Slow Sand filtration
Healthy root systems free of pathogens is the objective of every hydroponic gardener.
Battling the dreaded pythium and other root rot pathogens in a hydroponic system can be a demoralizing and long-term issue for some growers, with little in the way of effective chemical or other controls. Even when roots look pristine, white and healthy, we all worry from time to time if nasties are starting to invade our hydroponic nutrient or causing issues without us even knowing what might be occurring at the microscopic level. One of the best defenses against nutrient-borne pathogens is other beneficial microbes. In fact, if present in high populations and combined with effective microfiltration, control over problematic phytopathogens becomes an extremely effective practice.
“Since the 1980s, Slow Sand filtration haS been under inveStigation for itS uSe in cleaning up irrigation or waSte water from horticultural operationS.”
Slow sand filtration
Brown diseased roots (right) caused by pythium, a disease which is dispersed by the nutrient solution.
Slow sand filtration, sometimes termed biofiltration, is a method of drinking water purification that has been around for well over a century. Since the 1980s, slow sand filtration has been under investigation for its use in cleaning up irrigation or waste water from horticultural operations. Even more recent and precise studies have evaluated biofiltration as a means of eliminating nutrient-borne plant pathogens like pythium, phytophthora, verticillium, fusarium and others. So, large-scale commercial hydroponic operations around the world are now incorporating huge slow sand filters as a way of not only dealing with waste water, but to also purify and control nutrient-borne pathogens in recirculating hydroponic systems. What is particularly exciting about slow sand filtration methods for smaller growers and indoor gardens is that the system can be scaled down to fit any size system and is relatively easy to construct and run with little cost to the grower.
How does slow sand filtration work?
A slow sand filter works on a number of different levels. Firstly, the filter material (traditionally sand, though other materials can also be used) screens out any organic or suspended matter—for example, algae small pieces of root or plant material, sediment, etc.—from the nutrient solution. Secondly, and more importantly, the filter material provides a home with a large surface area for a wide range of beneficial microbial inhabitants. These beneficial microbes are what provide the biological filtration that has been shown to remove pathogens at up to 99% efficiency. The principle behind slow sand filtration is that the nutrient solution applied must flow very slowly through the bed of fine material. If rates of nutrient solution flow are too rapid, the removal of plant pathogens is compromised and the filter might not be effective for disease control. Nutrient solution flow rates for biofiltration must be within the range 2.4 to 6 gal. per square foot of filter surface area per hour. So, for a small hydroponic indoor 92
Maximum Yield USA | June 2013