Abstract
A hybrid capacitive deionization and humidification-dehumidification (CDI–HDH) desalination system is theoretically investigated for the desalination of brackish water. The CDI system works with two basic operations: adsorption and regeneration. During adsorption, water is desalted, and during the regeneration process the ions from electrodes are detached and flow out as wastewater, which is higher in salt concentration. This wastewater still contains water but cannot be treated again via the CDI unit because CDI cannot treat higher-salinity waters. The discarding of wastewater from CDI is not a good option, since every drop of water is precious. Therefore, CDI wastewater is treated using waste heat in a process that is less sensitive to high salt concentrations, such as humidification-dehumidification (HDH) desalination. Therefore, in this study, CDI wastewater was treated using the HDH system. Using the combined system (CDI–HDH), this study theoretically investigated brackish water of various salt concentrations and flow rates at the CDI inlet. A maximum distillate of 1079 L/day was achieved from the combined system and the highest recovery rate achieved was 24.90% from the HDH unit. Additionally, two renewable energy sources with novel ideas are recommended to power the CDI–HDH system.
Highlights
Earth’s quantity of freshwater—one of the vital components for life—is shrinking every day, and the situation is further exacerbated by rapid population growth
Capacitive deionization (CDI) unit (A) Stack #1 is in adsorption mode and Stack #2 is in regeneration mode. (B) Stack #1 is in regeneration mode and Stack #2 is in adsorption mode
The results showed that the distillate production rate for all cases of wastewater increased with an increase in the mass ratio (MR) up to three, and the distillate production rate decreased after that with a further increase in the MR
Summary
Earth’s quantity of freshwater—one of the vital components for life—is shrinking every day, and the situation is further exacerbated by rapid population growth. HDH desalination technology mimics the rain cycle: in a humidifier, either air or water is heated; hot water is sprayed inside the evaporator (humidifier) over packing material; and air flows against the water flow and transports the water vapor at the expense of the heat of the water, leaving behind high-density salts This hot, humid air is transferred to a dehumidifier, where cold water makes contact with the air and condenses it, thereby producing pure water. HDH desalination technology offers many advantages compared with other methods: it enables a stable and simple control system, does not require strict pretreatment, poses no scaling problem, enables operation at atmospheric pressure, is low maintenance, and has no sensitivity to water with a high salt concentration [15]. A theoretical study was carried out using the mathematical model of CDI and HDH desalination systems
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