Utilization of desalination wastewater for SOx, NOx, and CO2 reduction using NH3: Novel process designs and economic assessment

Abstract

Many countries discharge considerable amounts of desalination wastewater directly into the ocean, which cause environmental pollution, destruction of ecosystems, and economic losses. Desalination wastewater contains valuable metal ions such as Na+, Ca2+, and Mg2+, which react with carbonate and sulfate ions; therefore, it has the high potential to reduce the NOx, SOx, and CO2. Thus, this study designed process for the utilization of desalination wastewater to capture and utilize NOx, SOx, and CO2 using NH3. A process model was developed, which was composed of following three steps: (1) metal ion separation in desalination wastewater based on pH swing processes for separating Ca2+ and Mg2+ as Ca(OH)2 and Mg(OH)2, respectively; (2) NOx capture and SOx capture and utilization using generated Mg(OH)2, and (3) CO2 capture and utilization using NH3. Subsequently, to demonstrate the economic validity of the suggested process, an economic assessment was conducted and total annualized costs (TACs) of the conventional and proposed processes were compared. As a result, ~96 % of NOx was captured, the SOx capture efficiency was 99 %, and ~94.7 % of CO2 was captured. Thus, a reduction of 11.2 % in the TAC was achieved using the proposed process, indicating its high economic feasibility.