Case study: Lagoon sludge removal provides affordable solution for algae and H2S issues
DATE POSTED: May 25, 2021
- Lagoon sludge removal and dewatering
- Bishop Solids Management Solution
- O’Leary Wastewater Treatment Facility, O’Leary, PEI, Canada
The challenge: Algae blooms and corrosive gases caused by sludge accumulation
Sludge accumulation was thought to be causing significant operational challenges for the O’Leary Wastewater Treatment Facility (WWTF), a two-cell lagoon system on the west side of Prince Edward
Island, commissioned in the 1990s.
O’Leary’s treatment lagoon serves about 800 residents, several businesses and, for a period of time, was also receiving wastewater from a potato processing plant.
The lagoons were experiencing serious blooms of blue-green algae during the summer months and exceedances of TSS, BOD and coliform bacteria in treated effluent. Hydrogen sulfide (H2S) gas, which was also attributed to the algae and sludge, was building up in a below-grade chamber that housed the plant’s UV disinfection system.
Not only was the gas accumulation a hazard for operators, but it caused corrosion that damaged ductile iron pipes, an electrical panel and the plant’s UV system.
Operators also saw “islands of sludge” periodically rise out of the water before bursting and releasing clouds of methane and H2S gases.
The solution: Dredging and passive dewatering meets regulatory and budget requirements
In 2019, the Town of O’Leary began working with engineering consultants WSP to repair the damage to the UV system, alleviate the algae blooms and end the release of corrosive gases from the lagoon.
WSP began with a comprehensive sludge survey, obtaining sludge depth measurements from several locations in each of the lagoons.
The results revealed that despite their large area, the lagoons are relatively shallow, with a maximum depth of only 5 ft (1.5 m). Each cell had accumulated about 1.5 to 2 ft (0.45 to 0.6 m) of sludge, which significantly reduced their ability to remove nutrients and settle out solids.
The team evaluated several options and awarded the project to AJL Contracting and Bishop Water Technologies to desludge the lagoon and dewater removed solids with the Bishop Solids Management Solution. This simple, low-energy system uses Geotube® containers, optimal polymers and gravity to collect, dewater and consolidate dredged sludge.
Dredging the lagoon enabled it to remain in operation while sludge removal occurred and also complied with a provincial regulation that prohibits tracked heavy equipment from operating in lagoons with clay liners.
The project began in the summer of 2020, with the construction of a lined laydown area designed to accommodate a layer of three Geotube containers 85 ft in circumference and 114 ft in length (26 x 34.7m) and a second layer of two 95 x 100 ft (29 x 30.5m) containers that would be laid on top. This stacking arrangement minimizes the footprint and cost of the dewatering cell.
The results: No algae, no gases, no rush to haul away solids
Dredged sludge was first pumped through a 0.6 inch (15 mm) screen to remove debris, trash and improve the quality of the final dewatered biosolids for land application.
From the screening plant, the sludge was pumped to the Geotube containers. Bishop Water’s VEPAS™ (Venturi Emulsion Polymer Activation System) added and mixed polymer directly in the feed line, eliminating the need for polymer aging and mix tanks.
The Bishop Solids Management Solution accepts and dewaters solids as quickly as the dredge can pump, dramatically outperforming centrifuges or belt presses for speed and energy efficiency. Low-TSS filtrate released from the microscopic pores of the Geotube container was directed by gravity to cell two.
Technicians continually monitored polymer performance and dose rates to ensure optimal dewatering and retention of contaminants. Daily sampling showed that the system was achieving about 20% solids
concentration after just a few hours of dewatering.
Desludging of cell one was completed in about four weeks. Two more weeks of sludge removal filled the first layer of Geotube containers to capacity and technicians stacked a new container on top of the others.
One more week of dredging and pumping completed the project. The total volume of wet sludge removed was 26,480 m3, which corresponds to 872 bone dry tonnes.
A major advantage of Geotube containment is that the solids can remain at the site for months or even years, allowing ample time for the town to find a suitable location for land application and arrange funding for hauling. Throughout that time, passive dewatering will continue further consolidating the material.
A seasonal freeze-thaw cycle also significantly improves dewatering, potentially elevating the solids concentration of the dredged material to 40% or more in this case.
Since completing the project, operators report that there have been no issues with gas accumulation in the below-grade chamber or blue-green algae growth in the lagoons.
Learn more about the Bishop Solids Management Solution for lagoon sludge cleanouts.
Download the case study.
Contact us to discuss your sludge removal and solids management challenges.
Geotube shoreline system protects historic New Jersey lighthouse
DATE POSTED: January 27, 2021
Over the past several decades, the shoreline around the East Point Lighthouse has receded continually, posing a major threat to the more-than-170-year-old landmark. Despite the creation of a dune system designed to protect against erosion and rising sea levels, the ocean is nearly at the building’s doorstep. In March of 2018, a severe storm severely compromised the dune system forcing municipal work crews to hastily pile sandbags along the shoreline in front of the lighthouse.
But a better solution with more longevity was needed. Later that year, the New Jersey Department of Environmental Protection began a project to install 600 feet of Tencate Geotube™ to reduce the risk of further erosion and help restore a natural, living shoreline.
Eight Geotube containers were laid end to end to cover the distance. Each was filled with sand and set on top of a scour apron held in place with anchor tubes. The scour apron is a critical part of the system, extending several feet beyond the Geotube to prevent wave action from compromising the shoreline under the structure. The lee side of the structure is further protected with Tencate sand filled mattresses, which are designed to remain exposed, endure abrasion and UV light, and also trap and hold soil on the surface to help establish a covering layer of vegetation.
Unlike conventional sandbags, a Geotube container is massive. In this case, a sand-filled Geotube is five feet high, 10 feet wide and weighs more than 3,000 pounds. Once the Geotube is set in place, it’s virtually immovable and can withstand waves, wind, abrasion and impact.
The new Geotube shoreline system was covered with sand to help create a coastal dune habitat, protect the inland wetlands from erosion and prevent the ocean from advancing further towards the historic lighthouse.
Learn more about Geotube containers for shoreline protection.
Contact us to discuss Geotube containers for your shoreline protection project.