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[Display omitted] • UDB and DB at different pyrolysis temperatures played contrasting roles. • DB800-amended group displayed superior nitrogen removal performance. • DB at lower pyrolysis temperature imposed suppression. • Properties of dissolved organic matter released by DB were tracked at molecular level. Biochar has attracted increasingly attention in the biological wastewater treatment owing to its unique environmental behavior. However, the differential effects of undissolved and dissolved fractions of biochar (hereafter named as UDB and DB, respectively) on the anaerobic ammonium oxidation (anammox) process remain unclear. The study evaluated the nitrogen removal performance of anammox system in response to UDB and DB prepared at different pyrolysis temperatures (300 °C, 550 °C and 800 °C). The DB800-amended group displayed superior nitrogen removal performance with the total nitrogen removal efficiency (TNRE) of 92.8 ± 1.4 %. Compared with CK, TNRE was changed by +5.0 % (UDB300), +0.4 % (UDB550) and −22.3 % (UDB800) for UDB-amended groups, and by −16.0 % (DB300), −9.4 % (DB550), and +9.2 % (DB800) for DB-amended groups, respectively. The differences were closely related to the physicochemical properties of UDB and DB. Particularly, dissolved organic matter released by DB were tracked at molecular level, which revealed that CHO occupied the highest proportion of 70.3 % and lignin-like and carboxylic rich alicyclic molecules were dominant in DB800. This study would facilitate the understanding of the differences between the nitrogen removal performance of UDB and DB-amended anammox, thus providing deeper insights for the comprehensive assessment of the impacts of biochar on the anammox process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electro-oxidation of N-heterocycles produces N 2 , N H 3 / N H 4 + , N O 3 - , C O and C O 2. • N H 3 / N H 4 + and an apparent N 2 yield correlate linearly with carbon removal. • Both apparent N 2 and N O 3 - form directly from organic intermediates rather than N H 3 / N H 4 +. • Higher concentrations of parent compounds promote a higher apparent N 2 selectivity. • N O 3 - dominates when oxidation of carbon is mass transfer-limited or at basic pH. We report for the first time the carbon and nitrogen product distribution during the electrochemical oxidation (EO) of pyrazine and related N-heterocyclic compounds (NHCs) present in the hard-to-treat wastewater from a biofuel production process. The experimental study was carried out using a boron-doped diamond anode. Identified and quantified intermediate products included oxamic acid, formamide, oxalic acid, and formic acid. Analysis of the C and N yields as a function of the extent of carbon removal reveals the influence of the current- and mass transfer-control operating regimes on product distribution. Carbon monoxide, which was detected among the gaseous products, suggests a possible decarbonylation pathway in the current-controlled regime. An apparent nitrogen gas and ammonium yields correlated linearly with the carbon removal, while nitrate yields significantly increased in the mass transfer-controlled regime. Nitrate and apparent nitrogen gas appear to form directly from organic nitrogen intermediates, rather than from the ammonium that also forms in the process. The research gives new insights into the NHCs degradation pathways, product distribution, and final water composition as a function of operating regime in the EO of recalcitrant wastewater. [ABSTRACT FROM AUTHOR]

Highlights • Microalgae growth was inhibited at NH 4 +-N concentrations above 100 mg/L. • Microalgae growth in digestate was suppressed by high NH 4 +-N and competing microbes. • Nitrification based pre-treatment was effective in alleviating NH 4 +-N toxicity. • Excellent nitrogen and phosphorus recovery from nitrified digestate by microalgae. • Integrated nitrification and algae cultivation possible using membrane bioreactors. Abstract High ammonium concentration is considered a major challenge in cultivating autotrophic microalgae in anaerobic digestate. In this research, the feasibility of applying nitrification as pretreatment to alleviate ammonium toxicity on microalgae was investigated. Batch experiments conducted in synthetic medium showed that microalgae growth was inhibited at NH 4 +-N > 100 mg/L, but NO 3 −-N was benign at concentrations as high as 350 mg/L. Microalgae growth in 2–50% digestate (v/v) was also affected adversely by invading heterotrophic microorganisms. Digestate pre-treatment using activated sludge mitigated these challenges by converting NH 4 +-N to NO 3 −-N, and reducing organics content in the digestate. Microalgae exhibited excellent growth and nutrients removal in nitrified digestate (5–30% mixed with municipal wastewater) in batch mode. For example, COD, NH 4 +-N, NO 3 −-N and PO 4 3−-P removal in 10% digestate using two-stage bacterial-microalgal process were 87%, 100%, 30% and 77%, respectively. In continuous mode, using a microalgae-based membrane photobioreactor (MPBR) operating downstream to membrane bioreactor (MBR), 91% COD, 97% NH 4 +-N and >99% PO 4 3−-P could be continuously removed from 10% digestate. Although NH 4 +-N removal in the process was mainly through nitrification, total nitrogen removal was >75% at steady state. The effects of lower NH 4 +-N toxicity in the MPBR was also manifested in terms of high microalgae biomass accumulation of about 5 g/L. These results indicate that nitrification can be a promising pretreatment for anaerobic digestate for use in microalgae cultivation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Upgrading nitrogen removal performances in wastewater treatment plants by BES. • Enhancing the polishing action of secondary treatments to avoid tertiary treatments. • Nitrate and ammonium removal without nitrous oxide accumulation. • Disinfection of wastewater via electrochemical anodic oxidation. Economic options to retrofit wastewater treatment plants (WWTPs) without tertiary treatments need to be explored. In this regard, bioelectrochemical systems (BES) can be hybridized with existing technologies, upgrading the removal performance of original techniques while avoiding replacement costs. Yet, few demonstrations of merged systems have been given. For the first time, in this work it was built a lab-scale model of a BES merged with a secondary settler, namely e-settler, to enhance the polishing performance of already existing WWTPs. In particular, to concomitantly increase nitrogen removal and perform wastewater (WW) disinfection, avoiding further tertiary treatments. In the e-settlers, nitrogen removal was increased through bioelectrochemical stimulation. Concomitant ammonium and nitrate removal without nitrite accumulation and a negligible amount of nitrous oxide emissions were observed. Ti-MMO as anode material showed a high disinfectant action. In conclusion, it was demonstrated how a simple bioelectrochemical set-up can upgrade existing WWTPs. The following step requires the study at a larger scale, identifying optimal operational and structural parameters for the in-situ application. The main limitations of the e-settlers were discussed, linking them to possible solutions that need to be deepened in a lab-scale model of conventional secondary treatments (activated sludge followed by secondary settler). [ABSTRACT FROM AUTHOR]

[Display omitted] • The limited step for N removal depended on the presence of plants. • The plants and low water level improved NH 4 + - N rather than TN removal. • N genes and nitrifying populations were affected in later period by treatments. • Cooccurrence network and associated heatmap evidenced interaction of N removal. • The differences in six core pathways of N metabolism depended on CW type. With occurrence of emerging contaminants in wastewater, nitrogen metabolism in constructed wetlands (CWs) should be re-evaluated at different environmental variables to withstand adversely exogenous contaminants. This study investigated functional gene, key enzyme, and microbe regulating nitrogen metabolism in three different configuration design CWs (planted W1 and W3 with full and low water level, unplanted W2 with full water level) when exposed to graphene oxide, one of most popular carbon-based nanomaterials. It was found that nitrogen removal was achieved by classical nitrification and denitrification, which was limited by nitrification in W2 and denitrification in planted CWs, presenting optimal balance between nitrification and denitrification in W1. Compared to W2, ammonium removals increased by 48% and 107% in W1 and W3, conversely total nitrogen removals decreased by 6% and 14% due to nitrate accumulation. Ammonia monooxygenase was the most sensitive to variables among four key enzymes. Bacteria were more abundant than archaea in CWs, both of functional genes and nitrifying populations were obviously affected by plant and water level in later period. The dominant denitrification populations were class Gammaproteobacteria followed by Alphaproteobacteria with the highest abundance observed in W2. Their species richness at genus level was higher on day 30 in W2 than planted CWs, but similar on day 120 in three CWs. The cooccurrence network and associated heatmap evidenced complex interaction among key enzymes, functional genes, and functional genera for nitrogen removal. KEGG annotations revealed specific differences in six core pathways of nitrogen metabolism in three CWs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simultaneous V(V) and NH 4 +-N removals are achieved in a MBfR. • V(V) is reduced to insoluble V(IV) confirmed by SEM and XRD characterization. • Nitrification/denitrification bioprocesses achieve NH 4 +-N removal. • Pseudomonas cooperates with others for V(V) and NH 4 +-N removals. • The gene abundances increase with improved enzyme activities for nitrogen cycling. Ammonium (NH 4 +) is commonly used as either a precipitant or extractant in metallurgy of non-ferrous metal and rare earth ore (e.g., vanadium). This results in the coexistence of toxic metal and NH 4 +-N in the effluent. Despite its toxicity, there remains little in the way of biological treatments to synchronously eliminate vanadate [V(V)] and NH 4 +-N in vanadium smelting wastewater. In this study, simultaneous V(V) and NH 4 +-N removal was achieved using a membrane biofilm reactor (MBfR). The removal efficiencies for V(V) and NH 4 +-N reached 96.8 ± 0.8% and 75.4 ± 1.2%, respectively, with initial concentrations for both beginning at 10 mg/L along with a hydraulic retention time at 36 h. V(V) was mainly reduced to V(IV) precipitates. Complete nitrogen removal was achieved with negligible NO 3 –-N/NO 2 –-N accumulation. Pseudomonas was identified as the main contributor to V(V) reduction, nitrification, and denitrification. The identified V(V) reducers and nitrifying/denitrifying bacteria were positively related to the V(V) and NH 4 +-N removal capacity of MBfR. The increased gene abundance and improved enzymic activity for nitrogen cycling collectively evidenced that V(V) reduction was catalyzed by denitrification enzymes and NH 4 +-N was removed through nitrification/denitrification. Collectively, the results from this study offer a novel strategy for the treatment of vanadium-bearing smelting wastewater by eliminating V(V) and NH 4 +-N in a one-step bioprocess. [ABSTRACT FROM AUTHOR]

A chemical-less process using vacuum-UV (VUV) as radiation source was used for direct oxidation of ammonium to N 2 from the contaminated water. The effect of water pH, aeration, initial ammonium concentration, reaction time, and water anions on ammonium oxidation was evaluated in batch experiments. The oxidation of ammonium improved with the increase in water pH and the highest oxidation level obtained at the pH 8. Although the aeration partly improved ammonium oxidation efficiency, it inhibited the selective oxidation of ammonium to N 2 . The complete oxidation of ammonium at concentrations of 25, 50, 75 and 100 mg NH 4 + /L was obtained at the reaction times of 5, 6, 7.5 and 10 h, respectively, following pseudo first-order kinetic model. In addition, the selectivity to nitrate and N 2 formation obtained in the range of 7.7–14.8% and 85.2–92.3%, respectively. In continuous flow experiments, the complete oxidation of 50 mg/L ammonium observed at HRT of 8 h with N 2 selectivity above 99%. Sulfate had the lowest and carbonate had the highest scavenging effect among the selected anions on radicals species generated in the VUV photoreactor. Accordingly, the VUV photoreactor is an efficient and promising chemical-less advanced process for selective oxidation of ammonium to N 2 . [ABSTRACT FROM AUTHOR]

[Display omitted] • Continuous aeration in membrane-aerated biofilms resulted in full nitrification. • Intermittent aeration suppressed nitrite oxidation and supported anammox process. • Biofilm pH presented periodic upshifts with aeration switches. • Free ammonia speciation likely caused the inhibition of nitrite-oxidizing bacteria. • Heterotrophs established nitrous oxide-reduction zones under intermittent aeration. Membrane-aerated biofilm reactors (MABR) are being applied for autotrophic nitrogen removal, yet control of nitrogen turnover remains challenging in MABR counter-diffusion biofilms. In this study, we regulated microbial activities in two lab-scale MABRs by providing continuous versus intermittent aeration. Nitrogen consumption by different functional microbial groups was estimated from bulk measurements via a mass balance approach. Nitrite-oxidizing bacteria (NOB) proliferated under continuous aeration while they were significantly suppressed under intermittent aeration, and NOB suppression activated anaerobic ammonium oxidation. Nitritation performance in the MABR was studied through long-term bulk measurements and in situ biofilm microprofiles of dissolved oxygen (DO) and pH. During intermittent aeration pH effects rather than DO effects determined nitritation success, especially ammonia speciation, which serves as substrate and inhibitor in nitrification processes. Biofilm transition phases were monitored upon aeration switches. Canonical correspondence analysis suggested that the relative transition after anoxia and aeration intermittency were less decisive for biofilm performance than the relative aeration duration. Heterotrophic bacteria displayed minor denitrification rates with aeration control, but contributed to mitigation of nitrous oxide (N 2 O) emissions. N 2 O production hotspots were identified at the top of the anoxic biofilm zone under continuous aeration. Instead, under intermittent aeration an anoxic N 2 O reduction zone was established. Our observations support intermittent aeration control of MABRs as a simple strategy for energy-efficient nitrogen removal with low N 2 O emission.. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrophoretic deposition method to prepare biochar electrode. • ZnO modification increases mesoporous volume, hydrophilicity and conductivity. • Betaine introduce more reversible redox-active N-functional group. • BK-Z15%-N electrode shows high electro-sorption capabilities and good regeneration. In this work, functional mesoporous bean dregs-based biochar electrodes were prepared by electrophoretic deposition for perchlorate (ClO 4 -) electro-sorption. We characterized the textural and electrochemical properties of the biochar and determined the kinetics of electro-adsorption. The results show that 15% concentration of ZnO nanoparticle modification is recommended to increase the mesoporous volume, specific surface area, hydrophilicity and conductivity of biochar materials. After betaine functionalization, the obtained biochar (BK-Z15%-N) possesses an excellent electrochemical performance with high current density, charging capacity, and low ohmic impedance. As expected, it presents an electro-adsorption capacity of 28.31 mg g-1 toward 20 mg L-1 ClO 4 - at 1 V, which is four times higher than that without voltage and much better than other electrodes in this study and most reported data. The electro-adsorption of ClO 4 - on BK-Z15%-N electrode fits the fractal model, which is a complex process controlled by the electrical force and independent of solution pH. BrO 3 - and Cl- are the most competitive anion to ClO 4 - electro-sorption. Notably, it maintains a sustainable electrochemical regeneration ability due to the reversible redox activity of quaternary amine groups. Therefore, this study offers a remarkable and reliable method for improving the electro-sorption performance of perchlorate. [ABSTRACT FROM AUTHOR]