Chapter 11

Irrigation Water for Greenhouses

Treating Greenhouse Irrigation Water for Suspended Solids

Suspended solids need to be removed from water to prevent clogging of piping, valves, nozzles and emitters in the greenhouse irrigation system. Suspended solids include sand, soil, leaves, organic matter, algae and weeds. Municipal water supplies can pick up particles water flows through the delivery pipes. Ground water can be relatively free of particles or it can have large quantities of sand and/or silt that can enter greenhouse irrigation supply as water is pumped from the aquifer. A filtration system removes sand, silt, plant material, algae and other materials suspended in the water. No matter what the source of water, some filtration is needed. The kind of filtration needed depends on the water source and its characteristics.

Centrifugal Sand Separator

Centrifugal sand separators (See Figure 11.2), in theory, are not actually filters but are used as pre-treatment devices for other types of filters. A centrifugal sand separator removes larger particles of sand, silt, or other abrasive grit particles that can lead to the premature degradation of irrigation system components. These contaminants can reduce the efficiency of the irrigation system equipment by plugging and clogging valves and emitters. A sand separator is effective in removing up to nearly 98 percent of particle sizes too large to fit through an equivalent 200 mesh (0.074 mm) filter. The device does not remove organic material.

Media Filters

Media filters (See Figure 11.3) have been used extensively for micro-irrigation systems. These filters trap contaminants in irrigation water in a deep column of sand, recycled glass, packed mineral or glass fibers, and/or other dense substrates. The most notable of these is conventional sand of selected sizes placed in pressurized tanks. The main body of the tank contains sand, which is the active filtering ingredient. The sand is placed on top of a thin layer of gravel, which separates it from an outlet screen. Contaminants are filtered from the water as it flows through the filtering media. Media filters are often used to remove organic materials (bacterial slimes and algae), fine silt, or other fine organic or inorganic materials from ponds and surface water. Due to the three-dimensional nature, media filters have the ability to entrap large amounts of contaminants. Media filters can capture inorganic and organic contaminants smaller than 200 mesh (0.074 mm).

Screen Filters

Screen filter products are popular because they are inexpensive, easy to install and take up less space than a sand media filter. They come in various shapes and sizes, although most are horizontal cylinder types. Screen filters (See Figure 11.4) are most frequently used for removing inorganic contaminants. Screen filters are recommended for the removal of very fine sand or larger-sized inorganic debris. It is normally not effective to use screen filters for the removal of heavy loads of algae or other organic material, since filters clog rapidly, requiring too frequent cleaning to be practical.

Disk Filters

Disc filters (See Figure 11.5) are a cross between a screen filter and a media filter, with many of the advantages of both. Disc filters are good at removing both particulates, like small amounts of sand, and organic matter. The screening element of a disc filter consists of stacks of thin, doughnut-shaped, grooved discs, forming a three-dimension filter cartridge. The stack is enclosed in corrosion and pressure resistant housing. Each individual disc contains grooves, molded into its surface. These molded grooves provide for the mesh (or micron) rating of the filter.

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