Two massive domes sit motionless on the grounds of the Valley Creek Waste Water Treatment Plant. Like bunkers, they seem immovable, but cranes will soon lift the domes, or tops, placing them atop three digesters huddled on the plant’s grounds.

The digesters were built in 1967, according to Earl Luker, superintendent of the plant. The years have taken their toll on the original tops and their metal has deteriorated since their installation.

Luker noted that only two digesters are needed, but the third exists to ensure the facility can continue operations while one is being repaired.

Their purpose is to convert sludge, or solids in the waste disposal system, into a substance suitable for the landfill. Luker said sludge is pumped into the digesters and stays for about 60 days while microscopic bugs eat at it.

The bugs create methane gas as a by-product which collects in the digesters’ tops. Luker said in a city Selma’s size about 20,000 cubic feet of methane gas is produced daily.

The gas is burned off through a nearby torch, its faint flames barely visible in the July heat.

But burning the gas hasn’t stopped the inevitable &045;&045; damaging the digesters’ tops. Luker said the tops are domed to allow space for the gas, but over the years it has still made stress cracks.

The tops don’t just keep the gas in, they also keep the air out. Luker said the bugs eating the sludge can’t live with oxygen; the tops make sure it never enters their lair.

They also keep the elements from entering the digesters.

The new tops, though, aren’t the only improvements planned for the plant. Luker said explosion proof plugs and lights have already been installed, and a new floor could be in the works for one digester.

According to Ray Hogg, engineer with the Selma Water Works and Sewer Board, a digester was drained and cleaned recently. A new top was installed and it was filled with water.

That’s when a leak was discovered in the digester’s floor.

The water board has already received an estimate from the digesters’ builders, but they’re waiting for another estimate from a Birmingham-based structural engineer.

Hogg added the cost for the floor could be $50,000 to $100,000.