Wastewater Treatment Plant Schematic
· Screens - Just as in the Water Treatment process, this is the first step. It removes large debris and prevents pump damage.
· Comminuter - The purpose of the comminuter is to grind up coarse material with revolving cutting bars.
· Grit Chamber – The grit chamber removes sand, grit, pebbles, and other various sorts of small material flow. Usually does this by means of sedimentation or centrifugal force.
· Primary Settling Tank – Here the flow speed drops and suspended solids settle out by gravity. Typical detention times here are 2 – 3 hours. Up to this pointing the wastewater treatment process, approximately 35% of the Biochemical Oxygen Demand (BOD) and 60% of the influent suspended solids has been removed.
· Biological Treatment – The purpose of biological treatment in wastewater systems is to further reduce BOD and suspended solids. The Clean Water Act of 1972 required that the effluent BOD of secondary treatment be less than 30 mg/L. It also required that 90% of the suspended solids. The three approaches of biological treatment are trickling filters, activated sludge, and oxidations ponds. The wastewater treatment schematic shown above is for an activated sludge process.
· Secondary Settling Tank – A secondary settling tank must maintain the wastewater quality. It will also remove or restore sludge to the activated sludge system.
· Chlorine Contact Basin – The purpose of the chlorine contact basin is to simply help disinfect the treated wastewater after the secondary process. A benefit to using chlorine is that it adds a residual to the water that helps prevent it from becoming infected after leaving the wastewater treatment plant.
· Thickener – The purpose of the thickener is to remove some of the water from the sludge.
· Anaerobic Digester – The purpose of this step is to help with sludge disposal. The anaerobic digester stabilizes the solids by breaking down the organic material while at the same time removing the odor. The complex organics within the sludge are turned into carbon dioxide and methane. The anaerobic digester stabilizes the solids without the use of oxygen.
· Sludge Dewatering – Approximately 97 percent of sludge is water. In order to make the removal/transportation of sludge more cost efficient, the water must be removed. The sludge is usually dewatered via evaporation, vacuum filters, filter press, centrifuge, or incineration.
· Sludge Disposal – After the sludge has been processed, it is generally land filled, or in some cases applied to farmland.