Characterising landfill waste proves a testing time

In response to the new directive embodying Waste Acceptance Criteria regulations,
Severn Trent Laboratories has recently opened a dedicated Waste Acceptance Criteria (WAC) laboratory at its Midlands site. The laboratory has been designed to carry out all the leaching methodologies prescribed in the regulations, many of which are more complex than previous leaching methods. This article, based on material supplied by STL, describes the new facility and testing procedures to aid waste producers in characterising waste under the new regime

The Landfill Regulations (2002), when fully implemented, will have a major impact on the way that contaminated land remediation is carried out.

There will be a requirement for a waste producer to treat and characterise its waste in terms of chemical composition and leaching behaviour. This characterisation will require comparison of analytical results with waste acceptance criteria (WAC) to determine the class of landfill able to take the waste. This waste characterisation will also apply to the removal of any contaminated land waste destined for disposal at a landfill.

The regulations prescribe the leaching methodologies that the laboratories must follow, with the current, simple, contaminated land leaching methods deemed inappropriate.

The newly prescribed leaching methods will impact on the service offered by

laboratories. Whereas the turnaround time for chemical analysis for remediation work has reduced considerably over the past few years, with five days becoming the norm, some of these leaching and percolation tests could take up to 10 weeks to complete.

Laboratory team

At the STL’s new WAC laboratory, a team of dedicated technicians works in the laboratory preparing samples and carrying out the newly prescribed leaching process.

Leaching is carried out on the waste to generate “eluate” samples for analysis, the results of which can be compared with the WAC to identify the most appropriate class of landfill to accept the waste. These are no longer called “leachate” as that term is reserved for liquids generated on landfill sites.

Once leaching or percolation is completed the samples are analysed at STL’s UKAS accredited laboratory. The leaching processes available include BSEN 12457 versions 1,2 & 3, Upflow percolation, Maximum availability, pH dependence, Tank Test, NRA Interim leaching test and USEPA method 1311.

The most common leaching methods are likely to be the BS EN 12457-3, two-stage leaching and the up-flow percolation test. Analysis of the resulting eluate samples can then be compared with waste acceptance criteria, to decide the class of landfill site able to accept the waste.

Further leaching methods such as “Maximum Availability” and “pH Dependence Tests”

will also be employed for particular waste types, in addition to the “Diffusion Tank” and “Compliance Leaching test” for monolithic wastes.

There will be new laboratory testing procedures with analysis testing times far greater than those currently offered.

The laboratory methods employed in the characterising waste to the new WAC are dependent on the chemical nature of the parameters being assessed.

In the main, organic parameters such as, total organic carbon (TOC), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), benzene, toluene, ethyl benzene and xylene compounds (BTEX) and mineral oil are determined as “total” concentrations. That is, the samples are analysed “as received” rather than first undergoing one of the prescribed leaching tests. The term “total” is slightly misleading here, since the chemical methods used for some of the groups of compounds, such as PAH, only identify a particular list of compounds, for instance the USEPA

group of 16 priority PAHs and should not be considered as a total of every PAH that

might be there.

However, inorganic parameters, such as metals and anions, are not analysed “as received” but as the concentration that is leached under certain prescribed conditions, leading to an understanding of both the long term and short term leaching behaviour.

These leaching tests enable predictions of contaminant release to be made for different conditions, such as different pH conditions or very low liquid to solid ratios.

The Batch leaching test – BSEN 12457 – is the recently introduced British Standard, Characterisation of waste- Leaching-Compliance test for leaching of granular waste materials and sludges.

Three variants of the leaching test are available to the UK offering different liquid to solid (L:S) ratios and solids content.

These leaching methods generate eluates for analysis, enabling the assessment of leachability under mild extraction conditions for waste disposal or material reuse options.

The default version in the UK is the version BSEN 12457-3, the two stage leaching method.

The method is only applicable to waste material and sludge having a dry matter content ratio of at least 33%. Where sludges have a very low dried solids content and L:S ratio of 2:1 cannot be achieved, then the single stage BSEN 12457-2 (L:S 10:1) may be undertaken.

These new leaching methods are not only, more time consuming and therefore more costly than the Interim NRA leaching method, but also generate two water samples for analysis and hence twice the cost for chemical analysis.

Comparison with WAC

The cumulative result from the two stage leaching is the one that is used for comparison with the WAC in order to identify the most appropriate class of landfill to accept the waste.

This eluate analysis covers mainly the inorganic parameters and that the more volatile and organic parameters are analysed on the waste itself. The Up-flow percolation test – prEN 14405- method falls into the category of the “basic characterisation” and is used to provide information on short and long term leaching behaviour of inorganic constituents from granular waste.

This is not a quick test to perform and it is not uncommon for the leaching process to take 30 days.

With the pressure on the industry to categorise landfill waste correctly, the new lab means that STL is able to offer reliable data to customers and a service designed to meet their requirements. STL also provide a comprehensive range of expert analysis for monitoring all elements of the water cycle, the waste process, contaminated land testing, emissions measurements and microbiological investigation.

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