York City's 275th Anniversary

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Secondary Treatment

In SECONDARY TREATMENT the majority of pollutants are removed. This treatment phase utilizes MICRO-ORGANISMS to remove the food and nutrients(pollutants) that are found in wastewater.

As the wastewater enters this particular phase of treatment, the micro-organisms are introduced. Then an anoxic or low DISSOLVED OXYGEN zone follows. Next, this liquor is aerated so the dissolved oxygen can be increased to allow NITRIFICATION and BIOLOGICAL PHOSPHATE reduction to occur.

The York facility, through a patented process and tank design, is able to have these micro-organisms metabolize the organic matter and convert ammonia to nitrates. The process also allows the micro-organisms to uptake ortho-phosphates into their cells.

After the aeration stages, the MIXED LIQUOR (micro-organisms and wastewater) enter the SECONDARY CLARIFIERS. Here the velocity of the wastewater is slowed to allow for the biomass to clump together and settle to the bottom while allowing the clean water to flow over the tank weirs. Large pumps return the micro-organisms from the bottom of these secondaries and return them to the beginning of the secondary treatment phase to start the cycle all over again.

During secondary treatment the micro-organisms reproduce in great numbers. To keep the system in check a portion of these critters removed through a wasting process. This sludge is thickened in our DISSOLVED AIR FLOATATION THICKENER and this thickened material is sent to the anaerobic digesters.


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