Assessment and control of odour nuisance from waste water treatment: code of practice

2. GLOSSARY OF TERMS

Analytical assessment An assessment of an odorous sample using instrumentation to provide information on the concentration and possibly provide identification of the chemical species present. Compare with "sensory" assessment.

Area source A surface-emitting source, which can be solid (for example the spreading of wastes, material stockpiles, surface of a biofilter) or liquid (storage lagoons, effluent treatment plant).

BOD Biochemical Oxygen Demand

bpm Section 79(9) of the Environmental Protection Act 1990 provides that it is a defence against Statutory Nuisance action to prove that Best Practicable Means (bpm) have been used to control and mitigate the nuisance. The key parts of the term can be defined as:-

'practicable' means reasonably practicable having regard among other things to local conditions and circumstances, to the current state of technical knowledge and to the financial implications;

the ' means' to be employed include the design, installation, maintenance and manner and periods of operation of plant and machinery, and the design, construction and maintenance of buildings and structures ;

CEN OlfactometryBSEN 13725: 2003, Air Quality - Determination of Odour

Standard Concentration by Dynamic Oflactometry

CoP Code of Practice on Assessment and Control of Odour Nuisance from Waste Water Treatment Works

Detection threshold The point at which an increasing concentration of an odour sample becomes strong enough to produce a first sensation of odour in 50% of the people to whom the sample is presented. This is a laboratory-based test and should be conducted according to the relevant CEN standard. The odour concentration at the detection threshold is one odour unit.

Diffuse sources Sources with defined dimensions (mostly surface sources) that do not have a defined waste air flow, such as waste dumps, lagoons, fields after manure spreading, un-aerated compost piles.

Dilution factor The dilution factor is the ratio between flow or volume after dilution and the flow or volume of the odorous gas.

Emission factor The emission per unit product (e.g. for wastewater treatment works expressed in this report the emission rate in ou _E.s ^-1 per kg BOD, in screened sewage)

European odour unit That amount of odorant(s) that, when evaporated into 1 cubic

ou _E/m ³ metre of neutral gas at standard conditions, elicits a physiological response from a panel (detection threshold) equivalent to that elicited by one European Reference Odour Mass ( EROM), evaporated in one cubic metre of neutral gas at standard conditions.

European Reference The accepted reference value for the European odour unit,

Odour Mass ( EROM equal to a defined mass of a certified reference material. One EROM is equivalent to 123 μg n-butanol ( CAS 71-36-3) when evaporated in 1 cubic metre of neutral gas (this produces a concentration of 0.040 μmol/mol).

Fugitive releases Unintentional emissions from eg flanges, valves, doors, windows - that is, points which are not designated or intended as release points.

Hedonic scale A judgement of the relative pleasantness or unpleasantness of an odour made by assessors in an odour panel. A methodology is described in VDI 2882. Odours which are more offensive will have a negative hedonic score whilst less offensive will tend towards a positive score.

Nuisance A nuisance can be defined as "an interference with an interest in the use and enjoyment of private land, or the public interest in the use and enjoyment of public places", or "unacceptable material interference with the personal comfort or amenity of neighbours or a nearby community." There is always an element of professional judgement as to the point at which a nuisance occurs in respect of the particular circumstances of interference with comfort and amenity.

Odorant flow rate The odorant flow rate is the quantity of odorous substances passing through a defined area at each time unit. It is the product of the odour concentration c _od and the outlet velocity ν and the outlet area A or the product of the odour concentration c _od and the pertinent volume flow rate V, in e.g. m ³/h. Its unit is ou _E/h (or ou _E/min or ou _E/s, respectively).

Odour abatement The reduction of the odour concentration or the odorant flow

efficiency rate due to an abatement technique, expressed as a fraction (or percentage) of the odour concentration in the odorant flow rate of the untreated gas stream.

Odour concentration The amount of odour present in a cubic metre of sample gas at standard conditions. The odour concentration is measured in European odour units (ou _E/m ³). The odour concentration at the detection threshold is defined to be 1 ou _E/m ³. If an odour sample has been diluted in an olfactometer by a factor of 10,000 to reach the detection threshold, then the concentration of the original sample is 10,000 odour units.

Odour detection To become aware of the sensation resulting from adequate stimulation of the olfactory system.

Odour Nuisance In the Code, it has been assumed that only a local authority or Court can assess whether a particular odour constitutes a Statutory Nuisance. Therefore, the term 'odour nuisance' is used throughout the code to reflect an odour that, if subject to assessment by a local authority or Court, would be regarded as a Statutory Nuisance. In respect of this Code, there is no difference between the characteristics of an odour nuisance and a Statutory Nuisance.

Odour Potential This term is a measure of the total odour which could be released by a liquid - it is the odour concentration in air that has been brought to equilibrium with the liquid sample by blowing air through the sample in a standard apparatus

Odour unit The amount of odorant(s) that, when evaporated into 1 cubic metre of neutral gas at standard conditions, elicits a physiological response from a panel (detection threshold) equivalent to that elicited by one European Reference Odour Mass ( EROM), evaporated in one cubic metre of neutral gas at standard conditions

Offensiveness An expression of the degree of unpleasantness of one odour relative to another. The perceived offensiveness of an odour will vary between individuals as a result of both physical and psychosocial differences, but in a population a relatively consistent response on the relative offensiveness of different odours is returned.

Olfactometer Apparatus in which a sample of odorous gas is diluted with neutral gas in a defined way and presented to a odour panel under reproducible conditions.

Olfactometry Measurement of the response of assessors to olfactory stimuli. ( ISO 5492).

Olfactory Pertaining to the sense of smell ( ISO 5492).

OIP An Odour Improvement Plan ( OIP) should be prepared for all processes where the odour nuisance is not abated by the application of Baseline measures as detailed in Section 12. The fundamental requirement of the OIP is to evaluate the sources and causes of odour to ascertain whether a nuisance exists and to development an odour control scheme. The plan should review all available control options and compare the capital and operating costs for each option along with the environmental impacts (for example due to secondary pollutants and energy and raw materials use).

OMP The Odour Management Plan ( OMP) is a core document that is intended to detail operational and control measures appropriate to management and control of odour at the site. The format of the OMP should provide sufficient detail to allow operators and maintenance staff to clearly understand the operational procedures for both normal and abnormal conditions.

pe Population Equivalent - a term used to define the treatment capacity or load on a WWTW. The EC Urban Waste Water Directive 91/271/ EEC ( UWWT) defines the term and 1 pe is the biodegradable load in wastewater having a 5-day biochemical oxygen demand ( BOD) of 60g of oxygen per day.

PFI Private Finance Initiative - this is a way of funding major capital investments, without immediate recourse to the public purse. Private consortia are contracted to design, build, and in some cases manage and operate WWTW.

Point source An intentional point of release such as a vent or chimney, where it may be possible to obtain a sample in order to quantify the concentration and determine the mass release rate

ppb Parts per billion

ppm Parts per million

PPP Public Private Partnership - a mechanism for public bodies and private companies to work together on a project. Private Finance Initiative is one form of Public Private Partnership.

Recognition threshold The odour concentration which has the probability of 0.5 of being recognised under the conditions of the test. The recognition threshold is generally a higher concentration than the detection threshold. It is generally two or three odour units in a laboratory setting but may be higher than this outside the lab.

Sample The odorous gas sample which is assumed to be representative of the gas mass or gas flow under investigation, and which is examined to determine the odour concentration, to characterise the odour or to identify constituent compounds.

Sensitive receptor People who are exposed to odour released from a given source, or have the potential to be exposed. Unlike other pollutants, odour at environmental exposure levels is not considered in terms of possible detrimental effects on animals and plants.

Sensory Relating to the human response to a particular stimulus (in this case odour).

SEPA Scottish Environment Protection Agency

Statutory Nuisance As per Section 79 (1) (d) of the Environmental Protection Act 1990 - smell arising on industrial, trade or business premises and being prejudicial to health or a nuisance. In the Code, it has been assumed that only a local authority or a Court can assess whether an odour constitutes a Statutory Nuisance. Therefore the term has only been used where it relates to such as assessment - in all other cases the term 'odour nuisance' has been used. In respect of this Code, there is no difference between the characteristics of an odour nuisance and a Statutory Nuisance. The final decision on what constitutes a Statutory Nuisance rests with the Courts.

UWWT The EC Urban Waste Water Directive 91/271/ EEC

VOC Volatile Organic Compounds - Organic substance that will readily evaporate and transfer from a liquid into a gas phase.

WCCP Water Customer Consultation Panel

WICS The post of Water Industry Commissioner for Scotland

WWTW Waste Water Treatment Works - for the purpose of this Code, a WWTW is any location at which waste water is subject to physical, chemical or biological treatment. This Code only relates to treatment works and will not specifically address the potential odour issues associated with the sewerage transport system (drains, sewers and remote pumping stations).