Douglas Borgatti, Director of Operations
PROFILE
The Springfield Regional Wastewater Treatment Facility (SRWTF) is owned and operated by the Springfield Water and Sewer Commission. It is the largest of 171 activated sludge facilities in New England and second in size in the region only to Boston's 393 million gallon per day (mgd) primary treatment plant. Located in Agawam, Massachusetts, the SRWTF presently treats the domestic and industrial wastes from the eight communities of Agawam, Chicopee (small section), East Longmeadow, Longmeadow, Ludlow, West Springfield, Wilbraham, and Springfield with a combined population of 260,000.
The SRWTF is an activated sludge system permitted for treatment of an average daily flow of 67 million gallons. Peak design capacity, which results from stormwater runoff in areas with combined sewer systems, is 180 mgd. Treatment consists of primary settling, grit removal, secondary aeration, flocculation, final settling, chlorination and dechlorination. Solids collected from the primary and secondary systems, are gravity thickened and combined in mixing tanks. After further processing by the belt filter presses, solids are conveyed to a privately owned sludge composting facility or trucked to a landfill. The plant effluent is discharged into the Connecticut River.
The Commission is required, through its NPDES Discharge Permit issued by the U.S. Environmental Protection Agency and the Commonwealth of Massachusetts, Department of Environmental Protection, to treat influent flows up to a rate of 134 mgd with secondary treatment prior to discharge. All flows in excess of 134 mgd and up to 180 mgd are required to receive primary treatment. Effluent flow to the river must have a monthly average of less than 30 mg/L total suspended solids (TSS) and 30 mg/L biochemical oxygen demand (BOD).
The following describes the specific processes of the Springfield Regional Wastewater Treatment Facility:
INDUSTRIAL PRETREATMENT
The Industrial Pretreatment Division (IPD) controls wastewater discharges from commerical and industrial users to the treatment facility through the use of discharge permits, frequent monitoring, educational and technical assistance referrals, and enforcement of Federal, State, and Municipal wastewater codes. In addition, the IPD maintains a database and evaluates commercial and industrial facilities regarding their impact on the SRWTF and their compliance with Federal, State, and Municipal wastewater codes.
Primary Treatment
SCREENING
Each of the four inlet channels to the SRWTF is equipped with bar screens to remove coarse solids (rags, paper, sticks, etc.) which might damage treatment units. These screenings are discharged onto a conveyor belt system which carries them to containers which are trucked to a landfill.
PRIMARY SEDIMENTATION
The screened flow is measured and channelled to four rectangular primary sedimentation basins which remove most of the heavy solids suspended in the flow, thus reducing the loading on the secondary treatment process. Each tank is equipped with a traveling bridge, sludge scraper and skimming mechanism which removes skimmings and scrapes sludge and grit from the bottom of the tank. The skimmings are collected and pumped to the flotation thickeners for further treatment. Sludge and grit is pumped to degritters where the grit is separated from the sludge and conveyed to containers and trucked to the City's solid waste disposal area. The remaining sludge then flows to gravity thickeners for further treatment.
Secondary Treatment
AERATION BASINS
Effluent from the primary settling basins, and sidestreams, flow by gravity to the aeration basins feed channel. From here the flow is distributed to indivdual feed channels to each basin. These feed channels are gated along their full length so that wastewater can be introduced at the influent ends of the basins, at quarter points along the entire length of the basins, or in any combination that provides the desired level of bio-oxidation.
Return activated sludge, which supplies the bacterial floc, is fed to the aeration through its own channel, also gated at quarter points.
The function of the aeration basins is to hold the activated sludge bacterial floc in contact with the wastewater long enough for absorption and organic carbon assimilation to be completed. These basins provides the air-liquid interface which, along with submerged fine bubble diffused aerators, provides the mixed liquor with an adequate supply of oxygen.
Primary effluent and returned activated sludge are aerated together in each aeration basin by submerged fine bubble diffused aerators located at the bottom of the four basins. After aeration, the mixed liquor flows over effluent weirs into a cross collection channel where it is distributed through submerged, gated ports, to the four flocculation basins.
AERATION
The fine bubble diffused aerators create turbulence which enhances the transfer of oxygen into the contents of the aeration basins so that the aerobic microorganisms in the activated sludge can maintain their normal metabolism and absorb the suspended and dissolved organic matter in the wastewater. Without oxygen, the aerobic bacteria would die off and the organic waste materials previously synthesized into bacterial cells would undergo decomposition; eventually resulting in anaerobic (septic) conditions if the oxygen supply was not quickly reestablished.
The submerged fine bubble diffused aerators also provide mixing and turbulence in the aeration basins to keep the activated sludge flocs from settling and to ensure that the bio-degradable organic matter in the wastewater comes into intimate contact with the activated sludge.
FLOCCULATION BASINS
Mixed liquor flows by gravity from each of the aeration basins to each flocculation basin through six manually operated gates. Each flocculation basin contains two flocculation chambers separated by a baffle wall equipped with stop planks. Each chamber is equipped with four flocculators supported from a bridge above. Flocculated mixed liquor flows from one chamber to the other by flowing over and under the baffle wall through a six inch slot. The light stirring of the mixed liquor by these flocculators, prior to settling, provides for the conglomeration of sludge particles and results in better settling characteristics.
SECONDARY CLARIFIERS
The effluent compartment of the secondary clarifiers is longitudinally divided into four chambers. Sludge is removed from each of these four chambers by a chain and flight scraper which moves the settled sludge into the same centrally located sludge hoppers which service the influent compartment. On the influent side of the clarifier, sludge and scum is moved by traveling bridges which have blades that scrape sludge on the bottom and skimmers that collect solids on the surface of the clarifier. Treated effluent flows from the clarifier over effluent weirs, into the effluent cross collection channel, and on to the chlorine contact chambers.
RETURN SLUDGE FACILITIES
Sludge is removed from the floor of the secondary clarifiers and pumped to a collection channel which terminates at the screw pump stations. Each pump station contains two screw pumps, each with the design capacity to handle two clarifiers. The constant speed screw pumps move the sludge from the suction wet well to one of the tiered feed channels which supply the aeration basin with return sludge. Excess sludge is removed from the return pump stations by an adjustable overflow gate and conveyed by gravity to the mixed sludge gallery where it is pumped to the gravity belt thickeners.
Effluent from the secondary clarifiers flows to contact chambers where a chlorine solution is added, and adequate detention time is allowed to insure disinfection.
DECHLORINATION
Dechlorination is the final wastewater treatment step. A solution of sodium bisulfite is added to the chlorinated effluent to remove residual chlorine. The flow is conveyed to a 96-in. outfall and discharged through a series of diffusers into the Connecticut River.
PRIMARY THICKENING
During primary thickening, some of the water is removed from primary sludge, thereby reducing its volume. As the velocity of the flow slows, gravity causes sludge to settle to the bottom of the thickener where it is raked into a hopper and pumped to mixing tanks where it is combined with sludge from the secondary system. Meanwhile, the clarified liquid continuously overflows from the tanks and is returned to the primary sedimentation basins for further treatment.
FLOTATION THICKENING
Skimmings from the primary sedimentation tanks are pumped to two rectangular flotation thickeners. Solids are lifted to the surface by fine air bubbles where they are removed by a surface-skimmer.
GRAVITY BELT THICKENERS
Gravity belt thickeners process the excess solids from the secondary system, called waste acvtivated sludge (WAS). Chemicals (polymers) are added to separate the sludge from the water. The water is drained through a porous belt, and fed back to the secondary system for further treatment. Thickened sludge is collected from the top of the belt and pumped to mixing tanks where it is combined with sludge from the primary system.
BELT FILTER PRESS
Mixed sludge from the mixing tanks is pumped to the belt filter presses and dewatered on four two meter belt filter presses. Chemicals (polymers) are added to separate the sludge from the water. The water is then squeezed out through two porous belts and fed back to the primary sedimentation basins for further treatment. Sludge cake from the belt filter presses can be conveyed to trucks for disposal in a landfill or into the private composting facility.
SLUDGE COMPOSTING
A private company is presently operating a sludge composting facility on land leased to them for 20 years at the Springfield Regional Wastewater Treatment Facility. It is an in vessel system, using the Taulman-Weiss technology, with a minimum guaranteed plant capacity of 10,500 dry tons per year.
SRWTF LABORATORY
The laboratory is responsible for the collection and analysis of samples taken from the beginning and end of each treatment process. The results provide Operations and Management with the information necessary to determine the effectiveness of the treatment process, and the process control strategy. Data provided by the laboratory is also necessary for compliance monitoring and reporting required by the State and Federal permitting agencies. The SRWTF Laboratory is a State certified laboratory with an established Quality Assurance / Quality Control Program. Analyses include Biochemical Oxygen Demand, Total, Suspended, Volatile, and Settleable Solids, pH, Total Residual Chlorine, Ammonia, Phosphorous, Chemical Oxygen Demand, Heavy Metals, Total and Fecal Coliform, and microscopic examination of the activated sludge.
SENIOR STAFF
Senior Management is responsible for all aspects of the daily operation of the largest secondary wastewater treatment facility in New England. The Director of Operations leads a staff of four Senior Managers who are responsible for the following areas: Operations, Maintenance, Laboratory and the Industrial Pretreatment Division.
All Senior Managers have a Grade VII Massachusetts Wastewater Certification. The combined years of wastewater experience of the Senior Staff is greater than 86 years.
The combination of education and experience of the Senior Staff insures the most efficient and effective operation of the facility for the customers in the City of Springfield and the seven surrounding communities.