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Dewatering Sediments & Sludge: Reducing Treatment Time With Superabsorbents

Zappa SAP Time to Solidify Blog Final

One of the key principles of employing superabsorbent polymer (SAP) technology for the solidification of dredged sediments, wastewater treatment sludge, or other liquid-bearing waste materials, is the drastic time savings that can be realized with SAPs when compared to traditional, commodity drying products like sawdust or Portland cement.   

Two core features of SAPs are utilized to minimize time spent on solidification of liquid-bearing waste: 

1) Rapid hydration speed

2) Unrivaled liquid absorption capacity


Hydration Speed of Superabsorbent Polymers

One of the basic functions of superabsorbent technology is the rapid absorption of water immediately upon contact. In sludge or sediment waste, SAPs draw water out of the pore spaces of the waste and transform the liquid into a solid gel, which traps the water indefinitely.

The result is a dry stackable solid with no free liquids, that is suitable for loading in trucks, transportation, and disposal in landfills. For reference, a 20-yard roll-off box, approximately half full of liquid waste, can be solidified with SAPs in 15-20 minutes in most situations.


For comparison, pozzolanic and cementitious materials (cement, lime, LKD, etc) can take 24 hours or more to cure before the free liquid has been consumed and the liquid waste is suitable for hauling and disposal.

Furthermore, the presence of organics and other chemical species in the waste material can result in extended cure times, higher than expected amendment rates, and dangerous off-gassing (i.e. hydrogen sulfide gas) when using calcium-based cementitious products. 

Related Article: Coal Ash (CCR) Stabilization with Superabsorbents


Comparing Solidifier Absorption Capacity

The superior absorption capacity of SAPs (200-300 times their weight in DI water) translates into time savings on a solidification project by allowing a waste treatment contractor to solidify more waste with much less material, when compared to competing products. 

SAPs are typically effective at achieving full solidification at a dosage rate of 0.5% to 1.0% of the weight of the waste material. For comparison, sawdust, and other cheap bulking agents, are applied at rates of 50% to 200% of the volume of the waste. Cementitious material dosage rates can range from ~5% to above 25%, depending on the contents of the waste and the weather. 


Choosing a Solidification Material

To further explain how absorption capacity contributes to time savings during blending operations at a project site, consider the following example: 

A dredging site in a downtown urban area produces 20,000 cubic yards of wet sediments that are to be dried and transported to a landfill for final disposal. The contractor is faced with a decision: use low-cost sawdust from a local facility, portland cement, or superabsorbent polymer.

While the purchase price of sawdust and cement is attractive at first, the contractor decides to evaluate the total impact that the selected drying agent will have on the project. After evaluating the required dosage rates of each product, the contractor realizes that the sawdust and the cement will require nearly 20 times more drying amendment compared to SAP.


The much higher volume of sawdust and cement that would be required would impact the project timeline in the following areas:   

• Off-loading delivery trucks on-site – 20 times more delivery trucks to off-load, more shipping charges;  

• Much larger mixing and curing areas would be required to be constructed

• SAP use can avoid weeks of site work before dredging;

• Labor for mixing drying agent:

• SAP can eliminate hours to days of mixing time;

• SAP is less sensitive to variations in sediment contents and can be scaled up or down quickly and easily to respond to changes; 

• Waste transportation – sawdust would result in 85 additional truckloads of material being transported to the landfill;  Cement would result in 72 additional truckloads of material being transported to the landfill;

• Waste disposal – SAP more predictable performance and superior liquid retention will protect the contractor from rejected loads at the landfill due to leaching liquid.


Option 1: Sawdust

Amount of sawdust required (100% dosing rate): 20,000 cubic yards (1,890 tons) 

Option 2: Portland cement

Amount of Portland cement required (8% dosing rate):  1,600 tons 

Option 3: SAP

Amount of SAP required (0.5% dosing rate): 100 tons 

Related Article: Reducing Sludge Disposal Costs with SAPs


SAP Speed and Absorption Capacity = Time Savings 

SAPs are designed to absorb tremendous volumes of fluid very quickly. The efficiency and speed of liquid absorption with SAPs help environmental waste management professionals manage complex construction schedules and minimize risk. 

To learn more about why so many contractors and engineers choose SAPs for solidifying liquid waste, please leave a comment below or contact Whit Rawls at wrawls@chasecorp.com  

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This entry was posted in Super Absorbent Polymers, Liquid Solidification on April 30, 2024 by Whit Rawls P.E.