Degradation and conversion of organics in a continuous HNAD system treating incineration leachate

Abstract

The anaerobically treated incineration leachate contains high-strength ammonium and refractory organics, which is advisable to be biologically treated via heterotrophic nitrification-aerobic denitrification (HNAD) process. However, it is still unknown how the organics in leachate wastewater are degraded and utilized during HNAD process. In this study, a continuous HNAD based moving bed biofilm reactor was operated with actual anaerobically treated incineration leachate as the influent. During stable operation, besides superior nitrogen removal efficiency (88.73 %), the organics were effectively removed with a high average COD removal efficiency (85.05 %). Organic fluorescent spectra showed humic substances were significantly removed, with the intensities of the humic peak and fulvic peak decreasing by 96.59 % and 91.93 %, respectively. Furthermore, most of the dissolved organic matter within varying ranges of molecular weight could be degraded during the HNAD process, during which the benzene-based substances were removed and the medium-long chain alkanes (C > 12) were generated. Through carbon balance analysis, assimilation metabolism accounted for 44.75 % of the conversed organic carbon. According to the decrease in respiration inhibition rate from 52.21 % to 25.36 %, the toxicity of leachate wastewater was strongly reduced after treatment by HNAD process. Halomonas (43.72 %) was the dominant HNAD bacteria, and relative abundances of genes associated with refractory organics degradation were increased during the treatment of incineration leachate. These results provide new insights into carbon metabolism during HNAD process for treating wastewater with complex organics.