Wastewater treatment facilities that rely on lagoon-based systems face a sediment management challenge that is both predictable and easily deferred — until the lagoon’s treatment capacity is seriously compromised. Biosolid accumulation in wastewater lagoons is a slow-moving problem that can take years or decades to become critical, which is why many facility managers defer dredging until they face permit compliance issues or treatment system failures. Understanding the dredge options available for wastewater lagoon maintenance can help facility managers plan proactively rather than reactively.
How Wastewater Lagoons Accumulate Sediment
In a wastewater lagoon system, influent enters the first cell where heavy solids settle out and begin the anaerobic digestion process. Over time, partially digested organic matter — biosolids — accumulates on the lagoon floor. This material is dense, high in nutrients, and structurally different from the inorganic sediment found in lakes or harbors. Its high organic content means it is biologically active, generating methane and carbon dioxide as decomposition continues, and creating a variable-density profile across the lagoon floor.
As biosolids accumulate, the effective water depth in the lagoon decreases, reducing hydraulic retention time — the period during which wastewater remains in the lagoon for treatment. When retention time drops too low, effluent quality deteriorates and permit violations become likely. The solution is to remove accumulated biosolids through dredging, restoring the lagoon’s design volume and extending its operational life.
Hydraulic Dredge Options for Lagoon Biosolids
A hydraulic dredge is the most widely used equipment type for wastewater lagoon biosolids removal. In hydraulic dredging, a pump creates suction at the sediment surface, drawing a mixture of solids and water (slurry) into a pipeline that conveys it to a disposal or dewatering site. The ratio of solids to water in the slurry — called percent solids — determines how efficiently the system moves material relative to the volume of water handled.
For wastewater applications, pump selection is critical because biosolids contain fibrous material, gas pockets, and variable-density layers that can cause cavitation or pump blockage with standard centrifugal pump designs. Submersible pump configurations — where the pump operates at or near the sediment surface rather than drawing material up to a surface unit — are generally more effective in lagoon applications because they maintain consistent inlet pressure regardless of water depth variations.
The Wastewater Dredge Selection Process
Selecting the right wastewater dredge for a specific lagoon requires answering a series of site-specific questions that go beyond the standard “how much material needs to be removed” calculation.
What is the lagoon liner type? Many modern wastewater lagoons are lined with synthetic geomembrane materials to prevent groundwater contamination. Dredge equipment must be able to operate without contacting the liner — either through precise depth control systems or by maintaining a safe clearance above the liner surface. Cutterhead dredges that use rotating mechanical teeth create higher liner contact risk than suction-based systems that draw material from slightly above the bottom.
Is the lagoon in service or dewatered? Dredging a lagoon while it remains in service — receiving influent and discharging effluent — is significantly more complex than dredging a dewatered lagoon, but it may be the only option for facilities without bypass capacity. In-service dredging requires equipment that can work around active flow patterns, avoid disrupting the settling zones where treatment is occurring, and discharge removed material in a way that does not overload the treatment system.
What is the discharge management plan? Biosolids removed from a wastewater lagoon require appropriate handling. Options include pumping to mechanical dewatering equipment (belt presses, centrifuges, screw presses), discharge to geotextile tubes for passive dewatering, land application on agricultural fields where regulations permit, or transfer to a dedicated drying bed. Each option has different requirements for pump pressure, pipeline distance, and slurry percent solids.
Planning and Timing Considerations
Wastewater lagoon dredging is best approached as a scheduled maintenance activity rather than an emergency response. Facilities that track lagoon depth through annual bathymetric surveys can project when dredging will be needed and plan procurement, permitting, and contractor selection accordingly. Emergency dredging — triggered by a permit violation or imminent operational failure — is consistently more expensive and logistically difficult than planned work.
For municipal facilities, the timing of dredging must also consider the seasonal agronomic calendar if land application of biosolids is planned. In northern climates, field conditions may limit land application to specific months, which in turn constrains when dredged material can be discharged. Starting the planning process 12-18 months before the target dredging date allows adequate time to coordinate all elements of the project without schedule-driven cost increases.
The combination of the right equipment, realistic timeline planning, and coordinated discharge management is what separates a successful lagoon dredging project from one that runs over budget and over schedule. Understanding the available dredging technology options is the essential first step in building that plan.
Charles Perkins was born in California, Studied at California State University. Currently working as Manager at Hoonskate, Charles Perkins helps readers learn the Health, Marketing, Insurance, Lawyer etc hone their skills, and find their unique voice so they can stand out from the crowd.