November 2012, Vol. 24, No.11

Plant Profile

Niagara Falls, N.Y.

NY_PlantProfile_Map

Location: Niagara Falls, N.Y.
Startup date: April 1977
Service population: 50,000
Number of employees: 41
Design flow: 181,700 m3/d (48 mgd)
Average daily flow: 133,600 m3/d (30 mgd)
Annual operating cost: $14.4 million
 

The name Niagara Falls conjures images of enormous torrents of water cascading over the precipice and crashing down on the rocks below. But just upstream, at the Niagara Falls Water Board Wastewater Treatment Plant, diminishing flows are the main concern. 

When the treatment plant was built in the 1970s, the plan was to centralize the city’s various types of industrial wastewaters at one location to take advantage of the economy of scale. Nearby industries included electro-metallurgical, electro-chemical, organic chemical, paper, and abrasives businesses. In fact, in preparation for the heavy industrial flows, it was decided to avoid biological process and instead rely on physical–chemical processes that would be more resilient to industries’ wastes. 

Since the 1970s, federal pretreatment regulations, global economic pressures, and the local business climate have combined to greatly reduce the pollutant loadings that were intended for the plant. The residential population also declined. When the facility was planned in 1971, 84,000 people lived in the service area. That number was expected to grow to 114,000 by 2000. But according to the 2010 census, the population now hovers around 50,000. 

Significant industrial users account for about 40% of metered flow; the remaining 60% comes from residents, businesses, and small industrial users. Unaccounted for flow from infiltration and inflow and stormwater is high at more than 50% of total plant influent. 

The significant losses in customers have severely eroded the economy of scale envisioned for the plant. Although operational savings come from diminished use, a high overhead burden must be distributed among fewer users, increasing unit costs and encouraging those with a choice to discharge even less. 

What was once an expensive plant for many users has become a very expensive plant for fewer. Now the plant’s managers and operators find ways to streamline treatment to curb the costs of operating an oversized plant.  

 

The treatment process

Two influent streams reach the plant. About two-thirds of the flows arrive by gravity from the southern, central, and eastern parts of the service area. The other one-third comes from the 75,700-m3/d (20-mgd) Gorge Pumping Station and Force Main that serves the western and northern service areas. 

The two streams combine in the main influent channel and pass through three traveling bar screens. Concentrated sulfuric acid may be added here to counteract high pH events that can cause problems later in the process. Ferric chloride and polymer are added for phosphorus removal and clarification. 

Next, the flow is distributed among four 91-m × 18-m (300-ft × 60-ft) rectangular sedimentation basins. Chain and flights collect settled solids from the flocculation cells at the head end while traveling bridges collect it from the settling zone. 

The primary effluent passes to a pumping station with four 186-kW (250-hp) pumps that feed the plant’s carbon adsorption system. Here, 28 carbon filters containing 2 million kg (4.5 million lb) of granular activated carbon operate in a gravity downward flow mode to achieve secondary treatment by filtering solids and adsorbing pollutants. The system is built in two halves, with each having its own pair of backwash pumps and an air blower. 

Carbon filter effluent is then chemically oxidized using hydrogen peroxide and sodium hypochlorite, which also accomplishes disinfection. After final sampling, the effluent flows through the ice shaft and tailrace tunnel of the former E.D. Adams Generating Station to the outfall on the lower Niagara River, downstream from the American Falls. 

Solids captured in the primary sedimentation basins are pumped to one of two gravity thickeners and thickened to 8% solids or greater. Thickened sludge pumps then pump the underflow to one of three belt filter presses. Dewatered cake, which averages 30% solids, is mixed with lime to elevate pH and control pathogens. The stabilized cake averages 33% solids. The high percentage of solids with an industrial origin diminishes the stabilized cake’s fuel value and nutrient content, so it is disposed of in a local sanitary landfill. 

 

The pros and cons of chemical treatment

Niagara’s physical–chemical process remains insensitive to many influent character changes — which would upset a biological treatment process — but is still a more complicated and costly process to operate and maintain. A combined collection system prohibits downsizing of the facility, while the discharge permit prohibits deviation from the approved process train. 

Multiple studies over the years have examined the efficacy of converting to a less-expensive, traditional treatment process, but have concluded that the anticipated lower operating cost would not justify the expense of a conversion project, even assuming an equivalent treatment performance could be attained. This presents the utility with the ever-evolving task of optimizing the 35-year-old facility. 

 

Immense needs on a tight budget

A 2005 strategic wastewater treatment master plan established a 20-year treatment plant rehabilitation program. The projected $143 million cost would require an average $7 million expenditure in every year of the program. 

Without outside financial assistance, the program would place an unsustainable burden on the residential population that has a higher average age, a lower average income, and a higher unemployment rate than other western New York communities. Despite many efforts, outside funding never materialized. 

 

Small bites

A “no action” option was not a choice. The facility saw hard use in its early years and continued to deteriorate as plants do. Concurrently, the complex plant discharge permit continued to incorporate toughening performance requirements. 

In 2005, plant management and operators set in place a plan to attack the problems one piece at a time. This approach continues to work well for the now 35-year-old plant whose financial needs are growing as its economy of scale diminishes. 

The planning effort focused on the prioritization of plant repair needs, so that the funds available were used for the greatest benefit. Multiple repair and replacement tasks were bundled into biddable projects, allowing progress to commence. Smaller tasks are tackled by plant maintenance staff. 

Upgrades and repairs since 2005 have included the following: 

  • rebuilding each of the three 1992 belt filter presses; 
  • upgrading the sodium hypochlorite system; 
  • replacing valves, gates, and flowmeters in the entire carbon system; 
  • installing new odor scrubbing units; 
  • repairing the main wet well; 
  • replacing all three influent traveling bar screens; 
  • rehabilitating the electrical substation and related electrical work; 
  • replacing the drive, solids collection plows, and access bridge of one sludge thickener (work on the other thickener goes to construction this coming spring); 
  • rebuilding main pumps and sedimentation basin mechanical equipment; and 
  • replacing thickened sludge pumps. 

The third phase of rehabilitation work now is in construction, with reprioritization and planning on the next phase continuing. This third phase will replace two carbon backwash pumping systems, incorporate energy-saving measures, and enable the second-phase automated control system. Repairs and partial replacements of all facility roofs are planned for next spring. 

Additionally, Niagara also employs various strategies to attempt to control escalating costs. These include chemical-use procedure improvements, energy conservation measures, selective equipment replacement, carbon management improvements, development of a hauled-waste customer segment — which in 2011 grew to a revenue of $378,000 — and workforce reduction through attrition, job consolidation, and automation.