Municipal applications for Rotomites

As reported in WaterWorld, Serving the Municipal Water/Wastewater Industry

"The Town of Decatur, Ark., is using a self-propelled dredging system as part of a new biosolids management program designed to reduce the cost of sludge disposal and increase solids detention time in-plant. While less than 1,000 people live in Decatur, the town’s wastewater treatment plant handles flows equivalent to a population of 40,000. The primary contributor to these flows is a poultry processing plant.

Over the last several years, the town’s Utility Manager, Rick McClain, has been laying the groundwork for planned land application of Class B biosolids. Until early 1996, Decatur had contracted for the removal of pond wastes, which were dredged up by a private firm and hauled away for land application.

The total throughput of Decatur’s plant is 2 million gallons per day. The plant accepts combined storm and sanitary flows, as well as the industrial processing wastes of its primary customer. While certain types of trash and solids are more prevalent during storm water events, the plant typically handles high amounts of solids due to the industrial nature of the poultry waste.

To remove trash and large solids, flows are screened as they enter the plant. Material then goes through another four-stage process including a primary lagoon where settling occurs, an activated aeration cell, then a secondary lagoon (polishing pond), ending in a sludge handling pond from which the biosolids are extracted. The town also has two equalization ponds and a waste holding pond.

The city’s goal is to land apply an estimated 1 million gallons of biosolids each summer season. To accomplish this, the town needed a means of producing consistent solids flow from the final sludge handling pond.

In early 1996, Decatur purchased a Rotomite^TM dredge from SRS Crisafulli. The dredge is equipped with an auger/cutterhead and is capable of transferring approximately 800 to 1,000 gallons per minute of biosolids with its 6 inch J-Series sludge pump. The ponds are lined with clay, so Decatur elected to have the dredge fitted with a depth indicator which allows the operator to control the depth of the dredge cut.

The dredge is used to help keep all of the town’s lagoons cleaned out. Biosolids are dredged up for land disposal only about once a quarter, but the dredge is used about once a week in the other ponds. The dredge is propelled by an outboard hydraulic drive and has hydraulically controlled steering. It doesn't need a cabling traverse system. The town uses a crane to move the 12,000 pound dredge from pond to pond.

When pumping from the final sludge handling pond, the dredge pumps the biosolids ashore through a floating 8-inch discharge line. With an experienced operator, the dredging operation is capable of producing a consistent percentage of solids at the shoreline. It is not uncommon for the equipment to produce sludge of up to 10 percent solids by weight, or 60 to 80 percent solids by volume.

At the shoreline, the biosolids are fed to a waiting truck, from which they will be land applied (surface spread) on nearby farms. One truck equipped with a vacuum pump is being used in the operation. There is no surge tank at the shoreline; rather, any overflow is contained and returned to the pond.

Decatur expects to save approximately $50,000 a year with a fully operational biosolids management plan."
The dredge is powered by a 180 HP Isuzu diesel engine. It is approximately 27 feet long and eight feet wide. While it is designed to be operated by one person, it can carry two people safely. It can excavate to a depth of 15 feet and at a speed of up to 10 feet per minute.