Emitter clogging sensibility with increasing biofilm components under reclaimed water drip irrigation condition

Abstract: Reclaimed water reused for agriculture has become one of the most effective ways to relieve water shortage and water pollution in China, especially on the North China Plain, and drip irrigation was believed as the most appropriate way to use treated wastewater. Studies have verified that drip irrigation emitter clogging using reclaimed water was closely related to the formation and growing of biofilms those attached inside emitters. However, the exact effects of biofilms components' increase on drip irrigation emitter clogging were not clear. Besides, the sensibility of emitter clogging degree to the increasing biofilms' components as the system operated was also unknown. Based on these mentioned above, in this study, based on an on-site drip irrigation emitter clogging experiment using reclaimed water, which was conducted in the wastewater treatment plant, the emitters with seven different clogging degrees of 0, 20%, 35%, 50%, 65%, 80% and 100% were selected to reflect the growing process of biofilm, after the drip irrigation system accumulatively ran for 540 hours, and three kinds of key components (including Solid particles, Phospholipid fatty acids and Extracellular polymeric substances) of biofilms were tested, and then the sensitivity of emitter clogging degree to the increase of biofilms' components during the whole operating was analyzed. The results showed that drip irrigation emitter clogging became more serious as biofilms' components increased with the significant "S curve" relationship (R2 > 0.92**, significant level a=0.01). Therefore, the sensitivity of emitter clogging degree to the increase of biofilms' components showed obvious difference in different stages, with the variation trend of "sensitive - micro sensitive - extreme sensitive". When emitter clogging degree was under 10%-15%, the biofilm growth would obviously enhance emitter clogging, while the formation of biofilms was mainly controlled by the adhesion and proliferation ability of microorganisms and the sticky Extracellular polymeric substances they secreted. However, much less sensitive impact was found when emitter clogging degree was 15%-35%, which was due to the comprehensive influence of the flow velocity in different domains inside emitters and the surface characteristics of growing biofilms. However, minor increase of biofilms' components would raise emitter clogging degree rapidly since it was above 35%-40%, and then entered the extreme sensitive stage, and the significant increase of emitter clogging degree was caused by the growth-detach-regrowth process of biofilms and microorganisms was stimulated during their growth after adapting to the new environment. In conclusion, the dynamic solid particles and Phospholipid fatty acids increasing characteristics could both describe the mechanisms of biofilm formation and growth inside emitter and affected emitter clogging degree significantly, indicating that both solid particles and microorganisms played the important role in inducing emitter clogging when using reclaimed water drip irrigation. This study aimed at revealing the exact quantitative relationship between biofilms components and emitter clogging degree, in order to find out the most sensitive stage during emitter clogging. The results will provide theoretical reference to reclaimed water drip irrigation emitter clogging mechanism and the application of treated wastewater drip irrigation technology.