Drainage Water Evaporation & TDS Reduction
The PhytoVap, a closed-loop hydroponic evaporator, is an elegant solution to your agricultural drainage and RO brine disposal and treatment problems. Thinking about a thermal evaporator or hauling your drainage water to a 3rd party treatment facility? Our solution is a fraction (about 1/10th) of the cost of either of these solutions. Our system uses specially curated perennial plants to maximize the evapotranspiration of your drainage water or RO brine, while using the residual N-P-K-S in your drainage to fuel the growth of our plants. The system runs continuously using standard hydroponic equipment with the drainage water never touching the soil. Concerned about high total dissolved solids (TDS)? The system also removes measurable amounts calcium, sulfate, nitrate,and other ions from the water.
Regulatory Note: If you work in a heavily regulated area and cannot land apply your drainage water, this is an excellent solution. Once the drainage water enters our system, it never touches the ground.
New Solution to a Common AG Problem
Existing Solutions are Expensive.
We all want to try and recover and reuse as much of the drainage water as possible. But sometimes, the cost of conventional treatment to meet regulatory requirements is simply prohibitive.
Thermal evaporators require a very large amount of energy to evaporate the water. Most agricultural drainage water has very high TDS. This will cause rapid scaling and fouling of thermal evaporator components. Water hauling, a bit less expensive, requires you to pay for a tanker truck to come and pump out your drainage water, haul it to a disposal facility (usually a wastewater treatment plant), and then pay again to have the water pumped out at the disposal facility.
How PhytoVap System Helps You
What Kind of Plants Do We Use?
We use perennials, mostly from the grass family but also other families as well. Our plants are considered “halophytes” or salt-loving plants. Some of the plants are grown from seed and others are cloned- especially from wild cultivars. We are careful in our plant selection because some plants that might be considered invasive in your area are okay to use in other geographical areas. One characteristic that we look for is salt-tolerance, along with rapid growth and large above ground biomass. The term “salt” generally refers to chloride and sulfate anions. A typical starter bucket is shown below with about 9-12” of growth. Other plants can be substituted to remove a wide range of different dissolved ions in the water. Some of the plants will remove and store salt and can be used as food or forage.
Note: Using the above ground biomass for food for forage may be subject to review and comment by regional and state regulators.
The system has four major components:
As shown here, the plants are in a “grow bag”. The grow bag facilitates a lot of evaporation and keeps the substrate material from entering into the irrigation loop. The grow bag is filled a special substrate, not soil. If you need to replace or add buckets, we will recommend a substrate mixture.
For small systems, we like to put the reservoir underground to enable gravity return flow from the hydroponic array. Many other configurations are possible. The hydroponic array is a so-called “Dutch bucket” or “bato bucket” system. We use “buckets” that range from 11 liters (3 gallon) to 32 liters (7 gallon). Other configurations are possible but, we need to ensure that the water stays inside our closed loop system and prevents debris, leaf litter, and other foreign material from entering the return flow. The reservoir should be large enough to capture 2 or 3 days of drainage. The pumping system uses a submersible pump mounted in the reservoir. Commercial drip lines and filters connect the plants to the pump. The buckets drain into 1.5” PVC pipe that returns water to the reservoir.
How Much Drainage Water Can We Remove Via ETo?
The amount of water removed, or evaporated and transpired depends upon environmental, location, and drainage water characteristics. Environmental parameters include:
In addition to evaporating a lot of water, the system will lower your total dissolved solids (TDS). Using a sample from a commercial drip irrigation farm, we found that after 1 day of treatment (3 irrigation sets of 30 minutes each), the TDS was lowered from 1400 to 700- a 50% decrease. Ions that were removed in the largest quantities were: Potassium, Nitrate, Calcium, Sulfate and Hardness.
Note: Keep in mind that if you lower the TDS enough and lower the nitrate-as-N to below 10mg/L, it might be possible to reuse the water or discharge locally. Check with your local regulatory agency first.
Designing, Controlling, and Optimizing Your System
The design process consists of:
During normal operation, the irrigation controller does the following:
Optimizing your system should be done over the first season of usage. This may involve adding additional plants or different plants (we have a wide selection) or modifying the irrigation schedule.
The plants need frequent watering and feeding, especially when there is no drainage water to treat. We recommend filling your reservoir from a hose bib and adding a modest amount of all purpose fertilizer. Set your controller to run for 1 hour, once a day. This should be sufficient to keep the plants healthy until the drainage starts again.
Twice a year the plants should be trimmed from the maximum height of 5 to 7 feet, down to about 3 feet.
In line filters or other devices used to prevent the drip irrigation system from clogging should be cleaned periodically, as in any commercial system.
You should anticipate periodically pumping out the reservoir and storing or hauling this water to be discharged. The system comes with an extra zone controller valve for pumping the water to another holding tank.