Electrified Solar Zero Liquid Discharge: Exploring the Potential of PV-ZLD in the US

Abstract

Current brine management strategies are based on the disposal of brine in nearby aquifers, representing a loss in potential water and mineral resources. Zero liquid discharge (ZLD) is a possible strategy to reduce brine rejection while increasing resource recovery from desalination plants. However, treatment of high-salinity brine through ZLD substantially increases the energy consumption and carbon footprint of a desalination plant. The predominant strategy to reduce the energy consumption and carbon footprint of ZLD is through the use of a hybrid desalination technology that integrates with renewable energy. Here, we built a thermodynamic model of the most mature electrified hybrid technology for ZLD powered by photovoltaics (PV). The PV-ZLD system is comprised of a reverse osmosis system coupled with mechanical vapor compression and crystallization. By coupling the thermodynamic model with a computational model, we are able to examine the potential size and geographic distribution of ZLD plants in Arizona, California, Florida, and Texas (e.g., the top four states that produce desalination brine). A multi-objective optimization framework determines the potential plant size considering the location and a number of operational variables. The objective function aims to maximize the thermodynamic performance of the ZLD system and minimize the cost of water and environmental impacts. Texas has the lowest levelized cost of water (1.2 to 1.7 $/m3 ) which is largely attributed to the state having available backup power. California is the most effective at using solar energy to power ZLD plants (above 90%), but the state also has the largest projected land area requirements. The massive adoption of large-scale PV-ZLD systems depends on the inclusion of efficient preconcentration subsystems that decrease the energy requirements of the brine concentration process, the reduction in CAPEX for PV systems, and the development of a low-cost and low-carbon intensity electric grid. Treating all brine produced in Arizona, California, Florida, and Texas could allow the production of an additional 963 million gallons of freshwater per day.