A kinetic model for biofilm growth inside non-PC emitters under reclaimed water drip irrigation

Abstract

Emitter clogging is tightly related to the formation and growth of biofilms inside emitters applying reclaimed water. In order to control emitter clogging and achieve highly efficient drip irrigation (DI) system, understanding the kinetics of biofouling is important. In this paper, four types of non-pressure-compensating (non-PC) flat emitters and five types of non-PC cylindrical emitters were selected for reclaimed water DI experiment, and the growing processes of biofilms components (Solid particles, SD; Phospholipid fatty acid, PLFAs; Extracellular polymeric substances, EPS) inside emitter flow path were tested. The results showed that the entire growing processes of biofilm SD, PLFAs and EPS could all be divided in proper order, i.e., growing adaptive period, rapid growing period and dynamic stable period. To be specific, biofilms were adapting to the growing environment in the initial 408h, while their formation velocity was relatively slow. It was followed by the rapid growing period when the system accumulatively operated 408–1088h. Then biofilm growth and detachment tended to reach dynamic balance till 1224h. Therefore, based on the prototype of Logistic growing model, the paper established a kinetic model of biofilms growth (SD, PLFAs and EPS) after the comprehensive consideration of their growing response to emitter types, flow path geometrical parameters and lateral positions. The model was verified to present the biofilm growth process well (R2>0.85**, significant level a=0.01). On the other hand, another model was proposed to reflect the influential effects of biofilm components on emitter clogging degrees. When combining these two models together, the results showed that the emitter clogging controlling methods should be carried out in the appropriate time in case of more serious emitter clogging. The control point was the time when DI system operated 300h accumulatively or before emitter clogging degree reached 25%. The results in this paper could provide theoretical references to reveal DI emitter clogging mechanism and to establish a controlling strategy against emitter clogging.