It’s Time to Clear the Air on “Carbon Filtration”

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July 10, 2020

Hi, I am Dr. William Vizuete, Chief Scientific Officer at Pacific Environmental Analytics (PEA). At PEA, we work with both new and experienced commercial cannabis cultivators and processors, but one thing we continue to hear when listening to concerns about indoor air quality and odor is a misunderstanding of the proper approach to air filtration. In this month’s Better Business Column, we are going to take a closer look at “carbon filtration” and why it isn’t a one-size-fits-all solution.

As a preliminary matter, in this article we are going to focus on the filtration of molecules as opposed to particulates (e.g., dust or smoke) which are most often mitigated with MERV-rated HEPA or other similar filtration systems. Further, for cannabis operations, we are most concerned with one particular type of molecule – biogenic volatile organic compounds (BVOCs) (e.g., terpenes) emitted by the cannabis plant. There is no doubt that the use of carbon filtration to mitigate indoor cultivation and processing odors from BVOCs has been successful for decades. In fact, it is not uncommon to hear, “carbon kept my grow off the radar and kept me out of jail.” However, the yesteryear approach of simply installing a few “carbon can fans” in a grow or processing facility is insufficient for today’s modern commercial cannabis cultivation and processing operations. Moreover, even the term “carbon filtration” itself is misleading as it refers only to the media in the filter itself rather than the odor control process and underlying science. I will explain.

To begin with, let’s agree that the correct term is actually not “carbon filtration”. We’re not filtering carbon, we’re filtering molecules. The correct term is “molecular filtration” and the most common media for filtering cannabis BVOCs is activated carbon. The effectiveness of molecular filtration systems depends on the particular filter media’s ability to utilize adsorption. Adsorption is the scientific process by which molecules of a gas or liquid or solute adhere to a surface – in the case of a molecular filtration system, this refers to BVOC molecules adhering (or attaching) to a particular media filter such as activated carbon resulting in their sequestration. To put it simply, the more adsorptive the media used in the system, the more effective its filtration of BVOCs will be.

So now you understand how a molecular filtration system works, but what are the key factors cultivators and processors should be looking at when selecting and sizing a molecular filtration system? Two of them are readily available – plant count and the size of the indoor space – while the third, the BVOC emission types, and fourth, the gas-phase BVOC emission rates of the particular cannabis strains, are not. In order to determine the gas-phase BVOC emission rates along with the types of BVOCs that are or will be emitted from the plants to be handled by the cultivator or processor, a leaf enclosure study is necessary. While it could be the subject of its own article, to put it simply, conducting leaf enclosure measurements is a scientific method to collect samples of the actual BVOCs being emitted from a cannabis plant’s leaves at various stages of the plant’s lifecycle for analysis and calculation of the gas-phase emission rates. Leaf enclosure studies are a great tool for developing a complete quantitative profile of a cannabis operation’s BVOC footprint and yield much more accurate data than simple ambient air sampling.

Once armed with the critical data – plant count, space size, BVOC types and gas-phase emission rates –, cultivators and processors can select an appropriate, effective molecular filtration system based on their operation’s BVOC profile and load. However, this is also no easy task as not all molecular filtration systems – even those relying on the use of activated carbon media – are created equal and the key to effective indoor BVOC control through molecular filtration is a properly engineered system that utilizes specially-selected media optimizing potential adsorption based on the specific type and volume of BVOCs likely to be emitted by the particular strains of cannabis. Unfortunately, this level of detail is not often considered when the selection of molecular filtration systems and media is left to the HVAC system design team rather than an air quality and/or odor control professional with experience handling the unique needs of commercial cannabis. Overlooking any of the key factors is risky as not every filtration system will be equipped to handle the types or volume of BVOCs found in today’s large scale commercial cannabis facilities featuring multiple strains. An ineffective molecular filtration system can lead to not only odor issues and potential indoor air quality concerns but also ozone contributions depending on the location of the operation.

As you can see, there is much more to consider when selecting an appropriate molecular filtration system for your indoor cultivation or processing facility than simply deciding how many “carbon can fans” to install. Further, while activated carbon is likely to be utilized in most such systems, not all carbon media is created equal when it comes to its effectiveness of targeting and remediating BVOC emissions of different types and volumes. Given the critical importance of understanding their BVOC emission profile and load, commercial cannabis professionals would be wise to seek professional guidance on their molecular filtration options as well as the underlying data for consideration before leaving this decision and ultimately their investment in the hands of the HVAC design team alone.