Our total energy use includes purchased electricity, transport fuel, and static energy fuel such as
natural gas. Given the environmental risks posed by climate change and the rising costs of electricity, Severn
Trent Water has an extensive programme to promote energy efficiency.
In 2006/07 Severn Trent Water completed site energy reviews of all of its top 407 sites, which account for 85% of its electricity costs. The review has resulted in individual Site Energy Management Plans (SEMP) for 330 sites. These include local actions to improve plant / process optimisation, and they identify potential 'spend to save' opportunities, where there is potential to refurbish, replace or change the way some assets operate in order to reduce energy consumption. One such project is the replacement of some of Severn Trent Water's older variable speed drives, where technology improvements are delivering energy reductions. We believe the findings of these SEMPs will enable Severn Trent Water to save approximately 10,000 MWh of electricity during 2007/08.
In 2007/08 Severn Trent Water will develop SEMPs for a number of smaller sites not covered by the large-site SEMP programme. It will also continue work on a project to install automatic electricity consumption meters at 700 sites. A contract to install these was awarded in 2006/07, and around 200 meters had been installed and commissioned by the end of the year.
A vital part of the programme is to keep employees informed about the benefits of energy efficiency. An internal communications campaign aims to raise energy awareness among Severn Trent Water staff, and to make employees aware of their own role in reducing the company's energy consumption.
At Severn Trent Water's sewage treatment works, the aeration of activated sludge plant (ASP) modules is a major source of energy consumption. STW's Sewage Treatment Field Services team believed that controlling the amount of air used to regulate ammonia levels in these modules could result in significant power savings, so they set up a pilot study at Finham, Coventry.
Finham has three identically-sized ASP modules. In one of those modules, the project team installed an ammonia probe and modified the aeration controls so that the ammonia reading had the facility to override the normal controls. The idea was to prevent excess air being used when ammonia levels were low. Various safety features were built into the control system, to ensure there was no greater risk of exceeding consent standards than when operating under the existing controls.
The team then monitored power usage over one two-week period in summer, and one two-week period in winter. The summer period showed an average saving of 20% on power usage, and the winter period an average saving of 10%, giving an average saving of 15%.
As a result of the trial results, Severn Trent Water has decided to install ammonia controls at a number of large sewage works. This is currently ongoing, with controls already installed at ten sites, in addition to Finham.
Water Technologies and Services' (WTS) has introduced a web-based service for collecting data in the field. The service enables WTS to collect data through wireless input, using mobile phones, PDAs or laptops. The data can then be accessed and managed through internet-connected PCs or laptops.
WTS uses the technology to collect data on compliance with environmental regulations, process control, and meter reading. In some areas it reduces the need for operatives to travel to the office, and has enabled the company to cut mileage and reduce fuel usage.
Integra, one of WTS's Water Purification businesses, currently uses similar technology in 90 of their vehicles operating in the UK. In the Gulf region of Operating Services in Houston, Texas, the technology is being used at 135 water plants, 60 wastewater plants and over 50 distribution system monitoring locations and WTS expects to expand the service to other facilities in the future. As well as cutting fuel usage, the system has greatly reduced the time spent on paperwork.
