Greener Greenhouse

Nov. 7, 2018

Plant cultivation facility implements closed-loop water management strategy

About the author:

Kyle Lisabeth is director of business development, horticulture, for Silver Bullet Water Treatment. Lisabeth can be reached at [email protected] or 720.403.0652. 

A Northern California indoor plant cultivation facility sought an effective treatment solution for both source water and irrigation reuse. The facility’s water treatment requirements are irrigation water treatment for risk management of bacterial and fungal waterborne pathogens; ability to capture and reuse irrigation water to meet the business’ resource savings goals and to comply with regulatory requirements; and treatment technology that is compatible with hydroponic plant production, does not contribute to plant stress and mitigates crop loss. The grower also desired a cost-effective water treatment system that could scale with long-term plans for the business.

Sustainable & Safe

Incoming municipal source water is delivered and stored in four black poly tanks located indoors under controlled climate conditions. The facility uses reverse osmosis to treat all incoming source water. Each flower room is designed with custom rolling grow tables. Plants are grown on stationary flood and drain tables, and drip irrigated with a customized blend of nutrient fertilizers. The grow tables are fabricated to allow excess irrigation water that is not absorbed by the media or taken up by the plant to be gravity drained from the table. The leachate drain water is collected from each table and drains to a collection tank.

Water management plays a critical role in the function of this facility. The grower chose Silver Bullet because it is a sustainable, safe and green chemistry-based solution; treats and reuses irrigation runoff water; offers proven bacterial and fungal control for other customers; is a professionally designed, engineered and installed water treatment system; and has a service, maintenance and water analysis program.

AOP & UV Combination System 

To maximize the facility’s water treatment program, Silver Bullet installed an advanced oxidation process (AOP) system, paired with direct ultraviolet (UV) disinfection. The combined technologies provided redundancy in disinfection treatment. The AOP system ensures the recirculated, treated water has slight residual disinfectant properties, which further aids in keeping the storage tanks clean and free of microbiological growth. 

The facility uses a closed-loop irrigation system, where the required water pressure is provided by a pump. In this closed-loop system, water from the municipal utility, the climate control system and irrigation runoff are blended together, treated and reused as irrigation water. 

Within each plant production room, irrigation water is delivered to two vertical poly tanks. These tanks continuously are treated and conditioned using the UV treatment system. Irrigation water then is pumped to a single poly tank that is used to mix nutrient fertilizers and condition the water prior to being delivered to the plants. 

All runoff irrigation water is drained and collected in two holding tanks. Irrigation runoff is composed of several constituents that require disinfection and conditioning. Although this water allows for mineral nutrients not taken up by the plants to be recycled and reused, it also includes elevated levels of bacteria, unwanted organic content and suspended solids. Water from all three sources continuously was treated and blended into reliable irrigation water that is compatible with the facilities nutrient formula to prevent biological fouling.

Microbial Control

Silver Bullet developed an intensive water monitoring program around the production schedule for two of the facility’s plant production rooms to ensure the water treatment solution met customer expectations. For third-party validation of the solution’s performance, samples were delivered to North Coast Laboratories, a state-certified laboratory.

The Silver Bullet-treated water in makeup storage tanks in flower rooms A and B showed a high level of disinfection, while the untreated runoff water had significantly higher levels of bacteria. Analysis of heterotrophic plate count (HPC) confirmed the system’s efficacy in managing microbiology in the water.

On average, over the 10-week production cycle, Silver Bullet-treated runoff water in Flower Room A had 328,300 cfu/cc lower HPC count than the untreated runoff water with a 1.07 average bacteria log reduction. Flower Room B’s results showed a 58,034,200 cfu/cc lower average HPC count with a 1.88 average bacteria log reduction rate. The consistent log reduction for each sample demonstrates the system’s efficacy in managing microbiology over a multi-week period. Ongoing HPC monitoring since the end of this demonstration has resulted in continued grower satisfaction with microorganism levels.  

Phytotoxicity Management 

The water treatment solution helped manage phytotoxicity effectively in the plants by eliminating or significantly limiting the use of harsh or hazardous chemicals, such as chlorine, during the grow cycle. Phototoxicity typically occurs in plants that are overly sensitive to a wide variety of compounds, including trace metals, salinity, pesticides, phytotoxins or allelochemicals. 

Effective treatment of the irrigation runoff water has allowed the grower to eliminate their water discharge and reuse irrigation runoff water that otherwise would have been too contaminated to recycle. Water from all three sources was continuously treated and blended into reliable irrigation water that was compatible with the facility’s nutrient formula to prevent biological fouling and bacteria reduction results continue to meet the customer’s expectations. Silver Bullet also has observed no presence of algae, solids or biofilm within the storage or distribution systems, no plugging or fouling of drip emitters, and no compatibility issues with nutrient formulas or other irrigation water components.  

By implementing the water treatment design, the grower was able to achieve significant economic and operational benefits, including:

  • Avoided discharging untreated constituents or adding additional wastewater treatment processes;
  • Reduced reliability and demand on municipal water utilities for source water; 
  • Capitalized on reusing synthetic nutrient fertilizers and reducing operational costs associated with treating additional incoming source water; 
  • Compliance with regulatory statutes that require all future commercial cultivation facilities to integrate zero-liquid discharge standards; and 
  • Avoided costly future retrofits by integrating water collection and reuse into the facility’s initial design-build.

Using the solution, the customer has been able to implement a successful closed-loop water management strategy and has begun to recycle nutrients to offset operational costs. By collecting, treating and blending the irrigation runoff, many macro- and micro-plant nutrients can be reintroduced into the nutrient formula.

About the Author

Kyle Lisabeth

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