ABSTRACT: Different methods have been applied to recycle pistachio’s green hulls, the most important of which are siloing and drying pistachio hulls (using industrial dryers). In both methods, hulls should lose their initial moisture content, which constitutes a considerable portion of their weight. The high moisture content takes more time and energy during the drying process. The initial dewateringof hulls – pretreatment – could greatly contribute to improving the drying process. For this purpose, a prototype of continuous press with a tapered screw design was developed and tested for dewatering pistachio green hulls prior to feeding into a dryer. Results showed that the apparatus dewatered 27% of the hull moisture content. In order to study the effects of screw speed and pistachio variety on the moisture removal, a completely randomized design including three rotational speeds (26.41, 32.52, and 50.24 rpm) and three varieties (Kaleh-ghuchi, Fandoqi, and Ahmad-Aqa’e) was performed in three replications. According to the results, the maximum and minimum moisture removal were obtained in Kaleh-ghuchi (13.13%) and Ahmad-Aqa’e (5.72%) varieties, respectively. Moreover, the minimum and maximum dewatering were observed at speeds of 32.51 and 26.41 rpm, respectively. Economic appraisal showed that the profit gained from marketing this dried hull could be 30 thousands IR per one ton of pistachio. The 40-percent reduction in the drying time of hulls after pressing decreases production costs by 240 thousands IR per each ton of hull.
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