Preliminary surface topographical characteristics of biofilms attached on drip irrigation emitters using reclaimed water

Drip irrigation is the most effective and reliable method for reclaimed water irrigation. Emitter clogging is the bottleneck to restrain the application and popularization of reclaimed water drip irrigation technology, and some researchers have reported that this was tightly related to the formation of biofilms in the irrigation system. We selected reclaimed water treated with cyclic activated sludge system (CASS) and four kinds of labyrinth emitters in cusp-shaped saw-tooth, rectangular straight-tooth, arc-shaped saw-tooth and arc-angular straight-tooth and studied the surface topographical characteristics of biofilms in different positions of reclaimed water drip irrigation emitters with the 3D white-light scanning interferometer (WLSI). The results showed that biofilms in different positions of units were different with each emitter while showing the largest thickness in water-side tooth-tip zone (>20 μm); the biofilm thickness in the same monitoring sites inside one unit segment gradually decreased along the flow direction, while the flow at the inlets was much larger than that at the outlets; comparing the head, middle and tail parts, the biofilm thickness at the inlet and outlet showed the largest in the tail part, followed by the middle and the head parts. This can be explained by the equilibrium relation between hydrodynamic behavior and the transportation of nutrient and particles inside the emitters. The water-side tooth-tip zone of the first unit in the last emitter was selected to monitor surface topographical characteristics of biofilms, and its biofilm thickness also could be used as the indicator for evaluating the characteristics of surface topography. These results were aimed to provide references to explain the emitter clogging mechanism of reclaimed water drip irrigation as well as its technological application and popularization.