Evaluation of bioenergy potential from citrus effluents through anaerobic digestion

Abstract

At the global level, citrus production is around 92 million tons and citrus processing is about 22 million tons generating 28 million m3 of Citrus Effluents. In the last two decades, the generation of wastewater by the citrus industry has increased, and since earlier studies have focused mostly on solid citrus waste, there is inadequate information related to the potential energy value of these effluents. The main contribution of this work is the development of a methodology for conducting an energy analysis to determine the amount of electrical energy that can be derived from the biogas produced in the anaerobic digestion of citrus effluents at the global level. This determination was made through the operation of a novel, high-rate reactor, called the Anaerobic Hybrid Reactor. The aim of this paper was to evaluate the bioenergy potential of the effluents from the citrus industry by using anaerobic digestion to generate electrical energy. As part of the results of this evaluation, it was found that one ton of processed oranges generates 1.25 m3 of citrus effluents, 0.72 m3 of methane at standard temperature and pressure, 7.16 kWh of gross electricity, and 2.15 kWh of net electricity, which represents a cost of 0.17 USD. The worldwide bioenergy potential from citrus effluents by the main citrus processing countries is approximately 16 million m3 of methane/year at standard temperature and pressure, which is equivalent to approximately 159 GWh of gross electricity per year, about 48 GWh of net electricity per year, and about 111 GWh of thermal energy per year. The biogas that is produced can replace as much as 9% of the consumption of fuel oil and natural gas used in a citrus processing plant. Anaerobic digestion is a clean, simple energy technology, and it helps to minimize the social, environmental, and economic problems caused by poor management and the lack of alternatives for the treatment of the effluents from the citrus industry.