Biodrying as a biological process to diminish moisture in gardening and harvest wastes

Biodrying is a process that consists in reducing the moisture content of different organic wastes to obtain a useful product, such as fuel, or as a previous step to landfilling. This is achieved by using the heat generated in the aerobic fermentation of organic compounds. The main parameters that control the process are aeration, the temperature reached in fermentation and the initial level of moisture. In this work, the substrate was composed of agricultural harvest and gardening waste from an area in the east of Spain. The biodrying process was carried out in a greenhouse, where both the heat generated in the fermentation and the heat of the sun were used. In order to promote aeration, two factors were taken into account: One was the capacity of the shredded prunings to act as a bulking agent, and the other one was a perforated floor, which allowed air to pass through. An air outlet was installed at the top of the greenhouse to promote the "chimney effect." With this setup, drying times of 12-30 days were achieved (depending on the month), together with volume reductions greater than 50 %. The time of the trial has been assessed when the waste has received 75 kW/m ² by insolation. The final waste with a low level of moisture (7-15 %) had a heating value suitable for use as fuel (around 15,000 kJ/kg).