Combined Treatment of Leachate from Sanitary Landfill and Municipal Wastewater by Activated Sludge

A. Del Borghi, L. Binaghi, A. Converti and M. Del Borghi

Abstract
Two leachates from sanitary landfill, characterized by different biodegradability, were mixed with municipal wastewater in different proportions and aerobically treated by activated sludge. The overall removals of chemical oxygen demand (COD) and ammonia as well as the fraction of hardly-biodegradable substances were investigated to select the best operating conditions for the simultaneous removal of these pollutants. Preliminary batch tests were carried out to point out the optimum leachate/mixture volume ratio (ΨL/M) consistent with the biological treatment (0.10). Using this proportion, the performance of a bench-scale activated sludge system was checked under continuous working conditions at different hydraulic retention times (τHRTs), namely 2, 4 and 8 h. The removal yields of COD and ammonia (YCOD and YNH 4+) were studied either during the start-up or after reaching stationary conditions. The results obtained under steady-state conditions demonstrated that the organic substances were effectively removed (YCOD > 0.65) at τHRT = 8 h, while the best results were obtained for ammonia at τHRT = 2 h. Sludges produced by the continuous system were then used in batch activity tests to check the degradation improvement consequent to their acclimation to leachate/mixture volume ratios in the range 0.05–0.2. The best performance was obtained with sludge produced at ΨL/M ≤ 0.15 and τHRT = 4 h, that ensured, for both COD and NH4+, removal yields of Y = 0.67–0.76 and removal rates of r = 103–130 and 35–63 mg l–1 h–1, respectively.

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Keywords
Activated sludges, COD and ammonia removals, aerobic treatment, kinetics, leachate from sanitary landfill