Understanding, prioritising and controlling emissions
Throughout most countries in Europe by far the greatest proportion of waste is disposed of to landfill. In the UK this represents approximately 83% of all waste disposed1. Odours from landfill represent the single highest cause of complaint from waste management processes in the UK. These concerns also represent one of the most commonly cited reasons for refusal of extensions and applications for landfill operations. So is this a problem that we should be concerned with or an issue that will fade away as our dependency on landfill reduces and new technologies contribute to managing waste?
As the focus on disposal moves towards the prevention, waste minimisation, recycling and pre-processing many countries are adopting technologies to divert materials from the waste stream. Metals, plastics, wood, aggregates, green waste and other forms of biomass are all of potential value. Across Europe the pressure to pre-process material and reduce the dependency on landfill from Directive 1999/31/EC shows that there is scope for recovering value from the waste stream. However, it also recognises that final disposal in the form of landfill is likely to remain. Clearly, the potential for odour emissions and the potential for annoyance will not go away.
Annoyance from industrial odours has been documented for many differing sources. Research in this area has been ongoing to understand how to determine acceptable limits to exposure 2 . Despite quantitative assessments, complaints remain the most common indicator of problems albeit not always reliable as the sole indicator of annoyance. It is these links between complaints and predicted concentrations that have formed the basis of planning applications and appeals for decisions concerning odours 3 . Information from the locality represents a valuable source of information by providing data on the patterns of emissions, frequency of incidents and intensity of exposure. It is this knowledge that is central to understanding, prioritising and controlling emissions.
Odour from landfill has significant potential to cause of complaints. The source of odours can broadly be characterised from three sources; refuse odours from tipped waste or material awaiting tipping, odour from specific wastes where these are highly malodorous, and landfill gas odours. Sites may have additional sources such as leachate control or treatment processes and power generation plants but odours from these tend to be localised and unique to the individual process.
Odours can be a single chemical compound such a Hydrogen Sulphide [H 2 S] or most commonly a complex mixture of compounds. These are dispersed in air either as a gas or small particulates carried through air as discrete compounds or attached to other particulates. This complexity makes it difficult to directly relate complex mixes to direct sensory impacts or descriptions. For this reason, odours are characterised either by chemical descriptions or by their sensory impact in the form of odour units.
One odour unit represents the lowest concentration of a sample at which 50% of a selected group of human panellists report the detection of an odour. From this, one odour unit of a sample would prompt 3 out of a group of 6 panellists to reliably detect the presence of an odour when compared to clean air. Sampling and the analysis procedure can be complicated but most importantly if one odour unit [1 ou E /m 3 ] is just detectable this should indicate the significance of concentrations when we measure stronger odours.
Background odours in the environment can be low or non detectable using this method, whereas odours from industrial environments, pungent vegetation such as grass-cutting or pine woods, and even stuffy rooms can be as high as 400-500 ou E /m 3 . Importantly this is the concentration in air that may have built up over time and does not represent a continual emission rate from a source.
The impacts of odours from refuse and landfill gas varies greatly due to their odour concentration and the rate of emission from the site. Ongoing releases of low-level odour concentration can be as significant as small releases of odours at high concentrations. The human nose is good at detecting odours but relatively poor at assessing which odours are more concentrated than others. For this reason it can be difficult for site operators to determine which odours on site will cause problems when dispersed off-site.
|Source||Indicative concentration range [ou E /m 3 ]||Source of flux||Indicative surface flux rate [ou/m 2 /s]|
|Landfill gas||400,000 – 1,200,000||Capping failures, / fissures, drilling, gas infrastructure||Highly variable depending on extraction and capping|
|Freshly tipped refuse||500 – 2,000||Exposed / tipping refuse||4 – 12|
|Tipped, compacted||500 – 2,000||Exposed / uncovered waste||1 – 4|
|Covered waste||100 – 1000||Non – extracted wastes||0-3|
Work completed from a number of sites 5 gives an indication of the range of emissions that are likely to occur 6 . Typically concentrations from refuse are significantly lower than the concentration of odour from landfill gas. Table 1 shows the range of typical odour sources on an MSW landfill site alongside the concentration range that could be measured from these areas. The source of emission may vary depending on site conditions and operational factors and this in turn will influence the emission of odours from the surface, i.e. the surface flux.
Once gas generation from waste occurs the landfill site has a significant potential to cause annoyance. Gas concentrations at 1,000,000 ou E /m 3 will require diluting one million times for each cubic metre of the sample to reach the point of first detection by panellists. In such circumstances even small leaks from gas infrastructure can cause extensive impacts off site.
In addition to being alert to odour concentrations the surface area emitting odours directly influences the total odour emission for the site. Where sites have large or multiple tipping areas the total surface emission will be high. Similarly in cases where surfaces of capped areas are not controlled by gas extraction then emissions can take place over these large areas. A tipping area of 20 x 40 meters in operation for an average site is likely to double its emission rate from this surface if this is increased to 40 x 40 if a turning area or uncovered area within the daily operations. Factors such as safety between vehicles and reasonable sized operating areas are important yet it is rare that odour control features in these calculations.
Control by site management
The primary and most effective mechanism for control of odour impacts is to intervene at the earliest stage in the sequence of: emission – pathway – receptor exposure. The first step to assessing the opportunities from control requires an assessment of all potential sources. This enables the site to prepare an Odour Management Plan 7 which in turn can help all staff to understand their role in preventing impacts off site.
- Landfill gas (LFG) production of odours arising from methanogenesis;
- Effective monitoring of the gas abstraction & flaring system to control and prevent LFG loss is critical for odour control
- Refuse tipping odours from the municipal waste stream;
- Rapid covering and the use of capping materials placed on tipped waste to prevent refuse odours is a basic and effective measure
- Malodorous commercial or industrial waste streams;
- Where sites are particularly sensitive or have had significant complaints selected waste streams may have to be excluded
Odour control systems have a high visibility in the market place both as localised controls as well as a site boundary measure. These operate with varying levels of success depending on the exposure of the site, proximity of receptors and waste type. As each product type differs and the reasoning behind each method differs there is limited scientific evidence for the efficacy of most of these processes. The mechanisms can broadly be described as masking, absorption or wetting8.
Attempts to mask odours are notoriously risky with a probability that local populations will be exposed to masking odours that are either recognised or detected as equally unpleasant. Absorption relies upon direct contact of the spray or treatment liquid with the total volume of gas or odour emitted. Where contained processes are in place this is directly achievable. Landfill sites however are commonly large, exposed surfaces where it is difficult to achieve any form of containment that allows absorption processes to take place.
Perhaps the least anticipated mechanism for achieving additional odour control beyond operational measures is the use of liquids including water to wet or dampen the atmosphere directly around the operational area. It is known that particulates can carry odours. Where these conditions are prevalent during the tipping and operational phase then by reducing these conditions an increase in odour control can be achieved 9 .
Improving amenity and managing public perception
The single most effective mechanism for limiting amenity impact is to ensure that odours are kept to a minimum. Once in place it is important to maintain these controls by ensuring their visibility in a working plan which can be explained to site staff and the local community. Where increases in emission are unavoidable then local communities can be reassured of the confidence and capability of the operator by advanced notice of engineering works. Changes to the gas engineering system, drilling or the movement of degrading waste are all be conditions where planned notice can allow the site operator to demonstrate control and capability in their site management.
Management approaches where sites respond to complaints, are open, accessible, and responsive to investigating cause, enables operators to learn from problems whilst maintaining the confidence of the community.
Understanding events that cause odour complaints is central to the control and management of odours. If information provided by complainants is promptly investigated then the causes of incidents can be investigated in real time. For this reason management plans allow sites to recognise the significance of events for the complainant and the value of the information in preventing a future occurrence.
An example from historical complaint data, in Figure 1 can be compared with the prevailing met conditions in Figure 2 to understand the probability of repeated occurrence. In this case the reasons for incidents were as follows:
- Delays in capping wells (pipeline components unavailable)
- Odour control system failures (incorrectly positioned, pump failures)
- Excavation of degrading waste during engineering works
- Odours from malodorous waste (screenings & grit)
Landfill is likely to remain the single largest volume disposal method in the UK for the foreseeable future. Despite reductions in volume, waste pre-processing, recycling initiatives and material sorting landfill odour control will remain an issue. The odour potential for sources on site is significant. Landfill gas is highly malodorous and produced in significant quantities. In many sites, even if gas is retained by effective control systems small leakages are likely to risk causing annoyance. For operational areas, if these are not restricted to the minimum working areas then low concentration fluxes of odour can be significant in quantity and result in off-site impacts.
Odour management plans allow an understanding of site operations, a prioritising of controls, an opportunity to appraise abatements systems and most importantly an ongoing dialogue with the community at risk. Whilst it’s true that there’s no easy fix, the prevention of complaints is significantly cheaper than hoping that the problem will go away.
1 Defra (2000), http://www.defra.gov.uk/environment/waste/strategy/cm4693/ index.htm [Accessed: 20th Jan 2007]
2 Miedema H.M.E., Walpot J.I., Vos H., & Steunenberg C.F. (2000) Exposure annoyance relationships for odour from industrial sources, Atmospheric Environment, 34, 18, pp.2927-2936.
3 APP/F2930/A/92/206240 (DOE File No.), Wansbeck District Council – Appeal by Northumbrian Water Ltd.: Additional sewage treatment facilities on land adjacent to Spital Burn, Newbiggin-by-the-Sea, Inspector: Rosser P., Inquiry 4-5 & 9-12 March 1993.
4 Gostelow P, Longhurst P J, Parsons S A and Stuetz R M (2003) Sampling for the Measurement of Odours, IWA Scientific and Technical Report No.17, IWA Publishing, London, ISBN 1-843390-33-7
5 Sironi S., Capelli L/, Céntola P., Del Rosso R. & Il Grande, M. (2005) Odour emission factors for assessment and prediction of Italian MSW landfills odour impact, Atmospheric Environment, 39, 29, pp 5387-5394
6 Frechen FB, “A new model for estimation of odour emissions from landfill and composting facilities”, Proceedings from ‘Sardinia 95, Fifth International Landfill Symposium, Cagliari, Italy: 2-6 October, pp.815-828, 1995
7 Longhurst P.J., Cotter M. & Gostelow P. (2004) Odour management plans: a risk-based approach using stakeholder data, Water Science & Technology, 50, 4, pp.17-23.
8 American Society of Civil Engineers [ASCE] (1995) Odour Control in Wastewater Treatment Plants. WEF, Manual of Practice No. 22, ASCE Manual and Reports on Engineering Practice No. 82, NY, USA.
9 Cai L., Koziel J.A., Lo Y-C ,& Hoff S.J. (2006) Characterization of volatile organic compounds and odorants associated with swine barn particulate matter using solid-phase microextraction and gas chromatography–mass spectrometry–olfactometry, Journal of Chromatography A, 1102, 1-2, pp 60-72
Published: 01st Mar 2007 in AWE International