Page 17 - Simplified Wastewater Treatment Fundementals\Primary Treatment

Primary Treatment

Primary Sludge pumping requires Operator intervention. Simply allowing a primary sludge pump to run

constantly will result in sludge blanket coning. Coning is the process of pulling wastewater down through the

sludge blanket. Coning results in pumping wastewater instead of primary sludge.

The experienced Operator will know based on the speed of the primary clarifier collector drive and the sludge

blanket depth how often the primary sludge pump should be cycled on and off. The primary sludge pump’s OFF

time allows for primary sludge to be pushed into and fill the clarifier sump. The primary sludge pump ON time

allows for the collected sludge in the sump to be pumped.

Primary blanket depths can vary based on clarifier design but are typically maintained between 1 and 3 feet in

depth.

Primary sludge can gasify when summer temperatures are higher and or primary detention times exceed 3 to 4

hours. Gasification can lead to sludge blanket buoyancy and the possibility of a floating blanket. A floating

blanket will negatively impact the ability to collect surface grease. A floating blanket will also negatively impact

the quality of the primary effluent and impact the downstream activated sludge.