In most lagoon upgrades, when the existing lagoons are upgraded and are not de-sludged it may be better for the plant to operate the duty blower(s) as well as the standby blower unit during initial operation.

The existing sludge layer may contain a percentage of material that has settled to the bottom of the lagoon without being fully treated biologically. This percentage will vary from plant to plant depending on the effectiveness of the previous treatment system.

As the new EDI aeration system is installed, it can be expected that the lagoon’s existing sludge layer will be disturbed, resuspended sludge solids. These resuspended solids can create an additional oxygen demand on the lagoons treatment process until they are fully oxidized or re-settled on the lagoon’s floor.

Some observations the contractor or operator may observe during the initial start-up would include a DO measurement in the lagoons of less than 2 mg/l, water color that is blackish, and/or non-uniform air distribution in the aeration system. Non-uniform air distribution of air can result from some diffuser assemblies resting on top of the existing sludge, thus being at a different submergence depth than designed.

Operating the standby/spare blower in addition to the designated duty blower(s) will allow the lagoon system to treat the resuspended sludge (which may even reduce the amount of sludge in the lagoon) as well and re-distribute the sludge on the lagoon floor.

Depending on site conditions, running the standby blower may be needed for 2 – 6 weeks. Once the measured DO in the basin is consistently above 2-4 mg/l and the water in the lagoon is a light brown 9chocolate milk) color, then the treatment system has been able to treat the sludge that was disturbed during construction. The plant can then go back to operating only the duty blower.

Fill the basin with 4-6 feet of water and turn the air on. Anything less than 4 feet of water jeopardizes ice forming around the diffusers.

This is the most common place for the breach to happen in this type of system since the adapter is made so it breaks before the PE outlet on the lateral is damaged.

Causes are usually from the water level being lowered, then the unit gets stuck in sludge, then as water level rises it can snap the fitting before it breaks free of sludge. (#1 cause)

Another cause could be from 2 units getting tangled.
1 more could be from the unit resting on the floor and the hose whipping around until the adapter breaks.

Procedure for retrieving unit by hoses:

• Tie a slip knot at the end of a rope.
• Wrap the rope around the hose and through the slip knot to form a loop, or lasso.
• Attach a small weight to the loop so the rope will sink.
• Once the rope has sunk to the bottom, pull the rope tight making sure it doesn’t slide on the hose.
• Repeat on second hose if both of the original retrieval ropes are missing..
• Pull the unit to the surface.
• Tie a rope around the manifold before lifting the unit out of the water.

If there isn’t a boat with a winch system on it, it is recommended that a beam be fastened to the boat in a similar way. The beam should hang out over the end of the boat so the unit can be pull up without banging into the boat. Attach one or two pulleys to the beam. Thread the lifting ropes through the pulleys and pull the unit up onto the boat. This way the workers are pulling down on the lifting ropes and are less likely to get pulled off the boat.

The dry weight of these units is approximately 185 lbs [85 kg] without any accumulated rags or water inside the unit.