The Blade Compressor test programme is demonstrating the technology at speeds up to 5000 rpm
As an example, last year's June-July issue of Water & Wastewater International magazine detailed what the arrival of screw technology would mean for rotary lobe designs.
A test witnessed by the German Technical Monitoring Association (Technische Überwachungs-Verein) pitted the Atlas Copco ZS screw blower against a tri-lobe blower, in a performance test. The result showed the ZS screw blower was 23.8% more energy efficient at 0.5 bar (e)/7 psig, and 39.7% at 0.9 bar (e)/13 psig.
Funding the Blade
This year saw the UK's Carbon Trust granting £390,000 to start up company Lontra to help develop its Blade Compressor, which it claims could reduce energy spend on wastewater aeration by 20%. This, the company says, could help lead to a payback in as little as 18 months, within a five year AMP cycle, as seen in the UK. As the cost of electricity for aeration can constitute 30% of the operating costs for wastewater treatment, this is understandably attractive.
Furthermore, UK water and wastewater company Severn Trent has partnered with Lontra to provide a test site in Worcester for a pre-production prototype. The test programme is currently demonstrating the efficiency of the technology at pressures of up to 3 bar and at speeds up to 5000 rpm. Lab testing will be conducted up until Autumn 2011 and site testing until Spring 2012.
The trial has also established reasons for more energy efficient aeration in the UK:
• Energy efficiency and a drive to reduce costs
• Cap-ex constraints within five year regulatory AMP periods, requiring short payback
• Changing requirements, for example as space pressures increase the need to change designs of aeration tanks
• Diverse and expensive compressor maintenance schedules and parts stores across widespread sites
• Regulatory influences, in particular noise regulations but also general pressure on the water companies in the UK for increased innovation and reduced carbon footprint.
Swedish/Scottish aeration partnership
Elsewhere, Swedish aeration firm Sorubin has partnered with Scottish Water in the UK to conduct an operational performance test of the company's Microluft wastewater aerators, also touted to help improve energy efficiency by 20%.
The trial started in February this year and will last until August. An oxygen transfer test will be carried out by the firm, which consists of measuring the energy needed to fully oxygenate a body of clean water with Microluft.
This technology uses a bottom mounted aerator. As can be seen from the diagram (right), it works by generating a vortex in a tube that has contact with the atmospheric air, a pillar of air reaches all the way down to the bottom of the tube. Here, a special impeller sucks in a mix of air and water and puts it under very high pressure. Very small bubbles are dispersed from the aerator as a result. And it is the size of the bubbles which Sorubin says is fundamental to improving energy efficiency.
It says that the longer it takes for a bubble to rise through the water, the more time it will have to release oxygen. Naturally, as small bubbles rise more slowly than large bubbles, it is better to create small bubbles since they elevate slowly. Generating bubbles as deep down as possible is also important, the firm adds, as it allows them to travel upwards for as long as possible.
"The most energy effective aeration technology is the one that does nothing but creating small bubbles, deep down with the least energy input," Sorubin says.
