This blog is a summary of the RII Water Circularity Best Practices Guide. Our intention is to briefly outline some important points the guide makes, with the hopes that you, the reader, will then go on to read the RII guide. We also hope to show how we at Ceres are not only working with our clients to address their water needs, but also promoting the best practices for water circularity– as explained in the Water Circularity Guide.
To begin with– what is water circularity?
As defined in the guide, water circularity is the designed eradication of all water waste. There are three uses of water in grow facilities:
- Water for plants – irrigation/fertigation
- Water used to control the growing environment–climate control (fogging, wet walls, cooling, etc.)
- Water for non-plant processing (cleaning, toilets, sinks, etc.)
Why is water circularity important? (why should you care?)
According to the USDA approximately 80% of water used in the US is from agriculture, and even higher in some western states¹. Of the total amount of irrigation water used for plants, 80%-90% is transpired–effectively lost².
Growing crops requires a lot of water, and on top of that, most of the water used is not used efficiently or effectively. Surprisingly, this isn’t just the case for outdoor crops.
A conventional greenhouse uses around 22,000 ga/acre/dayl (83kL) for irrigation, while evaporative cooling systems use around 8,000 gal/acre/day (75 kL/ha/day)³.
When we move into greenhouses, or indoor grows, we are now adding water to control the grow environment and water for non-plant processing (in addition to water for plants). While there is no debate that water usage goes down in a greenhouse or indoor grow (less transpiration, higher efficiency irrigation systems, etc.), there is still a lot of water waste occurring.
But it is not just water that is the problem. The pollution of ecosystems from fertilizer and pest control chemicals is another agricultural concern. And another reason to consider water remediation systems when talking about water circularity.
Not every state regulates the discharge of irrigation water, but we can expect greater stringency in laws and regulations when it comes to the treatment (or lack of) of a grow facility’s water, as more growing facilities move to areas of greater population density.
Strategies for reducing water use
Now that we have covered why it is important to think about water circularity we can review some strategies for water reduction, recycling, and remediation.
Water Reduction:
Regardless of the chosen growing environment (greenhouse, indoor grow, outdoor, etc.) or irrigation method (hydroponic drip, NFT, overhead , etc.), there are reduction measures that anyone can and should take in order to keep one’s water usage down.
- Using VPD (Vapor Pressure Deficit) as a measure for optimizing water usage instead of temperature alone. Why? Because looking at temperature without also analyzing the relative humidity can lead to inefficient water use. For example, if the relative humidity of the environment is low, while the temperature is high the plant might intake too much water and not photosynthesize fast enough to keep up with transpiration.
- Employing a facility controller that can manage irrigation to ensure efficient water usage. More control=less waste.
A couple other measures one might want to consider (if possible) is opting for low water crops and grouping crops with similar water needs.
Water Recycling:
Wherever your water is coming from, there are a few systems that can be installed to employ the use of recycled water.
- Rainwater catchment. If permitted (check your state/local regulations), collected rainwater can serve as supplementary irrigation water. In The Netherlands, growers are required to have the capacity to store at least 500 cubic meters/hectare of rainwater (53,450 gallons/acre). In some cases, this can provide up to 65% of a facility’s irrigation water⁴.
- Dehumidification condensate recapture. Condensate from HVACD equipment can be collected in a drain pan, and funneled through plumbing pipes into storage tanks. Research published in 2020 from a vertical farm growing lettuce showed that their recycled condensate water was 67% of their annual water demand⁵. Most CEA facilities (greenhouses and indoor grows) have dehumidification equipment installed, so this can be a relatively easy addition.
- Irrigation leachate recapture. This is the water that is unabsorbed by the plant after watering. Depending on the irrigation method this recapture might look a little different. Essentially, this water is collected, treated and plumbed into storage tanks to be used again.
- Washdown recapture. This is the water that was used for cleaning as well as gray water from sinks. As stated above, it would need to be captured, treated and stored.
Important takeaways:
-The recycling of water has been shown to reduce water consumption by 20%-40% and fertilizer costs by 40%-50%⁶.
-A sealed facility (no outside air exchange) will allow for more water to be recycled, as water is not permitted to evaporate into the outside atmosphere.
-For all greenhouses that require MEP engineering, Ceres offers water source testing, custom water filtration design, as well as the option for condensate and leachate recapture systems.
Water Remediation:
Otherwise known as water treatment, every facility will use at least a few remediation methods, which include: physical water remediation, chemical remediation, and biological remediation.
“Physical technology will typically be combined with chemical technologies in order to filter particulate, adjust pH, purify, disinfect and recharge the nutrient balance of irrigation water. Likewise, they will be combined with chemical or biological technologies to treat water for discharge.” ⁷(RII, Water Circularity Best Practices Guide, p. 40).
Important takeaways:
-There are many systems and methods for water remediation, and we encourage the reader to consult the RII Guide to read the specifics.
-Remediation is an important part of water circularity, as dirty untreated water can cause havoc on a crop, the people working in the facility, and the outside environment. Investment in high-quality and well integrated systems will set you up for long term success.
-Consider each system before building a grow facility. Consult with a design/engineering firm (such as Ceres) to ensure that the water treatment system is integrated into the facility before building.
Conclusion:
Water is essential in a grow environment. What is often minimized or even overlooked when designing a greenhouse or other grow facility, is how to best optimize water usage. At Ceres, we take water optimization seriously. We consider methods and systems that will encourage the reduction, recycling, and treatment of the water that is being used. We encourage growers to consider a sealed greenhouse as water usage will only become more important.
As stated earlier, a sealed greenhouse will hold all transpired water within the facility, allowing for easier and more efficient recapture of that water to be used again, and again. Combine the sealed facility with an integrated water treatment system and automated control system and not only will your water usage go down, but so will your externalities.
For more information please contact us here.
Resources
- Center for Sustainable Systems, University of Michigan. (2021). “U.S. Water Supply and Distribution Factsheet.” Pub. No. CSS05-17.
- Center for Sustainable Systems, University of Michigan. (2021).
- Sabeh, N., Giacomelli, G., & Kubota, C. (2011). Water Use in a Greenhouse in a Semi-Arid Climate. Transactions of the ASABE, 54(3), 1069–1077.
- Raviv (2019)
- Pacak, A., Jurga, A., Drag, P., Pandelidis, D., & Kazmierczak, B. (2020). A Long-Term Analysis of the Possibility of Water Recovery for Hydroponic Lettuce Irrigation in Indoor Vertical Farm. Part 1: Water Recovery from Exhaust Air. Applied Sciences, 10(24), 8907.
- Mohammed, N. (2019). The Advantages of a Closed Hydroponic System in Commercial Greenhouses [Slide show; Powerpoint]. Government of Alberta.
- RII, (2023) “Water Circularity Best Practices Guide” p. 40
