Water quality improvement by destratification using aquaeration

Aquarius Marine’s Innovation Strategy during 37 years was to improve the quality of the Water and Marine Environments. The company was a founder member of the Environmental Industries Commission and has assisted UK Water Companies with the inspection of underwater structures. and gained experience of underwater aeration and mixing devices. Significant EU funding led to the invention of our cutting edge, patented “AQUAERATOR,” which is an energy efficient method of using ‘Bubble Plume’ Technology to destratify Reservoirs and improve Lakes, Fishfarms and Fishery water quality.

Site trials in Wraysbury Reservoir owned by Thames Water PLC represented temperate countries. The University of Barcelona was selected due to the excellent academic qualifications of Prof Joan Armengol (produced 38 published Journals on various aspects of water), to represent the tropics.

Figure 1. Bubble Plume on Surface of Water (18m deep)

The Aquaerator' is now the scientifically proved answer to many Reservoir problems. These include stratification, which causes water below 8 - 10m from the surface to be oxygen deficient and have metals in suspension. Unfortunately few people realise that bed water is a higher density than surface water, thus the cheapest form of surface water aeration is provided by the wind. It is vital to place aeration and mixing devices on the bed, using the simple principle that it takes more costly energy to force air down from the surface, whereas a Bubble Plume from the bed rises naturally upwards. Our technology is designed to mix air and near-bed water together to form a buoyant plume with an adequate initial vertical momentum flux and turbulence to maximise the rate of entrainment of near-bed water immediately above the device. The Bubble Plume rotates causing considerable additional entrainment by using an Aquaerator which has no moving parts to wear out. It has the capabilities of breaking both thermoclines and the stronger haloclines, located within deep bodies of fresh, brackish and saline waters. The "AQUAERATOR" assists with the reduction of phytoplankton, which can be extremely noxious and deplete the Dissolved Oxygen content of the water.

Introduction Overview of "Lakeside," Doncaster

Lakeside is a man made aquifer fed lake of 22 Ha and has no through flow of water, thus unmixed and heavily stratified. Earlier reports showed the lake was subject to toxic blue green algal blooms which require sunlight and nutrients to survive in large numbers and low Dissolved Oxygen (DO) in the deeper waters (11m). This low DO, coupled with a high temperature drop through the water column, that the lake was struggling to support the nature reserve and aquatic flora and fauna. Large algal blooms cut off sunlight to bottom waters, depriving plants of the ability to photosynthesise, thus decreasing the oxygen levels, which kills the aquatic life there.

'Lakeside' Figure 4. The Doncaster area, showing the AQUAERATOR system in use.

AMG Ltd undertook a detailed survey of the lake by using a YSI multi parameter 6600 sampling sonde, which accurately takes readings of temperature, pH, dissolved oxygen, depth, turbidity, chlorophyll A, conductivity and fluorescence. Aquarius Marine Group Ltd was asked to install an AQUAERATION system of 4 AQUAERATORS in winter of 2006. Water measurements were taken in May which showed that the lake was stratified. The thermal stratification of the lake decreased the dissolved oxygen in the bottom waters and decreased the pH. The AQUAERATORS were laid in 10m and turned on at the end of May 2007. Figure 4 shows the AQUAERATORS distributed throughout 'Lakeside'. They create a highly turbulent plume of water/air which entrains more water as it moves upwards. With an inflow of air of 11l/s the plume at the surface has a flow of 4.5tonnes/sec, as shown figure 4.

Measurements taken while the AQUAERATORS were turned on showed that the lake was no longer stratified and had higher concentrations of dissolved oxygen in the bottom waters and there was less of a decrease in the pH. The Chlorophyll A measurements showed a more even distribution of algae, helping to prevent the build up of algal blooms. Measurements were then taken in October when turnover had occurred. The even water temperature meant that the dissolved oxygen and pH also remained constant through out the water column.

This proved that the AQUAERATION system destratifies lakes, improves the water quality of bottom waters and can help to prevent algal blooms. The design of the AQUAERATOR ensures that it does not disrupt the recreational uses of the lake as its top is about 8m from the surface.

A Case Study of Blagdon Reservoir

Blagdon is a man made reservoir of 217 hectares with the water supplied from surrounding farmland by various streams. It has had several progressively improving aeration systems over the past 36 years. Originally there was an air curtain and finally five Aquaerators, which have successfully destratified the Reservoir since their installation in 2002.

However the main lowest water outlet, thus the water going to the Treatment Works, had a very low DO and previous reports have shown that in July each year there has been large quantities of manganese in the water column.

An Aquaerator was to be installed 13m from the 3m diameter outflow pipe grill, which is 2-3m below the surface of the surrounding mud deposits on the bed of the Reservoir. Due to the 1.5 knot outflow current it would need to be bolted to the Victorian granite apron to prevent movement and require Aquarius Marines Diving Team to airlift over 30cu m of silt.

The water temperature had risen to 15ºC, the DO fallen to less than 50% saturation and the Mn concentration in the outflow to the Treatment Works showed a steady rise from early April and peaked at 320µg/l by 10 May 2008. The Mn concentration then averaged about 70µg/l for a month and continued to rise to100µg/l mid June before the two Aquaerators were switched on 23 June 2008.

Another Aquaerator was laid to improve the water quality through the alternative outflow siphon.

The Mn concentrations in the main outflow reduced dramatically to 25µg/l and less in a few days and remained at that level through the next months July to September.

The water temperature of the outflow remained steady at about 18ºC and the DO rose gradually to 100% by 5 Aug 2008. This year, in other words, there was no need to treat the raw water for manganese removal.

The following figure shows the concentrations and conditions of the water observed by Bristol Water at the Blagdon Lake Lower Outflow, as described above.

Blagdon Lake Outflow

Fishfarming

A continuation of our Fishfarming Project is designed to help this Industry which produces 50% of the fish which we eat. Initial footage, now on DVD, was obtained showing normally lethargic salmon leaping into the air when the AQUAERATORS were switched on at Lochleven. Initial tests were successfully carried out by the largest Norwegian Salmon Farming Firm, resulting in the Norwegian Technical Institute in Stavanger accepting the Aquaerator as one of its 2010 Projects. This will scientifically prove to the Industry that Aquaeration will stop salmon being lethargic, enable them to grow faster without algal problems, helped by our decreasing the seawater temperature in summer and reducing surface ice in winter.

Aquaeration Aerating Fisheries

Our 2009 Project was to improve the water quality for the biggest Sport in the Country, namely Fishing. We have installed the six Aquaerators at Cross Drove and three at Avalon Fisheries.

Fish suffer if the dissolved oxygen (DO) concentrations fall below about 4mg/l and have to come to the surface to breathe. We reduced the 'Aquaerators' size to suit shallow fishing lakes. The patented device mixes small air bubbles with the near bed water at the base of a vertical outlet tube. The buoyant mixture of air and water is designed to rotate whilst rising up the tube, causing a great deal of turbulence, which facilitates the solution of oxygen in oxygen deficient water.

A system of Aquaerators is designed for each application depending upon the size, shape and constituents in the water body. The ecology of the bed is not disturbed as low DO bed water is removed by entering the base horizontally and its density is reduced by mixing. This expanding plume of 50l/sec of water rises above each Aquaerator entraining the still ambient water near the surface and spreads radially over it.

Aquarius Marine measured the DO and temperature in 8 positions at 0.3m below the surface and above the bed of the ~2m deep lake between1000 and 1600 on 27 June 09 to determine whether and where Aquaerators could be installed. The Fishing Lake has an area of about 4.5Ha including many elongated islands, narrow channels and lily beds, which make great fish holding targets.

At the end of June 2009 six Aquaerators with 1m high vertical outlet tubes were installed in the Lake at 6 of the observation positions, which had been carefully designated to maximise the naturally prevailing wind driven currents to enhance the aeration process. 1.1Kw Blowers each delivering 5ltr/s of air at 0.4Bar were used to power the Aquaerators.

Before installation at the end of June the water temperature averaged 21.6ºC with 0.4˚C bed to surface differential, which is considered to be a very mild form of stratification. The 0.3m below surface DO was 73% (6.5 mg/l) and the near bed DO was 54% (4.8mg/l), quite close to the 4mg/l threshold.

A second nearly identical survey was made on 30 July 09 by Aquarius Marine. This showed a lower average water temperature of 18.8ºC. The DO varied from an average of 111% Sat (10.4mg/l) at 0.3m below the surface to 65% (6.1mg/l) above the bed compared with 4.8mg/l on 27 June. This much improved DO, particularly above the bed was what had hoped for.

Finally, the survey concluded that the Fishery Aquaerator is a very applicable method of maintaining flow and DO levels in Fisheries containing carp, some in double figures, tench and bream of 5lb-plus.

Contact:

Tony Wynes
Aquarius Marine Group Ltd
The Beckery, Glastonbury          
Somerset, BA6 9NT
T: 01458 834734
E: tonywynes@AOL.com
www.aeration.UK.com