This study addresses the slow start-up and poor stability of aerobic granular sludge (AGS) in continuous-flow reactors (CFRs) by proposing a method using external CaCl2/FeCl3 to condition returned sludge, combined with dual-zone sedimentation tanks, for rapid AGS cultivation in an integrated oxidation ditch. The reactor was operated at an HRT of 16.7 h, OLR of 0.27-0.53 kg/(m3 & sdot;d), and temperature of 20 +/- 2 degrees C. External conditioning with CaCl2/FeCl3, together with the dual-zone sedimentation, promoted sludge granulation by day 51 and 47, respectively. Compared with the initial seed sludge and unconditioned control R3 (natural drying with only sludge reflux), SVI5 for the reactors using external CaCl2 and FeCl3 decreased to 40.4 mL/g and 32.1 mL/g, with average particle sizes reaching 0.59 mm and 0.57 mm. Both chemical conditioning and dual-zone sedimentation synergistically accelerated this granulation process, while R3 failed to achieve complete granulation even on day 80. FeCl3 performed slightly better than CaCl2, likely due to the higher charge density and flocculation capacity of Fe3+. Mechanistically, external conditioning significantly increased c-di-GMP concentration, stimulated EPS secretion, and significantly elevated the relative abundance of key functional genera including Proteobacteria, Zoogloea, and Rhodobacter, synergistically promoting granulation. Economic analysis confirmed that the benefits of accelerated granulation and sludge reduction outweigh the chemical costs. This study provides an efficient technical approach and theoretical support for rapid AGS start-up in continuous-flow systems.

Efficient formation of aerobic granular sludge (AGS) under low organic load and low chemical oxygen demand/total nitrogen (C/N) ratio conditions remains challenging in municipal wastewater treatment. In this study, a sequencing batch reactor (SBR) integrated with an Fe-C anoxic module was developed to promote sludge granulation and enhance nitrogen (N) and phosphorus (P) removal. Reactor performance, sludge characteristics, microbial community succession, functional genes and Fe mediated mechanisms were systematically investigated. A high proportion of AGS was successfully cultivated through selective sludge wasting combined with the Fe-C anoxic module. In R2, granular sludge particles larger than 200 μm accounted for 75%, with an average particle size of 278 μm. Compared with the R1, TN and TP removal efficiencies increased by 9% and 38%, respectively. Microbial community analysis revealed that the Fe-C anoxic module enriched heterotrophic denitrifying bacteria and iron related autotrophic denitrifying bacteria, including unclassified_f__Gallionellaceae and Ferritrophicum. Functional gene analysis further showed increased abundances of genes associated with denitrification, iron oxidation, and electron transfer, indicating that Fe-C anoxic module enhanced electron availability and promoted the coupling of heterotrophic denitrification and Fe(II) driven autotrophic denitrification under carbon limited conditions. Meanwhile, Fe2 +/Fe3+ released from Fe-C micro electrolysis and the resulting iron oxides promoted floc aggregation, granule stabilization, and p removal through adsorption, precipitation, and co-precipitation. Overall, this study provides mechanistic and gene level evidence for the role of Fe-C micro electrolysis in AGS formation and enhanced N and P removal under low C/N ratio conditions.

iron-carbon (IC) materials were packed as fillers into the anoxic and micro-aerobic zones of a biological filter, and for the first time, these two zones were electrically connected via a conductive wire to enable electron transfer from the micro-aerobic zone to the anoxic zone. Microorganisms in the anoxic zone utilized the cross-regionally transferred electrons to drive nitrate denitrification, thereby enhancing the denitrification efficiency, reducing the requirement for external carbon sources, and simultaneously achieving high total phosphorus (TP) removal. This configuration constitutes a novel self-driven bio-electrochemical system (SD-BES). A SD-BES trickle filter was established at a wastewater treatment plant, in which a current density of up to 45.7 mA m⁻³ was achieved. The system demonstrated a total nitrogen (TN) removal efficiency of 81.2% and a TP removal efficiency of 93.9%. Integrated analysis of microbial diversity and functional genes revealed significant enrichment of electrochemically active bacteria (e.g., Geothrix) and iron-autotrophic denitrifying bacteria (e.g., Dechloromonas), along with a marked increase in the abundance of key functional genes associated with nitrogen metabolism. The intensity of IC micro-electrolysis in the micro-aerobic zone consistently exceeds that in the anoxic zone, providing a natural potential difference for the cross-regional transfer of electrons. The wire serves as a bridge for electron transfer, and the enrichment of functional microorganisms enables the cross-regional transferred electrons to be utilized in an efficient pollutant removal process. The incorporation of a conductive wire in this study offers a novel application approach and theoretical basis for IC-assisted simultaneous nitrogen and phosphorus removal from wastewater.

The increasing urgency of effective sludge dewatering in wastewater treatment plants demands advanced technologies to reduce sludge volume and enhance sludge dewaterability. This study investigates the dewatering efficiency and mechanisms under low-temperature heating and acidification conditions combined with different flocculants, with a focus on identifying the optimal flocculant for enhancing sludge dewatering. The results show that under low-temperature and acidic conditions, the overall effect of organic flocculants is superior to that of inorganic flocculants and inorganic polymer flocculants, among which cationic polyacrylamide (CPAM) demonstrates the most outstanding dewatering performance. At a pH of 3.0 and a temperature of 60 degrees C, with CPAM dosage of 10.0 mg/g dry solid (DS), sludge water content decreased from 80.0 % to 70.6 %, and capillary suction time (CST) reduced from 34.2 s to 11.9 s. CPAM significantly enhances sludge dewatering by increasing floc particle size through charge neutralization and promoting cell lysis as well as the release of bound water. Furthermore, the flocculation behaviors of different flocculants under low-temperature and acidic conditions were compared by analyzing the composition and functional group characteristics of extracellular polymeric substances (EPS). Consequently, the synergistic mechanism of flocculants in enhancing dewatering under these conditions was revealed at the molecular level. In conclusion, this study establishes the theoretical foundation for sludge dewatering through low-temperature acidification combined with flocculants, thereby supporting the development of efficient technologies.

Low-temperature-induced filamentous sludge bulking has long represented a major operational challenge during winter operation of wastewater treatment plants, and practical engineering systems still lack a simple, stable, and reliable control strategy. At a municipal wastewater treatment plant where winter sludge bulking recurrently occurred and the sludge volume index (SVI) exceeded 200 mL g-1, this study proposed and implemented a bypass regulation strategy without altering the existing process configuration. Specifically, iron-carbon polyurethane packing (ICPP), composed of iron-carbon spheres coupled with polyurethane sponge, were installed in the sludge return corridor. The strategy synergistically improved sludge settleability through multiple mechanisms, including oxidative stress induced by iron-carbon micro-electrolysis, selective interception of filamentous bacteria by the packing structure, and intermittent drying effects associated with return sludge operation. During the winter period, while the Control Group(CG) exhibited severe bulking with SVI values ranging from 200 to 350 mL g-1, the Treatment Group(TG) successfully maintained SVI within 60 to 120 mL g-1. The abundance of Kouleothrix (Type 1851) was maintained at 8.58% in the TG, compared with 24.87% in the CG. This full-scale validation demonstrates that regulation via ICPP installed in the sludge return channel can serve as a low-intervention, implementable, and stable control strategy for winter sludge bulking. The approach provides a practical engineering solution and conceptual framework for maintaining stable wastewater treatment performance under cold-season conditions.

The ubiquitous occurrence of antibiotic residues in aquatic environments poses increasing risks to ecosystem stability and public health. Herein, sulfidated nanoscale zero-valent iron-nickel (S-nZVI/Ni) was synthesized by liquid-phase reduction and employed to activate peracetic acid (PAA) for ciprofloxacin (CIP) degradation. Sulfidation and Ni doping effectively alleviated particle agglomeration and produced a well-dispersed core-shell structure. Under optimized conditions, the S-nZVI/Ni/PAA system achieved 97.7% CIP degradation within 60 min, with a pseudo-first-order rate constant of 0.062 min⁻¹. Mechanistic analyses revealed a pronounced redistribution of reactive oxygen species toward ·O₂⁻ and ¹O₂. The hydrophobic FeSₓ shell suppressed the aqueous ·OH pathway while regulating interfacial electron transfer, whereas the Ni–Fe micro-galvanic effect accelerated electron transfer and Fe³⁺/Fe²⁺ cycling, thereby enhancing PAA activation. Quenching experiments combined with electron paramagnetic resonance analysis identified ·O₂⁻ and ¹O₂ as the dominant reactive species, contributing 37.9% and 35.4% to CIP degradation, respectively, compared with 14.7% for ·OH and 9.6% for R–O·. Density functional theory calculations revealed the preferred reactive and electron-transfer sites of CIP, while LC-MS identified 13 intermediates and supported four transformation pathways involving quinolone ring oxidation, decarboxylation, defluorination, and piperazine ring cleavage. The system maintained high degradation efficiency over pH 3–7 and in real water matrices and retained over 70% activity after five cycles. Toxicity assessment further indicated reduced biological inhibition after treatment. These findings demonstrate that coupling sulfidation with Ni doping provides an effective strategy for steering ROS generation during PAA activation and offers new insights into interface-engineered catalysts for antibiotic remediation.

To explore a new approach to reducing the use of external carbon sources and phosphorus removal chemicals in conventional wastewater treatment, this study developed an anaerobic-oxic-anoxic sequencing batch reactor (AOA-SBR) system (Rf) with iron shavings addition (180 g, 60 g/L), using a blank reactor (R0) as the control. Synthetic wastewater with a C/N ratio of 7.5 was used as the influent. The operating cycle of the AOA-SBR reactor consisted of a 120 min anaerobic phase, a 120 min aerobic phase, and a 60 min anoxic phase, with a hydraulic retention time (HRT) of 12 h. Results showed that the SVI30 of Rf remained at approximately 35 mL/g. The average removal efficiencies of TN and TP in Rf reached 70% and 96%, respectively, which were higher than those of the control. The addition of waste iron shavings improved sludge settleability and nitrogen and phosphorus removal performance of the biochemical system. Fe-C microelectrolysis significantly enriched Candidatus_Competibacter and Candidatus_Nitrocosmicus while inhibiting nitrite-oxidizing bacteria (NOB). This triggered persistent low-level nitrite accumulation within the system, diversified nitrogen-removal pathways, and ultimately improved the total nitrogen-removal efficiency. The extended anaerobic period in the anaerobic-oxic-anoxic (AOA) mode enriched phosphate-accumulating organisms, achieving synergistic chemical and biological phosphorus removal. This study provides a novel strategy for advanced wastewater treatment without external carbon sources or phosphorus additives.

To address the slow and unstable activity recovery of aerobic granular sludge (AGS) after room-temperature storage, iron shavings were added in this study to promote rapid performance recovery of AGS. After 200 days of storage, AGS showed color changes and declines in settleability and pollutants removal, though granular structure remained intact. Stored sludge was inoculated into R1 (with iron shavings) and R0 (without). R1 recovered settleability by day 49, while R0 had not by day 60. R1 restored total phosphorus (TP) and total nitrogen (TN) removal on days 1 and 9 (89.7% and 91.5%), whereas R0 recovered TN on day 15 (92.1%) but TP removal remained unstable. Microbial community analysis revealed that after storage, the community structure shifted from a Zoogloea-dominated "function-oriented" type to a "tolerance-oriented" type enriched with Candidatus_Competibacter, Oscillochloris, and Thiobaca. The rapid restoration of pollutants removal with iron shavings suggests they help reactivate functional microbes. It is hypothesized that Fe2+, Fe3+, & sdot;OH, and H2, generated from the micro-electrolysis of iron shavings, contribute to the recovery. Therefore, iron shavings enable rapid recovery of AGS after room-temperature storage, offering a feasible technical approach.

Achieving simultaneous nitrogen and phosphorus removal in continuous-flow municipal wastewater remains challenging. This study evaluated an aerated-volume-optimized continuous self-circulating fluidized bed (ACOAAP-Zier) treating real municipal wastewater inoculated with either flocculent sludge (R_floc) or anaerobic granular sludge (R_AnGS). Distinct seed-sludge evolutionary trajectories fundamentally shaped the structural and functional development of microbial aggregates. R_floc followed a bottom-up aggregation pathway and formed predominantly small-to-medium aggregates, whereas R_AnGS underwent a physical "top-down" structural reconstruction and retained a greater proportion of large aggregates. Under comparable conditions, the 500-1000 µm and > 1000 µm fractions in R_AnGS (P3) were 3.0- and 5.4-fold higher than in R_floc (P2), respectively. The resulting structural heterogeneity provided differentiated ecological niches for functional microorganisms. P2 exhibited superior ammonia oxidation, whereas P3 favored the enrichment of denitrifying and phosphorus-removing microorganisms, with denitrifying polyphosphate-accumulating organisms (DPAOs) being approximately 3.1 times higher than that in P2. Consequently, enhanced phosphorus removal and coupled nitrogen-removal pathways were achieved. Aggregate size was significantly positively correlated with polyphosphate-accumulating organisms abundance. These findings provide a basis for optimizing continuous-flow biological nutrient removal in municipal wastewater treatment.

To overcome the inhibitory effect of organic matter on sludge bioleaching, this study systematically evaluated the impacts of two pretreatment methods (aeration and anaerobic digestion) on subsequent bioleaching performance. Results demonstrated that aeration pretreatment significantly accelerated the acidification process, enhanced overall heavy metals (HMs) removal efficiency, and effectively minimized phosphorus loss. Following the selection of aeration pretreatment, three bioleaching processes (direct, aerated, and anaerobic bioleaching) were compared. Aerated bioleaching achieved the fastest acidification (pH 2.08 in 6 days) and optimal removal of Cu2+, Zn2+, and Pb2+. Microbial community analysis revealed that the bioleaching process greatly changed community abundance and diversity, while particularly enriching key bioleaching genera such as Acinethiobacillus and Alicyclobacillus. This evolution was closely associated with the selectivity of HMs removal. All bioleaching processes achieved effective sludge reduction (MLSS decreased by 26.99%- 63.21%) and improved dewaterability. Aerated bioleaching yielded the optimal dewatering performance (specific resistance to filtration, SRF: 1.24 & times; 1013 m/kg), attributed to its induced reorganization of extracellular polymeric substances (EPS)- characterized by protein enrichment in tightly bound EPS and polysaccharide stripping from loosely bound EPS. This study provides critical theoretical insights for optimizing sludge bioleaching parameters and pretreatment-process combinations to maximize HM removal while minimizing nutrient loss.

This study presents a novel method to improve aerobic granular sludge (AGS) formation in continuous-flow reactors(CFRs), which often face slow granulation and poor stability. By externally conditioning waste activated sludge with Fe3+ and recycling it into a two-zone sedimentation tank reactor, the process accelerates granulation and enhances stability. Complete granulation occurred in 60 days (from 0.28mm to 0.60mm of the initial sludge), and the sludge volume index at 5min (SVI5) stayed below 30mL/g. The CFR achieved average removal efficiencies of 87.17% for COD and 91.55% for NH4+-N. Additionally, sludge activity improved, with dehydrogenase activity rising from 6.70 to 16.90mg/(g MLVSS) and the specific oxygen uptake rate increasing from 7.80 to 36.80mg O2/(g MLVSS·h). The analysis of microbial communities indicated an enrichment of genera associated with the secretion of extracellular polymeric substances (EPS) and the stability of granular structures, such as Proteobacteria, Zoogloea and Flavobacterium. Additionally, the secondary messenger c-di-GMP was found to further accelerate granulation by modulating the secretion of EPS. Its concentration reached a peak of 380.50μg/(g MLVSS) during the granulation phase, mirroring the trend observed for EPS. In conclusion, the proposed strategy effectively enhances the formation and stability of AGS in CFRs, providing a viable approach for upgrading existing continuous-flow wastewater treatment processes.

Permanganate (PM, Mn(VII)) oxidation is attractive for water treatment because of its stability and operational simplicity, yet its moderate oxidizing power often limits the removal of recalcitrant trace organic contaminants, such as sulfonamide antibiotics. Here, we show that metal hydrolysis in situ generates dispersed metal (hydr)oxide colloids that markedly enhance PM oxidation of sulfonamides. Among the tested metals, Fe(III) showed the strongest promotion of sulfamethoxazole (SMX) degradation in a strongly pH-dependent manner. Transmission electron microscopy, zeta potential measurements, graded membrane filtration and preformed-colloid control experiments identified that Fe(OH)3 nanocolloids (80-120 nm) as the dominant active phase. Multiple probe experiments, electron paramagnetic resonance, sulfoxide probing, and Mn(III)-pyrophosphate assays revealed no measurable contribution from reactive oxygen species or reactive Mn intermediates under our experimental conditions. Instead, electrochemical measurements, selective probe reactions, and DFT calculations support a proximity-enabled interfacial electron-transfer pathway, in which Fe(OH)3 colloids associate with MnO4-, weaken Mn-O bonding, and co-enrich MnO4- and SMX at the interface. At a realistic PM dose (10 µM) and an optimized Fe(III) dosage of 0.1 mM, this colloid-assisted system rapidly removed five sulfonamides, with apparent rate constants enhanced by 6-151 times. ECOSAR predictions suggested reduced ecotoxicity of the degradation products, and the system remained effective in multiple real water matrices. These results establish hydrolysis-derived metal colloids as interfacial nanoreactors and offer a tunable strategy to improve PM-based removal of sulfonamide antibiotics.

This study aimed to evaluate the process of formation, storage and reactivation of aerobic granular sludge (AGS) in real dyeing wastewater. An SBR was employed for the AGS operation, and the results showed that AGS could form in the SBR within 30 days and was reactivated in 20 days after 300 days of storage. The nutrient removal efficiency remained stable after formation and reactivation. Metal ions (Fe and Ca) and inorganic matter from raw wastewater not only improved AGS formation efficiency but also ensured its structural stability during long-term storage. The initially formed AGS was enriched with Fe and Ca. However, during storage, Fe deposited on the AGS surface was lost due to iron-reducing bacteria (Shewanella). In the reactivated AGS, Ca deposited in the core became dominant. This work fully describes the formation, storage, and reactivation of AGS in real dyeing wastewater and reveals the stabilization mechanism of Ca- and Fe-rich AGS during long-term storage.

Simultaneous anammox and endogenous denitrification (SAED) process enables efficient nitrogen removal from low carbon-to-nitrogen wastewater, yet how carbon source type influences microbial synergy and system robustness remains unclear. This study evaluated the sludge characteristics, performance, and ecological traits of three SAED systems fed with acetate (HAc), propionate (HPr), and glucose (Glc) over 476 days. Results showed that the Glc-fed system achieved the highest and most stable nitrogen removal performance (95.0 % ± 2.4 %), significantly outperforming the HAc-fed (93.3 % ± 2.7 %) and HPr-fed (87.6 % ± 2.5 %) systems. Glucose promoted the formation of large (∼870 μm), dense granules with a high organic fraction (0.904), effectively mitigating the sludge washout and inorganic mineral precipitation observed in HAc-fed and HPr-fed systems. Microbial ecological network analysis reveals that different types of carbon sources reconfigured heterotrophic communities by mediating distinct microbial interactions. The Glc-fed system exhibited the highest proportion of positive correlations (90.9 %), particularly between Denitratisoma (13.5 %) and Candidatus Brocadia (22.2 %), bolstering system robustness. Furthermore, metagenomic analysis further confirms that nitrate reductase genes (nar/nap at 674.8 RPKM in total) were significantly more enriched than nitrite reductase genes (nir at 210.6 RPKM in total) in the Glc-fed system, facilitating an efficient nitrate-to-nitrite shunt for anammox bacteria while bypassing the competitive pathways (e.g., full denitrification in HAc-fed; DNRA in HPr-fed). Therefore, leveraging glucose-driven metabolic flux optimizes both sludge characteristics and microbial interactions in SAED process, providing a robust treatment for low-carbon wastewater.

To enhance the efficiency of rural wastewater treatment, this study applied iron shavings to a sequencing batch reactor, for the first time in a full-scale, real-life application. The results demonstrated that adding iron shavings significantly improved pollutant removal and sludge settling performance. Under conditions with a carbon to nitrogen ratio of 3.3 ± 0.8 and an influent chemical oxygen demand of 98.2 ± 18.0 mg/L, total nitrogen and total phosphorus removal increased from 34.8% and 41.4–67.4% and 84.5%, respectively, following the addition of iron shavings. Meanwhile, the sludge volume index dropped rapidly from 71.4 mL/g to below 40.0 mL/g. Metagenomic analyses revealed that iron shavings enriched microorganisms linked to the iron cycle and nitrogen metabolism, which facilitated nitrate removal. Additionally, the relative abundances of nitrifying bacteria, autotrophic denitrifying bacteria, glycogen-accumulating organism, and hydrolytic acidifying bacteria all increased. Collectively, these findings demonstrate that iron shavings hold excellent potential for improving nutrient removal from low strength rural wastewater.

Filamentous bacteria readily induce sludge bulking, which poses a significant challenge to wastewater treatment because sludge settling performance critically determines treatment efficiency, whereas aerobic granular sludge (AGS) exhibits excellent settling ability and treatment performance. Rapid granulation remained a bottleneck for AGS application, and powdered carriers were shown to shorten the granulation cycle. In this study, a natural material, attapulgite, was used as a micropowder carrier to investigate its effects on filamentous sludge. Forty dosage ratios of attapulgite/sludge (0.125-5) reduced SVI30 by 0.1-82.6%, enabling rapid regulation of sludge settling velocity. The hydrophilic attapulgite reduced the thickness of the hydration layer on extracellular polymeric substances (EPS), promoting the formation of larger microbial flocs. Microorganisms migrated to the surface of attapulgite and attached, forming an island effect. In sequencing batch reactors, the average granular size of sludge exceeded 200 mu m after 25, 45, and 55 days under one-time high-dose addition, daily low-dose addition, and no addition of attapulgite, respectively. Both granular and floc sludge cultivated with attapulgite exhibited excellent settling performance, with filamentous bacteria encapsulated within EPS, whereas in the control group, a large number of filamentous bacteria extended outside the EPS matrix. Attapulgite optimized microbial diversity and enhanced nutrient metabolic activity, maintaining efficient and stable treatment performance in real wastewater. These findings suggest that attapulgite provides an effective strategy for rapidly mitigating filamentous sludge.

This study investigated the feasibility of accelerating aerobic granular sludge (AGS) formation by short-term in-situ dosing of chitosan (CTS) in sequencing batch reactors. Compared with the control reactor, short-term CTS dosing during start-up markedly promoted biomass aggregation, shortened the complete granulation time from 27 to 9 days, and produced larger and denser granules with superior settleability. In the CTS-amended reactor, the mean granule size reached 752 µm, while sludge volume index at 30 min (SVI30) rapidly decreased to 59.4 mL/g within 24 h and stabilized at 38.2-44.8 mL/g during steady operation. Mechanistic analyses showed that CTS reduced sludge surface electronegativity, stimulated extracellular polymeric substance (EPS) secretion, and functioned as both a cationic bridging agent and a physical nucleation core. These roles were further supported by direct visualization using CTS-coated Fe3 O4 particles as a tracer. Temporary pH control applied to activate the cationic properties of CTS initially suppressed nitrification, but the inhibition was reversible. After recovery, the CTS reactor achieved superior total nitrogen (TN) removal, with an average effluent TN of 8.6 mg/L compared with 15.3 mg/L in the control. The enhanced TN removal may be associated with the combined effects of larger and more compact granules and the possible contribution of residual CTS as supplementary electron donor. Microbial analysis further revealed the enrichment of EPS-producing and structural bacteria, especially Thiothrix, in the CTS reactor. Overall, short-term in-situ CTS dosing provides a simple and biocompatible strategy for rapid AGS start-up and improved nitrogen removal.

The rotating biological contactor (RBC) demonstrates significant effectiveness in removing organic matter and ammonia nitrogen from decentralized wastewater sources. However, its single-tank continuous rotation operation mode limits denitrification and phosphorus removal. Iron-carbon (IC) can establish an efficient microenvironment for nitrogen removal and achieve high-efficiency phosphorus removal through chemical precipitation. For the first time, IC slices were inserted into the biological rotating discs to construct the IC-RBC system-a modification that significantly enhanced biofilm formation. Without chemical additives, the IC-RBC system achieved synergistic nitrogen and phosphorus removal. By day 16, the biomass in the IC-RBC system was 4.3 times that of the RBC system, and the extracellular polymeric substances content was 1.3-1.9 times higher than in the RBC system. Under a short hydraulic retention time (1.7 h), the removal efficiencies of ammonia nitrogen, total nitrogen, and total phosphorus by the IC-RBC system were 7.6 %, 20.0 %, and 16.6 % higher than those of the RBC system, respectively. Iron-autotrophic denitrifiers, such as unclassified_f__Comamonadaceae (6.3-28.3 %) and Sphaerotilus (0.7-16.1 %) were effectively enriched and established effective synergistic relationships with nitrifying and heterotrophic denitrifiers. The abundance of key denitrification genes (nar, nir, nor) was increased significantly. IC released iron ions through micro-electrolysis, and these ions precipitated phosphorus as Fe3(PO4)2 and Fe(H2PO4)2 & sdot;2H2O, thereby enabling highly efficient phosphorus removal. This study clarifies the enhancement mechanisms of IC in the RBC system, offering new insights for the optimization of RBC and costeffective wastewater treatment in small-scale municipal and rural applications.

Aerobic granular sludge (AGS) has attracted considerable attention in the field of wastewater treatment due to its numerous advantages. This paper presents a comprehensive review of the key factors influencing AGS particle size, highlighting the varying degrees of impact exerted by different factors. Particle size is a critical determinant in several aspects, including the removal efficiency of emerging contaminants, the energy consumption associated with the long-term stable operation of the system, and greenhouse gas (GHG) emissions. Smaller particles enhance the removal efficiency of emerging contaminants due to their larger specific surface area and increased number of reaction sites. In contrast, larger particles often lack internal structural mechanisms, which can facilitate the growth of filamentous bacteria, thereby undermining granule stability. Moreover, smaller AGS particles are linked to decreased simultaneous nitrification and denitrification (SND) efficiency, leading to increased GHG emissions. Consequently, the optimal size range for AGS is generally between 1.0 and 2.0 mm.