Effluents are used in agriculture as a viable alternative to freshwater in areas where water is scarce or there is strong competition for its use. Although micro irrigation is the most advantageous irrigation system for applying effluents, especially from public health and environmental points of view, the use of effluents can increase emitter clogging, which affects water distribution and, consequently, crop yields. So, filtration is a necessary process.
The three common filter types used in micro irrigation systems are screen filters, disc filters, and sand media filters. In screen filters, particles are trapped on the surface of a perforated cylinder. Disc filters have many grooved discs pressed together, and the particles are retained in the grooves of the discs. In media filters, solids are caught by the particles of gravel or sand. In screen and disc filters, the particles larger than the pores of the filtering media are retained on the surface of the media and accumulate layer by layer, forming a cake of increasing thickness that reduces the diameter of pores and allows smaller particles to be retained. In sand filters, the particles to be removed can be smaller than the filter pores since particle capture is controlled by both physical and chemical mechanisms.
Screen and disc filters are simple, economical, and easy to manage but sand filters are more complex and expensive, and are only appropriate for farms with high technical and professional standards.
Sand filters are also more suitable for waters with high suspended solids content, but disc filters, if properly designed, can give performance levels similar to those of sand media filters.
As suspended particles are trapped by the filters, the filtration rate decreases because the filter becomes clogged and must be cleaned to recover operational conditions. Most filters are cleaned with automatic backwashing based on a fixed head loss across the filter and/or an operation time. Both options allow for easy system automation.