Mobley Engineering, Inc. offers the design and installation of aeration systems for hydropower, water supply reservoirs and other applications.
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Reservoir Diffuser Systems:
The line diffuser system has been applied at twentytwo hydropower projects to meet dissolved oxygen targets in the releases downstream and has been applied at twentyfive water supply reservoirs to reduce anoxic products, taste and odor problems and treatment costs.
Installation sizes have ranged from the Saint Paul Regional Water Services Lake Vadnais Project, with an oxygen delivery capacity of 6,500 kg. per day (2011),to the US Army Corp of Engineers J. Strom Thurmond Project, with an oxygen delivery capacity of 200 tons per day (2011).
The MEI line diffuser design is the only diffuser system design widely applied to hydropower projects.
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Consulting Services:
Mobley Engineering also works as part of a team of experts that provide site-specific evaluation of water quality enhancement techniques at hydropower and water supply reservoirs (please see Links for a list of these individuals).
Services include water quality assessments, and conceptual designs for enhancement systems such as: reservoir diffuser systems, surface water pumps, bubble plume upwelling, hydro turbine aeration, side stream super-saturation, special operations, cone valves, and aerating weirs.
The team has extensive experience in evaluation of dissolved oxygen improvement and temperature control devices to meet FERC re-licensing requirements.
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The Problem:
The water quality of reservoir releases has become a recognized issue for hydropower projects. Many Federal Energy Regulatory Commission (FERC) licensing requirements now include minimum dissolved oxygen standards, and projects owned by Federal agencies like TVA and the US Army Corps of Engineers are under pressure by State agencies and private interest groups to improve water quality in the releases from their projects.
In many reservoirs, solar energy heating causes a stable temperature stratification during the summer months when the warm surface water floats over the colder deep water, referred to as the hypolimnion.
Oxygen demands near the sediments and in the water consume the dissolved oxygen (DO) in the hypolimnion, which is sealed off from the most significant sources of oxygen such as wind mixing and algae photosynthesis.
Thus, depending on water flows and the magnitude of the oxygen demands, the hypolimnion can become oxygen depleted.
If the DO levels are driven low enough, anoxic products like hydrogen sulfide and dissolved iron and manganese can reach troublesome levels in the water nearest the sediments. These anoxic products and nutrients released from the sediments at low oxygen levels can cause taste and odor problems in water supply reservoirs. If this water is withdrawn through hydropower intakes, the low DO water and anoxic products are released downstream and can often violate state water quality standards.
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The MEI line diffuser system is designed to deliver large quantities of oxygen with maximum oxygen transfer efficiency by providing an economical means to spread the oxygen into a large water volume in the reservoir. Diffuser lines are often more than a mile long. The buoyant oxygen bubble plume is spread out over the long lines to provide localized or widespread dissolved oxygen improvements in the reservoir while avoiding sediment disturbance or disruption of reservoir stratification.
Oxygen levels can be increased in the volume immediately upstream of a hydropower dam to increase dissolved oxygen levels in the releases or eliminate hydrogen sulfide odors. For a water supply reservoir, oxygen levels can be increased over the sediments in the entire reservoir to reduce nutrient releases from the sediments that feed algae blooms and eliminate anoxic products that would require chemical treatment.
The MEI diffuser is constructed of HDPE piping, stainless steel connections, concrete anchors and porous hose that runs the length of the diffuser. The porous hose is manufactured from recycled tires and provides a source of very small bubbles with high resistance to clogging. The diffuser system is deployed and retrieved (as needed for maintenance or relocation) from the surface without the use of divers.
The MEI line diffuser system can be supplied with compressed air or gaseous oxygen. The high oxygen transfer efficiencies achieved by this design assure maximum utilization of the supply gas.
Line diffuser systems have been in operation at the Tennessee Valley Authority since 1992. Typical diffuser installations have required no maintenance for 10 years of operation.
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Mark Mobley has been involved in the evalutation of alternatives for water quality enhancements at over forty hydropower or water supply reservoirs, and responsible for the design and installation of numerous enhancement systems. He started Mobley Engineering in 1999, atfer sixteen years with the Tennessee Valley Authority.
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