Briefings

PAS 100: Specification for composted materials

As part of its standards programme, WRAP has funded a programme to develop a standard for compost. The result of this work is the production of PAS 100, which is a Publicly Available Specification (PAS), published by the British Standards Institute as a commercial venture, and is not to be regarded as a British Standard.

PAS 100 has been adapted from the existing Composting Association Standards for Composts. The aim was to produce a baseline specification for compost that uses current expertise in the field. In addition, PAS 100 includes guidance to inform compost producers of what end users require from compost products. This information is supplementary to the main specification.

PAS 100: Specification for composted materials
Terms and definitions
All the terms and definitions used in PAS 100 are clarified to ensure consistency.

Process control
The section on process control contains general guidelines to ensure effective control of all operations undertaken during production, handling, storage and transport of compost. This includes planning, document control, record keeping and training.

Input materials
PAS 100 does not set down which specific materials are suitable for composting. However, according to the specification, inputs can be any biodegradable material that has been separately collected from non-biodegradables, or that has not by other means been mixed, combined or contaminated with other potentially polluting wastes, products or materials. The responsible persons should assess the suitability of the input material before it is used in the composting process.

Composting activity
PAS 100 does not set specific process conditions, but recommends the preferred ways in which composting should be carried out and the preferred conditions that should be achieved during the composting process.

Sanitisation and stabilisation
Operators will be expected to ensure sanitisation and stabilisation of the composted materials according to the principles of the hazard analysis and critical control points approach (HACCP). This sets down the monitoring of operating conditions at certain critical control points.

Compost Quality Requirements
The key focus of PAS 100 are the Compost Quality Requirements, which set down the standards that composts should meet in order to comply with PAS 100. These are included in full at the end of this document. Briefly, the quality requirements cover:
• human pathogens;
• potentially toxic elements (e.g. heavy metals);
• physical contaminants (e.g. glass, metal and plastic);
• phytotoxins; and
• weed propagules.

Compost sampling and analysis
This section sets out sampling techniques and covers frequency of testing for each of the quality requirements listed above.

Final product storage
PAS 100 does not set out how compost should be stored, but for the sake of traceability recommends that records are kept (see below).

Classification and designation
PAS 100 recommends that composts are classified in accordance with one of the following product types:
a) soil conditioner;
b) mulch;
c) growing medium;
d) growing medium constituent;
e) turf dressing;
f) turf dressing constituent;
g) topsoil constituent (manufactured);
h) biofilter
i) biofuel;
j) other (to be specified by the producer).

However, the document does not give details of how composts should be allocated into product type.

Labelling and marking
The other main element of PAS 100 is the labelling and marking requirements, which will enable end-users to identify the provenance of the compost, the identification or trademark of the producer, the product type (see above) and the fact that it is compliant with PAS 100.

Monitoring and traceability
PAS 100 sets out routine monitoring procedures and the data recording requirements to ensure a level of accountability and traceability for final compost products.

PAS 100: Compost Quality Requirements

This section provides a summary of the Compost Quality Requirements of PAS 100. Users should refer to the original document for the full text.

Human pathogens (indicator species)
When tested in accordance with BS EN ISO 6579, Salmonella spp shall be absent in a sample of 50 g.
When tested in accordance with BS ISO 11866-3 the concentration of Escherichia coli shall be less than 1,000 CFU g-1 (colony forming units per gram).

Potentially toxic elements (PTEs)
When tested in accordance with the methods given in Table 1, the value of mass kg-1 dry matter after normalization to 40% organic matter calculated in accordance with the equation below shall not exceed the upper limit given in Table 1 for the corresponding element.

PTE 40% = (PTE sample test result x 60) / (100 - organic matter sample test result)

Table 1 - Potentially toxic elements

Physical contaminants
When tested in accordance with Annex E, physical contaminants shall not exceed the upper limits given in Table 2.

Table 2 - Physical contaminants

Phytotoxins
As the measure of phytotoxicity, when tested in accordance with Annex E plant germination and growth supported by the compost sample shall be no less than 80% of the performance achieved by the controls when tested in accordance with Annex D.

Weed propagules
When tested in accordance with Annex E, viable weed propagules shall not exceed 5 per litre.

Product preparation
Documentation shall include the minimum criteria that a batch or portion of production is to meet in order to make it ready for product preparation. Criteria for composted material unsuitable for product preparation shall also be established and options or policy set out for its sale, release for use, re-composting, other treatment, or disposal.

Records shall be made and kept on how product preparation was carried out on each batch, set of batches or portion of production.

Any composted material deemed unsuitable for product preparation shall be identified and its sale, release for use, re-composting, other treatment or disposal, recorded.

If compost is packaged at a location different from the composting facility, documentation shall include the name and address of the person or body who carries this out and appropriate records shall be made and kept (see clauses 5 and 14).

November 2002