Proceedings

In April 2006 a statutory Code of Practice for the control of odour nuisance at wastewater treatment works (WWTWs) came into force in Scotland. A central requirement of this Code is to have an Odour Management Plan in operation at all works with a population equivalent
greater than 500, of which there are approximately 400 in Scotland. The OMPs have a fundamental role in enabling local authorities to assess Scottish Water’s compliance with the Code.

At the time, very few works had OMPs and it was clear that a significant amount of work was required to assess existing operations to establish odour risk and means for its control. Hyder Consulting were engaged through an OJEU tendering process to carry out this work at all the sites, except 20 of the largest works, which are operated under PFI contracts. The WWTWs varied in size from 500 to 600 000 population equivalent with rural and city locations. Only a small proportion of the WWTWs had identified odour issues. The objective
was to produce a document to assist the operator and the regulator in the management of existing assets to minimise the risk of odour nuisance under normal and abnormal conditions.

The development process included:
• the derivation of generic best practice techniques for individual process stages,
• site visits and audits and discussions with operations staff to identify current operations and odour critical plant for the individual WWTWs,
• selection and modification of the generic techniques as appropriate for the specific WWTWs, taking into account factors such as size, location and operational requirements and
• assessment of the impact of, for example, failure of odour critical plant and mitigation measures.

Each document also contained other information relevant to the control of odours, such as Scottish Water management and complaint handling procedures.

KEY WORDS
Odour nuisance, Odour control, Odour management plans, Wastewater treatment works