## 3.1 Mechanical/physical conversion techniques

Definition

Mechanical/physical (e.g., pressing, pre-treatment, milling, separation, distillation) processes do not change the chemical structure of the biomass components; they only perform a size reduction or a separation of feedstock components.

Example 1: First steps of grass refinery

Grass refinery seeks to add more value to the growing surplus of grass. The surplus is due to more extensive farming enforced by manure legislation as well as the expanding area of (natural) grassland. Refining grass aims to isolate the low-grade grass protein and then upgrade it for use in feed concentrates. To make this economically viable, the residual fibre must also be put to profitable use - for instance as an ingredient for the paper-making industry or as a co-product for biogas production.

The grass juice is pressed out and further refined to for example ethanol or a feed product. The remaining fibres can be applied as potting soil, construction material or paper or polymer extrusion products. The screw press is a typical example of a mechanical separation step.

https://www.youtube.com/watch?v=qht5D8Hn5d8

Example 2: Mechanical separation of manure

https://www.youtube.com/watch?v=hzZTISz4Rgw

Based on its high livestock density, The Netherlands has developed effective mechanisms for the environmentally sound handling and distribution of manure. Environmental quality is guaranteed by strict standards for the use of animal manure and artificial fertilisers. In addition, as of 2014 all farmers are obliged to process their surplus manure. This will lead to the transportation of manure to regions with a shortage, most probably in the form of high quality fertilisers. In addition, the agricultural sector is exploring methods of refining manure to produce novel products that contribute to a biobased economy and a resource-efficient Europe.

Pay specific attention to page 28 and 29 of the following publication " Manure a valuable resource", Wageningen UR, 2014. These pages give an illustration of the production of a liquid N concentrate by several separation steps. In this process reversed osmosis is one of the most complicated and sensitive physical separation steps.

Manure, a valuable resource