Experts Warn Florida's State-Subsidized Septic Biofilters Might Not Work as Intended

Florida is paying homeowners thousands of dollars apiece to install a type of nitrogen-reducing septic system that some of the state's own experts say has never been tested enough to prove it works, according to an investigation by WUFT reporter Rose Schnabel published Nov. 4. The systems, known as in-ground nitrogen-reducing biofilters, are one of the approved options for tens of thousands of properties near springs and other sensitive waters that state law requires to upgrade by 2030 and beyond.

The concerns land days after Gov. Ron DeSantis announced $100 million for 45 water quality, springs and water supply projects on Oct. 28, including septic upgrade money for several counties. If installation trends continue, WUFT reported, a large share of the new septic funding will go to biofilters.

What a biofilter is

A conventional septic system removes pathogens well but was never designed to capture nutrients, and it removes only about 30% of the nitrogen in household wastewater, according to WUFT. That nitrogen seeps into groundwater and feeds the algae that cloud Florida's springs, rivers and lagoons.

Biofilters add a treatment layer beneath the drainfield. The original design used layers of sand and wood chips packed with microbes that convert nitrogen from toilet and laundry water into harmless nitrogen gas. The state counts the systems as meeting its standard of a 65% reduction in nitrogen, compared with about 30% for a conventional tank.

The Florida Department of Environmental Protection recognizes three kinds of enhanced nutrient-reducing systems: in-ground nitrogen-reducing biofilters, aerobic treatment units certified to the NSF 245 standard, and performance-based treatment systems, according to the agency's published guidance. DEP materials note that biofilters do not require a maintenance contract or an operating permit, a big part of their appeal to homeowners.

Aerobic treatment units, the most popular alternative, are rigorously tested and certified by third parties. But they raise electricity bills by about $20 a month and come with operating permits, maintenance agreements, annual fees and inspections, according to Anthony Gaudio, a retired septic installer with 50 years in the business and a former chair of the Wakulla Springs Alliance.

Where the money is going

DEP's Septic Upgrade Incentive Program pays up to $10,000 per home to add nitrogen-reducing features to existing septic systems in priority areas of basin management action plans, the state's cleanup blueprints for polluted waters. The statewide program stopped accepting new applications after its funding ran out, and DEP has been setting up county-specific programs with Citrus, Hernando, Leon, Marion, Orange, Pasco, Seminole, Volusia and Wakulla counties, according to the agency's website.

The Oct. 28 announcement in Crystal River split $100 million evenly between the Springs Restoration Grant Program and the Alternative Water Supply Grant Program. The springs half, $50 million for 23 projects, is expected to cut nitrogen pollution by more than 55,000 pounds a year, according to WFTV. Awards included $3 million for Citrus County to convert homes from septic to sewer and upgrade remaining systems near Chassahowitzka-Homosassa Springs, Kings Bay and Crystal River Springs, and $4 million for Volusia County's septic upgrade incentive program. The state says it has invested $480 million in springs restoration since 2019.

WUFT reported the announcement included more than $10 million for septic upgrades in Alachua, Citrus, Leon, Marion and Volusia counties.

In Alachua County, DEP grants offer rebates of $10,000 for a biofilter and $16,000 for an aerobic system, roughly the full cost of installation, in two river basins. County materials say properties in the Santa Fe River and Silver Springs basins are covered. About a month after the program launched, roughly 200 residents had expressed interest, said Stacie Greco, the county's water resources program manager.

The law driving the upgrades

Florida has about 2.6 million septic systems, more than any other state, according to DEP. Several state laws now push homeowners near sensitive waters to upgrade or hook up to sewer.

House Bill 1379, passed in 2023, expanded the area of each Outstanding Florida Spring cleanup plan that must have a septic remediation plan from the priority focus area to the entire basin, according to a Florida Senate bill summary. Where sewer is not available, new septic systems on lots of one acre or less in those areas must be enhanced systems that achieve at least 65% nitrogen reduction.

The same law created the Indian River Lagoon Protection Program, covering the Banana River Lagoon, Central and North Indian River Lagoon and Mosquito Lagoon cleanup areas. Since Jan. 1, 2024, new septic systems there have been barred where sewer is available. By July 1, 2030, properties in the lagoon program area with existing septic systems must connect to sewer or upgrade to an enhanced system that reduces nitrogen by at least 65%, according to the Senate summary.

Deadlines and requirements vary by community, WUFT reported, and they touch tens of thousands of existing homes and future lots.

Why experts are worried

The biofilter design grew out of state-funded research. In 2009, the state hired a consulting team at the engineering firm Hazen and Sawyer to develop affordable nitrogen-reducing options. The firm spent $4.7 million and six years researching and ranking alternatives, according to WUFT. Biofilters cleared the 65% bar, though other options removed more nitrogen.

Damann Anderson, who led that team, said the early results were promising but preliminary, and he expected the state to keep testing. "We had only looked at a couple of them," he told WUFT, adding that the state should have installed 10 or 20 more and monitored them. "I haven't seen the data to increase my confidence," he said. "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."

The Department of Health's final report to the Legislature warned that "prior to implementing any of these systems, several actions need to occur," including experimental systems at homes to learn how long wood chips last, performance tracking and long-term maintenance and monitoring plans. WUFT reported that did not happen. Installation codes were written before pilot sites were fully tested, and contractors had been installing biofilters for about three years before state agencies began their own tests. WUFT reported that contractors have now dug more than 5,500 of them near sensitive waters.

Greg Mayfield, president of the Florida Onsite Wastewater Association, said real-world results are likely far below what the research projected. "What they tested and what's in the field are two totally different things," he said.

One reason is that the state's installation code does not require several design features from the original research: a liner, a specific blend of sand and wood chips, and perforated pipes that spread water evenly. Without them, Gaudio said, a biofilter could remove a lot of nitrogen in some sections and barely any in others.

An installer's view from North Florida

Brian Miller, a third-generation contractor who founded his Tallahassee septic company in 2005, has installed about 1,000 biofilters in North Florida. He digs a pool-sized hole and fills it with wood chips and sand. Over time, he said, wastewater can rot the chips, the ground sinks, water stops draining and toilets stop working.

About 100 of his systems have failed that way despite passing inspection, Miller told WUFT, and he expects more as the chips break down. No study has determined how long biofilters last. "The way the state has the system designed is really set up for failure," he said.

Because biofilters require no routine inspections or monitoring equipment, a poorly performing system can leak nitrogen for years without anyone knowing. Independent contractors inspect them twice during installation, and after that they can operate indefinitely. Homeowners still choose them, Miller said, because they avoid the fees and the intrusion of aerobic systems. "But people don't know that it's still being tested," he said.

What the state says

DEP took over the state's septic program from the Department of Health in 2021. It did not respond to WUFT's questions about how many biofilters it has monitored or for how long.

DEP presentations list five test sites with average nitrogen reductions ranging from 42% to 83%, and they acknowledge that "more data is required from more systems" for a robust evaluation, according to WUFT. Some of those sites fall below the 65% standard the systems are credited with meeting.

What's next

With the 2030 lagoon deadline approaching and new springs grant money flowing to counties, the number of biofilters in the ground is likely to keep growing. The open questions for state regulators are whether DEP will expand field monitoring of installed systems, tighten the installation code to require the liner and other features from the original research, or steer subsidies toward systems with stronger performance data.

For homeowners in springsheds and the Indian River Lagoon watershed weighing a rebate, the choice for now is between a cheaper, maintenance-free biofilter whose long-term performance is unproven and a costlier aerobic unit with ongoing fees but certified results. The Florida Press will follow DEP's response and any changes to the program.