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Two-stage treatment of a landfill leachate: aerobic biostabilization with lime-magnesium polishing Wong, Phillip Thomas


In the biostabilization phase, a BOD₅:N:P loading of 100:3.2:1.1 was found to be "adequate" for treatment, while the standard nutrient loading of 100:5:1 was found to be "excessive". This was evident by the much higher nitrite-nitrate concentration in the effluent of the BOD₅:N:P = 100:5:1 reactor. Organic removal by the first stage units was excellent. BOD₅ and COD removals of at least 99.4 and 96.4 percent, respectively, were achieved under all conditions investigated, except for the two units close to washout conditions (the 5-day sludge age units at 10° and 5°C). Temperature and sludge age also had minimal effects on the removal of metals, except under the two conditions mentioned above; removals were greater than 90 percent, for most of the metals monitored. The reactors only reduced magnesium concentrations by 32.5 to 52.7 percent, mainly because the mixed liquor pH's (about 8.5) were not high enough for magnesium precipitation as magnesium hydroxide. For the lime-magnesium polishing step, samples were dosed with lime to pH levels of 10.0, 10.7, and 11.4. Magnesium doses of 0, 10, 20, 35 and 50 mg/L were then added to the samples at each pH level. In general, removals of impurities were not enhanced significantly by these magnesium additions. This was due, in part, to the initial low concentrations of contaminants; in addition, there already existed greater than 20 mg/L of magnesium in the samples. Aerobic biostabilization, at a sludge age greater than 15 days, at BOD₅:N:P = 100:3.2:1.1, and liquid temperatures of at least 3°C, followed by lime precipitation (to pH greater than or equal to 10.0), is capable of reducing most contaminants of a medium strength leachate (BOD₅ = 8090 mg/L) to levels below local (Province of British Columbia) pollution control objectives.

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