Techno-economic assessment of multi-effect distillation process for the treatment and recycling of ion exchange resin spent brines

A treatment chain including nanofiltration, crystallization and multi-effect distillation (MED) is for the first time proposed for the treatment of an effluent produced during the regeneration of Ion Exchange resins employed for water softening. The goal is to recover the minerals and to restore the regenerant solution to be reused in the next regeneration cycle. MED is the most crucial unit of the treatment chain from an economic point of view. A techno-economic analysis on the MED unit was performed and a novel performance indicator, named Levelized Brine Cost, was introduced as a measure of the economic feasibility of the process. Different scenarios were analysed, assuming different thermal energy sources and configurations (plane-MED or MED-TVC). It was found that the plane-MED fed by waste-heat at 1bar is very competitive, leading to a reduction of 50% of the fresh regenerant current cost. Moreover, the thermal energy cost of 20US$/MWhth was identified as the threshold value below which producing regenerant solution in the MED is economically more advantageous than buying a fresh one. Overall, MED allows reducing the environmental impact of the industrial process and it results competitive with the state of the art for a wide range of operating conditions.