Dredging of saturated sediments from waterways, wastewater lagoons, and stormwater ponds generates massive quantities of waste material that require costly and time-consuming management practices, such as dewatering, solidification, transportation, and off-site disposal.
If solidification, transportation, and disposal of saturated sediments are a part of your scope of work, superabsorbent polymers (SAPs) can help to reduce your budget, time-on-site, and environmental risks.
Saving on Transportation & Disposal Costs
Transportation and disposal (T&D) of dredged sediments are typically major components of the overall project cost. Trucking dredged spoils from a project site to a landfill requires dump trucks, drivers, diesel fuel, and landfill tipping fees, costs that add up very quickly when managing thousands of tons of liquid-bearing waste.
The simplest solution to minimizing transportation and disposal costs on a solidification project is to minimize the amount of overall waste that needs T&D in the first place! This isn’t as far-fetched as it might sound. An efficient waste solidification reagent requires less material to eliminate free liquid, resulting in far smaller volumes of treated waste material for T&D.
This is why SAPs are widely used by dredging contractors to solidify saturated sediments. SAPs have an absorption capacity of 70x other solutions, resulting in ultra-low dose rates (0.5%-1.5% by weight) when compared to traditional bulking materials (sawdust) and pozzolanic, or cementitious materials (i.e., Portland cement).
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Comparing Expenses of Solidification Materials
For a head-to-head comparison of SAPs with sawdust and Portland cement, let’s start with the amendment, or dosage, rate.
Dosage Rates
Portland cement can require dosage rates ranging from 10% to 25% (by weight). Sawdust can require dosage rates from 100% to 200% of the weight of the waste. SAPs however are applied at dosage rates ranging from 0.5% to 1.5% by weight.
Material Costs vs Transportation and Disposal Fees
While Portland cement and sawdust are low-cost materials, their liquid absorbent inefficiencies result in a lot of unnecessary weight added to the waste. Keep in mind, that any material added to the waste to absorb liquid must be transported and disposed of along with the original waste quantity.
Every pound of treatment amendment costs extra dollars in transportation and disposal charges. This cost comparison calculator allows you to adjust the pricing and quantity inputs for sawdust, cement, and SAPs. See for yourself how SAPs compare to traditional commodity absorbents and pozzolans.
Reducing Expenses by Reducing Time-On-Site
In addition to the tangible cost component, SAPs help save time on-site. Cement can require 10-25 times more reagent than SAPs. Sawdust can require 100-200 times more material than SAPs. Imagine the extra time spent staging reagent, mixing it into the waste, and transferring the treated waste to dump trucks for off-site disposal if you used cement or sawdust over SAPs.
Drying Times of Solidification Material
This only touches upon the time spent staging and applying the material. When we discuss the dry times of superabsorbent polymers compared to other solidification materials, the difference becomes even more apparent. SAPs draw water out of the waste, trapping it as a gel. The result is a dry stackable solid with no free liquids.
For reference, a 20-yard roll-off box, approximately half full of high-liquid waste, can be fully solidified with SAPs in 15-20 minutes in most situations. Pozzolanic and cementitious materials (cement, lime, LKD, etc) usually require 24 hours or more to cure before the free liquid has been consumed and the liquid waste is suitable for hauling and disposal.
By the way, this assumes ideal conditions and consistent blends of liquid waste. Drying times of pozzolanic and cementitious materials tend to increase during rainy weather and depend on the organic content of the sediments, whereas SAPs feature consistent and predictable solidification rates regardless of organic loading and weather conditions.
For engineers, product specifiers, and estimators, the solidification speed of SAPs offers a clear advantage for sediment management. SAPs allow dredging contractors to eliminate the construction of on-site storage and treatment facilities for processing sediments with cementitious products (i.e. curing pits). Sediments can be prepared for off-site disposal in minutes, with minimal site footprint with SAPs. The incredible comparative efficiency of SAPs is a net win for all parties involved.
Superabsorbent Polymers for Environmentally-Friendly Solidification
Another factor to consider when evaluating solidification reagents is environmental impact. Portland cement is a known carcinogen, is a dust hazard, and contains heavy metals that can contribute to landfill leachate contaminants and greater leachate treatment costs.
SAPs, however, do not leach any chemical compounds into the environment. SAPs are used globally in operating rooms, baby diapers, and personal hygiene products. The FDA even approves them as an indirect food additive (the absorbent pads you see under raw meat). SAPs are extremely safe and environmentally friendly.
For an in-depth look at the benefits of superabsorbent polymers for environmental remediation, we encourage you to watch our appearance on Sean Grady’s Environmental Transformation Podcast.
When budgeting your next sediment dredging project, consider the impacts that the solidification reagent selection has on the overall project costs, timeline, and environmental risks. Superabsorbent polymers are designed to save time and money while protecting the environment.
