Landfill leachate nutrient removal using intermittent aeration

Abstract

The aim of this study was to investigate the biological removal of nitrogen and phosphorus from an intermediate age leachate diluted with domestic wastewater. A sequencing batch reactor (SBR) with alternate aeration was operated under aerobic (Ox) and anoxic (Ax) phases of different durations (Ox 3 or 6 h and Ax 1, 2 or 3 h), for a total cycle period of 24 or 48 h. Crude glycerol from biodiesel production was used as external carbon source to improve denitrification. Leachate mixture of 15 % v/v in municipal wastewater was found to be the optimum concentration at which no adverse effects were observed. Experiments without the use of external carbon source resulted in a low denitrification potential and a strong NO3--N and NO2--N accumulation. By contrast, denitrification was effectively achieved by using crude glycerol at the beginning of the anoxic phase, where a sCOD/NOx-N ratio of 5 was created. Comparing the different operation strategies applied, 6 h aeration and 2 h anoxic phase at the 48 h-cycle period scheme resulted in the greatest TKN, NH4+-N, NO3--N and NO2--N removal efficiencies, estimated as 75.9, 75.7, 99.9 and 99.9 %, respectively. For efficient phosphorus removal, sufficient time for the reduction of nitrate concentration (below 5 mg/L NO3--N) and the highest PO43--P release at the non-aeration stage was needed in order to favor a poly-P enriched biomass. In conclusion, an intermittently aerated SBR working at various aerobic/anoxic duration phases was used to treat a mixture of wastewater and semi-mature landfill leachate. Glycerol added as external carbon source was necessary to complete denitrification. Enhanced phosphorus removal was achieved at sufficient anoxic phase duration (2-3 h).