Underwater Mineral Processing Services: Water Treatment Plant – Alum Sludge Removal & Geotextile Tube Dewatering (Braintree, MA)
Project Type
Project Description
The Challenge
Many municipal and private water treatment plants need to condition their incoming raw water with the removal of suspended solids materials. This task is typically performed through chemical conditioning with the addition of an approved precipitating / flocculating chemical in preparation for gravity settling of these solids. In many water treatment plants, aluminum hydroxide (Al(OH)2) precipitates forming a “sweepfloc” that tends to capture suspended solids as it settles out of suspension forming an Alum sludge. Wet Alum sludge makes up to 5% in percent solids and is typically difficult and expensive to treat.
Following the initial sedimentation of solids, the pre-treated water is then typically sent to mixed media sand/gravel filters for a final polishing step prior to disinfection (i.e., chlorine addition) then pumped to reservoirs/storage tanks for consumer distribution.
The sand/gravel media filters at the Town of Braintree, MA Water Treatment Plant were fouling with solids much more frequently than normal requiring higher backwash cycles due to carryover of sludge from their Alum Sedimentation Pond No. 2.
The Braintree Water Treatment plant manager investigated several methods of removing Alum sludge from the basins and found large cost variables among pumping, dewatering and disposal methods. Braintree Townships’ consultant reviewed mechanical (i.e., belt filter press, plate & frame filter press) and concluded for their application that Geotube® engineered geotextile bags for dewatering and disposal of sludge on a bone-dry-weight basis was most cost-effective.
The Solution
The Braintree Township consultant contracted with Underwater Mineral Processing Services (UMPS), a division of Underwater Construction Corporation, to perform a SmartFeed™ P-GDT (Pressure-Gravity Dewatering Test – https://mpsmaine.com/smartfeed/pressure-geotube-dewatering-test/) incorporating the UMPS SmartFeed™ polymer chemical conditioning. This technology approach provided the highest economy by volume for reduction of sludge volume for subsequent off-site transportation and disposal.
The township operated a 6” diameter Dri-Prime centrifugal pump from the deep area of Alum Sedimentation Pond No. 2 using a backhoe to crowd Alum sludge to the screened suction hose. The pump delivered approximately 500 gallons/minute, over a 7 hrs/day operational shift, a distance of approximately 790’ to the Geotube® dewatering pad. The UMPS SmartFeed™ processed approximately 210,000 gallons/day of Alum slurry into the Geotube® geotextile dewatering bag.
The township operated a 6” diameter Dri-Prime centrifugal pump from the deep area of Alum Sedimentation Pond No. 2 using a backhoe to crowd Alum sludge to the screened suction hose. The pump delivered approximately 500 gallons/minute, over a 7 hrs/day operational shift, a distance of approximately 790’ to the Geotube® dewatering pad. The UMPS SmartFeed™ processed approximately 210,000 gallons/day of Alum slurry into the Geotube® geotextile dewatering bag.
The Braintree Township engineer designed a level lay-down area based upon UMPS’ estimate for the size of Geotube® containers needed for one year’s estimated volume of alum sludge wasting from their sedimentation basins. The lay-down pad’s design elevation allowed for the collection of clear filtrate from the 120-foot circumference by 90-foot long Geotube® which was pumped back to the headworks of the settling basins as shown in the photos below. The maximum dewatered sludge capacity of the 120-foot circumference by 90-foot long Geotube® is approximately 1,300 cubic yards.
A hydrant water source for polymer make-down along with an electrical power drop were installed near the lay-down pad for the SmartFeed™ chemical conditioning equipment needs.
A bi-annual schedule was proposed by Braintree Township’s consultant that would coordinate a SmartFeed™ processing trailer to be shipped to the prepared lay-down pad, connected in one day to the provided utilities, and be ready to receive Alum sludge the following day from the settling basins Alum sludge pumping operations.
The Outcome
Time & Patience
From the 2020 Alum sludge Geotube® dewatering that UMPS performed for the Braintree Water Treatment Plant, since the location of the filled Geotube was not affecting plant operations, the benefits of “time and patience” had a dramatic effect on the conditioning of the dewatered Alum sludge. By permitting the Geotube® solids to thoroughly slack dry and go through two “freeze/thaw” winter cycles, this dramatically decreased the % moisture, maximizing solids content to 86.7% and decreased the off-site disposal costs as shown in the photo.
“The folks at UMPS are confident, reliable, and enthusiastic to adjust to our needs. Being a certified Geotube® installer using proven Smartfeed® Technology for accurate chemical addition in real time resulted in water quality ≤ twelve total suspended solids and dryer solids filter cake than previous contractors.” – Lou Dutton Water Plant Director.
As the largest inland commercial diving services company in the United States, Underwater Construction Corporation and Underwater Mineral Processing Services has a staff of over 200 divers, supervisors and project managers operate from multiple regional locations in Maine, Connecticut, Maryland, Michigan, Tennessee, Wisconsin, Texas, South Carolina and the United Kingdom. Through our global network of offices and associates, UCC has performed projects in over 25 countries.
Contact Jim Meagher at 207.741.2955 / [email protected] for any of your pit, pond or lagoon sludge/sediment dredging and dewatering services.