Exhaustive fermentation of residual wastes with disinfection and degradation of harmful substances

On the laboratory scale, a multi-stage method concept with fermentation stages is in use to stabilise organic components in residual wastes. The degree of degradation of the organic dry substance is up to 80%. Furthermore, a mathematical model has been developed for the set-up of industrial-scale plants with which biogas production can be formulated at different volume loads.

At the beginning of the project, it was known that European landfill guidelines would be coming into effect. A technical opportunity for implementing these rules was the mechanical/biological treatment of wastes that were to be deposited in landfills, and with which composting (aerobic) and fermentation (anaerobic) could be applied to the biological processing stages.

In the framework of the combination project “Mechanical-Biological Treatment of Wastes to be Deposited in Landfills,” within this sub-project, an economically acceptable technology is to be developed for treatment of residual wastes that works without external energy. The goal was to stabilise native organic substances by optimising the anaerobic material conversion process so that they are biologically inactive after being deposited in a landfill.

Procedure:

The fundamental idea of the procedural concept is to separate the residual waste into individual material flows with specific treatment methods: After mechanical treatment with shredding, magnetic separation, sieving and, when applicable, homogenisation, the  treatment of material is continued with wet separation methods.

Materials used in for the laboratory studies were mechanically treated house waste from the test facility at the Scharfenberg (Wittstock) landfill, as well organically enriched residual waste from Quarzbichl (Landkreis Bad Tölz). In the treatment of these wastes, there were differences in the composition of the floating materials in particular.

The process engineering concept of the anaerobic stage tested on the laboratory scale involves multi-stage treatment (exhaustive fermentation). The mashed organic chemicals are hereby macerated in a primary reactor (agitating tank). For the second stage, material management that decouples the dwell time of light to heavy degradable substances is strived for. The mineralised fraction is periodically extracted on the reactor floor. In this way, processing to a highly enriched organic fraction and the broadest possible stabilisation are combined through anerobic fermentation for an effective process solution.

Results:

For the anerobic method stage, the reactor ratings show that, with this technically simple and operationally safe plant configuration, as well as a two-stage operation with 18.2 days dwell time, degradation rates of organic dry substances of 75% can be obtained. Through aerobic pre-treatment with decomposition of lignocellulose-containing organic components,  degradation can be increased to 85%.

For the solid from the biogas reactor cycle, the respiratory activity AT4  and (residual) gas build-up GB21 parameters were used as stability criteria. These serve to assess landfill capacity. Both parameters were under the limit values discussed. The treatment of process water opens up possibilities for the biological destruction of halogenated hydrocarbons.

Finally, a mathematical model has been developed for the set-up of industrial-scale plants with which biogas production can be formulated at different volume loads.

Conclusion:

The anerobic treatment stage led to high degradation rates of the native organic substances. Thus, for technical use, it should be considered for mechanical-biological residual waste treatment.




Source Of Supply: The final report (call number F 99 B 635, in German) can be borrowed from:
Technische Informationsbibliothek (TIB) Hannover
Welfengarten 1B
30167 Hannover



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