Pilot-scale evaluation of the sustainability of membrane desalination systems for the concentrate volume minimization of coal chemical wastewater

The integrated process of reverse osmosis (RO) membrane and evaporative crystallization device is being implemented to target zero liquid discharge (ZLD) in the coal chemical industry. Minimizing the volume of RO concentrate (ROC) to the evaporation unit is critical to reducing the cost of the ZLD process. However, the pilot-scale evaluation of various minimization approaches for ROC volume is lacking in previous studies. Herein, the performance and cost of the vibratory shear enhanced process (VSEP), disc tube reverse osmosis (DTRO), and forward osmosis (FO) were compared for minimizing ROC in a pilot-scale study. Three scenarios were proposed first: VSEP, DTRO, and FO-RO to reconcentrate ROC and recover fresh water. Further comparisons are made between the levelized capital expenditures (CAPEX) and operational expenditure (OPEX) for the three scenarios. Results showed that the FO-RO scenario, followed by DTRO and VSEP, recovered around 90% of ROC as fresh water. FO system is more resistant to fouling than VSEP and DTRO during the reconcentrating ROC process. For a full-scale plant (2000 m3 d-1), DTRO offered the lowest CAPEX and OPEX at 0.95 USD m-3 and 1.68 USD m-3, respectively. This study provides insight into the selection of the optimal technology for designing the ZLD system. 5 stars represents the best technical performance/highest cost.