https://doi.org/10.15255/KUI.2004.012
Published: Kem. Ind. 54 (11) (2005) 461–468
Paper reference number: KUI-12/2004
Paper type: Original scientific paper
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Treatment of Leachate Waters from Landfill Using Activated Carbon and Natural Zeolite from the Krapina Region

A. Farkaš, M. Rožić, K. Košutić and A. Pisarović

Abstract

The paper investigates the possibility of purifying leachate wastewaters from the waste dump Jakuševec, Zagreb, with natural zeolite clinoptilolite and activated carbon NORIT 0.8 SUPRA. Zeolite tuff with predominant content of the zeolite mineral clinoptilolite from the Krapina region, Croatia, was used in the trials. The results of testing leachate waters from collection reservoirs during a period of six months revealed a varying concentration of ammonium ions and other compounds that, according to the Croatian by-laws on marginal values for indicators of hazardous and other substances in wastewaters (Official Gazette 40/99 and 6/2001), exceed the maximum allowable concentrations in wastewaters. Concentrations of organic and inorganic pollutants in wastewater varied in dependence on water inflow and on meteorological conditions. Table 1 provides a comparison of the range of concentrations of the studied parameters of leakage water samples. Concentration of NH4 + ions in the examined leachate water sample was 820 mg L–1, that of K+ ions 801 mg L–1, Ca2+ ions 128 mg L–1, total organic carbon 1033 mg L–1, chemical oxygen demand 1940 mg L–1 while BOD5 value was 200 mg L–1. Figure 1 presents the exchange of ammonium ions from the studied sample of leachate water on zeolite after 15 and 30 min, and after 1, 2, 4 and 6 h of equilibration by the static procedure. After 6 h of equilibration, only 4.2 mg NH4 +/g zeolite was exchanged on zeolite, while 17.70 mg NH4 +/g zeolite was exchanged from the model solution of ammonium ions of 800 mg L–1 concentration (Figs. 2 and 3). Thus, about 75 % less ammonium ions was exchanged in the leachate water sample. Upon treatment of leachate water with w=0.04 % activated carbon, 5.60 mg NH4 +/g zeolite was exchanged on zeolite after 6 hours of equilibration (Fig. 1). Activated carbon enhanced the exchange of ammonium ions only by ca. 6.5 %. Further addition of activated carbon had no effect on the mass of ammonium ions exchanged. Increased mass of activated carbon reduced the content of total organic carbon in leachate water up to ca. w = 2.50 % of added activated carbon. Further increase of the mass of activated carbon in water did not reduce the organic carbon content to any considerable extent. Upon wastewater treatment with w = 2.50 % activated carbon, the value of total organic carbon dropped from 1033 to 510 mg L–1, and after treatment with w = 5.00 % activated carbon to 460 mg L–1 (Table 2). Some of the organic compounds that were not adsorbed onto activated carbon, most probably organic compounds of natural origin, reduced appreciably the exchange of ammonium ions through adsorption onto zeolite. 2.00 g zeolite adsorbed approximately 11 mg of total organic carbon/g zeolite, and 5.00 g zeolite about 7.2 mg of total organic carbon/g zeolite (Table 2). Wastewaters contain rather high concentrations of K+ ions, which due to high selectivity of clinoptilolite for K+ ions (clinoptilolite selectivity toward alkaline and alkaline-earth cations decreases in the sequence: K+ > NH4 + > Ca2+ > Na+ > Mg2+) may undermine the efficiency of the exchange of ammonium ions on zeolite. Therefore, the influence of K+ ions on the exchange of ammonium ions was investigated as well. Besides potassium ions, the effect of calcium ions was also investigated. Potassium ions of 800 mg L–1 concentration reduced the exchange of ammonium ions from the solution of 800 mg L–1NH4 + concentration by ca. 32 %, and calcium ions of 100 mg L–1 concentration by ca. 2.8 % (Figures 2 and 3). Figure 5 displays the curve of the NH4 + ions breakthrough from leachate water when passing through the pre-column filled with silica sand and activated carbon and the column filled with zeolite. The columns are represented schematically in Figure 4. Breakthrough of ammonium ions occurred after passage of 7 litres of leachate water. The total exchange capacity of ammonium ions for 10 L wastewater passed was 6.90 mg NH4 +/g zeolite, while the breakthrough capacity was 3.98 mg NH4 +/g zeolite. Breakthrough of ammonium ions from model water of ammonium ions occurred after 23 litres of water had been passed. The total exchange capacity of ammonium ions for 24 L model water was 13.65 mg NH4 +/g zeolite, while the breakthrough capacity was 13.1 mg NH4 +/g zeolite. The results indicate that the characteristics of wastewater have a strong influence on the efficiency of zeolite as a cation exchanger. As there are very few papers on the influence of organic compounds on the properties of zeolites as cation exchangers, further research is necessary in this area as well as in the area of the potential use of zeolite in combination with other techniques in order to improve the removal of complex pollution from leachate waters.

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Keywords

leachate water, landfill, clinoptilolite, activated carbon