Minimal Liquid Discharge (MLD) and Zero Liquid Discharge (ZLD) strategies for wastewater management and resource recovery – Analysis, challenges and prospects

Abstract

Brine is a saline wastewater generated from several industries (e.g., desalination, energy and oil production) and its disposal can have adverse environmental impacts. To address this issue, brine treatment seems to be a promising option to eliminate the wastewater discharge, while also recovering extra freshwater and valuable materials such as salts. This can be achieved through minimal liquid discharge (MLD) and zero liquid discharge (ZLD) strategies. In this work, MLD and ZLD frameworks are analyzed and evaluated under 9 criteria (framework stages, technologies, freshwater recovery target, feed brine salinity, energy consumption of each technology, GHGs emissions, cost impact, resource recovery and social impact). Moreover, a case-study is presented under two different scenarios, Scenario 1 (MLD system) and Scenario 2 (ZLD system). Results showed that the energy consumption of the ZLD system is 10.43 kW h/m3 which is 1.93 times higher than the energy consumption of the MLD system (5.4 kW h/m3). The total freshwater recovery of the MLD system is 84.6 %, whereas the total freshwater recovery of the ZLD system is 98.15 %. Overall, the results suggest that the MLD and ZLD strategies can be valuable strategies for wastewater utilization, reuse, and resource recovery.