Comparison of different physico-chemical methods for the removal of toxicants from landfill leachate

Our work was focused on investigation of different treatment procedures for the removal of toxic fractions from a landfill leachate, because sometimes the existing treatment in biological sequencing batch reactor (SBR) is not efficient enough, leading to a hazardous environmental impact of the present persistent and toxic compounds. The efficiency of the procedures used was monitored by chemical analyses and two toxicity tests (activated sludge and Vibrio fischeri). The existing SBR (HRT = 1.9 days) removed 46-78% of COD and 96-73% of NH4+-N. Experiments were conducted with three landfill leachate samples expressing significant difference in concentrations of pollutants and with low BOD5/COD ratio (0.06/0.01/0.03). The applied methods were air stripping, adsorption to activated carbon and zeolite clinoptilolite and Fenton oxidation. Air stripping at pH 11 was a viable treatment option for the removal of ammonia nitrogen (up to 94%) and reduction of toxicity to microorganisms. In the adsorption experiments in batch system with different concentration of PAC the most effective was the highest addition (50.0 g L−1) where 63-92% of COD was removed followed by significant reduction in toxicity to V. fischeri. In the column experiments with clinoptilolite 45/93/100% of NH4+-N as well as 25/32/39% of COD removal was attained. The removal efficiency for metals followed the sequence Cr > Zn > Cd > Ni. The procedure with zeolite was the second most efficient one regarding reduction of toxicity to both organisms. Fenton oxidation at molar ratio Fe2+:H2O2 = 1.0:10.0 assured 70-85% removal of COD but it only slightly reduced the toxicity.