The municipally-owned Milton Regional Sewer Authority (MRSA) serves many residential customers in Northumberland, Pa. It also treats...
Mention the name of this place and people will conjure up a variety of impressions. There's Niagara Falls the honeymoon capital of North America-or at least it used to be. Then there's the scenic wonder of the Falls themselves, the famous Rainbow Bridge, and the touristy but interesting character of the towns on either side of the Falls and the massive downstream gorge-Niagara Falls, New York and Niagara Falls, Ontario. How about the '50s movie, Niagara, with Marilyn Monroe? And the hydroelectric power plants, some in operation a century ago, which gave rise to the huge concentration of industry that developed nearby on the American side of the river-particularly a number of big chemical manufacturing complexes. Now there's something else to talk about, at least if you're in the wastewater field or have an active interest in environmental protection.
Thirteen years after the Buffalo Avenue wastewater treatment plant serving Niagara Falls, New York, "was in a state of total collapse," and in 1984 had been described by a joint U.S. and Canadian government report as "the largest toxic polluter of the Niagara River," the facility is operating efficiently and meeting the requirements of its complicated discharge permit regularly.
In view of all that has happened since this plant was started up in 1977, to say that it operates well and meets all effluent standards is a pretty bland statement. But it really is something to talk about, as the USEPA did in 1993 when the Agency is reported to have said that "the Niagara Falls sewage treatment plant is the most successful operation of any of the municipal carbon treatmant plants in the country." And later, in May of last year, an EPA source said that "today, this facility is the most advanced municipal wastewater treatment plant in operation." I wonder if any municipal wastewater authority has had to carry such a mixed bag of troubles as Niagara Falls' Department of Wastewater Facilities has been burdened with since the early '80s.
In some respects the reason for the municipality's wastewater treatment difficulties rests with the world-famous Horseshoe and American Falls themselves. Without them there would have been no hydroelectric power stations built, no resulting industrial development as we know it, and no chemical manufacturing facilities turning out the inorganic and organic compounds that began to be so important in commerce in the '40s and '50s. Many of the residuals from these industrial activities found their way into the Niagara River, and when the national environmental protection effort picked up speed in the early '70s, it became clear that major decisions would have to be made about suitable water pollution control measures in the Niagara area.
Off to a Poor Start
The existing wastewater plant, built in the 1930's into the side of the gorge some distance below the Falls, had become incapable of handling the influent from the city's collection system, with almost two thirds of the average flow being complex industrial waste streams. Work on the new Buffalo Avenue facility began in 1973, it came on line during 1977-and the following summer it experienced a major failure in its granular activated carbon (GAC) filtration system. And so started the troubles.
As Robert Game, director of the Department of Wastewater Facilities, described, the main problem arose when the carbon filter underdrain system, which supported the beds of gravel and carbon filter media, began to break, allowing carbon to be carried out with filter effluent. The advanced activated carbon filtration process, which provides both physical separation and chemical adsorption, had been specified for its ability to remove suspended and dissolved material that contained potentially harmful synthetic organic compounds and other toxic chemicals. It had been evident in this case that a conventional biological wastewater process would not be adequate to treat the numerous difficult residues from the local chemical, metallurgical and paper companies, and carbon and abrasive products manufacturers.
Seventy five percent of the original cost of this plant ($55 million) was covered by funds from the USEPA's Construction Grants Program. It might have been more, since this program included a provision for an additional 12.5 percent to encourage the use of innovative technology in wastewater projects. The physical-chemical GAC system for wastewater treatment was certainly an advanced process in the mid-'70s, but the agency for some reason did not consider it eligible for an innovative technology award at that time.
After the filtration section failure, the physical-chemical process at the Buffalo Avenue plant had to be by-passed, and it remained in partial service only for several years until the spring of 1985. Bob Game, who had worked for the wastewater department for 10 years from 1972, and came back to be director of the operation in 1984, said that the by-pass situation didn't sit well with the USEPA or the New York State Department of Environmental Conservation. In 1981 these agencies alleged that the plant was in serious violation of the Clean Water Act and New York State's Environmental Conservation Law. They claimed that the city was by-passing as much as two million gallons of contaminated wastewater a day into the river, and that this discharge frequently contained 700 to 800 pounds of priority pollutants. Several years of litigation activity followed, culminating in 1984 with a consent decree negotiated between the City of Niagara Falls and the federal and state environmental agencies.
While the GAC filter section of the plant went back in full service in August of 1985 (a revision of the original design was carried out and called for the installation of new underdrain sections fabricated from a plastic material), the legal proceedings continued for almost eight more years. Not satisfied with the plant's performance after the corrections, in 1986 the government agencies wanted modifications to a number of other processes and facilities. The city had to commit additional funds ($10 million) to undertake these projects, and implement a Sewer Fund increase of $2.9 million annually. This work went on into 1993, when the last remaining action to satisfy the amended Consent Decree was completed.
The consulting firm O'Brien & Gere Engineers, Inc., of Syracuse, New York, was selected by Niagara Falls' Department of Wastewater Facilities to develop a Corrective Action Plan that would not only improve the performance of the activated carbon filtration process still further, but also correct deficiencies in a number of other facilities in the plant and in the city's wastewater and stormwater collection system.
Managing Engineer Bob Lannon, O'Brien & Gere's senior representative who runs the firm's Niagara Falls office, has been closely involved with the corrective action work, as has Richard Roll, environmental engineer with the Department of Wastewater Facilities. Together with Bob Game, the department's director, they hosted me on a recent visit to the Buffalo Avenue plant, and provided the insight and information for this article.
The Plant Today
Current flow averages about 35 mgd, but the plant was designed to handle up to 48 mgd. Peak hydraulic flow is 85 mgd. As the schematic diagram shows, the plant's process train is a relatively simple one. Bar screens protect the four primary settling basins, which are equipped with travelling bridge sludge collectors. Ferric chloride and a polymer are added before sedimentation to the clarified stream. This proceeds to two bays of 14 GAC units each, which act as physical separators to retain solid particles, chemical adsorbers of dissolved organics, and, deep in the beds, biological filters to a certain extent since some anaerobic activity occurs. The filtered effluent is treated with hydrogen peroxide and chlorine for odor control and disinfection, and passes into a chlorine contact basin. Then the final discharge drops down a 180-ft shaft to what is known as the Tailrace Tunnel (shaft and tunnel are extremely useful relics from an early but dismantled power station), which carries it under the city to an outfall over a mile away in the gorge down river from the Falls.
Backwash of the carbon filter beds is accomplished using the treated plant effluent. Water from the backwash operation is sent to a fifth settling/equalization basin, similar to the four primaries. The clear decant flows directly to the chlorine contact basin, while the sludge becomes blended with the primary sludge in two thickeners. Belt press dewatering follows, bringing the cake to about 30 percent solids, and finally mixing with lime. The stabilized sludge is sent off site for landfilling.
The plant requires an inventory of more than 5 million pounds of GAC, which is periodically being turned over in the regeneration process. Spent carbon goes through regeneration about twice a year, with approximately 5.5 percent lost in the cycle. This along with some backwash loss means that a makeup of fresh activated carbon is required. Regeneration takes place in a multiple-hearth furnace and a transfer system returns the reconditioned material to the filter beds.
Many Projects Needed
The corrective action agenda undertaken by the Department of Wastewater Facilities and the consultant started with the evaluation of certain plant functions determined to be inadequate. Perhaps most important was an examination of the GAC filtration/adsorption process, and preparation of a design recommendation that would make the operation more efficient and reliable. As a result of this study, a revised mode of operations for the carbon beds was devised, and an automatic backwash system for the 28 filter units was designed and installed. New features included air scour by-pass lines and changes to the air-water backwash schedule to reduce the potential for disruption of the gravel beds that support the GAC layer above.
Another major corrective action, based on the results of a testing program to monitor the exhaust emissions, was to upgrade the carbon regeneration furnace and its ancillary carbon transfer system, and improve the air pollution control equipment on the furnace. The tests were required as part of the regulatory permitting program.
A significant project, mostly outside the Buffalo Avenue plant site, was a comprehensive evaluation of the Falls Street Tunnel. This 16,000-ft-long unlined rock tunnel, which serves as a combined sewer overflow conduit for the main interceptor carrying sanitary and industrial discharges to the treatment plant, previously had dumped contaminated infiltrated groundwater and contaminated stormwater directly to the river. This project called for appropriate repairs to reduce infiltration significantly, and to divert all dry-weather flows to the interceptor and thence to the plant.
Another task undertaken was a project to rehabilitate the 20 mgd Gorge Pumping Station, which was built on the site of the original treatment plant, and whose function as part of the collection system is to send the wastewater from a large area of the city back to the Buffalo Avenue facility. The station got new pumps, variable frequency drives, and renovated electrical and HVAC systems.
Additional projects completed at the plant included modifications to the travelling bridges on the settling basins, acquisition and implementation of a plant-wide computerized management system, and improvements to corrosion control procedures.
A Successful Ending
After 13 years of legal wrangling, testing, analyzing, evaluating, design work, construction, and probably a substantial amount of seat-of-the-pants decision making, the Niagara Falls treatment plant finally had the heavy millstone of non-compliance removed from its neck. In October of 1994, the Fall Street Tunnel diversion activities were completed, which started a 3-month plant performance evaluation period. It wasn't long before the plant met its discharge permit for three consecutive months without violations. Requiring about 1700 items to be monitored annually, and numerous parameters measured monthly, this is said to be the most stringent example of a municipal permit in the country. And so in February of 1994 a U.S. District Court judge signed the papers to end the lawsuit brought against Niagara Falls in 1981.
During the period from initial construction of the Buffalo Avenue plant to the end of the corrective action projects, $110 million had been spent-twice the original cost of the facility. About $39 million of this was put up by the city, the remainder coming from federal and state grants. Director Game is justly proud of the achievements of his staff, and appreciative of the support from the consultants and contractors. He pointed to the reductions in permit violations from 67 in 1985 to five in 1993 (before all projects had been completed), and said the quantity of priority pollutants reaching the river had dropped from the 800-lb average to about 12 pounds daily. To put icing on his cake, he added that the facility's inflation-adjusted operating costs are less than they were in 1984, and the Sewer Fund annual budget has been reduced by $3.1 million since 1990, almost negating an increase put in place four years before that.
Only 13 wastewater plants using the GAC filtration/adsorption technology are believed to have been built in the United States. Supposedly only a few of these remain in operation using the basic original design scheme. Niagara Falls is the largest of them, and after all the hard work, carries the title of "most successful."
About the Author:
Ian Lisk is editorial director of Water Engineering & Management and Water & Wastes Digest.