Microbiology mechanism and controlling methods for emitter clogging in the reclaimed water drip irrigation system

Abstract: Drip irrigation is considered as the most secure and reliable irrigation method for reclaimed water due to its precision and controllability. However, reclaimed water contains a large amount of particles, nutrient salts, organics, micro-organisms and other substances, which makes the emitter clogging mechanism become more complex and also significantly increases the risk of emitter clogging. In this paper, we analyzed the biofilm structure and composition variation characteristics, basing on the significantly "S-curve" relationship between the content of bofilm components: dry weight (DW), phospholipid fatty acid (PLFAs) and extracellular polymeric substance (EPS) and emitter clogging degree, which indicated clearly that the biofilm formation was the original causes to induce emitter clogging. The progress of emitter clogging was performed as follows: microbiology in reclaimed water firstly fixed on the internal lateral surface and formed the biofilm in drip irrigation system, and then continued to absorb, to consume water and nutrient-substrate for metabolism, thus they secreted large amounts of extracellular polymeric substance (EPS), and relied on its sticky characteristics to absorb solid suspended particles and micro-organisms constantly, which induced the formation, growth, as well as shedding of biofilm, and then clogging substances continued to gather, eventually led to emitter clogging. Therefore, the biofilm formation mechanism and its influencing factors were put forward from 5 aspects, which were the flow path structure and its geometry parameters, the characteristics of the water particles, the flow shear force near the wall, the water quality of irrigated water, and the irrigation frequency. After the compositive consideration of the aspects mentioned above, a new integration technology which aimed at holding up biofilm formation in order to control emitter clogging was proposed, which also included different perspectives, including the optimization of emitter flow path structure (enhancing self-cleaning capacity of flow path and promoting biofilm shedding), the development of antibacterial materials (the inhibition of microbial adhesion), chlorination, microbial antagonistic and Quorum-Sensing (QS), micro-nano air sterilization. Finally, several urgent problems needed to be solved in the future for controlling emitter clogging in the drip irrigation using reclaimed water were put forward from 3 aspects: the biofilm inside drip emitter of hydrodynamic - coupling mechanism of microbiology; drip emitter clogging forecasts with comprehensive simulation model and its reasonable emitter threshold determining design parameters, and controlling mode after considering emitter clogging clear synergistic effect and soil long-term sustainability of quality and health.