Effect of C/N Ratio on the Removal of Nitrogen and Microbial Characteristics in the Water Saturated Denitrifying Section of a Two-Stage Constructed Rapid Infiltration System

Qinglin Fang,Wenlai Xu,Gonghan Xia,Zhicheng Pan

doi:10.3390/ijerph15071469

Abstract

The aim of this study was to improve the removal of nitrogen pollutants from artificial sewage by a modeled two-stage constructed rapid infiltration (CRI) system. The C/N ratio of the second stage influent was elevated by addition of glucose. When the C/N ratio was increased to 5, the mean removal efficiency of total nitrogen (TN) reached up to 75.4%. Under this condition, the number of denitrifying bacteria in the permanently submerged denitrifying section (the second stage) was 22 times higher than that in the control experiment without added glucose. Elevation of the C/N ratio resulted in lower concentrations of nitrate and TN in the second stage effluent, without impairment of chemical oxygen demand removal. The concentration of nitrate and TN in effluent decreased as the abundance of denitrifying bacteria increased. Moreover, the bacterial biofilms that had formed in the sand of the second stage container were analyzed. The secretion of extracellular polymeric substances, a major constituent of biofilms, was enhanced as a result of the elevated C/N ratio, which lead to the improved protection of the bacteria and enhanced the removal of pollutants.

Highlights

The constructed rapid infiltration system (CRI) is a novel ecologically friendly technology for sewage treatment based on a modification of conventional sewage treatment [1]
The concentrations and removal efficiencies of ammonium in the effluent of the second stage over time was determined for T1, T2, and T3
The relative removal efficiency was calculated as the difference in concentration between the first-stage influent and the second-stage effluent divided by the concentration in the first stage influent

Summary

Introduction

The constructed rapid infiltration system (CRI) is a novel ecologically friendly technology for sewage treatment based on a modification of conventional sewage treatment [1]. The core of a CRI is a mixture of river sand and gravel that replaces conventional soil layers as the main infiltration media, which improves hydraulic load [2]. A dry-wet cycling of water feeding and draining is applied, which alternates the operation mode between an aerobic and (facultative) anaerobic environment, employing a more diverse mix of microorganisms. The unique operation mode and the rich diversity of microorganisms colonizing the filling medium of a CRI are favorable for efficient removal of pollutants from sewage [3]. Removal of total nitrogen (TN) is relatively poor, only reaching 10–30% [4]

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