Done Just Right

A Class A biosolids process keeps Stewartstown (Pa.) operations simple — and keeps area farmers coming back for more
Done Just Right

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Almost everything about the Stewartstown Borough Wastewater Treatment Plant speaks to its diminutive size. Though located on 20+ acres, the plant itself occupies less than an acre.

It’s designed for 740,000 gpd and is permitted for only 625,000 gpd. And when the plant was expanded in 2007, the cost was a modest $4.2 million. But what the plant lacks in size, capacity and cost, it makes up for in performance.

In fact, since the expansion, the facility has dramatically improved the quality of effluent discharged to Ebaugh Creek. Ammonia levels which once repeatedly exceeded 7 mg/l, are now routinely less than 1 mg/l, and total nitrogen levels, previously estimated at 25 mg/l, have been reduced to less than 6 mg/l.

The plant now also uses a heating and lime stabilization process to create about 130 dry tons per year of Class A biosolids, all used by area farmers.

Out with the old

Located in south central Pennsylvania, 30 miles from Baltimore, Stewartstown Borough is a quaint community nestled amid rolling hills and family farms. Since 1978, the treatment plant has served the borough and neighboring areas, with a total population of fewer than 2,000, according to Dennis Sarpen, president of James R. Holley & Associates, the consulting engineers on the 2007 expansion.

“The plant takes in material from the borough as well as parts of nearby Hopewell Township that are zoned for higher-density residential, but couldn’t qualify for onsite septic and well systems,” he says.

In addition, the plant takes in leachate from the York County Solid Waste & Refuse Authority landfill in Hopewell Township. The landfill collects the leachate in a liner system, directs it to a lagoon, performs pretreatment, and then pumps the liquid into the borough’s collection system. That represents 10,000 to 15,000 gpd — a bit less if the area has been rain-free for a time.

The old wastewater treatment facility generated a Class B biosolids which, while approved for land application, presented so many challenges that the borough needed an alternative treatment method.

“The old plant served its purpose, there’s no denying that,” Sarpen says. “However, the Class B biosolids could not be applied in winter and could not be kept on hand long before odor and flies became an issue.” The plant also needed to meet tougher discharge requirements.

High efficiency

The plant property includes mostly wetlands and hillsides, hardly ideal for an expansion. “We actually had to blast into a hillside to create a storage pad for the biosolids product,” says Ira Walker, borough water/sewer supervisor.

“We did a lot to save what we could from the previous plant, using a pair of existing tanks as part of the sequencing batch reactor (SBR) process, for example, and we built upon that. In the end, we had a nice, compact plant that does all that we want it to do and is giving us a far better byproduct than we had before.”

In that small footprint, wastewater is first screened through mechanically cleaned bar screens with 3/8-inch openings from Hydro-Dyne Engineering and then passed on to a pair of Aqua-Aerobic Systems SBR units where the wastewater is mixed and aerated. “That is one of the big differences between this plant and the one it replaced,” says Sarpen.

“The previous plant oxidized the ammonia to nitrate, but it was still a form of nitrogen. The plant was then free, and permitted, to discharge into the creek. However, the Chesapeake Bay requirements that are in place now say that Stewartstown must have lower levels of both total nitrogen and phosphorus. The SBR makes that happen, leaving low phosphorus, low solids and low BOD.”

While the previous plant used chlorine disinfection, the new one uses a 96-lamp UV system from the UV Technologies Division of Calgon Carbon Corp. “Most times of the year, discharge from the plant is required to be at no more than 200 fecal coliform units per 100 ml,” says Sarpen. “Stewartstown’s numbers are in the single digits and sometimes in the low double digits. It’s a much cleaner effluent entering the creek.”

Solids treatment

Biosolids at Stewartstown are first run through a Suburbia Systems (Unifilt) thickener (with an EMCO Flow Systems drive assembly), then pumped to an upper level in the building to be dewatered to about 17 percent solids in a 1.7 meter X-roll belt press from Envirodyne Systems. The dewatered material drops down to the first floor and enters a hopper at the start of the Schwing Bioset process that produces Class A material.

Quicklime and sulfamic acid are added to increase the temperature and the pH. A Schwing Bioset KSP 10V(K) piston pump sends the blended product, now about 35 percent solids, on to a reactor, where the temperature and pH are raised to sufficient levels to kill off pathogens.

“Schwing Bioset specs say it takes 30 minutes at 158 degrees F to make Class A biosolids,” says Walker. “But material here probably gets a couple of hours in that reactor before exiting to a truck. When the truck is filled, we haul the material over to the storage pad to be dumped and stockpiled until one of the area farmers calls for a load.”

Walker says the Bioset process is simple in design and operation and a good fit for a no-nonsense plant. “We have been really satisfied, both with the performance we’ve gotten out of the system and the support we’ve gotten from Schwing Bioset,” he says.

“We’ve really only had one issue in the two years the system has been in place — a problem with the sensors in the lime storage silo — but it occurred just as a huge snowstorm was about to hit. Schwing Bioset had a man out here quickly. He replaced the sensors with a newer, better type of sensor, and we were back in operation before the snow fell.”

Makes no scents

Perhaps Stewartstown Borough appreciates reliable support because that reflects how the borough treats its own customers. The borough delivers the Class A biosolids to the farmers at no cost.

“We do so because we farmers also haul grain or corn in their trucks and might not necessarily want to mix the two,” says Walker. “Plus we want to make it as easy as possible to get it to them.”

Sarpen says providing the biosolids for land application is as good for the borough as for the farmers. The alternative, taking untreated sludge to the landfill, would be cumbersome and costly.

“The landfill would charge the plant anywhere from $50 to $60 per wet ton to take the sludge,” says Sarpen. “If they were to take untreated material to them it would be at a point when it is 20 percent solids and 80 percent water. In terms of collection, transportation and disposal, that would be a huge cost to incur.”

Walker adds, “Mind you, the system was designed with a contingency where the mere push of a button switches the direction of a screw auger, allowing the sludge to bypass the Bioset system. But I hope we never have to use it. This is a great system providing a nice product to area farmers.”

Second time’s a charm

In 2009 alone, Stewartstown delivered more than 372 wet tons (130 dry tons) of Class A biosolids to area farms. Walker expected to surpass that tonnage in 2010.

“The treated solids have a real organic nutrient value, including lime, nitrogen and phosphorus which the farmers love,” says Walker. “To answer or even anticipate any questions, we provide a fact sheet for the farmers with information such as where they should and shouldn’t apply the biosolids product.

“We also make test data showing concentrations of pollutants in samplings readily available. We want to assure them in every way possible that they’ve made a good decision in taking this Class A biosolids for application.”

Walker will never forget the first load of Class A the plant sent out of the newly expanded facility. The customer (still the borough’s largest) was initially hesitant because he thought there would be a problem with flies and odor. “But after the first application, when he came back for seconds, we knew we were going to be all right.”


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