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4/2/2019 Effect of C/N Ratio on the Removal of Nitrogen and Microbial Characteristics in the Water Saturated Denitrifying Section of a Two-Stage C... <br /> jA looca�i of <br /> MDPT <br /> E <br /> Int J Environ Res Public Health. 2018 Jul; 15(7): 1469. PMCID: PMC6069465 <br /> Published online 2018 Jul 12. doi: 10.3390/ijerph15071469 PMID: 30002283 <br /> Effect of C/N Ratio on the Removal of Nitrogen and Microbial <br /> Characteristics in the Water Saturated Denitrifying Section of a Two- <br /> Stage Constructed Rapid Infiltration System <br /> Qinglin Fang,' Wenlai Xu,1,2,3,*Gonghan Xia,2 and Zhicheng Pana <br /> 'State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of <br /> Technology, Chengdu 610059, China; xiaofang20111009@126.com <br /> 2State Environmental Protection Key Laboratory of Synergetic Control and Joint Remediation for Soil&Water <br /> Pollution, Chengdu University of Technology, Chengdu 610059, China; txgsfy-@163.com <br /> 31-laitian Water Grp Co Ltd., Chengdu 610059, China; pan12487616@126.com <br /> Correspondence:xuwenlai1983@163.com; Tel.: +86-135-510-29646 <br /> Received 2018 May 27; Accepted 2018 Jul 7. <br /> Copyright©2018 by the authors. <br /> Licensee MDPT, Basel, Switzerland. This article is an open access article distributed under the terms and <br /> conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). <br /> Abstract <br /> The aim of this study was to improve the removal of nitrogen pollutants from artificial sewage by a <br /> modeled two-stage constructed rapid infiltration (CRI) system. The C/N ratio of the second stage <br /> influent was elevated by addition of glucose. When the C/N ratio was increased to 5, the mean removal <br /> efficiency of total nitrogen (TN)reached up to 75.4%. Under this condition, the number of denitrifying <br /> bacteria in the permanently submerged denitrifying section(the second stage) was 22 times higher than <br /> that in the control experiment without added glucose. Elevation of the C/N ratio resulted in lower <br /> concentrations of nitrate and TN in the second stage effluent,without impairment of chemical oxygen <br /> demand removal. The concentration of nitrate and TN in effluent decreased as the abundance of <br /> denitrifying bacteria increased. Moreover, the bacterial biofilms that had formed in the sand of the <br /> second stage container were analyzed. The secretion of extracellular polymeric substances, a major <br /> constituent of biofilms,was enhanced as a result of the elevated C/N ratio,which lead to the improved <br /> protection of the bacteria and enhanced the removal of pollutants. <br /> Keywords: two-stage constructed rapid infiltration system, water-saturated denitrifying section, C/N <br /> ratio, denitrifying bacteria, extracellular polymeric substances <br /> 1 . Introduction <br /> The constructed rapid infiltration system (CRI) is a novel ecologically friendly technology for sewage <br /> treatment based on a modification of conventional sewage treatment [1]. The core of a CRI is a mixture <br /> of river sand and gravel that replaces conventional soil layers as the main infiltration media, which <br /> improves hydraulic load [2]. In addition, a dry-wet cycling of water feeding and draining is applied, <br /> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6069465/ 1/18 <br />