Solid Electrolytes for Low-Temperature Carbon Dioxide Valorization: A Review.

One of the most promising approaches to address the global challenge of climate change is electrochemical carbon capture and utilization. Solid electrolytes can play a crucial role in establishing a chemical-free pathway for the electrochemical capture of CO2. Furthermore, they can be applied in electrocatalytic CO2 reduction reactions (CO2RR) to increase carbon utilization, produce high-purity liquid chemicals, and advance hybrid electro-biosystems. This review article begins by covering the fundamentals and processes of electrochemical CO2 capture, emphasizing the advantages of utilizing solid electrolytes. Additionally, it highlights recent advancements in the use of the solid polymer electrolyte or solid electrolyte layer for the CO2RR with multiple functions. The review also explores avenues for future research to fully harness the potential of solid electrolytes, including the integration of CO2 capture and the CO2RR and performance assessment under realistic conditions. Finally, this review discusses future opportunities and challenges, aiming to contribute to the establishment of a green and sustainable society through electrochemical CO2 valorization.

Tandem Acidic CO2 Electrolysis Coupled with Syngas Fermentation: A Two-Stage Process for Producing Medium-Chain Fatty Acids.

The tandem application of CO2 electrolysis with syngas fermentation holds promise for achieving heightened production rates and improved product quality. However, the significant impact of syngas composition on mixed culture-based microbial chain elongation remains unclear. Additionally, effective methods for generating syngas with an adjustable composition from acidic CO2 electrolysis are currently lacking. This study successfully demonstrated the production of medium-chain fatty acids from CO2 through tandem acidic electrolysis with syngas fermentation. CO could serve as the sole energy source or as the electron donor (when cofed with acetate) for caproate generation. Furthermore, the results of gas diffusion electrode structure engineering highlighted that the use of carbon black, either alone or in combination with graphite, enabled consistent syngas generation with an adjustable composition from acidic CO2 electrolysis (pH 1). The carbon black layer significantly improved the CO selectivity, increasing from 0% to 43.5% (0.05 M K+) and further to 92.4% (0.5 M K+). This enhancement in performance was attributed to the promotion of K+ accumulation, stabilizing catalytically active sites, rather than creating a localized alkaline environment for CO2-to-CO conversion. This research contributes to the advancement of hybrid technology for sustainable CO2 reduction and chemical production.

Unveiling the Occurrence and Non-Negligible Role of Amino Sugars in Waste Activated Sludge Fermentation by an Enriched Chitin-Degradation Consortium.

Polysaccharides in extracellular polymeric substances (EPS) can form a hybrid matrix network with proteins, impeding waste-activated sludge (WAS) fermentation. Amino sugars, such as N-acetyl-d-glucosamine (GlcNAc) polymers and sialic acid, are the non-negligible components in the EPS of aerobic granules or biofilm. However, the occurrence of amino sugars in WAS and their degradation remains unclear. Thus, amino sugars (∼6.0%) in WAS were revealed, and the genera of Lactococcus and Zoogloea were identified for the first time. Chitin was used as the substrate to enrich a chitin-degrading consortium (CDC). The COD balances for methane production ranged from 83.3 and 95.1%. Chitin was gradually converted to oligosaccharides and GlcNAc after dosing with the extracellular enzyme. After doing enriched CDC in WAS, the final methane production markedly increased to 60.4 ± 0.6 mL, reflecting an increase of ∼62%. Four model substrates of amino sugars (GlcNAc and sialic acid) and polysaccharides (cellulose and dextran) could be used by CDC. Treponema (34.3%) was identified as the core bacterium via excreting chitinases (EC 3.2.1.14) and N-acetyl-glucosaminidases (EC 3.2.1.52), especially the genetic abundance of chitinases in CDC was 2.5 times higher than that of WAS. Thus, this study provides an elegant method for the utilization of amino sugar-enriched organics.

Refining microbial potentiometric sensor performance with unique cathodic catalytic properties for targeted application scenarios.

Traditional microbial electrochemical sensors encounter challenges due to their inherent complexity. In response to these challenges, the microbial potentiometric sensor (MPS) technology was introduced, featuring a straightforward high-impedance measurement circuit tailored for environmental monitoring. Nonetheless, the practical implementation of conventional MPS is constrained by issues such as the exposure of the reference electrode to the monitored water and the absence of methodologies to stimulate microbial metabolism. In this study, our objective was to enhance MPS performance by imbuing it with unique cathodic catalytic properties, specifically tailored for distinct application scenarios. Notably, the anodic region served as the sensing element, with both the cathodic region and reference electrode physically isolated from the analyzed water sample. In the realm of organic monitoring, the sensor without Pt/C coated in the cathodic region exhibited a faster response time (1 h) and lower detection limits (1 mg L-1 BOD, 1 mM acetic acid). Conversely, when monitoring toxic substances, the sensor with Pt/C showcased a lower detection limit (0.004% formaldehyde), while the Pt/C-free sensor demonstrated superior reusability. The sensor with Pt/C displayed a heightened anode biofilm thickness and coverage, predominantly composed of Rhodococcus. In conclusion, this study introduces simple, cost-effective, and tailorable biosensors holding substantial promise for water quality monitoring.

Yield stress Measurement of municipal sludge: A comprehensive evaluation of testing methods and concentration effects using a rotational rheometer.

Accurate prediction and measurement of yield stress are crucial for optimizing sludge treatment and disposal. However, the differences and applicability of various methods for measuring yield stress are subjects of ongoing debate. Meanwhile, literature on measuring sludge yield stress is limited to low solid concentrations (TS <10%), understanding and studying the yield stress of medium to high solid concentration sludge is crucial due to increasingly stringent standards for sludge treatment and disposal. So, this study employed a rotational rheometer to measure sludge yield stress across a wide range of TS (4-50%) using steady shear, dynamic oscillatory shear, and transient shear. The study derived significant conclusions by comparing and summarizing the applicability and limitations of each testing method: Dynamic oscillatory shear methods, including G'-σ curve method, γ-σ curve method, and G**γc method can measure sludge yield stress ranging from 4% to 40% TS, while other methods are restricted to low or limited solid concentrations; The G' = G″ method, utilizing the intersection of G' and G″ curves, consistently yields the highest value for yield stress when 4%≤ TS ≤ 12%; The rotational rheometer cannot measure sludge yield stress when the solid concentration exceeds 40% TS; The relationship between sludge yield stress and solid concentration is stronger as a power-law for TS ≤ 25%, transitioning to linear for higher concentrations (28%≤ TS <40%). This study systematically explores the applicability and limitations of various measurement methods for characterizing sludge yield stress across a wide range of solid concentrations, providing valuable guidance for scientific measurement and highlighting challenging research issues.

Reactive Oxygen Species Promote Nitrous Oxide (N2O) Emissions from Soil/Sediment during the Anoxic-Oxic Transition.

Reactive oxygen species (ROS)-induced element/pollutant geochemical processes in fluctuating anoxic-oxic areas have received increasing attention in recent years. Nitrous oxide (N2O) is a strong greenhouse gas; however, the relationship between ROS and N2O emissions in these areas has not been established. This work revealed the essential role of ROS in promoting N2O emissions in soil/sediment during the anoxic-oxic transition. ROS decreased the rate of nitrate reduction by 26-31% and increased N2O emissions by 8.8-31.3% (at 48 h). ROS-induced N2O emission was via inhibiting the step of N2O reduction. During the anoxic-oxic transition, the contribution of ROS to inhibit the step of N2O reduction was higher than 52.6%, demonstrating the important role of ROS. The downregulated relative transcription of the NosZ gene demonstrated inhibition at the gene level. Hydrogen peroxide was the dominant ROS species inhibiting N2O reduction, while the role of hydroxyl radicals was negligible, suggesting a different behavior of N2O emission with common pollutant conversion induced by ROS during the anoxic-oxic transition. This study demonstrated an overlooked factor in promoting N2O emission in the soil/sediment and appealed to a re-examination of the mechanism of N2O emissions in fluctuating anoxic-oxic areas.

Sunlight Significantly Enhances Soil Denitrification via an Interfacial Biophotoelectrochemical Pathway.

Denitrification is an essential step of the nitrogen cycle in soil. However, although sunlight is an important environmental factor for soil, the investigation of the influence of sunlight on soil denitrification is limited to plant photosynthesis-mediated processes. Herein, a new pathway, denoted as a biophotoelectrochemical process, which is induced by the direct photoexcitation of soil, was found to greatly enhance soil denitrification. Using red soil as the research object, the soil with irradiation showed nitrate reduction that was 2.6-4.7 times faster than that without irradiation. The irradiation of soil accelerated the reduction of nitrite and enhanced the conversion of nitrous oxide to nitrogen, indicating that more electron sources were generated. This resulted from the photoinduced generation of ferrous substrates and photoelectrons. The contribution of irradiation to soil denitrification was almost half (45.4%), of which 30.9% was from photoinduced ferrous substrates and 14.5% was from photoelectrons. Moreover, a designed biophotoelectrochemical cell provided solid evidence for direct photoelectron transfer from soil photosensitive substrates to microorganisms. Irradiation promoted the enrichment of Alicyclobacillus, which participates in iron oxidation and electroautotrophy. This finding reveals a role of sunlight in soil denitrification that has been thus seriously overlooked and provides solid evidence for the natural occurrence of photoelectrotrophic effects.

Electricity-Driven Microbial Metabolism of Carbon and Nitrogen: A Waste-to-Resource Solution.

Electricity-driven microbial metabolism relies on the extracellular electron transfer (EET) process between microbes and electrodes and provides promise for resource recovery from wastewater and industrial discharges. Over the past decades, tremendous efforts have been dedicated to designing electrocatalysts and microbes, as well as hybrid systems to push this approach toward industrial adoption. This paper summarizes these advances in order to facilitate a better understanding of electricity-driven microbial metabolism as a sustainable waste-to-resource solution. Quantitative comparisons of microbial electrosynthesis and abiotic electrosynthesis are made, and the strategy of electrocatalyst-assisted microbial electrosynthesis is critically discussed. Nitrogen recovery processes including microbial electrochemical N2 fixation, electrocatalytic N2 reduction, dissimilatory nitrate reduction to ammonium (DNRA), and abiotic electrochemical nitrate reduction to ammonia (Abio-NRA) are systematically reviewed. Furthermore, the synchronous metabolism of carbon and nitrogen using hybrid inorganic-biological systems is discussed, including advanced physicochemical, microbial, and electrochemical characterizations involved in this field. Finally, perspectives for future trends are presented. The paper provides valuable insights on the potential contribution of electricity-driven microbial valorization of waste carbon and nitrogen toward a green and sustainable society.

Novel Insight into Microbially Mediated Nitrate-Reducing Fe(II) Oxidation by Acidovorax sp. Strain BoFeN1 Using Dual N-O Isotope Fractionation.

Microbially mediated nitrate reduction coupled with Fe(II) oxidation (NRFO) plays an important role in the Fe/N interactions in pH-neutral anoxic environments. However, the relative contributions of the chemical and microbial processes to NRFO are still unclear. In this study, N-O isotope fractionation during NRFO was investigated. The ratios of O and N isotope enrichment factors (18ε:15ε)-NO3- indicated that the main nitrate reductase functioning in Acidovorax sp. strain BoFeN1 was membrane-bound dissimilatory nitrate reductase (Nar). N-O isotope fractionation during chemodenitrification [Fe(II) + NO2-], microbial nitrite reduction (cells + NO2-), and the coupled process [cells + NO2- + Fe(II)] was explored. The ratios of (18ε:15ε)-NO2- were 0.58 ± 0.05 during chemodenitrification and -0.41 ± 0.11 during microbial nitrite reduction, indicating that N-O isotopes can be used to distinguish chemical from biological reactions. The (18ε:15ε)-NO2- of 0.70 ± 0.05 during the coupled process was close to that obtained for chemodenitrification, indicating that chemodenitrification played a more important role than biological reactions during the coupled process. The results of kinetic modeling showed that the relative contribution of chemodenitrification was 99.3% during the coupled process, which was consistent with that of isotope fractionation. This study provides a better understanding of chemical and biological mechanisms of NRFO using N-O isotopes and kinetic modeling.

Enrichment of biofertilizer-type hydrogen-oxidizing bacteria on urea containing Cu(II).

With the utilization of pesticides and fertilizers (e.g. urea), the presence of nitrogen and heavy metals (e.g. copper) can enter and pollute the environment. Biofertilizers can be used to replace chemical fertilizers to increase crop yields and reduce environmental stress. The utilization of hydrogen-oxidizing bacteria (HOB) to be biofertilizers has recently attracted more attention. However, the enrichment of HOB on urea and the effect of copper are undetermined. HOB were successfully enriched using urea in this investigation. The average urea conversion rate (AUCR) was 180.08 mgN/L/d with a hydraulic retention time of 10 h. Microbial community (R1) was dominated by Hydrogenophaga (83.92%), a biofertilizer-type HOB. After addition of 5.47 mg/L Cu2+, the AUCR was decreased by 16%-151.18 mgN/L/d, and the growth of HOB was inhibited by 48%. Meanwhile, inhibition was also reflected by the increase of polysaccharide content (20.27 ± 0.57 to 33.45 ± 2.53 mg/gVSS) and protein content (106.19 ± 19.39 to 125.14 ± 24.73 mg/gVSS) of extracellular polymeric substances in the HOB. The resulting microbial community (R2) was changed to Azospiralium-dominated flora (91.33%). Both enriched microbial communities (R1 and R2) exhibited the abilities of ACC degradation and phosphate solubilization. This study demonstrates that employing urea can directly enrich biofertilizer-type HOB and copper-tolerant HOB can be obtained in a 5.47 mg/L Cu2+ environment. The results provide potential methods to obtain biofertilizer from copper-containing urea wastewater via HOB.

What affects the accuracy and applicability of determining wastewater sludge water content via low-field nuclear magnetic resonance?

The accurate determination of waster sludge water content is crucial to sludge dewatering treatment and its disposal management. Though previous studies highlight the great advantages of low-field nuclear magnetic resonance (LF-NMR) in the determination of sludge water content, its accuracy and applicability are not well studied. Herein, this study investigated the settling of operating parameters and the properties of sludge samples on the accuracy and applicability of LF-NMR method in measuring sludge water content. The results showed that the setting of basic parameters such as standard curve, number of scanning times (NS) and sample weight affected the accuracy of sludge water content by LF-NMR. The standard calibration curve constructed by 3 g/L CuSO4, NS = 8 and the sample weight of about 5 g, were suitable for the accurate determination of sludge water content. Furthermore, the existence of magnetic substances in sludge can affect the distribution gradient of main magnetic field, and thus restricted the applicability of LF-NMR. The saturation magnetization of chemical reagents strongly correlated with the measured relative errors of sludge water content (r = 0.995, p < 0.01), the greater the saturation magnetization of the magnetic material, the greater the error of the test results. On the whole, it is necessary to fully consider the influence of process parameters and sludge properties to evaluate the accuracy and applicability of the LF-NMR method, rather than simply copying the parameters in literatures.

Enhancing data reliability in quantitative characterization of moisture distribution in sludge using DSC: Impact of sample attributes and test parameters.

Exploring moisture distribution, especially bound water content, is vital for studying and applying sludge dewatering. The differential scanning calorimetry (DSC) method has been extensively utilized for the quantitative characterization of moisture distribution in sludge. However, this method has certain limitations, such as low reproducibility of results, leading to controversial parameter values in different papers and hindering result comparison. In this study, we investigated the influence of key sample attributes on measuring sludge bound water using the DSC method.The findings demonstrated that the moisture content and mass of sludge samples substantially influenced the reproducibility and stability of DSC test results. To ensure data reliability, the moisture content of the sludge sample should be minimized and kept below 84%, with the mass not exceeding 10 mg. Compared to the influence of sludge moisture content and sample mass, the heating rate (1⁓5 °C/min) minimally affected DSC test results. This study offers a comprehensive insight into how sample attributes and test parameters affect the quantitative characterization of bound water in sludge using the DSC method. Furthermore, practical strategies are presented to enhance the method's applicability in sludge bound water characterization.

Super-fast Charging Biohybrid Batteries through a Power-to-formate-to-bioelectricity Process by Combining Microbial Electrochemistry and CO2 Electrolysis.

Extensive study on renewable energy storage has been sparked by the growing worries regarding global warming. In this study, incorporating the latest advancements in microbial electrochemistry and electrochemical CO2 reduction, a super-fast charging biohybrid battery was introduced by using pure formic acid as an energy carrier. CO2 electrolyser with a slim-catholyte layer and a solid electrolyte layer was built, which made it possible to use affordable anion exchange membranes and electrocatalysts that are readily accessible. The biohybrid battery only required a 3-minute charging to accomplish an astounding 25-hour discharging phase. In the power-to-formate-to-bioelectricity process, bioconversion played a vital role in restricting both the overall Faradaic efficiency and Energy efficiency. The CO2 electrolyser was able to operate continuously for an impressive total duration of 164 hours under Gas Stand-By model, by storing N2 gas in the extraction chamber during stand-by periods. Additionally, the electric signal generated during the discharging phase was utilized for monitoring water biotoxicity. Functional genes related to formate metabolism were identified in the bioanode and electrochemically active bacteria were discovered. On the other hand, Paracoccus was predominantly found in the used air cathode. These results advance our current knowledge of exploiting biohybrid technology.

Dissolved Organic Matter Acting as a Microbial Photosensitizer Drives Photoelectrotrophic Denitrification.

The biogeochemical fates of dissolved organic matter (DOM) show important environmental significance in aqueous ecosystems. However, the current understanding of the trophic relationship between DOM and microorganisms limits the ability of DOM to serve as a heterotrophic substrate or electron shuttle for microorganisms. In this work, we provide the first evidence of photoelectrophy, a new trophic linkage, that occurs between DOM and nonphototrophic microorganisms. Specifically, the photoelectrotrophic denitrification process was demonstrated in a Thiobacillus denitrificans-DOM coupled system, in which DOM acted as a microbial photosensitizer to drive the model denitrifier nitrate reduction. The reduction of nitrate followed a pseudo-first-order reaction with a kinetic constant of 0.06 ± 0.003 h-1, and the dominant nitrogenous product was nitrogen. The significant upregulated (p < 0.01) expression of denitrifying genes, including nar, nir, nor, and nos, supported that the conversion of nitrate to nitrogen was the microorganism-mediated process. Interestingly, the photoelectrophic process triggered by DOM photosensitization promotes humification of DOM itself, an almost opposite trend of pure DOM irradiation. The finding not only reveals a so far overlooked role of DOM serving as the microbial photosensitizer in sunlit aqueous ecosystems but also suggests a strategy for promoting sunlight-driven denitrification in surface environments.

Mixotrophic Cultivation of Microalgae Using Biogas as the Substrate.

Biogas utilization through biotechnology represents a potential and novel technology. We propose the microalgal mixotrophic cultivation to convert biogas to microalgae-based biodiesel, in which methanotroph was co-cultured to convert CH4 to organic intermediate (and CO2) for microalgal mixotrophic growth. This study constructed a co-culture of Methylocystis bryophila (methanotroph) and Scenedesmus obliquus (microalgae) with biogas feeding. Compared with the single culture of S. obliquus, higher microalgal biomass but a lower chlorophyll concentration was observed. The organic metabolism-related genes were upregulated, verifying microalgal mixotrophic growth. The stoichiometric calculation of M. bryophila culture shows that M. bryophila tends to release organic matter rather than grow under a low O2 content. M. bryophila rarely grew under five different light intensities, indicating that M. bryophila acts as a biocatalyst in the co-culture. The organic intermediate released by methanotroph increased the maximum biomass of microalgal culture, accelerated nitrogen absorption, accumulated more monounsaturated fatty acids, and improved the adaptation to light. The co-culture of microalgae and methanotroph may provide new opportunities for microalgae-based biodiesel production using biogas as a substrate.

Anthraquinone-2-Sulfonate as a Microbial Photosensitizer and Capacitor Drives Solar-to-N2O Production with a Quantum Efficiency of Almost Unity.

Semiartificial photosynthesis shows great potential in solar energy conversion and environmental application. However, the rate-limiting step of photoelectron transfer at the biomaterial interface results in an unsatisfactory quantum yield (QY, typically lower than 3%). Here, an anthraquinone molecule, which has dual roles of microbial photosensitizer and capacitor, was demonstrated to negotiate the interface photoelectron transfer via decoupling the photochemical reaction with a microbial dark reaction. In a model system, anthraquinone-2-sulfonate (AQS)-photosensitized Thiobacillus denitrificans, a maximum QY of solar-to-nitrous oxide (N2O) of 96.2% was achieved, which is the highest among the semiartificial photosynthesis systems. Moreover, the conversion of nitrate into N2O was almost 100%, indicating the excellent selectivity in nitrate reduction. The capacitive property of AQS resulted in 82-89% of photoelectrons released at dark and enhanced 5.6-9.4 times the conversion of solar-to-N2O. Kinetics investigation revealed a zero-order- and first-order- reaction kinetics of N2O production in the dark (reductive AQS-mediated electron transfer) and under light (direct photoelectron transfer), respectively. This work is the first study to demonstrate the role of AQS in photosensitizing a microorganism and provides a simple and highly selective approach to produce N2O from nitrate-polluted wastewater and a strategy for the efficient conversion of solar-to-chemical by a semiartificial photosynthesis system.

Electricity production and key exoelectrogens in a mixed-culture psychrophilic microbial fuel cell at 4 °C.

The electricity production via psychrophilic microbial fuel cell (PMFC) for wastewater treatment in cold regions offers an alternative to avoid the unwanted methane dissolution of traditional anaerobic fermentation. But, it is seldom reported by mixed-culture, especially closed to 0 °C. Thus, a two-chamber mixed-culture PMFC at 4 °C was successfully operated in this study using acetate as an electron donor. The main results demonstrated a good performance of PMFC, including the maximum voltage of 513 mV at 1000 Ω, coulombic efficiency of 53%, and power density of 689 mW/m2. The cyclic voltammetry curves of enriched biofilm showed a direct electron transfer pathway. These good performances of mixed-culture PMFC were due to the high psychrophilic activity of enriched biofilm, including exoelectrogens genera of Geobacter (6.1%), Enterococcus (17.5%), and Clostridium_sensu_stricto_12 (3.8%). Consequently, a mixed-culture PMFC provides a reasonable strategy to enrich exoelectrogens with high activity. For low-temperature regions, the mixed-culture PMFC involved biotechnologies shall benefit energy generation and valuable chemical production in the future. KEY POINTS: • PMFC showed a maximum voltage of around 513 mV under a resistance of 1000 Ω. • The coulombic efficiency was 53% and the max power density was 689 mW/m2. • Geobacter, Enterococcus, and Clostridium_sensu_stricto_12 were key exoelectrogens.

A unified operating procedure is crucial to evaluate sludge dewaterability, taking the setup of refrigerated storage time as an example.

Although extensive efforts have been carried out to study sludge dewatering mechanism, the lack of universal operating procedures makes it never be satisfactorily explained. This study evaluated the impact of a unified operating procedure on waste activated sludge (WAS) dewaterability by taking the setup of refrigerated storage time as an example. It was found that storage time played an important role in determining WAS dewaterability and sampled WAS should be refrigerated within 2 days. The results showed that after 2-d storage, sludge filterability was deteriorated significantly while the extent of dewatering efficiency had little change. Meanwhile, increasing storage time greatly increased the release of extracellular polymeric substances (EPS) and heavy metals, decreased sludge viscosity and weakened its network strength, but had little impact on the floc size and zeta potential of the sludge samples. It can hardly reveal the mechanism of storage time on sludge dewaterability due to the non-uniformity of operating procedures in literatures, which is normally ignored. This study emphasizes a unified operating procedure is crucial to evaluate WAS dewaterability. Therefore, more efforts shall be focused on establishing the uniform operating procedure while advancing applied research in the field of sludge dewatering.

Identification of Extracellular Key Enzyme and Intracellular Metabolic Pathway in Alginate-Degrading Consortia via an Integrated Metaproteomic/Metagenomic Analysis.

Uronic acid in extracellular polymeric substances is a primary but often ignored factor related to the difficult hydrolysis of waste-activated sludge (WAS), with alginate as a typical polymer. Previously, we enriched alginate-degrading consortia (ADC) in batch reactors that can enhance methane production from WAS, but the enzymes and metabolic pathway are not well documented. In this work, two chemostats in series were operated to enrich ADC, in which 10 g/L alginate was wholly consumed. Based on it, the extracellular alginate lyase (∼130 kD, EC 4.2.2.3) in the cultures was identified by metaproteomic analysis. This enzyme offers a high specificity to convert alginate to disaccharides over other mentioned hydrolases. Genus Bacteroides (>60%) was revealed as the key bacterium for alginate conversion. A new Entner-Doudoroff pathway of alginate via 5-dehydro-4-deoxy-d-glucuronate (DDG) and 3-deoxy-d-glycerol-2,5-hexdiulosonate (DGH) as the intermediates to 2-keto-3-deoxy-gluconate (KDG) was constructed based on the metagenomic and metaproteomic analysis. In summary, this work documented the core enzymes and metabolic pathway for alginate degradation, which provides a good paradigm when analyzing the degrading mechanism of unacquainted substrates. The outcome will further contribute to the application of Bacteroides-dominated ADC on WAS methanogenesis in the future.

Constraining nitrification by intermittent aeration to achieve methane-driven ammonia recovery of the mainstream anaerobic effluent.

Mainstream anaerobic treatment has the potential to capture organic energy, and represents a sustainable development trend, but with the problems of low biogas quality and dissolved methane emissions. In this study, methane-driven ammonia recovery of anaerobic effluent was proposed. A 380-day long-term experiment, which was divided into four phases according to different aeration modes, was conducted. The ammonia conversion and microbial characteristics shows that ammonia oxidizing bacteria (AOB) were constrained during Phases 2 (DO: <0.2 mg L-1) and 4 (DO: 0.1-1.6 mg L-1), and were active during Phase 3 (DO: 2-4 mg L-1). During phase 4, when the intermittent aeration was used, the total nitrogen removal rate was higher than during Phases 2 and 3, and nearly 100% ammonia was removed. Methylomonas, a genus of methane oxidizing bacteria (MOB), was enriched during Phase 4. The serum bottle experiment confirmed that the ammonia removal occurred through the MOB assimilation. The protein content in the CH4-added group was 35.5%, which was higher than in the group without CH4 (23.3%). The powerful ammonia assimilation and protein synthesis capabilities of MOB give a meaning to the anaerobic effluent for ammonia recovery and protein production. Intermittent aeration could be used to constrain AOB and improve ammonia recovery efficiency.