Mechanical-biological waste treatment plant

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A mechanical-biological waste treatment plant (MBT) , also a mechanical-biological pre -treatment plant or substance-specific waste treatment , is a waste treatment plant for waste from households and companies ( household waste or commercial waste similar to household waste). In Europe, waste is classified according to a waste catalog with more than 600 types of waste.

General

The aim of waste treatment in general is to treat the “ waste ” material during product manufacture, use and consumption in such a way that the substances it contains cause no or the least possible impairment of life on earth. In order to achieve this goal, the waste generated by the waste producer (household, company, public institution) is collected by a disposal company, transported to waste treatment and there, depending on the type of waste, physically, chemically and / or biologically (pre-) treated. “Pre” in the word pre-treatment indicates the treatment before the final disposal, treatment or recovery.

Household waste is characterized by a high proportion of organic matter (“organic matter”). Depending on the settlement structure (country / city), the socio-economic and cultural conditions (differences between regions and countries) as well as the selected investigation method and the breakdown of the waste type "household waste" into different waste fractions, this is between 30 and 60%. Other main fractions of household waste are glass, paper, plastics (possibly further subdivided), etc.

Objectives of a mechanical-biological waste treatment

The goals of a mechanical-biological waste treatment are

  1. to reduce the volume of waste to be landfilled and thus to conserve the required landfill volume or to increase the duration of the landfill,
  2. reduce the biological activity of the organic content in household waste to such an extent that the smallest possible amount of ( climate-damaging ) landfill gas can escape uncontrolled at the landfill ,
  3. to reduce to a minimum the amount of pollutants that would get into the groundwater with the seepage water or that would have to be treated in a seepage water purification system ("controlled landfill" with sealing systems),
  4. to reduce the proportion of waste to be incinerated or to avoid it entirely if waste incineration is politically or organizationally not feasible.

Political discussion

A consensus on whether the use of a mechanical-biological waste treatment plant in the context of a waste management system makes sense or not can only be reached on the basis of a general waste management plan for the respective disposal area, since in addition to technical criteria, there are also political (social assessment of treatment alternatives) and organizational criteria (Operator, financing, fees, etc.) aspects must be used. In Germany, the decision on this has been made in recent years. A total of 46 systems are operated with MBT technology (as of September 2009). In addition to the technical process concept of the "classic" MBT, this also includes mechanical-biological stabilization (MBS) and mechanical-physical stabilization (MPS).

Process steps of a mechanical-biological waste treatment plant

  1. The household waste is shredded after a rough precaution.
  2. The shredded material is divided into several material flows (“fractions”) by screening. Comminution and division of the material flows can also be combined in one step, depending on the comminution technology. Steps 1 and 2 essentially form the mechanical part of the MBA.
  3. The main part of the organic substance is found in the "fine fraction" (mostly grain size <40 mm) after comminution and sieving.
  4. In the "coarse fraction" (mostly grain size> 40 mm) there are foils, paper, hard plastics, wood, diapers, shoes, etc. Through ballistics, coarse, heavy and disruptive materials are discharged, which are disposed of separately and a so-called "calorific value enriched" light fraction (HwF) or "high calorie" fraction (HKF) won. This fraction should serve as fuel for so-called "high calorific power plants" (RDF power plants ).
  5. The fine fraction is transported to the biological part of the plant. There, the organic components are further treated by microorganisms either in ventilated windrows, reactors and / or halls aerobically (with a supply of air and thus oxygen) or anaerobically (with exclusion of air) in closed reactors that are closed from the outside air . There is a significant reduction in the organic matter. The treatment is carried out (in Germany) until a certain degree of biological degradation is reached.
  6. A heavy or contaminant fraction is transported directly to a waste incineration plant and incinerated. The resulting slag can be processed (sieved, scrapped) or disposed of in Germany for road construction.
  7. The enriched light fraction is processed into the fuel through subsequent post-treatment steps, which, in accordance with the 17th BImSchV, ends up in the so-called co-incineration of the cement, lime and large power plant industries. This processing takes place with the aim of producing a substitute fuel (RDF) of high quality and low in heavy metals . High quality means an improvement in the calorific value and the physical combustion properties (water content, grain sizes, density, flight and ignition properties). The already existing thermal systems and their combustion requirements dictate the processing technology to be used for the upstream process: Fuels for the main burner of a power plant boiler or cement rotary kiln place different demands on the fuel than e.g. B. a fuel that is to get into the calciner of a rotary kiln, in a fluidized bed or in a grate furnace.
  8. The biologically treated fine fraction is deposited (in Germany). It must comply with certain properties (legally prescribed parameters). The main criterion is biological activity (how much landfill gas can the treated waste fraction still produce? How much organic matter can still be washed out of this material with the rainwater?). From this, conclusions can be drawn about the long-term interaction of the biologically pretreated material with the environment and its hazard potential.

There are many variants of MBAs with regard to the technical equipment and combination of the main steps listed. The spectrum ranges from simple mechanical and biological treatment in open systems, e.g. B. on the surface of landfills (in many countries not licensable), up to highly complex systems that are largely closed to the environment (with vehicle locks, halls, ventilation systems, closed reactors, etc.).

The equipment of the MBT and thus the degree of subdivision of the material flows depends on the other components of the waste management system (waste fees, prices for fuels, market prices for fuels and other separated fractions, legal requirements, location of the location, distance to neighbors, distance to landfill, availability and Distance to an incineration plant, personal preferences of the decision-maker, etc.). The most important role when deciding on an MBT system is played by the treatment price per Mg (ton) of household waste and the resulting increase in overall disposal costs compared to pure (no longer permitted) landfill or the incineration of the entire waste stream in a waste incineration plant.

When considering the full costs of the MBA, the sales costs of all sub-streams must be taken into account. Thus, in addition to the pure treatment costs (variable and fixed system costs), additional transport, quality monitoring, additional payment for the resulting fuel fractions (marketing costs), the incineration costs in the waste incineration (disposal costs) and the legally compliant operation of the landfill for the biologically treated landfill have an impact.

Attempts to reduce these full costs by marketing scrap and other valuable fractions (e.g. plastic, paper, wood) are usually only partially successful for reasons of quality and sales.

literature

  • Doedens, H. et al. (2006): MBA and the 2020 target . Garbage and waste 3/2006
  • Grundmann, T. (2005): State of the MBA technology in Germany . in: Biological and residual waste treatment IX biological - mechanical - thermal. Edited by K. Wiemer, M. Kern. Witzenhausen 2005 (Witzenhausen Institute. News from research and practice), ISBN 3-928673-45-9
  • Heuel-Fabianek, B., Siebert, J. (2001): New regulations in the field of waste management - consequences for biological waste treatment and landfilling . Chemical Engineer Technology 2001, 73, No. 7, 901-906
  • Baier, H. (2005): Generation of substitute fuels for use in cement and power plants - The RDF plant in Ennigerloh . Pp. 321-336. Alternative fuels 5 - production and recovery, TK-Verlag Karl Thomé-Kozmiensky, ISBN 3-935317-20-4
  • Baier, H. (2006): Alternative fuels for use in co-incineration plants . In Zement-Kalk-Gips International, No. 3, pp. 78-85
  • Baier, H. (2007): Intermediate storage for high calorific fractions . Pp. 311-317. In Münsteraner Schriften zur Abfallwirtschaft, Volume 11, conference volume on the occasion of the 10th Münster Waste Management Days , ISBN 3-9811142-1-3

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