Denitrification performance and characteristics of untreated corncob for enhanced nitrogen removal of municipal sewage with low C/N ratio.

ABSTRACT

Unpretreated corncob was applied in denitrification bio-filter (DNBF) and anoxic tank of AAO system, respectively, to treat sewage with low C/N ratio, and both two approaches achieved good denitrification performance. Although shorter HRT could effectively decrease effluent chroma and COD of corncob-DNBF, nitrogen removal efficiency declined unexpectedly. Higher internal reflux ratio was beneficial for corncob-AAO without damage to anoxic environment for denitrification, while there was no risk of effluent chroma and excessive COD. Different supplement modes could realize same denitrification effect with distinct advantages, which were higher specific denitrification rate and biomass amount, respectively. The latter mode, applying corncob at secondary treatment, was preferable for its operational stability and convenience. Stoichiometry analysis indicated the unit COD demand of AAO decreased from 5.70 to 5.04 g COD/g N after adding corncob, and the oxygen demand (or energy consumption of aeration) decreased as well. The dominant substrates decomposer in corncob-AAO altered to Kouleothrix (affiliated to phylum Chloroflexi), and the main denitrifying bacteria were unclassified_f__Methylophilaceae and Azospira. Accordingly, functional enzymes for degrading glucan, xylan and lignin and processing denitrification showed satisfying abundance in the integrated system, especially in the newly formed biofilm.