Adsorption-based defluoridation unit integrated with a humidification-dehumidification system: towards a zero-fluoride rejection desalination

The present paper reports the energy and environmental impacts of integrating a column of activated alumina (AA) for fluoride adsorption with a humidification-dehumidification (HDH) desalination system. The effects of fluoride concentration (<i>C_i</i>), the mass of AA (<i>m_aa</i>), and the mass flow rate ratio (MR) on the yield and gained-output ratio (GOR) of the considered system have been investigated using an experimental approach. The experiments are conducted for 5 to 30 mg/L, 1 to 2 kg, and 1 to 6 for <i>C_i</i>, <i>m_aa</i>, and MR, respectively. The effect of brine recirculation on the investigated system is also reported in this paper. The obtained results have shown an enhancement of up to 21% in the value of GOR with this system. Moreover, nearly 80% of the fluoride disposal to nature as concentrated brine can be prevented using the adsorption unit. The current study is carried out to prevent fluoride disposal in the reject stream. However, the proposed system can obtain freshwater at the community level without disposing of harmful contaminants in rejected water by incorporating other adsorption materials. The results presented in this paper may be useful for the stakeholders working on sustainable freshwater production.