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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 /> Influent Grill 1'rchminary sedimentation tank <br /> l:tfluent Rapid infiltration tank Rapid infiltration tank <br /> (flooding period) (drying period) <br /> 011 <br /> Figure 1 <br /> Practical engineering of the Phoniex River CRI system operated successfully for 12 years in Chengdu, <br /> China. <br /> The microorganisms active in CRI system mostly form biofilms,and the necessary aerobic, anaerobic <br /> and facultative anaerobic processes for efficient water purification depend on large numbers of <br /> microbes attached to the surface of the filling medium [L2]. As an important component of biofilms, <br /> acellular polymericc,substances (EPS) constitute over 80%of biofilm organic matter[.L3]. These <br /> substances form a macromolecular gelatinous matrix with a three-dimensional network structure <br /> mainly made up of proteins and carbohydrates [14]. The overall biofilm community has been described <br /> as a"microbial city" [I S],whereby the EPS forms the"accommodation"for the microbial cells [.L6]. <br /> EPS that can easily be released into solution is described as the soluble EPS (S-EPS)fraction; EPS that <br /> remains bound to the bacteria(bound EPS or B-EPS)can be further divided into loosely bound EPS <br /> (LB-EPS)and tightly bound EPS (TB-EPS,Figure 2). Due to its typical physico-chemical properties, <br /> EPS enables a close packing of microbial cells,which protects them from external adverse effects. <br /> Moreover,EPS can serve as an energy and carbon source for the microbes after it is degraded into <br /> smaller molecules by extracellular enzymes. Lastly, EPS plays an important role in promoting <br /> microbial cell aggregation,as it accelerates biofilm formation and maintains collective structures. Due <br /> to these effects, EPS improves CRI performance, and has become the focus of research towards <br /> biological sewage treatment[17]. For instance,a positive correlation was found between the EPS <br /> content in sludge and its sludge volume index in a sequential batch reactor(SBR) [18]. The <br /> concentration of proteins and carbohydrates in LB-EPS of activated sludge correlated with the CN <br /> ratio in influent [19], although in those studies the EPS concentration of the biofilms in the water- <br /> saturated section of CRI had not been reported. <br /> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6069465/ 3/18 <br />