NIAGARA FALLS WATER BOARD DEPARTMENT OF WASTEWATER FACILITIES Treatment Capabilities With a design capacity of 48 million gallons per day (MGD), the Niagara Falls Wastewater Treatment Plant is the largest of the municipal physical-chemical activated carbon plants built and still operating. The current average plant flow of 37 MGD, combined with recent reductions in industrial waste loadings, have created a surplus in treatment capacity available for nonhazardous, noncatagorical hauled waste, either by tank truck or rail cars. Raw plant influent, also containing any hauled waste off loaded at the plant site, is pumped up to the main influent channel, where it passes through three mechanically-cleaned bar racks. Screenings are transported weekly to a local sanitary landfill. The screened influent can then have its pH adjusted in either direction, either upward with lime or downward using concentrated sulfuric acid. The primary coagulant, ferric chloride, is also added in the same location. The adjusted influent passes through rapid mix basins for grit removal on its way to the primary sedimentation flocculation cells. The plant has five rectangular sedimentation basins, each 300 feet long by 60 feet wide. At present, four are dedicated for primary treatment while the fifth is used for carbon filter backwash water treatment and flow equalization. A three-by-three flocculation cell matrix comprises the first 60 feet of each basin. Stage 1 involves a second grit removal zone; Stage 2 provides rapid flocculation; Stage 3 provides slow flocculation. Polymer may be added in a variety of locations, but is presently added between the Stage 2 and Stage 3 cells. The chemically-treated flow passes into the settling basins, where solids settle to the bottom while scum and floatables accumulate on the surface. Traveling bridges transport the sludge and scum to their respective withdrawal locations for further processing. Primary effluent from the basins is collected in a single channel which feeds the acid mix tanks, a second location where pH may be adjusted downward with sulfuric acid. The flow leads to the intermediate wet wells, from which the intermediate pumps draw to feed the carbon filter system. At the heart of the Niagara Falls plant is the activated carbon system. The system is makeup of 28 carbon filter beds, each containing 180,000 pounds of granular activated carbon (GAC). Primary effluent percolates downward by gravity through the GAC packed bed, averaging 8.5 feet in depth. Each filter bed provides chemical adsorption of pollutants from the wastewater, physical filtration of solids, and biological degradation from the incidental anaerobic activity which occurs within. Average dry weather flow usually requires 16 or 17 of the 28 filter beds to be in service; a minimum of 22 must be available for wet weather operations. The filtered carbon bed effluent (CBE) is chemically oxidized with a combination of chlorine, hydrogen peroxide and sodium hypochlorite. The oxidized CBE is either used as backwash water to clean individual filters, or it is directed to the chlorine contact tank where a trim dosage of chlorine is added to achieve disinfection. Disinfected effluent is sampled and discharged to a deep tunnel system which leads to the lower Niagara River. After a given exposure time, the GAC becomes laden with chemicals which must be removed to restore adsorptive capacity. This is performed onsite in a multiple hearth carbon regeneration furnace (CRF). Each filter bed is sequentially removed from service and emptied of carbon. The carbon is fed to the CRF at about 2500 pounds per hour. Regenerated carbon exits the CRF and is kept in storage until an empty bed becomes available. Normal operating losses require the addition of brand new, virgin carbon to maintain inventory levels. At present, the four month regeneration process is performed once per year. Solids which are collected in the primary sedimentation basins are pumped to circular gravity thickeners, where it is concentrated to over 5 percent solids. The thickened sludge is pumped to belt filter presses where it is dewatered to approximately 30 percent solids. The sludge cake is then chemically stabilized by lime blending equipment before final transport to a local sanitary landfill. Approximately 4000 dry tons are produced annually. Scum which is removed from the primary system is either concentrated in a dissolved air flotation device, or it is skimmed from the main wet wells on a periodic basis.