Functional gene groups controlling nitrogen transformation rates in a groundwater-restoring denitrification biofilter under hydraulic retention time constraints

A denitrification biofilter (DB), developed for the remediation of groundwater in this study, operated with increased removal efficiencies of total nitrogen (TN, 35.1-93.2%), nitrate (NO3--N, 61.6-97.7%), and chemical oxygen demand (COD, 43.2-82.4%) as hydraulic retention time (HRT) increased from 0.5 h to 4.0 h. Declined denitrification rates of NO3--N (123.1-24.9g/(m(3) h)), NO2--N (52.6-1.5 g/(m(3) h)), NO (22.9-3.2 mg/(m(3) h)) and N2O (64.8-11.1 g/(m(3) h)), were observed with increased HRTs from 0.5 h to 4.0 h. Gene abundances (total bacterial 16S rRNA, anaerobic ammonium oxidation (anammox) bacterial 16S rRNA, archaeal 16S rRNA, narG, napA, nirK, nirS, qnorB and nosZ) were estimated and their relative importance in denitrification rates were quantified based on path analyses. As a result, the ratio (napA + narG)/(nirK + nirS), followed by nosZ/bacterial 16S rRNA were the main drivers for the transformation of NO3--N and NO2--N, while (napA+narG)/(nirK + nirS), followed by nosZ/narG dominated the accumulation of NO and N2O. In the content of environmental changes, this study suggests that gene associations integrating denitrification rates and recent environmental changes are valuable index reflecting variations in denitrification processes in groundwater restoration. (C) 2015 Elsevier B.V. All rights reserved.National Natural Science Foundation of China [51179001]; National Key Technology R&D Program of China [2012BAJ25B01]; Jilin Province Transportation Science and Technology Projects [2011-1-7]; Collaborative Innovation Center for Regional Environmental QualitySCI(E)EIARTICLEjiguodong@pku.edu.cn45-528