The Regulatory Landscape Is Changing

The Water Services (Wastewater Environmental Performance Standards) Regulations 2025, which came into force on 19 December 2025, represent a significant shift in how New Zealand manages biosolids. For councils across the country, this legislation creates both clarity and opportunity.

For the first time, land application of treated biosolids is now explicitly prescribed as a permitted activity under national regulations. This wasn't the case before. Previously, councils navigated a patchwork of regional interpretations and consent requirements. Now, there's a clear national framework.

The Challenge: Meeting Grade A Standards

The regulations establish two critical classification systems that determine what councils can do with their biosolids:

1. Stabilisation Grades (Pathogen Control)

Grade A biosolids have undergone both pest-reduction and pathogen-reduction processes, meeting strict limits for E. coli, Campylobacter, Salmonella, human adenovirus, and helminth ova. These can be land-applied as a permitted activity when combined with Contaminant Grade 1 status.

Grade B biosolids have undergone pest reduction but not pathogen reduction. These face additional consenting requirements.

2. Contaminant Grades (Heavy Metals & PFAS)

Contaminant Grade 1 sets maximum levels for arsenic, cadmium, chromium, copper, lead, mercury, nickel, zinc, and importantly, PFAS compounds (PFOS, PFHxS, and PFOA). Biosolids meeting these thresholds can proceed as permitted activities.

Contaminant Grade 2 biosolids—those exceeding these limits—require discretionary activity consent, a more complex and uncertain pathway.

A Pathway Forward: The Co-Digestion Approach

Here's where the regulatory framework creates an interesting opportunity. The regulations specifically address biosolids—defined as residual material from treating wastewater that has been processed to produce a nutrient-rich product for land application.

Co-digestion—processing biosolids together with other organic feedstocks such as food waste, agricultural residues, or forestry biomass—produces a digestate that contains biosolids but is not wholly composed of biosolids. This is a materially significant distinction.

Why Co-Digestion Makes Sense

Dilution of contaminants: When biosolids are co-digested with cleaner organic streams, the concentration of heavy metals and PFAS compounds in the final digestate is reduced proportionally. This can shift borderline Grade 2 material toward Grade 1 compliance.

Enhanced stabilisation: Thermophilic digestion processes (operating at elevated temperatures) and appropriate hydraulic retention times naturally achieve pathogen reduction. A well-designed co-digestion system can reliably produce Grade A stabilisation as a function of process conditions, not as an additional treatment step.

Energy recovery: Anaerobic co-digestion produces biogas—a renewable energy source that can offset facility electricity costs or be upgraded to biomethane.

Waste stream consolidation: Councils managing multiple organic waste streams (green waste, food waste from commercial sources, biosolids) can achieve economies of scale through integrated processing.

Practical Considerations for Councils

What You Can Control

Stabilisation outcomes are largely within your control. Process temperature and retention time can be engineered to meet Grade A pathogen standards with reasonable confidence. These are design parameters, not variables subject to external factors.

What You Cannot Control

Contaminant levels in incoming biosolids depend on what enters your wastewater network. Regional variations exist based on industrial activity, and seasonal fluctuations occur. However, co-digestion with cleaner feedstocks provides a mechanism to manage this variability at the processing stage rather than attempting to control it at the source.

The Compliance Pathway

Under the new regulations, the path to permitted activity status for biosolids discharge to land requires:

1. Contaminant Grade 1 classification

2. Stabilisation Grade A classification

3. Compliance with permitted activity conditions (soil pH, slope, setbacks, application rates)

4. A biosolids application management plan submitted to the consent authority

Failure to meet Grade A/Grade 1 status moves the activity to controlled or discretionary consent categories, with associated time and cost implications.

Looking Ahead

The regulatory environment is becoming clearer, not more restrictive. These regulations provide a defined pathway that didn't previously exist at the national level. For councils considering long-term biosolids management strategies, co-digestion offers a technically sound approach that:

1. Improves the likelihood of meeting Grade A and Grade 1 thresholds

2. Consolidates organic waste management under a single processing platform

3. Generates renewable energy as a co-benefit

4. Positions councils for a permitted activity pathway rather than discretionary consent

The question for councils is not whether to manage biosolids differently—the regulations now require a higher standard. The question is which approach offers the most reliable path to compliance while delivering additional value.

This article provides general information about the Water Services (Wastewater Environmental Performance Standards) Regulations 2025. Councils should seek specific advice for their circumstances.

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