Nitrogen removal pathways during simultaneous nitrification, denitrification, and phosphorus removal under low temperature and dissolved oxygen conditions

Genera complying denitrifying phosphorus removal community contribute excellent SND-PR in a pilot cyclic SBR: Effect of DO, settling and recirculation rate on process performance

This work investigated the role of operational conditions and typical functional microbes to maximize the nutrient removal efficiency of a pilot-scale sequencing batch reactor (SBR) system (100 m3/d) that treated municipal wastewater. The pilot system was operated in five phases, including start-up and four runs at variable cycle times (2.0, 1.5, 1.7, 2.0, and 3.0h) with an average readily biodegradable chemical oxygen demand (rbCOD) to chemical oxygen demand (COD) ratio of ∼15.3%. The best TN removal 'ηmax' of 75.6 ± 5.6% (TNinfluent = 27.5 ± 6.5 mg/L, TNeffluent ≤ 5.9 mg/L) and TP removal 'pmax' 77.9 ± 6.3% (TPinfluent = 3.8 ± 1.3 mg/L, TPeffluent ≤ 1.0 mg/L) along with the COD, biochemical oxygen demand (BOD), and total suspended solids (TSS) removal efficiencies of 87.3 ± 4.5%, 92.7 ± 2.8%, 92.0 ± 3.5%, respectively, were observed during run 3 (2h cycle) at settling/total cycle times ratio (S/T) of 0.33 and recirculation/total cycle times ratio (R/T) of 0.017 (6.4%), and operating DO of 0.5-2.5 mg/L. The denitrifying polyphosphate accumulating organisms 'DPAOs' of Burkholderia (17.0%), Rhodocyclales (6.1%), and Flavobacterium (8.7%) classes, and Nitrifiers of Nitrospira (5.4%) and Nitrosomonas (5.4%) classes were dominant in accomplishing simultaneous nitrification, denitrification, and phosphorus removal (SND-PR) in the pilot system.

Simultaneous removal of nitrate, copper, carbamazepine, and calcium from micropolluted water by fulvic acid through promotion of denitrification and microbial-induced calcium precipitation: Performance and mechanism

In this paper, a study of the denitrification strain Cupriavidus sp. W12 was conducted to remove copper (Cu2+), carbamazepine (CBZ), and calcium (Ca2+) by microbial-induced calcium precipitation (MICP) after adding fulvic acid (FA). After the addition of 20 mg/L FA, the removal efficiencies of nitrate (NO3--N), Cu2+, CBZ, and Ca2+ reached 100.0 %, 98.7 %, 96.6 %, and 73.6 %, correspondingly and there was no accumulation of nitrite (NO2--N). FA stimulated the growth of strain W12, improved electron transfer activity, and facilitated the conversion of gaseous nitrogen. The research revealed that FA might enhance microbial activity and result in a more dense and porous structure of the biological precipitate. Cu2+ and CBZ were removed by co-precipitation and adsorption. As the initial report of FA promoting MICP to remove complex pollutants, this paper offers a theoretical foundation for NO3--N, Cu2+, CBZ, and Ca2+ remediation in micropolluted water.

A comprehensive floc model for simulating simultaneous nitrification, denitrification, and phosphorus removal

A comprehensive floc model for simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) was designed, incorporating polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), intrinsic half-saturation coefficients, and explicit external mass transfer terms. The calibrated model was able to effectively describe experimental data over a range of operating conditions. The estimated intrinsic half-saturation coefficients of oxygen values for ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, ordinary heterotrophic organisms (OHOs), PAOs, and GAOs were set at 0.08, 0.18, 0.03, 0.07, and 0.1 mg/L, respectively. Simulation suggested that low dissolved oxygen (DO) environments favor K-strategist nitrifying bacteria and PAOs. In SNDPR, virtually all influent and fermentation-generated volatile fatty acids were assimilated as polyhydroxyalkanoates by PAOs in the anaerobic phase. In the aerobic phase, PAOs absorbed 997 % and 171 % of the benchmark influent total phosphorus mass loading through aerobic growth and denitrification via nitrite. These high percentages were because they were calculated relative to the influent total phosphorus, rather than total phosphorus at the end of the anaerobic period. When considering simultaneous nitrification and denitrification, about 23.1 % of influent total Kjeldahl nitrogen was eliminated through denitrification by PAOs and OHOs via nitrite, which reduced the need for both oxygen and carbon in nitrogen removal. Moreover, the microbial and DO profiles within the floc indicated a distinct stratification, with decreasing DO and OHOs, and increasing PAOs towards the inner layer. This study demonstrates a successful floc model that can be used to investigate and design SNDPR for scientific and practical purposes.

Effects of carbon to nitrogen ratio on nitrogen removal in a single-stage microaerobic system: A model-based evaluation

Single-stage microaerobic systems have been proven to be effective for concurrent removal of ammonium and organic carbon from sewage. While mechanistic models derived from activated sludge models (ASMs) have simulated nutrients removal under microaerobic conditions, classic ASMs exhibit limitations in capturing the intricate effects of carbon to nitrogen (C/N) ratio on nitrogen removal performance. To address this issue, a mechanistic model modified from the classic ASMs was proposed to capture the combined inhibitory effects of carbon and ammonium on microaerobic systems. This modified model was established based on experimental data from a single-stage microaerobic reactor encompassing simultaneous nitrification-denitrification and anammox processes. The inhibition coefficient of C/N ratio was integrated into the process rate equations, and its effectiveness was validated through model performance evaluation. Compared to the classic models, the modified one achieved superior predictions for nitrite and nitrate nitrogen concentrations. Simulations revealed that under optimized conditions with a C/N of 4.57 and a dissolved oxygen (DO) of 0.41 mg/L, the system could achieve up to 95.5% of total nitrogen (TN) removal efficiency. Based on the simulation of substrate uptake/production rate, increasing the nitrogen loading rate (NLR) rather than organic loading rate (OLR) was crucial for efficient nitrogen removal. The proposed modified model served as a valuable tool for designing and optimizing similar biological wastewater treatment systems.

Simultaneous removal of nitrate, oxytetracycline and copper by ferrous-manganese co-driven immobilized bioreactor

The treatment of polluted water contaminated by nitrate, antibiotics, and heavy metals is a difficult problem in the current water treatment process. In this study, MnFe2O4 modified illite was mixed with sodium alginate (SA) to prepare a biological carrier illite@MnFe2O4@SA (IMFSA), which was used to immobilize strain Zoogloea sp. MFQ7 and construct a bioreactor. The bioreactor can use sodium acetate as a carbon source as well as ferrous and manganese ions as additional electron donors to achieve efficient nitrate removal. The denitrification capability of bioreactor was considerably enhanced by the addition of illite@MnFe2O4 (IMF) in comparison to SA biological carrier. The bioreactor was able to achieve a nitrate removal efficiency of 97.2% when hydraulic retention time is 5.0 h, C/N ratio is 2.0, and the concentration of Fe2+ and Mn2+ were 5.0 mg L-1. Furthermore, the bioreactor can achieve efficient removal of oxytetracycline (91.8%) and copper (85.6%) through the adsorption by IMF and biological iron-manganese precipitates. High-throughput sequencing results indicated that Zoogloea was successfully immobilized into the biocarrier. According to the KEGG database, it is suggested that the addition of modified IMF enhances denitrification and stimulates the expression of genes associated with the iron-manganese redox cycle.

Achieving simultaneous nitrification and endogenous denitrifying phosphorus removal in anaerobic/intermittently-aerated moving bed biofilm reactor for low carbon-to-nitrogen ratio wastewater treatment

In this study, an anaerobic/intermittently-aerated moving bed biofilm reactor (AnIA-MBBR) was proposed to realize simultaneous nitrification and endogenous denitrifying phosphorus removal (SNEDPR) in treating low carbon-to-nitrogen (C/N) ratio wastewater. The effect of different intermittent aeration modes (short and long aeration) on nutrients' removal was investigated. With the C/N ratio around 3, the removal efficiencies of total nitrogen and phosphorus were 90% and 74%, 88% and 59%, respectively, for short aeration and long aeration. The different aeration time also altered the nutrients' degradation pathway, biofilm characteristics, microbial community, and functional metabolic pathways. The results confirmed the occurrence of aerobic denitrifiers, anoxic denitrifiers, phosphorus accumulating organisms, glycogen accumulating organisms in AnIA-MBBR systems and their synergistic performance induced the SNEDPR. These results indicated that the application of AnIA in MBBR systems was an effective strategy to achieve SNEDPR, providing better simultaneous removal performance of nitrogen and phosphorus from low C/N ratio wastewater.

A sustainable integrated anoxic/aerobic bio-contactor process for simultaneously in-situ deodorization and pollutants removal from decentralized domestic sewage

The integration of anoxic filter and aerobic rotating biological contactor shows promise in treating rural domestic sewage. It offers high efficiency, low sludge production, and strong shock resistance. However, further optimization is needed for odor control, pollutant removal, and power consumption. In this study, the investigation on a one-pump-drive lab-scale device of retention anoxic filter (RAF) integrated with hydraulic rotating bio-contactor (HRBC) and its optimal operation mode were conducted. During the 50-day operation, optimal operation parameters were investigated. These parameters included a 175 % reflux ratio (RR), 5-h hydraulic retention time in the RAF (HRTRAF), and 2.5-h hydraulic retention time in the HRBC (HRTHRBC). Those conditions characterized a micro-aerobic environment (DO: 0.6-0.8 mg/L) in RAF, inducing improved deodorization (89.3 % sulfide removal) and denitrification (85.9 % nitrate removal) simultaneously. During the operation period, 84.79 ± 3.87 % COD, 82.71± 2.06 % NH 4 + -N, 74.83 ± 2.06 % TN, 91.68± 2.12 % S2-, and 89.04 ± 1.68 % TON were removed in RAF-HRBC. Based on large amount of operational data, organic loading rate curves of RAF-HRBC were validated and calibrated as a crucial reference to aid in full-scale designs and applications. The richness of microbial community was improved in both RAF and HRBC. In the RAF, the autotrophic sulfide-oxidizing nitrate-reducing bacteria (a-son) and heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-son) were selectively enriched, which intensified the sulfide removal and denitrification process. In the two-stage HRBC system, the 1st stage RBC was primarily composed of organics degraders, while the 2nd stage RBC consisted mainly of ammonium oxidizers. Overall, the integrated RAF-HRBC process holds significant potential for simultaneously improving pollutant removal and in-situ odor mitigation in decentralized domestic sewage treatment. This process specifically contributes to enhancing environmental sustainability and operational efficiency.

Biodegradability of algal-derived dissolved organic matter and its influence on methylmercury uptake by phytoplankton

Methylmercury (MeHg) uptake by phytoplankton represents a key step in determining the exposure risks of aquatic organisms and human beings to this potent neurotoxin. Phytoplankton uptake is believed to be negatively related to dissolved organic matter (DOM) concentration in water. However, microorganisms can rapidly change DOM concentration and composition and subsequent impact on MeHg uptake by phytoplankton has rarely been tested. Here, we explored the influences of microbial degradation on the concentrations and molecular compositions of DOM derived from three common algal sources and tested their subsequent impacts on MeHg uptake by the widespread phytoplankton species Microcystis elabens. Our results indicated that dissolved organic carbon was degraded by 64.3‒74.1% within 28 days of incubating water with microbial consortia from a natural meso‑eutrophic river. Protein-like components in DOM were more readily degraded, while the numbers of molecular formula for peptides-like compounds had increased after 28 days' incubation, probably due to the production and release of bacterial metabolites. Microbial degradation made DOM more humic-like which was consistent with the positive correlations between changes in proportions of Peaks A and C and bacterial abundance in bacterial community structures as illustrated by 16S rRNA gene sequencing. Despite rapid losses of the bulk DOM during the incubation, we found that DOM degraded after 28 days still reduced the MeHg uptake by Microcystis elabens by 32.7‒52.7% relative to a control without microbial decomposers. Our findings emphasize that microbial degradation of DOM would not necessarily enhance the MeHg uptakes by phytoplankton and may become more powerful in inhibiting MeHg uptakes by phytoplankton. The potential roles of microbes in degrading DOM and changing the uptakes of MeHg at the base of food webs should now be incorporated into future risk assessments of aquatic Hg cycling.

Nitrogen removal by algal-bacterial consortium during mainstream wastewater treatment: Transformation mechanisms and potential N2O mitigation

This work investigated nitrogen transformation pathways of the algal-bacterial consortium as well as its potential in reducing nitrous oxide (N₂O) emission in enclosed, open and aerated reactors. The results confirmed the superior ammonium removal performance of the algal-bacterial consortium relative to the single algae (Chlorella vulgaris) or the activated sludge, achieving the highest efficiency at 100% and the highest rate of 7.34 mg N g MLSS^-1 h^-1 in the open reactor with glucose. Enhanced total nitrogen (TN) removal (to 74.6%) by the algal-bacterial consortium was achieved via mixotrophic algal assimilation and bacterial denitrification under oxygen-limited and glucose-sufficient conditions. Nitrogen distribution indicated that ammonia oxidation (∼41.8%) and algal assimilation (∼43.5%) were the main pathways to remove ammonium by the algal-bacterial consortium. TN removal by the algal-bacterial consortium was primarily achieved by algal assimilation (28.1-40.8%), followed by bacterial denitrification (2.9-26.5%). Furthermore, the algal-bacterial consortium contributed to N₂O mitigation compared with the activated sludge, reducing N₂O production by 35.5-55.0% via autotrophic pathways and by 81.0-93.6% via mixotrophic pathways. Nitrogen assimilation by algae was boosted with the addition of glucose and thus largely restrained N₂O production from nitrification and denitrification. The synergism between algae and bacteria was also conducive to an enhanced N₂O reduction by denitrification and reduced direct/indirect carbon emissions.

A new insight in enhancing phosphate enrichment in biofilm process: Comparison of the key metabolic pathways in highly-efficient and dominant PAOs based on metagenomics

The formation of dominant phosphate-accumulating organisms (PAOs) is essential for the high enrichment of phosphate in biofilm sequencing batch reactors (BSBR) for phosphorus recovery. The dominant PAOs in the biofilm process have not been isolated and purified, and the key metabolic pathways that promote the formation of dominant PAOs are still unclear. In this study, four strains of highly-efficient PAOs were obtained by an innovative isolation procedure. The relationship between the abundance of highly-efficient and dominant PAOs and the phosphate removal ability was compared. We found that the abundance of PAOs was positively correlated with the phosphate removal efficiency in vitro pure culture and complex biofilm process. Metagenomics analysis revealed that compared with highly-efficient PAOs cultured in vitro, dominant PAOs in biofilms had unique key metabolic pathways, F-ATPases and N-Acyl homoserine lactones (AHLs). F-ATPases are important for maintaining the proton motive force (PMF) required for the uptake of carbon sources by PAOs, and AHLs are participating in phosphate metabolism through quorum sensing (QS) mediated secretion of extracellular polymeric substance (EPS). The formation of dominant PAOs was promoted by optimizing carbon source uptake and phosphate metabolism. This study revealed that the difficult isolation of dominant PAOs was due to the AHLs-mediated QS, and we identified the key pathways regulating the formation of dominant PAOs in biofilms through genomics analysis. Our findings provide insights in enhancing phosphate enrichment in BSBR by modulating the components of microbial community under the low concentration of carbon source consumption.

Changes of nitrogen and phosphorus removal pattern caused by alternating aerobic/anoxia from the perspective of microbial characteristics

The purpose of this study was to compare the impact of different numbers of alternating aerobic/anoxic (A/O) cycles on pollutant removal. Three sequential batch reactors (SBRs) with varying numbers of alternating A/O cycles were established. Under the tertiary anoxic operating conditions, the removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP) were 88.73%, 89.56%, 72.15%, and 77.61%, respectively. Besides, alternating A/O affected the dominant microbial community relative abundance (Proteobacteria and Bacteroidetes) and increased microbial richness and diversity. It also increased the relative abundance of aerobic denitrifying, heterotrophic nitrifying, and denitrifying phosphorus removal bacteria to change N and P removal patterns. Furthermore, the abundance of carbohydrate metabolism and amino acid metabolism was improved by alternating A/O to improve organic matter and TN removal.

Formation characteristics of algal-bacteria granular sludge under low-light environment: From sludge characteristics, extracellular polymeric substances to microbial community

In this study, the formation characteristics of algal-bacteria granular sludge (ABGS) under low-light environment (80, 110, and 140 μmol/m²/s) were investigated. The findings revealed that the stronger light intensity favored the improvement of sludge characteristics, nutrient removal performances, and extracellular polymeric substance (EPS) secretion at the growing stage, which were more preferential to facilitate the formation of ABGS. However, after the mature stage, the weaker light intensity ensured more stable operation of the system, as shown by contributing to sludge settlement performance, denitrification, and EPS secretion. According to the results of high-throughput sequencing, the dominant bacterial genus of the mature ABGS cultured under low light intensity were all Zoogloe, while the dominant algal genus was different. For the mature ABGS, the 140 and 80 μmol/m²/s light intensity had the most significant activation effect to the functional genes related to carbohydrate metabolism and amino acid metabolism, respectively.

New insight and enhancement mechanisms for Feammox process by electron shuttles in wastewater treatment - A systematic review

Ammonium oxidation coupled to Fe(III) reduction (Feammox) is a newly discovered iron-nitrogen cycle process of microbial catalyzed NH₄⁺ oxidation coupled with iron reduction. Fe(III) often exists in the form of insoluble iron minerals resulting in reduced microbial availability and low efficiency of Feammox. Electron shuttles(ESs) can be reversibly oxidized and reduced which has the potential to improve Feammox efficiency. This review summarizes the discovery process, electron transfer mechanism, influencing factors and driven microorganisms of Feammox, ang expounds the possibility and potential mechanism of ESs to enhance Feammox efficiency. Based on an in-depth analysis of the current research situation of Feammox for nitrogen removal, the knowledge gaps and future research directions including how to apply ESs enhanced Feammox to promote nitrogen removal in practical wastewater treatment have been highlighted. This review can provide new ideas for the engineering application research of Feammox and strong theoretical support for its development.

Simultaneous nitrification, denitrification, and phosphorus removal from municipal wastewater at low temperature

A lab-scale sequencing batch reactor was employed to study simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) when treating municipal wastewater at 10 °C for 158 days. An anaerobic/aerobic configuration that had previously been effective when treating synthetic wastewater was explored, however, these conditions were relatively ineffective for real municipal wastewater. Incorporation of a post-anoxic phase (i.e., anaerobic/aerobic/anoxic) improved nitrogen and phosphorus removals to 91.1 % and 92.4 %, respectively while achieving a simultaneous nitrification and denitrification efficiency of 28.5 %. Activity tests indicated that 15.8 % and 56.0 % of nitrogen were removed by denitrifying phosphorus accumulating organisms in the aerobic phase and heterotrophs using hydrolyzed carbon in the post-anoxic phase, respectively. 16S rRNA gene analysis and stoichiometric ratios indicated the system was rich in phosphorus accumulating organisms (Dechloromonas and Ca. Accumulibacter). Overall, implementation of the post-anoxic phase eliminated carbon uptake for denitrification in the anaerobic phase and was essential to maintaining SNDPR at low temperatures.

Nutrients and Environmental Factors Cross Wavelet Analysis of River Yi in East China: A Multi-Scale Approach

The accumulation of nutrients in rivers is a major cause of eutrophication, and the change in nutrient content is affected by a variety of factors. Taking the River Yi as an example, this study used wavelet analysis tools to examine the periodic changes in nutrients and environmental factors, as well as the relationship between nutrients and environmental factors. The results revealed that total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen (NH4+-N) exhibit multiscale oscillation features, with the dominating periods of 16-17, 26, and 57-60 months. The continuous wavelet transform revealed periodic fluctuation laws on multiple scales between nutrients and several environmental factors. Wavelet transform coherence (WTC) was performed on nutrients and environmental factors, and the results showed that temperature and dissolved oxygen (DO) have a strong influence on nutrient concentration fluctuation. The WTC revealed a weak correlation between pH and TP. On a longer period, however, pH was positively correlated with TN. The flow was found to be positively correct with N and P, while N and P were found to be negatively correct with DO and electrical conductance (EC) at different scales. In most cases, TP was negatively correlated with 5-day biochemical oxygen demand (BOD₅) and permanganate index (COD_Mn). The correlation between TN and COD_Mn and BOD₅ was limited, and no clear dominant phase emerged. In a nutshell, wavelet analysis revealed that water temperature, pH, DO, flow, EC, COD_Mn, and BOD₅ had a pronounced influence on nutrient concentration in the River Yi at different time scales. In the case of the combination of environmental factors, pH and DO play the largest role in determining nutrient concentration.

Performance of hydrogel immobilized bioreactors combined with different iron ore wastes for denitrification and removal of copper and lead: Optimization and possible mechanism

Reasonable and efficient removal of mixed pollutants (nitrate and heavy metals) in industrial wastewater under heavy metal pollution has attracted more attention in recent years. The target strain Aquabacterium sp. XL4 was immobilized with different iron ore wastes (IOW) using polyvinyl alcohol (PVA) to construct four immobilized bioreactors. The results showed that when the ratio of C/N was 1.5 and the hydraulic retention time (HRT) was 8.0h, the denitrification performance of the bioreactor was the best, and the maximum denitrification efficiency of the bioreactor with sponge iron (SI) as the iron source was 97.19% (2.42mg L^-1 h^-1). Furthermore, by adjusting the concentration of Cu²⁺ and Pb²⁺, the stress behavior of the bioreactor to heavy metals under the influence of each IOW was investigated. The bioreactor has stronger tolerance and removal efficiency to Pb²⁺ and Cu²⁺ in the presence of pellets ore (PO) and refined iron ore (RO), respectively. Moreover, the high-throughput data showed that Aquabacterium accounted for a high proportion in the immobilized bioreactor, and the prediction of functional genes based on the KEGG database showed that the addition of IOW was closely related to the acceleration of nitrate transformation and the inflow and outflow of iron in cells.

Eggshell based biochar for highly efficient adsorption and recovery of phosphorus from aqueous solution: Kinetics, mechanism and potential as phosphorus fertilizer

Development of an efficient and green adsorbent is of great significance for phosphorus removal and recovery from eutrophic water. This work prepared an eggshell modified biochar (ESBC) by co-pyrolysis of eggshells and corn stalk. ESBC exhibited an excellent performance for phosphorus adsorption over a wide pH range (5-13), and achieved a maximum adsorption of 557.0 mg P/g. The adsorption process was well fitted by pseudo-second-order model (R² > 0.962) and Sips model (R² > 0.965), and it was endothermic (ΔH⁰ > 0) and spontaneous (ΔG⁰ < 0) according to thermodynamic analysis. The column experiment confirmed the feasibility of ESBC as a filter media for phosphorus removal in flow condition, and obtained a P removal of 460.0 mg/g. Soil burial tests indicated P-laden ESBC has a good P slow-release performance (maintained for up to 25 days). Overall, ESBC has a promising application potential as an efficient adsorbent for phosphorus recovery and subsequently as a slow-release fertilizer.

Rapid start-up and stable operation of an aerobic/oxic/anoxic simultaneous nitrification, denitrification, and phosphorus removal reactor with no sludge discharge

An anaerobic/aerobic/anoxic mode simultaneous nitrification, denitrification, and phosphorus removal system was visited for enhanced low-strength wastewater treatment and dramatic in situ sludge reduction. Results showed that rapid start-up was achieved with conventional activated sludge after 15 days, with effluent ammonia nitrogen, total nitrogen, total phosphorus, and chemical oxygen demand being 0.25, 7.89, 0.12, 24.37 mg/L, respectively. A two-stage biomass growth rate was observed with the sludge yield of 0.285 (day 1-50) and 0.017 g MLSS/g COD (day 51-110) without sludge discharge. Dynamics of bacterial community has been identified with outstanding accumulation of Candidatus_Competibacter up to 29.06 %, which contributed to both simultaneous nutrients removal and sludge reduction. Further analysis via PICRUSt2 revealed the main pathway of nitrogen metabolism, while proposed mechanism for phosphorus removal with no sludge discharge was analyzed from the intracellular and extracellular perspectives. Overall, this study provided guidance and reference for the development and application of A/O/A-SNDPR technology.

Impact and microbial mechanism of continuous nanoplastics exposure on the urban wastewater treatment process

Contamination by nanoplastics in urban water has aroused increasing concern. The impact of nanoplastic exposure on the wastewater treatment process in the long term is still unclear. This study investigated the effect of continuous nanoplastic exposure (R1:0, R2:10, R3:100, and R4:1000 μg/L) on the nitrification and denitrification processes for over 200 days in a sequencing batch reactor (SBR). The results revealed that nanoplastic exposure does not demonstrate significant inhibition of total nitrogen removal. The ammonia oxidation rate (19.24 ± 0.01 mgN/gMLVSS/h, p < 0.05) and denitrification rate (11.78 ± 0.11 mgN/ gMLVSS/h, p < 0.05) in R4 was significantly lower than the control (R1: 0 μg/L). The maximal reaction velocities of N₂O reduction (Vmax) were improved after long-term exposure to nanoplastics in high concentrations. The R3 demonstrated the highest Vmax value-six times higher than R4 and approximately 20 times higher than R1 and R2. The microbial structure largely varied with the exposure to nanoplastics, where the exposure to a high concentration largely suppressed the nitrifier and selectively enriched the denitrifier. The percentage of the top 20 genera of denitrifiers increased from 31.76% to 63.42%, and the nitrifiers decreased from an initial 12.40% to 2.83% for R4. The predominant genera were found to be Thauera, Azoarcus, and Defluviicoccus in R4 and R3 which indicated their tolerance to nanoplastics. The function prediction results indicated that the membrane transport function was significantly enhanced and the lipid metabolism function was significantly reduced in R4 as compared with the control (R1, p<0.05). This may be attributed to the adsorption of nanoplastics on bacteria. Observation under a scan electronic microscope demonstrated that the nanoplastics were firmly attached to the microbe surface and aggregated in activated sludge at high nanoplastics dosed reactor. These results deepen the understanding of the effect of nanoplastics on the urban wastewater treatment process and provide valuable information for the management of nanoplastic contamination in urban wastewater.

Disintegration of waste sludge as an element bio-circular economy in waste water treatment plant towards carbon recovery for biological nutrient removal

The goal of the study was to evaluate the possibility of use of disintegrated excess sludge to enhance combined biological nutrient removal from wastewater. In the experiment lasting 295 days four runs were performed. Effectiveness of contaminants removal in sequencing batch reactor without and with applying sludge subjected previously to hydrodynamic disintegration at three energy density (Ɛ_L) levels was analysed. It was shown that Ɛ_L is a crucial parameters responsible for the characteristics of disintegrated sludge applied as a carbon source for biological nutrient removal. Using sludge disintegrated at 70 and 210 kJ/L the increase in effectiveness of N and P removal was noted, averagely by 16.1 % (N removal) and 70.3 % (P removal) at Ɛ_L = 70 kJ/L and by 17.8 % and 63.1 % at Ɛ_L = 210 kJ/L. On the contrary, use of sludge disintegrated at Ɛ_L = 280 kJ/L caused decline in N removal by averagely 12.8 %, what was a consequence of nitrification failure.

Metagenomics reveals the metabolism of polyphosphate-accumulating organisms in biofilm sequencing batch reactor: A new model

This study assessed the impact of the operating conditions of the biofilm sequencing batch reactor (BSBR) on the community structure and the growth/metabolic pathways of its polyphosphate-accumulating organisms (PAOs). There are significant difference with reference to the enhanced biological phosphorus removal (EBPR) process. The leading PAOs in BSBR generally are capable of high affinity acetate metabolism, gluconeogenesis, and low affinity phosphate transport, and have various carbon source supplementation pathways to ensure the efficient circulation of energy and reducing power. A new model of the metabolic mechanism of PAOs in the BSBR was formulated, which features low glycogen metabolism with simultaneous gluconeogenesis and glycogenolysis and differs significantly from the classic mechanism based on Candidatus_Accumulibacter and Tetrasphaera. The findings will assist the efficient recovery of low concentration phosphate in municipal wastewater.