Imagine a picturesque cannabis grow site set along a bucolic creek. The cannabis is grown indoors, but employees can enjoy the creek on their breaks on hot days. Unfortunately, they may not want to. Because instead of disposing of their wastewater properly, the owners of the cannabis farm have decided to dump it directly onto the ground adjacent to the creek.
While this may sound like a far-fetched, worst-case scenario, unfortunately it’s not. Ask many a cannabis production worker, and they will tell you, this kind of thing happens all the time. Even if the wastewater isn’t hazardous to humans directly, this type of waste causes algae blooms in natural bodies of water, depriving aquatic species of oxygen. For an industry that is so tightly regulated in most regards, this is one part of cannabis cultivation that largely seem to go ignored.
The main contaminants in cannabis wastewater are phosphates and nitrogen left over from nutrients. These are common remnants from horticultural operations, so there is method upon method to remediate water safely, either for reuse or reintroduction into the regular sewage system.
Federal Wastewater Regulations
Cannabis is still technically illegal at the federal level, making federal regulations a sort of gray area for cannabis growers. Still, it’s a good idea for cannabis growers, especially large-scale licensed producers, to comply with federal regulations, both for the health of the environment, and because if cannabis becomes federally legal, they’ll be ahead of the game.
Adopted in its current form in 1972, the main body of regulations for wastewater is the Environmental Protection Agency’s Clean Water Act. According to the EPA’s summary:
The Clean Water Act (CWA) establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters.
Reading through these regulations can give cannabis growers a good idea of what to do with their wastewater.
Local Wastewater Regulations
Local wastewater regulations vary from state to state, and even county to county. Climate conditions in your region may dictate wastewater regulations. For instance, wastewater treatment in California, where water is scarce, may focus more on water conservation, whereas in Washington state, where water is more plentiful, wastewater regulations may focus more on reducing pollution and protecting native species like salmon. Be sure to do your due diligence and find out which local regulations apply in your region.
What To Do With Cannabis Wastewater
So, how can cannabis growers properly dispose of wastewater from their cannabis grow ops? While legal regulations vary from state to state and region to region, there are some best practices that one can follow, no matter what their local laws stipulate. Keep in mind, wastewater treatment is a topic someone can spend a lifetime learning about, so the following descriptions barely scratch the surface. However, there is a ton of science out there if you’re interested in learning more.
Perhaps the most important and effective way to conserve water and reduce the need for wastewater disposal is to reduce your volume of wastewater altogether. This can be done by:
- Setting up effective irrigation systems.
- Not overwatering when hand watering.
- Having the appropriate amount of plants on a flood table.
- Using the correct amount of nutrients.
Many growers overuse water, nutrients and money by not taking steps to minimize their wastewater output. Doing so will also save money on filtration systems over time by requiring smaller systems and fewer filters.
Down The Drain
Pouring wastewater down the drain is really only an option for small-scale or hobby grows. If you have a small cannabis grow, and your sewage is not pumped into a septic tank, then pouring wastewater or excess nutrients down the drain is a viable option — certainly more so than dumping your waste straight into the ground. Before dumping anything down the drain, follow directions on nutrient bottles and make sure to research local laws.
Aside from only being viable for small-scale growers who don’t employ a septic system, this method of disposal is largely wasteful and doesn’t take conservation into account. Admittedly, however, this is the easiest option for small-scale cannabis growers.
Recirculating And Recycling Systems
If your grow is large, and especially if it’s hydroponic, a water recirculation system may be your best option for proper wastewater usage. Simply put, a recirculation system collects wastewater from either a hydroponic system or captures it from a flood floor, before transferring it to a reservoir. The water is then sterilized, rebalanced with nutrients, diluted, and then reused for watering your cash crop. Purchasing a recirculating system is pricey yet worth it in the long run to cut down on water usage and help run an altogether more environmentally friendly grow op.
Wastewater recycling systems are similar to recirculation, but different in the sense that the wastewater isn’t treated just for the sake of reuse for watering. Recycled water can be used for a variety of applications, even if it’s just to put it safely back in the water cycle via ending up in the drains. The process of water recycling goes as follows:
- Primary treatment, which removes sediment.
- Secondary treatment, which involves biological oxidation and disinfection.
- Finally, tertiary or advanced treatment, the level optimal for cannabis irrigation, which involves filtration and disinfection.
Cannabis growers often use reverse osmosis filtration to water their crops, which can turn regular tap water into ideal water for your sensitive plants. Reverse osmosis filters work, in a basic sense, when feed water is pushed through a reverse osmosis membrane, or membranes, depending on the system you’re using. The membrane filters out all the stuff you don’t want, and then the water is separated into reject water — where all of the nasty stuff is flushed — and ultrafiltration permeate water, which is the water you’ll want to use.
In addition to filtering questionable tap water, reverse osmosis systems can also be used to filter wastewater. In fact, this is the most common wastewater recirc and/or recycling system cannabis growers use. Flood floor water or hydroponic water is collected in a reservoir, then an external or submersible pump moves it from the reservoir back into the reverse osmosis filter.
Carbon is another filtration method for wastewater recycling or recirculation. Carbon filtration systems are less common in cannabis grows, but fairly popular when it comes to wastewater treatment in general. Carbon filters work by what’s known as adsorption. Carbon, which is typically found in the form of activated charcoal, works to attract any impurities in the water and creates a molecular film on the water’s surface containing all of the unwanted junk, which can then be filtered out using a particulate filter.
To learn more about using carbon to filter wastewater, check out this curriculum from Sustainable Sanitation and Water Management training, titled Adsorption (Activated Carbon).
Water Sanitation Methods
The final stage of most recirculation systems is water sanitation. If you’re planning on reusing wastewater for irrigating your cannabis, you want to be sure that it doesn’t contain any harmful bacteria or fungus. Reverse osmosis and carbon filter systems remove most bacteria, but not 100 percent of contaminants. It’s a good idea to have an additional means of water sanitation, particularly when you’re using wastewater. There are a number of methods cannabis growers can use to sanitize wastewater for the final stage.
- Heat pasteurization: Just as it sounds, heat pasteurization uses high temps to kill bacteria in the water. Water doesn’t need to reach a boil to be pasteurized, which can save energy. “Household Pasteurization of Drinking-water: The Chulli Water-treatment System” in the Journal of Health, Population and Nutrition goes over how to kill specific bacteria and viruses at different temperatures and lengths of time.
- UV disinfection: Water exposed to high-intensity UV rays will become disinfected without the use of chemicals, and as such this has become a popular choice for wastewater treatment in cannabis grows, especially among growers who use UV pipes to sterilize water.
- Iodine: Adding iodine to water can act as a final step in sterilizing wastewater for recirc, and is safe for cannabis if the concentration is not too high.
- Hydrogen peroxide: Like iodine, hydrogen peroxide can be used to sterilize wastewater effectively, as long as there isn’t too high a concentration. Hydrogen peroxide also adds oxygen to the root system of cannabis. The downside to any chemical water treatment is that in high concentrations, it kills bad and beneficial bacteria and fungi, making it less than ideal for organic grows.
Using Reservoirs For Cannabis Wastewater
No matter what methods you use to treat your cannabis wastewater, you’ll need somewhere to store it. There are a couple options out there for those looking to store their water, from tiny under-the sink-tanks, to backyard habitats.
Tanks For Cannabis Wastewater
Perhaps the most common storage method for any filtration system is a tank. For reverse osmosis systems, all you’ll need is a small tank, from three to five gallons. Of course, larger tanks for storage and further filtration are optimal. The most common choice for these larger tanks are 50-gallon plastic storage units, though depending on your needs, there are up to 950-gallon plastic, stainless steel and septic-style tanks as well. Research your options and what’s needed for your grow to make the right choice for you.
Ponds For Cannabis Wastewater
One option for water that is not reusable for your cannabis grow, yet is no longer toxic, is a retention pond. This is a choice many growers make, especially if they have lots of land or additional gardens that also need watering. Rather than pouring the water down the drain, a retention pond can create a wildlife habitat that allows the water to reenter the water cycle in a natural manner. It can also offer natural filtration. Wetlands can remove contaminants instinctively and are used at wastewater treatment plants all over the world.
You can learn more about the role of wetlands in wastewater treatment in the University of Florida’s article, titled “Wastewater Treatment Wetlands: Contaminant Removal Processes.”
Cannabis is no doubt an up and coming industry. So, why not use this opportunity to create an industry from scratch that is ecologically sound? Disposing of, and even reusing wastewater mindfully, is one way to make your cannabis grow more environmentally friendly and sustainable.