Controlling risk where there’s compost

Research recently released by Cranfield University should result in tighter control in the risk assessment of composting sites. Gillian Drew explains further

Tighter risk assessment procedures for composting and organic waste treatment sites are now available due to new research released by Cranfield University. The research examined the potential environmental impacts of a number of issues common to waste processing operations, such as odour and bio-aerosols. The potential effect of these on communities and their quality of life was also assessed.

The research, which was funded by the Environment Agency (EA), is the result of a three-year programme that set out to explore methods for the quantitative risk assessment of composting and other organic waste treatment facilities. One of the main tasks of this study was to provide scientific evidence to support the development of improved impact assessments. Resulting guidelines will affect the way waste operators carry out risk assessments.

A key part of the work programme was examining the quality of the risk assessments submitted to the EA in support of waste permitting decisions. The quality of these risk assessments was found to be variable – in particular, they were found to not be site-specific enough and were lacking in bio-aerosol monitoring data.

The research focused on bio-aerosols, which are airborne micro-organisms, and the constituent parts of these micro-organisms. The EA requires a risk assessment to analyse the potential for these bio-aerosols to be released from any composting facility that has homes, offices or schools (sensitive receptors) within 250m of the site boundaries.

Sampling new methods
The study also looked at the development of new methods for sampling and analysis of bio-aerosols, as well as testing the use of air dispersion models to predict downwind impact of these emissions. Some of the results show that the highest bio-aerosol emissions are related to agitation activities at composting sites, such as turning, shredding and screening.

The sampling approach within this research focused on the use of between three and six samplers side by side. This high level of repetition in the sampling allowed the use of detailed statistical techniques, which has highlighted the variability associated with bio-aerosols. Some of the key factors influencing this variability include wind speed and direction, season, processing activities, and type of facility. High winds in particular were shown to result in higher concentration of bio-aerosols being detected further downwind.

One of the outcomes from the study was a two-day training course designed for EA personnel involved in permitting waste composting facilities. The workshops aimed to introduce measures to improve the consistency of risk assessments, and started with an initial introduction to risk assessments, aimed at ensuring all attendees had the same basic understanding.

Putting the theory to the test
Attendees were then asked to develop a conceptual model of a theoretical composting site. Discussions focused on the key aspects of a risk assessment, namely problem definition and risk screening and prioritisation. Examples of risk assessments were used in exercise sessions to demonstrate both good and bad practice.

In addition, the workshops looked at bio-aerosols and covered topics such as sampling strategies and methods, health impacts, as well as providing data on the range of bio-aerosol concentrations that could be found at different composting facilities.

Attendees were also party to the latest scientific information, combined with hands-on exercises – for example, planning a sampling strategy for a theoretical composting facility. These exercises were designed to assist EA personnel in permitting decisions, and to provide them with an alternative view by giving them the opportunity to examine problems from the perspective of a consultant or operator.

The likely impact of these workshops is that EA permitting and operational staff will be able to make more informed decisions on the quality of the risk assessments presented to them. It is hoped that this will improve the regulatory process and provide more consistency across the different regions.

Lastly, the results provide a scientific evidence base to support the development of these impact assessments and will be used by the EA to underpin policy development and inform decision-making in waste management and monitoring.

Dr Gillian Drew is course director for the environmental management for business programme at Cranfield University

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