Eco-efficiency analysis of desalination by precipitation integrated with reverse osmosis for zero liquid discharge in oil refineries

In a process for industrial water reuse with zero liquid discharge (ZLD), a membrane separation step followed by an evaporative process is usually required. It is proposed here to maximize water conversion in the reverse osmosis (RO) membranes, in order to reduce the associated environmental impacts and economic costs from evaporative process. Considering a typical oil refinery wastewater with high inorganic scaling tendency, three ZLD virtual scenarios were proposed. A RO water recovery of 59% (default scenario SI) was increased to 89.2% with an upstream BaSO4 desupersaturation step (scenario SII). A 96.3% RO water recovery (SIII) was obtained adopting also a RO intermediate softening with CaO addition and calcite seeding, as well as MgSO4 dosing for additional silica removal. In all cases, the water not separated in the membrane was completely recovered in downstream evaporation and evaporative crystallization steps. A life cycle assessment (LCA) analysis suggests that the proposed scenarios enabled expressive reduction in the environmental impacts related to global warming, freshwater ecotoxicity and water consumption. Besides, it has been shown that the proposed scenarios were economically favorable. By means of an eco-efficiency analysis, economic, energetic and environmental implications appointed to benefits on developing of chemical precipitation techniques for a high RO desalting recovery in ZLD operations for aqueous effluents of petroleum refineries. It has also been found that some degree of intervention may lead to an improvement of all eco-efficiency indicators, but at some extent of intervention, at least some of the eco-efficiency indicators may become less favorable.