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Wednesday, 30 April 2014 17:08

Air quality monitoring for bioaerosols: A review of the occupational health risks in a materials recovery facility (MRF)

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D-Waste team has reached Dr Louise Fletcher, Lecturer in Environmental Engineering of the Faculty of Engineering at Leeds University, and Ikpe Emmanuel Ibanga, post graduate student at the same faculty, to find out more about the significance of air quality monitoring for bioaerosols generated at waste management facilities.

 Dr Louise Fletcher, bioaerosols and odours have been big news in the last years. Often media has picked up on the issue and a number of members of the public have claimed that living close to waste management facilities have damaged their health. And, the sector often hears complaints about odour travelling to nearby residential areas.

Could you please express your views on this matter?

Waste management activities and in particular composting facilities attract a lot of public attention and complaints from local residents primarily focussing on odour, dust and noise. Most of the complaints tend to be about nuisance and will include problems relating to odour generation, dust settling out on window sills etc. and also noise from machinery or more often from large amounts of HGV traffic moving in and out of the site. It is rare that members of the public will complain specifically about bioaerosols but may complain that their health is being adversely affected by the activities being carried out. Waste management and composting in particular have the potential to generate large amounts of bioaerosols including bacteria and fungi and these may cause adverse effects on the respiratory system and symptoms such as headaches, nausea and fatigue. However there is limited information in the literature regarding the effects of community exposure to bioaerosols, but there is some limited data that suggests that living close to a composting facility may be associated with an increased risk of adverse health effects. It is often difficult to relate symptoms such as headaches, nausea etc. specifically to activities being undertaken at a waste management facility. There are so many other unrelated causes of such symptoms within the general population that clearly establishing cause and effect is very difficult.

The regulatory authority, in this case the Environment Agency take this very seriously and has strict guidelines in place for composting activities that are located within 250m of persons in a dwelling or workplace. Research carried out on bioaerosol emissions from open composting sites have tended to show that bioaerosols decline rapidly within the first 100 metres from a site and generally decline to background levels within 250m. The EA have strict limits on the concentration of different bioaerosols that are permitted in the vicinity of the nearest sensitive receptor and operators are required to produce a Site Specific Bioaerosol Risk Assessment that shows that bioaerosols can, and will, be maintained no higher than acceptable levels at the sensitive receptors. Each site is then given different requirements for bioaerosol monitoring based on the level of risk identified.

How important is to apply air quality monitoring for bioaerosols at waste management facilities?

Monitoring of bioaerosols and odour from open waste management sites and in particular composting sites is a requirement of a permit granted by the EA to an operator. It is important to monitor the impact of any activity on the environment and this applies to waste management sites. However, although the impact of such activities on the environment is important what is becoming equally if not more important is the impact on workers. Over recent years more and more composting facilities are being enclosed and there is a move away from open windrow composting mainly due to the strict requirements of the Animal By-products Regulations (ABPR). This has also been accompanied by an increase in materials recovery facilities aimed at recovering, recycling and reusing more of the domestic waste that we generate. Although some of the waste sorting can be done using machines there is still a need for hand sorting of waste at many of these facilities. Enclosure of facilities like these has increased the potential exposure of workers to very high concentrations of bioaerosols over extended periods of time and I believe that this is becoming an area of increasing concern. There is a need for more research into the exposure of workers to potentially harmful bioaerosols and the impact on health.

Knowing your interest in the aerobiological aspects of waste treatment and disposal could you please provide us with a short description of your current and/or future research activities towards this direction?

I am currently in the final stages of a 1 year research project looking at the emission of odour and bioaerosols from enclosed biowaste treatments facilities, the removal of odour and bioaerosols by biofilters and scrubbers and the emission concentrations from the outlet from the biofilters. The ultimate aim of the project is to provide the Environment Agency with a recommendation for the Best Available Technology (BAT) for biofilters. My future research will focus on the exposure of waste management workers to bioaerosols and I currently have one research proposal submitted and another one in preparation.

Mr Ikpe Ibanga, you have recently conducted your research project dissertation on the occupational health risks of bioaerosols in a material recovery facility (MRF).

Could you please describe us the main points of your thesis?

In recent times, there has been a need to minimize the biodegradable waste sent to landfill in the UK, following the European Landfill Directive (Council Directive 1999/31/EC). Hence, the focus has been on recycling and resource recovery from waste as vital parts of the integrated waste management strategy. One of the technologies developed for resource recovery is Materials Recovery Facility (MRF) which is a specialised facility that separates, processes, and grades solid waste fractions, for onward dispatch to re-processing plants. There are several health concerns in carrying out the operations of a MRF particularly because of the airborne microorganisms (bioaerosols) that are generated.

This research was aimed at monitoring the indoor and outdoor concentrations of bioaerosols (focusing on two groups of indictor microorganisms: airborne mesophilic bacteria and Aspergillus fumigatus) generated during the waste handling operations on this material recovery facility in order to assess the potential impacts of generated bioaerosols on the workers, the environment and the local residential area of the facility.

Sampling for bioaerosols was undertaken during spring (March and April) and summer (June and July) of 2013, and the sampling was done using the 6-stage Andersen sampler. Microbial detection and quantification were carried out in accordance with the UK Composting Association Protocol. From the analysis of the results, the following conclusions were made.

  • The site operations released insignificant concentration of bioaerosols into the environment judging from the minimal concentrations of mesophilic bacteria and Aspergillus fumigatus measured at locations downwind of the site and near the sensitive receptor, which are similar to or near the upwind concentrations.
  • There was minimal impact of site operations on the environment, especially because of the structural strategies employed by the company to minimise escape of contaminated air to the outdoor environment.
  • The potential exposure of local residents to elevated concentrations of mesophilic bacteria and Aspergillus fumigatus was very low because of the effect of wind dispersal and dilution of the already low concentration released from the facility, and also because of the small proportion of the small sized particles (>2.1μm) in the concentrations recorded in the immediate vicinity of the site.
  • The site operations generated significant concentrations of bioaerosols (104 – 105 cfu/m3), far exceeding the Environment Agency’s guidance for exposure from waste facilities.
  • All operations generated bioaerosols, however, these concentrations varied from operation to operation depending on the degree of agitations involved.
  • There was a high risk to the health of workers within the facility because the observed concentrations exceeded the 5000 – 10000 cfu/m3 limit for an 8 hour working period recommended in the literature; and this was further aggravated by the high proportion (>50%) of the respirable fraction of inhalable particles (0.65 – 2.1μm) of the indicator microorganisms measured indoors.
  • The mitigation measures employed at the time within the facility had not been able to reduce the bioaerosol concentrations to the guideline limits. Hopefully, with the future plans to achieve 2 air changes per hour (ACH) and a negative air pressure within the facility, these levels would be significantly reduced to as low as reasonably practicable.
  • The prevailing weather conditions outdoor (especially air speed) had immense effect on the concentrations of mesophilic bacteria and Aspergillus fumigatus in the environment as evident in the very low concentrations recorded in the outdoor sampling locations. However, the concentrations indoors were not significantly impacted by the prevailing weather condition; they depended on the agitations of the various operations and the volume of waste being handled at any given time.

Which are the main activities in a MRF that generate bioaerosols and what are the main risks posed to public health and the environment.

All operations generated bioaerosols because they were either automated or manually handled. However, the concentrations varied from operation to operation depending on the degree of agitations involved. This waste management facility is an enclosed system; thus, very minimal waste agitations are done outdoors resulting in the low concentrations recorded for outdoor locations, further reduced by wind dispersal and dilution. Eight indoor locations were sampled, including the waste reception area, the eddy current separator area, areas around the wind sifter and below the wind sifter, the baling area and three picking stations. All eight indoor locations showed high concentrations of both indicator bioaerosols (104 – 105 cfu/m3), far exceeding the UK Environment Agency’s guidance of 1000 cfu/m3 and 500 cfu/m3 for mesophilic bacteria and Aspergillus fumigatus, respectively. 
In considering the risk to health, two important factors have to be taken into account – the hours of exposure and the size distribution of the particles of the bioaerosols. Some authors have argued that for an 8 hour working period, the concentration that a worker should be exposed to must not exceed 5000 - 10000 cfu/m3. The picking stations had the highest number of workers at any given time of operation; hence, these areas presented the most risk to workers particularly because of the high concentrations and close proximity of the agitated waste/re-aerosolised particles to the human breathing zone. Another important factor noticed was the high proportion (> 50%) of low size particles (0.65 – 2.1μm) of bioaerosols which are capable of penetrating deep into the lung alveoli to cause the various respiratory infections such asthma, chronic bronchitis, chronic airflow obstruction, allergic alveolitis, etc. The respiratory system is equipped with a mechanism to expel particles size > 2.1μm.

Which measures need to be taken to limit bioaerosols generated in waste management facilities and to protect public health and the environment?

From this study, it was evident that there was very minimal impact of the site operations on the environment, especially due to the enclosed system adopted at this facility, further enhanced by wind dilution. There are several measures that can be put in place to limit the impact of bioaerosols from waste facilities. Most waste facilities install automatics doors armed with motion sensors which only open in the presence of waste-carrying trucks, thereby preventing the escape of odour, dust and bioaerosols. For other facilities, the strategy has been the use of air cleaners such as Negative Air Ionisers, Ozone and Ultraviolet Germicidal Irradiation. Basically the bioaerosol-laden air is contacted with these agents for a specific retention time to effect the required kill.

This facility employed the use of Zehnder Flimmer® device for dust reduction. Dust reducing devices are known to simultaneously achieve bioaerosol reduction. Also, the picking stations were equipped with Local Exhaust Ventilation (LEV) units and ceiling vents for capturing the bioaerosol-laden air at source, thereby maintaining a clean air within the room. Strategically located at various points within the facility were water/mist spray generators for suppressing dust. The waste hall should also be designed to achieve at least 2 air changes per hour (depending on the size of the plant) to maintain a continuous supply of clean air, and a negative air pressure to prevent escape of contaminated air via the doors.

All these are strategies that can be put in place to minimise exposure to the level of bioaerosols generated within waste facilities. However, it is also important to provide appropriate Personal Protective Equipment (PPE) and to ensure compliance with the use of these equipments by the workers. As observed, the local residents were not at risk from the bioaerosols generated at this facility because they were contained, and also because residential houses were located at safe distances from the facility as provided by the UK Environment Agency’s guidance. Hence, the concern was for the workers within the facility. Appropriate Respiratory Protective Equipments (not just a nose mask) should be provided as well as boots, hard hats, gloves and coveralls. Appropriate supervision is also essential to ensure that the expected working ethics and practice are upheld. Regular training of workers on health issues is also a key strategy because when workers become aware of the dangers in their workplace, they will have the right attitude even without supervision.

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Dr Louise Fletcher is a Lecturer in Environmental Engineering in the School, of Civil Engineering at the University of Leeds. She has substantial experience in environmental microbiology and bioaerosol sampling, with particular interests in composting and waste management. Her previous research has included a number of projects on indoor air quality and control of bioaerosols and several projects focussing on bioaerosols from waste management activities. She is currently involved in two projects funded by the European Union focussing on the beneficial reuse of agricultural wastes and a project funded by Sniffer on behalf of the Environment Agency investigating the performance of biofilters at waste management facilities in terms of odour and bioaerosol removal.

Mr Ikpe Ibanga is a highly versatile environmental engineer with high profile exposure in environmental impact assessment, air quality monitoring and waste management. He has good understanding of project management, change management and quality control and possessing high academic qualifications of Masters in Environmental Engineering and Project Management.

Dr Costas Velis is coordinating the research on solid waste management and resource recovery at the School of Civil Engineering, University of Leeds and teaches the relevant MSc module. He is managing state of the art laboratories for solid waste and resources characterization and recovery. Dr Velis serves in many national and international committees addressing relevant challenges of global scale, including the  core editorial team of the first Global Waste Management Outlook as mandated by UNEP, the  Globalisation and Waste Management Task Force of International Solid Waste Association (ISWA), and the Waste Atlas, Chairing the Scientific Committee. He offers to his profession as Associate Editor of the academic journals Waste Management & Research, and Critical Reviews in Environmental Science and Technology. He is Vice Chair of the Waste to Energy Resource and Technology – UK WtERT-UK, member of the ISWA Working Group on Energy Recovery, and sits at the CIWM Thermal Treatment Special Interest Group in the UK. Costas was recently honoured with the prestigious ISWA 2013 Publication Award.

Read 4449 times Last modified on Friday, 02 May 2014 19:14
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