Performance and mechanism of modified biological nutrient removal process in treating low carbon-to-nitrogen ratio wastewater

Untangling the impacts of bacterial community on carbon dioxide and nitrous oxide across a drinking water reservoir

Reservoirs represent a critical component of greenhouse gas (GHG) emissions, yet the intricacies of how biotic and abiotic factors influence GHG dynamics within reservoirs remain largely unexplored. Herein, we investigated the spatiotemporal patterns of CO2 and N2O emissions and the underlying factors in the Danjiangkou Reservoir, Asia's largest artificial freshwater reservoir. We found that this reservoir was a significant source of GHGs to the atmosphere, with peak CO2 emissions observed in autumn (1544.39 ± 652.53 μatm) and N2O emissions in winter (32.57 ± 8.87 μmol/L). Moreover, we identified crucial bacterial biomarkers that regulate GHG dynamics, and these GHG biomarkers exhibited consistent seasonal patterns with the corresponding GHGs, concerning their abundance and niche breadth. Notably, GHG biomarkers displayed larger effects on the variations of N2O than CO2 emissions, while physiochemical variables were more critical for CO2 dynamics, highlighting the need to consider both biotic and abiotic factors when evaluating GHG emissions from reservoirs. Overall, this study advanced our knowledge of GHG emissions and their driving mechanisms in artificial reservoirs, emphasizing the importance of functional microbes in estimating and managing CO2 and N2O emissions from artificial reservoirs worldwide.

Response of wastewater treatment performance and bacterial community to original and aged polyvinyl chloride microplastics in sequencing batch reactors

Microplastics (MPs) are prevalent in wastewater treatment systems, and their behavior is further complicated after undergoing aging processes. This study explored the impact of original and aged polyvinyl chloride (PVC) MPs on wastewater treatment performance and bacterial communities. Results revealed that Fenton-aging treatment induced surface roughening of the MPs and altered their chemical properties. Prolonged exposure to original and aged PVC MPs severely inhibited the removal of chemical oxygen demand and NH4+-N, along with lower sludge concentrations. Additionally, PVC MPs increased the production of loosely-bound extracellular polymeric substances (EPS) and decreased protein levels in tightly-bound fractions. The presence of PVC MPs also shifted the bacterial community, reducing nitrogen removal bacteria while enriching EPS-forming bacteria. Furthermore, exposure to PVC MPs led to a decrease in the abundance of key genes involved in nitrogen metabolism. These findings offer insights into the effects of MPs, especially aged variants, on wastewater treatment processes.

Impact of glyphosate on soil bacterial communities and degradation mechanisms in large-leaf tea plantations

This study investigated the impact of glyphosate on bacterial communities and their degradation mechanisms in large-leaf tea soil, through exposure microcosm and enrichment culture experiments. Soils from three tea gardens in Yunnan, China, were used: two glyphosate-free (JM and KL) for microcosm study and one long-term exposed (G2) for enrichment culture experiment. The results revealed a two-phase degradation process with half-lives of 12.7 to 268 days, while the metabolite AMPA was notably persistent. The acidic conditions and high organic content of tea soils may retard glyphosate microbial availability and degradation. Glyphosate initially stimulated bacterial growth but led to abundance declines with prolonged exposure. It tended to enhance bacterial diversity at lower doses. Network complexity increased in JM soil where strong adsorption moderated glyphosate exposure, yet decreased in KL soil where weak adsorption enabled greater microbial-glyphosate interactions. Community structure analysis revealed soil-specific responses, with decreased Proteobacteria in JM soil and Actinobacteria in KL soil, while several phyla including Proteobacteria, Acidobacteriota, Chloroflexi, Myxococcota, and Verrucomicrobiota showed increased abundance. PICRUSt2 analysis indicated enhanced biosynthesis and cell growth pathways, while carbohydrate metabolism, nitrogen metabolism, and xenobiotics biodegradation pathways were reduced. LEfSe analysis identified potential degrading biomarkers primarily from Proteobacteria, Acidobacteriota, Myxococcota, Chloroflexi, and Actinobacteriota, suggesting their putative role in degradation. The enriched consortium G2 efficiently degraded 400 mg/L glyphosate within 7 days, with notable increases in Afipia, Dokdonella, and Cohnella abundance. This study provides insights into bacterial interactions with glyphosate in tea soils, suggesting strategies for contamination mitigation and environmental restoration.

Alum sludge-driven electro-phytoremediation in constructed wetlands: a novel approach for sustainable nutrient removal

In addition to their advantages as promising methods for wastewater treatment, CWs exhibit poor performance in terms of N and P removal efficiency in the effluent of wastewater treatment plants. By focusing on this issue, we designed CWs integrated with a biochar-doped activated carbon cloth (ACC) electrode and alum sludge from water treatment plants as a substrate to achieve concomitant organic matter and nutrient removal efficiency. Compared with the use of one layer of alum sludge in CWs (CWs-C3) with ACC electrodes inserted in two layers, which uses one layer of alum sludge, a significant improvement in removal efficiency was achieved (96% for COD; 89% for TN; and 77% for TP). The findings revealed that the application of potential accompanied by the insertion of a cathode ACC electrode into the first layer of alum sludge was beneficial for completing nitrification and facilitating denitrification in the cathode and anode regions, respectively, resulting in increased removal of organic matter and nutrients. Further evaluation revealed that the TN-TP synergetic removal mechanism was influenced by the use of Fe2+ as an electron donor and as a driving force for the development of autotrophic denitrifying bacteria to increase nitrate reduction. Additionally, the formation of FePO4 and AlPO4 and their adsorption through the interaction of FeOOH and AlOOH with phosphate constitute the main removal mechanism for TP in wastewater. Another reason for the increased removal efficiency in the CW-C3 reactor was the greater abundance and microbial diversity effectuated by the application of potential in the anode and cathode regions. In summary, a promising strategy for simultaneously promoting organic matter and nutrients and utilizing CWs on a large scale and in practical applications was proposed.

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.

Deep insights into the assembly mechanisms, co-occurrence patterns, and functional roles of microbial community in wastewater treatment plants

The understanding of activated sludge microbial status and roles is imperative for improving and enhancing the performance of wastewater treatment plants (WWTPs). In this study, we conducted a deep analysis of activated sludge microbial communities across five compartments (inflow, effluent, and aerobic, anoxic, anaerobic tanks) over temporal scales, employing high-throughput sequencing of 16S rRNA amplicons and metagenome data. Clearly discernible seasonal patterns, exhibiting cyclic variations, were observed in microbial diversity, assembly, co-occurrence network, and metabolic functions. Notably, summer samples exhibited higher α-diversity and were distinctly separated from winter samples. Our analysis revealed that microbial community assembly is influenced by both stochastic processes (66%) and deterministic processes (34%), with winter samples demonstrating more random assembly compared to summer. Co-occurrence patterns were predominantly mutualistic, with over 96% positive correlations, and summer networks were more organized than those in winter. These variations were significantly correlated with temperature, total phosphorus and sludge volume index. However, no significant differences were found among microbial community across five compartments in terms of β diversity. A core community of keystone taxa was identified, playing key roles in eight nitrogen and eleven phosphorus cycling pathways. Understanding the assembly mechanisms, co-occurrence patterns, and functional roles of microbial communities is essential for the design and optimization of biotechnological treatment processes in WWTPs.

Impacts of O2:CH4 ratios and CH4 concentrations on the denitrification and CH4 oxidations of a novel AME-AD system

Aerobic methane (CH4) oxidation coupled to denitrification (AME-D) is a promising process for the denitrification of low C/N wastewater. Compared with anaerobic denitrifying bacteria, aerobic denitrifying bacteria may enable AME-D have high denitrification ability under aerobic conditions. This study constructed a novel aerobic methane oxidation coupled to aerobic denitrification (AME-AD) system using the typical aerobic denitrifying bacteria Paracoccus pantotrophus ATCC35512 and the typical aerobic methane oxidizing bacteria Methylosinus trichosporium OB3b. The denitrification and CH4 oxidations of AME-AD with different O2:CH4 ratios (0:1, 0.25:1, 0.5:1, 0.75:1, 1:1 and 1.25:1) and CH4 concentrations (0, 14000, 28000, 42000, 56000 and 70000 mg m-3) were investigated in batch experiments. Higher O2:CH4 ratios can significantly improve the denitrification and CH4 oxidations of the AME-AD (P < 0.05). The treatment with an O2:CH4 ratio of 1.25:1 had the highest denitrification rate (0.036 mg h-1) and highest CH4 oxidation rate (0.20 mg h-1). The CH4 concentration in the headspace was positively correlated with the AME-AD denitrification rate. The calculated CH4/NO3-(mol/mol) in most treatments ranged from 5.76 to 6.84. In addition, excessively high O2 and CH4 concentrations can lead to increased nitrous oxide (N2O) production in AME-AD. The N2O production rate was up to 1.00 μg h-1 when the O2:CH4 was 1.25:1. These results can provide data support for the application of AME-AD for low-C/N wastewater treatment and greenhouse gas emission reduction.

Positive effects of appropriate micro-aeration on landfill stabilization: Mitigating ammonia and VFAs accumulation

The slow stabilization process of landfill had brought obstacles to urbanization. The paper investigated the efficacy and mechanism of micro-aeration intensity for landfill stabilization. The micro-aeration intensity of 0.05 L/(h·kg) resulted in a significant increase of volatile fatty acids (VFAs) in the hydrolysis stage, and the NH4+-N concentration was reduced by 22.1 %. At the end of landfill, VFAs were rapidly degraded and organic matter was reduced from 36 % to 16 %, which was 55.5 % more efficient than the control group. In addition, the community succession and structure of bacteria and archaea were analyzed. The micro-aeration intensity of 0.05 L/(h·kg) increased the abundance of hydrolyzing functional bacteria such as Pseudomonas and Bacillus, and allowed methanogenic bacteria such as Methanobacterium and Methanothrix to gradually establish oxygen tolerance in the microaerobic environment. The appropriate micro-aeration intensity can accelerate the stabilization process of landfill, which has environmental and economic benefits.

Multi-omics illuminates the functional significance of previously unknown species in a full-scale landfill leachate treatment plant

Landfill leachate treatment plants (LLTPs) harbor a vast reservoir of uncultured microbes, yet limited studies have systematically unraveled their functional potentials within LLTPs. Combining 36 metagenomic and 18 metatranscriptomic datasets from a full-scale LLTP, we unveiled a double-edged sword role of unknown species in leachate biotreatment and environmental implication. We identified 655 species-level genome bins (SGBs) spanning 47 bacterial and 3 archaeal phyla, with 75.9 % unassigned to any known species. Over 90 % of up-regulated functional genes in biotreatment units, compared to the leachate influent, were carried by unknown species and actively participated in carbon, nitrogen, and sulfur cycles. Approximately 79 % of the 37,366 carbohydrate active enzymes (CAZymes), with ∼90 % novelty and high expression, were encoded by unknown species, exhibiting great potential in biodegrading carbohydrate compounds linked to human meat-rich diets. Unknown species offered a valuable genetic resource of thousands of versatile, abundant, and actively expressed metabolic gene clusters (MGCs) and biosynthetic gene clusters (BGCs) for enhancing leachate treatment. However, unknown species may contribute to the emission of hazardous N2O/H2S and represented significant reservoirs for antibiotic-resistant pathogens that posed environmental safety risks. This study highlighted the significance of considering both positive and adverse effects of LLTP microbes to optimize LLTP performance.

Performances of a novel BAF with ferromanganese oxide modified biochar (FMBC) as the carriers for treating antibiotics, nitrogen and phosphorus in aquaculture wastewater

In this paper, a biological aerated filter (BAF) based on ferromanganese oxide-biochar (FMBC) was constructed to investigated the removal performance and mechanism for conventional pollutants and four kinds of antibiotic, in contrast of conventional zeolite loaded BAF (BAF-A) and bamboo biochar filled BAF (BAF-B). Results showed that the average removal efficiency of total nitrogen (TN), total phosphorus (TP) and antibiotics in a FMBC-BAF (named by BAF-C) were 52.97 ± 2.27%, 51.58 ± 1.92% and 70.36 ± 1.00% ~ 81.65 ± 0.99% respectively in running period (39-100 d), which were significantly higher than those of BAF-A and BAF-B. In the BAF-C, the expression of denitrification enzyme activities and the secretion of extracellular polymeric substance (EPS) especially polyprotein (PN) were effectively stimulated, as well as accelerated electron transfer activity (ETSA) and lower electrochemical impedance spectroscopy (EIS) were acquired. After 100 days of operation, the abundance of nitrogen, phosphorus and antibiotic removal functional bacteria like Sphingorhabdus (4.52%), Bradyrhizobium (1.98%), Hyphomicrobium (2.49%), Ferruginibacter (7.80%), unclassified_f_Blastoca tellaceae (1.84%), norank_f_JG30-KF-CM45 (6.82%), norank_f_norank_o_SBR1031 (2.43%), Nitrospira (2.58%) norank_f_Caldilineaceae (1.53%) and Micropruina (1.11%) were enriched. Mechanism hypothesis of enhanced performances of nutrients and antibiotics removal pointed that: The phosphorus was removed by adsorption and precipitation, antibiotics removal was mainly achieved through the combined action of adsorption and biodegradation, while nitrogen removal was realized by biologic nitrification and denitrification in a FMBC-BAF for aquaculture wastewater treatment.

Study on the enhancement of low carbon-to-nitrogen ratio urban wastewater pollutant removal efficiency by adding sulfur electron acceptors

The effective elimination of nitrogen and phosphorus in urban sewage treatment was always hindered by the deficiency of organic carbon in the low C/N ratio wastewater. To overcome this organic-dependent barrier and investigate community changes after sulfur electron addition. In this study, we conducted a simulated urban wastewater treatment plant (WWTP) bioreactor by using sodium sulfate as an electron acceptor to explore the removal efficiency of characteristic pollutants before and after the addition of sulfur electron acceptor. In the actual operation of 90 days, the removal rate of sulfur electrons' chemical oxygen demand (COD), ammonia nitrogen, and total phosphorus (TP) with sulfur electrons increased to 94.0%, 92.1% and 74%, respectively, compared with before the addition of sulfur electron acceptor. Compared with no added sulfur(phase I), the reactor after adding sulfur electron acceptor(phase II) was demonstrated more robust in nitrogen removal in the case of low C/N influent. the effluent ammonia nitrogen concentration of the aerobic reactor in Pahse II was kept lower than 1.844 mg N / L after day 40 and the overall concentration of total phosphorus in phase II (0.35 mg P/L) was lower than that of phase I(0.76 mg P/L). The microbial community analysis indicates that Rhodanobacter, Bacteroidetes, and Thiobacillus, which were the predominant bacteria in the reactor, may play a crucial role in inorganic nitrogen removal, complex organic degradation, and autotrophic denitrification under the stress of low carbon and nitrogen ratios. This leads to the formation of a distinctive microbial community structure influenced by the sulfur electron receptor and its composition. This study contributes to further development of urban low-carbon-nitrogen ratio wastewater efficient and low-cost wastewater treatment technology.

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.

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.

Wastewater treatment from a science faculty during the COVID-19 pandemic by using ammonium-oxidising and heterotrophic bacteria

During and after the pandemic caused by the SARS-CoV-2 virus, the use of personal care products and disinfectants increased in universities worldwide. Among these, quaternary ammonium-based products stand out; these compounds and their intermediates caused substantial changes in the chemical composition of the wastewater produced by these institutions. For this reason, improvements and environmentally sustainable biological alternatives were introduced in the existing treatment systems so that these institutions could continue their research and teaching activities. For this reason, the objective of this study was to develop an improved culture medium to cultivate ammonium oxidising bacteria (AOB) to increase the biomass and use them in the treatment of wastewater produced in a faculty of sciences in Bogotá, D.C., Colombia. A Plackett Burman Experimental Design (PBED) and growth curves served for oligotrophic culture medium, and production conditions improved for the AOB. Finally, these bacteria were used with total heterotrophic bacteria (THB) for wastewater treatment in a pilot plant. Modification of base ammonium broth and culture conditions (6607 mg L-1 of (NH4)2SO4, 84 mg L-1 CaCO3, 40 mg L-1 MgSO4·7H2O, 40 mg L-1 CaCl2·2H2O and 200 mg L-1 KH2PO4, 10% (w/v) inoculum, no copper addition, pH 7.0 ± 0.2, 200 r.p.m., 30 days) favoured the growth of Nitrosomonas europea, Nitrosococcus oceani, and Nitrosospira multiformis with values of 8.23 ± 1.9, 7.56 ± 0.7 and 4.2 ± 0.4 Log10 CFU mL-1, respectively. NO2- production was 0.396 ± 0.0264, 0.247 ± 0.013 and 0.185 ± 0.003 mg L-1 for Nitrosomonas europea, Nitrosococcus oceani and Nitrosospira multiformis. After the 5-day wastewater treatment (WW) by co-inoculating the three studied bacteria in the wastewater (with their self-microorganisms), the concentrations of AOB and THB were 5.92 and 9.3 Log10 CFU mL-1, respectively. These values were related to the oxidative decrease of Chemical Oxygen Demand (COD), (39.5 mg L-1), Ammonium ion (NH4+), (6.5 mg L-1) Nitrite (NO2-), (2.0 mg L-1) and Nitrate (NO3-), (1.5 mg L-1), respectively in the five days of treatment. It was concluded, with the improvement of a culture medium and production conditions for three AOB through biotechnological strategies at the laboratory scale, being a promising alternative to bio-augment of the biomass of the studied bacteria under controlled conditions that allow the aerobic removal of COD and nitrogen cycle intermediates present in the studied wastewater.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03961-4.

Integration of ammonium assimilation with denitrifying phosphorus removal for efficient nutrient management in wastewater treatment

Nutrient removal from sewage is transitioning to nutrient recovery. However, biological treatment technologies to remove and recover nutrients from domestic sewage are still under investigation. This study delved into the integration of ammonium assimilation with denitrifying phosphorus removal (DPR) as a method for efficient nutrient management in sewage treatment. Results indicated this approach eliminated over 80 % of the nitrogen in the influent, simultaneously recovering over 60 % of the nitrogen as the activated sludge through ammonia assimilation, and glycerol facilitated this process. The nitrification/denitrifying phosphorus removal ensured the stability of both nitrogen and phosphorus removal. The phosphorus removal rate exceeded 96 %, and the DPR rate reached over 90 %. Network analysis highlighted a stable community structure with Proteobacteria and Bacteroidota driving ammonium assimilation. The synergistic effect of fermentation bacteria, denitrifying glycogen-accumulating organisms, and denitrifying phosphorus-accumulating organisms contributed to the stability of nitrogen and phosphorus removal. This approach offers a promising method for sustainable nutrient management in sewage treatment.

Efficient reactivation of anammox sludge after prolonged storage using a combination of batch and continuous reactors

Due to the slow growth rate of anammox bacteria, enriched sludge is required for the rapid start-up of anammox-based reactors. However, it is still unclear if long-term stored anammox sludge (SAS) is an effective source of inoculum to accelerate reactor start-up. This study explored the reactivation of long-term SAS and developed an efficient protocol to reduce the start-up period of an anammox reactor. Although stored for 13 months, a low level of the specific anammox activity of 28 mg N/g VSS/d was still detected. Experimental Phase 1 involved the direct application of SAS to an upflow sludge bed reactor (USB) operated for 90 d under varying conditions of hydraulic retention time and nitrogen concentrations. In Phase 2, batch runs were executed prior to the continuous operation of the USB reactor. The biomass reactivation in the continuous flow reactor was unsuccessful. However, the SAS was effectively reactivated through a combination of batch runs and continuous flow feed. Within 75 days, the anammox process achieved a stable rate of nitrogen removal of 1.3 g N/L/day and a high nitrogen removal efficiency of 84.1 ± 0.2%. Anammox bacteria (Ca. Brocadia) abundance was 37.8% after reactivation. These overall results indicate that SAS is a feasible seed sludge for faster start-up of high-rate mainstream anammox reactors.

Integrating Bio-Electrochemical Sensors and Machine Learning to Predict the Efficacy of Biological Nutrient Removal Processes at Water Resource Recovery Facilities

Monitoring biological nutrient removal (BNR) processes at water resource recovery facilities (WRRFs) with data-driven models is currently limited by the data limitations associated with the variability of bioavailable carbon (C) in wastewater. This study focuses on leveraging the amperometric response of a bio-electrochemical sensor (BES) to wastewater C variability, to predict influent shock loading events and NO3- removal in the first-stage anoxic zone (ANX1) of a five-stage Bardenpho BNR process using machine learning (ML) methods. Shock loading prediction with BES signal processing successfully detected 86.9% of the influent industrial slug and rain events of the plant during the study period. Extreme gradient boosting (XGBoost) and artificial neural network (ANN) models developed using the BES signal and other recorded variables provided a good prediction performance for NO3- removal in the ANX1, particularly within the normal operating range of WRRFs. A sensitivity analysis of the XGBoost model using SHapley Additive exPlanations indicated that the BES signal had the strongest impact on the model output and current approaches to methanol dosing that neglect C availability can negatively impact nitrogen (N) removal due to cascading impacts of overdosing on nitrification efficacy.

Effect of ultrasound on the stability of partial nitrification: Under the interference of aeration rate

The fluctuation of dissolved oxygen is one of the primary cause of disruptions to the consistent operation of partial nitrification, and the level of dissolved oxygen is mainly controlled by the aeration rate. This study investigated the influence of ultrasonic treatment on the stability of partial nitrification of activated sludge under different aeration conditions. After being treated with ultrasound (energy density = 0.20 W·mL-1, treatment time = 10 min), partial nitrification process operated stably for 67 days, with the nitrite accumulation rate above 83.89 %. The effluent contained 42.50 mg·L-1 of nitrite, much higher than the control reactor (0.30 mg·L-1). The gap between the specific ammonia and nitrite oxidation rates widened continuously as the aeration rate increased, and nitrite-oxidizing bacteria activity did not recover even under conditions with a very high oxygen content. Further analysis showed that ultrasonic treatment had obvious stripping effect on excess extracellular polymeric substances (EPS), especially loosely bound EPS and protein. Additionally, long-term ultrasonic treatment promoted the enrichment of Nitrosomonas and strongly inhibited Nitrotoga. Based on these findings, it appears that under conditions of high aeration rate, ultrasound effectively suppress the recovery of Nitrotoga activity and improve the stability of partial nitrification.

Non-uniform dissolved oxygen distribution and high sludge concentration enhance simultaneous nitrification and denitrification in a novel air-lifting reactor for municipal wastewater treatment: A pilot-scale study

Achieving simultaneous carbon and nitrogen removal with sludge-liquid separation in a single reactor offers a solution to land shortages and improves treatment efficiency in municipal wastewater treatment plants of megacities. This study proposes a novel air-lifting continuous-flow reactor configuration with an alternative-aeration strategy that creates multi-functional zones for anoxic, oxic, and settlement processes. The optimal operational conditions for the reactor include a long anoxic hydraulic retention time, low dissolved oxygen (DO) in the oxic zone, and no specific reflux for external nitrifying liquid, which exhibit a high nitrogen removal efficiency of over 90% in treating real sewage with C/N < 4 in the pilot-scale study. Results show that a high sludge concentration and a low DO concentration facilitate simultaneous nitrification and denitrification, and a well mixing of sludge and substrate in different reaction zones promotes nitrogen removal. The long-term operation enriches functional microbes for carbon storage and nutrient removal.

Application and improvement methods of sludge alkaline fermentation liquid as a carbon source for biological nutrient removal: A review

Alkaline fermentation can reduce the amount of waste activated sludge and prepare sludge alkaline fermentation liquid (SAFL) rich in short-chain fatty acids (SCFAs), which can be used as a high-quality carbon source for the biological nutrient removal (BNR) process. This review compiles the production method of SAFL and the progress of its application as a BNR carbon source. Compared with traditional carbon sources, SAFL has the advantages of higher efficiency and economy, and different operating conditions can influence the yield and structure of SCFAs in SAFL. SAFL can significantly improve the nutrient removal efficiency of the BNR process. Taking SAFL as the internal carbon source of BNR can simultaneously solve the problem of carbon source shortage and sludge treatment difficulties in wastewater treatment plants, and further reduce the operating cost. However, the alkaline fermentation process results in many refractory organics, ammonia and phosphate in SAFL, which reduces the availability of SAFL as a carbon source. Purifying SCFAs by removing nitrogen and phosphorus, directly extracting SCFAs, or increasing the amount of SCFAs in SAFL by co-fermentation or combining with other pretreatment methods, etc., are effective measures to improve the availability of SAFL.

Using Genomics to Decipher the Enigmatic Properties and Survival Adaptation of Candidate Phyla Radiation

Microbial ecology is a critical field for understanding the composition, diversity, and functions of microorganisms in various environmental and health-related processes. The discovery of Candidate Phyla Radiation (CPR) through culture-independent methods has introduced a new division of microbes characterized by a symbiotic/parasitic lifestyle, small cell size, and small genome. Despite being poorly understood, CPRs have garnered significant attention in recent years due to their widespread detection in a variety of environmental and clinical samples. These microorganisms have been found to exhibit a high degree of genetic diversity compared to other microbes. Several studies have shed light on their potential importance in global biogeochemical cycles and their impact on various human activities. In this review, we provide a systematic overview of the discovery of CPRs. We then focus on describing how the genomic characteristics of CPRs have helped them interact with and adapt to other microbes in different ecological niches. Future works should focus on discovering the metabolic capacities of CPRs and, if possible, isolating them to obtain a better understanding of these microorganisms.

Effect of Fe3+ on the nutrient removal performance and microbial community in a biofilm system

In this study, the influence of Fe3+ on N removal, microbial assembly, and species interactions in a biofilm system was determined. The results showed that maximum efficiencies of ammonia nitrogen (NH4+-N), total nitrogen (TN), phosphorus (P), and chemical oxygen demand (COD) removal were achieved using 10 mg/L Fe3+, reaching values of 100, 78.85, 100, and 95.8%, respectively, whereas at concentrations of 15 and 30 mg/L Fe3+ suppressed the removal of NH4+-N, TN, and COD. In terms of absolute abundance, the expression of bacterial amoA, narG, nirK, and napA was maximal in the presence of 10 mg/L Fe3+ (9.18 × 105, 8.58 × 108, 1.09 × 108, and 1.07 × 109 copies/g dry weight, respectively). Irrespective of Fe3+ concentrations, the P removal efficiency remained at almost 100%. Candidatus_Competibacter (10.26–23.32%) was identified as the most abundant bacterial genus within the system. Determinism (50%) and stochasticity (50%) contributed equally to microbial community assembly. Co-occurrence network analysis revealed that in the presence of Fe3+, 60.94% of OTUs in the biofilm system exhibited positive interactions, whereas 39.06% exhibited negative interactions. Within the OTU-based co-occurrence network, fourteen species were identified as key microbes. The stability of the system was found to be predominantly shaped by microbial cooperation, complemented by competition for resources or niche incompatibility. The results of this study suggested that during chemical P removal in wastewater treatment plants using biofilm methods, the concentration of supplemental Fe3+ should be maintained at 10 mg/L, which would not only contribute to P elimination, but also enhance N and COD removal.

Insight into the temporal dynamics of microbial succession and ecology mechanisms in biological activated carbon tanks

Biological activated carbon (BAC) has long been applied in China to guarantee water quality and to achieve drinking water regulations. However, a knowledge gap remains regarding the temporal dynamics of microbial communities, particularly microbe-based assembly and co-occurrence patterns. Accordingly, this study investigated the evolution of BAC microbial communities using a pilot-scale system and examined by multivariate ecological combined with high-throughput Illumina sequencing and statistical methods. The results showed that BAC microbial diversity reached its peak in 2 years and declined thereafter. Microbial communities composition was accompanied by significant temporal evolution in the BAC biofilm. Deterministic processes gained in importance along with time, especially homogeneous selection which contributed 59.09 %-75.63 % to the community assembly in 8-yr, 9-yr, and 10-yr BAC. According to co-occurrence network analysis, microbial networks have more unstable structures over time, as evidenced by higher modularity, heightened connectivity, and fewer keystones. Moreover, the interaction between microbial taxa tended to have a higher proportion of competitive relationships during the operation of the BAC tank, ranging from 13.51 % to 76.35 %. Based on these dynamic ecological processes, microbial community succession in BAC biofilm might undergo four phases: community establishment (Years 0-2); community stability (Years 2-5); community quasi-degradation (Years 5-8); community degradation (Years 8-10). The performance of BAC was greatly influenced by community development, and contaminant removal gradually decreased as community succession proceeded. These results add to our knowledge of microbial ecology and provide the basis for further research into microbial communities' regulation strategies in BAC tanks.