Management of orange (Citrus sinensis) wastes from agroindustrial activities using sustainable biodrying and composting processes

The processing of lemon, orange, grapefruit and other citrus fruits represents one of the most important food industries in the world. Juice recovery from citrus fruits is about 40-55%; along with processing activities, several citrus wastes consisting of peel and bagasse, segment membranes, pulp-wash and seeds are simultaneously generated and deposited every year without treatment in landfills. This disposal method is unfavorable due to both economic and environmental arguments, such as high transportation costs, lack of disposal sites, and the accumulation of waste with high organic content in open dumps. Therefore, technological and management strategies are needed to reduce citrus wastes and to convert them into raw material for energy, organic fertilizers, livestock feed and other green products to increase the value chain. The goal of this research was to introduce a new process for producing solid biofuel from waste obtained from orange juice production using biodrying and composting techniques, to increase the value chain and evaluate its potential for energy cogeneration and application in citrus crops. Biodrying and composting are two aerobic bioprocesses used in the treatment of the agricultural, agro-industrial or organic fraction of special-handling solid waste. Both processes have a thermophilic phase as a result of intense microbial activity, developing the same biochemical and microbiological activity during the first weeks. In composting the aim is to obtain a product that can be used as a soil improver, whereas in biodrying the objective is to use the metabolic heat to dry the solid waste. This paper describes the temperature evolution in two biodrying piles, one with forced aeration and the other a semi-static pile with weekly turning as a method to maintain the volume of oxygen necessary to carry out the process, as well as a compost pile to compare the evolution of both processes. Throughout the experiment, the process temperature, relative humidity, ambient temperature and solar radiation were recorded. In the biodrying process with forced aeration, a homogeneous temperature distribution throughout the pile was observed, while in the pile with turning the highest temperature occurred in its centre. In the pile with turning, four temperature-behavior phases were identified: temperature-increasing phase, thermophilic phase, second temperatureincreasing phase and cooling phase, whereas in the pile with forced aeration the temperature has more of a bell-curve pattern and the process lasts for more than 20 days longer than in the compost pile with turning.