SAND FILTRATION IN IRRIGATION

SAND FILTRATION IN IRRIGATION

 

We are all aware of the existence of different filtration methods. There are varied systems on the market that are more or less suitable depending on the quality of the water to be filtered and the applications to be used after filtering. In this particular case, we will discuss sand filtration in drip irrigation.

In irrigation, the water comes from different catchments or intakes. The most common are water from rivers, canals, ponds, boreholes and even from water reclamation systems. Each effluent has its own characteristics which, in some cases, even fluctuate depending on the weather conditions and the time of the year.

Each specialised installer is perfectly aware of the characteristics of the water in the area and its problems. Apart from his preferences and work habits, he is the best person to determine the system that best adapts to the plot where the irrigation system is to be installed.

What everyone agrees on is that, when it comes to poor quality surface water or significant seasonal fluctuations in quality, sand filtration is the most suitable system.

Sand filtration ensures that the suspended solids in the water (TSS) are retained in the filter bed (usually silica or volcanic sand). The filter beds trap the particles suspended in the water by the mechanical screening itself (particles larger than the pores formed in the filter media and which are mechanically retained by the filter media). In addition, during the passage of solids through the bed, sedimentation processes are generated (a kind of decantation), centrifugal forces (the circulating water follows curvilinear trajectories, creating inertial forces that cause particles to collide, forming larger flocs), physical adsorption phenomena (Van der Waals and electrokinetic forces) and electrostatic interaction (depending on the characteristics of the filter media and the suspended particles).

All the aforementioned produces a large amount of suspended solids retention in the water, significantly reducing the raw water and obtaining water with a sufficient quality for subsequent irrigation.

In sand filtration applications for irrigation, bed heights between 60 -75 cm are commonly used, being the most suitable measures for the retention of solids. It is true that a higher bed height will produce water with lower turbidity, but for dripper applications higher turbidity will not be a problem regarding irrigation emitter clogging. It is also necessary to provide a back check or retention system to retain any particles that may pass through the bed (through the preferential channels that may form) and as security in case there is any breakage in the arms or crepins of the sand filters. 130 micron screen filters, either manual or self-cleaning, are widely used.

Finally, the most important thing is the filtration speed used in sand filtration for irrigation. This parameter is fundamental because the slower the water passes through the filtration system, the better the quality of the water will be. The flow rate is calculated by dividing the flow (m3/h) by the filtration surface (m2). The poorer the water quality is, the lower the flow rate I can use, which means more filtration surface is needed or less flow for the same surface area can be filtered. This parameter is fundamental for a correct dimensioning of the system. This means that the filtration surface area for the same flow varies very significantly depending on whether the water comes from a well, a pond, a river, etc. The quality of the water is the most important parameter for the sizing of a filtration system (this also includes screen and sand filters).

In summary, sand filtration is the filtration system that can produce the best water quality, it is the most suitable and versatile system for complex or heavily loaded water, and for its proper operation it is important to accurately size the necessary filtration surface. The experience of the installer and the manufacturer of the equipment is important, as they know the water problems in each geographical area and the type of water intake.

At Lama we are filter manufacturers, so we will recommend the one that best suits our customer’s needs according to the above parameters. In addition, more than 70 years of experience and 150,000 installations of different filtration systems all over the world, allow us to know almost all the applications in the market, although day after day we continue to find new challenges proposed by our customers.