Broader implementation of water reuse is becoming vital to maintaining economic growth and quality of life in the state of Florida. Recent changes to laws and regulations are being developed to meet these needs. Recently, Anna Ness, PE, an environmental engineer who has worked on water reuse pilots throughout her career, spoke with CDM Smith’s nationally-recognized expert Dave MacNevin, Ph.D., PE, LEED® AP about the state of reuse in Florida, newly-proposed potable reuse regulations, and how potable reuse will fit in Florida’s water future.
This transcript has been condensed and edited for clarity.
Anna Ness: It's a really exciting time to be involved with reuse in Florida. What’s your opinion of the draft potable reuse regulations?
Dave MacNevin: These new regulations are the result of a multi-year effort by WaterReuse Florida and the Florida Potable Reuse Commission, that began with proposing a technical framework for the regulations, and I think the recent surge in interest in potable reuse is a reflection of the growth that we've seen in Florida.
As a state, we use an estimated 6.4 billion gallons of water per day, and our population continues to grow. Over the next 20 years, we're expecting to add almost five million new residents, with our population getting up to over 26 million.
So, commensurate with that, our water needs are going to grow from 6.4 billion gallons per day by another billion gallons per day. The state has looked at this, and it's a real challenge to understand where this new water is going to come from to support our economy and the way of life we enjoy.
Ness: Can you talk about our experience with potable reuse in Florida, and are any utilities doing pilots or full-scale demonstrations in Florida?
MacNevin: Absolutely. Even though there aren't any potable reuse projects in our state, we are leading in various forms of water reuse. There are rapid infiltration basin projects, and we have public access irrigation. However, we don't actually have any full-scale potable reuse projects for water supply.
That being said, even though we don’t have any full-scale potable reuse facilities, many people are surprised to learn that Florida has been a leader in pilot testing of potable reuse. Since the 1980s, 17 different Florida utilities have run pilot tests of various potable reuse treatment processes for various reasons. While no utilities have constructed such a facility yet, what has been accomplished is that, as a state, we have accumulated an enormous body of data and operating experience with advanced treatment technologies. What we’ve seen time and again with each of these projects is that appropriate treatment technologies reliably produce purified water that is safe and of excellent quality for use as a potable supply. When you look at the pilot testing reports, you see consistent removal of pathogens and emerging contaminants.
Turning to the recently proposed regulations, one provision requires utilities to pilot test their proposed treatment process for a minimum of 12 months. The rules should change to allow utilities to test for a shorter time, especially when they are looking at advanced treatment technologies, like membrane filtration or reverse osmosis, that have already been proven at more than a dozen UF facilities. The new rules should acknowledge the wide base of experience with advanced treatment technologies that we have accumulated through the hard work of so many utilities pilot testing this approach.
Ness: Different states regulate potable reuse differently. How do Florida's new rules address pathogens?
MacNevin: The new contaminants require the advanced water treatment facility and any downstream water treatment plant to meet certain log-removal targets for the enteric viruses, Giardia, and Cryptosporidium. The requirements are 12-log removal of viruses, 10-log removal of Giardia, and 10-log removal of Cryptosporidium (Crypto). And they call for that being measured from the headworks of the raw wastewater treatment plant, all the way to the point of entry in the water distribution system.
There is a very significant body of data on Crypto and Giardia that has been collected over the past 30 years in Florida. It's actually the largest dataset of its kind for Crypto in reclaimed water that's available. Florida started requiring utilities who produce reclaimed water to begin measuring protozoa in reclaimed water, and through the investment and hard work of hundreds of Florida utilities we now have a very clear picture of protozoa in reclaimed water and what some of the most extreme values can be. What Greta Zornes and I have learned from looking at that is that the quality of Florida's reclaimed waters is good in terms of Crypto and Giardia. Comparable to surface water supplies, in fact. That being said, we need more data on viruses in reclaimed water. As an industry, the water reuse community simply does not have as much virus data for reclaimed water. This is partly because it is more time consuming and costly to measure viruses in water. That being said, I think the bottom line is that the proposed regulations should be revised to provide utilities’ flexibility for their pathogen treatment goals and how they get credits, whether they start measuring from the headworks, which can be challenging due to solids interference, or measuring pathogen removal in reclaimed water, which most utilities already have plenty of protozoa data from that location. The bottom line is public health must be protected. So as long as you get to the same risk benchmark used in the drinking water regulations, less than 1 in 10,000 annual risk of gastroenteritis, you're going to maintain the same level of public health protection that utilities achieve under current drinking water rules.
Many people are surprised to learn that Florida has been a leader in pilot testing of potable reuse...as a state, we have accumulated an enormous body of data and operating experience with advanced treatment technologies.
Ness: I know in other studies, we've learned that advanced treatment trains with reverse osmosis as well as alternative treatment technologies both produce very high quality, purified water. We know that disinfection byproducts are important to monitor. How do the new rules address unregulated contaminants and constituents of emerging concern [CECs]?
MacNevin: The advanced treatment trains do a great job getting rid of the different CECs, pharmaceuticals, and personal care products. But I think one of the biggest issues potentially, that a lot of people may not realize, is that disinfection byproducts can still be a concern. We've seen from piloting here in Florida and some full-scale facilities in California that sometimes there can be issues with bromate formation, even in RO-based treatment trains.
So even though these advanced treatment technologies do a remarkable job removing most organics, it's important to consider all the entire spectrum of chemical contaminants, and design the treatment train with appropriate safeguards, redundancy, and online monitoring through design, startup, and ongoing operations to ensure that you wouldn't have an MCL [maximum contaminant level] exceedance. So, I think DBPs are important to keep in mind. The good news though is usually TTHMs [total trihalomethanes] and HAA5 [haloacetic acids 5] are both low in purified water, with low formation potential, which is great meeting disinfection byproduct limits in the distribution system.
Another thing related to chemicals that is important is that there needs to be treatment provided for contaminant spikes in the reclaimed water. That leads into the whole discussion of the importance of online monitoring. And we've looked at strategies to address potential concerns of changing water quality.
Ness: What surprises you the most in the draft legislation?
MacNevin: I think the new legislation was very bold in the pretreatment program that it proposed. It called for an advanced online monitoring system for industrial pretreatment with event detection systems and operator warning system. While details are limited on how this would be enforced, on the face, it was very ambitious to propose, because this provision is calling for utilities to use technologies that would likely need to be based on artificial intelligence technologies that may still be maturing. I think it's a worthy ambition; however, the requirements need to be balanced to provide public health protection, while keeping the requirements achievable using commercially available tools.
We've seen from some of the recent headlines in February 2021 the importance of security at water plants, and we’ve also seen headlines about backflow and organic chemicals finished drinking water. So, with a robust online monitoring system at the advanced water purification facility, utilities and customers can be confident that the quality coming out moment to moment from this system and know that public health is being protected from pathogens and harmful chemical compounds.