By Marcus Allhands
Steady growth in population, industry and tourism has caused higher demands for potable water in Northern Sunrise County in Northern Alberta, exceeding the capacity of the two local water treatment plants.
In 2004, the county decided to initiate a program to lower the demand on potable water for non-potable uses. One aspect of this program was to discourage the use of potable water by farmers for irrigation by providing them with a ready source of non-potable irrigation water. To this end, 150-micron manually cleaned strainer baskets were installed in two locations.
Though not as clean as treated potable water, local producers supported the effort. The problem with the filtered water was that it was still not clean enough and using treated drinking water caused a suspected reaction between the chlorine in the water and the agricultural chemicals, with deposits plugging sprayer nozzles.
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To conserve water, irrigation systems in use today have micro-spray emitters close to the ground that spray a fine mist of water onto crops. This method increases irrigation efficiency by directing most of the water onto the ground right around the plants to cover the root zone and minimize drift and evaporation losses.
Because these micro-spray emitters have such a small orifice, the water must be free from all solid particles that could cause clogging. Some farmers may soon start using drip irrigation technology, which is more efficient than micro-spray emitters. However, it is even more dependent upon high water quality.
If water provided to farmers by the county is not clean enough, they will simply go back to using potable water for irrigation purposes, which strains public water supplies. Only quality filtration equipment can remove both heavy solids such as sand and lighter organics like algae, rendering non-potable water usable for irrigation purposes. A better filtration system was needed and Brent Schapansky, county utilities coordinator, was called upon to lead the project.
The solution
Stormwater and spring runoff is collected in ponds and basins, called dugouts, throughout Northern Sunrise County. This water picks up sand, grit and wind-blown debris, making it unfit for modern water-conserving irrigation systems. Schapansky contacted ORIVAL Inc. for an automatic self-cleaning filtration solution.
Subsequently, an ORG/A-040-LS automatic self-cleaning filter with a 50-micron weave-wire stainless steel screen was installed as a pilot filter to determine the feasibility of using this technology to treat the water from the dugouts to a high enough standard to prevent clogging of farmers’ irrigation systems. Farmers simply pull up to a dugout with their tanker trucks and fill up with water to haul back to their fields for irrigation. The filtration system sits between the pump and the truck, assuring high water quality for the most stringent irrigation system. Figure 1 shows the pilot filter installation.
Filter operation
Water passes into the filter body at the bottom (as show in Figure 2) and then through the 50-micron cylindrical screen element from the inside out. Suspended solids larger than 50 microns are retained on the screen surface and soon build up a layer called a filter cake. The openings between particles in this filter cake are smaller than 50 microns. This allows the filter cake to act as a filter medium, capturing smaller and smaller particles.
When a differential pressure switch senses a sustained pressure drop of 7 psi across the filter, it signals the controller to initiate a rinse cycle. A rinse valve opens the internal rinse chamber to atmosphere, dropping the pressure in the chamber. Water wants to move from the high pressure-filtering chamber to the rinse chamber but can only do so by passing into nozzles on the dirt collector and out the hydraulic motor in the rinse chamber.
This water movement causes the hydraulic motor to rotate the dirt collector. Nozzle openings are so close to the screen element that water rushes backwards through the screen (from clean side to dirty side) in a very small area at high velocity. This pulls the filter cake off the screen, into the nozzles, through the dirt collector, into the rinse chamber and out the rinse valve to a convenient drain.
A piston on top of the filter is normally pressurized by water pressure holding the dirt collector down to its lowest position. During the rinse cycle this pressure is bled off, allowing the dirt collector to be slowly pushed upward by pressure in the filter chamber. The combination of rotation and upward linear movement causes the nozzles to pass every square inch of screen area, assuring a clean screen.
After about 12 seconds the cleaning cycle is complete and the rinse valve closes, the dirt collector stops rotating and the piston is re-pressurized to place the dirt collector back into its lower starting position. While all this is happening, the filter continues to supply clean filtered water downstream to the truck without interruption.
Results
According to Schapansky, “water coming out of the ORIVAL filter tested at 1.1 NTU which is just over the Alberta drinking water standard by 0.1 NTU with no chemical treatment.”
As a result of this pilot test, a second ORIVAL filter was purchased and set up as a fully automatic self-cleaning filtration system requiring no operator intervention whatsoever. The pilot unit will be incorporated into the local treated water reservoir building with a new submersible pump that has sufficient output to make the unit fully automatic as well. Supply at the pilot location is two dugouts formerly feeding the small drinking water plant. A heated building and large supply mean this site could remain open year-round for industrial and firefighting use.
More ORIVAL automatic filters are to be purchased as the program expands. The county is considering a by-law that will require all agricultural water come from filtered dugouts.
Marcus Allhands, PhD, PE, is with ORIVAL Inc. For more information email: filters@orival.com or visit www.orival.com
Read the full article in ES&E Magazine’s April/May 2020 issue below.
