The battle against bioaerosols

Jeremy Jacobs provides an update on the revised standard protocol for monitoring bioaerosols at open air composting facilities

In the past decade, there has been significant growth in the processing of organic residues. This has grown from less than 1M tonnes in 2000-1 to 4.5M tonnes in 2007-8. This growth has mainly been in green waste feedstocks, either collected at the kerbside or from civic amenity sites, and is set to continue with the growth in food waste collections both from the domestic and commercial sectors.

The key driver for growth lies within Defra’s Waste Strategy 2000, which sets diversion targets for biowaste from landfill. Food waste and animal by-products, however, will need to be treated within enclosed systems for compliance with the 2005 Animal By-Products Regulations. This growth in biowaste facilities has triggered concerns over the potential health effects from the processing of these materials – some revolving around odour and, more recently, bioaerosols.

Bioaerosols explained

So, what are bioaerosols? Bioaerosol is a generic term used to describe a range of micro-organisms including, fungi, bacteria, viruses and moulds. Bioaerosols are ubiquitous in the environment but are particularly prevalent where there is disturbance of organic materials. This includes composting where shredding and turning operations are carried out as part of the controlled and managed operating regime.

In 1999 the Composting Association published guidance on the sampling and enumeration of bioaerosols at composting facilities to assist operators in carrying out this task and complying with regulatory requirements. A decade later, this guidance needed updating to better reflect a changing industry and also take into account revised sampling methods. In addition the revised protocol was developed to provide a standardised approach by which to carry out these monitoring requirements for the waste regulators and the biowaste industry.

In 2008, a working group was set up by the Environment Agency including specialists from the Health & Safety Laboratory, Cranfield University and industry to review and modify the protocol. A risk assessment guidance document was written for EA staff in evaluating bioaerosol risk assessments submitted to support permit applications. These two documents should be considered in parallel.

Key changes to action

So, what are the main changes? Biowaste facilities are more frequently required to sample for bioaerosols routinely. The protocol is a reference method to standardise data and ensure minimum standards are met through two standardised approaches to sampling. The main changes are:

  • the introduction of a second sampling method using filters
  • requirements for reporting are more stringent, including additional data recording such as wind direction, weather condition and site operations taking place
  • interpretation of results is now required as part of the reporting procedure
  • the protocol is flexible and allows for other recording equipment to be used when it can be proven to be as effective as the two chosen methods
  • the integration with the Environment Agency risk assessment guidance regarding when, where and how often to sample – this is essential on a site-specific basis.

The above places more emphasis on the site operator to not only record the information, but also interpret the findings and suggest any actions to mitigate the potential risks posed. Actions that site operators can take to reduce excessive emissions of bioaerosols include maintaining compost moisture in excess of 60% during shredding operations, as this is a prime opportunity for bioaerosol dispersal.

Also, ensuring that shredding, turning and screening operations are carried out when the wind direction is away from any sensitive receptors – in effect, an office other than that owned by the site operator. Public footpaths and open spaces are included. Construction of bunds and vegetation screens can be used to minimise the impact on the surrounding area. Cranfield’s risk assessment guidance proposes the following where a sensitive receptor lies within 250m of the site boundary:

  • stage 1: background sampling to be undertaken prior to site development to ascertain background bioaerosol levels
  • stage 2: new sites need to monitor quarterly for the first years of operation to build emission picture for the site
  • stage 3: under normal conditions twice yearly monitoring is requested.

The use of risk assessments are valuable in predicting the concentrations of bioaerosols surrounding a site and the potential risk to sensitive receptors. Managing the risks at biowaste facilities is essential to aid sector development and provide confidence to the wider community that the biowaste industry is professionally managed and effectively regulated.

Jeremy Jacobs is managing director of the Association for Organics Recycling

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