Green solutions for desalinated water drip irrigation systems: Organic acids outperform inorganic acids in fouling control

Abstract

Desalinated saline water (DSW) has been widely applied in many fields due to global water scarcity. However, fouling formation in desalinated saline water distribution systems (DSWDS) raises serious technical concerns. The conventional approaches (e.g., inorganic acids) for DSWDS fouling control is not only ineffective sometimes but also lead to serious environmental and health risks. Accordingly, this study introduces a greener method utilizing organic acids for antifouling in DSWDS. The performances and influences of three types of inorganic acids (hydrochloric acid (HCl), phosphoric acid (H3PO4) and hydrofluoric acid (HF)) and three types of organic acids (citric acid (C6H8O7), formic acid (CH2O2) and oxalic acid (H2C2O4)) on DSWDS fouling control were investigated and compared. The obtained results indicated that in general, organic acids exhibited higher antifouling capacities than inorganic acids. Among the selected six acids, CH2O2 was the most effective, followed by H2C2O4, H3PO4, C6H8O7, HCl, and HF. In comparison with the most commonly used inorganic HCl, the fouling dry weights in the samples treated with C6H8O7, CH2O2, and H2C2O4 reduced by an average of 8.9 %, 45.3 %, and 33.2 %, respectively. Despite the higher acidity of inorganic acid solutions compared to organic acids, the latter exhibited a stronger chelating capacity for cations (e.g., Ca2+, Mg2+) in DSW, showing a lower tendency to form precipitation in their treated groups. Moreover, organic acids could increase the crystal cell volume and change the chemical bond length of chemical precipitation, resulting in lattice distortions. Furthermore, organic acids can slow down the flocculation and settling of suspended particulate matter, thereby alleviating the formation of particulate fouling. Overall, these findings suggest that the application of organic acids is a more effective and environmental-friendly approach for fouling control compared to inorganic acids, which provides qualitative and quantitative insights into developing greener antifouling protocol for DSW delivery in actual field practices.