The clogging of emitters, orifices or laterals has turned out to be the main obstacle for further use of low rate applicators in wastewater irrigation. Granular filtration and screen filtration were studied and compared for particulate removal using small-scale pilot experiments. The removal ratio of particles larger than 10 µm in direct granular filtration was relatively large while smaller particles showed little removal. Particles in the 10-60µm size range were removed by 40–50 percent in depth and by 80 percent when surface filtration prevailed. Screen filters removed only 1–2 percent of the material but this was sufficient to cause their clogging. A release of particles from the screen into the effluent was observed, resulting in greater number of larger particles and thus greater clogging potential down the irrigation line. Deep-bed granular coarse media filters may serve for the control of particle size in effluents of oxidation ponds - deep reservoir systems while the conventional strainers are less recommended for this purpose.

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