With the improvement of wastewater discharge standards, wastewater treatment plants (WWTPs) are continually undergoing technological improvements to meet the evolving standards. In this study, a quartz sand deep bed denitrification filter (DBDF) was used to purify WWTP secondary effluent, utilizing high nitrate nitrogen concentrations and a low C/N ratio. Results show that more than 90% of nitrate nitrogen (NO-N) and 75% of chemical oxygen demand (COD) could be removed by the 20th day of filtration. When the filter layer depth was set to 1,600 mm and the additional carbon source CHOH was maintained at 30 mg L COD (20 mg L methanol), the total nitrogen (TN) and COD concentrations of DBDF effluent were stabilized below 5 and 30 mg L, respectively. Analysis of fluorescence revealed that DBDF had a stronger effect on the removal of dissolved organic matter (DOM), especially of aromatic protein-like substances. High throughput sequencing and qPCR results indicate a distinctly stratified microbial distribution for the main functional species in DBDF, with quartz sand providing a good environment for microbes. The phyla Proteobacteria, Bacteroidetes, and Chloroflexi were found to be the dominant species in DBDF.

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A pilot-scale quartz sand deep bed denitrification filter (DBDF) using sodium acetate as the additional carbon source was implemented to treat secondary effluent, with a high nitrate nitrogen (NO 3 -N) concentration and low C/N ratio, from an urban municipal water resource recovery facility. By the 18th day, results showed that the removal efficiency of NO 3 -N and the chemical oxygen demand (COD) were stable at above 85% and 70%, respectively. When the filter layer depth was set to 1,600 mm and the concentration of additional sodium acetate was maintained at 51 mg/L, the total nitrogen and COD concentrations of the DBDF effluent were stabilized below 5 and 30 mg/L, respectively. The quartz sand DBDF had a good effect on the removal of dissolved organic matter, especially for aromatic protein-like and tryptophan protein-like substances. Bacteria with denitrification function, such as Cloacibacterium and Zoogloea, became increasingly dominant with increasing filling layer depth. © 2018 Water Environment Federation • Practitioner points• The denitrification filter had a good effect on the removal of aromatic protein-like and tryptophan protein-like substances. • Cloacibacterium and Zoogloea became increasingly dominant with increasing filling layer depth.• Key words 3D-EEM; additional carbon source; deep bed denitrification filter; high-throughput; sodium acetate

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In the production process, some jobs can only be done sequentially, while others can be done synchronously. Given the time needed to complete each job, an oriented graph with a source vertex and a sink vertex can be generated. Each route starting from the source vertex and ending at the sink vertex represents a way of completing the project. It is possible to find the minimum production time and the optimal production path when time for each job is given by a rational number. However, this paper proves that there does not exist a computer program that can always generate the minimum time and optimal path when the time needed for each job is a constructive real number.