Coupling of nitrifying granular sludge into microbial fuel cell system for wastewater treatment: System performance, electricity production and microbial community shift

A novel electrochemical system coupling of nitrifying granular sludge (NGS) into microbial fuel cell (MFC) system was conducted for simultaneous electricity production and wastewater treatment under sequencing batch mode. After 60 days operation, the contaminants of organic and NH₄⁺-N removal efficiencies of the system were high of 95.43% and 98.55%, respectively. The maximum output voltage and power density of the MFC were average at 170 mV and 33.24 mW/m², respectively. According to EEM-PARAFAC model, the soluble microbial products (SMP) released from anode and cathode chambers could be identified two fluorescence components. Additionally, the fluorescence score of protein-like substances changed more obvious than those of humic-like and fulvic acid-like substances. Geobacter and Nitrospiraceae were the dominant functional populations in the anode and cathode chambers, respectively. The result could provide a potential application technology based on NGS-MFC for simultaneously treatment of organic matter and ammonia.

Biochemical characteristics and membrane fouling behaviors of soluble microbial products during the lifecycle of Escherichia coli

The complexity of production process and chemical compositions of soluble microbial products (SMPs) largely limits the understanding of membrane fouling in membrane bioreactors (MBRs). Herein, we used a model single-strain Escherichia coli to better understand the chemical natures of SMPs and their roles in membrane fouling. The effects of carbon source and growth phase on the chemical compositions of SMPs were identified at both the compound and molecular levels by using advanced techniques including excitation emission matrix and parallel factor analysis (EEM-PARAFAC), size exclusion chromatography coupled with organic carbon detection (LC-OCD), and untargeted ultra-performance liquid chromatography - Q-Exactive - mass spectrometry (UPLC-Q-Exactive-MS). Subsequently, the roles of SMPs in the propensity of membrane fouling during ultrafiltration (UF) were studied. The results showed that the chemical compositions and fouling potentials of SMPs were carbon source- and growth phase-dependent. In the exponential phase, SMPs mainly consisted of utilization-associated products (UAPs) and remaining substrates. As the microorganism progressed into the stationary and senescent phases, UAPs and biomass-associated products (BAPs) were the main components, respectively. The SMP contents generated in glucose medium were higher than those generated in acetate medium, and higher abundances of humic fluorescent components were observed in glucose-fed SMPs. Van Krevelen diagrams of the UPLC-MS results revealed that acetate-fed SMPs contained more carboxylic-rich alicyclic molecules, peptides-like, aromatic, and carbohydrates-like components than glucose-fed SMPs in the stationary and senescent phases. These components played a significant role in irreversible membrane fouling, as evidenced in UF experiments. Standard blocking and cake filtration were the main fouling mechanisms for the filtration of SMPs collected in the exponential and stationary/senescent phases, respectively. Our findings highlight linkages between SMP compositions and membrane fouling at both the compound and molecular levels and suggest that both the carbon source and growth phase strongly determine the production potential, chemical nature, and fouling behavior of SMPs.

Comparison of soluble microbial product (SMP) production in full-scale anaerobic/aerobic industrial wastewater treatment and a laboratory based synthetic feed anaerobic membrane system

This study focused on the characterisation of soluble microbial products (SMPs) produced from a full-scale multi-stage (anaerobic/aerobic) industrial wastewater treatment plant, and contrasted them to the SMPs detected in the effluent of a lab-scale AnMBR treating synthetic wastewater to determine if there were any common solutes detected irrespective of the feed organics. Recently developed analytical methods using gas chromatography coupled mass spectrometry (GC-MS) and liquid chromatography coupled quadrupole-time-of-flight (LC-Q-ToF) for SMP characterisation in a wide molecular weight (MW) range of 30-2000 Da (Da) were applied. Samples collected from the Industrial Wastewater plant were the upflow anaerobic sludge blanket (UASB) influent and effluent, and aerobic membrane bioreactor (MBR) effluent before discharge. The GC-MS detected a spike in cyclooctasulphur in the UASB effluent, an indicator of shock-loading, which disappeared after the MBR process. Alkanes, acids and nitrogenous compounds were found to be the end-products from the GC-MS results, while LC-Q-ToF analysis revealed that eicosanoids, a group of cell-signalling molecules, were produced in the aerobic MBR, and made up 71% of its effluent. A comparison of the submerged anaerobic membrane bioreactor (SAMBR) and aerobic MBR effluents using GC-MS showed that there was only a small degree of similarity between the SMPs, comprising mainly long chain alkanes and phthalate. On the other hand, LC-Q-ToF showed a large contrast in compound composition, mostly having cell-signalling functions, which deepened our understanding of the different metabolic processes occurring in aerobic and anaerobic systems. These data could be useful for future work in various areas such as controlling quorum-sensing and biofilm formation, process optimisation and control, and microbial ecology.

Evaluation of the fouling potential of sludge in a membrane bioreactor integrated with microbial fuel cell

This study focused on the fouling characteristics evaluation of the sludge in a membrane bioreactor integrated with microbial fuel cell (MFC-MBR) to reveal the mechanisms of membrane fouling mitigation. The filtration of soluble microbial products (SMPs) in MFC-MBR showed lower flux decline rate than those in the control system (C-MBR). Based on the extended Derjaguin-Landau-Verwey-Overbeek analysis, decreases in free energies of adhesion between the SMPs and clean membrane or SMP-fouled membrane were observed in MFC-MBR. When approaching the clean membrane or SMP-fouled membrane, the SMPs in MFC-MBR had to overcome a higher energy barrier compared to those in C-MBR, indicating the inhibition of adsorption of SMPs on the membrane surface in MFC-MBR. Additionally, sludge flocs in MFC-MBR exhibited lower hydrophobicity and were less negative surface charged in comparison to those in the C-MBR. In MFC-MBR, the sludge flocs approaching the clean membrane, SMP-fouled membrane and cake layer all experienced higher energy barriers and lower secondary energy minimums compared to those in C-MBR, exhibiting the lower potential of cake layer formation. These results confirmed that decreases of the fouling potentials of SMPs and sludge flocs were essential for the membrane fouling mitigation in the MFC-MBR.

Denitrification strategies of strain YSF15 in response to carbon scarcity: Based on organic nitrogen, soluble microbial products and extracellular polymeric substances

This paper aims to determine the denitrification strategies of strain YSF15 in carbon scarcity condition from novel view of organic nitrogen, soluble microbial products (SMP) and extracellular polymeric substances (EPS). The batch tests demonstrated that strain YSF15 could achieve complete denitrification at C/N of 3.0. The conversion ratio of nitrogen gas accounted for 89.03%, 85.29% and 82.95% among total nitrogen in C/N systems from 3.0 to 5.0, respectively, indicating denitrification instead of assimilation was the major contribution to nitrogen removal. C/N could affect composition and content of organic nitrogen, SMP and EPS. The biodegradability of EPS was better than SMP, whereas polysaccharide (PS) likely correlated with nitrogen removal, predating the protein (PN). These results implied high biodegradability of EPS and more electron donors for denitrification both improved denitrification capacity of strain YSF15, which revealed the potential contribution of bacterium with production of biodegradable SMP or EPS in biological treatment process.

Effect of salinity on removal performance in hydrolysis acidification reactors treating textile wastewater

Hydrolysis acidification (HA) is a classical method for synthetic textile wastewater treatment. However, the salinity effect on the functional mechanism of the microorganisms carrying out HA has rarely been researched. In the present study, the salinity effect on the dye removal efficiency was investigated, and the soluble microbial products (SMP), extracellular polymeric substances (EPS), and microbial community were analyzed at different salinities. The dye and COD removal rates in the HA reactor decreased with increasing salinity. Volatile fatty acids (VFAs) accumulated. The remarkable increases in SMP and EPS were found at high salinity, mainly because more polysaccharides were synthesized than protein. In addition, sequencing analysis showed that high salinity altered the microbial community structure, and Lactococcus, Raoultella and Enterococcus were the decolorizing bacteria at high salinity. This work will improve the understanding of the influence of salinity on the removal efficiency and microbial community during HA.

Membrane fouling caused by biological foams in a submerged membrane bioreactor: Mechanism insights

Though sludge foaming often occurs and thus causes serious membrane fouling in membrane bioreactors (MBRs), the fouling mechanisms related with the foaming phenomenon have not been well addressed, hindering better understanding and solving foaming problem. In this work, it was interestingly found that, the foulants during the foaming period possessed extremely high specific filtration resistance (SFR) (over 10¹⁶ m kg^-1) and strong adhesion ability to membrane surface. Chemical characterization showed that the proteins (178.57 mg/L) and polysaccharides (209.21 mg/L) in the foaming sample were about 6.4 times and 5.4 times of those in the supernatant sample, suggesting existence of a mechanism permitting continuous production of these foulants in the MBR during the foaming period. It was revealed that the fouling caused by foams was associated with gel layer filtration process, and the extremely high SFR can be interpreted by chemical potential change in the gel filtration process depicted in Flory-Huggins theory. Meanwhile, analyses by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed that the strong adhesion ability stemmed from the high interaction energy between the foaming foulants and membrane surface. In addition, 16S rDNA gene sequencing identified that the abundance of the foaming related bacteria species in the sludge suspension during the foaming period was more than 10 times of that during the non-foaming period. This study offered new mechanism insights into foaming fouling in MBRs.

Pioneering on single-sludge nitrification/denitrification at 50 °C

Thermophilic nitrification has been proven in lab-scale bioreactors at 50 °C. The challenge is now to develop a solution for thermophilic nitrogen removal, integrating nitrification with denitrification and aerobic carbon removal. This pioneering study aimed at a single-sludge nitrification/denitrification process at 50 °C, through exposing nitrification in a step by step approach to anoxia and/or organics. Firstly, recurrent anoxia was tolerated by a nitrifying community during long-term membrane bioreactor (MBR) operation (85 days), with high ammonium oxidation efficiencies (>98%). Secondly, five organic carbon sources did not affect thermophilic ammonium and nitrite oxidation rates in three-day aerobic batch flask incubations. Moving to long-term tests with sequencing batch reactors (SBR) and MBR (>250 days), good nitrification performance was obtained at increasing COD/N_influent ratios (0, 0.5, 1, 2 and 3). Thirdly, combining nitrification, recurrent anoxia and presence of organic carbon resulted in a nitrogen removal efficiency of 92-100%, with a COD/N_removed of 4.8 ± 0.6 and a nitrogen removal rate of 50 ± 14 mg N g^-1 VSS d^-1. Overall, this is the first proof of principle thermophilic nitrifiers can cope with redox fluctuations (aerobic/anoxic) and the aerobic or anoxic presence of organic carbon, can functionally co-exist with heterotrophs and that single-sludge nitrification/denitrification can be achieved.

Influence of immersion depth of membrane on filtration performance of anaerobic membrane bioreactor

Membrane fouling is still the main obstacle that hinders the development and implementation of anaerobic membrane bioreactor (AnMBR). In conventional upflow anaerobic reactors, sludge at different height usually presents certain differences in characteristics in terms of particle size, etc. The immersion depth of membrane modules in anaerobic reactors can also influence the fouling of membrane. Thus, it is of great interest to investigate the fouling mechanism with the membrane installed at different heights in reactors. The filtration performance and sludge properties were investigated at different heights of AnMBR. The fouling of membrane in the middle position was severer than that in the top and bottom positions. The total resistance of membrane in the top, middle, and bottom positions was 27.31 × 10¹¹ m^-1, 34.67 × 10¹¹ m^-1, and 25.29 × 10¹¹ m^-1, respectively. By comparing the characteristics and structure of bulk sludge and cake layer at three heights, the bulk sludge in the middle position presented higher content of soluble microbial products (SMP) and finer flocs, and the cake layer was also denser. The results obtained in this study indicated that small size of sludge flocs as well as adhesion of SMP might be the major factors governing membrane fouling at different height in the AnMBR.

Aerobic biodegradation of p-nitrophenol in a nitrifying sludge bioreactor: System performance, sludge property and microbial community shift

The system performance, sludge property and microbial community shift were evaluated in a nitrifying sludge (NS) bioreactor for simultaneous treating p-Nitrophenol (PNP) and high ammonia wastewater. After long-term acclimation for 80 days, the removal efficiencies of PNP and NH₄⁺-N reached to 99.9% and 99.5%, respectively. Meanwhile, the effluent PNP gradually decreased from 7.9 to 0.1 mg/L by acclimation of sludge. The particle size of NS increased from 115.2 μm to 226.3 μm accompanied by the decreased zeta potential as a self-protection strategy. The presence of PNP exposure altered the effluent soluble microbial products (SMP) fluorescent components and molecular composition. The increase in the relative abundance of Thauera, Nitrospiraceae and Nitrosomonas indicated the nitrification and denitrification capacities of NS increased, which maybe the PNP cometabolic biodegradation effect. Moreover, Ignavibacteria and Aeromonas were responsible as the dominant bacteria for degrading PNP in the nitrifying system.

Variation of effluent organic matter (EfOM) during anaerobic/anoxic/oxic (A2O) wastewater treatment processes

Here, we studied seasonal variation of effluent organic matter (EfOM), based on molecular weight distribution and fluorescent components, during the traditional anaerobic/anoxic/oxic (A²O) wastewater treatment processes. Microbial community structure and effect of temperature on some isolated pure strains were analyzed to explain the related mechanism. Results showed that the anaerobic process played a key role in EfOM removal by removing building blocks, low molecular weight (LMW) neutrals, biopolymers, and protein-related substances (C4 and C5), thus determining the fate of EfOM during the A²O processes. On the other hand, humic substances, LMW neutrals, large molecular-sized hydrophobic humic-like compounds (C3), and aromatic proteins (C4) were generated during the anoxic process in summer and winter. Proteobacteria (Gamma-, Beta-, and Alpha-proteobacteria) and Bacteroidetes constituted over 50% of the sludge community. Temperature was found to be positively correlated with the generation of soluble microbial products (SMP) based on the performance of the mixture of isolated Herbaspirillum sp. (Beta-proteobacteria) and Pseudomonas sp. (Gamma-proteobacteria). Through comprehensive analysis of the co-action of Proteobacteria and temperature, we proposed the Synergetic Effect of Temperature and Proteobacteria as a possible mechanism of the seasonal variation of EfOM. These findings are important for understanding the fate of EfOM during the wastewater treatment processes and therefore be helpful for better EfOM control.

Effects of molecular weight distribution of soluble microbial products (SMPs) on membrane fouling in a membrane bioreactor (MBR): Novel mechanistic insights

While molecular weight distribution (MWD) is one of the most important properties of soluble microbial products (SMPs), mechanisms underlying effects of MWD of SMPs on membrane fouling have not well unveiled. In this study, it was found that, the supernatant of sludge suspension in a membrane bioreactor (MBR) for wastewater treatment can be fractionated into a series of SMPs samples with different molecular weight (MW) fraction. The real gel sample mainly formed by the rejected SMPs on membrane surface had a high specific filtration resistance (SFR) of 1.21 × 10¹⁶ m^-1 kg^-1. The SFR of SMPs samples and the model foulants of polyethylene glycol (PEG) increased with their MW. The change trend of SFR with MW cannot be sufficiently explained by three-dimensional excitation-emission matrix (EMM) and chemical compositions. Tyndall effect analysis indicated that gelating ability of SMPs and PEG in the solution increased with their MW. Scanning electron microscope (SEM) confirmed gel structure changes with the PEG MW. Accordingly, mechanisms based on Carman-Kozeny equation and Flory-Huggins lattice theory were proposed to interpret SFR of SMPs with low and high MW, respectively. Simulating these two mechanistic models on PEG samples resulted in the comparable SFR data to the experimental ones, indicating the correctness and feasibility of the proposed mechanisms. The proposed mechanisms provided in-depth understanding of membrane fouling regarding MW, facilitating to develop effective membrane fouling mitigation strategies.

Role of soluble microbial product as an intermediate electron station linking C/N and nitrogen removal performance in sequencing batch reactor

The C/N ratio in wastewater differs in place and time and affects the nitrogen removal performance of wastewater treatment. However, studies have focused only on the direct relationship between C/N and nitrogen removal efficiency but disregarded the significant role of soluble microbial products (SMPs) as an intermediate electron station. In this work, the contribution of SMPs to TN removal for treating wastewater with different C/N in a sequencing batch reactor (SBR) was investigated to extend relevance from C/N-TN removal to C/N-SMP-TN removal. TN removal efficiency was improved by increasing the influent C/N. The relative contribution of SMPs increased from 15% (C/N = 2) to 54% (C/N = 8), including 25.5% via utilization-associated product (UAP)-dependent denitrification and 28.5% via biomass-associated product (BAP)-dependent denitrification. The direct contribution of influent organic substrates dramatically decreased from 85.1% to 46%. In addition, providing an anoxic phase effectively enhanced BAP-dependent denitrification and achieved an increment of the SMP absolute contribution from 20.3% to 43% at C/N = 8 with 6.7 mg/L of TN additionally removed. This work clarified the significant contribution of SMPs to the nitrogen removal process, particularly in treating wastewater with high C/N. It also presented a new strategy for improving nitrogen removal performance via SMP reclamation.

Accelerated tests for evaluating the air-cathode aging in microbial fuel cells

Air-cathode stability is a key factor affecting the feasibility of microbial fuel cells (MFCs) in applications. However, there is no quick and effective method to evaluate the robustness and durability of the MFC air cathodes. In this study, a three-phase decrease of power density was observed in multiple MFCs that have been operated for about a year. Quantification of the contributions of cathode biofilm and salt accumulation to the current decrease suggested that the biofouling was the major contributor to the cathode aging during the first 200 days, and salt accumulation gradually outpaced biofouling afterward. An accelerated test method was then developed using fast-growing Escherichia coli, simulated soluble microbial products (SMPs), and a concentrated medium solution. Using this method, the cathode aging can be evaluated quickly within hours/days compared to over a year of operation, benefiting the development of high-performing and durable cathode materials.

The chloramine stress induces the production of chloramine decaying proteins by microbes in biomass (biofilm)

In this paper, for the first time, we show in chloraminated systems, the chloramine decaying proteins (CDP) play an important role in bulk water and biomass (biofilm) in resisting disinfectant. Extracellular polymeric substances in biofilm/biomass are known to protect microbes from disinfectants and toxic materials, but the exact mechanism(s) is/are not known. Starting with the seed from a nitrifying chloraminated reactor, two 5 L reactors were fed intermittently with either chloramine or ammonia containing nutrient solution. The degree of nitrification increased with time in both reactors despite an increase in soluble CDP in the chloraminated reactor, while soluble CDP decreased in the ammoniated one. The suspended biomass collected after eight months of operation from chloraminated reactor contained CDP and responded to short-term chloramine stress (1.5 h with initial 1.5 mg-Cl₂·L^-1) by the additional production of soluble CDP. The suspended biomass from ammoniated reactor neither contained CDP nor produced soluble CDP as a stress response. The production, release and accumulation of CDP in biomass (biofilm) could be one of several mechanisms microbes use to defend against disinfectants (stress). The new understanding will pave the way for better disinfection management and better design of experiments.

In-situ utilization of soluble microbial product (SMP) cooperated with enhancing SMP-dependent denitrification in aerobic-anoxic sequencing batch reactor

Soluble microbial products (SMPs), as secondary pollutants, comprise a dominant percentage of residual COD in effluents from biological wastewater treatment processes. They can also be regarded as substitute electron sources if the in-situ utilization of SMPs could be achieved. In this study, the fate of SMPs in a sequencing batch reactor (SBR) treating artificial municipal sewage was investigated. Based on the regular SBR operation mode, a 3 h extension of anoxic phase was provided to promote SMP degradation. Meanwhile, the denitrification efficiencies achieved by adopting SMPs and influent organic substrates (IOSs) were compared to reveal the significant contribution of the in-situ utilization of SMP for nitrogen removal. Approximately 21.1 mg N/L of total nitrogen (TN) was removed over a single cyclic reaction, in which only 13.2 mg N/L was removed via IOS-dependent denitrification. The remaining 7.9 mg N/L of TN was realized via SMP-dependent denitrification, including 3.9 mg N/L by utilization-associated products and 4.0 mg N/L by biomass-associated products, which significantly contributed 37.4% of TN removal. The aromatic proteins, tryptophan-like proteins, polysaccharides and fulvic acids contained in SMP were the potential precursors of electron donors to support SMP-dependent denitrification process.

Viscosity dynamics and the production of extracellular polymeric substances and soluble microbial products during anaerobic digestion of pulp and paper mill wastewater sludges

The production processes of the pulp and paper industry often run in campaigns, leading to large variations in the composition of wastewaters and waste sludges. During anaerobic digestion (AD) of these wastes, the viscosity or the production of extracellular polymeric substances (EPS) and soluble microbial products (SMP) may be affected, with the risk of foam formation, inefficient digester mixing or poor sludge dewaterability. The aim of this study was to investigate how viscosity and production of EPS and SMP during long-term AD of pulp and paper mill sludge is affected by changes in organic loading rate (OLR) and hydraulic retention time (HRT). Two mesophilic lab-scale continuous stirred tank reactors (CSTRs) were operated for 800 days (R1 and R2), initially digesting only fibre sludge, then co-digesting fibre sludge and activated sludge. The HRT was lowered, followed by an increase in the OLR. Reactor fluids were sampled once a month for rheological characterization and analysis of EPS and SMP. The production of the protein fraction of SMP was positively correlated to the OLR, implicating reduced effluent qualities at high OLR. EPS formation correlated with the magnesium content, and during sulphate deficiency, the production of EPS and SMP increased. At high levels of EPS and SMP, there was an increase in viscosity of the anaerobic sludges, and dewatering efficiency was reduced. In addition, increased viscosity and/or the production of EPS and SMP were important factors in sludge bulking and foam formation in the CSTRs. Sludge bulking was avoided by more frequent stirring.

Importance of nutrient availability for soluble microbial products formation during a famine period of activated sludge: Evidence from multiple analyses

Much remains unknown about compositional variations in soluble microbial products (SMP) with the shift of the substrate condition from a feast to a famine phase in biological treatment systems. This study demonstrated that the formation of SMP could be suppressed by up to 75% during the famine phase with the addition of essential nutrients. In contrast, presence of electron acceptor did not play any significant role during the stress condition, showing the similar amounts of SMP (r = 0.98, p < 0.05) formation between the bioreactors supplied with air and N₂. The SMP formed in the famine phase was more bio-refractory in the famine versus the feast phase with a linear correlation shown between the production and their aromatic structures in the composition (R² > 0.95). The fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) revealed the presence of four different fluorescent components, including two protein-like (C1 and C4), fulvic-like (C2), and humic-like (C3) components, in the SMP and bEPS formed at different conditions. Both C1 and C4 showed increasing trends (R² > 0.95) with the length of starvation in the bioreactors without essential nutrients. Nutrient availability was found to be a key factor to quench the production of large-sized biopolymers. This study provides a wealth of information on operation conditions of activated sludge treatment systems to minimize large sized SMP molecules (particularly proteins), which typically exert many environmental concerns to effluent organic matter quality.

The effects of biodegradation on the characteristics and disinfection by-products formation of soluble microbial products chemical fractions

Soluble microbial products (SMPs) discharged into rivers from sewage treatment plants may increase the health risk for downstream drinking water by acting as a precursor of DBPs. Biotransformation or biodegradation could alter the characteristics of SMPs and affect the subsequent formation of DBPs. This study observed the relative contribution of chemical fractions in SMPs and explored the biodegradation of each fraction and their effect on disinfection by-products (DBPs) formation in surface water. The hydrophilic acid (HPIA) and hydrophobic acid (HPOA) constituted the major portion of the SMPs, which were dominated by fulvic acid and humic acids. The transphilic acid (TPIA) and hydrophobic bases (HPOB) were relatively minor but it contained a relative substantial portion of protein-like materials in SMPs. TPIA and HPOB produced insignificant amounts of DBP corresponding to 13% and 14% in the original samples, but they were collectively responsible for 50% of the DBPs yield. Much larger amounts of hydrophobic fractions were utilized than hydrophilic fractions after biodegradation. The increase in SUVA values indicating aromatic structures, except for HPOA fraction, was observed after biodegradation. The protein-like materials in both the HPOA and HPIA fractions and polycarboxylate-type humic acid in the HPIA fraction decreased but the enrichment of HPOA (MW > 100 kDa) and TPIA (MW < 1 kDa) was observed after biodegradation. The production of = C-H in HPIA fraction and the appearance of double peak at 1100 cm^-1 in TPIA and HPOB fractions occurred after biodegradation. In overall level, microorganisms effectively utilized DBP precursors from HPIA, HPOA and HPOB fractions but increased the DBPs precursors from the TPIA fraction. TPIA and HPOB fractions had higher DBP yield with chlorine but the DBPs yield of HPIA and HPOA changed little after biodegradation.

Nitrogen removal in a combined aerobic granular sludge and solid-phase biological denitrification system: System evaluation and community structure

In the present study, the feasibility of treating high ammonia wastewater was evaluated in a combination of aerobic granular sludge nitrification reactor (AGS-SBR) and poly(butylene succinate) solid denitrification reactor (PBS-SBR). After 90 days operation, the effluent NH₄⁺-N and total nitrogen (TN) removal efficiencies were high of 99.6% and 99.7%, respectively. According to typical cycle, N₂O emission rate in AGS nitrification process was much higher than PBS denitrification process. It was found from EEM-PARAFAC that the fluorescence intensity scores (protein-like and humic like substances) of soluble microbial products (SMP) in AGS-SBR were the significant higher than in PBS-SBR. Microbial community analysis showed that Thauera was main genus in AGS-SBR and Hydrogenophaga Simplicispira and Thiomonas were dominant genus in PBS-SBR. The obtained result implied that the combined technology is feasible to remove nitrogen compounds from wastewater to meet the stringent emission standards.

Heterotrophic denitrifiers growing on soluble microbial products contribute to nitrous oxide production in anammox biofilm: Model evaluation

In this work, a model framework was constructed to assess and predict nitrous oxide (N₂O) production, substrate and microbe interactions in an anammox biofilm bioreactor. The anammox kinetics were extended by including kinetics of autotrophic soluble microbial products (SMP) formation, which consisted of utilization-associated products (UAP) and biomass-associated products (BAP). Heterotrophic bacteria growing on UAP, BAP and decay released substance (SS) were modelled to perform four-step sequential reductions from nitrate to dinitrogen gas. N₂O was modelled as an intermidiate of heterotrophic denitrification via three pathways with UAP, BAP and SS as the electron donors. The developed model framework was evaluated using long-term operational data from an anammox biofilm reactor and satisfactorily reproduced effluent nitrogen and SMP as well as N₂O emission factors under different operational conditions. The modeling results revealed that N₂O was mainly produced with UAP as the electron donor while BAP and SS play minor roles. Heterotrophic denitrifiers growing on UAP would significantly contribute to N₂O emission from anammox biofilm reactor even though heterotrophs only account for a relatively small fraction of active biomass in the anammox biofilm. Comprehensive simulations were conducted to investigate the effects of N loading rate and biofilm thickness, which indicated that maintaining a low N loading rate and a thick biofilm thickness were essential for high total nitrogen removal efficiency and low N₂O emission.

Probing size characteristics of disinfection by-products precursors during the bioavailability study of soluble microbial products using ultrafiltration fractionation

Soluble microbial products (SMPs) discharged into surface water may increase the formation of disinfection by-products (DBPs) in downstream drinking water treatment plants. In this study, ultrafiltration (UF) fractionation was used to separate SMPs into homogenous components. An aerobic microbial experiment was conducted to evaluate the bioavailability of individual molecular weight (MW) fractions of SMPs in surface water and the impact on their DBP formation, facilitating the interpretation of SMPs characterization and DBPs reactivity. For SMPs, organics with MW < 1 kDa were the primary fraction, containing the most abundant humic substances. The 30 kDa < MW < 100 kDa fraction was the lowest in SMPs but had the highest SUVA values. After biodegradation, the bioavailability of physical fractions increased with the increasing MW size. However, the SUVA value, except for MW < 1 kDa, increased in individual fraction after biodegradation. Low molecular weight SMPs fractions (MW<10 kDa) were major precursors for DBP in which trichloromethane (TCM) was the most abundant. The 10 kDa <MW < 100 kDa fractions were found to be more active in formation of chloral hydrate (CH), and MW> 100KDa had relative abundant dichloroacetonitrile (DCAN) formation. After biodegradation, TCM precursors with MW < 1 kDa were removed by approximately 20%, whereas the increase of TCM formation was observed in 1 kDa < MW < 100 kDa fraction. CH formation from 1 kDa < MW < 10 kDa increased considerably, but those from 10 kDa < MW < 30 kDa decreased after biodegradation, as a result of the biotransformation of large organic acids to small organic acids. In terms of DBP reactivity, the TCM yield for the MW < 1 kDa fraction had no significant change while the 30 kDa < MW < 100 kDa fraction exhibited the greatest increase (approximately 8 times) in TCM yield.

Operational performance and biofoulants in a dynamic membrane bioreactor

In this study, a mathematical model was developed to have a better understanding of the process and be used in future reactor scale models to predict its process performance. This model utilizes the Activated Sludge Model NO.1 (ASM1) framework and incorporates bioprocesses of formation and degradation of soluble microbial products (SMP) and extracellular polymeric substances (EPS). Simulation result shows the model could very well predict the bioreactor performance. The average error of COD, BOD and NH₃-N removal efficiency was 0.48, 0.28 and 1.18%, respectively.

Effects of salinity on the biological performance of anaerobic membrane bioreactor

The performance of anaerobic membrane bioreactor (AnMBR) was evaluated treating synthetic wastewater with various concentrations of NaCl (0-40 g/L), as well as the recovery phase. The effluent COD removal efficiency decreased from 96.4% to 95.0%, 91.4%, 86.7% and 77.7% with stepwise increasing of salt concentration from 0 to 5, 10, 20 and 40 g NaCl/L, respectively, then gradually increased to 94.1% during the recovery phase. Additionally, the significant changes in the content and composition of soluble microbial products (SMP) and extracellular polymer substance (EPS) were obtained under higher salt stress. GC-MS analyses were carried out for the effluent, and some new types of compounds, such as Dodecane, Undecane, and Ethyl Acetate, were found during salt exposure phases. The characterization of the microbial community was also investigated based on the analysis of genomic 16S rDNA, revealing the increasing salinity (5-40 g NaCl/L) could reduce the diversity of sludge microbial community in AnMBR. Meanwhile, the significant effects on the composition of dominate phyla (Proteobacteria, Bacteroidetes, Firmicutes and Chloroflexi) were found during the salt exposure phase.

Combined Partial Denitrification (PD)-Anammox: A method for high nitrate wastewater treatment

Elimination of nitrogen pollution from wastewater containing high-strength nitrate (NO₃^--N) is a significant issue to prevent deterioration of water quality and eutrophication of receiving water body. Traditional denitrification process faces several challenges including the huge organic carbon demand, intermediate products accumulation, and long acclimatization period. In this study, an efficient solution was given by a novel two-stage Partial Denitrification (PD)-Anammox process. High NO₃^--N (1000 mg N/L) wastewater and municipal sewage (COD: 182.5 mg/L, ammonia (NH₄⁺-N): 58.3 mg/L) were simultaneously introduced to the PD reactor for NO₃^--N converting to NO₂^--N. The NH₄⁺-N and NO₂^--N in effluent of PD were removed in subsequent anammox reactor. Results showed that a satisfactory nitrogen removal was achieved by optimizing the volume ratios of influent NO₃^--N and municipal sewage, as well as the external organic matter dosage. The NO₃^--N removal efficiency reached up to 95.8% without accommodation period, along with the NH₄⁺-N removal achieving 92.8%. Anammox contributed to 78.9% of TN removal despite the high COD (76.5-98.6 mg/L) in PD effluent was introduced, indicating the significant stability of the integrated process. The microbial analysis suggested that the Candidatus Brocadia, identified as anammox bacteria, cooperated stable with denitrifying bacteria in 215-day operation. The PD-Anammox process offers an economically and technically attractive approach in the high NO₃^--N wastewater treatment since it has great advantages of much low carbon demand, minimal sludge production, enabling simultaneous treatment of municipal sewage, and avoiding the common issues in traditional denitrification process.