Denitrifying Phosphorus Accumulating Organisms Research Articles

Start-up of glycerol-driven denitrifying phosphorus removal from wastewater: The effects of the microaerobic environment

Glycerol, an abundant by-product of biodiesel production, represented a promising carbon source for enhancing nutrient removal from low C/N ratio wastewater. This study discovered a novel approach to initiate glycerol-driven denitrifying phosphorus removal (DPR) in situ by creating a short-term microaerobic environment within the aerobic zone. This approach facilitated the in-situ conversion of glycerol, which was subsequently utilized by denitrifying phosphate accumulating organisms (DPAOs) for DPR. The feasibility and stability of glycerol-driven DPR were validated in a continuous-flow pilot-scale reactor. Anaerobic phosphorus release increased from 1.0 mg/L/h to 2.5 mg/L/h, with fermentation bacteria and related functional genes showing significant increases. The stable stage exhibited 92.8% phosphorus removal efficiency and 55.5% DPR percentage. The microaerobic environment enhanced fermentation bacteria enrichment, crucial for glycerol-driven DPR stability. The collaborative interaction between fermentation bacteria and phosphate accumulating organisms (PAOs) played a key role in sustaining glycerol-driven DPR stability. These findings provide a robust theoretical foundation for applying glycerol-driven DPR in established wastewater treatment plants.

Nitrate and nitrite utilization during denitrifying phosphorus removal: Electron acceptor preference and feasible process combinations

Denitrifying phosphorus removal (DPR), which is dominated by denitrifying polyphosphate-accumulating organisms (DPAOs), is a promising process for nitrogen and phosphorus removal. Denitrifying glycogen-accumulating organisms (DGAOs) and DPAOs typically coexist in the DPR sludge, complicating the study of DPAOs’ denitrification capacity. In this study, two reactors were fed with nitrate and nitrite during the anoxic phase to cultivate nitrate-DPR and nitrite-DPR sludge. Both reactors yielded high and low DGAO abundance sludges, enabling the evaluation of the denitrification capacity of DPAOs. For the nitrate-DPR sludge, the nitrite reduction rate was 1.63 times higher than the nitrate reduction rate when DPAOs were the primary denitrifiers. For the nitrite-DPR sludge, the reduction rate of nitrite was more than three times that of nitrate, irrespective of DGAO abundance. These findings indicated that DPAOs preferred nitrite to nitrate and were well suited to reduce nitrite rather than reduce nitrate to supply nitrite.

Synergistic Integration of Anammox and Endogenous Denitrification Processes for the Simultaneous Carbon, Nitrogen, and Phosphorus Removal.

The feasibility of a synergistic endogenous partial denitrification-phosphorus removal coupled anammox (SEPD-PR/A) system was investigated in a modified anaerobic baffled reactor (mABR) for synchronous carbon, nitrogen, and phosphorus removal. The mABR comprising four identical compartments (i.e., C1-C4) was inoculated with precultured denitrifying glycogen-accumulating organisms (DGAOs), denitrifying polyphosphate-accumulating organisms, and anammox bacteria. After 136 days of operation, the chemical oxygen demand (COD), total nitrogen, and phosphorus removal efficiencies reached 88.6 ± 1.0, 97.2 ± 1.5, and 89.1 ± 4.2%, respectively. Network-based analysis revealed that the biofilmed community demonstrated stable nutrient removal performance under oligotrophic conditions in C4. The metagenome-assembled genomes (MAGs) such as MAG106, MAG127, MAG52, and MAG37 annotated as denitrifying phosphorus-accumulating organisms (DPAOs) and MAG146 as a DGAO were dominated in C1 and C2 and contributed to 89.2% of COD consumption. MAG54 and MAG16 annotated as Candidatus_Brocadia (total relative abundance of 16.5% in C3 and 4.3% in C4) were responsible for 74.4% of the total nitrogen removal through the anammox-mediated pathway. Functional gene analysis based on metagenomic sequencing confirmed that different compartments of the mABR were capable of performing distinct functions with specific advantageous microbial groups, facilitating targeted nutrient removal. Additionally, under oligotrophic conditions, the activity of the anammox bacteria-related genes of hzs was higher compared to that of hdh. Thus, an innovative method for the treatment of low-strength municipal and nitrate-containing wastewaters without aeration was presented, mediated by an anammox process with less land area and excellent quality effluent.

Towards in-site carbon utilization and highly efficient nutrients removal: Effects of ammonium on the phosphorus recovery performance in a biofilm-based system

An alternatively anaerobic–aerobic biofilm system was operated for treating synthetic municipal wastewater for 150 days, and the effect of ammonium concentration in range of 15 mg∙L−1 - 50 mg∙L−1 on the phosphorus recovery performance was discussed. The ammonium concentration was confirmed as an important factor for balancing phosphorus accumulating organisms (PAOs) and denitrifying phosphorus-accumulating organisms (DPAOs) to affect nutrients removal and phosphorus recovery. The PAOs dominated in phosphorus removal with the ammonium less than 30 mg∙L−1, the ortho-P concentration in recovery steam was plateaued at 52 mg∙L−1. The increase in ammonium to 40 mg∙L−1 caused the seriously deterioration in PAOs activity; however, the phosphorus removal and recovery performance was decreased slightly which attributed to the vital contribution of DPAOs in phosphorus removal. The adverse effect of ammonium can be eliminated by decreasing the volume exchange ratio (VER) from 3.0 to 1.5, leading to the phosphorus concentration in recovery steam of 72.21 mg∙L−1. Meanwhile, the phosphorus removal efficiency (PRE) and total nitrogen removal efficiency (NRE) were stable at 97.8 % and 99.2 %, respectively, indicating highly efficient phosphorus recovery and nutrients removal in the biofilm system. The outcome of the present study could facilitate the establishment of an integrative technology to realize in-site carbon utilization, highly efficient nutrients removal and phosphorus recovery simultaneously in the mainstream treatment of sewage wastewater, and the study reveals the transformation pathways of P and N in the BPRR system, as well as the complex interactions between functional microorganisms.

Evaluation of various carbon sources on ammonium assimilation and denitrifying phosphorus removal in a modified anaerobic-anoxic-oxic process from low-strength wastewater

A pilot-scale continuous-flow modified anaerobic-anoxic-oxic (MAAO) process examined the impact of external carbon sources (acetate, glucose, acetate/propionate) on ammonium assimilation, denitrifying phosphorus removal (DPR), and microbial community. Acetate exhibited superior efficacy in promoting the combined process of ammonia assimilation and DPR, enhancing both to 50.0 % and 60.0 %, respectively. Proteobacteria and Bacteroidota facilitated ammonium assimilation, while denitrifying phosphorus-accumulating organisms (DPAOs) played a key role in nitrogen (N) and phosphorus (P) removal. Denitrifying glycogen-accumulating organisms (DGAOs) aided N removal in the anoxic zone, ensuring stable N and P removal and recovery. Acetate/propionate significantly enhanced DPR (77.7 %) and endogenous denitrification (37.9 %). Glucose favored heterotrophic denitrification (29.6 %) but had minimal impact on ammonium assimilation. These findings provide valuable insights for wastewater treatment plants (WWTPs) seeking efficient N and P removal and recovery from low-strength wastewater.

Partial denitrifying phosphorus removal coupling with anammox (PDPRA) enables synergistic removal of C, N, and P nutrients from municipal wastewater: A year-round pilot-scale evaluation

Applying anaerobic ammonium oxidation (anammox) in municipal wastewater treatment plants (MWWTPs) can unlock significant energy and resource savings. However, its practical implementation encounters significant challenges, particularly due to its limited compatibility with carbon and phosphorus removal processes. This study established a pilot-scale plant featuring a modified anaerobic-anoxic-oxic (A2O) process and operated continuously for 385 days, treating municipal wastewater of 50 m3/d. For the first time, we propose a novel concept of partial denitrifying phosphorus removal coupling with anammox (PDPRA), leveraging denitrifying phosphorus-accumulating organisms (DPAOs) as NO2− suppliers for anammox. 15N stable isotope tracing revealed that the PDPRA enabled an anammox reaction rate of 6.14 ± 0.18 μmol-N/(L·h), contributing 57.4 % to total inorganic nitrogen (TIN) removal. Metagenomic sequencing and 16S rRNA amplicon sequencing unveiled the co-existence and co-prosperity of anammox bacteria and DPAOs, with Candidatus Brocadia being highly enriched in the anoxic biofilms at a relative abundance of 2.46 ± 0.52 %. Finally, the PDPRA facilitated the synergistic conversion and removal of carbon, nitrogen, and phosphorus nutrients, achieving remarkable removal efficiencies of chemical oxygen demand (COD, 83.5 ± 5.3 %), NH4+ (99.8 ± 0.7 %), TIN (77.1 ± 3.6 %), and PO43− (99.3 ± 1.6 %), even under challenging operational conditions such as low temperature of 11.7 °C. The PDPRA offers a promising solution for reconciling the mainstream anammox and the carbon and phosphorus removal, shedding fresh light on the paradigm shift of MWWTPs in the near future.

Disentangling microbial coupled fillers mechanisms for the permeable layer optimization process in multi-soil-layering systems

The multi-soil-layering (MSL) systems is an emerging solution for environmentally-friendly and cost-effective treatment of decentralized rural domestic wastewater. However, the role of the seemingly simple permeable layer has been overlooked, potentially holding the breakthroughs or directions to addressing suboptimal nitrogen removal performance in MSL systems. In this paper, the mechanism among diverse substrates (zeolite, green zeolite and biological ceramsite) coupled microorganisms in different systems (activated bacterial powder and activated sludge) for rural domestic wastewater purification was investigated. The removal efficiencies performed by zeolite coupled with microorganisms within 3 days were 93.8% for COD, 97.1% for TP, and 98.8% for NH4+-N. Notably, activated sludge showed better nitrification and comprehensive performance than specialized nitrifying bacteria powder. Zeolite attained an impressive 89.4% NH4+-N desorption efficiency, with a substantive fraction of NH4+-N manifesting as exchanged ammonium. High-throughput 16S rRNA gene sequencing revealed that aerobic and parthenogenetic anaerobic bacteria dominated the reactor, with anaerobic bacteria conspicuously absent. And the heterotrophic nitrification-aerobic denitrification (HN-AD) process was significant, with the presence of denitrifying phosphorus-accumulating organisms (DPAOs) for simultaneous nitrogen and phosphorus removal. This study not only raises awareness about the importance of the permeable layer and enhances comprehension of the HN-AD mechanism in MSL systems, but also provides valuable insights for optimizing MSL system construction, operation, and rural domestic wastewater treatment.

Enhanced phosphorus removal from biological secondary effluent using denitrifying phosphorus-removal granular sludge

With the phosphorus discharge standard getting more stringent, it is imperative to enhance phosphorus removal from biological secondary effluent (BSE) of wastewater treatment plants (WWTPs). This study proposed a semi-continuous process for enhanced phosphorus removal from BSE using denitrifying phosphorus-removal granular sludge (DPGS) in a fluidized reactor operating under the alternative anaerobic/anoxic mode. This study investigated the effects of hydraulic retention time (HRT) and treating volume of BSE on the enhanced phosphorus removal performance of this process. At the appropriate HRT and treating volume of BSE, this process reduced the total phosphorus of practical BSE from 0.54 to 0.14 mg/L with an average removal efficiency of 74.5 % and removed 2.1 mg/L nitrate in 95 days. Removed phosphorus from practical BSE was concentrated into a small volume of water via the anaerobic phosphorus release and anoxic phosphorus uptake of denitrifying phosphorus-accumulating organisms (DPAOs) in DPGS, which was conducive for phosphorus recovery via chemical precipitation. The metagenomic analysis reveals that the relative abundance of DPAOs in DPGS increased while that of denitrifying glycogen-accumulating organisms decreased during 95 days of operation. This study provides a more cost-efficient and eco-friendly process for WWTPs to enhance phosphorus removal from BSE and phosphorus recycling.

Performance and mechanism of glycerol-driven denitrifying phosphorus removal from low organic matter sewage

The performance and mechanism of the glycerol-driven denitrifying phosphorus removal (DPR) process were investigated in low organic matter wastewater treatment using the modified anaerobic-anoxic–oxic (MAAO) system. The results revealed that denitrifying bacteria preferentially utilized glycerol, reducing nitrate interference on anaerobic phosphate release. Fermentation bacteria converted excess glycerol into available carbon sources, which were utilized by denitrifying phosphorus-accumulating organisms (DPAOs). Optimize glycerol dosage (calculated in chemical oxygen demand) could be estimated based on 6 times the effluent NO3−-N of the anoxic zone. As glycerol dosage increased, the relative abundance of fermentation bacteria surged from 8.2% to 17.7%, subsequently boosting the DPR rate from 34.6% to 77.2%. Notably, denitrifying glycogen-accumulating organisms (DGAOs) decreased from 0.5% to 0.2% but remained instrumental in nitrogen removal. The collaborative actions of fermentation bacteria, DPAOs, and DGAOs were vital in upholding the stability of nutrient removal in the glycerol-driven DPR process.

Clarification of the phosphorus release mechanism for recovering phosphorus from biofilm sludge in alternating aerobic/anaerobic biofilm system

A novel wastewater treatment plant process was constructed to overcome the challenge of simultaneous nitrate removal and phosphorus (P) recovery. The results revealed that the P and nitrate removal efficiency rose from 39.0 % and 48.4 % to 92.8 % and 93.6 % after 136 days of operation, and the total P content in the biofilm (TPbiofilm) rose from 15.8 mg/g SS to 57.8 mg/g SS. Moreover, the increase of TPbiofilm changed the metabolic mode of denitrifying polyphosphate accumulating organisms (DPAOs), increasing the P concentration of the enriched stream to 172.5 mg/L. Furthermore, the acid/alkaline fermentation led to the rupture of the cell membrane, which released poly-phosphate and ortho-phosphate of cell/EPS in DPAOs and released metal‑phosphorus (CaP and MgP). In addition, high-throughput sequencing analysis demonstrated that the relative abundance of DPAOs involved in P storage increased, wherein the abundance of Acinetobacter and Saprospiraceae rose from 8.0 % and 4.1 % to 16.1 % and 14.0 %. What's more, the highest P recovery efficiency (98.3 ± 1.1 %) could be obtained at optimal conditions for struvite precipitation (pH = 7.56 and P: N: Mg = 1.87:3.66:1) through the response surface method (RSM) simulation, and the precipitates test analysis indicated that P recovery from biofilm sludge was potentially operable. This research was of great essentiality for exploring the recovery of P from biofilm sludge.

Effect of different types of volatile fatty acids on the performance and bacterial population in a batch reactor performing biological nutrient removal

Different ratios of four volatile fatty acids (VFAs) were used as the primary feed to a laboratory scale biological nutrient reactor during four operational stages. The reactor performed efficiently over 500 days of operation with over 90% dissolved phosphorus and over 98% ammonium-nitrogen (NH4+-N) removal. Through in the first experimental phase, acetate and propionate were present in a significant proportion as carbon sources, the relative abundance of Candidatus Accumulibacter, a potential polyphosphate accumulating organism, increased from 10% to 57% and the Defluviicoccus genus, a known glycogen accumulating organism (GAO), decreased from 41% to 5%. Further tests indicated the presence of denitrifying phosphorus accumulating organisms (DPAO) belonging to Clade IIC, that could use nitrite as the electron acceptor during P-uptake. In general, VFAs favored the increase of the genus Defluviicoccus and Candidatus Accumulibacter. High relative abundance of Defluviicoccus did not affect the stability and the performance of the BNR process.

Recovering phosphorus and lithium separately from wastewater and brine using a novel coupled biofilm-precipitation system

Phosphorus (P) and lithium (Li) are scarce resources. To address the situation of resource scarcity, a novel coupled biofilm-precipitation system was proposed to recover P and Li separately from wastewater and brine. The results indicated the denitrifying polyphosphate accumulating organisms (DPAOs) suitable for this operating process promoted their denitrifying phosphorus removal (DPR) capabilities at the aerobic phase, increasing the total P content in the biofilm (TPbiofilm) to 60.7 ± 2.7 mg/g SS. Moreover, the DPAOs performed a metabolic shift from glycogen accumulation metabolism (GAM) to polyphosphate accumulation metabolism (PAM) when TPbiofilm increased, which caused more P being released by DPAOs, and the P concentration of the enriched stream to rise to 185.8 ± 3.4 mg/L. Furthermore, the quadratic regression model was suitable for the struvite crystallization (R2 = 0.87–0.88) in the P recovery stage, and the pure struvite was obtained with a P recovery efficiency was 96.3–97.2 %. The pure lithium carbonate crystals were created with a Li recovery efficiency was 93.3–97.2 % in the Li recovery stage. Additionally, the enriched P stream was applied to natural brine, and pure struvite and lithium carbonate crystals were produced with the P and Li recovery efficiency was 94.7 % and 93.5 %, respectively. In general, using enriched P stream as P source to separate magnesium from brine and thus recover Li was a feasible option. This study provided support for the recovery of P and Li.

Enrichment denitrifying phosphorus-accumulating organisms in alternating anoxic-anaerobic/aerobic biofilter for advanced nitrogen and phosphorus removal from municipal wastewater

Eutrophication and the degradation of natural water can result from excessive nitrogen and phosphorus in aquatic ecosystems. The denitrifying phosphorus removal (DPR) process shows promise for simultaneous nitrogen and phosphorus removal from municipal wastewater. However, enriching denitrifying phosphorus-accumulating organisms (DPAOs) always in conventional wastewater treatment is a challenging. To enhance the synchronous nitrogen and phosphorus removal efficiency from domestic wastewater, this study employed the alternating anoxic-anaerobic/aerobic biofilter (alternating A-A/O BF) system for DPAOs enrichment. Results showed that DPAOs were successfully enriched after 60 days of operation, where DPAOs contributed 84 % to the overall phosphorus removal. The optimal removal of COD, NH4+-N, TN and PO43−-P was stable at 83.14 %, 99.02 %, 69.75 % and 85.19 %, respectively, when the influent NH4+-N, NO3−-N, PO43−-P and anaerobic COD concentration was in the range of 40 ± 2 mg/L, 15 ± 1 mg/L, 12 ± 1 mg/L and 300 ± 50 mg/L. Microbial community analysis showed that the relative abundance of major DPAOs such as Aeromonas (4.47 %), Hyphomicrobium (0.42 %), Pseudomonas (0.21 %), and Pseudofulvimonas (0.18 %) in the optimum conditions stage increased significantly compared with that in the start-up stage. The results in this study contributes to the understanding of the critical role of DPAOs in the biological nutrient removal (BNR) technology.

Effect of influent ammonia nitrogen concentration on the phosphorus removal process in the aerobic granular sludge reactor

The effects of different influent ammonia nitrogen (NH3-N) concentrations (stage I to IV: 20, 40, 60 and 80 mg/L) on the phosphorus (P) removal process were studied in an aerobic granular sludge (AGS) reactor under anaerobic/aerobic operating conditions. The phosphorous removal performance kept stable at first (stage I and II) and then significantly deteriorated at further increase of influent NH3-N concentration (stage III and IV). On the process of microbial metabolism, further increase of NH3-N aggravated the competition between phosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) for carbon sources in the anaerobic phase, and weakened the P absorption capacity of PAOs in the aerobic phase. Denitrifying phosphate accumulating organisms (DPAOs) showed higher resistance to the increase of NH3-N concentration than traditional PAOs. On the functional structure of the system, microorganisms related to phosphorus removal in the system were mainly enriched in the granules, while microorganisms with heterotrophic denitrifying function dominated the sludge flocs to obtain higher growth advantage at high ammonia nitrogen concentration. The results of this study provide more insight into the biological stability of AGS systems.

Simultaneous phosphorus recovery from wastewater and sludge by a novel denitrifying phosphorus removal system

A novel process was proposed for simultaneous denitrification and phosphorus (P) recovery. The increased nitrate concentration facilitated the activity of denitrifying P removal (DPR) in P enrichment, which stimulated P uptake and storage, making P more readily accessible for release into the recirculated stream. The total P content in the biofilm (TPbiofilm) rose to 54.6 ± 3.5 mg/g SS as the nitrate concentration increased from 15.0 to 25.0 mg/L, while the P concentration of the enriched stream reached 172.5 ± 3.5 mg/L. Moreover, the abundance of denitrifying polyphosphate accumulating organisms (DPAOs) increased from 5.6% to 28.0%, and the increased nitrate concentration facilitated the process of carbon, nitrogen, and P metabolism due to the rise in the genes involved in critical functions of metabolism. Acid/alkaline fermentation analysis indicated that the EPS release was the primary P-release pathway. Additionally, pure struvite crystals were obtained from the enriched stream and fermentation supernatant.

Achieving advanced nitrogen removal from low-carbon municipal wastewater using partial-nitrification/anammox and endogenous partial-denitrification/anammox

To achieve advanced nitrogen removal from low-carbon wastewater, a partial-nitrification/anammox and endogenous partial-denitrification/ anammox (PN/A-EPD/A) process was developed in a sequential batch biofilm reactor (SBBR). Advanced nitrogen was achieved with the effluent total nitrogen (TN) of 3.29 mg/L when the influent COD/TN and the TN were 2.86 and 59.59 mg/L, respectively. This was attributed to a stable PN/A-EPD/A, which was achieved through the integration of four strategies, including treating the inoculated sludge with free nitrous acid, inoculating anammox biofilm, discharging excess activated sludge and residual ammonium at the end of oxic stage. The 16S rRNA high-throughput sequencing results demonstrated that anammox bacteria coexisted with ammonia oxidizing bacteria, nitrite oxidizing bacteria, denitrifying glycogen accumulating organisms (DGAOs) and denitrifying phosphorus accumulating organisms (DPAOs) in biofilms. The abundance of anammox bacteria in the inner layer of the biofilm is higher, while that of DGAOs and DPAOs is higher in the outer layer.

Insights on nitrogen and phosphorus removal mechanism in a single-stage Membrane Aeration Biofilm Reactor (MABR) dominated by denitrifying phosphorus removal coupled with anaerobic/aerobic denitrification

In the study, the denitrifying phosphorus removal process coupled with anaerobic/aerobic denitrification was started in a single-stage Membrane Aeration Biofilm Reactor (MABR). When the influent NO3−-N was 50.2 mg/L and the total phosphorus (TP) was 30.5 mg/L, the maximum Total Inorganic Nitrogen Removal Efficiency (TINRE) can reach 99.79 % and the Total Phosphorus Removal Efficiency (TPRE) can reach 82.62 % without the addition of any flocculant or precipitant. The phosphorus content in the substrate sludge was 4.10 %–6.15 %, which was higher than that in the initial biofilm or activated sludge (1.27 %–1.83 %). Based on 16S rRNA sequencing technology, it was found that Phosphorus-Accumulating Organisms (PAOs, Acinetobacter, relative abundance 0.02 % to 1.92 %) and Denitrifying Phosphorus-Accumulating Organisms (DPAOs, Flavobacterium (0.26 % to 5.39 %), Bdellovibrio (0.12 % to 1.48 %), and Pseudomonas (2.29 % to 1.28 %)) played pivotal roles in phosphorus removal. The enzyme gene reads of Complex I and Complex V processes were much more than that of Complex II- Complex IV, which indicated that Complex I and Complex V can be the main process for oxidative phosphorylation in the MABR. Moreover, four inorganic nitrogen metabolic processes, Dissimilatory Nitrate Reduction to Ammonium (DNRA), Assimilatory Nitrate Reduction Ammonium (ANRA), nitrification, and denitrification were found. Nitrifiers (Nitrosomonas (0.09 % to 0.19 %), Nitrospira (2.48 % to 0.06 %)), denitrifiers (Dokdonella (6.95 % to 2.11 %), Denitratisoma (0.42 % to1.48 %)), and aerobic denitrifiers (Pseudomonas (2.29 % to 1.28 %) and Thauera (4.75 % to 1.78 %)) contributed to nitrogen removal in the MABR. This study provided insights into the removal mechanism of nitrogen and phosphorus in a single-stage MABR.

Integration of EBPR with mainstream anammox process to treat real municipal wastewater: Process performance and microbiology

The mainstream application of anaerobic ammonium oxidation (anammox) for sustainable N removal remains a challenge. Similarly, with recent additional stringent regulations for P discharges, it is imperative to integrate N with P removal. This research studied integrated fixed film activated sludge (IFAS) technology to simultaneously remove N and P in real municipal wastewater by combining biofilm anammox with flocculent activated sludge for enhanced biological P removal (EBPR). This technology was assessed in a sequencing batch reactor (SBR) operated as a conventional A2O (anaerobic-anoxic-oxic) process with a hydraulic retention time of 8.8 h. After a steady state operation was reached, robust reactor performance was obtained with average TIN and P removal efficiencies of 91.3 ± 4.1% and 98.4 ± 2.4%, respectively. The average TIN removal rate recorded over the last 100 d of reactor operation was 118 mg/L·d, which is a reasonable number for mainstream applications. The activity of denitrifying polyphosphate accumulating organisms (DPAOs) accounted for nearly 15.9% of P-uptake during the anoxic phase. DPAOs and canonical denitrifiers removed approximately 5.9 mg TIN/L in the anoxic phase. Batch activity assays, which showed that nearly 44.5% of TIN were removed by the biofilms during the aerobic phase. The functional gene expression data also confirmed anammox activities. The IFAS configuration of the SBR allowed operation at a low solid retention time (SRT) of 5-d without washing out biofilm ammonium-oxidizing and anammox bacteria. The low SRT, combined with low dissolved oxygen and intermittent aeration, provided a selective pressure to washout nitrite-oxidizing bacteria and glycogen-accumulating organisms, as relative abundances of

Onsite treatment of decentralized rural greywater by ecological seepage well (ESW)

Seepage well, as an ancient facility for sewage collection and treatment in China, still has reference significance for effective treatment of source-separated greywater in rural China under the background of rural revitalization. This study surveyed the discharge characteristic of rural greywater, and proposed onsite treatment of decentralized rural greywater using a novel ecological seepage well (ESW). In northwestern China, four rural households produced greywater with an average quantity of 128–146 L/d, with chemical oxygen demand (COD) of 213.6–235.9 mg/L as the main pollutant. For treating greywater, ESW with ceramsite and zeolite mixed in the packing layers and metallic corrugated plates (MCPs) set in the aeration zone achieved higher removal efficiencies of COD, total phosphorous (TP), total nitrogen (TN) and ammonia nitrogen (NH4+-N). When the influent C/N ratio was 16, the enhanced removal performance was realized by cutoff duration of 9 h, and the effluent met the Chinese standard for irrigation water quality with COD, TP, TN and NH4+-N removal efficiencies of 88.58%, 65.60%, 92.94% and 93.65%, respectively. Under the optimal condition, mechanism of pollutant removal by ESW was investigated. The variation of EPS and microbial morphology along the height illustrated that a micro-aerobic environment was formed in the lower layer of ESW. High throughput sequencing indicated plentiful denitrifying bacteria (DNB) and denitrifying phosphate accumulating organisms (DNPAOs), together with a higher relative abundance of ammonia oxidizing bacteria (AOB) than nitrite oxidizing bacteria (NOB) in the lower layer, which was relative to simultaneous nitrification, denitrification and phosphorous removal. This study provided theoretical and practical support for effective treatment mode of rural sewage.

Advanced nitrogen and phosphorus removal by the symbiosis of PAOs, DPAOs and DGAOs in a pilot-scale A2O/A+MBR process with a low C/N ratio of influent

Cooperating in harmony to avoid competition with dominant functional microbial symbiosis is an efficient way in advanced nitrogen and phosphorus removal in wastewater treatment processes. In this study, a niche-based coordinating strategy was implemented to cooperate in harmony with phosphorus-accumulating organisms (PAOs), denitrifying phosphorus-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) to advance nitrogen and phosphorus removal based on an anaerobic-anoxic-oxic-anoxic-membrane bioreactor (A2O/A+MBR) under low C/N in municipal wastewater influent. The niche-based strategy was conducted based on the ORP change during the process as an indicator combined with the adjustment of recirculation and anoxic zone shifting. The results indicated that the strategy of the post-anoxic unit could enable significant enhancement of biological nitrogen and phosphorus removal (BNPR) by 9.9% and 16.3%, respectively, with low effluent concentrations of 7.0 ± 2.2 mg N/L and 0.36±0.32 mg P/L. The satisfactory performance was dominated along with the shift in the microbial community: the relative abundance of Tetrasphaera (PAO genus) increased from 0.14±0.08% to 0.32±0.12%, while the relative abundance of Decchloromonas (DGAO genus) and Candidatus Competibacter (DGAO genus) also increased. The advanced combination of anaerobic phosphorus release, anoxic denitrification, denitrifying phosphorus removal and endogenous denitrification was qualified by the modeling simulation of the biochemical kinetics mechanism of activated sludge in the A2O+MBR and A2O/A+MBR processes, which means that cooperation in the harmony of PAOs, DPAOs and DGAOs could be efficiently realized by a promising control strategy to enhance BNPR in an A2O+MBR with a post-anoxic unit. This study provides an efficient and simple novel control strategy to overcome the limitation of traditional nitrogen and phosphorus removal under an insufficient carbon source.