Techno-economic Analysis of Concentration Technologies for the Treatment and Recycling of Industrial Wastewater Effluents

Kurzfassung

The significant increase of the amount of industrial wastewater effluents produced and disposed into the environment is leading to a severe pollution problem. In order to solve the problem, each industrial effluent may be treated through pretreatment and concentration steps. In this way, the removal of pollutants from the effluent, the recovery of valuable materials and/or the recycling of the solution are feasible. These wastewater treatment steps, however, are energy intensive and therefore need to be analyzed thoroughly. This work is focused on the comparison of different systems to treat the effluent produced by the coal mining industry. The proposed systems present different pre-treatment steps and/or different concentration technologies. In all cases, the solution sent to the concentration phase is concentrated up to saturation to recover water and NaCl salt. In particular, the pre-treatment includes nanofiltration and crystallization, while the concentration step is performed with a multi-effect distillation plant or with the coupling of reverse osmosis and membrane distillation. Finally, every system presents an end crystallizer to produce the crystals of NaCl. The considered systems differ with respect to a number of criteria, such as electricity demand, heat demand and costs. They are compared from an economic point of view via a representative cost, which is the levelized cost of the produced NaCl crystals (Levelized Salt Cost, LSC). The treatment chain which presents three crystallization steps to recover Mg(OH)2, CaSO4 and CaCO3 and a multi-effect distillation unit for the concentration phase ensures simultaneously the highest recovery of NaCl and the highest economic feasibility. Therefore, its levelized cost of salt falls within the typical range of price of high purity NaCl salt and it is lower than the ones of the other systems. In conclusion, the treatment of an effluent coming from coal mining industry is investigated considering different treatment chains. The proposed systems allow for recovering valuable materials, leading to a net reduction of the environmental pollution by the industrial processes, and are competitive with the market values.