Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
DATE ISSUED: February 2011
JOB NUMBER: ST11538
REPORT NUMBER: ST11538-RPT-004
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
Volume 3 – Odour Assessment
February 2011
PREPARED BY:
Claire Meddings Senior Environmental
Scientist
Joanna Smith Associate Director
APPROVED BY:
Mark Dawson Technical Director
This report has been prepared by Wardell Armstrong LLP with all reasonable skill, care and diligence, within the terms of the Contract
with the Client. The report is confidential to the Client and Wardell Armstrong LLP accept no responsibility of whatever nature to third
parties to whom this report may be made known.
No part of this document may be reproduced without the prior written approval of Wardell Armstrong LLP.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
CONTENTS
1 Introduction........................................................................................................................1
2 Technical Context ...............................................................................................................2
3 Assessment Methodology ..................................................................................................8
4 Proposed Mitigation .........................................................................................................12
5 Assessment of Effects.......................................................................................................15
6 Conclusion ........................................................................................................................21
APPENDICES
Appendix A – Predicted Odour Concentrations at Receptor Locations
DRAWINGS
ST11538/009 – Odour Dispersion Modelling Receptor Locations
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 1
1 INTRODUCTION
1.1.1 The proposed development comprises the installation of an anaerobic digestion (AD)
plant, at Mill Farm, Chebsey. The main element of the proposed development is the
construction of a single purpose-designed building, located immediately to the west
of the existing open windrow composting site, which will house the anaerobic
digestion plant.
1.1.2 The maximum design capacity for the proposed AD plant is 25,000 tonnes per
annum. The facility will take imported food waste amounting to approximately
15,000–20,000 tonnes per annum. The entire throughput of the site, including that
of the existing open windrow composting site, will be within the current throughput
limit (maximum 45,000 tonnes per annum) and within the current vehicle movement
limits as set out in the existing planning permission, for the open windrow
composting site.
1.1.3 This report considers the potential odour related issues associated with the
proposed development of the AD plant. The report considers in detail the
operational phase impacts of the development. The mitigation measures, which
have been incorporated into the design proposals, to minimise the potential adverse
impacts and risk associated with the proposals, are also described. The assessment
then considers whether adverse odour impacts are likely to arise and draws
conclusions as to whether these are significant.
1.1.4 In summary, this assessment considers the potential effects on air quality from
residual sources of odour, bioaerosols and particulate and dust emissions. The
sections of this report are as follows:
• Technical Context
• Assessment Methodology
• Proposed Mitigation
• Assessment of Effects
• Conclusion
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 2
2 TECHNICAL CONTEXT
2.1 Potential Sources of Emissions during the Proposed AD Process
2.1.1 The AD plant will convert the organic material, separated from the incoming waste
stream, into a biogas that can be used to produce renewable energy and heat.
2.1.2 There are four main elements to the AD process:
• The mechanical treatment of waste to extract the organic waste fraction;
• The biological treatment of the organic fraction using anaerobic digestion;
• The generation of electricity from the biogas produced during the digestion
process and harvesting of the waste heat for beneficial use both on and off
the site; and
• The separation of the liquid and solid fractions of the digestate.
2.1.3 The processes involved in the AD plant are:
• Waste Reception
• Mechanical Pre-treatment
• Anaerobic Digestion
• Dewatering and Drying
2.1.4 In addition to the processes taking place in each of these sections a number of
auxiliary functions will take place at the facility which are relevant to this air quality
assessment. They include the air pollution control measures which comprise the
ventilation system, UV light odour treatment system, charcoal and dust filters and
biofilters (as a means of controlling odour, bioaerosols and dust).
2.1.5 The potential emissions from each of the sections of the AD plant are detailed in the
following sections of this report. The potential emissions and the performance of the
ventilation system, dust filters and biofilters are also discussed. The ventilation and
odour control systems are part of the mitigation measures proposed at the site and
details are included in the Proposed Mitigation section of this report.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 3
The AD Process
Waste Reception
2.1.6 In this area imported waste will be delivered by collection vehicles and fed to the
plant. There is the potential for the delivered waste to generate odour, bioaerosols,
dust and particulates. The approach to minimising and controlling these emissions is
detailed in Section 4 of this report.
Mechanical Pre-Treatment
2.1.7 In this area the mixed waste is subjected to a variety of physical treatments in order
to separate fractions of the waste suitable for recycling, energy recovery, disposal
and the organic fraction for further biological treatment. There is the potential for
odours, bioaerosols, dust and particulates to be generated during the processes
taking place in this area. The approach to minimizing and controlling these
emissions is detailed in Section 4 of this report.
Anaerobic Digestion (AD)
2.1.8 In the AD section of the plant the organic fraction is subjected to anaerobic
digestion. Bacteria present in the waste decompose the organic material under
anaerobic conditions, producing biogas. Biogas is composed mainly of methane and
carbon dioxide, with smaller amounts of nitrogen and other gases. The biogas is
used to power the gas engines to produce renewable electrical power and heat.
Dewatering and Drying
2.1.9 In this area the residue from the digestion process is dewatered and dried to
produce a stabilised odourless organic material for export. There will be only a
minimal potential for odour and particulates to be generated in this area as
dewatering takes place in enclosed vessels.
Odour
2.1.10 Unpleasant odours can have an effect on the environment and the quality of life of
individuals and communities. The effects of odours can be a material consideration
in the determination of planning applications.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 4
2.1.11 Odorous compounds are derived from biological breakdown of complex organic
compounds and from direct volatilisation of organic compounds present within the
material being processed.
2.1.12 The commonest odour, arising from poorly controlled decomposing organic
materials, is ammonia (usually described as a pungent, sharp smell). This tends to
arise as a result of a low carbon to nitrogen ratio (i.e. where nitrogen is in excess).
2.1.13 The anaerobic stages of decomposition, i.e. anaerobic digestion, can produce
compounds including alcohols, esters and sulphur containing compounds such as
methanethiol. These have a known potential to cause odour problems. If anaerobic
conditions are permitted to become firmly established, concentrations of sulphur
containing compounds decrease and dialkylated compounds predominate (e.g.
dimethyl sulphide and dimethyl disulphide). Aromatic hydrocarbons, cycloalkenes,
alkenes and high molecular weight alkenes can also be formed.
Bioaerosols
2.1.14 Biological aerosols (bioaerosols) consist of finely divided biological organisms
suspended in air. These aerosols can vary in size from 0.5 to >100μm and can occur
as aggregates, as droplets or attached to inert dust particles. Bioaerosols are
complex in nature and may include1:
• Viruses
• Bacteria
• Actinomycetes
• Fungi
• Enzymes
• Endotoxins
• Mycotoxins
• Glucans
2.1.15 It is normal to find bacteria and fungi in both indoor and outdoor environments. The
concentrations of bioaerosols in the outdoor environment at any one time will
depend upon the surrounding landuses and the prevailing meteorological conditions.
1 M17 Environment Agency – Monitoring of particulate matter in ambient air around waste facilities
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 5
2.1.16 Levels of bacteria and fungi can be found in concentrations in excess of 1000 colony
forming units per cubic metre (cfu/m3) in agricultural and forest environments. For
example temporal airborne bacterial concentrations measured above a grass seed
field indicated a maximum of 1370cfu/m3 (Lighthart and Shaffer, 1995
2). Background
sources of these high levels of bacteria and fungi include decomposing organic waste
such as dead vegetation and manure.
2.1.17 Fungi and bacteria can also be found at high levels indoors, where they are
associated with the presence of organic matter (e.g. wood and foodstuff) (IEH,
19963). The outdoor air which enters the property is also one of the major sources
of fungi and bacteria in indoor environments, particularly during the summer and
autumn (Wanner et al, 19934).
2.1.18 Common indoor bioaerosols include fungi and bacteria and concentrations in the
indoor environment vary significantly. For example a study undertaken by Hunter et
al (1996)5
monitored 163 homes for the presence of fungi and bacteria over the
period of November 1990 to December 1992. The mean count was 234cfu/m3
air of
fungi and 366cfu/m3
air for bacteria. In a more intensive study of 35 of the houses
mean counts were 912 and 818cfu/m3 for fungi in living rooms and bedrooms
respectively, and 917 and 933cfu/m3
for bacteria.
2.1.19 As set out above, bioaerosols are present in both indoor and outdoor air. Airborne
micro-organisms are inhaled throughout normal everyday life and rarely cause any ill
effects, as the body’s own defence mechanisms normally provide adequate
protection.
2.1.20 Bioaerosols are generally less than 10µm in size and are not filtered out by hairs and
specialized cells that line the nose (Drew et al, 20046). Due to their airborne nature
and small size, many bioaerosols can penetrate the human respiratory system, deep
into the lungs, causing both respiratory and gastro-intestinal symptoms (CIWM,
2 B Lighthart and B Shaffer, Airborne Bacteria in the Atmospheric Surface Layer: Temporal Distribution above a Grass Seed Field. Applied
and Environmental Microbiology, April 1995, p1492-1496. 3 IEH. Assessment on Indoor Air Quality in the Home. Institute for Environment and Health, Leicester, UK. 1996.
4 Wanner H.U. Sources of Pollutants in Indoor Air. IARC Scientific Publications, 1993, 109, 19-30.
5 Hunter CA, Hull AV, Higham DF, Grimes CP, Lea RG. Fungi and Bacteria In: Berry, RW Brown, VM Coward, SKD et al (Eds). Indoor Air
Quality in Homes, the Building Research Establishment, Indoor Environment Study, Part 1 Construction Research Communications,
London. 1996. 6 Drew GH, Deacon LJ, Pankhurst L, Pollard SJT and Tyrrel SF. Guidance on the Evaluation of Bioaerosol Risk Assessments for Composting
Facilities, Environment Agency.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 6
20027), and inflammatory and allergic responses (Wheeler et al, 2001
8; Swann et al,
20039).
2.1.21 Bioaerosols are likely to be formed and released into the atmosphere when any
agitation of organic materials takes place, for example during the mechanical
shredding and screening of waste before processing in the AD plant.
2.1.22 In October 2001 the Environment Agency (EA) produced a guidance document10
on
composting operations that includes recommendations for best practice operating
procedures and consideration of environmental effects including bioaerosols. No EA
guidance has been produced in relation to the processing of waste at AD Facilities;
however elements of the physical treatment are similar to composting.
2.1.23 The EA’s 2001 guidance recognises that there are currently no exposure limits
defined for airborne micro-organisms. The guidance states that health outcomes are
dependent on the individual and therefore their potential effect on individuals is
virtually impossible to predict.
2.1.24 The EA’s guidance confirms that a review of threshold exposure limits suggested by
researchers, funded by the Agency, has indicated that fungi and bacteria levels
above 1000cfu/m3
may be appropriate to assess safety issues in the absence of
appropriate dose response relationships.
Particulates and Nuisance Dust
2.1.25 There is the potential for activities at the site to generate both primary fine particles
and coarse particles. For waste facilities in general, the Environment Agency M17
guidance11
indicates that primary fine particles are directly derived from combustion
sources such as road traffic, power generation and industrial processes. Coarse
particles may comprise emissions from a wide range of abrasion sources including
construction works, wind blown dust and soils.
2.1.26 There is the potential for fine particulates to be generated from loading shovels and
7 CIWM, 2002. Biological Techniques in Solid Waste Management and Land Remediation. Chartered Institute of Waste Management,
Northampton 69pp. 8 Wheeler PA, Stewart I, Dumitrean P, and Donovan B. 2001. Health Effects of Composting: A Study of Three Compost Sites and Review of
Past Data. R&D Technical Report P1-315/TR, Environment Agency, Bristol. 9 Swan JRM, Kelsey A, Crook B, and Gilbert EJ, 2003. Bioaerosol Components and Hazard to Human Health. Occupational and
Environmental Exposure to Bioaerosols from Composts and Potential Health effects – A Critical Review of Published Data, Research
Report130, HSE Books, pp 15-20. 10
Environment Agency. October 2001. Technical Guidance on Composting Operations
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 7
road vehicles. The physical handling and processing of the material in the reception
hall and mechanical pre-treatment area will also generate some coarse particles,
which may become suspended in air and windblown.
2.1.27 The size of the particles will influence how far they may potentially travel from the
site. The M17 guidance indicates that large particles (>30µm) responsible for most
dust annoyance mostly deposit within 100m of the source. Intermediate sized
particles (10-30µm) may travel up to 200-500m. Smaller particles (<10µm) can travel
further from the source.
2.1.28 The unloading and handling of waste may potentially result in the generation of dust
particles in the range of sizes from 1µm to 75µm diameter. Vehicle movements
around the site may also potentially entrain any mud/materials, on the floor of the
site, up into the air and generate dust.
2.2 Air Pollution Control Measures
2.2.1 The process air treatment system comprises a ventilation system, UV odour control
system, charcoal and dust filters and biofilters. Further information regarding these
control measures is included in the Proposed Mitigation section of this report.
2.2.2 Air from the ventilation system will be fed through the two enclosed biofilters for
treatment prior to emission to air.
2.3 Emission Sources
2.3.1 The odour emission sources proposed at the site, which have been included in the
air dispersion model, are as follows:
• Gases extracted from the odour control systems will be fed through the two
enclosed biofilters for treatment prior to emission to air via the proposed
11m high stack.
11
M17 Environment Agency – Monitoring of particulate matter in ambient air around waste facilities
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 8
3 ASSESSMENT METHODOLOGY
3.1 Proposed Scope
3.1.1 The scope of works included in this assessment is as follows:
Odour
3.1.2 An odour assessment has been carried out. This takes into account the mitigation
measures proposed at the site to control odour. The odour levels likely once the site
is operational have been predicted using air dispersion modelling software. The
predicted concentrations have then been compared with criteria outlined in the
relevant Environment Agency guidance to determine whether significant adverse
effects are likely to occur.
Bioaerosols
3.1.3 In view of the comprehensive abatement and controls of bioaerosols proposed at
the site a qualitative assessment has been carried out. This assessment includes
detailed consideration of the proposed mitigation measures and controls.
Dust and Particulates
3.1.4 The potential release of dust from the site has been assessed qualitatively and
information has been provided regarding the proposed dust control measures at the
site.
3.1.5 The significance criteria used for assessing the potential magnitude of particulate
and dust impacts are included in Table 1:
Table 1: Methodology for Assessing Magnitude of Particulate and Dust Impact.
Magnitude of Impact Criteria for Impact Magnitude
Substantial
Substantial impact; issue justifies consideration as a determining factor in
granting planning permission.
Significant release of dust from the site. Reduction in visibility and rapid
accumulation of dust on clean surfaces. Possible acute health effects in
people with existing respiratory and/or cardiovascular disorders.
Moderate
Moderate impact; issue justifies consideration as a determining factor in
granting planning permission.
Visible release of dust from the site. No significant loss of visibility, but
steady accumulation of dust observed on clean surfaces. Health effects
are very unlikely.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 9
Table 1: Methodology for Assessing Magnitude of Particulate and Dust Impact.
Magnitude of Impact Criteria for Impact Magnitude
Minor
Minor impact; issue need not be considered as a determining factor in
granting planning permission.
Air-borne dust occasionally visible over the site area. Slow accumulation
of dust observed on clean surfaces, but not significantly quicker than on
similar surfaces remote from, or upwind of, site activities. In comparison
it would be similar to normal dust accumulation over the summer. No
health effects associated with dust emission.
Negligible
Negligible impact; issue need not be considered as a determining factor in
granting planning permission.
Very little change from baseline conditions. Change barely
distinguishable, approximating to a 'no change' situation.
Potentially Sensitive Receptor Locations
3.1.6 The proposed development is located in a rural setting surrounded by agricultural
land and local woodland. There are no sensitive receptor locations in the immediate
vicinity of the proposed site boundary. The closest existing residential receptor is
Mill Farm Farmhouse which is located approximately 89m from the proposed site
boundary. Existing receptors are also located approximately 280m to the west,
285m to the north and 890m to the south of the proposed development. The village
of Chebsey is located approximately 680m to the south east of the proposed
development.
3.1.7 A number of representative, potentially sensitive locations have been included in the
assessment. The sensitive locations are set out in Table 2 and shown on drawing
ST11538/009.
Table 2: Sensitive locations included in the odour dispersion modelling assessment.
Location Receptor Address
Easting Northing
Bearing from
Site
Approximate
Distance to
Site Boundary
ESR 1 Mill Farm House 385406 329562 North 89m
ESR 2 Oxleasows Farm, Chebsey, 385566 330127 North 285m
ESR 3 Rose Tree Farm, Norton Bridge 386648 330287 North East 1355m
ESR 4 Scamnel Farm, Chebsey, 386265 329958 North East 938m
ESR 5 Manor Farm, Chebsey, 386244 329316 East 760m
ESR 6 Vicarage Fields, Chebsey, 385799 329070 South East 362m
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 10
Table 2: Sensitive locations included in the odour dispersion modelling assessment.
ESR 7 Old Vicarage, Chebsey, 385876 328986 South East 469m
ESR 8 7, Mill Farm Court, Chebsey, 385893 328658 South East 675m
ESR 9 Walton Farm, Walton 386000 327963 South 1320m
ESR 10 Walton Hall School, Walton 385130 328313 South 892m
ESR 11 Field House, Blurtons Lane 384615 328899 South West 716m
ESR 12 Wheelwrights Lane, Eccleshall 384966 329187 West 283m
ESR 13 Bridge Farm, Eccleshall 384207 329282 West 1033m
ESR 14 Hilcote, Eccleshall 384857 329703 North West 449m
ESR 15 1, Hilcote Gardens, Eccleshall 384708 329663 North West 603m
ESR 16 1, The Leas, Hilcote, Eccleshall 384459 329689 North West 847m
ESR17 Baden House, Stone Road 383787 329268 West 1453m
ESR18 Hilcote House Farm Cottage,
Hilcote
384190 330043 North West 1125m
3.1.8 A uniform Cartesian receptor grid has also been included in the dispersion modelling,
to consider pollutant concentrations over a larger area. Details of the Cartesian
receptor grid are shown in Table 3.
Table 3: Uniform Discrete Cartesian Grid Parameters
Grid Parameters X Axis Y Axis
South West Coordinates 385036.85 329005.95
Number of Points 45 45
Spacing Between Grid Points 15m 15m
Length of Grid 660m 660m
Total Number of Grid Receptors 2025
3.2 Significance Criteria
3.2.1 The significance of an air quality impact is determined by considering the magnitude
of the impact together with the sensitivity of the location as shown in Table 4.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 11
Table 4: Methodology for Determining Sensitivity
Sensitivity Examples
High The location has little ability to absorb change without fundamentally altering its
present character, or is of international or national importance.
Moderate The location has moderate capacity to absorb change without significantly altering
its present character, or is of high importance.
Low The location is tolerant of change without detriment to its character, is of low or
local importance.
3.2.2 The receptor locations, considered in the air quality assessment, are all residential in
nature and are considered to be moderately sensitive. The exception to this is
existing receptor location (ESR) 10 which is educational in nature and is also
considered to be moderately sensitive. Premises such as hospitals and nursing
homes would be identified as highly sensitive; however no premises of this type
were identified in the area surrounding the site.
3.2.3 The significance of an impact for odour, bioaerosols, particulates and dust is
determined by the interaction of magnitude and sensitivity. The Impact Significance
Matrix used in this assessment is set out in Table 5.
Table 5: Impact Significance Matrix
Sensitivity
Magnitude
High Moderate Low
Substantial Major
Adverse/Beneficial
Major - Moderate
Adverse/Beneficial
Moderate - Minor
Adverse/Beneficial
Moderate Major - Moderate
Adverse/Beneficial
Moderate – Minor
Adverse/Beneficial
Minor
Adverse/Beneficial
Minor Moderate - Minor
Adverse/Beneficial
Minor
Adverse/Beneficial Minor - Negligible
Negligible Negligible Negligible Negligible
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 12
4 PROPOSED MITIGATION
4.1 The Plant Design
4.1.1 The design of the AD plant is such that waste is fully enclosed for the duration of the
process between initial discharge and product loading.
4.1.2 Where there is the potential for odour to arise, the air from the activity will be air-
extract ventilated to the biofilters for treatment prior to release to atmosphere. This
system will control fugitive releases of odours and bioaerosols. It will also provide a
safe working environment for the plant operators.
4.2 Odour and Bioaerosol Control
4.2.1 At the proposed facility bioaerosols and odour will be minimised as the waste will be
fully enclosed except at the initial discharge point in the waste reception and process
building.
4.2.2 To control odour and bioaerosols, the entire waste reception and process building
will be fully air–extract ventilated to treatment by the biofilters. The doors of the
waste reception area will be kept closed at all times other than when the vehicles
need to enter and leave.
4.2.3 Any areas of the digestion plant, where potentially odorous air may develop, will be
extracted and the air ducted to treatment. The process air from the plant ventilation
system will be cleaned of odour, dust and bioaerosols by the UV odour control
system, charcoal and dust filters and biofilters.
4.3 The Proposed Air Pollution Control Measures
4.3.1 The proposed air pollution control measures will comprise:
• A ventilation system to extract air from the waste reception and process
building. The system will create negative pressure in these buildings reducing
the potential for fugitive emissions;
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 13
• A UV odour control system to treat odour in the air extracted from the
buildings;
• Charcoal and dust filters to remove odour and dust from the air extracted
from the buildings;
• Two enclosed biofilters to treat extracted air prior to release to atmosphere
from the proposed 11m high stack associated with the biofilters. The
biofilters will comprise two modified “rollonoff” containers measuring 6.5m
long by 2.4m wide by 2.4m high. The containers will be filled with bark and
processed oversize material, from the composting operation, which absorb
organic and inorganic compounds. The biofilters will be located on the
northern elevation of the waste reception and process building.
4.4 Measures to Mitigate Dust and Particulates
4.4.1 Dust from the reception and pre-treatment areas of the AD plant is unlikely to be
generated in any significant quantity. The delivered waste will be loaded promptly
into the pre-treatment plant. From this point until the digestate is removed from
the site the materials are under cover so dust will be completely controlled. Dust
can therefore only arise within the enclosed building where it will be controlled by
good housekeeping and air extraction.
4.4.2 In addition to the biofilters, dust filters will be installed at the site to filter air from
the ventilation system. Once the air has been filtered, it will travel to the biofilters
for treatment prior to release to air from the proposed 11m high stack associated
with the biofilters.
4.4.3 The plant, e.g. loading shovels, will emit particulates; however plant will undergo
routine maintenance to minimise potential emissions.
4.4.4 Measures will be implemented at the site to ensure that all areas are kept clear of
dust. These include:
• The site will be hard surfaced on all operational areas.
• All waste outside the waste reception and process building will be suitably
contained whilst on site and during its removal.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 14
• The site will be kept clean by manual and mechanical sweeping as
appropriate.
4.5 Summary of Effectiveness of Mitigation
4.5.1 The mitigation measures to be implemented at the AD plant may be categorised by
their effectiveness. The following basis has been used:
• High certainty of being effective: The measures can reasonably be expected
to be effective in avoiding or reducing the potential effect.
• Uncertainty of effectiveness: The measures cannot reasonably be expected to
be effective and should not therefore influence the assessment of the effect.
However the measures have been incorporated into the design of the
scheme on the basis that, despite its potential ineffectiveness, it is
worthwhile;
• No mitigation proposed: This may be because the effect is a positive one or
that no means of mitigating the effect has been identified.
4.5.2 Due to the effectiveness of the mitigation measures which include the ventilation
system, UV odour control system, charcoal and dust filters, two biofilters with
associated 11m high stack and general operational procedures (e.g. odour
generating processes being carried out inside air extracted buildings), it is considered
that the likely effectiveness of the mitigation measures at the site will be high.
4.5.3 Other measures that will be incorporated into the proposals at the site include a
proactive site management and general housekeeping maintenance measures; for
example ensuring all external doors remain shut in order to prevent unabated
release of bioaerosols or odour. Site staff will be trained in matters relating to risk of
odours and other amenity impacts, and will implement a range of measures to
mitigate any emissions as required
4.5.4 The measures proposed to control emissions at the AD plant will provide a high level
of protection for local residents and the local environment. The potential effects of
the emissions likely to be generated at the site has been assessed taking into
account these proposed mitigation measures.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 15
5 ASSESSMENT OF EFFECTS
5.1.1 This section of the report details the odour dispersion modelling undertaken to
assess the significance of the potential odour emission from the proposed Mill Farm
AD plant. Potential emissions of odour from the two proposed open biofilters have
been considered in the assessment.
5.1.2 The potential effects of odour, bioaerosols, dust and particulates likely to be
generated at the site are considered against relevant significance criteria.
5.2 Odour Dispersion Modelling
5.2.1 Potential emissions to atmosphere have been modelled using AERMOD (Lakes
Environmental model version 6.7). This is a proprietary quantitative air dispersion
model which is based upon the Gaussian theory of plume dispersion. The model uses
all input data, including the characteristics of the release (rate, temperature, release
height, location etc.), the terrain, meteorological data and the locations of the
buildings adjacent to the proposed emission point to predict the concentration of
the substance of interest at a specified point.
5.2.2 The model uses sequential hourly meteorological data and the locations of the
buildings to predict the concentration of each substance at each point for each hour
over the course of a year. This allows the long-term mean and short-term peak
ground level concentrations to be estimated over the modelled area as required. The
dispersion modelling has been carried out in accordance with the Environment
Agency guidance12
.
5.3 Assessing the Significance of Modelled Odour Concentrations
5.3.1 The predicted odour levels have been assessed with reference to the Environment
Agency’s Technical Guidance Note H4 – Odour Management13
. The H4 guidance
indicates that when considering the potential for annoyance not all odours have the
same potential. The activities at the site will involve the processing of putrescible
waste. This is identified as a more offensive odour in H4, i.e. it falls into the High
12
Environment Agency (EA) Air dispersion modelling requirements
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 16
Offensiveness category.
5.3.2 The indicative criterion for assessment of the high offensiveness category of odours
is 1.5ouE /m3 (1 hour 98
th percentile). Predicted concentrations of 1.5ouE/m
3 (1 hour
98th
percentile) or more are therefore considered potentially significant in this
assessment.
5.3.3 The odour source included in the model is the air collected from the waste reception
and process building. This air is transported to the biofilters for treatment prior to
release to atmosphere.
5.4 Study Inputs
Meteorology
5.4.1 Two meteorological stations are located in the vicinity of the proposed development.
• Shawbury recording station which is located 30.9km from the proposed
development at an approximate altitude of 72m AOD.
• Leek Thorncliffe recording station which is located 33.4km from the proposed
development at an approximate altitude of 298m AOD.
5.4.2 The proposed development will be situated at an approximate altitude of 108m
AOD. The Shawbury meteorological recording station is located closer to the
proposed development, at a similar altitude, and is therefore considered the most
representative recording station. Five years of hourly sequential meteorological
data (2005 to 2009) was obtained from the Shawbury recording station for use in the
dispersion model.
Terrain
5.4.3 To consider the impact of terrain surrounding the site, on the dispersion of
pollutants, x.y.z data for the surrounding terrain has been used in the model.
Proposed slab level data for the site has also been included when identifying the
ground heights of on-site buildings and emission sources.
13
Environment Agency Technical Guidance Note H4 – Odour Management, June 2009
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 17
Surface Characteristics
5.4.4 The predominant characteristics of land use in an area provides a measure of the
vertical mixing and dilution that takes place in the atmosphere due to factors such as
surface roughness and albedo.
5.4.5 Examination of the local setting has shown that the proposed site is surrounded by
agricultural land, localised woodland and scattered residential properties. The
village of Chebsey is located approximately 680m to the south east of the proposed
development.
Emission Parameters – Odour
5.4.6 Air from the waste reception and process building will be treated by the biofilters
prior to release to atmosphere. Dispersion modelling has been carried out to assess
the fugitive odour emissions from the two proposed biofilters. The odour emission
rate has been derived from an actual air flow through the biofilters of 16,200m3/hr.
5.4.7 A residual odour concentration of 1000ou/m3 from the enclosed biofilters has been
assumed. Treated air exiting the stack associated with the biofilters has been
modelled for a temperature range of 298 - 308°K. The odour modelling therefore
considers odour emission rates derived from this residual odour concentration, the
minimum and maximum gas exit temperatures and associated normalised flow rate.
5.4.8 The parameters included in the model are shown in Table 9. The emission rates are
shown in Table 10.
Table 9: Model Parameters – Odour
Parameter
Biofilters
Biofilters Stack Location (southwest corner) 385357, 329345
Base Elevation 108m AOD
Stack Diameter 0.45m
Gas Exit Flow Rate 16,200Am3/hr
Efflux Velocity 28.29m/s
Gas Exit Temperature 298°K/308°K
Stack Height 11m
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 18
Table 10: Emission rates modelled from the biofilters – Odour
Residual Odour Concentration Odour Emission Temperature Odour Emission Rate
298°K 4120ou/s 1000ou/m
3
308°K 3990ou/s
Treatment of Buildings and Site Plan
5.4.9 The buildings included in the dispersion model are summarised in Table 13.
Table 13: Buildings/structures included in the dispersion model.
Building Height
Grid Ref of South
Western Corner/ or
Centre for Cylindrical
Tanks
Length and Width or
Diameter (metres)
Proposed Onsite Buildings
Monitoring equipment and
underground AD tanks 2.5m 385293, 329296 55m x 35m
Proposed reception and
treatment building 11m 385330, 329343 25m x 15m
Gas storage balloon 4.1m 385344, 329356 5m
Odour
5.4.10 Odour emissions, from the proposed biofilter stack, were modelled using AERMOD
and the modelled concentrations (as 1 hour 98th
percentile concentrations) for each
of the considered receptor locations are included in Appendix A. The maximum
modelled odour concentration is shown in Table 14 for the representative existing
sensitive receptor locations considered.
Table 14: Maximum modelled odour concentrations (1 hour 98th
percentile) at considered existing
sensitive receptor locations
Modelled residual
odour concentration
Modelled
Temperature
Maximum
concentration at
receptor location
Maximum modelled
Cartesian grid
concentration
298°K 0.29ou/m3 at ESR1 1.05ou/m
3
1000ouE/m3
308°K 0.27ou/m3 at ESR1 1.01ou/m
3
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 19
5.4.11 The dispersion modelling indicates that the modelled 98th
percentile odour
concentrations (for a 1 hour averaging time) will comply with the indicative criterion
of 1.5ou/m3 for all existing receptor locations considered in the dispersion
modelling.
5.4.12 A Cartesian receptor grid has also been modelled. The highest modelled odour
concentration from this grid is shown in Table 14 and is detailed in Appendix A. The
maximum modelled grid concentration is significantly below the 1.5ou/m3 indicative
criterion.
5.4.13 On this basis, the control on emissions due to the proposed 11m high stack
associated with the biofilters is forecast to ensure that any residual odour is not
significant. It is also predicted that these emissions will give no reasonable cause for
annoyance due to odour.
Bioaerosols
5.4.14 With regards to the bioaerosols generated at the site the mitigation measures
detailed in this report will be implemented to ensure that any potential emissions of
bioaerosols are controlled and treated appropriately prior to release to air.
5.4.15 The biofilters and associated 11m high stack have been designed to ensure that
adequate bioaerosol control is provided. With the implementation of these control
measures the potential impact of bioaerosols generated at the site is forecast to be
negligible and no sensitive location close to the site will experience a significant
impact.
Dust and Particulates
5.4.16 The ventilation system and dust filters will be implemented to ensure that any
emissions of dust and particulates are contained within the waste reception and
process building and that any dust/particulates are removed prior to air being
released to atmosphere. These control measures will ensure that no significant
impact occurs.
5.4.17 Any dust which may be generated outside the building will be mitigated by routine
manual and mechanical sweeping as appropriate.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 20
5.4.18 Taking into consideration the measures that will be implemented at the site it is
anticipated that the magnitude of impact will be negligible in accordance with the
criteria set out in Table 1.
5.4.19 To summarise, the magnitude of the potential impact of dust and particulates
generated at the site will be negligible and any receptors surrounding the site will
therefore experience a negligible impact.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 21
6 CONCLUSION
Odour
6.1.1 With regards to the odour generated at the site the mitigation measures detailed in
this report will be implemented to ensure that any potential emissions of odour are
controlled and treated appropriately prior to release from the stack attached to the
two enclosed biofilters.
6.1.2 Dispersion modelling was undertaken to assess the odour concentrations at
representative existing sensitive receptor locations surrounding the site, due to
residual emissions from the 11m high stack, associated with the two proposed
biofilters. The modelling was carried out to consider a residual concentration of
1000ouE/m3.
6.1.3 The dispersion modelling indicates that the modelled 98th
percentile odour
concentrations (for a 1 hour averaging time) will comply with the H4 indicative
criterion of 1.5ouE/m3 at the existing sensitive receptor locations and modelled
Cartesian grid considered in the assessment.
6.1.4 On this basis, the control on emissions due to the proposed 11m high stack
associated with the biofilters is forecast to ensure that any residual odour is not
significant. It is also predicted that these emissions will give no reasonable cause for
annoyance due to odour.
Bioaerosols
6.1.5 With regards to the bioaerosols generated at the site, the mitigation measures
detailed in this report will be implemented to ensure that any potential emissions of
bioaerosols are controlled and treated appropriately prior to release from the
proposed stack.
6.1.6 The biofilters has been designed to ensure that adequate bioaerosol control is
provided. With the implementation of these control measures the potential impact
of bioaerosols generated at the site is forecast to be negligible and no sensitive
location close to the site will experience a significant impact.
JACK MOODY LTD
Anaerobic Digestion Plant, Mill Farm, Chebsey
ST11538-RPT-004
April 2011
Page 22
Dust and Particulates
6.1.7 The ventilation system and dust filters will be implemented to ensure that any
emissions of dust and particulates are contained within the building and process
areas and that any dust/particulates are removed prior to air being released to
atmosphere via the biofilter stack. These control measures will ensure that no
significant impact occurs.
6.1.8 Any dust which may be generated outside the building will be mitigated by routine
manual and mechanical sweeping as appropriate.
6.1.9 Taking into consideration the measures that will be implemented at the site it is
anticipated that the magnitude of impact will be negligible in accordance with the
criteria set out in Table 1.
6.1.10 To summarise, the magnitude of the potential impact of dust and particulates
generated at the site will be negligible and any receptors surrounding the site will
therefore experience a negligible impact.
Appendix A - Predicted Odour Concentrations at Considered Receptor Locations
RECEPTOR X Y ADDRESS 298K 308K
ESR 1 385406 329562 Mill Farm 0.29 0.27
ESR 2 385566 330127 Oxleasows Farm 0.05 0.05
ESR 3 386648 330287 Rose Tree Farm 0.02 0.02
ESR 4 386265 329958 Scamnel Farm 0.05 0.04
ESR 5 386244 329316 Manor Farm 0.05 0.05
ESR 6 385799 329070 Vicarage Fields 0.05 0.05
ESR 7 385876 328986 Old Vicarage 0.04 0.04
ESR 8 385893 328658 7 Mill Farm Court 0.03 0.03
ESR 9 386000 327963 Walton Farm 0.02 0.02
ESR 10 385130 328313 Walton Hall School 0.01 0.01
ESR 11 384615 328899 Field House, Blurtons Lane 0.02 0.02
ESR 12 384966 329187 Wheelwrights Lane, Eccleshall 0.09 0.08
ESR 13 384207 329282 Bridge Farm 0.02 0.02
ESR 14 384857 329703 Hilcote 0.03 0.03
ESR 15 384708 329663 1 Hilcote Gardens 0.02 0.02
ESR 16 384459 329689 1 The Leas 0.02 0.01
ESR 17 383787 329268 Baden House, Stone Road 0.01 0.01
ESR 18 384189 330043 Hilcote House Farm Cottage 0.01 0.01
1.05 1.01
385321.85, 329350.95
(onsite)
385321.85, 329350.95
(onsite)
Modelled Odour Concentration (ou/m3)
Maximum Modelled Cartesian Grid Concentration Location
Maximum Modelled Cartesian Grid Concentration