Battling the OozeBattling the Ooze
February 1, 1998
Ask any two landfill managers about the best way to manage leachate, and you're bound to get at least four different answers. From climate variables to the limitations at local publicly-owned treatment works (POTW), each landfill manager has his or her own combination of issues to deal with when planning for a leachate management program.
"[Programs] are site-specific," says Dan Strobridge, an associate regional solid waste practice leader for Cambridge, Mass.-based Camp Dresser & McKee's Pasco, Fla. office. "There doesn't seem to be a common thread; it just depends on what the project requires."
Strobridge, whose firm performs landfill engineering design analysis, has run the gambit of leachate treatment: from ultra-filtration, reverse osmosis to thermal mechanical processes to evaporation methods to the tried- and-true pump-and-haul routine.
"You look at pump and haul, travel time, distance and volume when you're developing some preliminary cost estimates for a client," he says. "Obviously, the least cost is the way your client usually wants to go. But, others will spend millions of dollars for on-site pretreatment to meet permit requirements."
There is no pat answer for leachate management. For example, he notes, in Florida, it is difficult to achieve a water balance when it rains 50 to 60 inches per year and where tactics such as building ponds aren't options. However, he adds, "out in the desert Southwest, it might be a great idea."
Wet or Dry? The Delaware Solid Waste Authority (DSWA), Dover, is in the midst of an experiment to determine if it is nobler to maintain a dry or wet landfill (see World Wastes, March 1997, page 28). With the approval and assistance of the U.S. Environmental Protection Agency (EPA), DSWA is conducting a waste characterization analysis on two one-acre cells of its solid waste management facilities.
The state of Delaware receives an average rainfall of 44 inches annually, which, in turn, produces a relatively high volume of leachate, says Anne Germain, DSWA's supervising engineer. DSWA's experiment will explore methods to reduce leachate volume and associated transportation and treatment costs. Currently, the authority's leachate is hauled to a New Jersey treatment facility about 90 miles away.
DSWA's Southern Solid Waste Management Center (SSWMC) generated 5.25 million gallons of leachate in 1996 for an annual $600,000 pump, haul and treat price tag. SSWMC, which generates between 14,000 to 15,000 gallons of leachate daily, was designated for the wet versus dry cell experiment.
The construction of a new geomembrane cap, which is being placed on the 45-acre area of two closed cells, began last summer, Germain says. Instead of laying soil over the geomembrane cap, a 36-millimeter reinforced polypropylene will be placed over a layer of soil.
On the other hand, DSWA is recirculating leachate back onto a wet cell instead of hauling it to the POTW. Theoretically, the wet cell has the added advantage of biodegrading and, thus, stabilizing faster, says Rick Watson, DSWA's chief engineer. "A lot of times it's a question of geometry: Can you get the leachate to the areas you want?" he says.
Although leachate volumes have decreased with the dry cell, when it is reopened and exposed to rain, the concentration levels go right back up, Watson says. So, there are pros and cons with both wet and dry areas, he concludes.
The verdict is still out on the success of DSWA's experiment. The next phase will include an excavation analysis on each site. Watson anticipates having results by December 1998 and a written report by early 1999.
A New Spin on Treatment A new technology, invented by John Zink Co., Tulsa, Okla., could help alleviate landfill gas and leachate problems simultaneously. This closed-loop leachate evaporation system uses landfill-generated methane gas to heat the leachate which then is converted into an evaporant and injected into a secondary combustion unit.
EMCON, San Mateo, Calif., which has purchased the rights to use this process for landfill applications, has developed a leachate evaporation system (LES) patent process called a "submerged combustion gas evaporator" (SCGE) which injects hot methane gas directly into the leachate for an efficient heat transfer.
Currently, EMCON's LES is online at a Amesbury, Mass., landfill and at the USA Waste (Dallas)-owned Olympic View, Wash. landfill. "With [LES], nothing goes off site," says EMCON's Mike Momboisse. "Residual sludge even can be put back into the landfill."
This system works as a service, not a product, where landfill owners sell the methane to EMCON, which charges a monthly fee for the service of evaporating the leachate, Momboisse explains.
Currently, private landfill operators have been the most receptive to LES, says Momboisse, who notes that the added tax credit of three to four cents per gallon (Section 29) for non-conventional fuel use is an incentive for them. However, as more landfills are cut off of POTWs and alternative leachate disposal methods are explored, Momboisse expects to see an increased interest from the public sector.
The local POTW remains a viable option for an Olympia, Wash., landfill - a 15-acre, 400-tons-per-day, government-owned facility that generates an average of 15 million gallons of leachate annually. This Subtitle D facility employs a lagoon filtration system which pretreats the leachate before it's pumped into a sewer and processed at an Olympia-based POTW.
"We have a permit to discharge as long as we meet certain guidelines," says Dave Merrell, Thurston County's solid waste manager. The lagoon has a 1.5 million-gallon-capacity and is equipped with three floating prop agitators to aerate the leachate. Its main purpose is to remove many of the suspended solids, he explains. The aerators also minimize biochemical oxygen demand and keep the leachate from turning septic by introducing oxygen.
Sludge build-up in the lagoon does not seem to be a factor. "We've been operating for seven years, and there hasn't been enough sludge in the lagoon to warrant dredging," Merrell notes. Habersham County, Ga., found an answer to its leachate problems through a reverse osmosis system, manufactured by Rochem Separation Systems Inc., Torrance, Calif.
When the county opened its government-owned landfill in 1993, it initially pumped and hauled the leachate to a POTW more than 100 miles away in Fairburn, Ga.
However, as the leachate exceeded the POTW's acceptable limits, the county was forced to review other options, says Landfill Superintendent Stanley Duckett.
The landfill started with a pilot project, and "we got the state to approve it," he explains. "Of course, back then, the state had never heard of the process." After completion of a successful pilot program, the state approved permanently installing the system at the landfill.
Currently, the system processes between 3,500 to 4,000 gallons of leachate daily - volumes that Duckett gauges would have cost the county approximately 14 cents per gallon to pump and haul.
"Now, we filter the effluence back onto the landfill, and we're using the clean water for dust control and irrigation," he says. "We only use it within the parameter of our monitoring area. We didn't try to get a discharge permit because we didn't feel we had enough leachate," he continues. "We've thought about installing a sprinkler system for irrigation and dust control, but it's just in the planning stage right now."
Handling Treatment Competition Like Habersham County, the Matlock Bend Landfill in Loudon County, Tenn., was pumping and hauling its leachate to a local POTW. However, in Loudon's case, the distance was a mere half mile to a nearby manhole. The Loudon County Solid Waste Disposal Commission (LCSWDC), the government body appointed to oversee the government-owned facility, in conjunction with its landfill management company, Santek Environmental Inc., Cleveland, Tenn., constructed a sewer line to tie into the POTW's sewer system.
Leachate management appeared to be progressing well at the Subtitle D facility until the local utility, Loudon Utility Board (LUB), informed the county that its leachate exceeded the limits for certain parameters such as phenols, toluene and zinc.
"There were a few constituents that were above the acceptable limits for those parameters set by LUB," explains Robert Burnette, Santek's vice president of engineering. "Of course, there were some pollutants that were compatible (BOD and COD), versus the non-compatible pollutants (phenols, toluene and zinc) which could be discharged to the wastewater treatment facility."
When LCSWDC and Santek approached LUB for a variance in the concentration limits for various parameters, LUB officials said their hands were tied due to the limits established by the Tennessee Department of Environment and Conservation Division of Water Pollution Control.
To bring Matlock Bend Landfill's leachate into compliance, LCSWDC authorized Santek to explore various pretreatment options. "In the case of Loudon, you're competing with different industries," explains Dennis Wheeter, an environmental consultant based in Knoxville, Tenn. "Each wastewater treatment facility has a state permit to discharge into a river or creek. The city [wastewater treatment facility] cuts that limit in half to protect itself, then allocates what's left over. In Loudon, others are competing, and there's not much left over.
"It's different from community to community," he continues. "I've had clients move facilities because they could get a better discharge permit. It's not that one place allows more pollution than another; there's just less competing industries discharging."
Wheeter prepared a cost analysis of four different pretreatment options for LCSWDC: chemical oxidation, activated carbon adsorption, pump and haul, and biological waste treatment.
"The challenge faced by pretreatment of leachate for this specific site was the natural variance encountered by the leachate constituents," Burnette says. "These changes can be caused by waste stream seasonality and actual developmental phases of the landfill. Landfills will go through a series of aerobic, anaerobic and methanogenic phases that also can affect the composite and level of constituents in landfill leachate."
It's difficult to place a generic condition on what pretreatment will be required because constituents and their concentrations can vary tremendously according to geography and demographics, Burnette notes.
"The type of system you may establish for pretreatment may be based on the actual leachate flow and the volume of leachate to be disposed. That's another parameter that varies greatly," he says. "We can make more scientific predictions to quantify leachate generation and subsequent disposal volumes better than we can predict the constituents or their levels."
For LCSWDC, the deciding factor was capital expenditures versus operation and management costs. Wheeter estimates that installing a chemical oxidation system would cost LCSWDC $53,000 to build and an additional $80,000 annually to operate and maintain.
Conversely, while pumping and hauling the leachate to a private wastewater treatment facility would require no capital expenditure, it would cost $92,000 a year to process.
Wheeter estimated the cost of an activated carbon adsorption system at $47,000 to build and a staggering $228,000 to operate and maintain.
"All these estimates were, of course, site-specific for Loudon County," Burnette notes. LCSWDC eventually chose to pump and haul leachate to a private wastewater treatment facility, Thompson Environmental, Etowah, Tenn., instead of building an on-site pretreatment system.
"Mainly, it was the capital investment for the other options and the hit-or-miss, come-and-go parameters we were having problems with," LCSWDC Vice Chairman Al Jorden explains.
A retired chemist and an environmental consultant for Loudon-based Viskase Corp., Jorden says that building a biological waste pretreatment system (one of the least expensive options), designed to treat specific constituents and not others, did not seem prudent.
"They're so sensitive to heat and can be wiped out, and then you have to start all over," Jorden says. "I couldn't see the other options for the big capital outlays."