The smell-good factor
Odour is a pollutant. It is defined as a pollutant under the Pollution Prevention and Control (England and Wales) Regulations 2000 that brought Integrated Pollution Prevention and Control (IPPC) into force on 1 August 2000. Bob Maloney, Bord na Mona, explores the implications of the new regime for odour control in the food industry, before looking at the Best Available Techniques (BAT) and technology on offer.
Under IPPC, operators of prescribed installations must obtain a permit. IPPC legislation in the food industry incorporates odour emissions both from a nuisance perspective and as pollution – where compounds in the gas are deemed to be pollutants. Unlike the previous regulations there is less emphasis on defining statutory limits, and limit values can be supplemented or replaced by equivalent parameters or technical measures. These can specify use of a management practice or technology to control odour.
The new IPPC regulations integrate Integrated Pollution Control (IPC) and Local Air Pollution Control (LAPC). Some 6,000 operations will be regulated, compared to the 2,000 under the IPC regime. The extra operations include around 1,000 currently regulated under the LAPC regime but for which local authorities will retain regulatory responsibility. In practical terms, regulation of the remaining 20,000 LAPC operations will be largely unchanged by the new regulations. Local Air Pollution Prevention and Control (LAPPC) will replace LAPC but it will still regulate emissions to air only. The changeover to LAPPC will be essentially an administrative one and will not involve payment of new application fees.
Existing operations in the food industry will move to LAPPC from 1 April 2004. However, new installations and “substantial changes” to existing operations results in an operation falling under IPPC with immediate effect. For substantial changes that have arisen between 31 October 1999 and 1 August 2000, applications must be made for an A2 permit by 31 December 2000. The Environment Agency provides practical guidelines to determine whether a change is substantial or not. They suggest that any increase in the mass release of an odorous substance, or any change in practices or activities that might reasonably be expected to increase fugitive odour releases should be considered. Broadly, if a change would result in a statutory nuisance within the meaning of Part III EPA 90 then it should be considered a substantial change.
The new regulations will see the Environment Agency and Local Authorities working much closer together. The Environment Agency regulates Part A (1) installations while Part A (2) installations are regulated by the relevant local authority. However, the local authority will always be a statutory consultee where the Environment Agency is the regulator, and vice versa.
Opt to BAT
In addition, there is a change in emphasis from BATNEEC to BAT (Best Available Techniques). Under the previous regulations only the costs to the operator were considered. IPPC considers a wider range of costs and benefits from different pollution control measures.
So how do you select the Best Available Technique for odour control? The Pollution Prevention and Control (England and Wales) Regulations 2000 define BAT as “the most effective and advanced stage in the development of activities and their methods of operation” to achieve emission limit values (ELVs). Special consideration should be given to a range of factors to determine BAT. These include minimisation, recovery, reuse and recycling, but also consider current best practice, technological advances, the environmental impact of the technology, its consumption of raw materials, energy efficiency and the length of time needed to introduce it. This has implications for installing odour control technologies. Some conventional odour treatment technologies that solve odour problems might no longer be regarded as a BAT on the basis of running costs, high raw material input or environmental impact resulting from the disposal issues.
A range of technologies are available to treat odour from the food industry and compounds contained in Schedule 5 of the PPC regulations, listing compounds for which an ELV can be set. The selection of appropriate technology relies upon adopting a problem solving approach. Regulation of odour emissions generally results from a nuisance complaint at the site boundary. So, an effective odour control system must ultimately achieve a defined boundary condition. Odour sampling and dispersion modelling allows a guaranteed emission standard to be defined and monitored, ensuring set odour concentration limits at the site boundary are not exceeded. Odour should be measured as olfactory units rather than a constituent compound such as hydrogen sulphide, as it is likely that the Environment Agency will support this in future guidance publications.
The selection procedure must also take account of any ELV to be achieved, the type of compounds in the air emission, the quantity and rate of emission, the temperature, the location of current equipment, the space available for treatment technologies, economic considerations and a net present value assessment. Selecting BAT requires knowledge of relevant technologies and some applications experience. The food industry should consider carbon adsorption, biofiltration, thermal oxidation processes, and wet scrubbing. Other niche technologies include condensation, cryogenic condensation and membrane separation. Chemical scrubbing has historically been favoured in the food industry with two or three scrubbing stages being used. This technology may suffer under the new regulations as it has low removal efficiencies for organic compounds and very high running and maintenance costs. In addition, concerns surrounding the environmental impact of the chemical scrubbing reagents raise questions over its suitability under BAT.
Selecting BAT is normally achieved by constructing a matrix for each specific application that assesses the key technical features of the technologies against the criteria in the regulations.
Activated carbon physically adsorbs organic molecules on the carbon surface by intermolecular attraction. It does need to be replaced or regenerated when it becomes saturated. Regeneration involves the use of steam or other hot gases and pressure changes across the activated carbon filter to break the weak interactive bonds between the carbon and organic molecules being adsorbed. Media replacement costs are the most expensive running costs.
Thermal oxidisers take a process exhaust stream, mix it with natural gas and typically heat it to in excess of 900°C, where compounds in the air emission are thermally oxidised. The main operating cost associated with thermal oxidation is its gas and electricity consumption. This technology can achieve high thermal efficiencies when regenerative units are used to treat emissions with high VOC contents.
Biofiltration is becoming increasingly popular as a treatment technology in the food industry. It relies on bacteria, supported on a media to metabolise the compounds in the process exhaust stream. Original woodchip-based biofilters were historically unreliable, but the technology has moved on considerably and biofilters are now robust, reliable and offer very low running costs. This is mainly due to extensive research on support media and biofilter operation that has led to the development of highly compact technology with excellent removal efficiencies and low environmental impact. Today’s biofilters are designed to treat up to 500,000ou/m3 (approximately 250ppm H2S) with an efficiency of 99.9% reduction.
Emerging technologies cryogenic condensation and membrane technology are establishing niche markets. Cryogenic condensation is a relatively new technology for treating VOCs. It uses the principle that at sub zero temperatures the vapour pressure of most organic compounds drops and they condense. Liquid nitrogen achieves these temperature reductions and condensate is collected at the bottom of an exchanger. The process stream is vented after the cold from the vapour is recovered using a heat exchanger.
Membrane technology is emerging as a potentially promising technology. Membrane-based gas separations have been commercially used to remove sulphur oxides from smelter gas streams and chlorofluorocarbon vapours from air. However, the quality of the gas separations still needs improving as does membrane permeability. Researchers are working on innovative ways to modify polymer materials and polymeric hollow fibre membranes are currently being used for VOC removal from off-gas streams of contaminated ground water.
A guidance document for odour control will be published by the Environment Agency later next year. “The Environment Agency is currently working with other regulators on odour guidance for IPPC,” confirms Mark Maleham. “It will cover regulation, measurement and control techniques illustrated with case studies. It provides robust, pragmatic solutions for the permitting and control of potentially odorous releases, recognising in particular the need to provide alternative regulatory approaches for different types of odour release.” Prior to publication a draft guidance document will be available for consultation. The Environment Agency suggests that interested parties should visit the Guidance for Business and Industry section of its web site for future developments. In the meantime, careful assessment of BAT for your site and effective implementation are the key to ensuring your site is compliant under IPPC.
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