1.3.1. Physical Properties

The size of the agro-waste particles is usually irregular in shape and size, with some being needle, leave shaped, etc., with different surface areas. This influences the feeding rate along with fluidizing and mixing parameters during processing and pre-treatment. Additionally, the storage conditions of the agro-waste may also affect these processes. The efficiency of the conversion and energy requirements for these processes is associated with the beneficiation of the agro-waste, which can be affected by the variation in shape and size of the initial agro-waste, and the preceding processes generating it. Another characteristic is the length/diameter of the particulate matter constituting the agro-waste is an aspect ratio tending to unity, even when the finely granulated, i.e., converging to a spherical shape [14]. Such an aspect ratio was determined to be suitable for further processing of the agro-waste in bioenergy generating processes.

Other characteristic considerations include particle and averaged bulk density to determine the grindability of the waste, a known energy-consuming process, which is influenced by quality characteristic parameters of the waste such as moisture content, surface properties, shape, and size [15]. For instance, some agro-waste containing a high lignocellulosic content are difficult to grind due to the presence of fibrous cellulose and lignin. Applying the "Hard grove grindability index method" is usually performed to assess the grindability of such agro-waste. Generally, a particle size of 0.6–1.2 mm for the agro-waste is required to have a suitable grindability index. Similarly, fluid ability must also be considered as it seems to impact the operations associated with waste movement from one point to another during beneficiation and/or processing. Fluid ability is influenced by the biomass particle angle repose, cohesion coefficient, flow index, and compressibility index.
