Last summer, my wife and I had the pleasure of helping develop an advanced hydroponics teaching greenhouse in Battle Creek, MI. The greenhouse is part of the Calhoun Area Technology Center’s Environmental Sciences Technology program, and it features the state’s first zero run-off water recirculation system for greenhouses.
Several styles of hydroponic systems are running in the 2-bay greenhouse, each with its own reservoir. Periodically, the reservoirs are emptied and fresh nutrient solution is added. Instead of dumping the wastewater down the drain, it is collected in underground wastewater tanks. Rainwater is also collected from the greenhouse roof.
When the storage tanks are full, the wastewater is pumped through a biofilter for cleaning. The biofilter, imported from Holland, uses columns filled with lava grains. Beneficial microorganisms colonize the lava pores and degrade any organic matter in the water passing through them. To improve the efficiency of the microorganisms, all of the dirty water entering the system is dosed with an organic biostimulant called PoCo. The biostimulant speeds up the metabolism of the microorganisms and activates the enzymes that the beneficial bacteria produce. Root diseases such as pythium are completely eliminated, and the system is extremely effective against a variety of pathogenic fungi. The biofilter is even effective against such recalcitrant diseases as tomato mosaic virus, breaking the protein coats.
Once the wastewater is cleaned, it is stored in clean water tanks, one for “grow” formula and another for “bloom” formula. The tanks are topped off with rainwater to lower the EC, and a water sample is sent to a lab for analysis. The results of the analysis are typed into a computer spread sheet, and the computer tells the students exactly how much of each fertilizer salt to add to the tank to replace the minerals that the plants took out. Nitrates and phosphates are recirculated, and nothing goes down the drain. The only wastes are from an occasional back-flushing of the system to remove accumulated sludge, just a quick rinse to the sewer once every couple of weeks. Automatic back-flushing is also an option.
The biofilter is a cost-effective alternative to other forms of water disinfection. Many growers use ultra-violet sterilization in recirculating hydroponic systems, but UV is expensive in electrical costs and it has some detrimental side effects, such as the oxidation and precipitation of iron. Another option is ozone treatment, but it is also an oxidizer, precipitating iron. Since iron is a catalyst in the formation of chlorophyll, iron deficiency can cause interveinal chlorosis and slow down plant growth. The biofilter, on the other hand, works at room temperature, uses very little electricity, does not affect pH or EC, and does not oxidize iron.
My wife, Sue, is the instructor at the tech center, and I am the chairman of the center’s agricultural advisory committee. So tours can be easily arranged for anyone wishing to learn more about water recirculation. The Great Lakes Hydroponic Association will be hosting a meeting at the facility next fall, on the evening of October 20th, and the public is welcome. We will be showing the tissue culture clean room, the Priva environmental controls, various hydroponic systems, aquaculture systems for raising tilapia and Australian Redclaw Lobster, and, of course, the new biofilter. The theme of the meeting will be recirculating hydroponic systems.
To learn more about zero run-off technology, Sue and I visited the Netherlands this summer. We flew into Amsterdam Saturday, June 11, and stayed in Utrecht for most of the week. This gave us an opportunity to see large-scale recirculating systems in commercial greenhouses for tomatoes, peppers, orchids and roses. Since the biofilter eliminates the buildup of pathogens, some of the growers have been able to reuse the same substrate for years, without compromising the health and vigor of the plants. Another surprise was the increase in dissolved oxygen in the systems using the filter. The biofilter physically oxygenates the water, but with biostimulant dosing, oxygen levels increased much higher than normally expected. Plant metabolism was increased, nutrient uptake was improved, and plant diseases were reduced. So in addition to preventing environmental pollution, the PoCo/biofilter combination also helps improve quality and yields for growers.
We also took a side trip to Belgium to look at exciting new applications for PoCo and other biostimulants. An independent research greenhouse is conducting controlled experiments on sweet peppers, with and without organic biostimulants. Even under ideal environmental and fertilization conditions, peppers dosed with biostimulants have achieved a ten percent increase in yield over the control, with four more months of production to go! We will share the documentation when the experiment is completed in October.
With increasing environmental concerns about concentrated phosphate and nitrate run-off from greenhouses, biofiltration offers an economical alternative to conventional recirculation strategies.
For more information on zero-runoff technology, please contact:
Harley N. Smith, Hydroponics Consultant
Superior Growers Supply, Inc.
4870 Dawn Ave.
East Lansing, MI 48823