Rewilding the Lagoon: Building with Nature to Remediate Municipal Sludge Landscapes

Originally posted on LinkedIn: https://www.linkedin.com/posts/s-bennett-drane-pe-phd-b7b747268_my-personal-passion-is-the-use-of-plants-activity-7464443921222295553-Fv2t?utm_source=share&utm_medium=member_desktop&rcm=ACoAAEGbDc8BMaiJLl2vx3D5olIBfR_sP6wX8X8

Across the Great Lakes region—and especially in northern Ohio—many municipalities are managing aging sewage lagoons constructed decades ago. These sites often contain stabilized but contaminated sludge with:

• Potentially toxic elements (Zn, Cu, Pb, Cr, Cd, Ni)

• Persistent organic pollutants (PAHs, PCBs, PCDD/F)

• Surfactants, phthalates, endocrine disruptors

• Pharmaceuticals and personal care products

• Pathogens and residual nutrients

Traditionally, the engineering solution has been straightforward: Excavate. Truck. Landfill. Replace. What a waste. Excavation is expensive, carbon-intensive, disruptive, and fundamentally linear. It removes nutrients and organic matter that are, paradoxically, valuable ecological resources.

There is another path; one rooted in rewilding, build-with-nature engineering, and phytotechnology.

From Waste to Substrate: Reframing Sewage Sludge

Dewatered sewage sludge typically contains:

• 50–70% organic matter

• 3–4% nitrogen

• 0.5–2.5% phosphorus

• Essential micronutrients

In other words, sludge is not merely waste. It is a nutrient reservoir requiring ecological stabilization and contaminant management.

The challenge is not whether sludge has value, but in how to unlock that value safely.

The Case for Rewilding as Engineering

Rewilding, in this context, does not mean abandonment. It means designed ecological succession.

It means:

• Reshaping lagoon basins into vertical and horizontal flow polishing wetlands

• Establishing engineered redox gradients

• Incorporating biochar and carbon amendments

• Deploying fungal and microbial consortia

• Planting high-biomass phytoremediators

• Transitioning toward native riparian forests

This is process engineering using biology as infrastructure and my personal calling. If you are interested in this idea, please read my Master's Thesis available on my website: Efficiency of Microbes, Fungi, and Plants in Passive Removal of PAH and Metals [ https://drive.google.com/file/d/16m_icb1tXxfIuyBUwwvui6B-eYGyxzMK/view?usp=drive_link].

The Engineering Framework

1. Hydrologic Retrofitting

Old lagoon cells can be reconfigured into:

Vertical Flow Wetlands

• Promote aerobic decomposition

• Enhance nitrification

• Accelerate pathogen die-off

Horizontal Subsurface Flow Wetlands

• Support denitrification

• Enable anaerobic PCB dechlorination

• Precipitate metals as sulfides

• Enhance rhizosphere-driven PAH degradation

Hydraulic residence time becomes the control variable while plants and microbes become the treatment plant.

 2. Biochar and Carbon Amendments

Biochar performs multiple engineering functions:

• Immobilizes bioavailable PAHs and metals

• Reduces ammonia volatilization

• Enhances soil structure

• Creates microbial habitat

• Sequesters carbon long-term

Rather than removing contaminated soil, we reduce bioavailability and stimulate degradation pathways.

 3. Fungi: The Overlooked Remediation Engine

White-rot fungi such as Trametes versicolor and Phanerochaete chrysosporium produce extracellular enzymes capable of degrading:

• PAHs

• PCBs

• Endocrine-disrupting compounds

These organisms perform oxidative chemistry that conventional treatment struggles to replicate economically.

Mycelium becomes a catalytic network woven through the soil profile.

 4. Arbuscular Mycorrhizal Fungi (AMF)

AMF increase root surface area and improve:

• Phosphorus uptake

• Drought and water stress tolerance

• Metal tolerance

• Reduced heavy metal translocation to shoots

In degraded soils, AMF inoculation can dramatically improve plant establishment and remediation efficiency. Rewilding without fungi is incomplete.

Plant Systems for Northern Ohio and Western Pennsylvania (Lake Erie Watershed)

A build-with-nature approach must be regionally adapted.

The area's glacial tills, clay soils, freeze–thaw cycles, and high water tables favor:

Early Phytoremediation Phase (Years 1–8)

• Hybrid poplar (high evapotranspiration, Zn reduction)

• Black willow (waterlogging tolerance)

• Sandbar willow (shoreline stabilization)

• Sunflower (strong Zn, Cu uptake)

• Switchgrass (deep root stabilization)

Wetland Polishing Species

• Typha latifolia

• Schoenoplectus tabernaemontani

• Carex stricta

• Juncus effusus

These species oxygenate rhizospheres, stabilize sediments, and support microbial biofilms.

Transition to Native Riparian Forest (Years 5–20)

• Silver maple

• Swamp white oak

• River birch

• American sycamore

• Red oak and bur oak

This is succession as strategy, guided by humans, but left up to the forest and rivers.

 Economic Reality: Nature Is Not the Expensive Option

For a 12-acre lagoon site, a 20-year conceptual comparison shows:

Excavation + Disposal

• $13–21 million

• Carbon-intensive

• No ecological return

• Permanent nutrient loss

Ecological Retrofit

• $5.7–6.9 million

• Lower lifecycle cost

• Carbon sequestration

• Habitat restoration

• Nutrient recovery

• Reduced long-term liability

Rewilding is not idealism, it is cost-competitive infrastructure with social, ecological, and political threads that can make communities more resilient and more independent.

Addressing the Hard Questions

What about metals?

• Phytoextraction (sunflower, poplar)

• Biochar immobilization

• Sulfide precipitation in anaerobic zones

• Mycorrhizal metal tolerance mechanisms

What about PAHs and PCBs?

• Fungal oxidative degradation

• Anaerobic microbial dechlorination

• Rhizosphere co-metabolism

• Sorption to biochar

What about pathogens?

• Aerobic drying

• UV exposure

• Freeze–thaw cycles

• Microbial competition

What about groundwater risk?

• Controlled hydraulic gradients

• Bioavailable contaminant monitoring

• Redox management

• Long-term adaptive monitoring

This is engineering discipline applied to ecological systems.

Beyond Remediation: Regenerative Infrastructure

A rewilded lagoon becomes:

• A carbon sink

• A nutrient recovery system

• A flood buffer

• Pollinator habitat

• Riparian corridor

• Community green space

• A climate adaptation asset

The site transitions from liability to infrastructure.

The Philosophical Shift

Traditional environmental engineering often treats biology as a constraint whereas rewilding treats biology as the primary tool. This lets us change the conversation from:

“How do we remove this problem?”

To:

“How do we guide ecological succession to solve it?”

The difference is profound, not only from a cost and engineering approach, but from a community redevelopment and reconnection with nature requirement.

 Why This Matters Now

Lake Erie continues to face nutrient loading challenges. Municipal budgets are constrained. Landfill capacity is finite. Climate resilience is urgent. Rural communities are more and more left out of infrastructure conversations, even as those communities lose touch with their natural resources and forest roots.

Rewilding lagoon systems:

• Reduces nutrient export

• Sequesters carbon

• Restores hydrology

• Supports biodiversity

• Costs less over time

This is not anti-engineering, it is the evolution of engineering. And frankly, given the cost of traditional infrastructure solutions, this should be a first choice instead of a poor 'green' alternative chosen more for optics than practicality.

Municipalities, consulting engineers, watershed planners, and regulators should consider:

• Phytoremediation as primary treatment, not pilot novelty

• Mycorrhizal inoculation as standard practice

• Biochar as structural amendment

• Wetlands as active infrastructure

• Successional design as a 20-year asset plan

We have the ecological science.

We have the engineering tools.

What we need is the willingness to build with nature instead of against it.