Scottish Government

1. Introduction

1.1 Overview

1.1.1 Waste water is produced as a by-product of human existence and numerous industrial processes. Although primarily water, waste water contains various other biological and chemical materials which, if released in an uncontrolled manner to the environment are capable of causing pollution. The production, transmission and treatment of waste water can result in the generation of odour.

1.1.2 There are many different means of preventing, controlling or reducing odours to minimise the impact of odour in the locality of waste water treatment works ( WWTW) and avoid creation of odour nuisance. It is acknowledged at the outset that these facilities are likely to produce odours from time to time. This guidance note provides advice on the application and selection of odour control measures for WWTW.

1.2 Development of Controls for Odour Emissions from WWTW

1.2.1 The incidence of complaints of odour nuisance from WWTW has been steadily increasing over the last two decades. There is little evidence of changes in the raw sewage itself to explain this, but there are a number of other reasons why this might have occurred.

1. The awareness of the public and expectation of a better environment have increased, as has the belief that complaint can lead to action.
2. Housing and other developments have significantly encroached on the land around WWTW increasing the number of people likely to be impacted by odour from WWTW.
3. The additional waste water produced by increased development can create capacity issues at existing WWTW that can result in inefficient operation and resulting odour releases.
4. Implementation of the Urban Waste Water Treatment ( UWWT) Directive during the 1990s has been a key environmental driver in requiring improvement of waste water treatment plant and discharges. The Directive primarily requires improvements in the discharge quality from WWTW and has resulted in many works installing additional treatment stages in the process. This has resulted in a substantial investment in the construction of new and upgraded treatment works to meet the water quality requirements of this Directive, many of these works being in odour-sensitive locations. There has also been an increased requirement to pump sewage for considerable distances leading to poor aeration that can result in odour. There are also a number of other legislative drivers that may potentially result in higher levels of treatment than required for the UWWT Directive.
5. Implementation of the UWWT Directive also prohibits the disposal of sludge to surface water. In addition, the Directive requires that sludge arising from WWTW is re-used where appropriate and in any case disposal routes must minimise adverse effects on the environment. This has resulted in the development of new treatment facilities for sludge and the associated significant increase in sludge storage capacity to collect sludge prior treatment.

1.2.2 There was a degree of uncertainty surrounding the application of nuisance provisions of the Environmental Protection Act 1990 to odours from WWTW resulting in a number of high profile Court cases in the UK and confusion over the application of nuisance powers. Whilst current precedent would suggest that Part III of the Environmental Protection Act 1990 does apply to odours from WWTW, the Scottish Ministers decided that it would be appropriate to clarify the situation and incorporate a specific legal duty on Scottish Water to control odours as part of the Water Services etc (Scotland) Act 2005 ( WSSA).

1.2.3 In preparation for adoption of new statutory controls, a voluntary Code of Practice ( CoP) on the control of odours from WWTW was issued in April 2005 to provide guidance on the levels of control appropriate for avoidance of odours amounting to Statutory Nuisance under Part III of the Environmental Protection Act 1990. The voluntary CoP has now been superseded by the Sewerage Nuisance (Code of Practice)(Scotland) Order 2006 and this guidance.

1.3 What this Guidance applies to

1.3.1 The Water Services etc (Scotland) Act 2005 provided powers to allow Scottish Ministers to make an order containing a code of practice (referred to as the Sewerage Code) for the purpose of assessing, controlling and minimising Sewerage Nuisance. The first of these codes is contained in the Sewerage Nuisance (Code of Practice)(Scotland) Order 2006 that came into force on 22 April 2006 and this document is supporting guidance to that CoP. A copy of the Order is attached as Annex 2 of this document.

1.3.2 The CoP specifies the framework within which Scottish Water and its contractors and local authorities will operate to minimise the impacts of odours from WWTW, and identify steps to tackle nuisance odours.

1.3.3 The first CoP only applies to Sewerage Nuisance arising from odour nuisance from WWTW and accordingly this guidance only relates to such Sewerage Nuisance. The standards required by the statutory code have been developed from the voluntary code although the new code introduces a more structured approach to management and regulation.

1.3.4 The legal framework relevant to this guidance note is further detailed in Section 2 below.

1.4 Status of this Guidance

1.4.1 The statutory requirements concerning odour nuisance from WWTW are contained in the WSSA and the CoP. This document is only intended to provide guidance to Scottish Water and it's contractors, local authorities, local communities and other stakeholders with an interest in regulation of odour from WWTW on the application and interpretation of the first Sewerage Code relating to odour from WWTW.

1.5 Structure of this Guidance

1.5.1 This guidance includes general information on WWTW and advice to local authorities on enforcement and inspection policy as well as a detailed review of the requirements of the CoP. In order to clearly differentiate the guidance from statutory requirements, all extracts from the CoP (which are requirements) are included in labelled, highlighted text boxes as shown below. All information not within these boxes should be regarded as guidance.

Code of Practice Requirement - Paragraph *

1.5.2 This guidance describes appropriate measures which include:

• The assessment of odour nuisance;
• the general management of the WWTW;
• the design, installation and maintenance of plant, buildings and structures
• the operation of the WWTW and its processes; and
• engineering solutions, e.g. containment, enclosure with venting and end-of-pipe odour treatment.

1.6 Responsibilities of Organisations with an Interest in this Code

1.6.1 There are a number of organisations involved in the operation and regulation of waste water treatment works and this CoP will be of interest to all stakeholders involved with, and affected by, odour from WWTW. These include:-

• Scottish Executive - responsible for policy development in environmental standards and nuisance and producing statutory Codes of Practice on Sewerage Nuisance
• Scottish Water - responsible for the collection and treatment of waste water ; in some circumstances they may appoint contractors ( PFIs) to supply, build and operate works on their behalf and the CoP will also apply to the PFI operators
• SEPA - the Scottish Environment Protection Agency are responsible for controlling surface water quality and regulating discharge standards for WWTW, enforcement of the IPPC regime of Part I of the Environmental Protection Act 1990 and the Waste Management Licensing provisions of Part II of the Environmental Protection Act 1990
• Local Authorities - responsible for enforcing the Sewerage Nuisance provisions of the Water Services etc (Scotland) Act 2005
• WIC - The Water Industry Commission for Scotland is the primary financial and service level regulator for the water services undertaken by Scottish Water and to promote the interests of customers of Scottish Water. The Commission advises Scottish Ministers on the amount of revenue that Scottish Water needs to provide a sustainable service to customers and to fund its investment programme efficiently.
• WCCP - the Water Customer Consultation Panels represent the views and interests of Scottish Water customers and may make recommendations to Scottish Ministers and industry regulators. The Convenor of WCCP is responsible for investigating complaints about Scottish Water's core services.
• SOSG - the Scottish Odour Steering Group was established by the Scottish Executive and includes representation from the above-mentioned organisations (see 1.7 below).

1.7 Scottish Odour Steering Group ( SOSG)

1.7.1 The Scottish Odour Steering Group ( SOSG) is a group with representation from all parties involved in odours from WWTW including the Scottish Executive, SEPA, WIC, WCCP, local authorities and Scottish Water. The primary aim of SOSG is to provide a forum for all stakeholders to review the development and progress of the CoP and to determine the prioritization of control measures at the various sites.