Power Plant FGD Lagoon Dredging, Dewatering and Disposal

Power Plant FGD Lagoon Case Study Header


Power - Sludge Management FGD Lagoons
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A contractor for St. Johns River Power Park (SJRPP), a large coal-fired power plant located in Jacksonville, Florida, has two turbine/generators that each supply 632,000 KW. They brought in Veolia to dredge, dewater and transport filter cake material from the plant's East and West flue gas desulfurization (FGD) ash lagoons. There are two individual FGD lagoons that are membrane lined. The lagoons sit side by side, are approximately 230 feet by 245 feet, and hold the same non-hazardous sludge stream. 

Prior to Veolia beginning work, the plant had removed some of the materials via yellow iron and relied on natural dewatering methodologies. However, the customer was not able to clean the side slopes of the lagoons as they did not want to penetrate the tank membranes. Additionally, the EPA had placed a mandate on the customer that the lagoons had to have their sludge evacuated in less than 30 days. Compounding the problem, the filter cake was thixotropic in nature, meaning it could change viscosity when moved, threatening the dry disposal classification of paint filter spec. Veolia was challenged to quickly mobilize and complete an extensive dredging, dewatering and filter cake disposal project in less than a month using three high pressure plate and filter presses while working 24/7. 


With Veolia having one of the largest fleets of dewatering equipment in the U.S., we were able to design a temporary mobile system, which included three plate and frame filter presses. Two of the presses were 4.0 CY in capacity while the third press was 7.5 CY in capacity. The combination of high mobile equipment capacity and quantity provided Veolia with the ability to take on this challenge despite the timetable limitations. 

The lagoons had 3:1 side slopes that transitioned to flatter, centrally sloped bottoms. Veolia alternated moving a manned floating dredge between the ponds by crane and then pumped the material to Veolia's set up area located to the southwest of the western pond. The material then flowed over a shaker screen, which served to extract some of the larger particulate, before proceeding into one of three mix tanks. 

The filter presses separated the solids from the liquids inside the recessed chambers. The filter presses have recessed chambers, high pressure (225 psi) polypropylene plates covered with 5-micron filter cloths. As the chamber filled with solids, the feed pump approaches shut off head pressure and the filtrate discharged through the filter cloth was slowed to a trickle. 

Next, the feed pump was shut down and the press core and filtrate lines were cleared with compressed air. The plates were opened to allow the filter cake to fall onto the discharge conveyor of the mobile press. The conveyor transferred the cake to the rear of the trailer and dropped it into a three-sided cake pan. From the cake pans, a Veolia provided front-end loader extracted the filter cake and loaded it into Veolia sub-contracted end dumps for disposal at the on-site landfill. 


Veolia fast tracked the job walk, proposal and bid. The contract was negotiated and signed, all of which was completed in 10 days. The work was completed in less than a month with the Labor Day holiday taking place during project operations. The paint filter spec filter cake was directed into a cake pan where it was moved to the plant's on-site landfill. Veolia successfully dredged, dewatered and transported to the on-site landfill a total of 8,000 cubic yars of in-situ (in place) sludge/solids from both of the plant's large FGD ash lagoons. 

The recessed chamber filter process helped the customer maximize their waste volume reduction, including minimizing their waste stream transportation and disposal costs. The process also helped remove and dewater pond sludge, producing a filter cake that was 66.05% solids and met the paint filter test specification at a rate of approximately 385 cubic yards (532 cake tons) per day of operations. Veolia then transported the paint spec filter cake to the on-site landfill, where the customer spread and compacted it. The project was completed on time and within budget with zero change orders. 

"Veolia successfully partnered with a large coal-fired power plant to meet an EPA mandate to evacuate their FGD lagoons within an extremely tight time frame."
-Dennis O'Brien, Product Development Manager, Veolia North America