Sustainable Odour Control in Urban Environments James Scott-Bowden MBA, BSc (Hons) Managing Director, ERG (Air Pollution Control) Ltd

Introduction About ERG Leading specialist odour control and air pollution control supplier Odour control systems - UK and Middle East waste water and recycling industries Air pollution control - wide range of global industries More than 30 years’ experience UK headquarters and Middle East based subsidiary Global network of V-texTM technology licensees Maintenance division supplying maintenance services for odour control and air pollution control systems Consultancy services to assist clients with the specification of their air pollution or odour control requirements

Trends in the municipal sector With increasing focus on sustainability, the municipal sector is increasingly locating recycling and treatment facilities: in urban environments to be closer to their waste sources, and housing facilities in enclosed buildings Challenges for the odour control industry: Efficiency – the need is for ever more efficient odour extraction technologies to minimise any odour nuisance to their residential community neighbours Carbon footprint - cost pressures (and social responsibility) drive need for more energy efficient odour control systems for reduced carbon footprint

Cost saving illustration Example: a new sewage treatment works in a sensitive urban area for a town with a population of 250,000 Design guideline - the specified hourly air change rate is 3 times the internal volume of the enclosing structure, i.e 240,000m3/hr the resulting odour control system consumes a staggering 1,200kW each hour If, instead, an hourly air change rate of 1 is selected, the extracted overall volume would be 30% less and the power usage 25% less At 9p per kW this is a running cost saving of £27/hr or £236,500/yr Over the 20 years design life this equates to a £5million saving However odour control is often a highly political local issue, and specifiers are “encouraged” to be excessively conservative! Maintaining a low carbon footprint can sometimes become secondary to eliminating odour complaints.

Municipal recycling example - Manchester Odour control system need to be designed such that operators can minimise the energy consumption whilst still providing maximum odour removal to avoid complaints. Examples of this in practice are the new TEG Group Plc in-vessel composting facilities being built for the Greater Manchester Waste Disposal Authority (GMWDA) at Rochdale, Bredbury and Trafford Park Rochdale processes 750 tonnes of green waste together and 50 tonnes of food waste per week, and converts this into about 600 tonnes of top soil suitable for agricultural use by employing a composting and maturation process which takes about 8 weeks. The Bredbury and Trafford Park facilities are approximately twice as large as Rochdale.

Manchester example, cont’d Peak extraction rates for the Rochdale plant are determined by need to prevent odour escape even when the vehicle access doors are open, giving an extraction rate of rate of 118,800m3/hr, ( 3.3 air changes per hr) An additional challenge – water vapour fog. The waste gives off significant quantity of water vapour as the compost reaches 70oC during processing cycle, which condenses within the building forming a fog. The extraction rate therefore has to also be able to clear the fog to improve visibility inside the building so that operators can work safely. Solution Modulated air extraction rates – the odour control system is able to modulate the volume of extracted air to meet the requirements at weekends and at night the extraction rate falls to 20% of the peak rate when the doors are closed during the working day the extraction is 50% of peak rate only when the doors are open or there is a need to clear the fog in the building do the fans ramp up to peak extraction rate.

Manchester example, cont’d Solution Modulated air extraction rates – the odour control system is able to modulate the volume of extracted air to meet the requirements at weekends and at night the extraction rate falls to 20% of the peak rate when the doors are closed during the working day the extraction is 50% of peak rate only when the doors are open or there is a need to clear the fog in the building do the fans ramp up to peak extraction rate. This increased sophistication gives at least a 70% saving on the fan power consumption compared with the fans operating at full extraction continuously

Dispersion vs Treatment Most odours are not harmful, so atmospheric dispersion is an alternative approach which minimises the carbon footprint of the odour control system Sophisticated computer dispersion models are able to model the pattern of odour dispersion over the locality, and predict the frequency with which specific locations will experience odour concentration above defined levels

Dispersion vs Treatment, cont’d “Isopleths” or contour lines around the odour emission source represents a particular odour concentration, say 10ouE/m3 at the 98%ile This means that based on, say, 1 year’s worth of digital hourly recorded weather data, the isopleth indicates that for 98% of the time the odour along this line will not exceed 10ouE/m3

Dispersion vs Treatment, cont’d Example: Odour is generated from a single 10m stack with an outlet concentration of 1,000ouE/m3, Under the Integrated Pollution Prevention Control (IPPC) H4 technical guidance note waste water sewage works must adhere to a maximum odour limit of 1.5ouE/m3 at the 98%ile levels at locations of resident who might consider the odour a public nuisance and so complain Treatment At the 10ouE/m3 isopleth line the odour has been diluted 100 times In this hypothetical case 10ouE/m3 exceeds the required 1.5ouE/m3 level by a factor of ±7 Re-running the model indicates that a maximum odour level of 500ouE/m3 is required at the 10m stack outlet Dispersion Alternatively to meet 1.5ouE/m3 in this example the stack height would be 26m. Dispersion is normally by-far the cheapest and lowest carbon footprint solution, instead of adding another stage of odour removal odour is simply dispersed by a taller stack For one of the 3 Greater Manchester composting plants, the odour control stack is 37m high and the allowable odour concentration at the stack is 4,000ouE/m3 The stack might perhaps be considered a visual polluter but from the carbon footprint perspective it is a highly sustainable method of odour abatement

Regenerable Carbon Activated carbon is ideally suited adsorbing the odour from environments of complex low solubility VOC based odour, and is able to achieve high removal efficiencies This is the approach being used at the Greater Manchester composting sites Benefits: the carbon is capable of being regenerated and reused up to 6 times before it is considered spent and disposed of to landfill the physical footprint of the carbon unit is highly compact as a single annular carbon filter 3.6m diameter by 8m in height is able to treat about 80,000m3/hr of contaminated exhaust the carbon needs only to be changed every 6 to 12 months.

Air blast cooler at Rochdale For Manchester, the hot wet extracted gas from the in-vessel composting area is cooled by a sub cooler direct contact scrubber to condense out up to 2m3/hr of water from the extracted exhaust and so protects the activated carbon from becoming saturated The scrubber also washes out some of the soluble VOCs and so reduces the VOC loading onto the carbon

New lower carbon footprint technologies H2S adsorbing re-generable carbon ERG regularly installs re-generable carbon filters at waste water treatment works in the Middle East which adsorb H2S to 99% efficiency The carbon can then be regenerated by rinsing in water washing away the leached dilute sulphuric acid back to the head of the works. Thus the carbon can be used up to 6 times before replacement. This re-generable technology is more complex than the straightforward caustic impregnated carbon widely in the UK which is sent to landfill once it is spent. It is likely to become more widely accepted in the coming years as landfill costs continue to escalate.

New lower carbon footprint technologies, cont’d Compact bio-logical filters Lava rock bio-filters are able to sustain bio-media depths of up to 6m unlike wood-chip or similar bio-media which are only operate at up to 2m depth Thus lava rock bio-filters are able to treat the same gas flow with 1/3 of the footprint while still achieving the same residence time for the gas. Benefits This technology has a low carbon footprint as it uses no chemicals, and its only waste is the sulphurous acid, which on a waste water works is simply returned to the head of the works Until now, large gas flows have generally been treated by chemical scrubbing, but as the cost of chemicals rise biological systems are being preferred as both their carbon footprint and operating costs are so much cheaper

New lower carbon footprint technologies, cont’d Recovery of Nitrogen Secondary waste water sludge processing, such as composting with wood chip and drying, can generate high levels of ammonia which can be converted to 30% ammonium sulphate solution by scrubbing with dilute sulphuric acid Benefits As the cost of fertiliser continues to rise this option may well become attractive to waste water processors This type of fertiliser production has a far lower carbon footprint than fertiliser generated using natural gas

New lower carbon footprint technologies, cont’d Recovery of Sulphur At present, most caustic bleach scrubbers are designed to convert H2S to sodium sulphate using 4 moles of bleach. An alternative stoichiometric path is to use 1 mole of bleach to form sulphur. Benefits This approach uses ¼ of the bleach and so has a lower carbon footprint It recovers sulphur which can be returned to soil However this complicates the gas cleaning system which has to be able to operate the sulphur recovery stage by scrubbing with a slurry.

New lower carbon footprint technologies, cont’d Recovery of Energy The composting of sewage sludge and municipal kerbside green waste generates considerable heat which could be recovered to supply hot water via heat pumps or other exchangers. Where a local use for this hot water can be identified this significantly reduces the carbon footprint.

New lower carbon footprint technologies, cont’d Integrated odour control Designers of odour control systems need to be constantly looking for integration opportunities so that the carbon footprint of the odour control plant can be minimised. ERG for example has been able to use filtered final effluent (FFE) at a waste water works as the scrubbing liquor to scrub out ammonia given off from sludge stabilisation plants using lime and sludge dryers. This alkali liquor is then directed to parts of the works where the effluent is acidic. Benefit Using filtered final effluent removes the need to treat the ammonia using expensive chemicals such as sulphuric acid to neutralise the ammonia.

Conclusion Carbon footprint reduction ERG’s technology and design approach can achieve significant carbon footprint reductions at minimal additional cost. Process integration and optimisation The Greater Manchester odour control plants, with the use of inverter driven fans properly integrated with the process they are supporting, together with the use of re-generable adsorbent media, show what can be achieved relatively simply. Early involvement in process design The ERG approach to achieving sustainable odour control is to invest more effort into the initial stages of the design and to involve odour control suppliers earlier in the design process so that the overall optimum process plant which includes the integrated odour control, can be developed.

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