Microbial synergies drive Simultaneous Biodegradation of Ethoxy and Alkyl chains of Nonylphenol Ethoxylate in Fluidized Bed Reactors.

The widely-used surfactant Nonylphenol Ethoxylate (NPEO) produces endocrine-disrupting compounds during biodegradation, with these byproducts being more harmful than untreated NPEO. This study investigates the effectiveness of a Fluidized Bed Reactor (FBR) in reducing the production of 4-Nonylphenol (4-NP) during the biodegradation of NPEO. Two identical Fluidized Bed Reactors (FBR) filled with sand were used to assess the NPEO degradation and to enhance the microbial consortia capable of breaking down the complex byproducts, ethanol and fumarate were introduced as co-substrates. Our findings demonstrate the significant potential of the FBR, especially when coupled with fumarate, for enhancing the surfactant degradation. It outperforms the efficiency achieved with ethanol as the primary electron donor, albeit with a higher rate of byproduct production. Microbial community taxonomy and metabolic prediction revealed the high abundance of Geobacter (1.51 - 31.71%) and Methanobacterium (1.08 - 13.81%) in non-conductive sand. This may hint a new metabolic interaction and expand our understanding of Direct Interspecies Electron Transfer (DIET) in bioreactors applied to micropollutants degradation. Such an intricate relationship between facultative and anaerobes working together to simultaneously biodegrade the ethoxy and alkyl chains presents a new perspective on NPEO degradation and can potentially be extended to other micropollutants.

Nitrate removal in iron sulfide-driven autotrophic denitrification biofilter: Biochemical and chemical transformation pathways and its underlying microbial mechanism.

Iron sulfides-based autotrophic denitrification (IAD) is effective for treating nitrate-contaminated wastewater. However, the complex nitrate transformation pathways coupled with sulfur and iron cycles in IADs are still unclear. In this study, two columns (abiotic vs biotic) with iron sulfides (FeS) as the packing materials were constructed and operated continuously. In the abiotic column, FeS chemically reduced nitrate to ammonium under the ambient condition; this chemical reduction reaction pathway was spontaneous and has been overlooked in IAD reactors. In the biotic column (IAD biofilter), the complex nitrogen-transformation network was composed of chemical reduction, autotrophic denitrification, dissimilatory nitrate reduction to ammonium (DNRA) and sulfate reducing ammonium oxidation (Sulfammox). Metagenomic analysis and XPS characterization of the IAD biofilter further validated the roles of functional microbial communities (e.g., Acidovorax, Diaphorobacter, Desulfuromonas) in nitrate reduction process coupled with iron and sulfur cycles. This study gives an in-depth insight into the nitrogen transformations in IAD system and provides fundamental evidence about the underlying microbial mechanism for its further application in biological nitrogen removal.

Evaluation of Nanaerobic Digestion as a Mechanism to Explain Surplus Methane Production in Animal Rumina and Engineered Digesters.

Nanaerobes are a newly described class of microorganisms that use a unique cytochrome bd oxidase to achieve nanaerobic respiration at <2 µM dissolved oxygen (∼1% of atmospheric oxygen) but are not viable above this value due to the lack of other terminal oxidases. Although sharing an overlapping ecological niche with methanogenic archaea, the role of nanaerobes in methanogenic systems has not been studied so far. To explore their occurrence and significance, we re-analyzed published meta-omic datasets from animal rumina and waste-to-energy digesters, including conventional anaerobic digesters and anaerobic digesters with ultra-low oxygenation. Results show that animal rumina share broad similarities in the microbial community and system performance with oxygenated digesters, rather than with conventional anaerobic digesters, implying that trace levels of oxygen drive the efficient digestion in ruminants. The rumen system serves as an ideal model for the newly named nanaerobic digestion, as it relies on the synergistic co-occurrence of nanaerobes and methanogens for methane yield enhancement. The most abundant ruminal bacterial family Prevotellaceae contains many nanaerobes, which perform not only anaerobic fermentation but also nanaerobic respiration using cytochrome bd oxidase. These nanaerobes generally accompany hydrogenotrophic methanogens to constitute a thermodynamically and physiologically consistent framework for efficient methane generation. Our findings provide new insights into ruminal methane emissions and strategies to enhance methane generation from biomass.

High-rate iron sulfide and sulfur-coupled autotrophic denitrification system: Nutrients removal performance and microbial characterization.

Iron sulfides-based autotrophic denitrification (IAD) is a promising technology for nitrate and phosphate removal from low C:N ratio wastewater due to its cost-effectiveness and low sludge production. However, the slow kinetics of IAD, compared to other sulfur-based autotrophic denitrification (SAD) processes, limits its engineering application. This study constructed a co-electron-donor (FeS and S0 with a volume ratio of 2:1) iron sulfur autotrophic denitrification (ISAD) biofilter and operated at as short as 1 hr hydraulic retention time (HRT). Long-term operation results showed that the superior total nitrogen and phosphate removals of the ISAD biofilter were 90-100% at 1-12 h HRT, with the highest denitrification rate up to 960 mg/L/d. Considering low sulfate production, HRT of 3 h could be the optimal condition. Such superior performance in the ISAD biofilter was achieved due to the interactions between FeS and S0, which accelerated the denitrification process and maintained the acidity-alkalinity balance. Metagenomic analysis found that the enriched nitrate-dependent iron-oxidizing (NDFO) bacteria (Acinetobacter and Acidovorax), sulfur-oxidizing bacteria (SOB), and dissimilatory nitrate reduction to ammonia (DNRA) bacteria likely supported stable nitrate reduction. The metabolic pathway analysis showed that completely denitrification and DNRA, coupled with sulfur oxidation, disproportionation, iron oxidation and phosphate precipitation with FeS and S0 as co-electron donors, were responsible for the high-rate nitrate and phosphate removal. This study provides the potential of ISAD as a highly efficient post-denitrification technology and sheds light on the balanced microbial S-N-Fe transformation.

Metatranscriptional characterization of metabolic dynamics in anaerobic membrane bioreactor producing methane from low-strength wastewater.

An anaerobic membrane bioreactor (AnMBR) with media is an emerging carbon-neutral biotechnology for low-strength wastewater (LSWW) treatment and methane recovery. Understanding metabolic dynamics among methanogens and syntrophic bacteria is important in optimizing the design and operation of AnMBR. However, little is known about it, especially in media-attached microbial communities. This study explored metabolic dynamics to compare media-attached and suspended conditions. Accordingly, metagenomes and metatranscriptomes from AnMBRs with polymeric media and fed with different influent concentrations (350 and 700 mg-COD/L) were analyzed. Metabolic dynamics were profoundly influenced by the different growth habitats and influent conditions, although the applied influent concentrations are within the range of typical LSWW. Metabolic dynamics prediction results suggest that media-attached-growth habitats may have provided a more favorable microenvironment for methanogens to grow and produce methane, especially under low influent conditions. These findings provide significant implications for optimizing floating media design and operation of AnMBR-producing methane from LSWW.

Theoretical characterisation of electron tunnelling from granular activated carbon to electron accepting organisms in direct interspecies electron transfer.

Direct interspecies electron transfer (DIET) has been identified as an efficient metabolism between symbiotically interacting organisms. One method of DIET uses conductive materials (e.g., granular activated carbon (GAC)) as a medium to shuttle electrons from electron donating organisms (eg., Geobacter metallireducens) to electron accepting organisms (e.g., Geobacter sulfurreducens and Methanosarcina barkeri). Conductive materials such as GAC, become negatively charged in DIET processes due to reduction by electron donating organisms. This high excess electron density in GAC leads to quantum tunnelling of electrons being a significant electron transfer mechanism for DIET. Thus, a theoretical model obeying the Wentzel-Kramers-Brillouin (WKB) approximation and Fermi-Dirac statistics was developed and simulated. In the model, the electron tunnelling transfer barrier was described by an effective rectangular barrier. The result of our 1D tunnelling simulations indicates that within 29.4 nm of the GAC, tunnelling can sufficiently supply electrons from GAC to G. sulfurreducens and M. barkeri. The phenomenon of tunnelling may also have significance as a stimulant of chemotaxis for G. sulfurreducens and other electron accepting microbes when attempting to adsorb onto GAC. This study sheds light on quantum tunnelling's significant potential in both bacterium and archaeon DIET-centric processes.

Roadmap from Microbial Communities to Individuality Modeling for Anaerobic Digestion of Sewage Sludge.

Biological models describing anaerobic digestion (AD) of sewage sludge have been widely applied to test various control and operation strategies. Anaerobic digestion model 1 (ADM1) provides a generic platform that includes the main processes of AD, excluding homoacetogenesis and the microbial structure. Homoacetogenic bacteria have been identified as important competitors for hydrogen consumption and acetate production. Although recent advances in meta-omics techniques have improved our characterization of AD microbial communities, conventional models treat functional groups as homogeneous and overlook the physiology and behavior of microbial individuality, limiting insights into mechanisms governing process performance. A novel microbial individuality model (MIM) that integrates kinetics, energetics, and agent-based modeling to describe a microbiome's behavior as heterogenic populations, including homoacetogenesis, was developed. The MIM was validated with two datasets from previous studies through daily biogas production, methane content, compound concentrations, and microbial relative abundance changes. The MIM identified the emergence of Methanosaeta at low concentrations of acetate. Moreover, this simulation supports experimental studies confirming that the overlooked homoacetogenesis is an important hydrogen sink in AD. Validated MIMs are expected to provide insights into syntrophic and competitive interactions among microbiomes in AD systems while testing different operational parameters in a virtual environment. The MIM offers a methodological framework to other biological treatment systems and their microbial community dynamics.

Partitioning of nutrient removal contribution between granules and flocs in a hybrid granular activated sludge system.

Sludge granulation in continuous-flow systems is an emerging technology to intensify existing activated sludge infrastructure for nutrient removal. In these systems, the nutrient removal contributions and partitioning of microbial functions between granules and flocs can offer insights into process implementations. To this end, a reactor system that simulates the continuous-flow environment using an equal amount of initial granule and floc biomass was investigated. The two operational strategies for maintaining granule growth in the continuous-flow system were (a) the higher solids retention time (SRT) for the granules versus flocs, as well as (b) selective feeding of carbon to the granules. The SRT of the large granule fractions (>425 µm, LG) and floc/small granule fractions (<425 µm, FSG) were controlled at 20 and 2.7-6.0 days, respectively. Long term operation of the hybrid granule/floc system achieved high PO43- and NH4+ removal efficiencies. Higher polyphosphate-accumulating organisms (PAO) activity was observed in the FSG than LG, while ammonia-oxidizing bacteria (AOB) activities were similar in the two biomass fractions. Nitrite shunt was observed in the FSG, possibly due to out-competition by the high NOB activity in LG. More importantly, washing out the FSG caused a reduction in LG's AOB and PAO activity, indicating a possible dependency of LG on FSG for maintaining its nutrient removal capacity. Our findings highlighted the partitioning and potential competition/cooperation of key microbial functional groups between LG and FSG, facilitating nutrient removal in a hybrid granular activated sludge system, as well as implications for practical application of the treatment platform.

Combined Effect of Activated Carbon Particles and Non-Adsorptive Spherical Beads as Fluidized Media on Fouling, Organic Removal and Microbial Communities in Anaerobic Membrane Bioreactor.

The combined effect of acrylonitrile butadiene styrene (ABS) spherical beads and granular activated carbon (GAC) particles as fluidized media on the performance of anaerobic fluidized bed membrane bioreactor (AFMBR) was investigated. GAC particles and ABS beads were fluidized together in a single AFMBR to investigate membrane fouling and organic removal efficiency as well as energy consumption. The density difference between these two similarly sized media caused the stratified bed layer where ABS beads are fluidized above the GAC along the membrane. Membrane relaxation was effective to reduce the fouling and trans-membrane pressure (TMP) below 0.25 bar could be achieved at 6 h of hydraulic retention time (HRT). More than 90% of soluble chemical oxygen demand (SCOD) was removed after 80 d operation. Biogas consisting of 65% of methane was produced by AFMBR, suggesting that combined use of GAC and ABS beads did not have any adverse effect on methane production during the operational period. Scanning Electron Microscope (SEM) examinations showed the adherence of microbes to both media. However, 16S rRNA results revealed that fewer microbes attached to ABS beads than GAC. There were also compositional differences between the ABS and GAC microbial communities. The abundance of the syntrophs and exoelectrogens population on ABS beads was relatively low compared to that of GAC. Our result implied that syntrophic synergy and possible occurrence of direct interspecies electron transfer (DIET) might be facilitated in AFMBR by GAC, while traditional methanogenic pathways were dominant in ABS beads. The electrical energy required was 0.02 kWh/m3, and it was only about 13% of that produced by AFMBR.

Genomic driven factors enhance biocatalyst-related cellulolysis potential in anaerobic digestion.

Anaerobic digestion (AD) is a promising technology to recover bioenergy from biodegradable biomass, including cellulosic wastes. Through a few fractionation/separation techniques, cellulose has demonstrated its potential in AD, but the performance of the process is rather substrate-specific, as cellulolysis bacteria are sensitive to the enzyme-substrate interactions. Cellulosome is a self-assembled enzyme complex with many functionalized modules in the bacteria which has been gradually studied, however the genomic fingerprints of the culture-specific cellulosome in AD are relatively unclear especially under processing conditions. To clarify the key factors affecting the cellulosome induced cellulolysis, this review summarized the most recent publications of AD regarding the fates of cellulose, sources and functional genes of cellulosome, and omics methods for functional analyses. Different processes for organic treatment including applying food grinds in sewer, biomass valorization, cellulose fractionation, microaeration, and enzymatic hydrolysis enhanced fermentation, were highlighted to support the sustainable development of AD technology.

Synergistic association between cytochrome bd-encoded Proteiniphilum and reactive oxygen species (ROS)-scavenging methanogens in microaerobic-anaerobic digestion of lignocellulosic biomass.

Intermittent (every other day) microaerobic [picomolar oxygen by oxidation-reduction potential (ORP) set at +25 mV above anaerobic baseline] digestion of lignocellulosic biomass showed higher digestibility and better stability at a high organic loading rate (OLR) of 5 g volatile solids (VS)/L/d than that under strict anaerobic conditions. However, the microbial mechanisms supporting the delicate balance under microaeration remain underexplored. On the basis of our previous findings that microbial communities in replicate experiments were dominated by strains of the genus Proteiniphilum but contained diverse taxa of methanogenic archaea, here we recovered related genomes and reconstructed the putative metabolic pathways using a genome-centric metagenomic approach. The highly enriched Proteiniphilum strains were identified as efficient cellulolytic facultative bacterium, which directly degraded lignocellulose to carbon dioxide, formate, and acetate via aerobic respiration and anaerobic fermentation, alternatively. Moreover, high oxygen affinity cytochromes, bd-type terminal oxidases, in Proteiniphilum strains were found to be closely associated with such picomolar oxygen conditions, which has long been overlooked in anaerobic digestion. Furthermore, hydrogenotrophic methanogenesis was the prevalent pathway for methane production while Methanosarcina, Methanobrevibacter, and Methanocorpusculum were the dominant methanogens in the replicate experiments. Importantly, the two functional groups, namely cellulolytic facultative Proteiniphilum strains and methanogens, encoded various antioxidant enzymes. Energy-dependent reactive oxygen species (ROS) scavengers (superoxide reductase (SOR) and rubrerythrin (rbr) were ubiquitously present in different methanogenic taxa in response to replicate-specific ORP levels (-470, -450 and -475 mV). Collectively, cytochrome bd oxidase and ROS defenders may play roles in improving the digestibility and stability observed in intermittent microaerobic digestion.

Alternative strategies of nutrient acquisition and energy conservation map to the biogeography of marine ammonia-oxidizing archaea.

Ammonia-oxidizing archaea (AOA) are among the most abundant and ubiquitous microorganisms in the ocean, exerting primary control on nitrification and nitrogen oxides emission. Although united by a common physiology of chemoautotrophic growth on ammonia, a corresponding high genomic and habitat variability suggests tremendous adaptive capacity. Here, we compared 44 diverse AOA genomes, 37 from species cultivated from samples collected across diverse geographic locations and seven assembled from metagenomic sequences from the mesopelagic to hadopelagic zones of the deep ocean. Comparative analysis identified seven major marine AOA genotypic groups having gene content correlated with their distinctive biogeographies. Phosphorus and ammonia availabilities as well as hydrostatic pressure were identified as selective forces driving marine AOA genotypic and gene content variability in different oceanic regions. Notably, AOA methylphosphonate biosynthetic genes span diverse oceanic provinces, reinforcing their importance for methane production in the ocean. Together, our combined comparative physiological, genomic, and metagenomic analyses provide a comprehensive view of the biogeography of globally abundant AOA and their adaptive radiation into a vast range of marine and terrestrial habitats.

Catabolism and interactions of uncultured organisms shaped by eco-thermodynamics in methanogenic bioprocesses.

BACKGROUND: Current understanding of the carbon cycle in methanogenic environments involves trophic interactions such as interspecies H2 transfer between organotrophs and methanogens. However, many metabolic processes are thermodynamically sensitive to H2 accumulation and can be inhibited by H2 produced from co-occurring metabolisms. Strategies for driving thermodynamically competing metabolisms in methanogenic environments remain unexplored. RESULTS: To uncover how anaerobes combat this H2 conflict in situ, we employ metagenomics and metatranscriptomics to revisit a model ecosystem that has inspired many foundational discoveries in anaerobic ecology-methanogenic bioreactors. Through analysis of 17 anaerobic digesters, we recovered 1343 high-quality metagenome-assembled genomes and corresponding gene expression profiles for uncultured lineages spanning 66 phyla and reconstructed their metabolic capacities. We discovered that diverse uncultured populations can drive H2-sensitive metabolisms through (i) metabolic coupling with concurrent H2-tolerant catabolism, (ii) forgoing H2 generation in favor of interspecies transfer of formate and electrons (cytochrome- and pili-mediated) to avoid thermodynamic conflict, and (iii) integration of low-concentration O2 metabolism as an ancillary thermodynamics-enhancing electron sink. Archaeal populations support these processes through unique methanogenic metabolisms-highly favorable H2 oxidation driven by methyl-reducing methanogenesis and tripartite uptake of formate, electrons, and acetate. CONCLUSION: Integration of omics and eco-thermodynamics revealed overlooked behavior and interactions of uncultured organisms, including coupling favorable and unfavorable metabolisms, shifting from H2 to formate transfer, respiring low-concentration O2, performing direct interspecies electron transfer, and interacting with high H2-affinity methanogenesis. These findings shed light on how microorganisms overcome a critical obstacle in methanogenic carbon cycles we had hitherto disregarded and provide foundational insight into anaerobic microbial ecology. Video Abstract.

Energy-Efficient Single-Stage Nitrite Shunt Denitrification with Saline Sewage through Concise Dissolved Oxygen (DO) Supply: Process Performance and Microbial Communities.

Single-stage nitrite shunt denitrification (through nitrite rather than nitrate) with low dissolved oxygen (DO) supply is a better alternative in terms of energy-efficiency, short-footprint, and low C/N-ratio requirement. This study investigates the optimal DO level with temperature effect, with saline sewage at the fixed hydraulic and solids retention times of 8 h and 8 d, respectively. Moreover, 16S rRNA gene sequencing analysis corresponding with total nitrogen (TN) and chemical oxygen demand (COD) removals in each operating condition were performed. Results showed that DO of 0.3 mg/L at 20 °C achieved over 60.7% and over 97.9% of TN and COD removal, respectively, suggesting that such condition achieved effective nitrite-oxidizing bacteria inhibition and efficient denitrification. An unexpected finding was that sulfur-reducing Haematobacter and nitrogen-fixing Geofilum and Shinella were highly abundant with the copredominance of ammonia-oxidizing Comamonas and Nitrosomonas, nitrite-oxidizing Limnohabitans, and denitrifying Simplicispira, Castellaniella, and Nitratireductor. Further, canonical correspondence analysis (CCA) with respect to the operating conditions associated with phenotype prediction via R-based tool Tax4Fun was performed for a preliminary diagnosis of microbial functionality. The effects of DO, temperature, nitrite, and nitrate in various extents toward each predominant microbe were discussed. Collectively, DO is likely pivotal in single-stage nitrite shunt denitrification, as well as microbial communities, for energy-efficient saline sewage treatment.

Superior resolution characterisation of microbial diversity in anaerobic digesters using full-length 16S rRNA gene amplicon sequencing.

In the past decade, the characterisation of the microbial community in anaerobic digestion was primarily done by using high-throughput short-read amplicon sequencing. However, the short-read approach has inherent primer bias and low phylogenetic resolution. Our previous study using Illumina MiSeq suggested that the heterogeneity of AD microbiome was operation-driven. To advance our knowledge towards the complexity of the AD microbiome, we performed full-length 16S rRNA gene amplicon sequencing using PacBio Sequel for a more accurate phylogenetic identification. To this end, purified DNA samples from 19 global anaerobic digesters were sequenced. Sixteen methanogenic archaea were identified at the species level. Among them, Methanosarcina horonobensis and Methanosarcina flavescens had significant presence under specific operating conditions. Methanothrix concilii presented in all digesters sequenced. Unexpectedly, over 90% of the Smithella detected were closely related to alkane-degrading Smithella strains D17 and M82, not Smithella propionica. Using LEfSe and network analysis, the interspecies relationship between the fermentative and syntrophic bacteria was addressed. Comparison of the short- and long-read sequencing results were performed and discussed. From sample preparation to data analysis, this work characterised the digester microbiomes in a superior resolution.

Flocs in disguise? High granule abundance found in continuous-flow activated sludge treatment plants.

To date, high performance of full-scale aerobic granular sludge (AGS) technology has been demonstrated on a global scale. Its further integration with existing continuous flow activated sludge (CFAS) treatment plants is the next logical step. All granular sludge reactors operated in sequencing batch reactors (SBR) mode with anaerobic feeding conditions select for growth of phosphorus and glycogen accumulating organisms (PAO and GAO, respectively), which are known to enhance sludge settling characteristics. Therefore, we hypothesized that AGS are commonly present at full-scale CFAS processes with enhanced biological phosphorus removal (EBPR) and low sludge volume index (SVI). This hypothesis was confirmed at 13 EBPR plants, where granules were found present (at plants where SVI was lower than 100 ml/g) with a strong correlation between high granule abundance and low SVI. A wide range of granule abundance was found among the plants, ranging from 0.5% to as high as 80%. Evaluations of the EBPR plant process configurations showed that high granule abundances may be related to selector design features such as high anaerobic food to mass (F/M) ratios, unmixed in-line fermentation, and high influent soluble COD fraction. Granules were also observed at a non-EBPR plant with an aerobic selector receiving high F/M feeds. Quantitative PCR and 16S rRNA gene sequencing analyses revealed higher relative gene abundance of Accumulibacter PAO and Competibacter GAO in the granules over flocs, as well as a correlation between granule abundance and some possible EPS producers such as Flavobacterium and Competibacter. Our results indicated that process configurations that select for slow-growing or EPS-producing heterotrophs play an important role for granule formation in full-scale CFAS systems as previously shown in SBR configurations.

Evolution of microbial dynamics with the introduction of real seawater portions in a low-strength feeding anammox process.

The salinity effect on anammox bacteria has been widely reported; however, rare studies describe the microbial dynamics of anammox-based process response to the introduction of real seawater at mainstream conditions. In this study, an anammox process at mainstream conditions without pre-enriching anammox bacteria was shifted to the feeds of a synthetic wastewater with a portion of seawater mixture. It achieved over 0.180 kg-N/(m3 day) of nitrogen removal rate with an additional seawater proportion of 20% in the influent. The bacterial biodiversity was significantly increased with the increase of seawater proportions. High relative abundance of anammox bacteria (34.24-39.92%) related to Ca. Brocadia was enriched and acclimated to the saline environment. However, the introduction of seawater caused the enrichment of nitrite-oxidizing Ca. Nitrospira, which was responsible for the deterioration of nitrogen removal efficiency. Possible adaptation metabolisms in anammox bacteria and other nitrogen transforming bacteria are discussed. These results highlight the importance of microbial diversity for anammox process under the saline environments of 20% and 40% seawater composition.

Increasing ammonia recovery from high-level ammonium wastewater via adding sodium sulfate to prevent nitrogen generation in the cathode.

The high-level ammonium-nitrogen (NH4+-N) is a contaminant for aqueous environment but a potential hydrogen fuel. This study investigated an approach of increasing ammonia recovery via adding sodium sulfate of 0-1.5 M to prevent from nitrogen generation. The results of experiment tests, electrochemical analysis and MD simulation demonstrated that the added Na2SO4 assisted ammonium transport inhibited nitrogen gas generation in a certain concentration range. In electric double layer (EDL), with Na2SO4 concentration increasing, both the migration velocities of NH4+ and Na+ are accelerated for Na2SO4 of 0-0.25 M, whereas they are decelerated for concentrate Na2SO4 that 0.5 M). A thick layer formed by Na+ that imposed a fierce competitive adsorption blocked the migration of NH4+ and the transportation of electrons. The decrease of electrons and the accumulation of water molecules caused the potential drop in the EDL. 0.25 M Na2SO4 was the optimal concentration from the aspect of ion transports. The results obtained in this study can allow the manipulation of EDI capacity optimization.

Beyond Energy Balance: Environmental Trade-Offs of Organics Capture and Low Carbon-to-Nitrogen Ratio Sewage Treatment Systems.

Several life-cycle assessments (LCAs) have evaluated the environmental impacts (EIs) of different wastewater treatment (WWT) configurations, attempting resource recovery and energy efficiency. However, a plant-wide LCA considering up-concentration primary treatment and low carbon-to-nitrogen (C/N) ratio sewage at the secondary biological treatment (SBT) has not yet been conducted. This study identifies the environmental trade-offs and hotspots for the chemically enhanced primary treatment (CEPT) and low C/N ratio SBT emerging processes compared to conventional WWT. The life-cycle inventories were calculated using a stoichiometric life-cycle inventory framework that couples stoichiometry and kinetics to obtain site-specific water, air, and soil emissions. The midpoint results of LCA show that CEPT with anaerobic digestion (AD) for sludge treatment achieves energy self-sufficiency, but increases marine eutrophication (MEu) by 1 order of magnitude compared to conventional WWT. A mainstream anaerobic fluidized-bed bioreactor and a partial nitritation-anammox fluidized-bed membrane bioreactor which can reduce all environmental impacts by 17-47%, including MEu, are proposed as the SBT of the low-carbon CEPT settled sewage. Integrating the standardized S-LCI framework resulted in a site-specific LCA that aids decision-makers on choosing between higher reductions in most EIs at the expense of high MEu or less but consistent reductions in all EI categories.

Performance Recovery in Degraded Carbon-Based Electrodes for Capacitive Deionization.

Limitations of capacitive deionization (CDI) and future commercialization efforts are intrinsically bound to electrode stability. In this work, thermal treatments are explored to understand their ability to regenerate aged CDI electrodes. We demonstrate that a relatively low thermal treatment temperature of ∼500 °C can sufficiently recover the lost salt adsorption capacity of degraded electrodes. Furthermore, a systematic study of electrode replacement clarifies that the desalination ability loss and regeneration for a CDI cell are isolated to the aged anode, as expected. Characterizations of surface functionalities support that the acidic oxygen-containing functional groups formed in situ during cycling undergo thermal decomposition during treatment. The modified Donnan model quantitatively confirms that the surface charges originate from the formation/decomposition of functional groups. Accordingly, the lost pore volume and the increased resistance are recovered during thermal treatments, while the surface morphologies and pore structure of the electrodes are well-preserved. Therefore, thermal treatment can be applied practically to extend the lifetime of aged electrodes. This study also offers insights into strategies for minimizing electrode degradation or in situ regeneration such that the technology gains momentum for future commercialization.