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Traditional denitrification often produces high operating costs and excessive sludge disposal expenses due to conventional carbon sources. A novel electric–magnetic field (MF) 48 mT with Fe0 and C-Fe0 powder in an upflow microaerobic sludge reactor (UMSR) improved nitrogen removal from wastewater without organic carbon resources and gave richness to the heterotrophic bacterial community. In the current study, the reactor was operated for 78 ± 2 days, divided into five stages (without Fe0, with Fe0, coupling with MF, without coupling with MF, and coupling with MF again), at a hydraulic retention time (HRT) of 2.5 h, with an influent loading of ammonium (NH4+-N) 50 ± 2 mg/L, at 25–27 °C, and less than 1.0 mg/L dissolved oxygen (DO). The results demonstrated nitrogen removal efficiency enhanced after coupling with MF on the levels of NO3−-N by 76% with an effluent concentration of 8.7 mg/L, NH4+-N by 72% with an effluent concentration of 13.6 mg/L, and total nitrogen removal (TN) by 76%, respectively. After coupling the MF with the reactor, the microbial community data analysis showed the dominant abundance of ammonia-oxidizing bacteria, heterotrophic nitrifying bacteria, and denitrifying bacteria on the level of Anaerolineaceae_uncultured 2%, which is capable of denitrification that uses Fe2+ as an electron source, Gemmatimonadaceae_uncultured 4%, Hydrogenophaga 4% which is capable of catalyzing hydrogenotrophic denitrification and correlating to nitrate removal, denitrification and desulfurization bacteria SBR1031_norank 18%, anammox-bacteria Saccharimonadales_norank 2%, and (AOM) Limnobacter 3% in the sludge. [ABSTRACT FROM AUTHOR]

[Display omitted] • The approach resulted in enhanced nitrate removal efficiency of 67 % for the actual wastewater. • The approach resulted in the continuous release of Fe2+ and Fe3+ ions from the Fe0. • The approach increased in (Nitrospira , Hydrogenophaga , Hyphomicrobium , Sphingobium , Thermus , and Meiothermus). • The approach increased enzymes associated with nitrate metabolism (narB, narG, narH, narI, nirA, nasB, and nasC). This study aimed to investigate the effectiveness of combining zero-valent iron (Fe0) with an electric-magnetic field (EMF) with an intensity of 48-mT generated by an alternating current (AC) of 6 V and 50 Hz applied deep within a reactor using actual wastewater obtained from a secondary stage of a wastewater treatment plant (WWTP). The lab-scale experiment was conducted using the UMSR reactor, maintaining a controlled temperature of 25 ± 2 °C and a hydraulic retention time (HRT) of 5-hour, with a dissolved oxygen (DO) level below 1.5 mg/L. Fine Fe0 particles with a size of ≤ 0.3 µm were added into the reactor at a concentration of 3 g/L. The actual wastewater had an approximate nitrate nitrogen (NO 3 –-N) concentration of 30 ± 2 mg/L, and the substrate mass ratio of carbon to nitrogen (C:N) was at 1:1. The results examined the performance of the EMF-Fe0 system in terms of nitrate removal efficiency and the enrichment of denitrifying bacteria, achieving a nitrate removal rate of 67 % with an effluent NO 3 –-N concentration of 10 mg/L and a chemical oxygen demand (COD) concentration of 11.8 mg/L at removal rate of 60 %. Illumina sequencing revealed various enriched denitrifying bacteria after coupling EMF with Fe0, including autotrophic Nitrospira (NOB) at 4 %, denitrification bacteria like Hydrogenophaga at 1.3 %, Hyphomicrobium at 1 %, and Sphingobium at 5 %, along with thermophilic bacteria Thermus at 1.1 % and Meiothermus at 3.5 %. PICRUSt predicted bacterial functions and analyzed interactions, while KEGG and GO analyses linked nitrogen removal pathways to specific species, genes, and enzymes in the EMF-Fe0 system. [ABSTRACT FROM AUTHOR]

• A novel upflow microaerobic sludge reactor was constructed. • The removal efficiencies of NH 4 +-N and TN reached 90.53% and 80.77%, respectively. • AOB, NOB, anammox, autotrophic and heterotrophic denitrifiers cooperated in UMSR. • Partial denitrification/anammox was dominant nitrogen conversion pathway. • The small height waterfall was applicable to treat low strength NH 4 +-N wastewater. A novel falling water aeration-external reflux upflow microaerobic sludge reactor (UMSR) was designed to treat wastewater with the low chemical oxygen demand (COD) to total nitrogen (TN) ratio. The result showed the concentration of dissolved oxygen (DO) in the reactor could be accurately controlled by adjusting the reflux ratio of oxygenated water. The higher aeration efficiency in pollutant removal could be obtained by the reoxygenation mode of the small height falling water. At the reflux ratio of 5:1, the ammonium, nitrite and nitrate nitrogen concentrations in the effluent of UMSR were 6.0, 0.4 and 6.1 mg/L on average, respectively. The removal efficiency of ammonium nitrogen and total nitrogen reached 90.53% and 80.77%, respectively with the influent COD/TN as being 1.0. The structure of the microbial community confirmed the existence of partial-denitrification/anaerobic ammonium oxidation (anammox) bacteria, autotrophic and heterotrophic denitrifiers contributed to nitrogen and carbon removal in UMSR. [ABSTRACT FROM AUTHOR]

To improve anaerobic digestibility of waste activated sludge (WAS), a novel treatment was explored by a plant-derived biosurfactant (saponin biosurfactant (SB)). SB showed positive effects on WAS hydrolysis and acidogenesis with increasing concentration, but was insignificant at dosage >0.20 g SB/g total suspended solids (TSS). Soluble protein and carbohydrate concentrations reached 2029 ± 28 and 343 ± 52 mg chemical oxygen demand (COD)/L (0.20 g SB/g TSS, 48 h), which were 4.77-fold and 5.87-fold higher than that without treatment. Volatile fatty acids (VFAs) bioproduction showed a 3.51-fold increase in 72 h. Moreover, acetic acid increased already after 2 h with SB treatment, but after 8 h in the control, indicating that SB accelerated syntrophic acetogenesis from butyric acid degradation to acetic acid. Additionally, methane production was enhanced at lower dosage (<0.05 g SB/g TSS) and inhibited at higher dosage (>0.10 g SB/g TSS), with 63.0 and 20.3 mL/g volatile suspended solids (VSS), respectively, while it was 46.5 mL/g VSS in the control. The results obtained are in good agreement with previous ones obtained with chemosynthetic surfactants. Moreover, SB has advantages of easy production and sustainability of supply, which should promote the implementation for WAS treatment. [ABSTRACT FROM AUTHOR]

The development of slow-release carbon sources is an effective biological treatment to remove nutrients from wastewater with low carbon-to-nitrogen ratio (C/N). Most filling-type slow-release carbon could not fulfil the needs of current wastewater treatment plants (WWTPs) process. And most adding-type slow-release carbon sources were prepared using some expensive chemical materials. In this study, combining the advantages of the aforementioned types, a novel adding-type wastepaper-flora (AT-WF) slow-release carbon source was proposed, aiming to realise wastepaper recycling in WWTPs. The screening and identification of the mixed flora, AT-WF carbon source release behaviour, and denitrification performance were investigated. The results showed that through the proposed screening method, a considerable proportion of cellulose-degradation-related genera was enriched, and the cellulose degradation ability and ratio of readily available carbon sources of flora T4, S4 and S5 were effectively strengthened. AT-WF had significant carbon release ability and stability, with an average total organic carbon (TOC) release of 8.82 ± 2.36 mg/g. Kinetic analysis showed that the entire carbon release process was more consistent with the first-order equation. Piecewise fitting with the Ritger-Peppas equation exhibited that the rapid-release (RR) stage was skeleton dissolution and the slow-release (SR) stage was Fick diffusion. Denitrification efficiency can achieve a high average removal efficiency of 94.17%, which could theoretically contribute 11.2% more to the total inorganic nitrogen (TIN) removal. Thus, this study indicated that AT-WF could be utilised as an alternative carbon source in WWTPs. [Display omitted] • A novel adding-type biological slow-release carbon source AT-WF was proposed. • Short-term organic nitrogen source stimulation enhanced the function of the flora. • AT-WF had great ability of carbon release and realized the stable NO 3 −-N removal. • The production of AT-WF provided a new way for wastepaper recycling in WWTPs. [ABSTRACT FROM AUTHOR]

Nitrogen contamination is regarded as a major threat to terrestrial net productivity and environmental sustainability. Anaerobic ammonium oxidation (anammox) is a cost-effective and promising technology in wastewater treatment. In this study, the effects of pH/temperature and their short-term shocks on a hybrid system of anammox coupled with iron-carbon micro-electrolysis (IC-ME) were investigated. Results indicated that the hybrid system significantly enhanced the total nitrogen (TN) removal and expanded the stable pH operating range (TN removal efficiencies over 50%) from pH 6.5–8 to pH 5.5–8.5. Free nitrous acid (FNA) in acid environment, when its concentration was higher than 396.36 ± 5.51 μg/L, was thought to be one critical degradation inhibitor. After suffering a short-term (one day) pH shock, the hybrid system exhibited the improved performance of both stability and nitrogen removal, mainly because Fe corrosion maintained the pH value by IC-ME. More diverse nitrogen removal processes promoted by IC-ME enhanced the TN removal of hybrid after high temperature shocks. However, the susceptibility and inferior adaptability of anammox bacteria were considered to inhibit the nitrogen removal performance of the hybrid and individual anammox system. Microbial analysis identified Candidatus Kuenenia as the major anammox genus, accounting for 3.61% of the microbial community biomass, and the genus of SM1A0 2 might be one novel potential strain that help the anammox process. • Effects of pH/temperature on anammox with Fe–C micro-electrolysis were explored. • Hybrid system showed better stability and nitrogen removal under acid environment. • Free nitrous acid in acidic condition was thought to be a critical inhibitor. • A short-term shock of high temperature was positive for promoting nitrogen removal. [ABSTRACT FROM AUTHOR]

• It was the first time to integrate anammox process with IC-ME. • TN removal efficiency of CAE was achieved up to 90.2%. • Feammox, NDFO and denitrification processes contributed to parts of nitrogen removal. • Candidatus Kuenenia and Candidatus Brocadia were major anammox genera accounted for 1.01% and 0.15%, respectively. In this study, a process that combines iron-carbon micro-electrolysis (IC-ME) with the anammox process was successfully established for promoting nitrogen removal, especially the removal of nitrate by-product. Compared with the conventional anammox process, the average total nitrogen removal efficiency of the combined system increased from 64.6% to 90.2% and 83.8% when the system was effectively operated for 4 days (Phase 2) and 13 days (Phase 3), respectively. In this combined system, IC-ME played a dual role: 1) converting the nitrate to ammonia as the nitrogen substrate for further degradation, and 2) producing Fe2+, Fe3+ and H 2 for the nitrogen removal processes of NH 4 + oxidation with Fe3+ reduction (Feammox), nitrate-dependent Fe2+ oxidation (NDFO), and denitrification, in addition to the anammox process. Microbial analysis using 16S rRNA high-throughput sequencing revealed Candidatus Kuenenia and Candidatus Brocadia as the major anammox genera, accounting for 1.01% and 0.15%, respectively. [ABSTRACT FROM AUTHOR]