JACK MOODY LTD Anaerobic Digestion Plant, Mill Farm ...

JACK MOODY LTD

Anaerobic Digestion Plant, Mill Farm, Chebsey

Volume 3 – Odour Assessment

April 2011

DATE ISSUED: February 2011

JOB NUMBER: ST11538

REPORT NUMBER: ST11538-RPT-004

JACK MOODY LTD


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.

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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

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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

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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.

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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.

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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

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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.

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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

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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

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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


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.

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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


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


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

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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.

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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

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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;

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• 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.

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• 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.

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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

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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

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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

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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

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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.


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.

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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.

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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.

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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 Receptor Locations

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

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