High-rate nitrogen removal in a continuous biofilter anammox reactor for treating low-concentration nitrogen wastewater at moderate temperature

Anammox process in anaerobic baffled biofilm reactors with columnar packings: Characteristics of flow field and microbial community

The enrichment of anammox bacteria is a key issue in the application of anammox processes. A new type of reactor － anaerobic baffle biofilm reactor (ABBR) developed from anaerobic baffle reactor (ABR) was filled with columnar packings and established for effective enrichment of anammox bacteria. The flow field analysis showed that, compared with ABR, ABBR narrowed the dead zone so as to improve the substrate transferring performances. Two ABBRs with different types of columnar packings (Packings 1 and Packings 2) were constructed to culture anammox biofilms. Packings 1 consisted of the single-form honeycomb carriers while Packings 2 was modular composite packings consisting of non-woven fabric and honeycomb carriers. The effects of different types of columnar packings on microbial community and nitrogen removal were studied. The ABBR filled with Packings 2 had a higher retention rate of biomass than the ABBR filled with Packings 1, making the anammox start-up period be shortened by 21.28%. The enrichment of anammox bacteria were achieved and the dominant anammox bacteria were Candidatus Brocadia in both R1 and R2. However, there were four genera of anammox bacteria in R2 and one genus of anammox bacteria in R1, and the cell density of anammox bacteria in R2 was 95% higher than that in R1. R2 has the advantage of maintaining excellent and stable nitrogen removal performance at high nitrogen loading rate. The results revealed that the packings composed of two types of carriers may have a better enrichment effect on anammox bacteria. This study is of great significance for the rapid enrichment of anammox bacteria and the technical promotion of anammox process.

Simultaneous nitrogen and phosphorus removal through an integrated partial-denitrification/anammox process in a single UAFB system

With the aim of obtaining enhanced nitrogen removal and phosphate recovery in mainstream sewage, we examined an integrated partial-denitrification/anaerobic ammonia oxidation (PD/A) process over a period of 189 days to accomplish this goal. An up-flow anaerobic fixed-bed reactor (UAFB) used in the integrated PD/A process was started up with anammox sludge inoculated and the influent composition controlled. Results showed that the system achieved a phosphorus removal efficiency of 82% when the influent concentration reached 12.0 mg/L. Batch tests demonstrated that stable and efficient removal of chemical oxygen demand (COD), nitrogen, and phosphorus was achieved at a COD/NO3--N ratio of 3.5. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis indicated that hydroxyapatite was the main crystal in the biofilm. Furthermore, substrate variation along the axial length of UAFB indicated that partial denitrification and anammox primarily took place near the reactor's bottom. According to a microbiological examination, 0.4% of the PD/A process's microorganisms were anaerobic ammonia oxidizing bacteria (AnAOB). Ca. Brocadia, Ca. Kuenenia, and Ca. Jettenia served as the principal AnAOB generals in the system. Thauera, Candidatus Accumulibacter, Pseudomonas, and Acinetobacter, which together accounted for 27% of the denitrifying and phosphorus-accumulating bacteria, were helpful in advanced nutrient removal. Therefore, the combined PD/A process can be a different option in the future for sewage treatment to achieve contemporaneous nutrient removal.

Microbial activity along the depth of biofilm in the simultaneous partial nitrification, anammox and denitrification (SNAD) system

Simultaneous partial nitrification, anammox and denitrification (SNAD) is a sustainable and cost-effective technology for nitrogen removal from low-strength wastewater. However, knowledge of the biofilm microenvironment of the SNAD system is currently unsatisfactory. The purpose of this study was to evaluate organic carbon effects on the microenvironment and microbial growth in the SNAD biofilm system. Microelectrodes were used to investigate microbial activity in-depth within biofilms. ORP distribution of the SNAD system was positively related to anammox activity(R2 = 0.9), and had some influence on microbial community structure. The synergistic effect of anammox bacteria and denitrifiers could be achieved when the abundance ratio of anammox bacteria to denitrifying bacteria is greater than 1.2.

Simultaneous nitrification and denitrification in membrane bioreactor: Effect of dissolved oxygen

Membrane bioreactor with the floc activated sludge (mixed liquor suspended solids (MLSS) = 7500 mg/L) was constructed in this work for simultaneously nitrification and denitrification (SND). The effect of dissolved oxygen (DO) on SND process and the nitrogen pathways were investigated. The average TN removal efficiencies were 63.05%, 91.17%, 87.04% and 70.02% for DO 0.5, 1, 2 and 3 mg/L systems, respectively. The effluent ammonia concentration was continuously lower than 5.0 mg/L when the DO was higher than 1 mg/L. Nitrogen in DO 1 and DO 2 mg/L systems was mainly removed via the SND process. The rise of DO concentration increased the abundance of nitrite oxidizing bacteria (NOB) and Nitrospira was the predominant NOB in all the four MBRs. Dechloromonas and Azoarcus were the dominant denitrifying bacteria (DNB) in DO 1 systems responsible for nitrite denitrification. The dominant aerobic DNB Pseudomonas also contributed SND via nitrate denitrification and was little affected by DO changes. Nitrate reductase was the main enzyme for the reduction of NO₃^--N to NO₂^--N, and narG was the main responsible gene. Nitrite oxidoreductase was the main enzyme for the oxidation of NO₂^--N to NO₃^--N, and nxrA was the main responsible gene in all the four MBR systems.

Simultaneous Anaerobic Ammonium Oxidation and Electricity Generation in Microbial Fuel Cell: Performance and Electrochemical Characteristics

In this study, a microbial fuel cell (MFC) that can achieve simultaneous anode anaerobic ammonium oxidation (anammox) and electricity generation (anode anammox MFC) by high-effective anammox bacteria fed with purely inorganic nitrogen media was constructed. As the influent concentrations of ammonium (NH4+-N) and nitrite (NO2−-N) gradually increased from 25 to 250 mg/L and 33–330 mg/L, the removal efficiencies of NH4+-N, NO2−-N and TN were over 90%, 90% and 80%, respectively, and the maximum volumetric nitrogen removal rate reached 3.01 ± 0.27 kgN/(m3·d). The maximum voltage and maximum power density were 225.48 ± 10.71 mV and 1308.23 ± 40.38 mW/m3, respectively. Substrate inhibition took place at high nitrogen concentrations (NH4+-N = 300 mg/L, NO2−-N = 396 mg/L). Electricity production performance significantly depended upon the nitrogen removal rate under different nitrogen concentrations. The reported low coulombic efficiency (CE, 4.09–5.99%) may be due to severe anodic polarization. The anode charge transfer resistance accounted for about 90% of the anode resistance. The anode process was the bottleneck for energy recovery and should be further optimized in anode anammox MFCs. The high nitrogen removal efficiency with certain electricity recovery potential in the MFCs suggested that anode anammox MFCs may be used in energy sustainable nitrogen-containing wastewater treatment.