Despite the great potential to valorise bio-waste – as compost, fertiliser or energy – recycling rates lag behind the growing level of material recycling, with the majority of the 88 million tonnes of bio-waste produced in the EU each year lost through landfilling (40%) or incineration (20%). One significant barrier for bio-waste recycling is the difficulty of separating bio-waste from other waste fractions, with methods such as source separation and mechanical separation based on agricultural techniques leaving many impurities.
The SEPARATE Waste System, developed by db technologies in the Netherlands, significantly increases the efficiency of bio-waste separation.
Central to the system is the innovative hydraulic ‘OREX’ press, into which the waste is inserted. Under the extreme pressure of the press, the cell structure of the soluble organic matter is broken up. This makes the organic matter behave like a liquid, and become separated from the dry fraction.
This first step alone eliminates up to 98% of all inorganic impurities from the organic fraction.
If required, the organic fraction can be purified further using the ‘CYCLONE’ cleaning system. This system rotates the material at high speed, whereby the organic material escapes and the solid impurities are caught in a filter. This process reduces the remaining impurities such as plastics and inert materials to less than 0.5%.
The resulting wet organic and dry non-organic fractions can be made into numerous quality products.
The homogenised wet paste is perfectly suitable for anaerobic digestion (AD), producing biogas which can be transformed into electricity and heat. The digestate can then easily be prepared into high-quality compost. The dry fraction undergoes another separation process, recovering recyclables and refuse derived fuel (RDF).
The SEPARATE Waste System received funding from the Eco-innovation initiative of the European Union to carry out comprehensive testing to validate its performance. The SEPARATE project organised short and long term trials with MSW and separately collected bio-waste in Germany, Spain and the United Kingdom, with the results analysed by certified external laboratories.
A very high level of separation was achieved for each waste stream, whether collected from urban or rural communities. The organic fraction was very pure, and had a very high methane and biogas yield, with the dry fraction having a high calorific content.
Why did it work?:
The utilisation of a hydraulic press represents an innovative change which breaks from past techniques. Previous methods of physical separation were based on the cutting and slicing of material, which can never limit impurities as effectively.
The system also realises a number of economic benefits, particularly with regard to the use of the organic fraction for AD. Because the organic fraction is so low in impurities, it causes fewer problems for AD plants thereby reducing maintenance costs. Additionally, due to the way the cell structures have been broken up, the organic fraction generates a high gas yield in a short time period, reducing overall investment costs.
The testing undertaken by the SEPARATE project has helped overcome key barriers to the market expansion and replication of bio-waste separation and cleaning systems. Beyond Europe, the system may also find receptive markets in developing countries, where urban waste to biogas is a natural fit for the twin challenges of waste management and local grid stabilisation.