Albion’s ABC of Waste Management – O – Open Windrow Composting

Organic waste can be treated through physical, chemical, or biological forms of waste management. The fundamental aim of organic treatment is to degrade the easily available compounds; stabilise the material; and reduce its volume. Biological treatment includes composting, which has multiple benefits, including:

  • Employment opportunities
  • Reduction of waste to landfill/incineration, which helps control greenhouse gas emissions
  • Recovery of useful organic matter for use as soil amendment, assisting with soil quality improvement (increasingly important due to intensive cultivation and climate change)
  • Stabilisation of waste in order to remove pathogens

Commercial-scale composting is available in two forms – open air windrows (organic materials are placed in long heaps) or in-vessel systems (material is enclosed). In-vessel composting is often used to handle food wastes and animal by-products, as this option isolates the waste from the environment, and people. This is important as these wastes have a higher risk of containing pathogens, compared to garden wastes.

Garden wastes contain items such as twigs, leaves, grass clippings, and also larger items like tree stumps, which are broken down prior to the composting treatment through shredding. These materials are often collected via garden waste kerbside collections or recycling centres, and they are an ideal feedstock material for open-air windrow composting.

PAS100 (Publicly Available Specification for Composted Materials) is a recognised set of standards laid out as guidance for organics recycling. The standards specify that compost reaches a minimum of 60˚C for at least 7 days, to inactivate any pathogens that may be present within the waste. Once composting is complete, the product is graded and sold. This allows any contaminants or materials not quite broken down to be removed. The compost sold can be used as agricultural soil conditioners, or for gardening purposes, or may even be used on golf courses.

However, there can be some issues with composting – for example, concerns over heavy metal pollution of agricultural soils due to composts containing contaminants such as metals and plastic, which may then have a pathway to enter the food chain. Composting sites may also create issues with odours, noise, vermin, VOCs, and bioaerosols – the latter of which arises due to micro-organisms within the waste.

Composting encourages micro-organisms to grow, as these are crucial to actually break the waste down. For composting to be efficient, the material needs to be well-aerated, so these micro-organisms have access to oxygen. Open windrows are aerated by regularly turning material. Additionally, compost is often screened (sieved) to produce the end-product – a quality soil supplement. These processes, along with shredding of large items within incoming waste, all involve handling the compost and moving the material, which can generate dust, and create bioaerosols.

Bioaerosols have the potential to present environmental issues and occupational hazards at any waste treatment facility, if it handles large quantities of organic material. A number of serious health effects, including respiratory and gastrointestinal illnesses, have been linked to high bioaerosol concentrations. As such, composting sites may be required to conduct bioaerosol monitoring, in order to manage the risk of bioaerosols.

In Scotland, composting sites must have a Waste Management Licence (or they will require an exemption). SEPA licences composting sites, and when doing so, they must consider the issue of bioaerosols. In England, sites carry out monitoring according to standards from The Environment Agency. A site’s operations and the amount and type of waste it handles, its possible high-risk areas, and the guidance provided by the relevant environmental authority, are all things that a site may factor in when considering which type of bioaerosol monitoring they want to conduct.

Albion can supply consultants with the knowledge and expertise necessary for conducting a range of bioaerosol assessments, including:

  • Occupational bioaerosol monitoring – assesses exposure for site staff
  • Environmental monitoring – determines possible exposure levels at residencies or workplaces near the site
  • Site-specific bioaerosol risk assessments

By analysing the risks associated with bioaerosols at a certain site, and who may be affected by them, we can then also provide guidance on how to manage and lower a site’s bioaerosol emissions. Albion Environmental has a number of environmental monitoring specialists, trained to complete a wide range of services within the field of environmental monitoring, including those related to bioaerosols. Find out more about the environmental work we do here.