Sugarcane Stillage Treatment Using Direct Contact Membrane Distillation

Abstract

Direct contact membrane distillation (DCMD) was evaluated as an alternative for the treatment of sugarcane stillage obtained in the bioethanol production process. First, a synthetic stillage solution was prepared in order to study the influence of the main operational parameters of DCMD in the permeate flux, as well as to analyze the separation of volatile components (such as ethanol and acetic acid) and the concentration of non-volatile components presented in the feed stream (sucrose and other salts). Secondly, an industrial sample of sugarcane stillage was treated using DCMD. The highest flux achieved was 13.4 kg/m2·h for a transmembrane temperature difference of 55 °C, reaching a recovery degree of 70% with a specific thermal energy consumption of 671 kWh/m3. Then, sugarcane stillage was concentrated until 60°Brix. A preliminary economic study was also presented, an estimated cost of 1.25 $ per m3 of recovered permeate was obtained without any heat integration or DCMD operational optimization. DCMD showed to be suitable for stillage disposal allowing to recuperate the permeate stream as process water (containing mainly water and a low concentration of volatile components) and the concentrated stillage as biofuel to be used in the steam boiler (for producing more energy making the process thermally sustainable) or for ferti-irrigation (for reducing the transportation cost due to the volume reduction).