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.
Partial lagoon cleanouts help balance performance and budgets
DATE POSTED: August 28, 2020
If you’re going to clean out a cell or two at your wastewater lagoon, there are circumstances when a partial cleanout might be the best, fastest way to quickly fix an urgent capacity or performance issue until the lagoon is ready for a full desludging.
Partial cleanouts, using the Bishop Solids Management Solution, can most often be completed while the lagoon remains in operation, so there’s no need to decommission the cell or disrupt the process flow. Bishop Water can quickly diagnose lagoon performance issues caused by excess sludge and determine the volume and locations of sludge that should be removed from the cell.
Once a plan is ready, the team can mobilise a dredge, its mobile polymer conditioning system and prepare a laydown area for Geotube® containers, are used to collect, dewater and consolidate the solids. Or, if the volume of sludge is small, they can be filled and removed inside 30-yard roll off boxes, making transportation and disposal fast and simple.
Partial sludge cleanouts can also become part of an ongoing lagoon maintenance program to ensure optimum performance. Rather than waiting until sludge accumulation reaches a critical level, lagoon operators or Bishop Water technicians can monitor sludge accumulation in the lagoon and when needed, proactively perform a partial cleanout to maintain an optimized level of performance.
Partial lagoon cleanouts have been used by many lagoon operators to achieve operational and economic benefits including:
- Quickly restore lost storage and treatment capacity in the lagoon;
- Correct flow issues caused by sludge accumulation that create short-circuiting of lagoon flow and reduced retention time;
- Defer the cost of a full lagoon cleanout over an extended period of time;
- Maximize the capacity and dewatering of each Geotube® container. Partially filled containers can remain onsite for continued filling at the next cleanout interval. They will experience significant volume reduction between fill intervals, which will reduce the number of containers needed as well as hauling and disposal costs.
Learn more about Bishop Solids Management Solutions for partial lagoon cleanouts.
Contact us to discuss your lagoon clean out needs.
Spring is coming. Get ready to remove your lagoon’s sludge blanket
DATE POSTED: January 29, 2020
It won’t be long before spring weather arrives and wastewater lagoons begin to thaw and return to more efficient operation. But as this happens, non-aerated lagoons can experience benthal feedback—a process where the turbulence of the warming water stirs up the sludge blanket and releases hydrogen sulfide gas along with nutrients that have accumulated in the settled sludge.
The result is not only wafting odours, but also potentially high concentrations of TSS, BOD, phosphorus and ammonia in treated effluent. In some cases, the concentrations of some wastewater constituents can be higher in the treated effluent than the influent.
An excessively thick sludge blanket can often be the cause of these symptoms. Too much sludge also reduces lagoon capacity, retention time and can change the flow path of the wastewater.
Removing some, or all, of the sludge blanket can quickly restore lagoon capacity and eliminate performance issues. In some cases, the installation of baffles, aeration and/or fixed-film biological treatment can also provide a significant, cost-effective improvement to lagoon performance.
Map the blanket to fully understand the problem
Creating a sludge map is an important first step to measure the thickness of the sludge blanket and how it’s distributed throughout the lagoon cell. Once the measurements are complete, Bishop Water can discuss important sludge management considerations and actions including:
- Current lagoon capacity vs. design capacity
- Depth and distribution of sludge
- Location and volume of recommended sludge removal
- Budget and long-term planning for sludge removal
Bishop Water Technologies can provide comprehensive services to measure, plan, remove and dewater sludge from wastewater treatment lagoons of all sizes. Our advanced hydraulic dredge enables lagoon cleanout to occur while the facility remains in operation and the Bishop Solids Management Solution—using Geotube® dewatering containers—dramatically reduces the cost of sludge disposal and truck traffic.
Contact us to discuss your lagoon’s sludge blanket and a sludge management plan.
Learn more about the Bishop Solids Management Solution