Particle and debris removal
Pre-treatment or Filtration
Dr. Youbin Zheng, Siobhan Dunets and Diane Cayanan
University of Guelph, Guelph, Ontario, Canada
Pre-treatment or pre-filtration of irrigation water involves the use of various filter types to remove organic
and inorganic particulate matter (debris, sediment, soil particles, algae, etc.) from the water prior to treatment
for pathogens. Pre-filtration is important for 2 reasons. Firstly, larger particulate matter has the potential to
clog the irrigation system (e.g. emitters). Secondly, the effectiveness of many pathogen treatments (e.g. all
chemical treatments using oxidizers, UV) is decreased significantly in the presence of particulate organic matter.
There are a variety of filter types available. The most important way in which these filter types differ is in their
“fineness”, or the size of the smallest particle they are able to filter out. Fineness may be expressed in micron size or,
for coarser (less fine) filters, mesh size (a mesh to micron conversion table can be found here
http://www.netafimusa.com/files/literature/wastewater/Mesh-vs-Micron.pdf). “Mesh” refers to the number of openings
(or “pores”) present along a one inch transect (so 1 in./width of one pore= mesh number) (Netafim, n.d.a). “Micron”
refers to the filter pore diameter in micrometres (µm).
Ultimately, the fineness of filter required for a particular operation will vary, and will depend on the water source
used (which determines the size of particles present in the water). Multiple levels of filtration are often required
as much larger particles must be filtered out before water reaches the filter intended for finer particles. Otherwise,
these large particles may damage the finer filter. Whether multiple filtration levels are required or not depends on
how dirty the water source is. For example, if the water source is municipal water, only a single filtration level of
200 mesh (75 micron) fineness may be required. However, if the source is a slow moving or stationary body of water such
as a pond, multiple levels of filtration may be required, as well as a finer end filter around 600 mesh (25 microns; this
is to remove fine particulate organic matter) (Fisher, 2011).
It is also important to choose the correct size of filter. The “size” of the filter refers to the maximum flow rate that
it is able to accommodate. There are often multiple filter sizes available for each level of fineness. Water pressure of
the irrigation system must also be taken into consideration. Each filter model will have a limit to the maximum pressure
at which it can operate. As well, the minimum operating pressure required for your irrigation system must be noted in order
to ensure this pressure will be maintained when a self-cleaning filter is backflushing (see below for an explanation of this
phenomenon) (Tekleen, 2003).
Regular cleaning of filters is very important, and required frequency of cleaning will depend on how clean the original water
source is. Some filters (ex. screen, disc) are available in both manual and automatic-cleaning varieties. While manual-cleaning
filters are less expensive, these filters are only practical if source water is clean (Netafim, n.d.b). Automatic-cleaning, while
more costly, will ensure the filter is cleaned on time (Netafim, n.d.b).
Deciding whether to add another level of filtration is ultimately a question of balancing costs. While any pre-filtration requires
extra cost, the operator must take into consideration the maintenance costs or losses that would be incurred without the particular
level of filtration. For example, if an operator was thinking of installing a fine membrane filter, it would be important to compare
the cost of the filter to the cost of increased UV power or increased chlorine injection that would have to take place if finer
organic materials were not removed. While often some level of pre-filtration is necessary or beneficial, increasingly fine
filtration may not be appropriate for every operation. With a fine enough filter, anything can be filtered out of irrigation
water, but the issue is ultimately cost.
The table below shows different filter types available for different levels of filtration, starting with filters for the removal
or coarser particles at the top to finer particles at the bottom. Click on a particular filter type to be directed to a description.
For more information on exact costs and what filtration would be right for your system, please contact a supplier. Some filter suppliers include:
Pelmar Engineering Ltd.: Screen, disk, cartridge, media filter, sand separator
Fisher, P. 2011. Water treatment: A grower’s guide for nursery and greenhouse irrigation.
Netafim. N.d.a Mesh vs. micron comparison chart.
Netafim. N.d.b Water filtration: Why it’s needed.
Tekleen. 2003. Automatic water filter streamlines drip irrigation.
This work was supported in part by the Canadian Ornamental Horticulture Research and
Innovation Cluster and Canadian Ornamental Horticulture Alliance
For more infomation please contact Dr. Zheng (firstname.lastname@example.org)