Microbial community analysis using MiSeq sequencing in a novel configuration fluidized bed reactor for effective denitrification

Enhanced denitrification of the AO-MBBR system used for expressway service area sewage treatment: A new perspective on decentralized wastewater treatment

Decentralized wastewater treatment warrants considerable development in numerous countries and regions. Owing to the unique characteristics of high ammonia nitrogen concentrations and low carbon/nitrogen ratio, nitrogen removal is a key challenge in treating expressway service area sewage. In this study, an anoxic/oxic-moving bed biofilm reactor (A/O-MBBR) and a traditional A/O bioreactor were continuously operated for 115 days and their outcomes were compared to investigate the enhancement effect of carriers on the total nitrogen removal (TN) for expressway service area sewage. Results revealed that A/O-MBBR required lower dissolved oxygen, exhibited higher tolerance toward harsh conditions, and demonstrated better shock load resistance than traditional A/O bioreactor. The TN removal load of A/O-MBBR reached 181.5 g‧N/(m3‧d), which was 15.24% higher than that of the A/O bioreactor. Furthermore, under load shock resistance, the TN removal load of A/O-MBBR still reached 327.0 g‧N/(m3‧d), with a TN removal efficiency of above 80%. Moreover, kinetics demonstrated that the denitrification rate of the A/O-MBBR was 121.9% higher than that of the A/O bioreactor, with the anoxic tank biofilm contributing 60.9% of the total denitrification rate. Community analysis results revealed that the genera OLB8, uncultured_f_Saprospiraceae and OLB12 were the dominant in biofilm loaded on carriers, and OLB8 was the key for enhanced denitrification. FAPROTAX and PICRUSt2 analyses confirmed that more bacteria associated with nitrogen metabolism were enriched by the A/O-MBBR carriers through full denitrification metabolic pathway and dissimilatory nitrate reduction pathway. This study offers a perspective into the development of cost-effective and high-efficiency treatment solutions for expressway service area sewage.

Influence of cell lysis by Fenton oxidation on cryptic growth in sequencing batch reactor (SBR): Implication of reducing sludge source discharge

The cell lysis-cryptic growth was implemented by Fenton oxidation in sequencing batch reactor. Optimizing sludge lysis condition could maximize the release of nutrients and sludge disintegration degree. After Fenton oxidation, the extracellular polymeric substance was obviously destroyed with the sludge average particle decreased from 64 μm to 36 μm. After 5% of the settled sludge in sequencing batch reactor (SBR) was oxidized by Fenton and then returned to SBR, the mixed liquor suspended solids (MLSS) decreased by 19.3% at the end of 35 days operation, the average mixed liquor volatile suspended solids/mixed liquor suspended solids (MLVSS/MLSS) was promoted by 13.3% during the entire operation. Returning lysed sludge had no significant influence on the organics and nitrogen removal, but the total phosphorus removal was distinctly enhanced by generating FePO4 precipitate. Additionally, returning lysed sludge suppressed nitrifying bacteria and promoted denitrifying bacteria slightly. Consequently, the cell lysis-cryptic growth for reducing sludge source discharge from wastewater biological treatment could be achieved on the premise of ensuring effluent quality.

Coupling of electricity generation and denitrification in three-phase single-chamber MFCs in high-salt conditions

High-salt conditions reduce the efficiency of electricity generation and nitrogen removal in microbial fuel cells (MFCs). In this work, we propose a three-phase single-chamber MFC (TP-MFC) by setting up a phase with immobilized cells in a conventional bipolar single-chamber MFC (common MFC). Cells from Halomonas were used as the immobilized phase, because these cells secrete the compatible solute ectoine and exhibit simultaneous nitrification and denitrification (SND). This enhanced the efficiency of SND and subsequent electricity generation under high-salt conditions. The average voltage of TP-MFC generated during the stable period in the presence of 30 g/L NaCl was 439.3 mV, which was 55.2% higher than that generated in common MFC. In addition, the N-removal rate of TP-MFC at 72 h was 63.4%, which was 38.4% higher than that of common MFC. The 16S rRNA diversity analysis showed an improved abundance of Pseudomonas, Acinetobacter, Alcaligenes, and Halomonas in TP-MFC, indicating that the ectoine secreted by immobilized Halomonas conferred substantial salt-tolerance on the electrogenic bacteria growing in a high-salt environment. This paper establishes an efficient and convenient method for improving the salt tolerance of microbial flora in MFCs, which is of great significance for the application of MFCs in high-strength wastewater treatment.

Mixed carbon source improves deep denitrification performance in up-flow anaerobic sludge bed reactor

To investigate the advantages of mixed carbon source over a single one in deep denitrification, sodium acetate, glucose and their mixture were used as carbon sources in present study. Denitrification performance, effluent pH, microbial community and carbon source cost were taken into account. With the same influent NO₃ ^--N concentration of 50 mg/L and the same C/N ratio of 1.5, the NO₃ ^--N removal rate with the mixed carbon source (96.53%) was slightly lower than that with sodium acetate (98.15%), but significantly higher than that with glucose (74.69%). The specific denitrification rates of the sodium acetate, glucose and sodium acetate/glucose reactor were 47.7, 29.7 and 45.4 mg N/g VSS d, respectively. The effluent pH with sodium acetate varied in the range of 9.13-9.60, exceeding the discharge standard limit of 9.0, whereas the sodium acetate/glucose reactor could keep pH in the range of 7.80-8.23. The 16S rRNA gene-based high-throughput sequencing revealed that carbon sources determined the microbial community structure and the sludge Shannon index with the mixed carbon source was the highest. Furthermore, cost estimation indicated that the mixed carbon source was the cheapest. This study is significant as it tests reasonable selection of carbon sources for deep denitrification in practice.

Electrons transfer determined greenhouse gas emissions in enhanced nitrogen-removal constructed wetlands with different carbon sources and carbon-to-nitrogen ratios

A constructed wetland (CW) was established to explore the influence of carbon addition (glucose or sodium acetate) on nitrogen removal and greenhouse gas (GHG) emissions at chemical oxygen demand to nitrogen ratios (COD/Ns) of 0, 4, 7. Results showed that the type of carbon source and COD/N significantly influenced the CW performance, in which the electrons transfer determined the regulation of denitrification, methanogenesis and respiration. Higher N₂O emissions were consistent with higher nitrite accumulation at low COD/N because of electrons competition. The residual carbon source after near-complete denitrification could be further utilized by methanogenesis. Sodium acetate was superior to glucose in promoting denitrification and reducing global warming potential (GWP). In addition, bacteria sequencing and functional genes confirmed the important role of the type of carbon source on controlling nitrogen removal, carbon consumption and GHG emissions in microbial communities.

Effects of carbon sources and COD/N ratio on N2O emissions in subsurface flow constructed wetlands

A set of constructed wetlands under two different carbon sources, namely, glucose (CW) and sodium acetate (YW), was established at a laboratory scale with influent COD/N ratios of 20:1, 10:1, 7:1, 4:1, and 0 to analyze the influence of carbon supply on nitrous oxide emissions. Results showed that the glucose systems generated higher N₂O emissions than those of the sodium acetate systems. The higher amount of N₂O-releasing fluxes in the CWs than in the YWs was consistent with the higher NO₂^--N accumulation in the former than in the latter. Moreover, electron competition was tighter in the CWs and contributed to the incomplete denitrification with poor N₂O production performance. Illumina MiSeq sequencing demonstrated that some denitrifying bacteria, such as Denitratisoma, Bacillus, and Zoogloea, were higher in the YWs than in the CWs. This result indicated that the carbon source is important in controlling N₂O emissions in microbial communities.

Study on ammonium and organics removal combined with electricity generation in a continuous flow microbial fuel cell

A continuous microbial fuel cell system was constructed treating ammonium/organics rich wastewater. Operational performance of MFC system, mechanisms of ammonium removal, effect of ammonium on organics removal and energy output, C and N balance of anode chamber and microbial community analysis of anode chamber were studied. It was concluded that 0.0914kg/m³d NH₄⁺-N and 5.739kg/m³d COD were removed from anode chamber and simultaneous nitrification and denitrification (SND) occurred in cathode chamber resulting in COD, TN removal rate of 88.53%, 71.35% respectively. Excess ammonium affected energy output and the MFC system reached maximum energy output of 816.8mV and 62.94mW/m³. In anode chamber, Spirochaetes bacterium sp., Methanobacterium formicicum sp. was predominant in bacteria, archaea communities respectively which contributed to wastewater treatment and electricity generation. This study showed the potential for practical application of continuous flow MFC system treating ammonium/organics rich wastewater and achieving electricity generation simultaneously.

Effects of iron and calcium carbonate on the variation and cycling of carbon source in integrated wastewater treatments

Iron and calcium carbonate were added in wastewater treatments as the adjusting agents to improve the contaminant removal performance and regulate the variation of carbon source in integrated treatments. At different temperatures, the addition of the adjusting agents obviously improved the nitrogen and phosphorous removals. TN and TP removals were respectively increased by 29.41% and 23.83% in AC-100 treatment under 1-day HRT. Carbon source from dead algae was supplied as green microbial carbon source and Fe²⁺ was supplied as carbon source surrogate. COD concentration was increased to 30mg/L and above, so the problem of the shortage of carbon source was solved. Dead algae and Fe²⁺ as carbon source supplement or surrogate played significant role, which was proved by microbial community analysis. According to the denitrification performance in the treatments, dead algae as green microbial carbon source combined with iron and calcium carbonate was the optimal supplement carbon source in wastewater treatment.