Development of a SBR bench-scale to optimize the partial nitrification process in landfill laechate treatment and its possible application in Vietnam.

Landfill leachate treatment is a major issue in many developing countries including Vietnam. Leachates are characterised by very high nitrogen concentrations, especially ammonium, needing an appropriate treatment technology. Conventional treatment technology has some drawbacks: mostly its high costs and problems to meet discharged standards requirements. This study applies a more recent approach for nitrogen removal, which is known as partial nitrification, by using a sequencing batch reactor (Bernet et al., 2005) technique. For the first step, the experiments were done with Belgian leachates. Based on mathematical models derived from generally accepted ASM Model, specific growth rates of biomass (μ(T)) found is 0.48 (d-1), 0.39 (d-1), 1.56 (d-1) and 0.82 (d-1) for ammonium nitrifiers, nitrite nitrifiers, nitrite denitrifiers and nitrate denitrifiers respectively. Concentration of the active part of these four kinds of bacteria is estimated of 22.3 mg/L, 12.4 mg/L, 464 mg/L and 12.3 mg/L. Maintaining dissolved Oxygen concentrations in the range 0.8 to 2.1 mgO2/L, with typical value around 1.5 mg/L, the system yields nitrite accumulation (preliminary step of partial nitrification/denitrification). SBR cycle was changed from 4 hours/4 hours of aeration/mixing in turn to 5 hours/3 hours and then 6 hours/2 hours. The last cycle has shown the best partial nitrification capacity of the SBR (a nitrite accumulation of 89 %) but not yet yielding a 50/50 ratio of ammonium/nitrite at the end of nitrification process. However, a well managed SHARON process will be processed in the next step of the study to obtain higher nitrogen removal efficiency and the expected ammonium/nitrite ratio. It has also been shown that free ammoniac concentration affects the nitrite/(nitrite + nitrate) ratio at the end of aeration phase.