Abstract
The landfill is the most common final destination of the municipal solid wastes. Therefore, the landfill leachate is a serious environmental priority. The characteristics of the leachate are mainly related to the high ammonia concentrations, the low bioavailable carbon, the heavy metals and the inorganic salts. Consequently, the biological activated sludge treatment of landfill leachate is considered a low efficiency process in terms of nitrogen removal and of aeration transfer capacity and it is characterized by elevated stripping of ammonia. For these reasons, best operative practices have to be performed for the optimization of the removals and for the energy savings when, as in this case, the biological process is applied. First of all, the increment of the soluble free ammonia (up to NH3 of 13.9 mg/L) coupled with the dissolved oxygen limiting conditions (<1 mg/L) caused the inhibition effect of the nitrite oxidizing bacteria. Therefore the kinetic of the nitrogen removal is developed via nitrite up to 0.160 kgNH4-N/kgMLVSS/d. The nitritation process permitted to treat a specific nitrogen load up to 0.8 kgTN/m3/d. Moreover, the installation of elastomeric polyethylene diffusers determined an increment both of 53 % for the standard oxygen transfer rate (%) and of 40 % for the standard aeration efficiency (kgO2/kWh). The kinetic improvement together with the optimized aeration permitted to transform from 950±323 mgNH4-N/l in the influent to 29± 20 mgNH4-N/l in the effluent. The specific biological energy consumption was 2 kWh/m3 with a global energy saving of 50 %. In terms of the gases emission, the ammonia stripping phenomenon was quantified. The NH4-N load in the air resulted negligible and equal to 0.006 % of the total ammonia nitrified load. The increment of the removed nitrogen load in the liquid phase reduced the stripped ammonia amount.
