Obtaining a alternative fuel from waste horticultural biodrying

Biodrying is a biological process that aims to decrease the moisture in the waste. During biodrying, the energy released by microbial activity increases the temperature of the waste mass, which promotes evaporation of water. In the present study, four windrows with an approximate weight of 75 kg were monitored for 40 days; each unit was prepared with a mixture of organic waste. Three windrows were placed inside a greenhouse to accelerate the dehydration of materials and the fourth one was placed outside the greenhouse. During the experiments, environmental conditions were recorded (temperature, relative humidity and solar radiation) inside and outside the greenhouse, and the reduction in moisture, weight and volume of waste was quantified from each windrow. At the beginning and the end of the process the nitrogen content, organic matter and combustion heat were determined. The temperature in the windrows increased from the first day and the thermophilic phase was reached at the second day and maintained for a period of seven days, then the temperature decreased from day seven and the temperature was similar to environment temperature. After 28 days, yielded a mass reduction of about 80 %, volume decreased about 50 % humidity under 90 % compared to the initial values. In addition, nitrogen content and organic matter were lightly decreased. The combustion heat of waste at the end of biodrying process in all windrows increased approximately 200 %, reaching an average value of 18 000 kJ/kg, which is comparable to the caloric value of charcoal. Therefore it could be suggested that these bio-dried residues could be used as an alternative fuel in boilers or furnaces.