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Advanced electronic controls harness landfill pollutants

March 2012

The Keithly Electric crew at the LRI landfill project

The Keithly Electric crew at the LRI landfill project include (left to right) Curt Davis, Mike White, and Mike Roten. Not pictured here, but a vital part of the group, is Joe Garcia.

In Pierce County, Washington, it’s garbage in…period. But that’s hardly the end of the story.

Getting Tacoma-area garbage into the county landfill is the easy part. The challenge for private operator Land Recovery, Inc. (LRI) is to keep the nasty stuff from getting out again.

Even after it’s been crushed and compacted by giant trash movers, and buried under a cap of earth, trash still acts pretty trashy. Some of it gets digested by bacteria, in the process turning into acid and emitting CO2 and methane gas. Other waste contains hazardous chemicals and harmful metals like PCBs, dioxin, mercury, and lead that can be released in the landfill, then washed out by rainwater to flow into streams or underground aquifers.

What emerges is a vile-smelling soup called “leachate,” a concoction of metals and chemicals that acts as bad as it sounds. It often starts out black (and may even bubble with dissolved gases), then turns brown or yellow as the oxygen it absorbs from the air affects dissolved iron salts. Bacteria move in, and the result is more than disgusting. It’s an environmental hazard.

But just as much of what we once called “garbage” is now recycled, leachate that emanates from the 168-acre LRI landfill can now be cleaned up to keep streams and aquifers safe. It’s not a simple formula, but LRI, working with Seattle’s Keithly Electric Company, is installing an updated leachate processing facility, monitored and controlled through state-of-the-art electronics. You wouldn’t want to drink the end product, but it’s clean enough for final processing in the area sewer system. (For a step-by-step view of the process, see “How Leachate Cleans Up its Act.”)

Mike Roten uses his Fluke 87V to check motor relays

Mike Roten uses his Fluke 87V to check motor relays on the low-voltage side of this control cabinet built off-site at the Keithly panel shop.

Complex processes, complicated controls

Keithly Electric is a full-service shop focused on heavy industry, with extensive experience designing and building custom programmable controls. The systems and controls being installed for LRI make this one of the more complex jobs tackled by the Keithly operations manager and Keithly technical team.

Located on a 320-acre site, the LRI landfill can hold approximately 29.2 million cubic yards, and will accept waste for at least 20 years. This is no simple hole in the ground, but a sophisticated system engineered to contain waste and control its harmful potential far into the future. The landfill is made up of cells, each with a state-of-the-art liner and leak detection system beneath it. Other technical and regulatory design elements, including the leachate collection and processing facility, meet and exceed all regulatory requirements.

Control begins with the site itself, which lies over a 40 to 50 foot (12 to 15 meter) thick layer of glacial till, also called hardpan. Hard for water to penetrate, it’s a natural protective barrier between the landfill and the underlying aquifers. Another advantage: the aquifers themselves are naturally pressurized. When a well is drilled, water naturally flows to the ground surface.

The refuse disposal cells are excavated to the hardpan. Each cell has a gas extraction system, a composite bottom liner, an underlying leak detection/collection system, a cover cap (except when in operation), and a leachate collection system. Thanks to the hardpan, most rainfall on the site either runs off as surface water or is returned to the atmosphere through evaporation. A key goal is preventing leachate from escaping and polluting a waterway that crosses the site, the unfortunately named Muck Creek.

Multi-mode operation

Far from a “plug and play” solution, the LRI system came together through Keithly’s collaboration with waste plant managers, environmental engineers, equipment manufacturers, plumbers, and the mechanical and general contractors. The goals: treat a higher volume of leachate and produce a better end product, all while using fewer chemicals in a system that costs less to operate. “It’s a one-of-a-kind system,” said the Keithly operations manager. “Nobody’s done this before.”

The many process steps needed to make leachate less dangerous (see sidebar, “How Leachate Cleans Up Its Act”) required the Keithly team to engineer a complex solution. The system includes 37 different pumps, five mixers, motors to drive the flocculent rake and the solids press, and 18 variable frequency motor drives (VFDs). Each motor, pump, and valve has manual, semi-automatic, and fully automatic operating modes. Also integrated into the system are dozens of sensors, and control and position indicators. Alarms may indicate both high and low readings. Dosing pumps, motors, pumps, and compressors send run signals. The system reads data from float switches, flow meters, pressures switches, and PH metering devices.

“The only thing we aren’t monitoring at this time is the coffeepot,” said Curt Davis, Keithly’s project manager. “But we’re not done with the project yet.”

These many inputs are managed through touch screens built into a jumbo human-machine interface (HMI) control panel 90 inches (2 meters) tall and nearly 16 feet (5 meters) wide, put together at the Keithly panel shop near Seattle’s Boeing Field. The screens lay out the process and all key components graphically, so operators can easily see and act on what’s happening anywhere in the plant. An Allen-Bradley ControlNet™ ControlNet Network Ethernet network sends control signals over RG6 quad-shielded coaxial cable to the system components. Each element - motors, valves, level sensors and more - has a unique network address. All programming is done at the Keithly shop.

“We were all electricians”

The Keithly team takes special steps to build panels that technicians can work on easily - and safely. “We were all electricians before we got into this,” the operations manager explained. Plastic shields are installed to prevent fingers from making accidental contact with hot conductors. Wherever possible, 24-volt control circuits are installed at a distance from hazardous 480-volt systems, and reached through separate access panels.

And do customers appreciate the extra care that Keithly applies? “They sure do,” the operations manager said. “They all do when we’re done.”

Mike Roten uses the Fluke 87V to check motor contactors.

In several locations throughout the building, Mike Roten uses the Fluke 87V to check motor contactors.

Connector by connector, the panel is fully tested in the shop, then tested again on-site. Every connector is torque-tested to make sure it was tightened properly, followed by a tug test, just to make sure. An electrical continuity test using a Fluke digital multimeter - often a model 87V - confirms the results of those physical tests. Communications links are checked and all contactors are cycled to ensure proper operation. When necessary, testing with a Fluke ScopeMeter® portable oscilloscope reveals whether VFDs are producing the required outputs. Because the system is fully networked, it’s possible to log in from miles away to diagnose any problems that might develop. You could even run the plant remotely, the operations manager said, though that is not in the plans.

As he talks about the project, and even though construction is still ongoing, the operations manager’s pride is clear. Keithly and LRI are creating a system that will help protect the sensitive Pacific Northwest environment for years to come.

“We took a concept,” he said, “and turned it into an actual, usable design.”

How Leachate Cleans Up Its Act

Leachate that percolates down through refuse at the LRI landfill is collected on the bottom liner and pumped to six storage tanks. From there, the nasty liquid is pumped to a 9,200-gallon (34-liter) equalizer tank in the pretreatment facility. The tank aerates the leachate and provides interim storage and flow equalization before the liquid enters the chemical treatment unit. Variable frequency drives (VFDs) control the two pumps.
Step One of pre-treatment is to remove metals and solids. From the equalization tank, leachate is pumped to a three-chamber chemical treatment unit.

  • Unit one is a coagulation tank where ferric chloride is added so that the suspended solids are electrically neutralized. This allows the solids to agglomerate.
  • In unit two, sodium hydroxide (lye) is added to increase pH above 9.0, precipitating metals into insoluble hydroxide ions.
  • In the third unit, anionic polymer is added, causing the particles suspended in the leachate fluid to collide and further agglomerate into flocculent or “floc.” The leachate then flows into a solids separator, where the floc drops to the bottom.
  • From here the metal sludge is pumped into tanks for further treatment. It is mixed with diatomaceous earth, then pressed into solid 16-inch by 16-inch (41-cm by 41-cm) cakes and removed.
  • The liquid rises through an inclined plate separator and into a pH adjustment tank. Sulfuric acid is added in the adjustment tank to re-adjust pH to neutral.

Step Two uses a moving bed biofilm reactor (MBBR) system to reduce biological oxygen demand while degrading volatile organic compounds. Pretreated leachate moves to one of four MBBR tanks, where it is aerated. The leachate comes in contact with a thin microbial film, which converts the organics to carbon dioxide and water.
From there the fluid flows to the dissolved air flotation (DAF) vessel, where a Nikuni pump infuses the mixture with fine air bubbles to remove any remaining solids. That sludge is pumped out, and the remaining effluent, while far from potable, is ready to be pumped into the county sewer system.