Process Description

Preliminary Treatment

The 2.2 million gallon average daily flow of sanitary sewage is conveyed through 102 miles of piping and (8) sewage pumping stations to the Water Pollution Control Facility.  The wastewater then enters the facility through 24” and 36” diameter pipes.  A fine mechanical screen filters the wastewater to remove solid material.  The solids are removed, washed, compacted and chopped up for ultimate disposal.  Further preliminary treatment consists of grit removal early in the treatment sequence due to its abrasive nature and to reduce undue wear on subsequent equipment, clogging of pipes and valves as well.  This is accomplished via a vortex grit removal system installed at the Headwork’s building.

Primary Treatment

Two circular clarifiers provide for the removal of settleable and floatable solids from the wastewater flow, in order to reduce the load of solids and increased oxygen demand on the subsequent processes and ultimate discharge of the final effluent.

Clarification is a physical process which rely on gravity and buoyancy to accomplish the solids-liquid separation.  As the wastewater passes through the tank at very low velocities settleable materials removed from the influent wastewater (primary or raw sludge), and floatable materials (scum) are removed.

Sludge and scum removed through the treatment process are further processed by thickening then pumped into tanker trucks for final disposal at a contracted disposal site.

Secondary Treatment

After primary treatment the wastewater flows into aeration tanks designed to operate in a four-stage nitrogen removal process. The influent portion of the tank is an anoxic zone (limited air) which is divided into three selector zones.  Following the anoxic zone is an aerobic (increased air) which includes fine bubble diffusers.  A second anoxic zone further provides necessary nitrogen removal. The final zone is a re-aeration zone which includes fine-bubble diffusers to increase dissolved oxygen levels. This configuration allows for the removal of total nitrogen from the wastewater by the conversion of influent ammonia-nitrogen to nitrogen gas that is safely released to the atmosphere.

After several hours of treatment in the aeration basins the mixed wastewater flows into secondary clarifiers for further treatment. The secondary clarifier; similarly to the primary clarifiers separates the treated mixed wastewater again heavier solids are settled and lighter materials float. At this point 90-98% removal of pollutants has occurred. A certain amount of solids from this process is continuously returned to the aeration basins to maintain an effective biological population. In addition constant monitoring of the biological population for micro organisms no longer effective must be disposed of as waste sludge. Finally the wastewater flows to Ultra Violet units for disinfection before discharging into the Connecticut River.

The entire wastewater process requires daily monitoring and testing performed by a full time lab technician in order to ensure permit compliance. The plant operation must meet strict State and Federal discharge permit parameters for discharge to the Connecticut River.

Questions regarding our process or to schedule a tour of our facility, please call (860) 652-7772 or email the staff at the WPCF.