Project Appreciation and Objectives
The Environment Agency's Monitoring Certification Scheme - MCERTS has been operating for five years and many wastewater treatment plant certificates are coming up for renewal. However, concern has been raised by MCERTS Inspectors and by the MCERTS Effluent Flow Scheme project steering committee (comprising water utility, inspector and regulator representatives) about the uncertainty of a major component of the flow measurement system - the level sensors.
Top-down ultrasonic sensors are the most widely used type of device, however their accuracy can be reduced by environmental factors such as temperature and solar radiation. A recent report suggested that current assumptions on such effects were too low, and that most sites would fail their re-certification if more realistic values were used.
Clear guidance, based on sound theory and hard experimental data, is therefore needed to ensure that measurement accuracy is maintained. Such guidance would also allow adequate specifications to be given to relevant contractors. The impact of target plates for sensor verification and sensor location on measurement accuracy will also be investigated.
Ultrasonic level sensors are also used in many other wastewater applications, such as CSO spill detection and pump control for wet wells and thus the benefits would extend beyond effluent discharge applications.
Benefits to Clients
- Confidence that the installation and use of ultrasonic level sensors will meet MCERTS requirements.
- Reducing the uncertainty for a level sensor will reduce its contribution to the overall uncertainty budget which may allow some flexibility in other areas.
- Improved level measurement in other common applications, e.g. CSO's, wet wells etc. leading to better control and monitoring.
- Review existing industry practice, seeking input from users, equipment manufacturers and consultants and identifying good practice.
- Undertake a full experimental programme on a range of instruments to investigate specific performance issues.
- Produce the Good Practice Guide.
- Technical report covering all aspects of the project and full experimental results.
- Specific recommendations for the use of level sensors in wastewater applications.
- Specific recommendations regarding the use of top down ultrasonic level sensors for open channel flow measurement to meet obligations for discharge monitoring under MCERTS.
- Investigation into open channel flow measurement structures for MCERTS, CP073, 2003.
- Numerous level sensor evaluations, various clients, 1990 - 2009.
- Evaluation International open channel flowmeter selection guide, 2005.
- MCERTS product standards development for open channel flow measurement equipment, 2000, 2009