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WATER QUALITY IMPROVEMENT BY DESTRATIFICATION USING AQUAERATION Thermal stratification in lakes is caused by a heating of the surface waters. As convection is the major method of heat transfer within a water body, hot air rises and cool air sinks, the water is unable to mix. This leaves a very warm top layer (epilimnion), a cold bottom layer (hypolimnion) and the transition layer (thermocline or metalimnion). As plants require light for photosynthesis, which creates oxygen, this leaves the epilimnion with plentiful oxygen but the hypolimnion with very little or no oxygen and no way to mix the two layers. The majority of reservoirs or lakes in the UK and indeed Worldwide usually suffer with significant increases in concentration of Mn and Fe in the water column in the summer. Academics believe increases of Mn and Fe are attributed to the anoxic bottom water, caused by the onset of thermal stratification. Together with a lowering of pH and the presence of certain bacteria is thought to contribute to the release of these elements from the bottom sediment. Algal blooms are caused by an increased concentration of algae in the surface waters. These blooms are unsightly and can be toxic. The blooms require sunlight and nutrients to survive in large numbers. If the algal blooms become too large they can cut off sunlight to the bottom waters, depriving the plants there of the ability to photosynthesise. The lack of photosynthesis decreases the oxygen levels in the bottom waters, killing the aquatic life living there. This in turn increases the amount of bacteria needed to break down the food, which further decreases the oxygen concentration in the bottom waters. The cycle will continue until there is no marine life left in the lake except algae and bacteria. H R Wallingford have developed and calibrated a mathematical model of the “Aquaerator” and the bubble plume – including detrainment in the presence of thermal stratification. For example 15 l/s of compressed air is injected into the stainless steel manifold and by the time the air has mixed with the water and reached the top of the draught tube (approx 2m) this mixed water increases to175 l/s. At 10m above the “AQUAERATOR” this volume of mixed air and water increases to 4.5 tonnes/sec and at 20m height the entrained bubble plume mixes 13.4 tonnes per second of air and water, giving a scientifically calculated plume diameter of 9.8m. We have also investigated using a shorter draught tube (0.66m), due to possible conflicts with capsized sailing masts, hence interfering with the units. Our Bubble Plume software has shown that there is only a 30% decrease in the mixed air and water volume at the top of the draught tube, compared to one at 2.00m, which is negligible. It was concluded by HR Wallingford, that the “AQUAERATOR” is a highly efficient aeration and mixing device, which 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. HR Wallingford comparative tests concluded that the performance of the AQUAERATOR is significantly better than the nearest competition – the Helixor. As a result of the R & D of the “AQUAERATOR”, further potential markets have been found, namely within the fish farming, waste water and industrial effluent treatment. Relationships between Imperial College of London and Yorkshire Water PLC have been developed to progress the R&D of the waste water treatment project, whilst Stirling University and Bangkok University are currently being investigated to progress with the R&D of the fish farming project. We have so far commercially installed 4 AQUAERATION Systems into reservoirs and lakes over a two year period. During the summer of 2006, Blagdon reservoir (217Ha) was stratified with a stable thermocline. The 5 AQUAERATOR units mixed the entire water column, easily breaking the thermocline and increasing the DO from 5% to 60% within 5 days. We know that there are several reservoirs in the UK which are experiencing problems, such as high concentrations of manganese, iron and aluminium, being released into the water column during stratification. It is also widely assumed that phosphates are released in similar conditions contributing to algal blooms, causing taste and odour problems. It is known that the AQUAERATOR will prevent stratification and therefore could prevent the release of these metals and phosphates into the water column. Click here to find out more about Aquarius Marine Group Ltd 
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