Effects of manganese and copper ions on fouling formation in agricultural irrigation pipelines fed with brackish water

Abstract

Brackish water utilization has emerged as a promising solution to address water scarcity issues. However, fouling poses significant technical and economic challenges to brackish water distribution systems (BWDS). Manganese (Mn2+) and copper (Cu2+) ions are common in brackish water, yet their impacts on BWDS fouling remain largely unknown. This study investigated the effects of four concentrations of Mn2+ (0.05, 0.5, 1.5, and 3.0 mg L−1) and four concentrations of Cu2+ (0.02, 0.2, 0.6, and 1.2 mg L−1) on fouling dynamics in BWDS. The results indicate that BWDS fouling significantly increased at higher concentrations of Mn2+ and Cu2+. Compared to a concentration of 0.05 mg L−1 of Mn2+, concentrations ranging from 0.5 to 3.0 mg L−1 increased fouling total weight by 29.9 % to 63.0 %. Similarly, compared to a concentration of 0.02 mg L−1 of Cu2+, concentrations ranging from 0.2 to 1.2 mg L−1 increased fouling weight by 16.9 % to 59.1 %. Although Mn2+ and Cu2+ aggravated BWDS fouling, no Mn2+ or Cu2+ chemical precipitations were detected in the fouling components. It is likely that Mn2+ and Cu2+ cations act as a “bridge” between water particles, facilitating flocculation and particle deposition, thereby increasing particulate fouling (e.g., quartz and silicates) in BWDS. Additionally, increased particulate fouling provided more nucleation sites for calcium carbonate precipitation, which significantly raised the content of calcium carbonate fouling. Therefore, it is recommended that the concentrations of Mn2+ and Cu2+ be maintained below 1.5 mg L−1 and 0.6 mg L−1, respectively, to mitigate BWDS fouling. This study elucidates the underlying mechanisms of Mn2+ and Cu2+ influence on BWDS fouling, offering valuable insights for the utilization of brackish water in efforts to mitigate global water scarcity.