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UK water company Severn Trent Water handles more than 2.5 billion litres of wastewater every day and turning that into fresh water uses a lot of electricity. Given the cost of electricity consumption, and the associated CO2 emissions, the company investigated alternative solutions with lower energy costs, improved operational efficiency and reduced environmental impact. It found the solution in a 21st century version of traditional technology.
The underlying principle behind the technology at the heart of wastewater treatment has remained unchanged for nearly a century. But Severn Trent Water spotted the potential of Lontra’s new Blade Compressor, a viable alternative to the traditional blowers and compressors that are used to pump air into wastewater to feed the micro-organisms that clean it. So it undertook a site trial and performed exhaustive tests that showed its potential for the global water and wastewater utility businesses, to deliver a step change reduction in electricity usage, maintenance costs and CO2 emissions.
Background
Severn Trent Water is one of the largest of the ten regulated water and wastewater services companies in England and Wales, employing more than 5,000 people and serving around 4 million households and businesses across the heart of the UK.
Overseas, Severn Trent Services is one of the world’s major commercial suppliers of water and wastewater treatment products and services, with customers in the USA, Europe, the Middle East and Asia. In the UK, Severn Trent Water’s territory stretches from the Bristol Channel to the Humber and from mid-Wales to the east Midlands. It delivers 1.8 billion litres of drinking water each day to customers through 47,000 km of water mains. Wastewater is safely returned to the environment through a system comprising 93,000 km of sewers and more than 1,000 wastewater treatment works.
The business has a reputation in the development and application of water and wastewater treatment technology and systems, building on the Midlands’ long and proud history of engineering expertise. The activated sludge process, invented in Manchester in 1914 and used at full scale for the first time in the world at Severn Trent Water’s Worcester treatment works in 1916, remains at the heart of the wastewater treatment process, worldwide, to this day.
Business need
Severn Trent’s wastewater treatment works operate around the clock, handling more than 2.5 billion litres of wastewater every day. Like all water and wastewater businesses, Severn Trent has to meet strict quality standards governing the treatment of the bacteria, organic matter and other materials contained within wastewater, before it is returned to the environment. In stringent tests, Severn Trent’s 1,026 treatment works met more than 99.5% of the required standards.
Operating and maintaining the vast network of sewers and treatment works is a huge and resource intensive engineering challenge that requires regular, large scale investment programmes to maintain the quality standards demanded by regulators, politicians and customers.
The activated sludge process relies on the injection of air into tanks containing wastewater to encourage the large scale growth of natural bacteria that break down the impurities it contains.
Depending on the type of wastewater being treated, the resulting liquid from this aeration process can usually be returned to the environment, although in some cases further treatment processes may be required. The traditional compressors, or ‘blowers’, used to inject air into wastewater use large quantities of electricity.
Severn Trent spends around £9 million a year on electricity to run 300 blowers at its treatment works, more than half of the entire cost of wastewater treatment in the region. Industry estimates suggest that 1% of all of the UK’s electricity is consumed by compressors used for the aeration of wastewater at the nation’s utility businesses.
Given the cost of electricity consumption, and the associated CO2 emissions, Severn Trent Water has been investigating alternative solutions with lower energy costs, improved operational efficiency and reduced environmental impact.
Solution
Severn Trent saw the potential in Lontra’s Blade Compressor, which takes the traditional compressor’s basic design and engineering principles and gives them a new spin – literally.
With a traditional piston and cylinder, as the piston drops down in the cylinder it draws in air above it and, as it goes up again, it compresses air in front of it. The Lontra Blade Compressor is best imagined as a piston and a cylinder, but with the piston wrapped around inside. There is a constantly open intake port, without valves. As the piston rotates, it induces a volume of air behind it in the same way as the piston dropping down in the cylinder.
As it gets back to the starting point, it has induced a complete volume behind it. But unlike the traditional piston and cylinder that has to stop and change in direction, the blade passes through the disc with the volume that was trapped behind the piston now in front. This means that it has an almost continuous cycle of inducing air behind and compressing air in front, a new geometry that is quieter, smoother and highly efficient.
The first step for Severn Trent was to work out how just how important the Lontra technology could be to its business and so the company worked for over a year with Lontra on a study evaluating its entire wastewater estate. The knowledge gained from this study allowed Lontra to take a fresh look at the challenges faced in wastewater treatment and to design a solution specifically optimised to the needs of the industry as whole.
The results were so encouraging that Severn Trent agreed to part-fund a full scale trial alongside the Carbon Trust, the organisation that assists businesses, governments and the public sector to accelerate the move to a sustainable low carbon economy.
And where better to validate the Lontra Blade Compressor’s performance and reliability against existing machines, in a real time production environment, than back at Worcester Wastewater Treatment Works, where the world’s first large scale wastewater aeration system, powered by conventional compressors, burst into life almost a century ago?
Said Mark Jones, Severn Trent’s Wastewater Research and Development Manager: “To make the test as representative as possible, only the existing blower and motor were replaced, with the Lontra Blade Compressor fitted into an existing enclosure and running from an existing variable speed drive. This ensured that only the gains in the blower technology, and not those from optimising the supporting systems and drives, were captured.”
In addition, the conventional blower that the Blade Compressor was to be compared against had been replaced just six months before the trial commenced, ensuring that the Lontra solution wouldn’t have an unfair advantage by being tested against an ageing or worn alternative.
Benefits
The Lontra Blade Compressor was first run at Worcester in September 2012 and after running full time as a ‘duty blower’ without issues for more than seven months, Severn Trent Water acknowledged its core reliability and performance.
The site’s instrumentation and supervisory control and data acquisition system (SCADA) showed that the conventional blowers used more than 20% more electricity to deliver an equivalent amount of air when compared to the Lontra Blade Compressor.
These results prompted Severn Trent Water’s chief executive Tony Wray, in his presentation of preliminary results to the City in May 2013, to report that, were the Lontra Blade Compressor to be rolled out across all of Severn Trent’s wastewater treatment works, the company could save more than £1.8 million a year in electricity costs, with a commensurate reduction in the company’s overall carbon emissions of three per cent.
The magnitude of the potential savings was enough for Severn Trent to consider a large scale replacement programme. To confirm the savings beyond doubt, it was decided that the on-site instrumentation for the Blade Compressor and the comparative blower should be upgraded to laboratory standard. Consultants ABB were engaged to specify and supply the instrumentation and the flowmeters were replaced by brand new Orifice plates to ISO standard 5167.
True saving potential
The data from this instrumentation was logged for seven months between June 2013 and December 2013 over all conditions, from summer to winter, to give a view of the true saving potential of the Lontra Blade Compressor in a fully operational wastewater treatment works.
“Our upgraded instrumentation showed that from summer to winter the Lontra Blade Compressor used, on average, 21.2% less electricity to deliver an equivalent amount of air when compared to the existing blowers, which is a really positive result”, said Mark Jones.
“Importantly for us, as well as being efficient, the machine is simple, using well understood and proven materials and engineering. The bearings are traditional and the rotor runs at low speed, being directly coupled to the motor without step-up gearboxes or belt drives. This fits well with the needs of an industry that needs minimal downtime and long service life from its assets.
The Blade Compressor has now run for more than 10,000 hours, the equivalent of more than three years of normal operation, without issue. This gives us significant confidence in its reliability. We have worked closely with Lontra over a number of years to bring to reality the tremendous potential of this very clever invention. This technology should make a significant contribution to the business efficiency challenges we have, to allow us to keep bills low for our customers. We look forward to taking the next steps together to make the most of this exciting development.” Concluded Mr Jones.
The Lontra Blade Compressor was voted the Most Innovative New Technology of the Year at the 2013 Water Industry Achievement Awards.
The digital edition of the magazine is distributed free of charge to readers who meet our qualifying criteria. You can apply to receive your free copy by completing this short registration form.
