Modernizing a 20-Year-Old Treatment Plant

by Keneck Skibinski

The Herkimer County Wastewater Treatment Plant was constructed by the Herkimer County Sewer District and began operations in October 1981. Through the last 22 years, the plant has served the District well and has produced an excellent quality effluent for discharge into the Mohawk River.

Like many other facilities across the state, our plant has seen the want and need for a few changes along the way. This article will provide some details about how the district has gone about keeping our facility up to date with maintenance demands and improvements as well as why we have done what we have done.

History

The plant is designed for 6.1 million gallons per day (mgd) and sees an annual average of about 4 mgd. Because the plant is not operating at design capacity, we have hydraulic capacity as well as additional organic capacity. Therefore, the plant has "saleable capacity" in that the district has been able to offer treatment for a variety of trucked in waste streams including landfill leachates, septages, non-hazardous commercial wastes, treatment plant sludges, and other commercial/industrial wastes for a fee. As a result, for example, a total of 4,056,570 gallons were hauled in during 2002 with a total revenue of $232,877.60 for hauled in wastes. This represents approximately 18 percent of the district plant's budgeted revenue. A nice sum, to be sure.

As the waste hauling business began around 1985, the district has had some extra capital with which to accomplish things. The first planned change was in the solids handling system. The plant originally had been designed with a plate and frame pressure filter system that utilized ferric chloride and lime for dewatering. A by-product of the lime usage for dewatering was a high-lime stabilized sludge that also met landfill requirements. Maintenance with the plate and frame filter was a burden as was the chemical systems. Stearns & Wheler Engineers was retained to change it to a belt filter press system. The project was completed in 1990 with the installation of a two-meter Belt Dewatering Press (BDP) Company belt press along with related equipment for polymer feed, conveying, mixing, and post-lime stabilization of the solids after dewatering. The project has been successful in many ways. It has resulted in a 25-percent reduction in total tonnage of sludge generated, which, at that time, was going to a landfill. It also has proven to be much easier to operate well, a fact that has not gone unnoticed by the operations staff, and has been much less burdensome with maintenance.

Upgrade

In 1999, the district began the planning and engineering for the replacement of the grit bucket elevator and conveyor systems. The existing unit, as depicted in Figure 1, was constructed of carbon steel and was very badly corroded. It was even a concern that the existing unit might not last until the replacement unit could be installed. Fortunately, it did last until it was shut down permanently and removed on schedule. As Stearns & Wheler was the firm that designed the plant originally, and the district has been satisfied with their work, they were chosen to design this new project as well.

The project design phase examined two options. The first option, the one eventually chosen, was an in-kind replacement with similar units constructed of stainless steel (see Figure 2). The second option that had been examined was changing to a grit pump system with a cyclone separator and dewatering screw. The second option was proven not to be the most cost effective due to the building arrangement, complications of a new piping system in the building and hence was forecasted as costing considerably more than an in-kind replacement. The contractor, Faulter Construction of Syracuse, did an excellent job in getting all the old equipment removed, a feat that we looked upon as almost miraculous. The new system was placed in service in June 2000 at a cost of $300,000. The district had opted to utilize a five-year bond anticipation note (BAN) for financing this project. As the replacement units are constructed of stainless steel, they should prove to be much more durable over the next 20 years.

From a community safety standpoint, and well before the events of September 11, 2001, the district had realized the benefit of changing from the use of gas chlorine cylinders using ton containers. In 2000, the services of Stearns & Wheler were again enlisted, and the firm began the planning and engineering to change the system to a liquid sodium hypochlorite system. There were many delays along the way, principally relating to the district's inexperience with handling the bidding and funding of large-scale projects. Many items were handled "in-house" by various county departments and lessons were well learned. This project was also funded by a five-year BAN at a cost of $320,000.

At first, it seemed logical to locate the new equipment in the existing chlorine storage room located in the raw sewage pump station building. After reviewing the three usage points of chlorine, namely 1) year-round chlorination of the gravity sludge thickeners, 2) seasonal disinfection of the effluent (largest volume usage), and 3) intermittent chlorination of return activated sludge as filamentous organism control dictates, it became apparent that the operations building basement would be a better location for both the storage as well as pumping equipment. This location provided more space for the tanks and the required secondary containment. Along the way, we investigated the usage of the two existing 5,000-gallon storage tanks that were previously used for ferric chloride storage with the plate and frame press system. It was determined that these existing tanks were not suitable for long-term storage of the sodium hypochlorite and thus needed to plan for a totally new system. They were, however, suitable for short-term storage, and one tank has been piped to receive any spillage from the truck unloading pad should a spill event occur. As we had long used a sludge thickener for landfill leachate storage, which is slowly fed into the plant influent, it was desirous to have a concrete pad for the leachate truck unloading as well as for the sodium hypochlorite unloading. Construction began in fall 2002, just in time to get the outside piping work completed before the onset of an early winter. Work continued inside during the winter months with completion in May 2003. The system was first started up on May 28, 2003, just in time for the seasonal effluent disinfection period from June 1 to September 30. All progressed well after a few start-up adjustments were made in pump hose size, fittings, and calibration. We have just completed our first disinfection season very successfully as this article is being written. Chlorination of the sludge thickener has also gone well. We have not yet had opportunity to use the return activated sludge chlorination system, which is altogether not a bad thing.

Maintenance

Maintenance of a treatment plant involves more mundane items that aren't exactly exciting or process related. In 2001, we had our 20-year-old built-up asphalt inverted roofing system (insulation on top of the asphalt roof, covered by stone ballast) replaced with a rubber roofing system on all four major roof areas. This was done at a total cost of $91,326, which included one change order for adding tapered insulation so that a roof area would drain properly. This was paid for from a capital reserve fund that the district had accumulated for several years, with $25,000 being deposited annually. The roofing was completed by the end of September 2001. The contractor issued a two-year workmanship warranty for the period of October 3, 2001, to October 3, 2003. I mention this because on October 15, 2003, about 20 percent of a major roof area blew off and folded back onto itself during a storm event. An area of approximately 60 feet by 30 feet will have to be replaced, plus repair of numerous holes created by the lightning arrestor system spikes when the roof flipped over. Now has begun a time of a lot of visits of the engineer, contractor, roof membrane company, and insurance company. Naturally there has been a lot of discussion about why it failed. One thing for certain though was that we needed to fix the roof first, then point fingers and argue later!

Operation

In the operation of an activated sludge process, it's not unusual to produce floating solids on the final clarifiers. While being unsightly, they usually don't cause problems unless they can't be collected on a continuous basis and malicious odors result. Algae also grow prolifically on the weir surfaces, baffles, and effluent troughs due to the presence of nitrogen and phosphorous in the wastewater. In order to combat both of these problems, the district went out to bid for the installation of an algae sweep system (Figure 3) and scum bum system (Figure 4) as manufactured by the Ford Hall Company. The algae sweep system looks kind of like an erector set that I remember from my younger years but does a nice job cleaning the algae from surfaces on either an intermittent or continuous basis, depending on how you choose to operate the system. The cleaning arms can be placed in a raised "parked" position if you desire intermittent usage, which also reduces brush wear. This project was also funded during 2001 from a capital reserve fund. It came in at a price of $59,983. One unit was installed in October 2001; the second unit was done in April 2002. The algae sweep has proven to be a very useful tool and has minimized operator cleaning of the weirs during the summer from weekly, about three hours per tank (times two tanks) at a minimum, to simply cleaning the algae sweep brushes with a hose once a week, which takes a total of about 30 minutes. The plant personnel love them.The scum bum system is a flexible shingle-type baffle that extends from the center inlet well of both of the district's circular final clarifiers out to the beginning of the scum beach area. This helps to prevent the floating solids from being wind-blown to the opposite side of the tank and also helps to concentrate the solids which are notoriously light and diffuse and hard to corral with a circular clarifier skimmer arm. These arms with only one scum beach per tank are terribly inefficient with this type of solids, and the scum bum is a 200 percent improvement.

Summary

So far, the district has been able to accomplish projects that have been both necessary and helpful. They have helped the district meet present and future challenges, helped protect the district's investment, and even made our jobs as wastewater professionals more enjoyable and efficient! We are not done yet, however, as projects are being planned for the future, both short and long term. An upgrade to our Frankfort Pumping Station is in the works. A few examples of the types of projects being considered as time and funds allow are the installation of new raw sewage pump controls at the treatment plant, replacement of the mechanical bar screen that has served as an elevator for 20 years as the hand raked screen is many times more efficient, and installation of a diffused air system to replace the mechanical aerators in the activated sludge process complete with fine bubble diffusers and an anoxic or anaerobic selector. The plant's capital bond finally retires in 2008, and the reduction in those payments should go a long way towards other projects. The district has not yet made application to use New York State Environmental Facilities' State Revolving Fund, but plans are to look at consolidating bond anticipation notes once we're further ahead with projects.

Stay tuned for more developments. As for the roof, well…we know that in this business "feces occurs." Remember that you heard that one here first! The roof will be repaired and effluent flow will continue, and the district is well poised to meet its next challenge.

Keneck Skibinski is a certified grade 4A wastewater plant operator and a certified environmental trainer. He has over 29 years of operating experience in New York State and has been the chief operator of the Herkimer County wastewater plant since April 1980. He is also the NYWEA president elect for 2003-2004.

—Keneck Skibinski

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