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Circular Divider

Dewatering of the residual sludge (digestate) generated from biogas generation processes.

Circular Divider

An introduction to this case study

Biogas waste-to-energy plants, while being an environmentally friendly technology, also generate a process-specific by-product known as digestate which requires processing.

Technologies used in this case study:


Look at how we deal with the followingchallenge:

1. Bio-gasification



The physical state of the digestates is dependent on the conversion processes of the biomass. One of the main issues is the high-water content that the digestate produces (90–95%) which makes the transport of these by-products (e.g., from a biogas plant to an agricultural field) difficult and not economical. Separating the digestates into liquid and solids to produce pellets can represent a solution to storing and transferring this valuable nutrient source for longer distances and increase nutrient recycling opportunities.

The dewatering of sludge produced from biogas waste-to-energy plants in South Africa is currently performed primarily with belt presses and screw presses. These presses are found to be problematic because of low efficiency and high maintenance.

The low capture rate of these methods allows the finer particles to cause a blinding layer on irrigated soils preventing water penetration making the liquid fraction unsuitable for irrigation.


The characteristics of the Fournier Rotary PressTM address the problems mentioned above since this technology guarantees high efficiency and low maintenance. This technology ensures:

  • high cake dryness,
  • minimal polymer consumption,
  • high capture rate
  • high throughput and production per channel
  • liquid fraction suitable for irrigation

A full-sized Fournier Rotary PressTM dewatering pilot unit is available to determine the dewatering potential of the digestate sludge.

It is important to underline that the channels on the pilot unit are full-sized, giving accurate performance and production data, on a per-channel basis while making the results 100% scaleable.

The Fournier Rotary PressTM has a modular, channel design, which allows for precise equipment sizing and performance prediction.

Tests were done at a bio-gasification plant and the piloting unit produced good cake dryness and production rate. The low total suspended solids measured in the filtrate, demonstrate an excellent capture rate preventing the blinding effect on irrigated soil.

Benefits for clients:

  • The opportunity to be able to invest in a full-scale demonstration of the technology on the specific biogas digestate on the site of the plant offers much comfort that the potential capital investment is justified.
  • The Fournier Rotary PressTM is among the most advanced and reliable dewatering technologies available.
  • Due to its reliability and simplicity, the Fournier Rotary PressTM requires minimal supervision. It is the only dewatering technology that is safe for stand-alone automatic operation and can be monitored and operated by remote control.
  • Lower operating costs
  • High performance, easy operation, reduced polymer usage, low power consumption and low maintenance.
  • The equipment can shut down, cleaning itself automatically, as scheduled, or due to low sludge feed levels.
  • Another unique feature of the Fournier Rotary PressTM is the ability to order units that can be expanded at a future date. This allows customers to benefit from lower capital costs at the time of purchase and expand according to need. Any combination of channels can be obtained, up to a maximum of 8 channels per press.

Let's talk  about your specific challenges in this field.