energy balances and compared to the theoretical drying potential. Based on these experiences, optimal conditions for the biological process
and parameters for its control can be derived.
INTRODUCTION
In the last years, many efforts have been made to introduce biological treatment processes for
municipal solid waste (MSW) prior to disposal. With these processes, the amount as well as the
environmental problems related to MSW disposal could be remarkably reduced. Meanwhile, mechanical-biological waste treatment (MBWT) has become an alternative to mere disposal. Even
with simple technological means, the process is very effective. The large-scale application
proved a considerable limitation of degradation processes in the disposal body and a significant
increase of the waste compaction density (up to the two-fold or even somewhat more) due to improved separation of materials. Whereas also the emissions during the aerobic degradation in
open windrows cause no extreme enhancement with concentrations in the order, of or less than,
the disposal background.' A critical and often controversial issue discussed is the natural (and
much more technical) limit for the reduction of the organic content. By long-term biological
treatment, the minimal achievable content of organic matter, expressed in terms of ignition loss,
is about 20% of mass. This organic content may still implicate some disposal problems. Only by
thermal treatment processes (e.g., incineration) the organic content could be further reduced to
values of about 5%, which are, for example, prescribed by German disposal law. However, one
of the major disadvantages of that biological treatment is that the energy (or organic content)
contained in the waste is not used at all.
The combined application of biological and thermal treatment is also very promising with respect to an energetic utilization of MSW. By using the biological treatment as a drying step, the
input water content for a subsequent incineration could be considerably reduced and optimized.
Thus the energy efficiency compared to direct waste incineration is improved. To investigate the
drying effect by aerobic biological treatment, several laboratory and pilot-scale tests were carried
out. Main objectives of these tests were to determine the amount of the reaction heat generated
and the air needed for a controlled biological drying process. Furthermore, a first assessment
should be made upon the possible reduction of the waste moisture content and the implicated enhancement of the calorific value. For the experiments, both a static fixed bed and a rotary reactor
52nd Purdue Industrial Waste Conference Proceedings, 1997, Ann Arbor Press, Chelsea, Michigan 48118. Printed in
U.S.A.
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