Drip irrigation is the most effective and reliable method for reclaimed wastewater irrigation. Emitter clogging is the major problem for extending the drip irrigation technology. The existence of suspended particulates in irrigation water is the main reason for the emitter clogging. However, the reclaimed wastewater quality is extremely complex, and there is a series of physical, chemical, and biological reactions between suspended particulates and other materials contained such as microorganisms, which make the characteristics of suspended particulates in reclaimed wastewater complicated. In this paper, two types of widely used wastewaters treated with fluidized-bed reactor (FBR) and biological aerated filter (BAF) processes respectively were selected. The scanning electron microscope (SEM) technology and fractal theory were used to quantitatively describe the characteristics of the surface topography of suspended particulates. The results showed that the suspended particulates in two reclaimed wastewater were flocculent and porous. The pore system mainly consisted of solid suspended particulates, and most areas between the particulates were filled with microbes and extracellular polymers (EPS). The complex structure of biofilms was formed. That the biofilms grew and detached in irrigation system and deposited continuously at the inlet and outlet of labyrinth path was the major reason for the emitter clogging. The surface topography of suspended particulates in both reclaimed wastewaters showed fractal and multifractal characteristics, and the fractal dimension could not characterize the local and microsingularity of particulates but multifractal dimension could. The uniformity of the distribution of sediment pores increased with the size. Comparatively, the uniformity of suspended particulates in reclaimed wastewater treated by FBR was lower. With operation of reclaimed wastewater irrigation system, the average discharge of emitters decreased continuously with obvious fluctuations. The clogging degree of emitters was low during the first 256 h, and the clogging degree of the two types of reclaimed water was similar. But then, the degree of clogging increased greatly, and the FBR treatment on the emitters discharge were more obvious than BAF. It was closely related to the growth, detachments and sediment of biofilms in the irrigation system. Hence, using the reclaimed wastewater treated by BAF for drip irrigation is more suitable.

Emitter clogging, a phenomenon commonly seen in reclaimed wastewater drip irrigation systems, is a severe obstacle to the wide applications and popularization of the irrigation technology. Some experiments showed that the emitter clogging was tightly related to biofilms formation attached to the irrigation system. In this paper, two types of wastewaters reclaimed respectively by fluidizedbed reactor (FBR) process and biological aerated filter (BAF) process were chosen as the experiment objects and then the effects of the average velocity on the growth and topography of biofilms attached to the irrigation laterals were studied. The parameters of biofilms reached their maximal values at a critical velocity of 0.45 m/s. The formation of biofilms was primarily controlled by the transport of the nutrients and suspended particles within the laterals when the average velocity is below the critical velocity, whereas it was primarily controlled by the hydraulic shear force when above the critical velocity. The main mechanism for emitter clogging was that the biofilms detached from laterals accumulated and grew at the inlets and outlets of emitters. A similar variation pattern was observed for both reclaimed wastewaters. However, the growth of biofilms for BAF process was more affected by the shear force than that for FBR process, since the nutrients and suspended particles for BAF were larger than those for FBR.