UMPS Pit-Hog Robotic Dredge: Photo J. Meagher – UMPS

The hydraulic dredging of pits, ponds & lagoons necessitates the integration of critical slurry processing operations for the dewatering and subsequent management of solids.  

For mechanical dewatering operations of dredge slurries up to 2,000 gallons/minute (gpm) with typical solids contents of 4 – 8 %, basic unit process operations required are: debris scalping (<2-inch diameter), followed by coarse fraction vibratory screening (2-inch diameter x 3/8-inch diameter) and intermediate to fine fraction separation employing a combination of hydrocyclones for slurry thickening and “High-G” vibratory (i.e., high-frequency) screening will separate 3/8 inch” diameter x 45-micron sized fractions.  The selection, sizing and operation of these unit process operations are typically straightforward, but what to do about the removal of the large slurry volume of fine silt, clay and colloidal materials in the <45-micron x 0 size range necessary to meet regulatory permit water discharge criteria?

The application of inclined plate clarifiers has traditionally been the equipment of choice. However, to meet temporary transportable requirements for short-term project, multiple units would be necessary to meet a 2,000-gpm hydraulic flow requirement.  In addition, their inclined plate packs require periodic removal and cleaning of accumulated solids.  With proper polymer/coagulant addition and hydraulic loading, the typical percent underflow solids concentration can vary anywhere between 13 and 23 %  dependent on the mineral settling characteristics of the <45-micron x 0 size range fines fractions.

With no moving parts or power requirements, the Underwater Mineral Processing Services (UMPS) High-rate Clarifier / Paste Thickener is specifically designed for enhanced flocculation/sedimentation of fine silt, clay and colloidal materials in the <45-micron x 0 size range with no high maintenance inclined plate packs. 

The UMPS clarifier’s compaction zone in the lower conical section enhances gravity densification of the settled solids typically increasing the underflow solids content percentage to between 35 and 45% for mineral sludges.

The thickened paste underflow is ideally conditioned for supplemental dewatering by Geotubes® /or geotextile tubes, decanting centrifuges or plate & and frame filter press.

The UMPS High-rate Clarifier/Paste Thickener is easily transported to a client’s site by a heavy-duty pick-up truck courtesy to of the unit’s integrated triple axle, hitch and brake design. 

Once on-site, the user prepares a competent, level base (i.e., compacted Density Media Aggregate [DGA], crane or DuraBase mats) approximately 16-feet x 16-feet to accommodate the High-rate Clarifier/Paste Thickener’s 12-foot x 12-foot footprint. 

Using two 25-ton cranes, the High-rate Clarifier/Paste Thickener is quickly tilted upright.  Interconnections are made and the clarifier is immediately ready for operations.  There are no electrical service connections needed for this unique clarifier/paste thickener.  The empty weight of the clarifier is 28,000 pounds and operational weight (full) is 240,000 pounds.

Once in place and connected to the client’s fine material screening underflow discharge line and polymer feed system, the UMPS High-rate Clarifier/Paste Thickener is ready for immediate operations.

Below provides an example of raw fine fraction dredge slurry prior to polymer condition in preparation for flocculation/sedimentation, the conditioned slurry, the clear clarifier overflow and clarifier paste underflow.

It is recommended that in preparation for the rental of the UMPS High-rate Clarifier/Paste Thickener that the potential user complete the UMPS “Spec Your Project” form ( to facilitate an initial determination of applicability of the unit for meeting a client’s fine solids slurry dredge water clarification goals. 

The client will need to perform bench-scale flocculation/sedimentation jar tests to determine the optimum selection of an appropriate polymer and dosage rate.

As the largest inland commercial diving services company in the United States, Underwater Construction Corporation and Underwater Mineral Processing Services have a staff of over 200 divers, supervisors and project managers operate from multiple regional locations in Connecticut, Maine, Maryland, Michigan, South Carolina, Tennessee, Texas, Wisconsin and the United Kingdom. Through our global network of offices and associates, UCC has performed projects in over 25 countries. 

For monthly lease rates, contact Jim Meagher at 207.741.2955 / , or Contact Us ( for any of your pit, pond or lagoon sludge/sediment dredging and dewatering services.