TABLE小2 Typical data on the composition of leachate from new and mature landfills Value, mg/L- New landfill (less than 2 years) Mature landfill (greater the BODs(5-day biochemical oxygen demand) 2,00030,000 10,000 TOC(total organic carbon) 150020,0o CoD(chemical oxygen demand) 3,00060,000 Total suspended solids 200-2,000 100-400 Organic nitrogen 10-800 Nitrate 5-40 Total phosphorus Ortho phosphorus 1,00010.000 3000 200-1,00 4.57.5 Total hardness as Caco3 300-10.000 Calcium 2003,000 m 100400 Magnesium 50-1.500 50200 Potassium 2001,000 300 50400 Sodium 2002500 00 100-200 2003,000 500 Sulfate 60-1,000 300 2050 Total iron 50-1,200 60 20200 Developed from Refs. 2, 8, 9, 11, 39, 46. bExcept pH, which has no units. ative range of values. Higher maximum values have been reporte pical values for new landfills will vary with the metabolic state of the landfil Variations in Leachate Composition. Note that the chemical composition of leachate will vary greatly depending on the age of landfill and the events preceding the time of sampling For example, if a leachate sample lected during the acid phase of decomposition, the ph value will be low and the concentrations of BODs, TOC, COD, nutrients, and heavy metals will be high If, on the other hand, a leachate sample is collected during the methane fermentation phase, the pH will be m the range from 6.5 to 7.5, and the BODs, TOC, COD, and nutrient concentration values will be significantly lower Similarly the concentrations of heavy metals will be lower because most metals are less soluble at neutral pH values. The pH of the leachate will depend not only on the concentration of the acids that are resent but also on the partial pressure of the COz in the landfill gas that is m contact with the leachate The biodegradabil ity of the leachate will vary with time. Changes in the biodegradability of the leachate n be monitored by checking the BOD/COD ratio. Initially, the ratios will be in the range of 0.5 or greater. Ratios in the range of 0. 4 to 0.6 are taken as an indication that the organic matter in the leachate is readily biodegradable. In mature landfills, the BODs/COd ratio is often in the range of 0.05 to 0.2 The ratio drops because leachate from mature landfills typically contains humic and fulvic acids, which are not readily biodegradable As a result of the variability in leachate characteristics, the design of leachate treatment systems is omplicated. For example, a treatment plant designed to treat a leachate with the characteristics reported for a new landfill would be quite different from one designed to treat the leachate from a mature landfill, The problem of Interpreting the analytical results is complicated further by the fact that the leachate that is being generated at any point in time is a mixture of leachate derived from solid waste of different ages Water balance and Leachate generation In landfills The potential for the formation of leachate can be assessed by preparing a water balance on the landfill The water balance involves summing the amounts of water entering the landfill and subtracting the amounts of water consumed in chemical reactions and the quantity leaving as water vapor. The potential leachate quantity is the quantity of water in excess of the moisture-holding capacity of the landfill material Description of Water Balance Components for a Landfill Cell The principal sources include the9 Variations in Leachate Composition. Note that the chemical composition of leachate will vary greatly depending on the age of landfill and the events preceding the time of sampling. For example, if a leachate sample is collected during the acid phase of decomposition, the pH value will be low and the concentrations of BOD5, TOC, COD, nutrients, and heavy metals will be high. If, on the other hand, a leachate sample is collected during the methane fermentation phase, the pH will be m the range from 6.5 to 7.5, and the BOD5, TOC, COD, and nutrient concentration values will be significantly lower. Similarly the concentrations of heavy metals will be lower because most metals are less soluble at neutral pH values. The pH of the leachate will depend not only on the concentration of the acids that are present but also on the partial pressure of the CO2 in the landfill gas that is m contact with the leachate. The biodegradability of the leachate will vary with time. Changes in the biodegradability of the leachate can be monitored by checking the BOD5/COD ratio. Initially, the ratios will be in the range of 0.5 or greater. Ratios in the range of 0.4 to 0.6 are taken as an indication that the organic matter in the leachate is readily biodegradable. In mature landfills, the BOD5/COD ratio is often in the range of 0.05 to 0.2. The ratio drops because leachate from mature landfills typically contains humic and fulvic acids, which are not readily biodegradable. As a result of the variability in leachate characteristics, the design of leachate treatment systems is complicated. For example, a treatment plant designed to treat a leachate with the characteristics reported for a new landfill would be quite different from one designed to treat the leachate from a mature landfill, The problem of Interpreting the analytical results is complicated further by the fact that the leachate that is being generated at any point in time is a mixture of leachate derived from solid waste of different ages. Water Balance and Leachate Generation In Landfills The potential for the formation of leachate can be assessed by preparing a water balance on the landfill. The water balance involves summing the amounts of water entering the landfill and subtracting the amounts of water consumed in chemical reactions and the quantity leaving as water vapor. The potential leachate quantity is the quantity of water in excess of the moisture-holding capacity of the landfill material. Description of Water Balance Components for a Landfill Cell. The principal sources include the 15-2