A removal mechanism for organics and nitrogen in treating leachate using a semi-aerobic aged refuse biofilter

A removing mechanism for organics and nitrogen using a semi-aerobic aged refuse biofilter (SAARB) was evaluated based on the space structure, the aged refuse conformation and characteristics, as well as the degradation theories of organic matter and nitrogen-based substances, which could provide a fundamental theory to more effectively treat organic matter and nitrogen-based pollutants in leachate. The experimental results indicated that the average removal rate of chemical oxygen demand and total nitrogen reached 96.61 and 95.46%, respectively. The aerobic–anoxic–anaerobic zones appeared alternately in both the space structure and the granule conformation inside of the SAARB, which promoted various physical, chemical and biological reactions. Most biodegradable organic matter was converted to CO2 and CH4. The average CO2 release rate was 1.567 L/(h m2) in the winter and 1.467 L/(h m2) in the summer during a single-period experiment. The average CH4 release rate was 0.303 L/(h m2) in the summer; however, it could not be detected in the winter. Moreover, the nitrogen-based pollutants were mostly converted to N2 and N2O through denitrification. Some of the refractory organic matter and nitrogen-based pollutants were likely adsorbed by the aged refuse and biodegraded more slowly. The adsorption rate of biologically degradable matter (BDM) was 0.624 g/(kg d) during the first 40 weeks and the largest absorbance of total nitrogen (TN) was about 7.0 g/kg during this experiment. Therefore, the SAARB can maintain stable and highly efficient environment for removing organic matter and nitrogen-based pollutants.

► The SAARB could simultaneously remove nitrogen and organic matter.
► The average removal rate of COD and TN reached 96.61% and 95.46% respectively.
► The aerobic-anoxic-anaerobic zones appeared alternately in the SAARB.
► The biological reactions played a dominant role in the removal of pollutants.