October 2010, Vol. 22, No.10

Spillproofing WWTPs

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Legend has it that many years ago, somewhere outside Chicago,

a memorable oil spill occurred. This wasn’t your average burst petroleum pipeline or wrecked tanker ship. No, by this account, a chemical plant leaked a load of palm oil — the stuff used for deep-frying — into the local sewer system. This leak made it all the way down to the wastewater treatment plant (WWTP), and in some quantity, too. As winters go in the Midwest, it was a cold one, and all the palm oil froze. 

The plant had no choice but to shut down, bypassing treatment while workers went in and cut out the solid oil, chunk by greasy chunk.

As this year’s events in the Gulf of Mexico, Michigan, and China demonstrate, oil spills and slicks do happen, and when they make their way to a WWTP, they have to be dealt with — even if that means using a saw. Talk to anyone in the business, and you will hear one thing: The goal is to stop oil before it gets to the plant.

The easiest way to stop the flow of oil is with booms, said Kim Riddell, chair of the Water Environment Federation (Alexandria, Va.) Plant Operations and Maintenance Committee. Various types of booms are on the market, and many are absorbent, forming a barrier and soaking up any oil headed toward the WWTP.

Once oil enters the collection system, it can lead to more work for operators, problems with plant equipment, and, ultimately, fines for the polluter. But the thought of losing valuable oil down the drain is usually enough to keep most sewer permitees wary of any misdeeds.

“They’re going to be very proactive about calling us and getting on top of it, because they don’t want to lose product down the sewer,” said Kelly Christensen, source control supervisor at the Orange County (Calif.) Sanitation District (OCSD). According to Christensen, there are about two dozen still-active oil wells in Orange County that discharge wastewater to OCSD.

While Christensen said there hasn’t been a spill that reached a treatment facility in his district in several years, he has had experience with crude-oil spills before, and his source control team remains ready to handle one should it occur again.

The spills Christensen has seen occur when oil-storage tanks, generally holding tens to hundreds of gallons of crude oil, fail and aren’t spill-contained enough, allowing the oil to reach the sewer.

Occasionally, Christensen also has seen oil–water separators fail at some of the permitted wells, sending oil into the collection system along with wastewater. In that case, the district often knows about the spill before the well owner does, as the wells are not always monitored.

When OCSD operators notice oil at the headworks of the WWTP, they trap the oil in primary clarifiers.

“We shut down any connections so that the skimming doesn’t go anywhere else — we try the best we can to trap it there and then we have the pump trucks come in, and generally it’s the responsible party who brings a contractor in to suck it all out, and that’s usually where it all ends for us,” Christensen said, adding that any cost to mitigate the spill for the sanitation district is billed to the polluter.

Christensen said that no matter how much oil they see, bringing in a pump is the safest response.

“We usually won’t know for some time how much oil we’re dealing with, so we prepare for the worst and hope for the best,” Christensen said.

In the case when a well owner doesn’t know that oil is being dumped, it’s up to the source control team to find the leak so it can be stopped as quickly as possible.

“Then we activate our oil-spill-response plan,” Christensen said. OCSD uses a geographic information system to help teams fan out, locate the source, and stop the flow.

One complication that can arise, Christensen added, is the presence of volatiles, such as benzene and toluene, gassing off in the sewer, creating the potential of an explosive atmosphere. Then, the sewer manholes must be opened, and intrinsically safe ventilation is installed.

Riddell, who previously worked for the City of Delphos (Ohio) WWTP, said that operators often had to remediate spills of hydraulic machining oil due to the plant’s proximity to industrial users.

“You have to rely on the industrial user to be honest and tell you when they’ve had a problem and not just send it down the sewer on its merry way without saying anything to anybody,” Riddell said.

Riddell said her plant used a dissolved-air flotation system to float the grease and oil up and auger it down the tank to be removed from the system, though she said plants use a variety of different setups. She said the plant also has used chemical dispersants and enzymes in lift stations upstream to break up oils and grease, making sure they get to the plant for treatment and don’t clog the collection system.

The severity of the spill and the response taken also depend on what type of oil is involved. Riddell recalls one incident in which a tanker spilled soybean oil, which was mostly contained at the spill site, but some found its way into a storm drain.

“That food grade would not have been a problem had it gotten to the wastewater plant, because the activated sludge — the bugs in the system — would have eaten that up or used it up as fuel or food source,” Riddell said.

In many cases, oil skimmed from wastewater can be reclaimed and reprocessed. Ken Gray of Oil Skimmers Inc. (Cleveland) said that skimmed pure vegetable or animal oils can be converted into biodiesel, while reclaimed petroleum oils can be processed into boiler feed, recovering some of the cost of lost product.

However, unlike the soybean oil, petroleum products can be a nightmare if they make their way past primary treatment.

“The bugs will not like it one bit,” said Jack Saltes, wastewater operation engineer at the Wisconsin Department of Natural Resources, about the microorganisms working in the aeration basins. “Once in the aeration tanks, even very small amounts of any kind of petroleum product [means you can] kiss [the microorganisms] goodbye.”

Saltes said that the aeration basins would have to be totally cleaned of dead sludge, and new sludge should be started again from seed.

In Saltes’ experience, petroleum often gets down the sewer and to the plant when old heating-oil tanks are removed and new ones installed improperly, allowing the oil to reach a basement drain, he said.

The most important factor in the response and mitigation of an oil spill, no matter what kind of oil or how it is leaked, is preparedness.

“Having a good spill plan at the treatment plant, reacting quickly, and knowing what to do when oil is coming into a wastewater treatment plant goes a long way in mitigating the effects of a WWTP oil event and, at worst, being able to bring the plant back on-line very quickly once it has passed,” Saltes said. “Operators should review their spill plans on a regular basis.”

 

Calder Silcox , WE&T

 

Show me the savings

Missouri cities profit from energy conservation challenge

When Dan Scherer received a letter from the U.S. Environmental Protection Agency (EPA) inviting the City of O’Fallon, Mo., to participate in a new EPA-led energy management initiative, the first thing he did was to set it aside.

“I get things like this all the time and was skeptical,” admitted Scherer, managing director of water and sewer operations for O’Fallon, a city of more than 75,000 near St. Louis.

Ruben McCullers, environmental management systems coordinator for EPA Region 7, understands.

“Missouri is the ‘Show-Me’ state,” McCullers said. “It’s also a place where electricity is still relatively cheap.”

In fact, that was one reason EPA Region 7 chose this region to pilot the initiative, McCullers said. “If the water and wastewater utilities here can find ways to reduce energy consumption, there’s a good chance that those in other parts of the country can, too,” he explained.

With some prodding from the Missouri Department of Natural Resources — a partner in the initiative — Scherer eventually changed his mind and submitted an application. And he’s glad he did. Less than 2 years later, O’Fallon has a plan that is projected to reduce energy consumption at its wastewater treatment plant (WWTP) by more than 15% while improving the plant’s reliability and lessening its environmental impacts.

Making the commitment

O’Fallon was one of 12 midsize Missouri water and sewer utilities that EPA Region 7 initially invited to participate in the pilot initiative. Ten accepted the invitation, and eight completed it.

“To take part, cities had to agree to several things,” explained Kris Lancaster, spokesperson for EPA Region 7. “They had to let us conduct an energy audit at their treatment plants and help them identify projects that would improve their energy efficiency by at least 15 percent.”

“The reality is, 30 to 40 percent of a city’s energy budget is typically spent treating water and wastewater,” Lancaster said. “But most cities don’t have a good handle on where and how that energy is used.”

For this reason, participants also had to agree to use Energy Star® Portfolio Manager, an online energy management tool that enables cities to track and assess energy and water consumption.

Each also participated in four workshops hosted by EPA and its partners: Missouri University of Science and Technology (Rolla), the Missouri Department of Natural Resources, and Siemens Building Technologies (Kansas City, Mo.).

The workshops were designed to provide participants with the information and tools they needed to develop their own energy management plans, McCullers said. “We didn’t want them to come back in 4 or 5 years wondering what to do next,” he said. “We wanted them to be able to do it themselves.”

The ‘biggest loser’?

The eight participating cities came together in July to present their plans publicly. They are now in various stages of implementing projects that are collectively projected to reduce energy consumption by more than 8 million kWh while cutting greenhouse gas emissions by 7.3 million kg (16 million lb), according to Lancaster.

The “biggest loser” thus far appears to be St. Peters, Mo., a city of 55,000 located just east of O’Fallon. There, Public Works Director Russ Batzel and his colleagues identified two projects alone that will cut the WWTP’s energy usage by 25% to 30%.

One involves replacing the old aerators at its WWTP with ones equipped with variable-frequency drives linked to a computer system that adjusts motor speed based on real-time treatment needs.

“This project enabled us to optimize the energy used to turn the motors,” Batzel said. “Before, they turned at a constant speed, regardless of the treatment requirements. Now, we’re matching motor speeds with treatment needs.”

This single adjustment is expected to save 1 million kWh/yr, representing a 16% reduction in energy use at the WWTP. At current rates, this translates into annual savings of $46,000.

Over at St. Peter’s water treatment plant, meanwhile, plans are in the works to replace the 30-year-old motors on seven pumps with either premium efficient motors or ones with variable-speed drives. Estimated to cost approximately $165,000, this project is projected to save about $20,000 a year in energy costs, translating to a 7- to 8-year payback, according to Batzel.

 “One thing we learned is that it isn’t necessarily a good idea to wait for your equipment to break or reach the end of its life cycle before you replace it,” Batzel said. “It can really pay to replace a motor before the old one wears out or add controls to vary your speeds.”

 

Back in O’Fallon

Like St. Peters, the City of O’Fallon learned through its initial energy audit that it could achieve substantial cost and energy savings with relatively modest investments.

By replacing the blower used for aeration at the city’s WWTP, for example, the city will reduce energy costs by an estimated $58,000 a year, or more than 11% of the plant’s $520,000 energy budget, according to Scherer. The new blower is expected to come on-line next year.

Scherer said that approximately 70% of the $500,000 needed to fund the project will be paid for by a grant from the Missouri Department of Natural Resources. “Based on what the city itself will invest, the project will have a 2-year payback,” he said.

Also on O’Fallon’s energy-saving agenda is a new automated meter-reading system. Still in the planning stages, Scherer said the city hopes to replace 12,000 existing water meters with new ones fitted with radio transmitter technology that can be read remotely.

In addition to eliminating the energy and other costs associated with reading meters manually, the new system is expected to increase accuracy from the current 92% to 98.5%. Eventually, residents may also gain the ability to access their accounts online to track their water use trends and find opportunities to conserve.

The price tag on that program is $5.8 million, an investment that will go “cash-positive” in 4 years, according to Scherer.

 

Looking ahead

Examples like these are music to McCullers’ ears.

“One of the things we want cities to realize is that just because their equipment is working, it’s not necessarily working efficiently,” McCullers said.

“We want to encourage the use of alternative energy sources,” McCullers added. “But we also support energy efficiency. We want cities to see that the best dollar they spend on energy is the dollar they don’t spend.”

Batzel credits the initiative with enabling the city of St. Peters for the first time to understand its energy usage and compare it with other utilities across the country. On a scale of 1 to 100, St. Peters received a rating of “58 or 59” on its initial energy efficiency assessment 2 years ago, Batzel said. “Our goal was to raise that number to 75,” he said. Today, the city’s rating has risen to 84.

Batzel said the energy management initiative has also given the city the opportunity to create better energy awareness among staff. He expects St. Peters will soon expand its use of Portfolio Manager beyond its water and wastewater facilities to include the city’s parks and recreation facilities and police justice center.

For Scherer and the City of O’Fallon, the energy management initiative had yet another benefit: It compelled them to move from planning to action.

“For us, this program substantiated what we had been thinking and helped us find ways to proceed with our ideas,” Scherer said.

With these successes under its belt, EPA Region 7 would now like to offer the program again to other cities in Missouri and elsewhere.

“These eight cities proved that it can be done,” McCullers said. “Just imagine what’s possible if everyone got on board.”

 

Mary Bufe , WE&T