**5. Technology readiness level**

It must be noticed that each mentioned process of bioenergy production is placed in a certain level of technical maturity as briefly demonstrated in the **Figure 3** [114–116]. The maturity level of each technic is represented by a term which is called technical readiness level (TRL) and it is divided from lab scale (1–3), pilot-scale (4–6) to the highest level of maturity which is proven, tested, and qualified all parameters with a full commercial plant and industrialized scale (6–9) to produce products for public usage [114].
