Dynamic characteristics of microbial community and soluble microbial products in partial nitrification biofilm system developed from marine sediments treating high salinity wastewater

A new perspective on the simultaneous removal of nitrogen, tetracycline, and phosphorus by moving bed biofilm reactor under co-metabolic substances

With the burgeoning growth of aquaculture industry, high concentration of NH4+-N, phosphorus and tetracycline are the prevalent pollutants in aquaculture wastewater posing a significant health risk to aquatic organisms. Therefore, an effective method for treating aquaculture wastewater should be urgently explored. Simultaneous removal of NH4+-N, phosphorus, tetracycline, and chemical oxygen demand (COD) in aquaculture wastewater was developed by moving bed biofilm reactor (MBBR) under co-metabolic substances. The result showed that co-metabolism substances had different effects on MBBR performance, and 79.4 % of tetracycline, 68.2 % of NH4+-N, 61.3 % of total nitrogen, 88.3 % of COD, and 38.1 % of total phosphorus (TP) were synchronously removed with sodium acetate as a co-metabolic carbon source. Protein (PN), polysaccharide (PS), and electron transfer system activity were used to evaluate the MBBR performances, suggesting that PN/PS ratio was 1.48, 0.91, 1.07, 3.58, and 0.79 at phases I-V. Additionally, a mode of tetracycline degradation and TP removal was explored, and the cell apoptosis was evaluated by flow cytometry. The result suggested that 74 %, 83 %, and 83 % of tetracycline were degraded by extracellular extracts, intracellular extracts, and cell debris, and there was no difference between extracts and non-enzyme in TP removal. The ratio of viable and dead cells from biofilm reached 33.3 % and 7.68 % with sodium acetate as a co-metabolic carbon source. Furthermore, Proteobacteria and Bacteroidetes in biofilm were identified as the dominant phyla for tetracycline and nutrients removal. This study provides a new strategy for tetracycline and nutrients removal from aquaculture wastewater through co-metabolism.

Selective nitrogen removal in constructed wetlands enhanced by MnX-GAC (X=Fe or Zn): Performance, mechanism and removal pathway

Constructed wetlands (CWs) are widely used to treat wastewater containing nitrogenous due to their low energy consumption, low maintenance costs, and significant ecological benefits. However, they face challenges such as low denitrification efficiency and greenhouse gas emissions during treatment. Enhancing the synergistic performance of the "substrate-microorganism" system within CWs is considered an effective way to address these problems. Granular activated carbon-supported Mn-based composite fillers (MnX-GAC, X = Fe or Zn) were prepared and placed in the upper and lower positions of the CW. Mn and Fe within these fillers act as electron acceptors or donors to enhance nitrogen removal and reduce nitrous oxide (N2O) emissions. MnX-GAC boosted microbial interspecies electron transfer and improved the total nitrogen removal efficiency to 77.1 %. Moreover, the CW with MnX-GAC reduced N2O emissions during the denitrification process and increased nitrogen (N2) selectivity by 43.4 % compared with the control. The addition of MnX-GAC enhanced microbial interspecies electron transfer by stimulating microorganisms to secrete more protein and increasing their Cytochrome c content. Macrogenomic analyses revealed that MnX-GAC increased the abundances of denitrifying microorganisms (Anaerolinea and Thauera), conducive to nitrogen removal, extracellular polymeric substance secretion or aggregation, and nitrite nitrogen (NO2--N) reduction to N2. In the nitrogen transformation pathway, MnX-GAC increased the abundance of functional genes related to nitrification (amoABC, nxrAB and hao), denitrification (napABC, narGHI, nirKS, norBC and nosZ) and anaerobic ammonia oxidation (hzsABC and hdh), resulting in high nitrogen removal and selectivity towards N2. In this study, MnX-GAC showed excellent performance in selective nitrogen removal in CWs, providing a new strategy to improve the performance of wastewater treatment in CWs and reduce the emission of greenhouse gases.

Rapid start-up of nitrogen and organic matter removal in sequencing batch biofilm reactors treating hypersaline mustard tuber wastewater with autochthonous microorganisms

The treatment of hypersaline industrial wastewater (≥50 g NaCl L-1) faces persistent challenges in start-up and nitrogen removal efficiency due to microbial inhibition under extreme salinity. However, leveraging native microbial consortia for rapid system establishment remains underexplored. This study proposed a rapid-start strategy for sequencing batch biofilm reactors (SBBRs) treating hypersaline mustard tuber wastewater (MTWW) through in-situ enrichment of autochthonous microorganisms in MTWW. Five SBBRs, each with distinct inoculation (municipal sludge vs. autochthonous microorganisms) and salinity-increase strategies (direct vs. gradual increase), were systematically compared. Systems acclimated with autochthonous microorganisms achieved start-up within 30 days (Phase Ⅰ:0-30 g NaCl L-1 and Phase Ⅱ: 30-70 g NaCl L-1), with COD and TN removal efficiencies of 82.40 %-92.85 % and 85.72 %-94.68 %, respectively. Notably, rapid-start systems maintained comparable TN and COD removal to gradual acclimation (p > 0.05) despite transient nitrification instability during dissolved oxygen fluctuations (recovered within 5∼6 cycles). The rapid-start reactors demonstrated greater ammonia oxidation activity, driven by the dominance of ammonia-oxidizing archaea (AOA) over bacteria (AOB). Rapid salinity increases selectively enriched halophilic functional bacteria, such as Halomonas, Nitratireductor, Arcobacter, and Phaeodactylibacter, supporting anoxic/aerobic and sulfur-driven autotrophic denitrification processes. Most of the functional microorganisms across all reactors originated directly from the MTWW, confirming the indispensability of autochthonous inoculum. Our findings demonstrate that autochthonous microorganisms in hypersaline MTWW can be directly engineered for rapid system establishment, bypassing lengthy acclimation. This strategy reduces start-up costs and provides a scalable solution for industries requiring immediate hypersaline wastewater treatment capacity.

Guardians of Future Food Safety: Innovative Applications and Advancements in Anti-biofouling Materials

Biofilm formation is a widespread natural phenomenon that poses a substantial threat to food microbiological safety, with direct implications for consumer health. To combat this challenge effectively, one promising strategy involves the development of functional anti-biofouling layers on food-contact surfaces to deter microbial adhesion. Herein, we explore the methodologies for fabricating both hydrophilic and hydrophobic anti-biofouling materials, along with a detailed examination of their inherent antiadhesive mechanisms. Furthermore, we provide concise insights into exemplary applications of anti-biofouling materials within the context of the food industry. This comprehensive analysis not only advances our understanding of biofilm prevention but also sets the stage for innovative developments in anti-biofouling materials and their future applications in food science. These advancements hold the potential to significantly enhance food microbiological safety, ensuring that consumers can confidently enjoy food products of the highest standards in terms of hygiene and quality.

Effect of biofilm physical characteristics on their susceptibility to antibiotics: impacts of low-frequency ultrasound

Biofilms are highly resistant to antimicrobials, often causing chronic infections. Combining antimicrobials with low-frequency ultrasound (LFU) enhances antimicrobial efficiency, but little is known about the underlying mechanisms. Biofilm physical characteristics, which depend on factors such as growth conditions and age, can have significant effects on inactivation efficiency. In this study, we investigated the susceptibility of Pseudomonas aeruginosa biofilms to tobramycin, with and without LFU treatment. The biofilms were grown under low and high fluid shear to provide different characteristics. Low-shear biofilms exhibited greater thickness, roughness, and porosity and lower density, compared to high-shear biofilms. The biofilm matrix of the high-shear biofilms had a three times higher protein-to-polysaccharide ratio, suggesting greater biofilm stiffness. This was supported by microrheology measurements of biofilm creep compliance. For the low-shear biofilms without LFU, the viability of the biofilms in their inner regions was largely unaffected by the antibiotic after a 2-hour treatment. However, when tobramycin was combined with LFU, the inactivation for the entire biofilm increased to 80% after 2 h. For the high-shear biofilms without LFU, higher LFU intensities were needed to achieve similar inactivation results. Microrheology measurements revealed that changes in biofilm inactivation profiles were closely related to changes in biofilm mechanical properties. Modeling suggests that LFU changes antibiotic diffusivity within the biofilm, probably due to a "decohesion" effect. Overall, this research suggests that biofilm physical characteristics (e.g., compliance, morphology) are linked to antimicrobial efficiency. LFU weakens the biofilm while increasing its diffusivity for antibiotics.

Impact of salinity and time on structure and functional potential of wastewater treatment biofilms in intermittent sand bioreactors

High salt wastewater is produced in industries, including seafood and pickling processing. The salinity in such wastewaters has been shown to negatively impact biological treatment efficacy. Little is known about the changes in the microbial community structure in the mature biological 2 treatment systems, the impacts of salinity on community composition, and the shifts over time during operation. This study aimed to identify the changes in the microbial community due to both salt and days of operation through 16s rRNA sequencing and KEGG functional predictions. Intermittent sand bioreactors (ISBs) with a focus on ammonia treatment were utilized. Results showed that the overall community structure and diversity were distinct as wastewater salinity varied from 0%-1.3%. At 1.3% salinity Zoogloea, a common genus in wastewater treatment plants, was not present and Aequorovita, Thauera and Dokdonella became the dominant genera. Nitrosomonas, an important ammonia oxidizing bacteria, increased in abundance with days of operation but was not significantly impacted by an increase in salinity. This finding was further supported by an increase in predicted nitrification potential with time of operation within all intermittent sand bioreactors tested. These results provide a deeper understanding of the impacts of salinity on microbial community development in biological treatment systems and elucidate the shifts in community structure occurring during early operations and into system maturity.

Revealing bioresponses of biofilm and flocs to salinity gradient in halophilic biofilm reactor

Understanding the different biological responses to salinity gradient between coexisting biofilm and flocs is crucial for regulating the ecological function of biofilm system. This study investigated performance, dynamics, and community assembly of biofilm system under 3 %-7% salinity gradient. The removal efficiency of NH4+-N remained stable and exceeded 93 % at 3 %-6% salinity, but decreased to below 80 % at 7 % salinity. The elevated salinity promoted the synthesis of extracellular polymer substrates, inhibited microbial respiration, and significantly regulated the microbial community structure. Compared to flocs, biofilm exhibited greater species diversity and richer Nitrosomonas. It was found diffusion limitations dominated the microbial community assembly under the salinity gradient. And microbial network revealed positive interactions predominated the microbial relationships, designating norank Spirochaetaceae, unclassified Micrococcales, Corynebacterium, and Pusillimonas as keystone species. Moreover, distinct salinity preferences in nitrogen transformation-related genes were observed. This study can improve the understanding to the regulation of biofilm systems to salt stresses.

Effects of temperature on nitrifying membrane-aerated biofilms: An experimental and modeling study

Temperature is known to have an important effect on the morphology and removal fluxes of conventional, co-diffusional biofilms. However, much less is known about the effects of temperature on membrane-aerated biofilm reactors (MABRs). Experiments and modeling were used to determine the effects of temperature on the removal fluxes, biofilm thickness and morphology, and biofilm microbial community structure of nitrifying MABRs. Steady state tests were carried out at 10 °C and 30 °C. MABRs grown at 30 °C had higher ammonium removal fluxes (5.5 ± 0.9 g-N/m2/day at 20 mgN/L) than those grown at 10 °C (3.4 ± 0.2 g-N/m2/day at 20 mgN/L). The 30 °C biofilms were thinner and rougher, with a lower protein to polysaccharides ratio (PN/PS) in their extracellular polymeric substance (EPS) matrix and greater amounts of biofilm detachment. Based on fluorescent in-situ hybridization (FISH), there was a higher relative abundance of nitrifying bacteria at 30 °C than at 10 °C, and the ratio of AOB to total nitrifiers (AOB + NOB) was higher at 30 °C (95.1 ± 2.3%) than at 10 °C (77.2 ± 8.6 %). Anammox bacteria were more abundant at 30 °C (16.6 ± 3.7 %) than at 10 °C (6.5 ± 2.4 %). Modeling suggested that higher temperatures increase ammonium oxidation fluxes when the biofilm is limited by ammonium. However, fluxes decrease when oxygen becomes limited, i.e., when the bulk ammonium concentrations are high, due to decreased oxygen solubility. Consistent with the experimental results, the model predicted that the percentage of AOB to total nitrifiers at 30 °C was higher than at 10 °C. To investigate the effects of temperature on biofilm diffusivity and O2 solubility, without longer-term changes in the microbial community, MABR biofilms were grown to steady state at 20 °C, then the temperature changed to 10 °C or 30 °C overnight. Higher ammonium oxidation fluxes were obtained at higher temperatures: 1.91 ± 0.24 g-N/m2/day at 10 °C and 3.19 ± 0.40 g-N/m2/day at 30 °C. Overall, this work provides detailed insights into the effect of temperature on nitrifying MABRs, which can be used to better understand MABR behavior and manage MABR reactors.

Nutrients recovery by coupled bioreactor of heterotrophic ammonia assimilation and microbial fuel cell in saline wastewater

Heterotrophic ammonia assimilation (HAA) process had been widely used in the treatment of high salt wastewater, but the electro enhanced coupling process and electron transfer process were rarely studied. In this study, a HAA process coupled microbial fuel cell (MFC) system was established to treat ammonia-containing wastewater under increasing salinity to achieve nitrogen recovery and electricity generation. Up to 95.4 % NH4+-N and 96.4 % COD removal efficiencies were achieved at 2 % salinity in HAA-MFC. The maximum power density and current density at 2 % salinity were 29.93 mW/m2 and 182.37 mA/m2, respectively. The residual organic matter in the cathode effluent was effectively removed by the anode. The increase of salinity not only enhanced the sludge settling performance and activity, but also promoted the enzyme activity and amino acid production of the ammonia assimilation pathway. Marinobacter and Halomonas were gradually enriched at the anode and cathode with increased salinity to promote ammonia assimilation and electron production. This research offered a promising solution to overcome salinity-related challenges in wastewater treatment and resource recovery.

Occurrence, characteristics, and microbial community of microplastics in anaerobic sludge of wastewater treatment plants

Wastewater treatment plants (WWTPs) usually contain microplastics (MPs) due to daily influents of domestic and municipal wastewater. Thus, the WWTPs act as a point source of MPs distribution in the environment due to their incapability to remove MPs completely. In this study, MPs occurrence and distribution in anaerobic sludge from WWTPs in different regions (Kaifeng "KHP", Jinan "JSP", and Lanzhou "LGP") were studied. Followed by MPs identification by microscopy and Fourier transform infrared (FTIR) spectrum. The microbial communities associated with anaerobic sludge and MPs were also explored. The results showed that MPs concentrations were 16.5, 38.5, and 17.2 particles/g of total solids (TS) and transparent MPs accounted for 49.1%, 58.5%, and 48.3% in KHP, JSP, and LGP samples, respectively. Fibers represented the most common shape of MPs in KHP (49.1%), JSP (56.0%), and LGP (69.0%). The FTIR spectroscopy indicated the predominance of polyethylene polymer in 1-5 mm MPs. The Proteobacteria, Chloroflexi, Actinobacteria, Bacteroidetes, and Planctomycetes were the abundant phyla in all anaerobic sludge. The bacterial genera in KHP and LGP were similar, in which Caldilinea (>23%), Terrimonas (>10%), and Ferruginibacter (>7%) formed the core bacterial genera. While Rhodococcus (15.3%) and Rhodoplanes (10.9%) were dominating in JSP. The archaeal genera Methanosaeta (>69%) and Methanobrevibacter (>10%) were abundant in KHP and LGP sludge. While Methanomethylovorans accounted for 90% of JSP. Acetyltransferase and hydratase were the major bacterial enzymes, while reductase was the key archaeal enzyme in all anaerobic sludge. This study provided the baseline for MPs distribution, characterization, and MPs associated microbes in WWTPs.

Performance analysis of microbial fuel cell - membrane bioreactor with reduced graphene oxide enhanced polypyrrole conductive ceramic membrane: Wastewater treatment, membrane fouling and microbial community under high salinity

The application of membrane bioreactor (MBR) in high salinity wastewater treatment was mainly hindered by membrane fouling. Microbial fuel cell (MFC)-MBR coupling system was established to alleviate membrane fouling and save energy. Reduced graphene oxide/polypyrrole ceramic membrane (rGO/PPy CM) with high conductivity and stability was innovatively placed in MFC-MBRs as both cathode and filter, with PPy CM, rGO/PPy CM and CM placed in other reactors. MFC-MBR (rGO/PPy) and MFC-MBR (PPy) achieved higher pollutant removal efficiencies (90.73 % and 90.45 % for TOC, 87.22 % and 86.56 % for NH4+-N, respectively) and superior anti-fouling performance (1.86 and 1.93 kPa/d for average membrane fouling rates) than both conventional MBRs (CMBRs). The stable voltage generation was around 287 and 242 mV, respectively. Through high throughput sequencing, electric field showed a positive correlation with the abundance and activity of most dominant phylum (Bacteroidetes, Chloroflexi, Actinobacteria, and Firmicutes) and functional genes (amoA, hao, narG, napA, nirK, norB, and nosZ), thereby improving pollutant removal efficiency. The higher conductivity of rGO/PPy CM resulted in enhanced electric field intensity, leading to superior performance of anti-fouling and pollutant removal. This study inventively explored the effects of conductive membrane property on electricity generation performance, microbial community, pollutant removal and membrane fouling, providing theoretical support for the selection of electrode materials in MFC-MBR.

Novel strategy for treating high salinity oilfield produced water: Pyrite-activated peroxymonosulfate coupled with heterotrophic ammonia assimilation

Existing conventional biological treatment techniques face numerous limitations in effectively removing total petroleum hydrocarbons (TPHs) and ammonia (NH4+-N) from oilfield-produced water (OPW), highlighting the pressing need for innovative pre-oxidation and biological treatment processes. In this study, a pyrite-activated peroxymonosulfate (PMS)-coupled heterotrophic ammonia assimilation (HAA) system was established to achieve satisfactory system performance for OPW treatment. Pyrite sustained-release Fe2+-activated PMS was used to produce SO4•- and •OH, and 71.0 % of TPHs were effectively removed from the oil wastewater. The average TPHs and NH4+-N removal efficiencies in the test group with pre-oxidation were 96.9 and 98.3 %, compared to 46.5 and 77.1 % in the control group, respectively. The maximum fluorescence intensities of tryptophan protein and aromatic protein in the test group declined by 83.7 %. Fourier transform ion cyclotron resonance mass spectrometry revealed that pre-oxidation degraded more long-chain hydrocarbons and aromatic family compound, whereas the HAA process produced more proteins and carbohydrates. Pyrite-PMS promoted the enrichment of ammonia-assimilating bacteria, alleviating the explosive increase in extracellular polymeric substances and reducing sludge settleability. The low cost, efficiency, green chemistry principles, and synergies of this approach make it a powerful solution for practical OPW treatment to reduce environmental impacts and promote sustainable wastewater treatment.

Improving denitrification performance of biofilm technology with salt-tolerant denitrifying bacteria agent for treating high-strength nitrate and sulfate wastewater from lab-scale to pilot-scale

This study focused on the application of salt-tolerant denitrifying bacteria (DBA) in an optimized biofilm process to treat high sulfate-nitrate wastewater from lab-scale to pilot-scale. Lab-scale results demonstrated the salinity, DBA inoculum, supplementary carbon and phosphorus source significantly varied the startup periods at the range of 36-74 d, and the optimum initial start-up conditions were as follows: >0.6 g/L of DBA, 2-4 of C/N ratio, 0.3-0.6 mg/L of phosphorus and a salinity-gradient domestication method. A pilot scale of biofilm technology with DBA was further developed for treating real wastewater from the desulfuration and denitration with both high nitrate (≈200 mg/L) and sulfate (2.7%). The denitrification efficiency reached above 90% after one-month gradient-salinity of 0.5%-2.7%. Mature biofilm had dominant genera Hyphomicrobium (31.80%-61.35%), Methylotenera (0.85%-20.21%) and Thauera (1.42%-8.40%), etc. Notably, the largest genera Hyphomicrobium covered the complete denitrification genes.

Response of biofilm-based systems for antibiotics removal from wastewater: Resource efficiency and process resiliency

Biofilm-based systems have efficient stability to cope-up influent shock loading with protective and abundant microbial assemblage, which are extensively exploited for biodegradation of recalcitrant antibiotics from wastewater. The system performance is subject to biofilm types, chemical composition, growth and thickness maintenance. The present study elaborates discussion on different type of biofilms and their formation mechanism involving extracellular polymeric substances secreted by microbes when exposed to antibiotics-laden wastewater. The biofilm models applied for estimation/prediction of biofilm-based systems performance are explored to classify the application feasibility. Further, the critical review of antibiotics removal efficiency, design and operation of different biofilm-based systems (e.g. rotating biological contactor, membrane biofilm bioreactor etc.) is performed. Extending the information on effect of various process parameters (e.g. hydraulic retention time, pH, biocarrier filling ratio etc.), the microbial community dynamics responsible of antibiotics biodegradation in biofilms, the technological problems, related prospective and key future research directions are demonstrated. The biofilm-based system with biocarriers filling ratio of ∼50-70% and predominantly enriched with bacterial species of phylum Proteobacteria protected under biofilm thickness of ∼1600 μm is effectively utilized for antibiotic biodegradation (>90%) when operated at DO concentration ≥3 mg/L. The C/N ratio ≥1 is best suitable condition to eliminate antibiotic pollution from biofilm-based systems. Considering the significance of biofilm-based systems, this review study could be beneficial for the researchers targeting to develop sustainable biofilm-based technologies with feasible regulatory strategies for treatment of mixed antibiotics-laden real wastewater.

An In Silico Analysis of Synthetic and Natural Compounds as Inhibitors of Nitrous Oxide Reductase (N2OR) and Nitrite Reductase (NIR)

Nitrification inhibitors are recognized as a key approach that decreases the denitrification process to inhibit the loss of nitrogen to the atmosphere in the form of N2O. Targeting denitrification microbes directly could be one of the mitigation approaches. However, minimal attempts have been devoted towards the development of denitrification inhibitors. In this study, we aimed to investigate the molecular docking behavior of the nitrous oxide reductase (N2OR) and nitrite reductase (NIR) involved in the microbial denitrification pathway. Specifically, in silico screening was performed to detect the inhibitors of nitrous oxide reductase (N2OR) and nitrite reductase (NIR) using the PatchDock tool. Additionally, a toxicity analysis based on insecticide-likeness, Bee-Tox screening, and a STITCH analysis were performed using the SwissADME, Bee-Tox, and pkCSM free online servers, respectively. Among the twenty-two compounds tested, nine ligands were predicted to comply well with the TICE rule. Furthermore, the Bee-Tox screening revealed that none of the selected 22 ligands exhibited toxicity on honey bees. The STITCH analysis showed that two ligands, namely procyanidin B2 and thiocyanate, have interactions with both the Paracoccus denitrificans and Hyphomicrobium denitrificans microbial proteins. The molecular docking results indicated that ammonia exhibited the second least atomic contact energy (ACE) of -15.83 kcal/mol with Paracoccus denitrificans nitrous oxide reductase (N2OR) and an ACE of -15.20 kcal/mol with Hyphomicrobium denitrificans nitrite reductase (NIR). The inhibition of both the target enzymes (N2OR and NIR) supports the view of a low denitrification property and suggests the potential future applications of natural/synthetic compounds as significant nitrification inhibitors.

Application of urease-producing microbial community in seawater to dust suppression in desert

In order to solve the dust problem caused by sandstorms, this paper aims to propose a new method of enriching urease-producing microbial communities in seawater in a non-sterile environment. Besides, the difference of dust suppression performance of enriched microorganisms under different pH conditions was also explored to adapt the dust. The Fourier-transform infrared spectrometry (FTIR) and Scanning electron microscopy (SEM) confirmed the formation of CaCO₃. The X-ray diffraction (XRD) further showed that the crystal forms of CaCO₃ were calcite and vaterite. When urease activity was equivalent, the alkaline environment was conducive to the transformation of CaCO₃ to more stable calcite. The mineralization rate at pH = 10 reached the maximum value on the 7^th day, which was 97.49 ± 1.73%. Moreover, microbial community analysis results showed that the relative abundance of microbial community structure was different under different pH enrichment. Besides, the relative abundance of Sporosarcina, a representative genus of urease-producing microbial community, increased with the increase of pH under culture conditions, which consistent with the mineralization performance results. In addition, the genus level species network diagram also showed that in the microbial community, Sporosarcina was negatively correlated with another urease-producing genus Bacillus, and had a reciprocal relationship with Atopostipes, which means that the urease-producing microbial community was structurally stable. The enrichment of urease-producing microbial communities in seawater will provide empirical support for the large-scale engineering application of MICP technology in preventing and controlling sandstorms in deserts.

Cooperation of heterotrophic bacteria enables stronger resilience of halophilic assimilation biosystem than nitrification system under long-term stagnation

Long-term stagnation of biosystems (with no or very little wastewater) owing to seasonal downtime or failure maintenance brings great challenges to the performance recovery after system restart. In particular, the reduction of microbial activity and change of dissolved organic matter (DOM) affect the effluent quality and subsequent treatment procedures. Monitoring the dynamics and resilience of biosystems after long-term stagnation is important to formulate targeted countermeasures for system stability. However, the influence of long-term stagnation on autotrophic nitrification (AN) and heterotrophic assimilation (HA) biosystems has not been systematically explored. Here, we used halophilic AN and HA systems to study the stability and resilience of two nitrogen removal consortia after long-term stagnation. The results showed that 97.5 % and 93 % of ammonium and 47.0 % and 90.1 % of total nitrogen were removed using the halophilic AN and HA systems, respectively, in the stable period. After four weeks of stagnation, the HA system showed stronger resilience than AN system, in terms of faster recovery of treatment performance, and less fluctuations in sludge settleability and extracellular polymeric substances. In addition, after the stagnation period, the DOM of AN system was rich in low-molecular refractory humic acid, whereas that of HA system was rich in high-molecular proteins. The stagnation period led to the replacement of the dominant heterotrophic functional microorganisms, Paracoccus and Halomonas, with Muricauda and Marinobacterium in the HA system. The microbial network results revealed that the cooperation of heterotrophic bacteria enables stronger resilience of the HA system from prolonged stagnation than the AN system. In addition, the nitrogen removal efficiency, protein to polysaccharide ratio of EPS and fluorescence intensity of DOM were significantly correlated with the microbial community composition. These results suggest that AN system has greater risks in terms of treatment performance and sludge stability than the system after long-term stagnation.

Steel pickling rinse wastewater treatment by two-stage MABR system: Reactor performance, extracellular polymeric substances (EPS) and microbial community

A bench-scale two-stage membrane-aerated biofilm reactor (MABR) system was applied to treat steel pickling rinse wastewater with high salinity and refractory organic. The effects of salinity and aeration pressure on the treatment efficiency, extracellular polymeric substances (EPS) characteristics and microbial community structure were studied. The optimal removal efficiencies of COD, NH+ 4-N and TN reached to 62.84%, 99.57% and 51.65%, respectively. Shortcut nitrification was achieved at low aeration, and the salinity less than 4% did not remarkable affect system performance. Colorimetric determination, three-dimensional exaction-emission matrix (3D-EEM) and Fourier transform infrared spectrum (FTIR) were employed to characterize the content and composition of proteins (PN) and polysaccharides (PS) in EPS of the biofilm. The results indicated that PN, not PS, response to changes of environmental conditions played a key role. Moreover, EPS might alleviate intracellular and extracellular osmotic pressure imbalance induced by high salinity, which imparted the biofilm in MABR with prominent salt-tolerant. High-throughput sequencing displayed that nitrifiers (Nitrosomonas, Nitrospira), denitrifiers (Dechloromonas, Hyphomicrobium, Denitromonas, Denitratisoma, Candidatus_Competibacter) and aerobic denitrifiers (Pseudomonas, Thauera) were predominant salt-tolerant bacteria.

Development of a fluorescence EEM-PARAFAC model for potable water reuse monitoring: Implications for inter-component protein-fulvic-humic interactions

Measuring the surrogate parameters total organic carbon and dissolved organic carbon (TOC/DOC) is not adequate, alone, to reveal nuances in organic character for optimizing treatment in potable water reuse. Alternatively, analyzing each organic compound contributing to the surrogate measurement is not possible. As an additional analytical tool applied between these extremes, the use of excitation-emission matrix fluorescence spectroscopy with PARAllel FACtor (EEM-PARAFAC) analysis was investigated in this research to track categories (components) or families of organic compounds during treatment in recycled water schemes. Although not all organic molecules fluoresce, many do, and fluorescence helps track their fate through water treatment processes. The sites investigated in this research were Lake Lanier, in Gwinnett County, Georgia, USA; the F. Wayne Hill Water Resources Center (FWH WRC) advanced wastewater treatment facility; and two pilot facilities operated in parallel representing the current indirect potable reuse (IPR) scheme as well as a pilot that evaluated direct potable reuse (DPR). A four-component nonnegativity PARAFAC model-elucidating protein-like (including tyrosine- and tryptophan-like fluorescence in a single component), soluble microbial product (SMP)-like, fulvic-like, and humic-like components-was fitted to the data. Each of the four components was spectrally and mathematically separated, implying that the fluorescing SMP-like component was not comprised of protein-, fulvic-, or humic-like components. PARAFAC excitation loadings with dual (double) pairs of fluorescing regions centered at the same emission wavelengths but different excitation wavelengths oriented parallel to the excitation axis and perpendicular to the emission axis were attributed to individual PARAFAC components. Significantly, the observation of PARAFAC emission loadings with multiple peaks-where the protein-like component exhibited fluorescence in both protein and fulvic/humic regions-is proposed to signify an intermolecular energy transfer (< 10 nm). Correct identification of EEM-PARAFAC components is fundamental to understanding water treatment.

Enhancing robustness of halophilic aerobic granule sludge by granular activated carbon at decreasing temperature

High salinity seriously inhibits the growth and metabolism of microorganisms, resulting in poor settleability, excessive biomass loss and low treatment efficiency of biological wastewater treatment systems. The development of halophilic aerobic granular sludge (HAGS) is a feasible strategy for addressing this challenge. However, there are problems with the granulation of HAGS and the stability of granules at decreasing temperatures. In this study, granular activated carbon (GAC) with a large specific surface area and good biocompatibility was used to enhance the robustness of HAGS. The results showed that the addition of GAC shortened the granulation time from 60 d (control system) to 35 d (GAC-addition system). The proteins contents of extracellular polymeric substances (EPS) in the GAC-addition system was significantly higher (p < 0.05) than that in the control system during granulation. Satisfactory NH₄⁺-N and chemical oxygen demand (COD) removal efficiencies reached more than 96% in both systems at 18-26 °C. When the operating temperature was lower than 15 °C, the GAC-addition system exhibited better NH₄⁺-N removal performance (>80%) than the control system (<60%). Moreover, the abundance of almost all nitrogen metabolism-related genes in the GAC-addition system was higher than that in the control system. During the granulation process, the enrichment of functional microorganisms, including family Flavobacteriaceae, Rhodobacteraceae, and Cryomorphaceae, may promote the production of EPS by significantly upregulating (p < 0.05) the metabolic pathway "Signaling Molecules and Interaction" in the GAC-addition system. The overexpression of the nitrogen assimilation gene glnA in heterotrophic bacteria (Halomonas and Marinobacterium) may promote the conversion of inorganic nitrogen to extracellular proteins to adapt to the decreased operational temperature. Our findings confirm that GAC addition is a simple but effective strategy to accelerate granulation and enhance the robustness of HAGS in saline wastewater treatment.

Effects of the metabolic uncoupler TCS on residual sludge treatment: Analyses of the microbial community and sludge dewaterability potential

Residual sludge is a by-product with a large volume and complex composition from wastewater treatment plants. It is significant to reduce sludge volume to decrease the negative effects of sludge on environmental pollution and needless land use. We investigated the effects of uncoupler 3, 3', 4', 5-tetrachlorosalicylanilide (TCS) on the properties of sludge. After adding 0.12 g TCS/g VSS with 24 h mixing, the sludge concentration and total ATP content decreased by 51.1% and 60.8%, respectively. At the same time, the microbial community also changed significantly, leading to the decrease of richness and diversity. Additionally, the secretion of extracellular polymeric substances (EPS) reduced approximately 43% under the addition of 0.12 g/g VSS compared with the control. The decrement of EPS may be explained by the decreased relative abundance of functional bacteria (i.e. Chloroflexi reduced about 60% and Nitrospirota reduced about 31%). Notably, the addition of TCS before coagulation conditioning (FeCl₃) promoted the adhesion of sludge flocs according to the theory of Extended Derjaguin Landau Verwey Overbee (XDLVO), leading to the increased hydrophobicity of the residual sludge. Therefore, energy uncoupling has the potential of improving sludge dewaterability.

Effects of salinity shock on simultaneous nitrification and denitrification by a membrane bioreactor: Performance, sludge activity, and functional microflora

Physical and chemical treatments of Tungsten smelting wastewater, with high salt content and low C/N ratio, are often tedious. As a solution, this study suggested a simultaneous nitrification and denitrification membrane bioreactor (SND-MBR) for salinity gradient domestication. During the salinity acclimation period, we observed 20% and 11% removal of NH₄⁺-N and Chemical Oxygen Demand (COD), respectively. However, the SND efficiency reached 95.55% after stable operation at 3.0% salinity. Through stoichiometric and kinetic analyses, we confirmed that increased salinity significantly inhibited electron transport system activity, nitrification, and denitrification, evidenced by the extremely low ammonia monooxygenase and nitrite reductase activities. Further high-throughput sequencing showed that Nitrosomonas dominated the functional microbial flora succession and denitrification in high salinity environments. In comparison with a control, the Kyoto Encyclopedia of Genes and Genomes analysis showed that wastewater salinity weakened the functional gene level of MBR microbial flora, and the enzyme key to the assimilation nitrate reduction changed from nitrate reductase to assimilation nitrate reductase.

Solid-phase denitrification in high salinity and low-temperature wastewater treatment

Nitrogen removal from wastewater is often deteriorated under high salinity and low temperature. Solid-phase denitrification (SPD) might improve total nitrogen removal efficiency (TNRE) by stably supplying carbon resources under adverse conditions. In this study, an SPD biofilm reactor was successfully established by inoculating halophilic sludge and filling poly (butanediol succinate) (PBS) granules, and achieved over 96% TNRE at low temperature. More extracellular polysaccharides were produced at low temperature. Microbial network analysis evidenced dominant heterotrophic denitrifiers (Marinicella, Fusibacter, Saccharicrinis and Vitellibacter) at 25 °C were replaced by genera Melioribacter, Marinobacter, Desulfatitalea and Thiomicrospira at 15 °C. At low temperature, genes nirS and narG might be mainly responsible for denitrification. Fluorescence spectrum coupled with fluorescence regional integration and parallel factor analysis revealed low temperature increased the proportion of proteins of soluble microbial products. This study provides guidance for the practical application of SPD in the treatment of high salinity and low-temperature wastewater.