Dewatering fermentation residues

Polymers for dewatering fermentation residues

Background

A large number of biogas plants in predominantly agricultural areas have a high proportion of manure content in the fermentation substrate. The subsequent effect is an increasing oversupply regionally of digestate to be recycled. Due to their high performance, biomethane production plants require fermentation substrates from large catchment areas and produce corresponding large amounts of digestate at one site. Energy production through anaerobic recycling of domestic waste and residual materials from the food industry often produces digestate not suitable to be used as fertilizer, which only can be used thermally. Due to the partially low solids content, high transport costs may apply to recycling. For economical as well as ecological reasons, a reduction of the water content in the digestate by dewatering is necessary.

Process steps

Gärrestentwässerung

The separation of coarse materials (fibers, etc.) is generally carried out without the use of chemical products via screw presses or decanter centrifuges. For a more extensive removal of finely distributed solid particles from the liquid phase of the coarse material separation, decanting centrifuges are used almost exclusively.

Problem

In these fast-moving units, the suspended particles are exposed to an increased gravitational field in order to accelerate separation by sedimentation. Despite the sometimes large energy input, only a small amount of separation can be achieved without the use of chemical additives.

Why is that?

Basic information on the application of polymeric flocculants

The sedimentation rate of particles in a liquid depends on following conditions:

  • Particle size
  • Particle density
  • Liquid density
  • Acceleration of the particles

Due to the low density difference between the sludge particles and the surrounding liquid, the settling rate is very long even at high accelerations in a centrifuge. An improvement in the separation can be achieved by an increase in particle size. This does not take place spontaneously due to repulsive interactions between the particles.

  • Cationic flocculants in the GoFloc® product series compensates for the repulsive surface charges and supports the particle enlargement by bridging
  • With equal energy consumption, the effectiveness of the dewatering of digestate can be significantly increased by the addition of GoFloc® polymers
  • A wide range of products enables a comprehensive optimization of the treatment process

220 Gärrestentwässerung