Thousands of advanced septic systems in Florida yards may not remove as much pollution as they advertise, industry professionals say.
So-called “biofilter” systems use wood chips to extract nitrogen from toilet flushes and laundry cycles to keep the nutrient out of waterways, where it can cause environmental damage. They’re one of three advanced septic options the state will require in tens of thousands of properties by 2030 and more after that. Counties give homeowners state grants to install them.
But septic experts say they’re missing data.
Damann Anderson led the consulting team the state hired to design affordable, nitrogen-reducing septic options in 2009. His crew reported promising reductions with biofilters, he said, but those results were preliminary, meant to be refined by the state through further testing.
“I’m like, my God, I hope they did some more work before they just went hog wild with these things,” he said.
State records show limited testing.
Septic designers, installers and testers say the state had limited data on how well biofilters worked and none on how long they lasted before allowing contractors to dig over 5,500 of them near some of the most environmentally sensitive waters of the state.
Unlike other advanced systems, biofilters don’t require routine inspections. They aren’t installed with any monitoring equipment, meaning pollution can easily go undetected. Nutrients can escape even if toilets are flushing like normal. Homeowners may not notice, but waters will. What went wrong?
Design
Florida has more septic systems than any other state, about 2.6 million according to the Florida Department of Environmental Protection.
That’s a remnant of the state’s rural roots before its 1950s population boom, said Mary Lusk, a University of Florida professor in soil, water, and ecosystem sciences.
Backyard wastewater treatment “was a really viable technology for a sparsely populated place,” she said. Conventional septic systems did a good job of removing pathogens and keeping neighbors safe, but weren’t designed to capture nutrients.
“I don't think anybody was making the connections between septic systems and water quality at that time,” Lusk said.
That changed in 1983 with Florida’s Water Quality Assurance Act: a landmark environmental law clamping down on pollution. The Florida Department of Health contracted a team of researchers who found that even when they were working properly, septic systems were spewing nutrients into the groundwater below.
Anderson moved from Wisconsin to Florida to be the team’s on-the-ground specialist. He continued to work with the state in 2009, through a different firm, to work on a fix. That firm, Hazen & Sawyer, spent $4.7 million and six years researching, ranking and refining options.
Biofilters were the most similar to conventional systems. They used microbe-packed layers of sand and wood chips to convert groundwater-polluting forms of nitrogen into nitrogen gas. Prototypes were relatively cheap and easy to install. Other systems removed more nitrogen, but biofilters met the state’s requirement of a 65% reduction and tripled the efficacy of conventional systems, which sits around 30%.
The Department of Health’s final report to the Florida Legislature cautioned “prior to implementing any of these systems, several actions need to occur.” That included setting up experimental residential systems to determine how long wood chips last, how to track performance and “long term needs for maintenance and monitoring.”
“We had only looked at a couple of them,” Anderson said. “And it's like, ‘Okay, you guys, that's going great, but you need to put 10 or 20 more in and monitor them.’”
That didn’t happen.
Officials created installation codes before pilot sites. By the time state agencies started their own tests on biofilters, contractors had already been digging them into Florida yards for three years.
The Florida Department of Environmental Protection took control of the state’s sewage program in 2021.
The agency didn’t respond to WUFT’s inquiries as to how many biofilters it has monitored and for how long. Its presentations list five test sites with average nitrogen reductions from 42% to 83% and note “more data is required from more systems to provide a more robust evaluation of the INRB (biofilter) performance in Florida.”
Anderson worries the handful of systems the state has tested don’t justify the thousands contractors have installed. “I haven’t seen the data to increase my confidence,” he said.
Installation
Greg Mayfield, president of the Florida Onsite Wastewater Association, said he’s skeptical that real-world systems are achieving the results Hazen & Sawyer’s report previewed.
“What they tested and what’s in the field are two totally different things,” Mayfield said.
Installation code doesn’t require key parts of the report’s design, such as a liner, a particular blend of wood chips and sand and hole-lined pipes that spread water evenly throughout the system.
Biofilters without those things could have some sections removing lots of nitrogen and others barely trapping pollutants at all, said Anthony Gaudio, a retired septic tank installer of 50 years and former chair of the Wakulla Springs Alliance.
In more extreme cases, the systems can fail.
Brian Miller started his Tallahassee-based septic company in 2005, branching off from his family’s business as a third-generation contractor.
He’s installed about 1,000 biofilters in North Florida despite concerns about their efficacy.
“I don't think they've been out long enough to know if they work or not,” Miller said. “The way the state has the system designed is really set up for failure.”
To build a biofilter, Miller digs a swimming-pool-sized hole in a homeowner’s yard and lines it with wood chips and sand. Wastewater can cause the wood chips to rot as it seeps through, Miller said, causing the ground to sink and settle.
Water can’t move through the sunken system, so toilets stop working. That’s happened in about 100 systems that Miller has installed, despite them all passing inspection.
He expects more to fail as microbes naturally eat away at the wood chips, but doesn’t know how long that will be. No studies have definitively determined how long biofilters last.
Inspection
Various Florida laws require homeowners who live near sensitive waterways to upgrade their septic systems or connect to sewer lines. Exact requirements and deadlines vary by municipality but affect tens of thousands of current residents, plus future lots, too.
Homeowners can typically choose between different types of advanced septic systems. Aerobic treatment units, which operate like mini wastewater treatment plants, are the most popular.
They’re rigorously tested and third-party certified, Gaudio said, but raise electricity bills by about $20 per month. They also require operating permits and maintenance agreements, which each come with annual fees and inspections.
“Nobody wants that,” Miller said. “They don’t want the fees and they don’t want the invasion of privacy.”
Biofilters don’t require any continuous maintenance or monitoring.
Independent contractors inspect the system twice during installation. That gives it the greenlight to operate indefinitely.
“That's what people like,” Miller said. “But people don't know that it's still being tested.”
Multiple municipalities are spending state dollars to help homeowners install advanced systems, including biofilters.
Alachua County received grants from FDEP to offer $10,000 rebates for biofilters and $16,000 rebates for aerobic systems, about full installation costs, in two area river basins.
A month after announcing the program, “we have about 200 people that at least have expressed interest,” said Stacie Greco, the county’s water resources program manager.
On Oct. 28, Gov. DeSantis announced more than $10 million in additional grant funding for septic upgrades in Alachua, Citrus, Leon, Marion and Volusia counties.
If past installation trends hold, a significant portion of that funding will go towards biofilters.
That worries Anderson.
“I just don't want to see all this money spent and then we don't gain what we think we're gaining for water quality,” he said.
