Realization of partial nitrification and in-situ anammox in continuous-flow anaerobic/aerobic/anoxic process with side-stream sludge fermentation for real sewage

Simultaneously ammonium and perchlorate remove via the partial nitrification-anammox coupled sulfur autotrophic system

In this study, partial nitrification-anammox coupled sulfur autotrophic (PNA-SA) system was constructed for removing ammonium and perchlorate from composite wastewater simultaneously. The removal rates of ammonium and perchlorate could reach 94.2% and 93.1%, respectively, at an ammonium concentration of 60 mg N∙L-1 and a perchlorate concentration of 30 mg N∙L-1. Ammonium was mainly removed by anammox bacteria (AnAOB) in PNA reactor, while perchlorate removal was attributed to perchlorate reducing bacteria (PRB) in SA reactor. Furthermore, combined with Pearson analysis, N-acylhomoserine lactones (AHLs)-mediated quorum sensing regulated the production of TB-EPS, improving biofilm stability and thus ensuring the removal performance of reactors. 16sRNA gene sequencing results indicated that the key functional bacteria in the PNA reactor were Comamonas and Candidatus Kuenenia, and the key functional bacteria in the SA reactor were Sulfurimonas, Thiobacillus, and Defluviimonas. These key functional bacteria ensured PNA-SA system feasibility and stability. Such results indicated that PNA-SA system could be used to treat ammonium and perchlorate composite wastewater, thereby providing a new strategy for removing such composite wastewater.

Novel control strategy employing anaerobic/aerobic/anoxic/aerobic/anoxic mode to enhance endogenous denitrification and anammox for municipal wastewater treatment

Anaerobic/Aerobic/Anoxic (AnOA) process utilizes endogenous denitrification to remove nitrogen. However, low endogenous denitrification activity critically restricts its application owing to insufficient carbon sources. In this study, a novel control strategy employing anaerobic/aerobic/anoxic/aerobic/anoxic (AOAOA) mode was introduced to treat low Carbon/Nitrogen (C/N) ratio municipal wastewater over 262 days. The concentration of total inorganic nitrogen (TIN) was only 3.9 ± 2.0 mg/L in the effluent, with a high nitrogen removal efficiency (NRE) of 94.3 %. The relative abundance of Candidatus Competibacter increased from 1.2 % to 2.3 %, ensuring an efficient endogenous denitrification process. Additionally, Candidatus Brocadia enriched from 0.02 % to 0.6 %, contributing to 63.1 % nitrogen removal during the anoxic stage in Phase Ⅲ. This study presents a promising approach for enhancing endogenous denitrification and anammox in the AnOA process, contributing to sustainable wastewater treatment.

Advanced N removal from low C/N sewage via a plug-flow anaerobic/oxic/anoxic (AOA) process: Intensification through partial nitrification, endogenous denitrification, partial denitrification, and anammox (PNEnD/A)

Achieving low-cost advanced nitrogen (N) removal from municipal wastewater treatment plants (WWTPs) remains a challenge. A plug-flow anaerobic/oxic/anoxic (AOA) system with a mixtures bypass (MBP) integrating partial nitrification (PN), endogenous carbon denitrification (EnD), partial denitrification (PD), and anaerobic ammonium oxidation (Anammox), was constructed to treat actual sewage with a low C/N ratio. The effluent concentrations and removal efficiency of total inorganic nitrogen (TIN) during stable operation were 2.9 ± 0.9 mg/L and 93.1 ± 2.0 %, respectively. EnD was enhanced by the MBP through the efficient utilization of polyhydroxyalkanoates generated in the anaerobic zone. PD was promoted by the addition of carries and sodium acetate to the anoxic tank and the subsequent implantation of the Anammox biofilm successfully coupled PD/A. Stable PN was obtained with a satisfactory nitrite accumulation ratio of 92.6 %, facilitated by carriers and the introduction of hydroxylamine in the oxic zone. Mass balance analysis revealed that EnD and Anammox contributed 40.8 % and 48.2 % of TIN removal, respectively. The enrichment and synergistic effects of ammonia-oxidizing bacteria, denitrifying bacteria, glycogen-accumulating organisms, and anaerobic ammonia-oxidizing bacteria formed a diverses bacterial basis for the establishment of PN, EnD, PD, and Anammox (PNEnD/A) in the AOA system. The successful integration of PNEnD/A into the AOA process provides an innovative approach for low-cost advanced N removal in WWTPs.

First application of the novel anaerobic/aerobic/anoxic (AOA) process for advanced nutrient removal in a wastewater treatment plant

The stringent effluent quality standards in wastewater treatment plants (WWTPs) can effectively mitigate environmental issues such as eutrophication by reducing the discharge of nutrients into water environments. However, the current wastewater treatment process often struggles to achieve advanced nutrient removal while also saving energy and reducing carbon consumption. The first full-scale anaerobic/aerobic/anoxic (AOA) system was established with a wastewater treatment scale of 40,000 m3/d. Over one year of operation, the average TN and TP concentration in the effluent of 7.53 ± 0.81 and 0.37 ± 0.05 mg/L was achieved in low TN/COD (C/N) ratio (average 5) wastewater treatment. The post-anoxic zones fully utilized the internal carbon source stored in pre-anaerobic zones, removing 41.29 % of TN and 36.25 % of TP. Intracellular glycogen (Gly) and proteins in extracellular polymeric substances (EPS) served as potential drivers for post-anoxic denitrification and phosphorus uptake. The sludge fermentation process was enhanced by the long anoxic hydraulic retention time (HRT) of the AOA system. The relative abundance of fermentative bacteria was 31.66 - 55.83 %, and their fermentation metabolites can provide additional substrates and energy for nutrient removal. The development and utilization of internal carbon sources in the AOA system benefited from reducing excess sludge production, energy conservation, and advanced nutrient removal under carbon-limited. The successful full-scale validation of the AOA process provided a potentially transformative technology with wide applicability to WWTPs.

Achieving synchronous and highly efficient removal of nitrogen and phosphorus by rapid enrichment and cultivation denitrifying phosphorus accumulating organisms in anaerobic-oxic-anoxic operation mode

Realizing the quick enrichment and development of denitrifying phosphorus accumulating organisms (DPAOs) in actual household wastewater and industrial nitrate wastewater has significant research significance. In this study, a novel operation mode of anaerobic-oxic-anoxic (AOA) was adopted to successfully realize the enrichment and cultivation of DPAOs in urban domestic wastewater. Adjusting influent COD to PO43--P ratio, shortening the aerobic time and decreasing the aeration volume were conducive to select DPAOs in microbial populations. The system was operated for 180 days and the DPAOs were well enriched during the stable operation with the percentage of Dechloromonas increased to 5.1 %. Accordingly, the effluent PO43--P was < 0.3 mg P/L, the removal efficiency of phosphorus was 96.9 % and the removal efficiency of nitrate was 92.5 %. Above all, DPR can be successfully applied to AOA systems with good phosphorus removal performance.

Overlooked role in bacterial assembly of different-sized granules in same sequencing batch reactor: Insights into bacterial niche of nutrient removal

The unique ecosystem within different-sized granules affects microbial assembly, which is crucial for wastewater treatment performance. This study operated an aerobic granular sludge system to evaluate its performance in treating synthetic municipal wastewater. Subsequently, the microbial community within different-sized granules was characterized to investigate bacterial assembly, and elucidated their biological potential for nutrient removal. The nutrient removal efficiencies were as follows: 93.8 ± 2.8 % chemical oxygen demand, 65.4 ± 4.0 % total nitrogen, and 93.8 ± 6.8 % total phosphorus. The analysis of microbial assembly unveiled remarkable diversity among different-sized sludges, the genus relative abundance displayed 61.4 % positive and 33.0 % negative correlation with sludge size. The excellent potential for organic degradation, denitrification, and polyphosphate accumulation occurred in sludge sizes of > 0.75 mm, 0.20-0.50 mm, and < 0.20 mm, respectively. Functional annotation further confirmed the nutrient removal potential within different-sized sludges. This study provides valuable insights into the bacterial niche of different-sized sludges, which can enhance their practical application.

Enhancing nitrogen removal performance through intermittent aeration in continuous plug-flow anaerobic/aerobic/anoxic process treating low-strength municipal sewage

Advanced nitrogen removal cannot be achieved through the conventional biological nitrogen removal process, which requires higher carbon sources and aeration energy. The proposal of intermittent aeration in the aerobic chambers offered an innovative approach to enhance nitrogen removal in low carbon-to-nitrogen ratio (C/N) municipal sewage, using a plug-flow reactor with anaerobic/aerobic/anoxic (AOA) process. Due to the effective utilization of internal carbon sources through the intermittent aeration, the total inorganic nitrogen removal efficiency (NRE) increased to 77.9 ± 3.2 % with the mean aerobic hydraulic retention time of only 3.2 h and a low C/N of 3.3 during the operation of 210 days. Polyhydroxyalkanoates dominated the nitrogen removal in this AOA system, accounting for 48.0 %, primarily occurring in the alternant aerobic/anoxic chambers. Moreover, the microbial community structure remained unchanged while the NRE increased to 77.9 %. This study provided an efficient and economic strategy for the continuous plug-flow AOA process.

Achieving partial nitrification: A strategy for washing NOB out under high DO condition

This study investigated the effect of high DO concentrations on PN. The experimental setup involved operating at high DO concentrations (1.5-2.5 mg/L) and environmental temperatures (15-20 °C) over a period of 180 days. Through a sludge enrichment process, the kinetic parameters of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were determined. Surprisingly, contrary to conventional reports, it was observed that NOB exhibited a stronger affinity for DO compared to AOB. As a result, high DO concentrations were necessary to provide favorable conditions for the growth of AOB. In order to establish PN, strategies including intermittent aeration, free ammonia (FA), and controlled sludge retention time (SRT) were employed. The successful PN was achieved with a specific ammonia oxidation rate of 24 mg N/g MLVSS/h and a specific nitrite oxidation rate below 0.10 mg N/g MLVSS/h. The nitrite accumulation rate (NAR) was maintained at 100% during stable operation. The abundance of Nitrosomonas, a typical genus of AOB, was found to be 68.62%, which surpasses previous studies in similar research. A slightly higher DO concentrations may increase energy consumption, but achieve higher efficiency and stability in PN. This study provided new insights into the application of PN in wastewater treatment.

Magnetite enhancing sludge anaerobic fermentation to improve wastewater biological nitrogen removal: Pilot-scale verification

Alkaline anaerobic fermentation for acids production has been considered as an effective method to recover resources from waste activated sludge, and magnetite could improve the quality of fermentation liquid. Here we have constructed a pilot-scale sludge alkaline anaerobic fermentation process enhanced by magnetite to produce short chain fatty acids (SCFAs), and used them as external carbon sources to improve the biological nitrogen removal of municipal sewage. Results showed that the addition of magnetite could significantly increase the production of SCFAs. The average concentration of SCFAs in fermentation liquid reached 3718.6 ± 101.5 mg COD/L and the average concentration of acetic acid reached 2368.8 ± 132.1 mg COD/L. The fermentation liquid enhanced by magnetite were used in the mainstream A²O process, and the TN removal efficiency increased from 48.0% ± 5.4%-62.2% ± 6.6%. The main reason is that the fermentation liquid is conducive to the succession of microbial community in the denitrification process, increasing the abundance of denitrification functional bacteria and realizing the enhancement of denitrification process. Besides, magnetite can promote the activity of enzyme to enhance biological nitrogen removal. Finally, the economic analysis showed that magnetite enhancing sludge anaerobic fermentation was economically and technically feasible to promote biological nitrogen removal of municipal sewage.

Redirecting carbon to recover VFA to facilitate biological short-cut nitrogen removal in wastewater treatment: A critical review

Wastewater treatment plants (WWTPs) are facing a great challenge to transition from energy-intensive to carbon-neutral and energy-efficient systems. Biological nutrient removal (BNR) can be severely impacted by carbon limitation, particularly for wastewater with a low carbon-to-nitrogen (C/N) ratio, which can significantly increase the operational costs. Waste activated sludge (WAS) is a valuable byproduct of WWTPs, as it contains high levels of organic matter that can be utilized to improve BNR management by recovering and reusing the fermentative volatile fatty acids (VFAs). This review provides a comprehensive examination of the recovery and reuse of VFAs in wastewater management, with a particular focus on advancing the preferable biological short-cut nitrogen removal process for carbon-insufficient municipal wastewaters. First, the method of carbon redirection for recovering VFAs was reviewed. Carbon could be captured through the two-stage A/B process or via sludge fermentation with different sludge pretreatment and process control strategies to accelerate sludge hydrolysis and inhibit methanogens to enhance VFA production. Second, VFAs can support the metabolism of autotrophic N-cycling microorganisms involved in wastewater treatment, such as AOB, NOB, anammox, and comammox bacteria. However, VFAs can also cause inhibition at high concentrations, leading to the partition of AOB and NOB; and can promote partial denitrification as an efficient carbon source for heterotrophic denitrifiers. Third, the lab- and pilot-scale engineering practices with different configurations (i.e., A²O, SBR, UASB) were summarized that have shown the feasibility of utilizing the fermentate to achieve superior nitrogen removal performance without the need for external carbon addition. Lastly, the future perspectives on leveraging the relationships between mainstream and sidestream, nitrogen and phosphorus, autotrophs and heterotrophs were given for sustainable and efficient BNR management.

Superior nitrogen removal and efficient sludge reduction via partial nitrification-anammox driven by addition of sludge fermentation products for real sewage treatment

Efficient retention and enrichment of anammox bacteria (AnAOB) are essential for the application of municipal wastewater anammox. Herein, an innovative process for highly enriching AnAOB within suspended carrier was developed in a single-stage anaerobic/oxic/anoxic reactor with 5.5 % carrier filling ratio for real sewage. Addition of sludge fermentation products promoted stable maintenance of partial nitrification (nitrite accumulation rate > 90.0 %) and achieved efficient external sludge reduction (27.6-37.9 %). Continuous nitrite supply and carrier addition promoted AnAOB enrichment (2.4 × 1011 gene copies/g dry sludge). Candidatus Brocadia was the predominant bacteria in carriers (18.6 %). The average effluents of total inorganic nitrogen (TIN) and NH4+-N were 1.9 and 0.8 mg/L with removal rates of 97.0 % and 98.7 %. In the anoxic stage, TIN removal rate reached 71.5 %, and the proportion of anammox to nitrogen removal accounted for 82.7 %. This study broadens the application of mainstream sewage anammox and the resource utilization of waste activated sludge.

Balancing denitrifying phosphorus-accumulating organisms and denitrifying glycogen-accumulating organisms for advanced nitrogen and phosphorus removal from municipal wastewater

Given the carbon limitation of municipal wastewater, the balance of biological nitrogen and phosphorus removal remains a challenging task. In this study, an anaerobic-anoxic-oxic combining with biological contact oxidation (A²/O-BCO) system treating real municipal wastewater was operated for 205 days, and COD-to-PO₄^3--P ratio was confirmed as the key parameter for balancing denitrifying phosphorus-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) to enhance N and P removal. When DPAOs dominated in nutrients removal, the increase in COD/P from 17.1 to 38.1 caused the deterioration in nitrogen removal performance decreasing to 71.8 %. As COD/P ratio decreased from 81.3 to 46.8, Ca.Competibacter proliferated from 3.11 % to 6.00 %, contributing to 58.9 % of nitrogen removal. The nitrogen and phosphorus removal efficiency reached up to 79.3 % and 95.2 %. Overall, establishing DGAOs-DPAOs balance by strengthening the effect of DGAOs could enhance the nutrients removal performance and accordingly improve the stability and efficiency of the system.

Evaluating the role of algae in algal-bacterial granular sludge: Nutrient removal, microbial community and granular characteristics

Algal-bacterial granular sludge (ABGS) and bacterial granular sludge (BGS, control group) were operated over 240 days to investigate the role of algae in treating synthetic municipal wastewater. The results showed that algae significantly improved the removal efficiency of total nitrogen (TN). The nitrogen removal load of ABGS was 2.6 mg-N/g-VSS/day (22.8 %, light) and 1.1 mg-N/g-VSS/day (9.6 %, dark) higher than that of BGS, respectively, which was attributed to algae enhanced NH₃-N removal capacity in the anaerobic stage and increased the utilization efficiency of organics in denitrification. Algae increased the relative abundance of denitrifying bacteria, and ABGS (28.83 %) was higher than BGS (14.28 %). Moreover, the dominant phylum of algae was Chlorophyta (98.39 %), the chlorophyll-a was sustained at 1.28 ± 0.26 mg/g-VSS. Algae significantly increased the content of extracellular polymeric substances (EPS), and the increased polysaccharide came from the tightly bound EPS. This study expands the understanding of the role of algae in ABGS.

Stable enhanced nitrogen removal from low COD/N municipal wastewater via partial nitrification-anammox in the traditional continuous anoxic/oxic process through bio-augmentation of partial nitrification sludge under decreasing temperatures

The application of partial nitrification-anammox (PNA) in continuous flow processes for treating low COD/N (C/N) sewage remains a critical challenge. Here, a traditional continuous anoxic/oxic (A/O) process was operated to investigate nitrogen removal from municipal wastewater by the bio-augmentation of partial nitrification sludge combined with the inoculation of biocarriers under decreasing temperatures. Stable enhanced nitrogen removal via PNA was achieved. The average total inorganic nitrogen in influent and effluent was 44.3 and 7.1 mg N/L under a low C/N ratio (3.4) and a short hydraulic retention time (8.2 h). The bio-augmentation of partial nitrification sludge enhanced the PNA process under low temperatures (16.9 ± 0.6 °C). The nitrogen removal efficiency remained stable at 83.3 ± 5.7 % as the temperature decreased from 29.1 to 16.3 °C, and the relative abundance of Ca. Brocadia in carrier biofilms increased from 2.22 % to 4.31 % and 3.27 % in two aerobic chambers after 70 days of operation.

Coupled process of in-situ sludge fermentation and riboflavin-mediated nitrogen removal for low carbon wastewater treatment

Volatile fatty acid recovery from waste activated sludge (WAS) was highly suggested to supplement carbon source for nitrogen removal. However, it was not easy to separate them from the metabolites under the ex-situ fermentation. In this study, in-situ WAS fermentation combined in the denitrification system was established to treat low carbon wastewater (COD/TN = 4), and riboflavin was employed as a redox mediator. This coupled process could simultaneously enhance the WAS fermentation and nitrogen removal, and riboflavin could significantly enrich the fermentative bacteria (Firmicutes phylum), denitrifying bacteria (Denitratisoma genus) and related functional genes (narGHJI, napABC, nirKS, nosZ, norBC), generating more available carbon sources for efficient nitrogen removal. This resulted in the effluent TN (<15 mg/L) satisfying the required discharge standard in China. This study provided new insights into the efficient nitrogen removal from low carbon wastewater, realizing the carbon-neutral operation of new concept wastewater treatment plant in China.

Removal of Mg2+ inhibition benefited the growth and isolation of ammonia-oxidizing bacteria: An inspiration from bacterial interaction

Ammonia-oxidizing bacteria (AOB) play an important role in the global nitrogen cycle and have broad applications in the nitrogen removal from wastewater. However, the AOB species are sensitive to environmental factors and usually form tight relationships with other microbes, making the AOB isolation and maintenance are difficult and time-consuming. In this study, the relationship that occurred between AOB and their bacterial partners was found to be able to improve the ammonia oxidation; during the co-cultivation, the magnesium ions (Mg²⁺) with removal rate as high as 36.7% was removed from culture medium by the concomitant bacterial species, which was regarded as the main reason for improving ammonia oxidation. During the pure cultivation of AOB isolate, when the concentration of Mg²⁺ reduced to low levels, the ammonia-oxidizing activity was more than 5 times and the amoA gene expression was more than 12 times higher than that grown in the initial culture medium. Based on a newly designed culture medium, the ammonia oxidation of AOB isolate grown in liquid culture was significantly promoted and the visible AOB colonies with much more number and larger diameter were observed to form on agar plates. With the addition of high concentration of calcium carbonate (CaCO₃), AOB colonies could be easily and specifically identified by following the hydrolytic zones that formed around AOB colonies. Another AOB isolates were successively obtained from different samples and within a short time, suggesting the feasibility and effectivity of this culture medium and strategy on the AOB isolation from environments.

Enhanced nutrient removal from mainstream sewage via denitrifying dephosphatation, endogenous denitrification and anammox in a novel continuous flow process

It is a challenging subject to realize nitrogen and phosphorus elimination synchronously from limited-carbon sewage through conventional biological processes. Herein, a novel continuous flow anaerobic/oxic/anoxic/oxic (AOA-O) process, which integrated denitrifying dephosphatation, endogenous denitrification and anammox in the anoxic zone, was developed to enhance nutrient elimination from low carbon/nitrogen sewage (3.4 in average). After the long-term operation (280 days), a satisfactory nutrient removal performance (effluent PO43--P: 0.2 mg P/L, total inorganic nitrogen (TIN):8.9 mg N/L) was obtained. Mass balance indicated that anammox contributed to 26.1% TIN removal and denitrifying dephosphatation contributed to 25.6% phosphorus removal, respectively. The cooperation of anammox bacteria retained in biofilms and endogenous denitrifying bacteria in flocculent sludge was responsible for the enhanced nutrient removal in the anoxic zone. Dechloromonas carried out phosphorus uptake both under oxic conditions and anoxic conditions. This study can broaden the application prospect of mainstream anammox.