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Replacing solar drying beds reduces time and labour costs for sludge dewatering
Geotubes replaced the solar drying beds and can process the same volume of sludge in a day, that used to take operators about a month.
It used to take almost a month to dewater the same volume of sludge that is now done in less than a day at the Meteghan Sewage Treatment Plant in the Municipality of Clare, Nova Scotia, according to treatment plant operator Jody Comeau. The dramatic savings are possible after replacing sand drying beds with a simple, low-energy Bishop Solids Management Solution, which uses only Geotube® containers, polymers and gravity to collect and dewater the sludge in a single step.
Waste sludge from the plant is now pumped directly from the sludge storage tank to a Geotube container. As the sludge is pumped, Bishop Water’s Venturi Emulsion Polymer Activation System (VEPAS™) activates the polymer with no mechanical mixing required and injects it directly into the sludge line. In many cases, the optimal polymer dose can produce dry solids from waste sludge in excess of 50%. The comprehensive dewatering system has been operating since November 2016.
The one-step, venturi-based VEPAS eliminates many of the components used in mechanical polymer systems, such as mixers and aging tanks, which not only increase the size of mechanical systems, but also require operator attention for maintenance and cleaning.
“Our sludge does experience some variability, depending on the time of year and how long it’s been held in the storage tank,” Comeau says. “It only takes a few minutes to test the sludge and set the VEPAS, using the touch screen interface, to add the ideal polymer dose.” VEPAS enables operators to easily change the rate of polymer flow, prior to starting the waste sludge pumps, or while the system is operating, to address any variability in the sludge consistency.
Once the run is finished, Comeau says he can clean any remaining polymer out of the compact VEPAS system in about 10 minutes and have it ready to go for the next session. “I now have much more time to spend on more important tasks like plant process optimization and reducing inflow and infiltration in the collection system,” says Comeau.
Prior to commissioning the Bishop Water system, Comeau says that operators would spend many hours raking dry sludge by hand from the drying beds and piling it onto wheelbarrows. Each bed contained about 50 wheelbarrows of dry sludge, that was then loaded onto trucks for disposal.
The municipality is investigating the possibility of land applying composted solids from the Geotube containers onto a former landfill site, further reducing disposal costs and truck traffic.
