Wastewater Primary Treatment
Primary wastewater treatment removes material and debris from wastewater that will either float or readily settle out by gravity. It includes the processes of screening, comminution, grit removal, and sedimentation. Screens made of narrow metal bars first block the large material, and then a comminutor may be used to grind and shred debris that passes through a screen.
Grit chambers then use a series of parallel metal bars to remove sand grains from water flow by settling them in batches at intervals along the chamber. Grit is defined as any material found in sewer lines that will damage sewer pumps, sewer mains, sewer piping, sewer valves or sewer fittings.
Sedimentation tanks are used to remove water from the grit chamber. The tank usually contains a series of compartments called baffles. Each compartment has floating debris resting on its bottom and rising water above it which causes the debris to slowly settle out in each compartment. Sand grains form at the top of these compartments while grease, oil and grit settle below into sludge layers that are periodically removed by sewer cleaning crews who use high-pressure vacuums to clean sewer lines and pumps. The next step in the sewer treatment process is secondary treatment.