Agency publishes leaf litter trial data

The Agency found it could not draw reliable conclusions from the trials and maintains its stance that leaf litter could not be used in the production of quality compost.

The report entitled Leaf litter in street sweepings: investigation into collection and treatment was published on December 13 (see Leaf litter report)

Detailing a series of trials, the reports studies were undertaken with 22 local authorities to sample and analyse batches of seasonal street leaf sweepings in 2012 and 2013. The aim of these trials, which were managed by the Environment Agency and the REAs Organics Recycling Group, was to try and identify generic circumstances whereby seasonal street leaf sweepings could be collected and composted without compromising compost quality and safety.

As stated earlier this year, the trials found that most seasonal street sweepings were too contaminated to be used in the production of quality compost or compost for agricultural use (see letsrecycle.com story). However it noted that composted street leaf sweepings may be suitable as a compost-like output (CLO) for less sensitive uses such as the redevelopment of previously developed land.

Conclusions

However, the Agency admits that the data from these trials are not always sufficient to draw reliable conclusions. A total of 22 councils participated providing more than 60 samples of street sweepings and 30 samples of composted outputs.

The Agency states in the report: As the local authorities were self-selecting and participation was low, it was challenging to draw reliable conclusions to give a national perspective on the composition of collected street leaf sweepings or the subsequent quality of their composted outputs but it was possible to make some important observations about the data collected.

Levels of physical and chemical contaminants were found to vary considerably within samples of compost from source-segregated green waste and street leaf sweepings. In general, the concentrations of potentially toxic elements such as arsenic, chromium, copper, lead, nickel and zinc were not too dissimilar to levels observed in green wastes and green and green/food composts. However, levels of polycyclic aromatic hydrocarbons (PAHs) were found to be much higher in street leaf sweepings and the composted output than in the other materials.

PAHs often originate from polluting sources such as vehicle exhaust emissions, oil spills and leaks and tyre wear and can pose a significant risk to human health and the environment, according to the Agency.

Recommendations

The trials highlighted a number of gaps in the evidence base around the collection and biological treatment of street sweepings and as such the report makes three recommendations as to how these can be addressed. They are:

• Further work to examine the suitability of street leaf sweepings for producing CLO;

• Further work to better understand the variation in contamination in street leaf sweepings and trial outputs; and,

• Further work on the treatment options to improve compost quality.

The report concludes: Although this trial was larger than the previous Welsh study, the data were not always sufficient to draw reliable conclusions. Recommendations are made for further work that could be carried out to better understand the variability of contaminants within street leaf sweepings and the effects of different collection methods, and the routes and timing of collections, within individual authorities and on a national basis. Further studies on pre-treatment and composting options to tackle the issue of PAHs might also be beneficial.