Sludge Waste Classification

Absolute entries and mirror entries

The List of Waste, also called the European Waste Catalogue or EWC, contains two kinds of entry. An absolute entry is hazardous or non-hazardous by definition. A mirror entry appears twice, once as hazardous and once as non-hazardous, and the correct version depends on the substances present and their concentrations.

For mirror entries, you cannot decide from the process name alone. A sludge from a named industrial process may be hazardous in one works and non-hazardous in another because of raw materials, additives, cleaning chemicals or effluent mixing. The composition needs to be established from sufficiently detailed process knowledge, testing or a combination of both before choosing between the paired codes.

Some sludges have an absolute entry. In those cases the code follows from the source and process, and sampling may still be useful for treatment or landfill acceptance even though it does not change the hazardous status.

The WM3 assessment in practice

WM3 sets out a sequence of steps. In outline, the assessment:

1. Identifies the waste and the process that produced it.
2. Checks the List of Waste for relevant absolute or mirror entries.
3. Establishes the chemical composition, using process knowledge or testing.
4. Applies the hazardous property criteria, including HP codes.
5. Considers persistent organic pollutants and other specific rules.
6. Selects the most appropriate code and status.
7. Records the reasoning so it can be reviewed or defended.

The assessment is not only about metals. Organic content, pH, flash point, sulphur, phenols and other parameters may be relevant depending on the waste and the hazardous properties being assessed. Appearance alone cannot establish whether sludge is hazardous.

Laboratory suites for sludge

The right suite depends on the process and the suspected contaminants. A typical industrial sludge screen may include:

• Metals, including cadmium, chromium, copper, lead, nickel, zinc and mercury.
• Total petroleum hydrocarbons with aromatic and aliphatic markers.
• pH and, where relevant, acid neutralising capacity.
• Flash point for solvent or oil-bearing material.
• Loss on ignition or total organic carbon.
• Sulphate, sulphide and phenols where the process suggests them.
• Polychlorinated biphenyls or other persistent organics for older industrial sites.

Landfill acceptance adds another layer. Waste acceptance criteria testing, usually called WAC, looks at leaching behaviour and is specific to the landfill class. WAC does not replace hazardous classification. A waste can be non-hazardous and still fail WAC for a particular site, or pass WAC while remaining hazardous.

What the report should show

A classification report needs to be usable by the people who handle the waste. It should identify the producer and the process, describe the sampling method and date where sampling was used, list the relevant evidence or laboratory results, and set out the WM3 reasoning. The selected List of Waste code and hazardous or non-hazardous status should be stated clearly with the basis for that conclusion.

For a collector or landfill, the report should also cover the physical form, estimated quantity, storage arrangements and any known hazards. If WAC testing has been done, the results should be presented against the relevant landfill criteria.

Documentation supports traceability. It does not by itself prove legal compliance, and it does not remove the producer’s duty of care. The waste duty of care code of practice explains those responsibilities in England and Wales.

Common problems and how to avoid them

One frequent issue is classifying from a process name without checking the mirror entry. Another is sampling only the top of a lagoon and assuming the rest is the same. A third is treating WAC as if it settles the hazardous question.

Mixing sludges from different processes before classification can also create difficulty. The mixture may have a different code and status from either input, and the paper trail becomes harder to follow. Where mixing is unavoidable, classify the mixture as produced.

If the hazardous status is uncertain, do not assume the sludge is non-hazardous. Complete a competent classification assessment before selecting the removal or disposal route. The hazardous waste guidance sets out additional requirements for hazardous waste.

Where classification fits with removal

Classification usually comes before removal because the receiving facility needs the code, status and waste description to assess the load. The classification can also affect documentation, handling precautions and the treatment or disposal route.

We can help with classification, sampling and the removal planning that follows. Related pages cover sludge EWC codes, sludge sampling and hazardous sludge disposal.