Composite fouling of drip emitters applying surface water with high sand concentration: Dynamic variation and formation mechanism

Drip irrigation applying surface water with high sand concentration leads to a higher risk of composite fouling, which is the most complex material type of clogging. Thus, understanding the dynamic variation and formation mechanism of composite fouling is the prerequisite for controlling clogging substance and establishing rational anti-clogging method to promote high-sand surface water for drip irrigation. In this paper, the components of the composite fouling were studied through the emitter composite fouling experiment under three drip irrigation frequencies. The results indicated that the particulate fouling composition (solid particle, SP), crystallization fouling composition (CaCO3 and MgCO3 precipitate, C-MP), and biofouling composition (extracellular polymeric substance, EPS, and microbial activity, MA) grew as the system operated. Significant positive linear correlations were obtained among different compositions (R-2 > 0.82, p < 0.01), and the microorganism attached on the surface of SP and continuously secreted EPS mutually promoted the formation of biofouling and particulate fouling. The condensation of microcrystals formed by C-MP with SP promoted the formation of crystallization and particulate fouling, and phosphorus anions enhanced flocculation and agglomeration between particles. Thus, physical-chemical-biological reactions occurred to promote mutual growth, which ultimately led to composite fouling formation. Meanwhile, various components in the composite fouling increased gradually with higher operating frequency, which could aggravate the emitter clogging and decrease the relative discharge of the drip irrigation emitters (Dra) and the uniformity coefficient (CU).