Drying of agricultural wastes by a microwave dryer

The purpose of drying agricultural waste is to reduce waste and moisture, increase shelf-life and maintain material properties. In this study, microwave drying with airflow was used to dry apple pomace to reach moisture content of 12% w.b. In this design, the effect of microwave’s power on the drying time has been predicted. Generally drying is to reduce the moisture content of the product resulting in reduced enzymatic and microbial activity and increasing the shelf life of the product [1]. The advantages of drying include increasing the shelf life of the dried product compared with other methods, producing a product with a lower weight and volume, no need for cold storage, reducing shipping and packaging costs [2,3]. In microwave drying, waves are influence on the surface of the material, so the heat source is supplied and the water vapor can be removed. If the wave enters the system at a constant temperature and humidity, it is noticeable that the drying process takes place in two separate steps. At first, the drying rate is constant and then slowly decreases until the material is completely dry and the drying rate reaches to zero. this final moisture is called critical moisture. Old methods such as natural drying and hot air drying, due to the use of minimal facilities and inexpensive machines, are still the most important methods used in the production of dry material [3]. Drying, like all maintenance methods, can cause some valuable nutrients to be lost. For example, vitamin C disappears during vegetable drying .