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Organic Waste

Uni recycling

Separating biogenic waste products into liquids and solids

Biodegradable waste refers to biowaste that is collected separately. Just like kitchen waste and leftover food from catering establishments, as well as out-of-date packaged foods, biodegradable waste can be separated into solid and liquid fractions with the aid of Doppstadt’s screw press.

The bioavailable components are enriched in the liquid phase and can be fed to a wet fermenter. As a result of the gentle preparation and pressing step, the digestate usually does not need any further processing and already contains less than 0.5 % contaminants upstream of the fermenter, based on dry matter. The solid phase mainly consists of packaging material and other solids. The contained residual organic materials are implemented as part of a biological drying process. After subsequent screening, residual packaging can be incinerated. The fine fraction is clean compost.


In cases where a dry fermenter is used, the screw press can make the digestate stackable and thus easy to store, by removing the pumpable liquid phase. This moreover ensures the permeability required for the subsequent composting. The Doppstadt mixer can mix the digestate’s solid matter fraction from the press with green waste before it is supplied to the rotting process. This ensures a more intensive rotting process and thus a better level of rotting.


For turning aerated trapezoidal and static windrows of up to 3.5 m in height, Doppstadt’s DU windrow turner is a cost-effective solution that is not sensitive to contaminants. The raw compost can be classified after the rotting process with the aid of Doppstadt’s SM screening machine, which prepares the finished compost.

Mixed construction waste is generated with every demolition, renovation or construction site. It cannot completely be disposed of in landfill due to its organic content. Thermal disposal on the other hand is too expensive due to the high mineral content. That is why it is necessary to first separate the waste by density so that inert material can go to landfills while combustible material can be utilized effectively. We offer different separation processes that are combined into an individual package solution that effectively separates the material into:

  • Refuse derived fuel (plastic films)
  • Plastics and wood for utilization as an energy source (lightweight fraction)
  • Stones and metal (heavy fraction)

The Process at a glance

Process Description

SCREW PRESS: The solid-liquid separation of the digestate from dry fermenters (tunnel or box) ensures that it can be stored in a more space-saving manner and is better aerated in a subsequent rotting process, reducing the duration due to less water to be evaporated.

MIXER: Solid fraction of digestate can be mixed with shredded green waste and, if necessary, other additives prior to composting to optimize aeration and pH value.

SCREENING: The compost is screened after rotting. The result is fine finished compost and coarse screen oversize which can then be returned to the composting process as structure material or, depending on its quality, used as biomass fuel in an accordingly specialized power plant.


  • Elimination of plastic contamination already in the biogas substrate
  • Robust solid-liquid separation, tolerant to impurities up to 80 mm in diameter
  • No subsequent digestate screening required
  • Ideal final composting by adjusting the pH value and structure content

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Uni recycling