‘RWB has the solution for the digestate problem’

The processing of livestock and agricultural waste into energy has enjoyed significant growth. The products, especially agricultural waste, corn and manure, are converted into methane gas in a fermenter, and the gas is sold as is or first converted into electrical energy and then sold. The waste product from a biogas facility is called digestate. If this digestate cannot be resupplied to the surrounding agricultural operations, then it has to be up-worked into an economically reusable products and clean water.

To this end, RWB has developed a three-step digestate treatment:

Pre-separation: desiccation of the digestate
The digestate is first separated into a thick fraction (desiccated silt) and a centrate. This is accomplished by a slow-turning screw press. This press is characterized by high separation production and low operational costs. The thick fraction produced is phosphate-rich and can be utilized as fertilizer. It is also possible to dry the fraction and sanitize it under high temperature, so that it can better be sold abroad. The centrate can be further processed in the second step of the process.

The ceramic microfiltration system: removal of suspended substances
The centrate must be cleaned of the remaining suspended substances. This is achieved through application of ceramic membranes. These membranes result in 30% lower energy use and 3x higher production relative to the use of polymer membranes in the same application. The concentrate from the membrane filtration contains a relatively high amount of suspended substances and bacteria from the fermenter. This return flow has a very favourable effect on the fermenter and increases the biogas production. The filtrate produced is free of particles and can be further processed in the reverse osmosis installation.

Reverse osmosis: separation of nutrients and water
The filtrate from the microfiltration still contains many nutrients, including potassium and ammonium. These nutrients can be concentrated through the application of reverse osmosis. This is a membrane technology whereby the membrane is nearly impenetrable to salt (nutrients), but whereby water passes through the membrane relatively easily. The result is a clean permeate stream that can be discharged into the surface water or sewer and a concentrated nutrient stream that can be used as (artificial) fertilizer.

RWB’s digestate treatment has already proven itself in various installations. Both the design and the execution and placement into operation involving all disciplines is done by RWB’s in-house talent. In addition, the key parts of the installation come from RWB’s own delivery package.