Dissolved organic nitrogen (DON) formed by microbial metabolism in wastewater treatment processes adversely impacts wastewater reuse and receiving waters quality, and microbial metabolism is greatly ...influenced by temperatures. However, little is known about the effect of microorganisms on DON and bioavailable DON (ABDON) formation under low temperatures. In this study, six reactors were operated at low (8 °C and 15 °C) and room (25 °C) temperatures to evaluate the relationship between microbial activity, microbial communities, and DON and ABDON. Results showed that DON and ABDON concentrations significantly increased at low temperatures (p < 0.05, t-test). DON formation was significantly correlated to microbial activity only, with adenosine triphosphate (negative, r = -0.64) and polysaccharide (positive, r = 0.61) as key indicators; however, ABDON formation was influenced by both microbial activity (polysaccharide > triphenyltetrazolium chloride-dehydrogenases > adenosine triphosphate) and microbial community structure. Short-term tests using the biomass from six reactors were performed at room temperature to further validate the relationship. The distinct differences between these results provide a basis for different strategies on reducing effluent DON and ABDON under low temperatures.
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•Low temperatures result in more DON and ABDON produced by microbes.•DON production is strongly correlated with microbial activity only.•Both microbial activity and microbial communities associate with ABDON formation.•ABDON formation is more sensitive to microbial activity than the communities.•A basis on the strategy of reducing effluent DON and ABDON under low temperatures.
Sewage sludge (SS) alkaline fermentation (especially at pH 10) can efficiently enhance volatile fatty acids (VFAs) production. VFAs are considered an excellent carbon source for the biological ...nutrient removal (BNR) process. Dissolved organic matter (DOM) in fermentation liquid is the direct substrate used for producing VFAs and can greatly influence the effluent quality of BNR process. However, knowledge of DOM characteristics in sludge alkaline fermentation is limited. This study focused on the functional groups, fluorescent components and molecular features of DOM as well as molecular weight of proteins in SS alkaline fermentation (at pH uncontrolled, 7, 8, 9 and 10). Results showed a significantly improved generation of tryptophan-like and tyrosine-like substances as well as molecular weight <1 kDa proteins (381.5 ± 38.4 mg/L) was observed at pH 10 (p < 0.05). Further analysis of DOM molecular characteristics indicated that pH 10 resulted in the highest molecular diversity and the generation or degradation of easily biodegradable lipid-like and proteins/amino sugars-like formulas. The improved solubilization of DOM contributed to VFAs production. Meanwhile, increasing pH to 10 also promoted the release of hard-biodegradable organic matter, e.g., humic-like and lignin-like substances. Additionally, a high diversity of resistant N-containing organic molecules was generated at pH 10. Fermentation of SS at pH 10, is favored to enhance VFAs production and, can also result in a higher content of refractory DOM. This study helps to achieve a comprehensive understanding of SS alkaline fermentation and provides fundamental information for further treatment.
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•DOM features in SS alkaline fermentation with different pH were investigated.•pH 10 led to improved generation of protein-like substance and MW < 1 kDa protein.•Higher diversity and biodegradable formulas contributed to VFAs production.•Increase of pH also promoted the generation of hard-biodegradable organic matter.
Regulation of process parameters is a cost-effective approach to control microorganism-derived dissolved organic nitrogen (mDON) formation in low-temperature biological wastewater conditions. ...However, the integrated influence of multiple parameters in this process is poorly defined. In this study, mathematical methodology was used to evaluate the combined effects of hydraulic retention time (HRT), solids retention time (SRT), and mixed liquor suspended solids (MLSS) on mDON formation at 8 °C. This study also systematically explored how multiple combinations of those three parameters affected mDON chemodiversity (fluorescent properties and molecular compositions), microbial compositions, and specific relationships between mDON molecules and microbial species in activated sludge systems. Results showed that combined effects significantly controlled the mDON formation at 8 °C (P < .05). The systematic analysis suggested that the multi-parameter effects modulated the distribution of different mDON compositions and shaped the microbial communities. Most bacterial phyla as the generalist and a few as the specialist were displayed in 2487 pairs of strong microbe-mDON connections (|r| ≥ 0.6, P < .05). Moreover, network analysis on microbe-mDON relationships identified the network centers as crucial media in terms of combined effects of process parameters on mDON formation. Our results provide comprehensive insight on the roles of multi-parameter covariation influences in regulating the high complexity of mDON traits and microbe-mDON linkages, thereby highlighting the necessity to focus on the combined effects of process parameters for effective and correct controlling strategies on mDON concentrations.
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•Parameter covariations significantly control mDON formation at 8 °C (P < .05).•Multi-parameter combined effects include linear and interactive functions.•mDON molecular traits exhibit different responses to different parameter combinations.•Most phyla show high connectivity with mDON molecules as network centers.•Multi-parameter covariations enable various microbe-mDON relationships.
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•The effect of carbon-to-nitrogen ratios in mDON generation dynamics was considered.•The simulation of mDON generation in four-denitrification was accurate (R2 = 0.909–0.986).•mDON ...formed in real wastewater was provided a reasonable prediction (1.16–1.63 mg/L).•Production of new nitrogenous molecules confirmed the model applicability.•High carbon-to-nitrogen ratios are of benefit to reduce effluent-associated ecological risk.
Quantifying microorganism-derived dissolved organic nitrogen (mDON) formed from microbial activities is a prerequisite for reducing effluent nitrogen. In this work, a new model based on activated sludge model for nitrogen (ASMN) is proposed for determining mDON formation together with its dynamics in post-denitrification under different carbon-to-nitrogen (C/N) ratios of 3, 4, 5, and 6. This model incorporates mDON as a separate component among four-step denitrification and introduces three new mDON-related parameters (i.e., fH,mDON, KH,mDON, and KI4SS) to develop mDON production and utilization equations. The model was calibrated and established with data from an experiment using synthetic wastewater, demonstrating its capability of accurately simulating mDON generation (R2 = 0.909–0.986). Accordingly, the simulated results successfully captured the experimental trends, suggesting that higher C/N ratios were preferred for mitigating mDON generation. The model applicability was further tested by predicting mDON generation in real wastewater, producing reasonable predicted results of formed mDON (1.16–1.63 mg/L). These predicted results were also indirectly confirmed by newly produced nitrogenous molecules (i.e., lipid-, carbohydrates-, and protein/amino sugars-like molecules). Overall, this work offers a tool to quantify mDON which benefits controlling mDON toward minimizing the adverse impacts of effluent organic nitrogen on receiving waters.
•Effluent DON and NDMA precursors significantly increased at low DO (p<0.05).•Proteins-like DON contributed to 73.6% positive NDMA precursors-DON relationships.•Increased proteins-like DON was ...related to the accumulation of microbe-derived DON.•Low-DO effects on NDMA formation were delivered by DO-microbe-DON-NDMA links.•Good side and bad side of low-DO strategies should be simultaneously considered.
The presence of dissolved organic nitrogen (DON) in biological nutrient removal (BNR) effluent has led to increased concern about its adverse effects on wastewater discharge and reuse applications. Previous studies have demonstrated efficient biological inorganic nitrogen removal in BNR under low dissolved oxygen (DO) conditions; however, information on DON is scarce. This study investigated low-DO effects on DON and N-nitrosodimethylamine (NDMA) precursor concentrations in BNR effluents. Identical BNR reactors consisting of an external real-time DO intelligent control system were operated at three different DO concentrations (0.3, 1.0, and 4.0 mgO2/L). Surprisingly, significantly higher values of effluent DON (p<0.05, t-test) and NDMA precursors (p<0.01, t-test) were observed at lower DO levels. Ultrahigh-resolution mass spectrometry analysis showed that molecules produced by microbes at low-DO levels exhibited high proteins/amino sugars-like and low normal oxidation state of carbon characteristics, which possibly acted critical roles in NDMA formation. Furthermore, path analysis by partial least-squares path modeling suggested that NDMA formation potential had strong associations with microbe-DON network stability of microbe-DON co-occurrence interactions (r=0.979, p<0.01). These results highlight the necessity of reconsidering the feasibility of BNR systems operating at low-DO concentrations considering the adverse effects of DON on wastewater discharge and reuse applications.
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Previous research has focused on dissolved organic carbon (DOC) as a surrogate for soluble microbial products (SMPs) and found that temperature has a significant influence on the production of ...SMP-based DOC (SDOC) during biological processes. Little is known about the SMP-based dissolved organic nitrogen (SDON), although some nitrogenous organic matter has been identified as an important part of SMPs. This study investigated the effect of temperature (8 °C, 15 °C and 25 °C) on the characterization of SMPs in an activated sludge system with special emphasis on SDON. Results showed the positive effect of reduced temperature on SDON production. Fluorescence spectroscopy and ultrahigh-resolution mass spectrometry showed the produced SDON at 8 °C and 15 °C exhibits more lability than at 25 °C. This was also supported by the algal bioassay, indicating the SDON produced at low temperature is highly bioavailable and prone to stimulate algae and microorganisms. In addition, principal component analysis demonstrated that the effect of temperature on the chemical characterization of SDON is different from that of SDOC. Overall, this study highlights the importance of SDON control during biological processes at a low temperature to reduce the potential impact of effluent SMPs on receiving waters or wastewater reuse.
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•The effect of temperature on the characterization of SDON was investigated.•Results showed the positive effect of reduced temperature on SDON production.•SDON produced at low temperature was highly bioavailable.•The effect of temperature on the characterization of SDON was different from that of SDOC.
Wastewater-derived dissolved organic nitrogen (DON) should be minimized by municipal wastewater treatment plants (MWWTPs) to reduce its potential impact on receiving waters. Solids retention time ...(SRT) is a key control parameter for the activated sludge (AS) process; however, knowledge of its impact on effluent DON is limited. This study investigated the effect of SRT on the bioavailability, fluorescent components, and molecular characteristics of effluent DON in the AS process. Four lab-scale AS reactors were operated in parallel at different SRTs (5, 13, 26, and 40 days) for treatment of primary treated wastewater collected from an MWWTP. Results showed the positive effect of prolonged SRT on DON removal. AS reactors during longer SRTs, however, cannot sequester the bioavailable DON (ABDON) and occasionally contribute to greater amounts of ABDON in the effluents. Consequently, effluent DON bioavailability increased with SRT (R 2 = 0.619, p < 0.05, ANOVA). Analysis of effluent DON fluorescent components and molecular characteristics indicated that the high effluent DON bioavailability observed at long SRTs is contributed by the production of microbially derived nitrogenous organics. The results presented herein indicate that operating an AS process with a longer SRT cannot control the DON forms that readily stimulate algal growth.
Knowledge of endogenous-source dissolved organic nitrogen (esDON) produced in wastewater treatment processes is critical for evaluating its potential impacts on receiving waters because esDON is a ...recognized concern, as it causes eutrophication. However, differentiating esDON from influent residual DON in real wastewater is always a challenge. Here, we deciphered esDON information in DON transformation processes along a full-scale wastewater treatment train by combining multiple chemometric tools with ion-mobility separation quadrupole time-of-flight mass spectrometry (IMS-QTOF MS) analyses. In total, DON became more refractory and compact with shorter carbon chains and fewer nitrogen atoms, and esDON composed a nonnegligible fraction that dominated DON transformation and characteristics. New esDON produced in treatment processes constituted a crucial part (>35.5%) of wastewater DON, and its contributions to wastewater DON are augmented along the train. Evidence of molecular conformations further confirmed dominant roles of esDON in DON characteristics. Moreover, esDON participated in 46.7% of core biochemical reaction networks, explaining the importance of esDON in DON transformation. Our study offers a tool to gain esDON characteristics and transformation mechanisms, and highlights the importance to control esDON for alleviating adverse influences from DON in receiving waters.
Microorganism-derived dissolved organic nitrogen (mDON) represents a significant and inevitable portion of dissolved organic nitrogen (DON) in the wastewater biotreatment processes. In the existing ...method, mDON concentrations are indirectly measured by the values of DON concentrations from the reactors with DON-free influent. However, this becomes problematic when influent contains DON. Especially when the real wastewater is involved, the paucity of the direct methods to quantitatively measure mDON is a major barrier to further research. This limitation is due to the difficulty of segregating mDON from the other nitrogenous organics, e.g., influent DON. In this study, we propose the ASM-mDON model based on ASM #1, which incorporates the production and consumption of mDON in the activated sludge processes to predict the mDON concentrations. In four independent lab-scale tests, our model was established and calibrated to obtain the accurate values of mDON (R2 = 0.929, p < 0.05), and the validity and applicability of the model were successfully examined by comparing the simulated and measured data. Moreover, the universality of the ASM-mDON model was further confirmed by simulating mDON production in a full-scale wastewater treatment plant. A reasonable prediction of mDON formation was shown in a full-scale test (1.98 ± 0.71 mg/L in June and 1.51 ± 0.54 mg/L in July) and is indirectly supported by an algal bioassay (p < 0.05, t-test). This study provides a useful approach to the efficient and accurate evaluation of mDON formation, which will improve current strategies designed to minimize the effluent mDON in wastewater bioprocesses.
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•Production and consumption of microorganism-derived dissolved organic nitrogen is incorporated into the conventional models.•Microorganism-derived dissolved organic nitrogen formation is accurately quantified (R2 = 0.929, p < 0.05).•Microorganism-derived dissolved organic nitrogen is correctly simulated under various operational conditions.•A useful tool is provided for controlling strategies and further research.
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•Carbon source type affected postdenitrifying MBBRs effluent DON characteristics.•Produced DON contributed to the differences in the bioavailability of effluent DON.•Phyla and ...metabolic pathways responsible for produced DON were identified.•Bioavailable DON dominated phytoplankton growth rather than DIN.•Acetate was recommended as the preferred carbon source in postdenitrifying MBBRs.
Despite the higher potential for eutrophication of dissolved organic nitrogen (DON) than dissolved inorganic nitrogen, the influence of the types of external carbon sources on DON remains largely unknown. This study investigated the effect of external carbon source type (acetate, glucose, methanol, and ethanol) on effluent DON characteristics in postdenitrifying moving bed biofilm reactors (MBBRs) from chemical molecular and microbial insights. The results showed that the effluent DON concentration in postdenitrifying MBBRs fed different carbon source types followed the order of ethanol > glucose > methanol > acetate. Interestingly, the acetate-fed postdenitrifying MBBR effluent DON contained a less labile molecular composition (5.03%), indicating that these effluent DON are not prone to stimulate algae production in receiving waters. Principal component analysis demonstrated that the produced DON instead of removed and/or resisted DON during the denitrification process mainly contributed to the differences in DON molecular composition and bioavailability in effluent. The key microbes, including Proteobacteria, Chloroflexi, etc. and amino acid metabolism were potentially responsible for the produced DON. Overall, this study demonstrated that MBBRs used for postdenitrification could be optimized to minimize eutrophication effects by accounting for optimal carbon sources and that acetate is recommended as the preferred external carbon source in wastewater treatment using postdenitrifying MBBRs.
