The population growth and climate change result in the global water shortage problem, which increases demands of seawater desalination. However, seawater desalination is generally an energy-intensive process and causes a large amount of carbon emission for both plant construction and operation. Osmotic dilution using forward osmosis (FO) can be a good idea to decrease the energy consumption and carbon emission by seawater desalination. Wastewater treatment plant (WWTP) effluent can be used as feed solution for FO and seawater is used as draw solution, which is diluted through FO and enters into reverse osmosis (RO) process for desalination.
One can easily expect that the introduction of FO results in the decrease in energy consumption, which is related to less carbon emission. However, the construction of FO process to reduce may cause an increase in carbon emission. In this work, we estimated the FO-RO hybrid process for seawater desalination in terms of carbon emission from both construction and energy consumption.
In order to evaluate carbon emissions, it is necessary to be able to design the FO and RO process. The RO design program is provided by the manufacturer, but there is no design program for FO. Therefore, in this study, a novel design program for FO with a prediction error of 10.01% was developed. As a result of calculating energy consumption with the FO design program and RO design program, it was calculated that the total energy consumption of the FO-RO hybrid system can be reduced up to 24.7% compared to the RO process.
As a result of calculating total carbon emission(Operation+Construction) for the 1,000 m3/d scale desalination plant, in the case of generating power using fossil fuels, the carbon emission of the FO-RO hybrid system was lower than that of the RO process. However, in the case of renewable energy and nuclear power plants, the total carbon emission of the FO-RO hybrid system was higher because the amount of carbon emission generated during energy production was less.