Guidance on applying for approval to use biosolids in compost


Biosolids are stabilised organic solid residues produced from municipal wastewater treatment plants.

Biosolids contain nutrients and are used as fertilisers for:

  • crops
  • horticulture
  • home garden application.

However, biosolids can contain significant levels of:

  • pathogenic (disease causing) microorganisms
  • heavy metals
  • pesticides
  • chemicals that can cause adverse health effects.

Therefore, their pathogen (P) and chemical contaminant (C) grade must be classified in order to determine their suitable end use and the measures required to protect public health.


Compost is a type of biosolid with lower pathogen concentrations that can be used in home gardens or lawns.

In the composting process, biosolids from wastewater treatment plants (usually P3C2 class) are mixed with other organic materials such as:

  • green waste
  • shredded timber
  • sawdust.

This will create a product with relatively high nutrient and low pathogen levels classified as P1C1.

The quality of the final composted product needs to be assessed to ensure they achieve in a reliable manner the P1C1 classification.

Consequently these can be used as an unrestricted product, which means that the compost is suitable for any land use application.

Biosolids regulations

Composts and related products manufactured from biosolids need to comply with the Western Australian Guidelines for Biosolids Management (external site).

These Guidelines provide information and guidance on appropriate management practices for the beneficial use of biosolids.

The Australian Standard AS 4454-2012 – Composts, soil conditioners and mulches contains guidelines for the minimum requirements for the physical, chemical and biological properties of composts, soil conditioners and mulches and the labelling and marking requirements.

It also sets the minimum standards for product certification.

Biosolids classification

The Western Australian Guidelines for Biosolids Management uses a system for assessing the suitability of biosolids and derived products for land application.

Biosolids are classified into two grades.

Contaminant grade

The contaminant grade is based on the concentration of chemical contaminants in the biosolids product.

There are 3 grades, with:

  • grade C1 corresponding to the highest quality of biosolids (lowest contaminant level)
  • grade C3 representing the lowest quality (highest contaminant level).

Pathogen grade

The pathogen grade is based on the level of treatment undertaken to reduce pathogen levels, vector attraction and odour in the biosolids product.

Four pathogen grades are used being P1 (high quality) to P4 (low quality).

Both contaminant and pathogen grades are used to assess the class of biosolids, which then determines the permitted uses and associated conditions of approval.

The minimum contaminant and pathogen grades required for different land uses are detailed in Table 1.

As mentioned above, compost materials shall comply with the P1C1 classification.

Biosolids which do not comply with the P1C1 treatment and quality criteria will not be able to be provided to the general public.

Application requirements

Proposals involving the use of biosolids for the production of composts must be submitted to the Department of Health (DOH) for assessment.

There is no minimum volume trigger and therefore all applications must be submitted for approval.

Applications will need to include the following:

  • description of the treatment process including materials to be mixed with the sewage sludge or biosolids
  • details of the production control process including mixing volumes, moisture content, temperature levels and composting duration
  • a quality assurance program (QAP) in accordance with AS/NZS ISO 9001:2008 – Quality management systems. The QAP ensures that procedures are in place to demonstrate capability to produce products to requirements, and to prevent an unacceptable product being made at all stages of production
  • the final composting product to be tested/certified by an accredited third party (such as SAI Global) to Australian Standard AS 4454 (2012) Composts, soil conditioners and mulches
  • a contract between the compost operator and the sewage sludge supplier is required to ensure minimum quality requirements of the biosolids are met – confirmation of biosolids quality should be an essential process control measure
  • transportation details in accordance with the Western Australian guidelines for biosolids management
  • soil incorporation and application rates
  • health and safety management plan including a risk assessment which complies with AS/NZS ISO 31000:2009 Risk management - principles and guidelines
  • application manual containing health and safety measures to handle the composting product, procedures in the event of an incident and emergency contact numbers.

Once approval has been granted the following will be required on a yearly basis to maintain that approval:

  • a minimum of 1 sample a year of the product being submitted for bacterial and chemical examination
  • an annual report containing a summary of the monitoring program results including the:
    • date and location
    • type and volume of feedstock received and processed
    • the amount of compost produced, stored, and shipped
    • summary of incidents and complaints and details of any corrective action undertaken.
Table: End uses of biosolids according to classification
Biosolids end use Pathogen grade Contaminant grade
Unrestricted use1
Unrestricted use P1 C1
Restricted use
Agricultural direct land application (crops that may be consumed raw and in contact with biosolids) P1 C2
Urban landscaping (not household use) P2 C2
Horticulture P2 C2
Agricultural direct land application (crops that may be consumed raw but not in contact with biosolids) 2 P2 C2
Agricultural direct land application (pasture and crops that are cooked/processed before being consumed, but not root crops)3 P3 C2
Forestry direct land application P3 C2
Rehabilitation (eg mine sites, contaminated or degraded sites etc) P3 C2
Not suitable for direct use
Municipal landfill disposal4 P4 C3
Secure landfill P4 C3
Thermal processing (incineration, oil extraction, metal smelting or use in building products) P4 C3
  1. Unrestricted use biosolids may still be subject to regulatory control, such as through labelling laws for fertilisers or Unauthorised Discharges Regulations 2004 where environmental harm may be caused by inappropriate use (i.e. over application causing nutrient issues).
  2. Includes fruit trees, grapes, etc.
  3. Includes cereal crops. May also include a soil improvement application such as shelter belts, revegetation of firebreaks, fodder crops, deep rooted plants for long-term cropping, etc.
  4. Biosolids being disposed to landfill need to meet the relevant requirements of the Landfill Waste Classification and Waste Definitions (1996), as amended

 More information

  • Water Unit, Environmental Health Directorate
    Department of Health
    PO Box 8172
    Phone: 9222 2000
Last reviewed: 29-10-2020
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Public Health