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.

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.

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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