Design and Evaluating a Hydraulic Pelletizing Machine for Producing Feed Pellets from Pistachio Shells

Due to the shortage of water resources and frequent droughts, optimizing the use of food resources to provide feed for animal is an important issue. In this study, pistachio shells were collected and stored in open air environment to reduce their moisture content. Then, they were powdered using a grinder to produce pellets using a developed hydraulic pelletizer, and the mechanical properties of the produced pellets were measured using a biological material testing machine. An experimental design with four factors, including moisture levels of 15 and 20%, particle sizes of 0.6 and 1 mm, mold diameters of 8 and 10 mm, and compression pressures of 6,000, 8,000 and 11,000 kPa, was carried out in a completely randomized design. The density, fracture energy, and toughness of the produced pellets were measured. The results showed that the independent effects of moisture, mold diameter, and compression pressure were significant on all the above properties (P ≤ 0.05), and the effect of particle size was significant on the density and toughness of the pellets (P ≤ 0.05). Additionally, some of their interactions had a significant effect on the density, fracture energy, and toughness of the pellets (P ≤ 0.05). The coefficient of variation and determination coefficient were 1.92% and R2= 0.83 for density, 25.42% and R2= 0.49 for fracture energy, and 66.23%, R2= 0.41 for pellet toughness, respectively. Therefore, producing pellets from pistachio shell waste can be a good option to reduce transportation costs, produce Animal feed, and reduce environmental pollution.