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How It Works

The Treatment Process

The Mattabassett District Water Pollution Control Facility is designed to treat an average wastewater flow of 12 to 21 million gallons per day (MGD) with a peak flow in excess of 80 MGD. The plant also accepts and treats septage from septic tank cleaning trucks and liquid biosolids from other wastewater treatment plants.

The Liquid Treatment process removes the solids and dissolved organic matter in the wastewater. The solids treatment process disposes of the resultant biosolids. Between May 1 and October 31, the months that people typically are involved in water contact sports, the liquid treatment process disinfects the effluent.

Liquid Treatment

The wastewater collected from the served communities flows in the District's trunk sewer to the Pump Station where two Bar Screens remove any large materials which could clog equipment. The Bar Screens then direct this debris to a grinder for shredding. The wastewater is then pumped to two Detritors which slow the flow of wastewater, causing heavy particles and grit to sink to the bottom where they are removed by collection arms. (Grit is sand, coffee grounds, egg shells, etc.) Ejectors move this grit to a storage tank in the Dewatering building for combustion.

Once other large floatable solids are removed (sticks, rags, etc.) by the Comminutors, two Parshall Flumes measure the wastewater volume. A distribution channel aerates the wastewater to prevent deposition of solids, and splits the flow into two of four Primary Clarifiers. Wastewater remains in the Primary Clarifiers for 2.5 hours, where organic solids and excess secondary biological solids settle, forming biosolid wastes, which are pumped into storage tanks.

Aeration Tanks begin the secondary treatment and nitrification/denitrification process, where bacteria present in the wastewater remove the dissolved organic and nitrogen matter. From the Aeration Tanks, the liquid biomass flows into Secondary Clarifiers, where movement is stilled to remove and recycle the biomass. Clear liquid from the Secondary Clarifiers then flows into a Mixing Chamber where chlorine kills disease-causing bacteria. The District routinely provides treatment at the 95% to 99% levels of all monitored parameters. This is significantly higher than the minimum requirement. The disinfected effluent flows through the outfall line - two hundred sixty feet from shore - into the 160-foot long diffuser pipe twenty feet below the surface of the Connecticut River.

Biosolids Treatment

From the Biosolid Storage Tanks, biosolids are pumped to the Belt Filter Presses. These presses remove 25% of the water from the biosolids. The dewatered biosolids, called a "filter cake," are pumped to the Fluidized Bed Incinerator. Here, the biosolids are completely combusted in 19 tons of "boiling" sand heated to 1400° Fahrenheit.

The gas temperature increases to 1550° Fahrenheit, further ensuring complete destruction of organics and providing odor free emissions. In addition to providing odor free emissions, the incinerator emissions are processed through a state-of-the-art mercury emissions control system, a carbon canister, to ensure that The District's emissions are not only odor free but are consistently a factor of 10 below CTDEP mercury emissions limits. The significant research conducted by The District in mercury emissions control is recognized by DEP and industry professionals. The sterile ash is disposed of at the District's Ash Disposal Site or used as cover material at landfill sites.

Odor Control

Odor control and treatment systems began to be installed in 1991 and were completed in 2005. Since the full implementation of all of the odor control systems, some of which are state-of-the-art systems, The District has not had any odor complaints.

These systems consist of a Wet Chemical Scrubber to treat odors from the Biosolids Storage Tanks, six Biofilters (consisting of a three foot deep bed of wood chips) to clean the air from the Liquid Treatment Processes, and a state-of-the-art proprietary Biological filter. This system consists of a 12 foot diameter 20 foot high proprietary philcon unit followed by four, two each in parallel, 6x6x20 foot Biofilters. This unit treats the Odorous air from the Belt Filter Presses, and the Odorous Air from the Dewatering Building.

In addition to these physical odor control systems, The District also utilizes odor control masking agents and chemicals. The most prominent is the use of sodium permanganate for the control of odors in the aeration tanks.

To date, The Mattabassett District has spent over $6.3 million on odor control systems, and we are constantly evaluating and refining our methods and our equipment. Our underlying stated goal has always been to be a good neighbor. To this end, we are committed to making certain that our facilities are odor free.