Experimental study on integrated membrane processes in the treatment of solutions simulating textile effluents, energy and exergy analysis

Experiments on a reverse osmosis (RO) pilot plant and a membrane distillation (MD) laboratory plant were made using simulant fluids. Hydrodynamic behavior, rejection characteristics of the modules, maximum attainable concentration, permeate flow decay, fouling of the modules by simulant components, and suitable cleaning techniques were studied. Some cycles for recovering dyes and chemical auxiliaries were also proposed. For each cycle an energy and exergy (the maximum useful work that a system can do when it passes from an actual state to the reference state where it is in equilibrium with the surroundings) analysis was developed for evaluating the efficiency in using the energy and for comparing the cycles without recovery and those with recovery in which different integrated membrane processes were used. An energy and exergy analysis was applied to a simulant textile cycle with reverse osmosis recovery and with a sequence of RO+MD recovery. With respect to the cycle without recovery, significant energy and exergy decreases for both the cycles were obtained. Further decrease in the required energy and exergy for the RO+MD with respect to the RO was also observed. In principle , this showed a convenience in using integrated RO+MD plants for obtaining concentrate solutions. Experiments on concentration of salts and dye solutions by RO showed good performances for the modules used. Cleaning procedures had a reversible fouling by the various aqueous salt solutions in the range of tested concentrations. When dyes were used, cleaning was relatively more difficult and an irreversible decrease in the flux was observed. For dye concentrations, the results indicate it was possible to reach dye concentration on the order of 40-50 g/l in the MD plant