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Secondary Treatment of Wastewater

Once wastewater is treated by primary treatment methods, it is passed along to secondary treatments as primary effluent. Secondary treatment serves the purpose of removing soluble organic matter and any remaining suspended solids that made it past primary treatment. Secondary treatment methods utilize a biological process in which microbes consume organic impurities within the wastewater as food, which converts the impurities into carbon dioxide, water, and energy for the microbe’s growth and reproduction. The most commonly used secondary treatment methods are trickling filter and activated sludge.

Trickling Filter

The tricking filter secondary treatment method consists of a tank filled with a deep bed of stones. Sewage is continuously sprayed into the tank where it slowly trickles through the layers of stones. As the wastewater flows through the tank, bacteria gather and multiple on the stones, where they absorb dissolved organics, resulting in a low biochemical oxygen demand (BOD) of the sewage. As wastewater settles at the bottom of the tank, it is pumped into clarifies that serve the purpose of removing microbes that were wasted off the rocks.

Activated Sludge

The activated sludge secondary treatment method utilizes a large aeriation tank and a secondary clarifier. Primary effluent is pumped into the aeriation tank where it is mixed with recirculated sludge. Compressed air is injected into the mixture through diffusers at the bottom of the tank. As the air bubbles to the surface it provides oxygen and rapid mixing action, which allows the bacteria in the sludge to absorb dissolved organic. After 6 hours in the aeriation tank, the water is pumped into a secondary clarifier where gravity settles out the sludge. The sludge sinks into a hopper at the bottom of the clarifier which recirculates about 30% back into the aeriation tank. The remaining sludge is pumped away to be disposed of.

Shanley Pump offers both key pumps for the activated sludge treatment method. Our SEP progressive cavity pumps and our sister company Liberty Process’s Millennium Series Pumps are designed specifically to handle the highly viscous liquids. Shanley also offers Edur DAF pumps, which offer improved efficiencies within the aeriation tank. The Edur DAF pump eliminates the need for an air compressor because it is able to generate dissolved air into the pumped liquid by itself. The dissolved air not only serves the purpose of oxygenating the wastewater, allowing for microbes in the activated sludge to thrive, but it also causes suspended solids to attach to the micro bubbles for easy solid removal in the secondary processes. Call or email us below today to discover how Shanley Pump can improve efficiencies within your wastewater treatment plant.

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*Shanley Pump Group is not affiliated with nor distributor for Seepex®, Allweiler®, Moyno®, Tarby®, Netzsch®, or Continental Inc.® all referenced product names, brands, models, or part numbers is solely for identification purposes. Seepex® is a registered trademark of Seepex®. Moyno® and Tarby® are registered trademarks of Robins and Myers® and NOV®, Netzsch® Incorporated is a registered trademark of the Netzsch® Group, Allweiler® is a registered trademark of Colfax® Corporations Continental® Pumps is a Trademark of Continental® Ultra Pumps.