Environmental Protection

A Hole in One

When the Oneida Indian Nation was expanding its operations from a small bingo/casino facility to a full resort complex, it began professionally designing new nine-hole and 18-hole golf courses. The two courses were initially designed to include both groundwater and public water systems to support their irrigation needs. However, when it was determined that tapping into a groundwater source would be extremely difficult logistically, the tribe approached the City of Oneida with the idea of using reclaimed water from the city's wastewater treatment plant.

The city and the tribe worked out an arrangement whereby the city provides reclaimed water to irrigate the resort's golf courses. The tribe pays no fees for the water, but it did pay the entire cost of the reclaimed water system plus a $1 million, four-mile pipeline that delivers the water to several large holding ponds located adjacent to the 18-hole course. The city operates the reclaimed water system and is the system's permit holder. The tribe pays the city for the operation and maintenance of the water reclamation system and is responsible for operating and maintaining the pipeline. The New York State Department of Environmental Protection's jurisdiction stops at the reclamation system's discharge point. The system is located at the city's wastewater treatment plant site.

The City of Oneida, 34 miles east of Syracuse, is part of the Syracuse metro area. The city operates an advanced secondary wastewater treatment facility that serves a population of approximately 10,000. Daily flows to the plant average 2.5 million gallons per day (MGD).

The plant's chlorine contact tank is equipped with an auxiliary pumping system originally designed to discharge excessive flows during wet weather events to Oneida Creek, the plant's receiving stream. Because this system is typically used only a few hours per year at the most, it made sense to add variable frequency drives to the low lift pumps and install piping and valves to adapt the system for directing treated effluent to the new water reclamation system.

Water Reclamation System
The new water reclamation system provides the additional disinfection and filtration required to produce reclaimed water of quality suitable for beneficial reuse at the golf course sites. From the city wastewater treatment plant, the treated effluent is directed to a disk filtration system housed inside the onsite 866-square-foot water reclamation facility. Flows first enter a disk filtration unit where a cloth-membrane filter provides enhanced solids removal. Following filtration, flows proceed to a 10,000-gallon clearwell and then are delivered by two 50-horsepower main lift pumps to the golf course site. Chlorine solution is injected directly into the disk filtration system to provide the additional benefit of protecting the filter media from biofilm deposition.

Choosing A Chlorination Agent
Disinfection is a critical component in any municipal wastewater treatment operation, but is most critical in reclaimed water applications where the water is used in areas accessible to the public. Water leaving the reclamation facility must maintain a minimum 0.5-milligrams per liter (mg/l) and maximum 2.0-mg/l chlorine (Cl2) residual. The city uses gaseous chlorine for disinfection at its wastewater treatment plant, but management wanted to avoid Cl2 gas use at the new reclamation facility.

Oneida's wastewater treatment plant uses gaseous chlorine for disinfection, which is stored in 150-pound cylinders. Because of the low chlorine use at the plant, the facility is able to maintain onsite chlorine inventory of less than 1,250 pounds, which is below the regulatory threshold and therefore requires less regulatory oversight and restrictions than if chlorine inventory exceeded that amount. Gaseous chlorine is listed under the Occupational Safety and Health Administration's (OSHA) Process Safety Management (PSM) regulation at a threshold level of 1,500 pounds. The U.S. Environmental Protection Agency (EPA) lists gaseous chlorine under its Risk Management Program Rule (RMPR) with a threshold level of 2,500 pounds. If gaseous chlorine was selected for use at the new water reclamation facility (in addition to that used at the treatment plant), the plant would have to begin having the chemical delivered in larger quantities, thereby exceeding the regulatory threshold and, in turn, requiring more extensive oversight and restrictions.

Management also did not want to use commercial 15 percent sodium (NaOCl) hypochlorite at the reclamation facility for a number of reasons, including the heavy regulatory oversight and expensive transfer and storage requirements involved.

New York State's requirements for chemical containment, delivery and off-loading are some of the most stringent in the nation. Tanker off-loading of commercial NaOCl at the facility would be categorized as a chemical transfer point under the New York State Bulk Chemical Storage Rule, and the plant would have to provide comprehensive spill control measures, including the provision of containment areas that the tanker trucks could drive and park on while off-loading chemical. In addition, because 15 percent sodium hypochlorite solution is deemed a hazardous substance under state regulations, the plant would have to address issues of secondary containment in the bulk storage systems at the facility site.

There were also the maintenance concerns associated with sodium hypochlorite usage, such as the high potential for creating a corrosive environment inside the water reclamation building, and the common problem of chemical metering pumps becoming air-bound due to NaOCl off-gassing.

When considering disinfection options for the reclamation facility, ultraviolet light (UV) was also ruled out, primarily because water leaving the reclamation facility is required to maintain minimum chlorine residual protection of 0.5 mg/l. And because the reclaimed water was not used for drinking purposes, there was no concern or restrictions regarding residual chlorine breakdown products.

Calcium Hypochlorite Provides Solution
The city ultimately selected the use of calcium hypochlorite (Ca(OCl)2), using dry calcium hypochlorite briquettes in a new "spray technology" feed system. The Constant Chlor® Plus Dry Calcium Hypochlorite Feeding System, designed and manufactured by Arch Chemicals Inc., Norwalk, Conn., uses solid calcium hypochlorite briquettes containing a minimum of 65 percent available chlorine (AVCl) by weight, along with an inhibitor to reduce the potential for carbonate scale associated with the alkalinity component of water.

Plant management was no stranger to calcium hypochlorite. A year earlier, the plant had volunteered to participate in a research project being conducted by the Environmental Training Center at nearby SUNY Morris College. As part of that project, a spray technology calcium hypochlorite feeder was installed and used for disinfection at the Oneida wastewater treatment plant, and the same type of system also was installed at a drinking water plant operated by the City of Sylvan Beach, a small lakeside community located approximately 10 miles from Oneida. During the research project, Oneida plant management became impressed with the efficiency and simplicity of the calcium hypochlorite feed system.

At the Oneida water reclamation facility, the highly soluble briquettes are loaded into the unit's 100-pound hopper. Supply water from the reclaimed water line is injected into the chlorinator through a level/timer controlled solenoid valve and sprays upward into the bed of briquettes. A short intermittent spray cycle produces an approximate 1.0 percent available chlorine solution, which is stored in the lower solution tank. The calcium hypochlorite solution is then pumped on demand to the filter through a chemical metering pump.

The chlorinator is turned on simultaneously when water flow is turned on to the filter. Operators set the desired feed rate, which is adjusted based on scheduled chlorine residual test results. There is very little chlorine demand in water entering the reclamation system because the wastewater treatment plant nitrifies and chlorinates its total effluent from May 15 to October 15. Flows entering the water reclamation system typically contain a chlorine residual of 0.1 mg/l to 0.3 mg/l. If, for example, residual in the flows entering the reclamation facility is 0.2 mg/l and is coming out at 1.3 mg/l, then 1.1 mg/l from the calcium hypochlorite unit is being added to the flow, multiplied by the existing flow rate.

The calcium hypochlorite spray feeder has operated as designed since startup in May 1998, with minimum maintenance requirements. Benefits found by Oneida plant personnel in using calcium hypochlorite in the spray technology feed system include:

  • Onsite Generation. By generating its hypochlorite solution on site, the facility makes hypochlorite solution only as it needs it, thereby eliminating the need for bulk solution storage or large cylinder storage.
  • Operator Safety. Based on chemical strength, calcium hypochlorite solution provides for reduced potential hazards to plant personnel, compared to commercial sodium hypochlorite and gaseous chlorine. However, proper safety gear remains essential for dealing with calcium hypochlorite in solid form.
  • Less Restrictive. Chlorine solution less than 1.0 percent is not subject to the state's chemical bulk storage rule and is not subject to certain state hazardous substance requirements that are in effect for commercial sodium hypochlorite and gaseous chlorine. Bulk dry chemical delivery and storage is easy to handle and secondary containment is not required. The calcium hypochlorite briquettes specifically engineered for the Oneida unit are shipped in 50-pound containers. The facility can store up to 200 pounds of briquettes under a standard exception in the fire code for the point of treatment.
  • No Off-Gassing. Calcium hypochlorite solution demonstrates good stability.
  • Small Footprint. The footprint of the Constant Chlor Plus system is only 9 square feet and no bulk liquid storage is required, allowing for a smaller, more cost-efficient reclamation building.
  • Long Shelf Life. Calcium hypochlorite briquettes have up to a two-year shelf life, as opposed to commercial sodium hypochlorite, which can begin to show signs of degradation in less than 30 days.
  • Reduced Maintenance Requirements. Because the calcium hypochlorite exhibits no problems with off-gassing, operators and maintenance personnel do not have to deal with problems associated with chemical metering pumps becoming air-bound, and maintenance personnel also do not have to deal with problems from corrosion due to disinfection chemical storage and use.
  • Reduced Labor Requirements. Due to the consistency of the chemical solution concentration, operator dosage adjustment is minimal.

Not All Calcium Hypochlorite Tablets Are the Same
A lesson learned in using the spray technology feed system concerns the significant performance differences when using different dry calcium hypochlorite media. For a period of time, the Oneida water reclamation facility used standard calcium hypochlorite tablets not specifically designed for use in the Constant Chlor feed system, and this created performance problems and maintenance headaches for plant staff.

Scaling was a major problem when using the standard tablets. Hard mineral scale quickly formed at the bottom of the feed system hopper. Chlorine residual entering the reclamation facility's filter would deteriorate due to this scaling and fall below required limits. The hopper bottom had to be scraped and cleaned thoroughly every three to four days, a 30-minute to 45-minute procedure each time. When using the Constant Chlor Plus calcium hypochlorite briquettes specifically engineered for the unit, however, the bottom of the hopper has only needed to be cleaned about every two weeks.

The Oneida facility also found that using the proper briquettes with the unit provides more accurate control of the solution and, therefore, more consistent dosage. This is due, in part, to the design of the briquettes, which have been specifically engineered for the system.

The briquettes are designed for optimum packing in the unit's hopper, as opposed to standard tablets, or pill-shaped calcium hypochlorite media. Pill-shaped tablets have sharp edges that can hang up on each other in the bed. If the pill on the bottom of the bed dissolves while the pill directly above is hung up by other pills in the bed, a void is created in the spray surface, resulting in lower residual concentration in the final solution. But once enough pills dissolve, the bridges created by the pills' sharp edges can collapse abruptly, suddenly bringing more pills to the spray surface, and the unit has then gone from an underfeed to an overfeed situation.

By filling the hopper with the briquettes designed for the specific feeder unit, the Oneida facility has found the spray technology feeder provides very consistent residual in the solution at all times with only minimal scale formation at the bottom portion of the unit's hopper.

Cost Considerations
Cost also played an important role in the decision to use calcium hypochlorite. Although calcium hypochlorite costs more than the equivalent amount of sodium hypochlorite on an available chlorine basis, the capital costs for the calcium hypochlorite spray feeder system are two times to three times less than a typical sodium hypochlorite system. When management looked at capital costs and operating costs combined, it mitigated the higher cost of the chemical. When the much higher labor and maintenance costs associated with sodium hypochlorite use (including the construction of an outside containment area at the facility's chemical transfer point as well as secondary containment for on-site storage) were also factored in, switching to calcium hypochlorite made good economic sense.

A Growing Resort, A Growing Reclamation Program
The City of Oneida and the Oneida Indian Nation joint water reclamation program has been very successful from the beginning.

In 2002, the water reclamation system provided more than 90 million gallons of irrigation water to the resort complex. In 1999, a year of considerable drought conditions, the system provided more than 100 million gallons of reclaimed water.

Treatment requirements for water reuse for irrigation purposes are essentially the same as the contact standard for bathing as regulated by the New York State Department of Health. Besides maintaining a minimum 0.5 mg/l and maximum 2.0 mg/l chlorine residual in flows leaving the reclamation facility, the reclaimed water has a total coliform limit of 2,400 most probable number (mpn) per 30-day geometric mean/1000 mpn per seven-day geometric mean, and a fecal coliform limit of 200 mpn per 30-day geometric mean/400 mpn per seven-day geometric mean. In addition, the nitrate levels in water leaving the reclamation facility are monitored and maintained at 20 parts per million (ppm) to meet a local area groundwater standard.

The volume of reclaimed water used by the resort complex will only continue to grow as the resort complex grows. The Oneida Indian Nation's Turning Stone Casino Resort has developed into an upscale destination resort and one of the top five tourist attractions in New York State. The resort says it is shifting Turning Stone from a casino that happens to have a golf course to a golf destination that happens to have a casino.

To that end, the resort is currently operating two championship golf courses, one nine-hole course with a third championship 18-hole course set to open in 2004. Plenty of water will be required to irrigate the two new courses, both of which span more than 7,200 yards. The highly efficient Oneida Water Reclamation System is ready.

e-Sources

This article originally appeared in the 11/01/2003 issue of Environmental Protection.

comments powered by Disqus

Free e-News Subscription

I agree to this site's Privacy Policy