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Separating biogenic waste products into liquids and solids

Converting organic materials present in biodegradable waste into biogas and clean fertilizer for agricultural applications


Preparation of biowaste materials

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 Just like kitchen waste and leftover food from catering establishments, as well as out-of-date packaged foods, biodegradable waste can be separated into solid and liquid fractions with the aid of Doppstadt’s screw press.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

Doppstadt’s screw press can be used both as pretreatment step for bio-waste and food wastes upstream of the wet fermenter and as post-treatment step for digestate downstream of the dry fermenter. Equipped with a feed hopper, it can digest the input material and then separate it into solid and liquid fractions.

Processing biodegradable waste such as kitchen waste results in:

  • Liquid phase as biogas substrate fr wet fermenter
  • Solid phase for energy-related utilization

Digestate from the dry fermenter (charged with biodegradable waste and green waste as substrate) can be processed into the following fractions:

  • Solid phase for subsequent rotting and finally composting
  • Liquid phase as agricultural fertilizer

Biowaste processing with well-thought-out ALLRECO solutions:

  • Avoidance of plastic in the digestate
  • Robust solid-liquid separation, contaminan-tolerant up to 80 mm space diagonal
  • No additional full flow screening of the digestate required
  • Ideal re-rotting thanks to adjustment of the pH value and the bulking material
  • Including ALLRECO service and quality

Separating biogenic waste products into liquids and solids

The ALLRECO screw extruder can be used both for the pre-treatment of biowaste and food waste before the wet fermenter and for the after-treatment of the digestate after the dry fermenter. Equipped with a feeding hopper it can disintegrate the infeed material and separate a solid and a liquid fraction.  

The material streams using kitchen waste as an example are as follows:

Input Kitchen waste

Liquid target fraction for digestion

Solid fraction with packaging materials

The process at a glance