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Sewage Treatment Plant
Pollution Control Plant

R Mark Crandall,
Chief Operator


700 William T. Field Dr.
Watertown, NY 13601

Ph: (315) 785-7840
Plant Ops: (315) 785-7841
Fx: (315) 779-2095

24 Hours / 7 Days

The Watertown Pollution Control Plant is a 16.0 MGD (million gallons per day) Facility with Secondary Treatment. The Facility first went on line as a primary plant in 1966. On December 1st, 1981 the secondary Trickling Filter process went "on line". The trickling filter process is capable of providing effective secondary treatment for sustained flows up to 8 MGD per day. On August 8th, 1989 a new Activated Sludge process was added to facilitate the Fort Drum expansion.

We currently have two influents and two effluents which discharge into the Black River and can now sustain flows up to 16 MGD. Our discharge permit requires 85% removal of suspended solids and BOD (Biochemical Oxygen Demand).


Preliminary treatment is preformed to protect the operation of the wastewater treatment plant.

This is accomplished by removing from the wastewater any items which can clog or damage pumps or interfere with subsequent treatment processes.

Pollution Plant

That equipment performing a preliminary function is numbered from 7 to 11 on the wastewater flow schematic. Most of this equipment is housed within the Control Building. The bar screens are heavy steel bars spaced about ¾" apart, and intercept all large objects present in the influent water (i.e. rocks, lumber, branches, cans, bottles, etc.) The screens may actually be considered as trash racks.

Front End Loader

Motorized rakes and buckets mechanically clean the screens and convey the trash up to the operation floor where it is then loaded into the front end loader and subsequently trucked to a landfill. The detritors are grit removal equipment.

Grit is that inert material such as sand, pebbles, and cinders which are small enough to pass through the bar screens, yet large enough to have the potential of clogging, damaging, or interfering with subsequent equipment or processes

The Detritors are designed to slow the wastewater to approximately 1 foot per second. This velocity is low enough to allow the grit to settle and large enough to maintain the organic solids in suspension. There are sweeps in the Detritors which continuously scrape along the bottom of the tanks and collect the grit into adjacent pits. The grit is then conveyed to the operation deck and eventually hauled by truck to the landfill. About 25 cubic feet of grit and screenings are removed daily. From the Detritors the wastewater then flows to the raw sewage wet well where it is then pumped to the aerated grit chambers. There are 5 raw sewage lift pumps. Three of the lift pumps are variable speed with the remaining two being fixed speed. Each pump is driven by a 100 HP electric motor with the capability of pumping approximately 4500GPM. The pumps are sequenced by an indicator responding to the level of water in the raw sewage wet well.

Aerated grit chambers preceding the Primary Settling Tanks replenish the wastewater with dissolved oxygen to prevent septic conditions from developing in the settling tanks or clarifiers. Additionally, the agitation caused by the aeration separates the grease and scum from the organic solids facilitating their removal as skimming in the primary settling tanks. A third function of the aerated grit chambers is to allow additional grit to settle during the approximately 20 minute holding times. The grit is removed from the chambers and is hauled to the landfill (approximately 3 to 4 cubic feet per day

Primary treatment is designed to remove organic and inorganic solids by the physical process of sedimentation and floatation. The primary settling tanks (clarifiers) measure 250’ x 40’ x 8.2’ and have a hydraulic detention time of about 1.8 hours. Organic and inert settleable solids will settle and are pumped to the gravity thickener as primary sludge at about 0.1% solids by weight. The grease and scum float to the surface and are skimmed off the tank by simple decanting. Primary Settling Tanks

Flow splitter box. This structure receives the flow from the primary settling tank (clarifier) and splits the flow between the Trickling Filter Process (A train) and the Activated Sludge Process (B train). The flow is split 50/50 with the "B" side never receiving more the 8 MGD. The "A" side Trickling Filter Plant can handle the large swing in flows due to the nature of the Trickling Filters. 


The effluent from the primary treatment contains large quantities of colloidal and dissolved solids. For average domestic wastewater, about 80% of the original total solids still remain in the water after primary treatment. The secondary treatment process consists of the biological treatment of wastewater by utilizing many different types of microorganisms that convert colloidal and dissolved solids into larger settleable solids which can later be removed from the water. This facility presently has two processes for secondary treatment. They are the Trickling Filters process and the Activated Sludge process.

Trickling Filter

Trickling Filter:

The Trickling Filters at Watertown are large circular tanks 5’ deep and filled with gap graded stone.

Waste water is distributed over the large surface area of filter media (stones) by radial revolving arms.

As the water trickles down through the media, the solids within the water come in contact with and cling to the microorganisms which also cling to the rocks. The colonies lend the appearance of a grayish-green and brown slime.

As the microorganisms feed on the solids, they grow and eventually become a "heavy" biomass which sloughs off the rocks and is carried by the wastewater stream to the final settling tanks.

The trickling filters measure in excess of 120’ in diameter and are covered to maintain a satisfactory environment during the cold winter months. A provision for venting incinerator flue gas to the trickling filters has been provided to heat the filter when necessary. It is in the final clarifier that the biomass is removed from the wastewater by the physical process of sedimentation. Each trickling filter is designed to treat between 6 and 8 million gallons of wastewater per day. The pump station located at the center of the trickling filter complex automatically selects the proper hydraulic loading for each filter. The pump station can re-circulate flow back to the head of the filters. Under normal conditions the filters operate in a two stage manner with pairs in series. Additionally the plant has the capability of alternating lead and lag filters. This practice is called Alternating Double Filtration (ADF), a concept developed in England with the advantage of being able to control slime thickness which tends to reduce clogging problems. Under abnormal conditions of high flow (greater than16 MGD) the filters are operated in parallel mode.

Activated Sludge:

Activated sludge is a biological wastewater treatment process which speeds up the decomposition of waste in wastewater being treated. Activated sludge is added to the wastewater and the mixture is aerated and agitated. After some time in the aeration tanks, the activated sludge is allowed to settle out and is disposed of (wasted) or reused (returned to the aeration tanks) as needed. 

Primary settling tank flow diverted to the head of the Aeration Tank is mixed with the return sludge from the final settling tank. When the primary effluent and return sludge is then mixed with the activated sludge in the aeration tank, it is called the mixed liquor. To keep this mixture in suspension and to maintain a dissolved oxygen of 2.0 mg/l we have air blowers which feed air through a fine air bubbler distribution system located in the bottom of each aeration tank

Activated Sludge

This is a necessary process as oxygen is required to sustain the life of certain microorganism. After the wastewater (mixed liquor) leaves the aeration tanks it enters the final settling tanks (clarifiers). At this point the heavier solids settle to the bottom of the tank. A proportion of these settleable solids are returned to the head of the aeration tank (70%) as return activated sludge. A portion of this settled sludge is also wasted to our gravity thickener. It is necessary to waste sludge because we do not want our solids concentration to exceed 2500 mg/l – 4500 mg/l of Total Suspended Solids (TSS) in our aeration tanks (TSS is subject to seasonal adjustments). 

Sludge treatment and disposal:

The sludge from the primary and secondary clarifiers is pumped to the gravity thickener at about 0.1% solids. The thickener utilizes the physical process of settling and gravitational compaction to thicken the sludge to approximately 6% solids by weight.

Each thickener is equipped with an exhaust ventilated scrubbing system for odor control. An approximate 1.5 days of sludge retention time is maintained.

Sludge Thickener Tanks

Anerobic Digester

Longer retention times run the greater risk of sludge becoming septic. Currently a portion of the sludge is pumped from the gravity thickener to the anaerobic digester. To preserve BTU value in the sludge the majority of the sludge from the bottom of the gravity thickener is directly conditioned and burned.

The reason for this dates back to 2008. With the rising cost of fuel oil, the cost to burn digested sludge became prohibitive

Maintaining the higher percent volatile solids (BTUs) in raw sludge reduced the amount of fuel oil required as a supplemental fuel for incineration. The net reduction in fuel oil consumption has been roughly 85%.

Anaerobic digesters:

Thickened sludge is systematically transferred to the primary digesters. We have two primary digesters and one secondary digester. A two stage digester scheme is used to allow bacterial action to reduce the solids to a more stable, less toxic form at the end of the process. The primary digesters have provisions for heating the sludge to maintain a uniform temperature of 95° F.
Anaerobic Digester

Additionally, a compressed gas mixer keeps the sludge well mixed to insure good bacterial action as well as preventing the formation of scum blankets which could adversely impact the digester operation. The sludge is in the primary digester for approximately 19-25 days. The sludge is then transferred to the secondary digester where the digestion process is completed. A by-product of digestion is the production of methane gas. We produce approximately 10,000 cubic feet per day and use this gas as the primary fuel for the digester complex boiler heating system. During spring, summer and fall months this plant produces enough gas to satisfy much of the facility’s heating requirements. The secondary digester is equipped with a floating cover to provide a minimal amount of gas storage.


The sludge incineration system is composed of two independent subsystems:

1.   Chemical conditioning and dewatering
2.   Incineration.


Chemical conditioning and dewatering cycles are done in the sludge disposal building. Sludge is pumped from either or both the thickener and /or digester to the sludge conditioning column. Polymer is added at the conditioning column, and from there the conditioned sludge will enter the aging tanks to complete the mixing and chemical curing of the sludge. From there, the sludge will gravity feed to the batch tanks. The batch tanks serve as a reservoir from which the filter press feed pumps will draw sludge to feed the filter presses on the second floor. Checmical Conditioning
The filter presses operate at 250 psi and will produce a sludge cake of approximately 35 % solids by weight. The sludge cake will then be conveyed via drag conveyors to a sludge storage silo, and eventually feed the fluidized bed incinerator via the screw feeders. A flue gas heat exchanger (called a re-couperator) heats the incoming fluidizing air to approximately 1000° F. making the reactor a hot windox design. The routine operating temperatures of the reactor are approximately 1400°F to 1560°F. A venture scrubber system is provided to clean the flue gas of particulates. Ash is reduced to slurry and pumped to a drying lagoon. As an alternate means of sludge disposal a truck conveyor has been provided to convey the sludge to trucks for land application

Final Clarifiers:

In addition to separating the floatable and settleable solids, the Final Clarifiers have the additional physical process for phosphorous removal.

We use Ferric Chloride (FeCl3) for the precipitation of the phosphorous. The finished water is finally discharged to the receiving stream.

Final Clarifier

We have two finals, and they operate in a parallel fashion.

In final settling tank "A" the settled sludge is removed from the tank by two final sludge pumps.

For Final Settling Tank "B," the settled sludge is removed from the tank by means of a return sludge pump which recycles sludge back to the head of the aeration tanks. Excess or waste activated sludge (WAS) is removed from the tank and transferred to the sludge thickeners for processing in the sludge Disposal building

Disinfection is currently being added to the waste water treatment facility in order to meet the new effluent limits placed on the Facility for both fecal coliform and total residual chlorine. To accomplish the new level of treatment, sodium hypochlorite solution will be used to reduce the fecal coliform count below the new permit limit of 200mpn/100ml, Sodium bisulfite will then be used for de-chlorination to reduce the concentration of residual chlorine below the new permit level of 0.8 mg/l. The chlorine contact tanks for both trains are sized for a minimum contact time of 15 minutes at peak flow.

Industrial Pretreatment program:

This program deals with Industrial users which are hard piped to our facility (examples are the NY Airbrake, Knowlton Technologies, Stature Electric, seven ground water recovery units on Fort Drum, etc.) along with sludge haulers and septic haulers from outside the city.

The facility currently has 36 different point sources outside the City that are permitted to haul sludge to the facility.
Sludge Haulers

Pretreatment is a method by which an industry can be brought into compliance with local waste discharge ordinances as well as Federal and State regulations.

The types of waste originating from such point sources depend on the raw material used, production processes and the ability to recover and recycle waste on site. To ensure that industrial discharges meet acceptable standards, the pretreatment facility inspector must inspect each treatment process or facility at each point source, as well as routinely sample tanker deliveries at the City’s facility.


(supervisory control and data acquisition) system that is currently being used at the facility was installed by the facility’s staff and is currently maintained by the plant staff.

The operating system employed is Lookout 6.6.

SCADA system

SCADA Chart The SCADA offers the operator a quick snapshot of the facility along with automatic or semi-automatic control of pumps, gates, flow charts and chemical dosing. The system is also tied into the City’s remote lift stations. If there is a problem at one of the lift stations an alarm is signaled on the display panel alerting facility staff of impending issues.

As the data is recorded in the SCADA, the data is automatically manipulated to trend plant performance, further enhancing process control.


Flow Schematic

Environmentally Responsible

Environmentally Responsible! The Plant on a Winter's Night

The Plant in Winter