Friend or Foe

WASTE AGE STAFF

At its essence, leachate management consists of two basic steps: pump and treat. But take into account local climates, limitations at local publicly owned treatment works (POTW) and innovations in leachate recirculation, and you now have several options to properly handle your oozy goo.

Among the leachate management techniques available are:

* Treatment of raw leachate by a POTW;

* Pretreatment of leachate onsite, then discharging to POTW for final treatment;

* Onsite treatment, then discharging it into a stream;

* Evaporation using landfill gas;

* Membrane separation, including reverse osmosis (RO) and direct osmosis (DO); and

* Ultrafiltration.

Additionally, what was once considered sacred - the dry tomb landfill - currently is being challenged by wet tomb advocates who say that recirculating leachate back through the landfill will speed up decomposition, stabilize the organics and possibly reduce expensive, long-term landfill care.

What's right for you?

Ultimately, choosing the best route for your flow will depend on the economics and your individual site's characteristics. continued from page 84

Haul it Away Hauling untreated leachate directly to a POTW may be the easiest leachate management system to implement. However, looking long-term, this can be an expensive alternative as hauling costs escalate over time.

Consequently, younger landfills with less leachate may find POTWs easily accessible, but a local POTW may not be able to handle landfills with larger volumes of fluid.

Landfills that pretreat their leachate and then dispose of it at a POTW also may face the same access problems. As POTWs become overburdened and local jurisdictions set limits, landfills may be forced to look elsewhere for an appropriate leachate disposal system.

Treating leachate onsite then discharging it into a stream can an expensive haul. Also, it may be controversial in some communities.

Up in the Air Leachate evaporation is the only option that disposes of the water in leachate. Currently being used in a number of sites, this option consists of a system in which landfill methane is captured and burned as a fuel to burn landfill leachate.

To evaporate leachate, you'll likely need an air permit for the enclosed landfill gas flare and a separate permit to cover the leachate management practices.

Paperwork and equipment in hand, you then can begin heating the leachate to produce water vapor. The metals in the leachate will be concentrated and precipitated, while the organics will be volatilized in a process similar to air stripping. Because of the lower temperatures used, most heavy metals don't evaporate.

Keeping it Separate Semi-permeable membranes are used to separate the inorganic and organic elements from water. Reverse osmosis (RO) uses a high-pressure pump to force leachate through a membrane to divide the water from the contaminants, which exit as brine. To lessen clogging and biofouling, pretreatment may be necessary, depending on the membranes.

Direct osmosis (DO) uses low pressure and places a membrane between the leachate and an osmotic agent. Here, the membrane passes the leachate through, but rejects the contaminants. This process continues until the water concentrations are equal on both sides and the osmotic agent is diluted.

Reverse and direct osmosis methods produce a concentrate, which must be managed.

Plain or Filtered? Filtration falls into two categories: ultrafiltration, which removes larger organic molecules and particles down to 0.1 to 0.01 microns, while allowing dissolved salts and most small organics to pass; and microfiltration, which removes particulate matter and micro-particles from 1.0 to 0.1 microns. Similar to osmosis, you will have to manage the concentrate this method produces.

Recirculating and Bioreacting Recirculation has been experimented with throughout the 1990s. This is a simple process whereby the leachate is collected and returned into the landfill either through spraying, flowing over the land or injecting the leachate directly below the surface.

At some point, however, the recirculated liquid must be removed and treated like any other leachate, either at a POTW or onsite.

There is increasing interest in recirculation because of its ability to speed the decomposition of a landfill's organics. While this process puts the materials' degradation on the fast-track, it also produces additional leachate and landfill gas. Traditionally, this wet-tomb approach has been viewed negatively among solid waste professionals in the United States. However, many Europeans have been enamored with its contrasting benefits.

Today, recirculation is enjoying its newfound relationship with the bioreactor landfill concept sweeping the country. Now, several landfills are studying the overall affects of speeding up the process, comparing its advantages to the cost of additional collection and treatment.

However, as with virtually every aspect of the solid waste system, the best leachate treatment system will end up being what's most appropriate for your facility and budget.

Depending on the type of waste at your site, rate of water movement, stage of decomposition and landfill depth, leachate will vary from one landfill to another. However, there are some common measurements that can be taken to determine the quality of your specific flow, including:

* Biochemical Oxygen Demand (BOD): This determines the level of oxygen required by aerobic bacteria to completely oxidize the organic matter at your landfill within a certain time and at a certain temperature. Typically, BOD levels are taken over five-days and labeled as a five-day BOD, or BOD5.

* Chemical Oxygen Demand (COD): This is the amount of oxygen required to oxidize organic and oxidizable inorganic compounds in water.

* Metals: Solid waste contains metals. As some metals are solubized by landfill leachate, the pH decreases. Typical metals that can be found in leachate include cadmium (Cd); chromium (Cr); copper (Cu); iron (Fe); lead (Pb); mercury (Hg); nickel (Ni); silver (Ag); and zinc (Zn).

* Nitrogen: Nitrogen present in leachate usually is measured as total Keldjahl nitrogen (TKN) - a mixture of organic nitrogen and ammonia. Nitrates also can be present in leachate, depending on the degree of nitrogen transformation.

* pH: Typically, landfill leachate is acidic and has a pH of about 6. However, pH can range from 5.8 to 8.5.

* Specific Conductance (k): This describes how well the leachate conducts an electrical current. High levels of specific conductivity indicate total dissolved solids (TDS), chloride ions and sulfate ions.

* Total Dissolved Solids (TDS): This is the portion of total solids in the water that are dispersed as single molecules or ions.

* Total Organic Carbon (TOC): TOC is the amount of organic matter present in the water. It can be measured by oxidizing the organic carbon to carbon dioxide by using a catalyst, then measuring the carbon dioxide. However, some organic compounds do not oxidize. As a result, the TOC value may be slightly less than the actual amount of organic carbon present in a sample.

* Total Suspended Solids (TSS): This represents the undissolved solids substances that, when present in significant concentrations, are visible. TSS can be determined by a specific test procedure.

As part of its current review of its landfill regulations, the U.S. Environmental Protection Agency (EPA), Washington, D.C., has invited "comments and information" - specifically on comparisons between how alternative liners and composite liners perform when landfill leachate is recirculated.

Additionally, the EPA is investigating the performance and design of bioreactor landfills.

Currently, the EPA requires a municipal solid waste landfill to have a composite liner before it can recirculate leachate. Citing information from "various stakeholder groups," which include state and local governments, solid waste associations, and industry, the EPA is attempting to determine whether alternative liners work at least as well as, if not better than, the liners required by the existing regulations.

EPA also is requesting data and information on the design and performance of bioreactor landfills. By adding liquids such as leachate back into the facility to enhance the microbiological processes, bioreactor landfills generally are credited with quickly stabilizing organic waste.

One original and two copies of your response can be sent to the RCRA Information Center (RIC), Office of Solid Waste (5305G), U.S. EPA (EPA, HQ), 1200 Pennsylvania Ave., NW, Washington, D.C. 20460.

You also can send your response electronically to rcra-docket@epa. gov. Electronic responses must be submitted as an ASCII file. Do not use special characters or encryption. Identify your comments with docket number F-2000-ALPA-FFFFF.

More information is available on the Internet at www.epa.gov /epaoswer/non-hw/muncpl/landfill /leachate.htm. Or call the RCRA/Superfund hotline (800) 424-9346.