28 WATER / WASTEWATER
Management Plan was developed which defi nes how air from the proposed TTT is vented in and out of the system and how air releases are controlled and treated. Activated carbon fi lters were chosen for use in ventilation shafts to trap odours. Another incorporation in the design of the TTT project is the use of high ventilation columns to discharge foul air at height, to prevent the impact of odour to the surrounding area and minimise the risk of odour complaints. To allow for the proposed air management and odour control system to be sized, extensive research and development work including a series of fi eld trials to determine the impact of septicity during tunnel operations, hydraulic modelling studies, air movement modelling and dispersion modelling studies were undertaken as part of the TTT project. Overall, the TTT air management system designed achieves over 99.7% treatment of typical year exhausts. Once operational, the TTT will use hydrogen sulphide sensors to monitor odour at all shafts to ensure system effi ciency.
Ventilation of the Thames Tideway Tunnel, from Georgaki et al, 2018.
and enable the operator to respond rapidly. The same forecasting models can be used to generate an odour risk forecast for the next 72 hours, so that operational tasks can be altered or reconsidered, to help reduce the risk of the facility impacting the local community. Should offsite complaints be registered, reverse trajectory modelling (back tracking) can be deployed to model the parcel of air from the complaint back to the likely source of the odour. Therefore, reverse trajectory modelling can be used to narrow down the focus of investigations into the source of a historic odour problem.
A higher-level dashboard can be used to summarise Key Performance Indicators (KPIs) on a single interface, for example threshold breaches and odour complaints, to present the headline data to management or to site managers (Figure 3).
Besides chemical dosing, another way to control odour is to incorporate preventative measures at the design
stage.The Thames Tideway Tunnel (TTT) project in London, has incorporated a ventilation and odour control system to mitigate the potential risk of odour nuisance in the vicinity of tunnel shafts. For this reason, an Air
“We undertook fi eld trials including a review of commercially available hydrogen sulphide monitors,” explains Dr Sofi a Georgaki, Odour and Ventilation Lead for the TTT Air Management System, “we discovered that detection of hydrogen sulphide at low concentrations is diffi cult due to several issues identifi ed during the TTT trials. Some of the issues include power requirement, diffi culties in transmitting the data and maintenance of the equipment but also sensitivity of most sensors available to ambient temperature and humidity.” To overcome the problems identifi ed, the team designed their own bespoke self-powered solution combining a H2
S analyser (using a gold leaf sensor) with solar panels and telemetry.
To conclude, compliance with an odour monitoring plan is a vital fi rst step, but you cannot rely solely on monitoring to refl ect reality, and the human receptor is always paramount. “You can use surrogate measures to monitor odour,” explains Mr Preger, “but should always recognise that nothing is better at picking up issues than the human nose.”
Rosa Richards is an Independent Environmental Consultant specialising in water policy and monitoring. She is Programme Manager of the Sensors for Water Interest Group (SWIG), and a freelance writer of science and technology. This article is based on a SWIG webinar ‘Odour Measurement and Control’ held in June 2020
www.swig.org.uk
Author Contact Details
Rosa Richards, Independent Environmental Consultant • Bristol • Tel: 01934 830658 • Email:
rosapmrichards@gmail.com • Web:
https://www.linkedin.com/in/rosa-richards-7a515936/
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