EFFECTS OF FLOW PATH DEPTH ON EMITTER CLOGGING AND SURFACE TOPOGRAPHICAL CHARACTERISTICS OF BIOFILMS

Abstract

ABSTRACTThe depth of the flow path of a drip irrigation emitter can affect the anti‐clogging ability of a drip irrigation system by changing the flow velocity distribution and material transportation process. In order to evaluate these effects, in this paper a drip irrigation experiment using reclaimed water was performed, and four types of emitters with four flow path depths were chosen for the experiment. The dynamic outflow changes of the emitters were tested with constant intervals and the surface topographical characteristics of biofilms at the inlets and outlets of emitters and the inner lateral walls were tested with the 3D‐WLSI (3D white‐light scanning interferometer). Thus, the effect of flow path depth on emitter clogging was analysed. The results showed that emitter clogging with different degrees in the 204 hrs was observed. The discharge ratio variation (Dra) and coefficient of uniformity (CU) of emitters all slightly decreased with fluctuant changes. Moreover, clogged emitters were more likely to occur at the end part of the lateral, which revealed obvious difference among emitters with different flow path depths. The average thickness (Sd) and relative average thickness (RSd) of biofilms increased with deeper flow path, while surface topographical characteristics of biofilms varied from smooth to rough. On the other hand, the average thickness and relative thickness of the biofilms at different positions of the lateral represented the order as: Sd head < Sd middle < Sd end and RSd head < RSd middle < RSd end. This was because the flow velocity decreased from the head to the end part of the lateral. Higher flow velocity resulted in limited nutrient supply and slower microbial metabolism, as well as higher turbulence intensity and hydraulic shear stress, which led to the easier detachment of biofilms. In contrast, the lower flow velocity and turbulence could result in the accumulation of biofilms and more serious clogging in the end part. Moreover, the average biofilm thickness at the emitter inlet closest to the end part of the lateral could be selected as a suitable site for monitoring emitter clogging and biofilm growth characteristics. On the other hand, the appropriate range of flow path depths for drip irrigation emitters using reclaimed water was 0.70–0.75 mm, which will provide the reference for exploring the emitter clogging mechanism of reclaimed water drip irrigation and developing efficient clogging control strategies. Copyright © 2013 John Wiley & Sons, Ltd.