Energetic comparison for leaching waste liquid from citric juice production using both reverse osmosis and multiple-effect evaporation

In citric juice production a waste leaching liquid stream is obtained. This stream contains a high level of sucrose (about 10 °Brix) which makes its pouring into the public sewer inconvenient and even illegal since it can become a great environmental problem. It is, therefore, necessary to find a valorization way for these pollutant streams. A sucrose concentration contained in the leaching stream is proposed in order to get citrus molasses and a water stream which could be reused in the citric juice process. To achieve these valorized streams, there are two main possibilities: the first one is the use of a membrane technology such as reverse osmosis (RO) as a preconcentration system until 25–30 °Brix [1] with later evaporation to 65 °Brix, whereas the second one is the use of a multiple-effect evaporation (MEE) system. The election of the concentration option, out of other factors, depends on the energy consumption that both alternatives have for the same concentration level. The aim of this work is firstly to get a model function describing the RO experimental process to design series-parallel systems. Secondly, to select a design among different systems considered. Energy consumption requirements by both RO and MEE were calculated and compared. In a design using 24 membrane elements, it was found that RO had a 7.7 times lower consumption than MEE.