Waste management in London saves CO2

Written by: RWW | Published:

In 2011/12, London’s municipal waste activities ‘saved’ more carbon dioxide equivalent (CO2e) emissions than they emitted, according to a Eunomia report published earlier this month by the mayor of London.

Street leaf sweepings have high and variable levels of polycyclic aromatic hydrocarbons (PAHs), which means that contamination is “too high to produce ‘quality compost’ marketed as non-waste, or compost that can be spread to agricultural land under waste controls. The evidence shows that we need to re-affirm our guidance to local authorities that seasonal street leaf sweepings are not suitable for producing any compost that could be used on agricultural land.”

These preliminary findings of the trials run by the Environment Agency were not what local authorities had been hoping for. 

The final results and report from the project involving 21 local authorities have yet to be published. But the interim results mean that, for the time being at least, the Agency’s approach to leaf litter collected on the streets will not change. For local authorities it’s the difference between £18 and £100 per tonne to dispose of their street sweepings.

Where it all began

This story started back in 2011/12, when a much smaller trial involving four local authorities showed compost that was “too contaminated to be safely spread on agricultural land, containing high levels of metals such as nickel and zinc”. 

The EA updated its website: “Due to the potential for contamination our current guidance is that dedicated street cleansing collections of untreated leaf litter should not be used as a feedstock for composting or used as a feedstock to produce quality compost.”

It then wrote to all composters in England and Wales to warn them against using street sweepings and gully waste residues to produce compost. 

Agency staff would also be auditing the waste types accepted at all sites to ensure that only “appropriate feedstocks” are accepted. 

Leaf litter would have to be landfilled or incinerated.

The news didn’t go down too well back then, and so the interim results of this, more expansive trial have also disappointed. 

So, what did the agency find and what does this mean for councils and composters?

Hardline approach

The agency has historically been well known for its hardline approach when it comes to waste regulations, and this situation is no different. 

Its concerns lie in PAHs, which are “known to be carcinogenic and persistent”; in other words they pose a potential risk to human health and they don’t break down well in the environment. In some cases the PAH levels were noted as “variable”, but in others the agency says they were “high”. 

In the leaf litter collected, the research report reads, one-third of the samples had levels of PAH less than the detection limit (1 mg kg-1 dry weight), but the remaining two-thirds had a median PAH level of “nearly 50 times” higher than the median level in English urban herbage found by the UK Soil and Herbage Survey (which mainly sampled parks and open spaces). 

There are no internationally agreed thresholds for PAH compounds in agricultural soil and in compost, although guidelines have been developed for foodstuffs, water and air. 

The European Joint Research Commission’s technical group has proposed a maximum PAH level for biodegradable waste of 6 mg kg-1 dry weight to meet end-of-waste, but this has not been adopted, the agency notes. 

Of the pure street leaf sweepings and combined street leaf sweepings and green waste compost in the agency’s survey, 90% had PAH levels that exceeded 6 mg kg-1 dry weight. Similar results were also found for benzo[a]pyrene (BaP), a PAH “widely considered to be genotoxic carcinogens and human exposure via air or diet therefore poses a potential risk to human health”. 

A secondary conclusion was that about a third of the composted outputs failed to meet quality compost PAS 100 standards for potentially toxic elements (PTEs), but most met the PTE standards commonly used for compost spread to agricultural land under environmental permitting controls. 

A precautionary approach

In conclusion, the agency briefing states: “Although we want to encourage recovery of biodegradable waste through composting, we need to ensure that the resultant compost is fit for purpose and only used where it can confer agricultural or ecological benefit without harm to human health or the environment.”

The agency’s stance is best known as a “precautionary approach”. Some would say it’s overly precautionary and fails to factor in the variety of other sources that are composted alongside street leaf sweepings.

Jeremy Jacobs is technical director at the Renewable Energy Association (REA), which joined forces with the Association for Organics Recycling last year. 

He explains: “The agency do not like the disperse by dilute philosophy, however, the reality is that sites take a wide range of inputs and these are thoroughly mixed as part of the composting process prior to them being applied to land.

“Leaves, as a percentage of total arisings, is very small and these are mixed with other inputs such as green waste prior to them being sent to land. The EA have, I believe, examined the input material of leaves and some outputs [post composting]. I am unsure if this included mixed outputs or just leaves only.”

It appears that it did, though hopefully more detail will be revealed in the final report when it is finally published. 

Environmental and economic burden

For local authorities, the changes have been an environmental and economic burden. 

Rather than sending the material to the local composting facility, the only available routes are landfill. “We know the impact of biogenic waste and its impact on greenhouse gas emissions,” says Jacobs - or MBT - “which are relatively few and far between,” he adds. 

For local authorities this means a significant increase in the gate fees they pay: typical gate fees for green waste are £18 to £25 per tonne, whereas for landfill it can be up to £100, and rising. 

“The main effects have been financial,” says Andrew Bird,
recycling strategy and commissioning manager at
Newcastle-under-Lyme Borough Council. In particular, it’s waste disposal authorities that have been hardest hit because the “disposal costs are considerably higher than those for composting. The other effect is on recycling performance, which has seen up to 2% drop for some authorities in their performance,” he adds. 

Bird admits that authorities were “obviously hoping for a different outcome”, but again will have to wait for the final report. 

LARAC, the Local Authority Recycling Advisory Committee, says its members are “continuing with these new arrangements, which effectively means [street leaf sweepings] are being disposed of mainly via landfill and energy from waste”. The latter, through MBT, can produce a ‘compost like output’ (CLO), but this can only be used for land restoration projects.

The agency has suggested what councils could do with their sweepings instead. 

Its briefing states: “In many cases, local authorities may choose not to go to the expense of having seasonal, dedicated street leaf sweeping rounds and simply deal with street sweepings as they do for the rest of the year. Dewatering street sweepings considerably reduces the volume and weight that is sent for disposal by incineration or landfill.”

It also suggests the use of street sweepers with blower attachments to reduce the quantity of leaf litter in the street sweepings. 

“Blowing the leaves off the road and pavement into the verge, where this is possible, allows them to mulch down naturally,” it adds.

Until the final results are published, local authorities will need to keep diverting the leaf fall this autumn to landfill or MBT, it seems. 

However, it’s worth noting that sweepings from parks remain ideal for composting.


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