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Treatment of wastes and leachate evolved in landfills is today an imperative due to rigorous environmental protection legislation. In this work, biodegradation of the organic fraction in tobacco-waste leachate was studied. Experiments were carried out in a batch reactor at initial concentration of activated sludge of 3.03 g dm-3 and different initial concentrations of organic matter in leachate, expressed as COD, which ranged from 0.5 to 3.0 g dm-3. The working volume of the reactor (Fig. 1) was 7 dm3 within the cylindrical porous liner and it was filled with the suspension of leachate and activated sludge. The liner was designed such that it did not allow activated sludge to pass through. Continuous up-flow aeration was provided by a membrane pump. The temperature during the biodegradation process was 23 ± 2 °C. Dissolved oxygen, pH and temperature in reactor were monitored continuously by probes connected to a remote meter. Toxicity of leachate was performed by toxicity test using marine bacteria Vibrio fischeri before starting with the biodegradation in the batch reactor. The obtained results showed that effective concentration of leachate is EC50 = 1.6 g dm-3 and toxicity impact index is TII50=9.99, meaning that untreated leachate must not be discharged into the environment before treatment. The results of the biodegradation process of leachate in batch reactor are presented in Table 1 and Fig. 2. The ratio γXv/γX was almost constant throughout the experiments and ranged from 0.69 do 0.73. This implies that the concentration of biomass remained unchanged during the experiments, and average yield was 5.26 %. The important kinetic and stoichiometric parameters required for performance of the biological removal process, namely the Y, Ks, kd, and μmax were calculated from the batch experiments (Table 2). The experimental results of the influence of initial substrate concentrations on substrate degradation rate, and influence of initial substrate concentrations on biomass growth rate in comparison with Monod model are presented in Figs. 3 and 4. These results suggest that selected model describes well the biodegradation process of leachate in batch reactor. Microscopic examination of activated sludge showed that flocs were healthy and compact, with simultaneous formation of young flocs (Table 3, Figs. 5a and 5b). Figure 6 presents the decrease in organic matter in the leachate and increase in activated sludge concentration within two days of biodegradation during which activated sludge showed strong ability to degrade organic matter, while process efficiency (Fig. 7) was approximately 80.3 %. [ABSTRACT FROM AUTHOR]