Achieving enhanced biological nitrogen removal via 2450 MHz electromagnetic wave loading on returned sludge in anaerobic-anoxic-oxic process.

To evaluate the enhancing of the biological nitrogen removal effectiveness by electromagnetic wave loading on returned sludge in the A/A/O reactor, some experiments were completed with the returned sludge loaded by 2,450 MHz electromagnetic wave. The excess sludge yield and pollutant removal effect of the system were evaluated. Results showed that stronger denitrification effect and less sludge yield were achieved. When 30% of the returned sludge was loaded by electromagnetic wave, the actual denitrification efficiency increased by 7% without dosage. The dissolution of carbon, nitrogen and phosphorus from loaded returned sludge was detected, thus providing the system with a supplemental carbon source of 4.6 g/d SCOD. The specific oxygen uptake rate of the oxic activated sludge increased by 14%, and the denitrification rate of the anoxic activated sludge increased by 29%. Illumina MiSeq analysis showed that the microbial richness increased obviously, and denitrifying bacteria (i.e. Dechloromonas, Zoogloea and Azospira, etc.) were accumulated.

Start-up performance of anaerobic/aerobic/anoxic-sequencing batch reactor (SBR) augmented with denitrifying polyphosphate-accumulating organism (DPAO) and their gene analysis.

This paper was aimed at investigating the bio-augmentation performance of anaerobic/aerobic/anoxic-type sequencing batch reactor (SBR) during its start-up period by introducing a strain of denitrifying polyphosphate-accumulating organism (DPAO). Two SBR reactors were inoculated to study the start-up performance, with one for DPAO introduction and the other as the control specimen. A comparison, of microbial community diversity based on the reactor which obtained a better performance, was made between polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analyses encoded by 16S rRNA and functional genes (nirS, nirK). The results indicated that the introduction of DPAO had a positive effect on the biological system, including a reduction of the start-up period, the improvement of sludge characteristics and the removal efficiency of nutrients, especially for phosphorus. By comparing the phylogenetic relationship of 16S rRNA and functional genes (nirS, nirK) of the reactor augmented with DPAO, it could be found that the phylogenetic relationship of these genes were remarkably inconsistent with each other. Therefore, 16SrRNA should not be used to determine the microbial community diversity of functional bacteria which could accomplish denitrification, and gene nirK should not be neglected when determining functional bacteria.

[Identification of a denitrifying polyphosphate-accumulating organism (DPAO) and study on its denitrifying functional genes].

A denitrifying polyphosphate-accumulating organism (DPAO) was isolated and identified, and the denitrifying functional genes were investigated. The strain ZQN2 was isolated using denitrifying medium. It was distinguished as DPAO by tests of aerobic phosphorus uptake, nitrate reduction, metachromatic granules and PHB (poly-beta-hydroxybutyrate) granules dyeing. Test of anaerobic phosphorus release/anoxic phosphorus uptake showed that strain ZQN2 released phosphorus and synthesized PHB at the anaerobic phase and used NO3- as acceptor to oxidize PHB during the anoxic phase with luxury phosphorus uptake, performing the function of simultaneous denitrifying phosphorus removal. The 16S rRNA gene sequence of strain ZQN2 was used for homology analysis and construction of phylogenetic trees. The results suggested that the 16S rRNA gene sequence of ZQN2 had up to 99% homology with those of many strains of Bacillus cereus strains in GenBank database. With physiological and biochemical reactions, the strain ZQN2 was identified as Bacillus cereus. The result of denitrifying functional gene study suggested that strain ZQN2 was the type of nirS+ and nirK-, which confirmed its denitrifying function from molecular biology point of view. Moreover, the phylogenetic analysis of nirS gene of ZQN2 showed that it was closely related to many strains of Pseadomonas aeruginosa, which was different from the analysis results of the 16S rRNA.