Environmental Works currently has eight Geotube® containers baking in the scorching summer sun at Springfield, Missouri’s Southwest Treatment Plant. The massive synthetic tubes, which could be mistaken for those inflatable water catapult “blobs,” favorites of summer camps everywhere, are actually filled with solid waste, not air. Once the Geotube® containers are done dewatering, the waste will be disposed of safely and efficiently at a nearby landfill.
EWI has offered this alternative pond dredging service since 2010, and has been dredging the Southwest Treatment Plant’s waste lagoons since November 2017. Each of the plant’s lagoons gets dredged every few years or so depending on capacity. The most recent dredging took place over two weeks in April.
Dredging into Geotube® containers is much faster and more energy efficient than traditional belt press dredging, according to Mitch Busch, Field Services project manager at EWI.
“You can remove more solids faster (with a Geotube® container),” says Busch. “You can dredge to a belt press, but a single belt press can’t dewater the sludge as fast as a Geotube® (container). You may need three or four belt presses to keep up with the dredge.”
For the most recent dredging project, EWI’s dredge boat, which looks like a small pontoon boat, started at one end of the football field-sized waste lagoon, suctioning sludge into a rubber hose that ran around the perimeter of the pond until it was intercepted by an environmentally-safe polymer being pumped into the line. Together the polymer and sludge ran into one of three Geotube® containers positioned on the bank of the lagoon, where the polymer worked to separate the solid waste from the water, which worked its way through the Geotube® container’s porous fabric and back into the pond.
EWI’s field services team on site, including Evan King, Field Services project manager, and environmental technicians Chad Hathaway and William Walker, worked together to dredge the entirety of the lagoon and fill the three Geotube® containers so that they could dewater. The Geotube® containers will continue to dewater for several months.
Busch first used Geotube® containers on a dredging project in 2010, and has been using chemistry to test ideal polymer volumes for dewatering sludge since.
“I do a lot of testing with different polymers to find the one that works the best with the (Geotube®) containers and treats the water the best,” says Busch. “The test we do is called the cone test. We find a polymer that seems to floc well and then we pour a measured amount into a piece of Geotube® (container) fabric that is in the shape of a cone inside a funnel and we see how much water passes through the fabric and we see what solids are trapped in the fabric. We have to ensure the polymer and sludge don’t blind off the Geotube® (container) fabric and prevent dewatering.”
A floc is a loosely clumped mass of fine particles.
“Depending on the waste stream, you may need a coagulant to go with a polymer,” Busch adds.
The Geotube® containers on site at the Southwest Treatment Plant aren’t the only ones currently dewatering.
“I have other (Geotube®) containers in service at Westar Energy. They are dewatering centrate from (Westar’s) centrifuges that they use to dewater their FGD (flue gas desulfurization) sludge.”
Centrate is the water leaving a centrifuge after most of the solids have been removed, while a centrifuge is a machine with a rapidly rotating container that applies centrifugal force to its contents, often to separate liquids from solids. And flue gas desulfurization is a set of technologies used to remove sulfur dioxide from exhaust flue gases of fossil-fuel power plants, and from the emissions of other sulfur oxide emitting processes (i.e. trash incineration).
EWI has also discussed using Geotube® containers for agricultural lagoon dredging projects. TenCate, creator of the Geotube®, has introduced a Geotube® Nutrient Recovery System that can remove and store solids from lagoons for later land application as opposed to sending the compost solids to a landfill.
“If the client has the space and some time, this technology is very good for dewatering,” says Busch.