Enhancing nitrogen removal in mature landfill leachate by mixed microalgae through elimination of inhibiting factors

Nitrogen removal from landfill leachate (LL) using microalgae is a promising method and can realize CO₂ mitigation. But the performances are usually inhibited by high chromaticity, high free ammonia (FAN) and some complex macro molecular organic matter (MOM) in the LL. To achieve efficient nitrogen removal from LL, this study firstly pretreated the mature LL with ozone, decolorizer and activated sludge (AS) respectively, and then inoculated with mixed microalgae. The results showed that the synergistic effect of ozonation and microalgae was the best among the three, with 99.7% ammonia removal, 0.77 g/L (dry weight) microalgae biomass, and a maximum growth rate of 160 mg/L/d. Ozonation pretreatment significantly reduced the chromaticity and macromolecular organic matter of LL, with the chromaticity reduced from 2225 to 225 times and the 3D fluorescence intensity representing MOM reduced from 4089 a.u. to 986.1 a.u.. And it was found that the mixed microalgae grown after pretreatment by three different methods all were mostly Chlorella and very few Microcystis, and the density of microalgal populations (number of cells per unit volume) after ozonation was up to 10,650 cells/μL. This work provides a feasible and an economical way to remove ammonia nitrogen (NH+ 4-N) from landfill leachate.