Stop the Sludge. Save Manatees. Support Composting.

Date: August 28, 2025
Author: Indianhead Soil & Compost Team
Category: Environmental Action, Community Empowerment, Sustainable Solutions

Why this essay—and why now

When you flush in St. Johns County, our treatment plants do an excellent job cleaning the water—
screening, settling, biological treatment, and disinfection. But the story doesn’t end there. Those
steps create a concentrated solid byproduct called biosolids (sewage sludge) that plants must remove
to keep operating. Florida’s Department of Environmental Protection (FDEP) explains that biosolids can
be used or disposed through several pathways and are regulated under Chapter 62‑640, Florida
Administrative Code.^FDEP
The U.S. EPA provides the federal framework and definitions for biosolids programs nationwide.^EPA

For years, much of Florida’s minimally treated Class B biosolids was land‑applied on pastures in the
Upper St. Johns River Basin after the state curtailed land disposal in the Lake Okeechobee watershed.
District scientists and advocates have since documented rising phosphorus in watersheds receiving
biosolids and field results showing storm‑event runoff from biosolids sites with roughly 9× more
phosphorus than comparable sites that did not use biosolids—fuel for harmful algal blooms.^{SJRWMD – Canion et al.}^{St. Johns Riverkeeper}

“We do not inherit the Earth from our ancestors; we borrow it from our children.” — David Brower

Manatees are the messenger

The Indian River Lagoon (IRL) has endured repeated harmful algal blooms fueled by nitrogen and
phosphorus from sewage, septic leakage, fertilizers, and stormwater. The blooms block sunlight,
killing seagrass—the primary food for Florida’s beloved manatees. During the 2020–2022
Unusual Mortality Event, starvation drove record manatee deaths as seagrass meadows collapsed.
Save the Manatee Club reports that more than 90% of seagrass biomass was lost in parts of the
lagoon and that thousands of acres of seagrass died due to nutrient pollution and blooms.^{Save the Manatee Club}
Florida researchers likewise tie decades of nutrient runoff to seagrass decline and the shift of
manatee diets toward algae during shortages.^{FIU / The Conversation}

The Florida Fish and Wildlife Conservation Commission maintains detailed mortality records and notes
the IRL starvation event started in December 2020. While emergency feeding and seagrass work have
helped, durable recovery depends on cutting nutrient inflows so light can return and seagrass can
re‑establish.^{FWC Mortality Stats}^{Save the Manatee Club}

What went wrong with sludge

Biosolids are nutrient‑rich—a reason land application took root. But they are an imbalanced
fertilizer in Florida’s sandy soils: when managers spread them to meet a pasture’s nitrogen needs,
they often over‑apply phosphorus. Storms then flush bioavailable P and N into ditches, canals,
and rivers. SJRWMD field studies documented P runoff about nine times higher at biosolids sites,
and basin‑scale analyses show phosphorus concentration increases that track application rates over
time—evidence that practice and impact are linked.^{SJRWMD – Canion et al.}^{SJRWMD – Dobberfuhl & Marzolf}

Landfilling the material is no panacea: organic wastes decompose anaerobically in landfills and produce
methane, a potent greenhouse gas. EPA identifies municipal landfills as the third‑largest source of
human‑related methane in the U.S. and notes that wasted organics dominate the landfill stream; composting
is a key action to prevent methane and return carbon to soils.^{EPA – Composting}^{EPA – Benefits of Using Compost}

The new risk you can’t see: PFAS in biosolids

Per‑ and polyfluoroalkyl substances (PFAS) are “forever chemicals” used in many products and firefighting foams.
Wastewater treatment plants are not designed to remove PFAS, so they tend to partition into the solids; land
application then spreads PFAS onto fields, with pathways to groundwater, crops, and livestock. In Florida,
biosolids are not routinely tested for PFAS, and the St. Johns Riverkeeper and Waterkeepers Alliance have urged
the state to require testing and limits to reduce risk to farmers and rural communities.^{WUSF / Central Florida Public Media}
A recent statewide assessment by 1000 Friends of Florida similarly flags PFAS as a major information gap in
biosolids oversight.^{1000 Friends of Florida}

Solutions are emerging: the City of Orlando, with FDEP support, is piloting supercritical water oxidation
(SCWO) to destroy PFAS in sludge and reduce solids volume—evidence that better, safer solids management is
both possible and practical when communities invest in modern systems.^{EPA Case Study – Orlando SCWO}^{City of Orlando}

Composting: science‑backed solutions for Florida soils and waters

EPA’s 2025 synthesis of the scientific literature concludes that the overarching consensus is clear:
using compost improves soil health across applications—from agriculture to stormwater retrofits to ecosystem
restoration. Benefits include improved infiltration and water holding capacity, aggregate stability, nutrient
cycling, vegetation performance, and reduced erodibility. Composting also helps decrease greenhouse gases
by avoiding landfill methane and by enabling fertilizer reduction.^{EPA – Environmental Value of Applying Compost (2025)}^{EPA – Program Page}

Peer‑reviewed work further shows that compost amendments can increase soil carbon stocks, an important
co‑benefit as Florida communities plan for resilience. UC Berkeley and UC Davis teams have documented deep
soil carbon gains from compost additions on rangelands and croplands, providing a climate dividend alongside
water‑quality protection.^{Silver et al., California 4th Climate Assessment}^{UC Davis – Compost & Carbon}

For St. Johns County, compost‑amended soils are perfectly matched to our challenges: sandy textures, intense
rainfall, and expanding reuse programs. St. Johns County Utilities explains that reclaimed water is highly treated
and safe for contact but still retains nitrogen and phosphorus; compost‑rich soils buffer those nutrients, reduce
irrigation needs, and curb runoff—exactly what our waterways require.^{St. Johns County – Reclaimed Water}^{EPA – Compost Soil Health}

What about “legacy phosphorus”?

In watersheds with years of over‑application, soils can become saturated with phosphorus. Even after new inputs
stop, those soils may continue to leach P for years—a phenomenon scientists call legacy P. SJRWMD’s watershed
trend work and field studies show that recovery can begin once applications decline, but there’s a lag as legacy
P bleeds off.^{SJRWMD – Canion et al.}^{SJRWMD – Dobberfuhl & Marzolf}
The right response is twofold: stop new loads (replace land application and landfilling with composting
and destruction technologies), and remediate hotspots with restoration tools. Compost is a
foundational piece because it immediately reduces future pulses and stabilizes nutrients in soils
where we live, work, and grow.

The dollars and sense

A recent economic analysis estimated at least $1.12 billion in potential cleanup costs over the next four
decades tied to land‑applied biosolids in the Upper St. Johns River Basin. That figure does not include
PFAS liabilities or broader health costs. The “cheap” disposal of yesterday becomes tomorrow’s
taxpayer bill; composting and modern treatment are how communities keep value local and costs under
control.^{Jax Today}^{The Invading Sea / 1000 Friends of Florida}
EPA also notes that organics recycling and compost markets create local jobs and reduce methane—a real
win‑win for resilient economies.^{EPA – Composting}

Blog 18: Stop the Sludge. Save Manatees. Support Composting.