What Are PFAS?

Per- and polyfluoroalkyl substances — commonly known as "forever chemicals" — are a group of thousands of synthetic compounds characterised by extremely strong carbon-fluorine bonds. That bond strength is what makes them useful (non-stick coatings, water-repellent textiles, food packaging, firefighting foams) and what makes them persistent: they do not break down meaningfully in the environment, in water treatment, or in biological systems.

PFAS enter wastewater systems from two primary pathways. The first is legacy contamination from aqueous film-forming foams (AFFF) used historically in firefighting and training exercises. Sites where AFFF has been used — airports, military bases, fire stations — can carry significant PFAS loading in soil and groundwater that eventually reaches municipal wastewater networks. The second, lower-concentration pathway is the diffuse contribution from consumer products: food packaging, textiles, personal care products, and industrial surfactants that collectively introduce PFAS into domestic wastewater at detectable levels.

The science on PFAS toxicity is still developing, but the direction is clear. Two specific compounds — perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) — were addressed by the Stockholm Convention on Persistent Organic Pollutants. They are persistent, bioaccumulative, and toxic to both aquatic and terrestrial organisms. Shorter-chain PFAS compounds, which replaced PFOS and PFOA in many commercial applications, are increasingly being scrutinised as research catches up with their environmental fate.

New Zealand's PFAS Limits for Biosolids

The WEPS 2025 regulations introduce New Zealand's first national PFAS limits for biosolids destined for land application. To achieve Contaminant Grade 1 — and with it, the permitted activity status that allows land application without resource consent — biosolids must meet the following thresholds:

These thresholds are strict. To contextualise them: the limits are set in milligrams per kilogram of dry biosolid, which means even relatively low PFAS concentrations in incoming wastewater can accumulate in the solids fraction to levels that approach or exceed the threshold. For councils with legacy AFFF contamination in their catchment — or significant industrial inputs — these limits represent a genuine compliance challenge.

Biosolids that exceed these limits are classified as Contaminant Grade 2, requiring discretionary activity consent for land application. This is a more complex, costly, and uncertain regulatory pathway, and it eliminates the "consent-free" commercial positioning that makes a bio-fertiliser product viable at scale.

What the national survey found

Until 2023 New Zealand had no national picture of PFAS in groundwater. ESR's survey for the Environmental Protection Authority and the regional authorities sampled 131 wells across 11 regions — the first national-scale look at general groundwater resources rather than known contaminated sites.

The pattern is consistent and it is about infrastructure, not geography. Contamination concentrates where firefighting foam was used repeatedly: military bases, fire stations and training grounds, and airports. At RNZAF Base Woodbourne a plume extends roughly seven kilometres east into the confined aquifer beneath Blenheim, with five samples exceeding the drinking-water maximum acceptable value.

Sources

Why PFAS Is Particularly Difficult

Three characteristics make PFAS a fundamentally different compliance challenge from heavy metals:

Persistence. PFAS compounds do not degrade through conventional biological wastewater treatment. Unlike organic contaminants that break down during aerobic or anaerobic digestion, PFAS pass through treatment processes largely intact. They concentrate in the solid fraction — the sludge — rather than being destroyed or transformed.

Source diversity. While heavy-metal contamination in wastewater is typically traceable to specific industrial dischargers, PFAS enters from diffuse, ubiquitous sources. Every household contributes trace amounts through consumer products. This makes upstream source control — the traditional approach to managing wastewater quality — impractical for PFAS at any meaningful scale.

Analytical complexity. PFAS testing is more expensive and technically demanding than conventional contaminant analysis. The compounds are present at very low concentrations, they can contaminate sample containers and laboratory equipment, and the analytical methods are still evolving. Commercially available testing may not cover all relevant compounds, and regulatory definitions of which specific PFAS to measure are still being refined globally.

Co-Digestion: Managing PFAS Through Dilution

If PFAS cannot be destroyed during processing, and cannot be controlled at source, the remaining lever is concentration management. This is where co-digestion provides a mechanism that single-stream biosolids processing cannot offer.

Co-digestion processes sewage sludge alongside other organic feedstocks — food waste, green waste, agricultural residues, grape marc, industrial organic by-products. These co-feedstocks carry negligible PFAS concentrations compared to sewage sludge. When they are combined in the digester, the total PFAS mass is distributed across a larger total mass of digestate.

The mathematics is straightforward. If incoming biosolids carry PFAS at or near the Grade 1 threshold, and those biosolids constitute (for example) one-third of the total feedstock volume entering a co-digestion plant, the concentration of PFAS per kilogram of dry digestate is reduced by approximately two-thirds — assuming the co-feedstocks contribute negligible PFAS. This is a mass-balance outcome, not a treatment claim. The total PFAS in the system is unchanged; its concentration per unit of product is diluted.

For councils where incoming sludge is borderline Grade 2, co-digestion provides a processing pathway to Grade 1 compliance without requiring expensive PFAS-specific treatment technologies — most of which remain at pilot or early-commercial scale and carry significant capital and operating costs. The BRRP's multi-stream feedstock design makes this dilution mechanism intrinsic to the process, not an afterthought.

Can PFAS Be Destroyed?

Research into PFAS destruction technologies is active globally. Approaches under investigation include high-temperature incineration (above 1,100°C), supercritical water oxidation, electrochemical oxidation, sonochemical treatment, and photocatalytic degradation. Some show promise in controlled laboratory settings. Fewer have demonstrated cost-effective, scalable, reliable destruction at full commercial scale.

Thermal destruction at temperatures well above those used in conventional anaerobic digestion or thermal hydrolysis is one pathway. Gasification technologies operating above 1,000°C can break the carbon-fluorine bond. Alimentary Systems' partnership with Sierra Energy on the FastOx gasification platform represents a next-iteration approach: a potential pathway for treating concentrated PFAS residuals at temperatures that achieve molecular destruction, not merely concentration management.

For the current regulatory and commercial environment, however, the pragmatic approach is to design for Grade 1 compliance through co-digestion dilution as the primary mechanism, while monitoring the maturation of destruction technologies for future integration. The regulations are performance-based and technology-neutral — they do not prescribe how councils achieve compliance, only what the output must look like.

Two emerging removal pathways

Neither PFAS nor microplastics is destroyed by conventional treatment, and both concentrate in the solid fraction. Research on removing them is moving quickly. Two lines of work are worth councils' attention — one aimed at PFAS, one at microplastics — though both remain some distance from routine plant-scale use.

1. Coagulation and flocculation — for PFAS

Coagulation is a long-established chemical water treatment step: it destabilises suspended and colloidal impurities so they clump together and settle out. Standard practice uses metal salts such as alum or ferric chloride to neutralise the negative charges on fine particles, turbidity and organic matter.

Three variations are being developed to change that:

• Enhanced or modified coagulation. Traditional coagulants are combined with cationic surfactants or activated carbon, so that PFAS co-precipitates and is captured into settleable flocs rather than passing through.
• PRAS (pH-responsive amphoteric starch). A bio-based polymer carrying both amino and carboxyl groups, which responds dynamically to changes in water pH to bridge and settle pollutants — a lower-impact alternative to bulk synthetic coagulants.
• Electrocoagulation. Metal coagulant ions are generated in situ by electrical current instead of dosing external chemicals, which reduces the volume of chemical sludge the process creates in the first place.

2. Magnetic micro-robots — for microplastics

This second line of research addresses microplastics rather than PFAS. It matters here because microplastics accumulate in the same solid fraction, and because the two contaminants raise the same question for councils: what is actually in the material before it goes to land?

Microplastics are plastic particles five millimetres or smaller. In a short space of time we have gone from not knowing they existed to finding them nearly everywhere — in food, in everyday products, and in human organs, and in locations as remote as deep caves and the deepest parts of the ocean. They degrade soil quality, harm wildlife and disrupt natural nutrient cycles, and they move readily through food chains and across whole ecosystems. Because they lodge between soil minerals and organic matter, removing them is far harder than lifting a plastic bottle out of the sea.

A team in the Czech Republic, publishing in NPG Asia Materials, has developed one promising approach: a swarm of microscopic robots that travels through soil and water, filtering out microplastic particles as it moves. The particles are made from MXene, a material that naturally attracts plastic to its surface, and are coated with magnetic nickel nanoparticles so that an external magnetic field can make them spin and tumble through contaminated ground.

Those are laboratory results. Real environments — oceans, rivers, lakes and working soils — would present far greater difficulty for the micro-robots to navigate, and no council should plan on this being available at scale in the near term. Removing microplastics from everything they have contaminated is a very large problem, and it will almost certainly need several approaches and technologies working together.

Testing and Monitoring Obligations

Under the WEPS 2025 framework, all biosolids samples must be tested by International Accreditation New Zealand (IANZ) certified laboratories. For PFAS specifically, this means engaging laboratories with validated analytical methods for the target compounds (PFOS, PFHxS, PFOA) at the sensitivity levels required to demonstrate compliance with the mg/kg thresholds.

Councils planning a biosolids management programme should build PFAS monitoring into their baseline characterisation work well before a processing facility is operational. Understanding the PFAS profile of incoming sludge — its range, seasonal variability, and relationship to catchment characteristics — is essential for designing a co-digestion process that reliably achieves Grade 1 classification.

For co-digestion operations, the monitoring programme should cover both the incoming sludge and the outgoing digestate, establishing a documented track record of compliance that supports the biosolids application management plan required under the regulations.

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