Case studies on the identification of environmental impact indicators in brine and distinguish the direct and indirect contributions of the desalination process

Abstract

Discharge brine is perceived to be the major hurdle for desalination. Different from the dispersion properties of salinity and temperature, various chemicals in brine could have a lasting impact on the marine environment. So, identifying the chemical environmental impact indicators in brine and tracing their source is crucial for monitoring, regulating, and mitigating the brine's effects. We first investigated risky chemicals introduced and created by the operating desalination facility. Based on the in-situ studies verified monitoring of diverse risky chemicals in brine, we identified 27 chemical indicators in brine from five desalination plants in China. These chemical indicators represented global relevance and a steady state of temporal variability, which should be considered to continue monitoring and regulation. Especially total phosphorus (T-P), iron (Fe), aluminum (Al), copper (Cu), and chromium (Cr) in some desalination plants that exceed the current standards. Combined with different statistical methods to trace the sources of these indicators, the results exhibited that most chemical indicators in brine mainly come from the raw seawater by the concentration effects. However, phosphate, total organophosphorus, T-P, residual and total chlorine, Fe, Al, Cu, nickel, Cr, cadmium, and trihalomethanes in brine can be derived from the desalination process by the water treatment agent residual, metal corrosion, and disinfection by-products. This finding identifies the chemicals to be monitored and regulated in brine, enabling effective targeted interventions for mitigation in desalination plants.