[Characteristics of Organics Transformation and Sludge Morphology in an ABR for Sewage Treatment with Different HRTs]

The characteristics of organics transformation and sludge morphology of in an ABR(anaerobic baffled reactor) for sewage treatment with different HRTs were investigated based on reactor performance, particle size distribution, and scanning electron microscopy (SEM). Results showed that the COD removal rate was stably maintained above 90.0% when the HRT decreased from 15 h to 4 h. However, the first compartment of ABR contributed to 90%, 78.56%, 74.18%, and 58.91% of the total COD removal when the HRT was 10, 7.5, 5, and 4 h, respectively. When the HRT was reduced, the total amount of volatile fatty acids (VFAs) in the first compartment of ABR significantly increased, and the abundance of acetic acid, being the major constituent of VFAs, gradually increased from 51.36% to 58.77%; the concentrations of butyric acid and propionic acid were maintained and constituted a minority of the VFAs. The sludge morphology in ABR significantly changed in the wake of run time. On day 111, granulation of sludge was achieved. Additionally, the degree of sludge granulation showed a decreasing trend with the direction of water flow. SEM observations of granular sludge showed that the separation of biomass did occur in the ABR. Along the direction of water flow, filamentous bacteria, M. methane, monococci, and bacilli were the dominant microbes in each compartment of the ABR.

[Effect of Substrate Ratio on Nitrogen Removal Performance of ANAMMOX in ABR]

In order to solve the problem of low nitrogen removal caused by incomplete removal of anaerobic ammonium oxidation (ANAMMOX) substrate, The nitrogen removal performance of the ANAMMOX was investigated by controlling different influent substrate ratios in an anaerobic baffled reactor (ABR). The result showed the optimal influent NO₂^--N/NH₄⁺-N was 1.34 with which the NH₄⁺-N and NO₂^--N removal efficiencies were about 99.99% and the total nitrogen removal efficiency reached a peak of 87%. When the influent NO₂^--N/NH₄⁺-N gradually reduced from 1 to 0.49 and increased from 1.34 to 1.62, the absolute removal of NH₄⁺-N and NO₂^--N was stable in the reactor and no significant inhibition was observed in the system. Under the condition of different substrate ratios, the removal of NH₄⁺-N and NO₂^--N was basically consumed in the first compartment of ABR, the change of substrate ratio did not have an obvious impact on the nitrogen removal performance of each compartment in the ABR, thus, the ABR ANAMMOX system had good stability to the change of substrate concentration.

[Quick Start-up of Anaerobic Ammonium Oxidation Process]

In order to study the quick start-up process of anaerobic ammonium oxidation (ANAMMOX), two types of reactors with different hydraclic flow state inoculated with aerobic nitrifying sludge were investigated, the membrane bioreactor (MBR) and anaerobic baffled reactor (ABR), respectively. The result showed that both reactors successfully started up ANAMMOX process. The start-up period of the MBR (90 d) was 20% shorter than the ABR (111 d). During the stable operation, the average nitrogen (NH₄⁺-N+NO₂^--N) removal capacity of 0.098 kg·(m³·d)^-1 in the MBR was also higher than that of 0.089 kg·(m³·d)^-1 in the ABR. In addition, the differences of sludge morphology were obvious in the two reactors; flocculent sludge was developed in the MBR while ANAMMOX granular sludge was mainly formed in the first compartment of the ABR. Moreover, the quantitative relationship analysis between NH₄⁺-N, NO₂^--N and NO₃^--N showed that the MBR system contained more kinds of bacteria with nitrogen removal function, compared to the ABR, and it was therefore more conducive to the removal of nitrogen. MBR exhibited a more excellent performance for ANAMMOX start-up.

[Characteristics of Microbial Community in Each Compartment of ABR ANAMMOX Reactor Based on High-throughput Sequencing]

In order to investigate the characteristics of microbial community in each compartment of ABR anammox reactor, a five-compartment ABR reactor was used to analyze the microbial community by Miseq High-throughput Sequencing during the steady operational process. The results indicated that the denitrifying bacteria coexisted in the reactor, such as Proteobacteria, Planctomycete, and Nitrospirae bacteria, and the percentages of these three microbial populations in the sludge were 11.66%-20.28%, 2.18%-7.94% and 0.19%-6.30%, respectively. In addition, there were four dominant genera in the phylum Proteobacteria:Rhodoplanes, Dok59, Rubrivivax and Bdellovibrio. Furthermore, Candidatus brocadia and Candidatus kuenenia were the main genera in the phylum Planctomycete. The color of sludge in the five compartments, in turn, varied from red to black. In addition, the biodiversity index of Chao, ACE, Shannon and Simpson indicated that the richness and diversity of microbial community increased gradually, and at the same time, the relative abundance of Proteobacteria increased while that of Planctomycetes gradually decreased. The above conclusion was consistent with the laws of substrate degradation and enrichment of functional microorganisms.