The document discusses odour control for anaerobic digestion (AD) facilities. While AD is often perceived negatively in terms of odour, well-designed and operated facilities should not cause odour impacts. The risk of odour issues comes from biogas leaks, handling odorous feedstocks, and unintentional releases. Control measures include containment of materials, odour abatement systems, and following an odour management plan. Proper maintenance and monitoring are also important to minimize odour and ensure control measures are effective.

1. ODOUR CONTROL FOR
THE AD SECTOR
#ADBARegDay @adbioresources
PAUL OTTLEY
SENIOR CONSULTANT, ODOURNET UK

2. Odour control and AD
Paul Ottley, Senior Consultant
ADBA Regulatory Forum - Leeds 21st May 2015

3. Scope of Presentation
• Perception of AD
• The reality of the situation
• What is the risk
• Control measures

4. Perception
Bury Times, March 2014

5. Perception
• “MP joins objectors against Gedling food waste recycling centre “
(Nottingham Post, October 2014)
…MP worried about the smell caused by the site, which would deal with 63,000
tonnes of food waste per year
• “Kicking up a stink over power plant“ (Mid Devon Gazette, May 2014)
…local residents could have their enjoyment of the tranquil waterway ruined by
smells from a proposed energy plant, opponents say
• “MP presents petition to Parliament rejecting proposed biomass and
anaerobic digestion facility”
…protested on the grounds that properties in the vicinity would be devalued
and that there would be increased air/smell pollution from the
transportation/storage of animal slurry, animal waste and food waste

6. How real is the ‘problem’?
• Is anaerobic digestion an inherently odorous operation?
Activity Organic waste AD Crop AD
Outdoor reception of odorous materials X ?
Outdoor handling of organic waste X X
Uncontrolled release of process air X X
Odorous process emissions released
from stacks
X X

7. How real is the ‘problem’?
• Can an objective independent assessment of odours be undertaken?
• Odour emissions from industrial sites can be measured

8. How real is the ‘problem’
– materials handled
• Odour emissions from materials at AD facilities are generally lower than other waste
processing or industrial facilities

9. How real is the ‘problem’
– materials handled

10. How real is the ‘problem’
- total emissions
• Odour emissions from AD facilities are generally much lower than other waste processing or
industrial facilities

11. How real is the ‘problem’
- total emissions

12. How real is the ‘problem’?
- unintentional releases
• Unintentional/abnormal releases can potentially be very significant
• Biogas leakage, failure of odour control plant

13. How real is the ‘problem’?
- unintentional releases

14. What is the risk?
• Inherently low odour emitting process
• Low and high odour materials handled
• Well designed, managed and operated facilities should not cause an odour impact
• But potential exists for the escape of significant amounts of odour
• Once a population is annoyed, it can be difficult to regain a neutral perspective

15. Magnitude of risk
• Higher risk : Large quantities of odorous feedstock, close to receptors
• Lower risk : Low odour feedstocks, smaller quantities handled, larger
distance from receptors

16. Magnitude of risk
• Modelled distances of ‘odour impact’ C98 1 hour = <3 ouE/m3:
– No abatement plant, some uncovered feedstock and digestate storage,
outdoor feed hopper (typical maize crop AD) = 100-150m
– High level of odour control (contained and extracted reception area,
odour control plant, covered digestate storage, back vented digestate
tankers) = up to 50m

17. Control measures
• Feedstock control and management:
– Inspection procedures
– Rejection procedures for excessively odorous or degraded (offensive
odours) materials.
– Prioritise processing of more odorous feedstock.
– Minimise feedstock holding times (ensure raw materials do not
accumulate).
– Housekeeping, cleaning.

18. Control measures
• Fugitive emissions - containment:
– Enclosed hoppers
– Local containment and extraction
– Regular inspection of containment/extraction systems
– Door management, air curtains
– Odour controlled buildings – how many air changes per hour? 2 to 4?
Dependent on building integrity, quantity and nature of materials
handled
– Level of containment can be tested – smoke, pressure tests

19. Control measures
• Containment testing

20. Control measures
• ‘End of pipe treatment’ - Odour abatement plant
– Combustion of odours in a CHP likely to almost entirely destroy all odours. ‘Residual’ combustion
odours unlikely to contribute to offsite odours.
– Biofilters – operational parameters

21. Operating parameter Typical value
Media type
A wide variety of materials are available which are suitable for construction of biofilters. Media should be
selected with reference to the following criteria:
 Biologically active, but reasonably stable
 Organic matter content >60 %
 Porous and friable with 75 – 90 % void volume
 Resistant to water logging and compaction
 Relatively low fines content to reduce gas head loss
 Relatively free of residual odour.
Media height
Will depend upon the characteristics of the media but can be up to 1.5m for peat and compost media and in
excess of 1.5-2m for woodchip and inorganic or synthetic media.
Surface loading <500 m3/m2/hr
Volumetric loading 5 – 500 m3/m3/hr
Mean effective gas residence time 40 - 100 seconds
Inlet odour concentration 500 – 350,000 OUE/m3
Inlet ammonia concentration <5 mg/m3
Inlet hydrogen sulphide
concentration
<10 mg/m3
Inlet air temperature 15 – 30°C
Outlet air temperature <50oC
Inlet air relative humidity
> 95% (Devinny et al (1999)
>98% (VDI)
Media moisture content 60% - 75%
Media pH 6 to 8.5 Stability of pH is important. Variations should be avoided.
Air distribution
Air should be distributed uniformly through the media using a plenum chamber or distributed pipe work.
Up-flow and down-flow systems can be considered.

22. Control measures
• Biofilters – common problems
– Defects in media (weed growth, fissures, siltation, shrinkage)
– Infrequent media replacement – media quality can be tested
– Damage to air distribution pipework during media filling/replacement
– Media humidity problems – poor/insufficient irrigation/humidification
– Maintenance and monitoring essential

23. Control measures
• Scrubbers pre biofilter?
– Reduced sulphur compounds - dimethyl sulphide, dimethyl disulphide, mercaptans
– Very low odour threshold value ratios
– Unlikely to be soluble enough to be removed within biofilter
– Particularly prevalent where pasteurisation tanks are extracted
– Scrubbers can be effective pre-treatment

24. Control measures
• Liquid digestate storage
– Cover and extract to CHP?
– Alligator storage bags
• Digestate cake
– Storage under cover
– Minimise quantity and surface areas (skips)
• Tankers
– Back vent displaced air
• Odour management plans
• Avoid unintentional releases – avoid any gas leakage, flare

25. Control measures
- guidance
• Anaerobic Digestion TGN – Nov 2013 latest draft
– Reception building under negative pressure and 3 acph, fast acting doors,
extracted to abatement plant, ‘consider’ airlocks where site is sensitive
– Digestate separation in building under negative pressure, extracted to
abatement plant
– Digestate must be stored within covered tanks or covered lagoons with
appropriate emissions control and abatement systems
– leak detection tests and other plant monitoring
– Covering of skips and vessels
– Avoidance of outdoor or uncovered stockpiles
– Provision of enclosed flare

26. Control measures
- guidance
• PPC_Technical_Guidance_Note_35 (SEPA) – BAT requirements:
– Reception building air tight and 3 acph
– Demonstrate containment effectiveness
– Airlock or air curtain
– Lids on hoppers and storage bins
– Annual testing of abatement plant, 95%

27. Control measures
- guidance
• Waste Treatment BREF under review – will define BAT for odour
control - implications for some AD plant

28. Summary
• Perception of AD often negative
• Unlikely justified where well designed and operated
• Risk areas – biogas, odorous feedstock,
• Control measures – containment, abatement, OMP measures
• Abatement plant must be maintained
• ‘Impact’ distances should be low

29. Thank you
Questions?

30. ODOUR CONTROL FOR
THE AD SECTOR
#ADBARegDay @adbioresources
PAUL OTTLEY
SENIOR CONSULTANT, ODOURNET UK