Effects of coupling multiple factors on CaCO3 fouling in agricultural saline water distribution systems

Abstract

Saline water is an alternative resource that could be used to meet agriculture irrigation demands. Fouling, particularly that caused by calcium carbonate (CaCO3), often occurs in saline irrigation water distribution systems, and severely restricts the utilization of saline irrigation water. So far, water acidification is the common practice for avoiding CaCO3 fouling. However, this approach is often ineffective and regularly contributes to environmental pollution. This study investigated an effective practice to overcome CaCO3 fouling issues by regulating shear stress, temperature and ions in saline irrigation water irrigation systems. The effects of different near-wall shear stress at 0.05, 0.20, 0.40 and 0.60 Pa, coupling with temperature of 10, 20 30 and 40 ºC and cations Mg2+ and Fe3+ were analyzed. Results demonstrated that the CaCO3 fouling rate was linearly increased at initial shear stress, while decreased at higher shear stress, and the highest fouling rate was observed at 0.40 Pa, ranging between 21.4%−80.3%. The coupling of temperature and cations with shear stress significantly (p < 0.05) affected the fouling growth rate at each shear stress. The differences in fouling rate (fitting curves slopes k > 1) among different shear stress get larger with increasing temperature, while they decreased and increased with the addition of Mg2+ and Fe3+, respectively, when compared with pure solution of CaCO3. Refinement analysis showed the largest unit-cell volume and lattice parameter of calcite at shear stress of 0.40 Pa, resulting in a significant effect on distribution of fouling particle sizes and morphologies. Moreover, some anti-fouling measures were further proposed based on the formation behavior of CaCO3 fouling. These findings might provide a new perspective to control CaCO3 with potential implications for sustainable saline water management for irrigation.