The Problem
To maintain their industry leading water quality compliance, Severn Trent Water monitor all the way from source to tap the quality of the drinking water we supply. They collect in excess of 500,000 samples annually which are expertly analysed in accredited laboratories, these samples are subjected to millions of separate tests. The parameters routinely monitored by continuous automatic analysers include a number of tests including turbidity.
Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can contain suspended solid matter consisting of particles of many different sizes.
Locally monitoring the water supply, a local water bore hole had experienced Turbidity issues which could lead to closure. The current starting method was Star delta motor starting. Sentridge Control was asked to deliver an alternative starting method to attempt to overcome the Turbidity issues.
Sentridge’s Solution
In addition to the above Severn Trent Water have 1,100 permanently installed continuous automatic analysers which monitor the water quality 24 hours per day, 365 days per year to ensure the quality of your water supply fully complies with the stringent standards laid down by the Drinking Water Inspectorate.
The parameters routinely monitored by continuous automatic analysers include:
•chlorine residual •turbidity, colour and clarity •aluminium •iron •nitrate •pH
We attended site with the local engineers and discussed the options available. It was decided a no cost trial would prove its worth on the actual site.
The trial provided impressive results with the Turbidity recorded well below the recommended safety level of 0.5. This resolved any previous issues with Turbidity with production now going to supply with smoother controlled Starts and Stops.
A further benefit was that with the Drives running at 42Hz, a saving of more than 40% was made on Energy consumed compared with previous energy consumption levels.
The Full Story
Traditional On/Off control with two 90kW pumps duty/standby both with mechanical throttling back on pumps. Constant running 24/7 with Turbidity issues which may cause site to be considered for permanent closure.
Sentridge offered a trial unit to be installed to verify if improvements in control would deliver a reduction in turbidity. This was carried out with the support of local engineers from STW. More tests were carried out with a huge reduction in Turbidity of 80%.
The drive also allowed smooth control kept the borehole above a troublesome depth of 53 – 55 metres where water entering the borehole caused turbidity spikes. The level could now operate at a much narrower bandwidth.
VSD Control allowed the site to restart the borehole and return to supply in 30Minutes. In the past the site would have to run to waste for several hours, sometimes over night, wasting both water and electricity.
Overall results allowed The Energy team to fund this project with an estimated payback of just over 1.5 years on the whole project.
Drive Installed~ Turbidity Reduced~ Impressive results
- The Turbidity recorded well below Safety level of 0.5 problem solved, production now going to supply
- Smooth controlled Start/Stops
- Drives running at 42Hz
- Saving >40% Energy over previous method
- Producing 2.7M/L per day of fresh water for supply
The VSD did exactly what we expected it to do with an immediate reduction in turbidity. Residual is really low and has saved us a lot of time in settling the system
Paul Stevens~ Senior Technician
