Landfill Leachate and Hazardous Waste

Leachate, the rainwater which becomes contaminated as it seeps through a coal pile, mine tailings or landfill can pose a significant threat to aquifers, rivers, lakes and watersheds if left untreated. Pall's new generation of filtration and separations systems remove micro-organisms, chemicals, metals, arsenides and radioactive particles. These filtration systems transform wastewater into a reusable resource, by purifying landfill leachate for reuse. These systems also reclaim effluent from municipal wastewater plants.

The most economical and environmentally friendly way to treat landfill leachate is to reduce its volume by 75-80% using reverse osmosis, and then return the concentrate to the landfill through controlled reinjection. Until now, reverse osmosis and other membrane filters were hampered by quick scaling and fouling, which resulted in poor efficiency and short membrane life. Pall patented Reverse Osmosis Disc Tube™ (DT) technology offers significantly improved performance through its flow path design, the use of high pressure in the vessel, and a self-cleaning system.

Suspended solids carried in the feedwater cannot easily settle out on the membrane surface due to the short, controlled and turbulent flow system. The hydraulics result in a high flow velocity across the membranes at minimum feed flow. An open channel over the membrane surfaces ensures optimal membrane cleaning from fouling deposits. Occasional use of the built-in cleaning system typically will return and restore the membrane to peak capacity in two hours or less.

The Pall DT system offers many advantages. It will process highly contaminated feedwater without the need for extensive preconditioning. For processing landfill leachate, only a coarse sand filter is used to pre-treat influent waters, which may contain 10.000 ppm dissolved solids, and 5.000 ppm suspended solids. (By comparison, river water may contain 5 to 10 ppm suspended solids.) Other advantages are a large contaminant rejection rate and a high water recovery rate. The system is capable of recovering more than 90% of leachate volume as clean water (permeate). Remaining leachate may be disposed of in a Municipal Solid Waste (MSW) landfill (through recirculation) or processed further. Methods for additional processing include solidification and evaporation.

The patented DT module removes organic and inorganic pollutants, including heavy metals. Even hazardous substances are reduced to the low levels required by the most stringent regulatory criteria. Traditional reverse osmosis systems operate between 400 and 800 psi, so they are limited to treating leachate with maximum TDS of 40.000 to 50.000 ppm (4%-5% total solids content). The DT system can operate at pressures up to 3.000 psi, so it can handle TDS content of about 200.000 ppm (20% solids content).

When the BFI landfill site in Morgantown PA chose to outsource, Pall Rochem's filtration system gave improved flexibility and economic performance, reduced environmental impact and treated the leachate to drinking water quality. The DT system's capabilities were put to the test when it was used to treat leachate from a contaminated section of the Central Landfill in Johnson, Rhode Island.

The Pall DT system is now in service at 125 leachate sites in Europe and the United States. At the largest site in Ihlenberg, Germany, the system treats 750.000 gallons of leachate per day. In the past, membrane separation processes have been used as a secondary or polishing step in treating landfill leachate. With Pall's innovative DT technology, tertiary quality effluent can now be considered a single-step treatment option.