Leachate management is fast becoming one of the most costly and troublesome components of landfill operations. Leachate is treated and disposed of in many different ways, depending on site conditions, discharge limits, costs, or other factors. Some of the more common approaches include on-site management through recirculation to the landfill, evaporation, discharge to sewer or hauling untreated to a nearby wastewater treatment plant (either treated or untreated), or treated and directly discharged to surface waters.
In the first attempt to characterize what approaches are used from the above scenarios in the United States (U.S.), the Solid Waste Association of North America (SWANA) leachate management subcommittee surveyed its members on leachate treatment and disposal options. A total of 184 responses from the U.S. and a few other countries were received. Almost half (47.3%) discharged untreated leachate to a Publically Owned Treatment Works (POTW) split almost evenly between trucking and direct discharge to a sewer system through gravity or force main pumping. Approximately 12.5% discharged treated wastewater to a POTW. Landfills treated about 18% entirely on-site, mostly through recirculation, while 22.3% reported that they managed leachate by other means, including treatment and direct discharge. Facilities that discharged reported limitations that typically include flow, biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonia, Total Kjeldahl Nitrogen, Total Nitrogen, and pH; while a third of the respondents who had limitations indicated that there were other effluent parameters that needed to be met. A more comprehensive analysis is currently being completed for other parameters, including spatial distribution, and will be available from SWANA in the near future.
In general, there were some interesting geographical approaches based on anecdotal information from this survey and from personal experience. Nutrient limitations were most stringent for total nitrogen when discharging to nutrient (i.e., nitrogen and phosphorous) sensitive locales, including the Chesapeake Bay, while arsenic appeared as a limitation in many Florida locales. For landfills that discharge into small to medium size wastewater treatment plants with ultraviolet disinfection, we found that there are limitations on UV transmittance that cause a POTW to incur an effluent below 65% transmittance, failing to meet disinfection requirements. The absorbance is typically caused by organic matter (e.g., humic and fulvic acids) in leachate, as documented by various EREF and other studies.
Treatment technologies for off-site disposal frequently encountered ranged from natural based systems (lagoons and land disposal/constructed wetlands) to mechanical systems, such as sequencing bioreactors (SBR), membrane bioreactors (MBR) and moving bed biofilm reactors (MBBR). Effluent filtration as a separate step is less common. On-site disposal, where treatment technologies were implemented, include chemical precipitation and settling, while some landfills reported reverse osmosis treatment for discharge with the reject flows, which may be as much as 30 to 40% , discharged back to the landfill.
Other questions remain unanswered and will be the subject of future analyses, including operation and maintenance issues, capital and O&M costs, labor staffing, and troublesome compliance issues.
Ivan Cooper, PE, BCEE, has served as the National Practice Leader at Civil & Environmental Consultants since 2012.