Influence of loosely bound extracellular polymeric substances (EPS) on the flocculation, sedimentation and dewaterability of activated sludge

A new perspective on the simultaneous removal of nitrogen, tetracycline, and phosphorus by moving bed biofilm reactor under co-metabolic substances

With the burgeoning growth of aquaculture industry, high concentration of NH4+-N, phosphorus and tetracycline are the prevalent pollutants in aquaculture wastewater posing a significant health risk to aquatic organisms. Therefore, an effective method for treating aquaculture wastewater should be urgently explored. Simultaneous removal of NH4+-N, phosphorus, tetracycline, and chemical oxygen demand (COD) in aquaculture wastewater was developed by moving bed biofilm reactor (MBBR) under co-metabolic substances. The result showed that co-metabolism substances had different effects on MBBR performance, and 79.4 % of tetracycline, 68.2 % of NH4+-N, 61.3 % of total nitrogen, 88.3 % of COD, and 38.1 % of total phosphorus (TP) were synchronously removed with sodium acetate as a co-metabolic carbon source. Protein (PN), polysaccharide (PS), and electron transfer system activity were used to evaluate the MBBR performances, suggesting that PN/PS ratio was 1.48, 0.91, 1.07, 3.58, and 0.79 at phases I-V. Additionally, a mode of tetracycline degradation and TP removal was explored, and the cell apoptosis was evaluated by flow cytometry. The result suggested that 74 %, 83 %, and 83 % of tetracycline were degraded by extracellular extracts, intracellular extracts, and cell debris, and there was no difference between extracts and non-enzyme in TP removal. The ratio of viable and dead cells from biofilm reached 33.3 % and 7.68 % with sodium acetate as a co-metabolic carbon source. Furthermore, Proteobacteria and Bacteroidetes in biofilm were identified as the dominant phyla for tetracycline and nutrients removal. This study provides a new strategy for tetracycline and nutrients removal from aquaculture wastewater through co-metabolism.

Heterogeneous microstructure induces floatation in high-rate anammox granules

The floatation of anammox granules can be a serious challenge in practical wastewater treatment, as it can deteriorate reactor performance and cause bacterial loss. To deepen the understanding of floatation mechanism, in this study, both the floating (F-AnGS) and settling anammox granules (S-AnGS) from a high-rate anammox reactor were comparatively investigated. F-AnGS demonstrated 1.6 times higher specific anammox activity compared to S-AnGS, but only 65 % of produced gas could be successfully released, as quantified by anaerobic respirometry. In addition to the overall EPS accumulation, F-AnGS exhibited a heterogeneous microstructure distinct from that of S-AnGS, as revealed by 3D X-ray microscopic imaging at the single granule level. The heterogeneous distribution of EPS, which can form a dense surface layer, was the main cause for granule floatation. The heterogeneous microstructure of F-AnGS can reduce the distance between microorganisms and enhance the metabolic interaction between anammox bacteria and heterotrophs. The abundance of community members did not have a significant variation, but the functional genes related to anammox and partial denitrification pathway were significantly increased, indicating the enhanced nitrite loop in F-AnGS. This study proposed new structural insights into mechanism of anammox granule floatation, suggesting the appropriate activity control of granule-based anammox process.

Achieving rapid granulation and long-term stability of partial nitritation /anammox process by uniquely configured airlift inner-circulation partition bioreactor

To maintain the long-term stability and efficiency of the partial nitritation/anammox (PN/A) process, a novel partition bioreactor featuring a uniquely sieve plate was developed to improve the airlift inner-circulation. The bioreactor achieved startup within 38 days, effectively handling influent containing 150 mg-N/L ammonium nitrogen and 50 mg-N/L nitrite. By reducing hydraulic retention time, nitrogen loading rate was escalated to 0.60 kg-N/m3/d, maintaining over 80 % nitrogen removal. Additionally, fluctuations in nitrite-oxidizing bacteria (NOB) were automatically controlled through dissolved oxygen (DO) partitioning. Moreover, the average granules size expanded from 85 μm to 338 μm by day 127, coinciding with robust anammox activity reaching 1.02 ± 0.05 g-N/g-VSS/d by day 179. The results demonstrate that the bioreactor effectively enhanced the enrichment of functional bacteria, enabled spatial distribution of DO, promoted NOB self-regulation and sludge granulation. This approach provides an efficient solution for rapid granulation while maintaining stable performance in the PN/A process.

Lipid-lowering drug clofibric acid promotes conjugative transfer of RP4 plasmid carrying antibiotic resistance genes by multiple mechanisms

Antibiotic resistance represents a growing global health crisis, predominantly driven by the selective pressure imposed by antibiotics, which facilitates horizontal gene transfer. However, the potential role of non-antibiotic pharmaceuticals in promoting or enabling the spread of antibiotic resistance genes (ARGs) remains poorly understood. This study provided novel insights into the capacity of clofibric acid, a lipid-lowering drug, to enhance the conjugative transfer of ARGs, and deeply explored the underlying multiple mechanisms. The findings revealed that clofibric acid, at concentrations ranging from 0.01 to 1000 μg/L, significantly promoted the transfer efficiency of the RP4 plasmid carrying multiple ARGs. This enhancement was accompanied by a cascade of stress responses in bacterial cells, including elevated production of reactive oxygen species, increased secretion of extracellular polymeric substances, reduced bacterial surface zeta potential, and heightened cell membrane permeability. The physiological alterations were closely linked to significant changes in the expression of genes associated with these processes. Our results highlighted the potential of non-antibiotic pharmaceuticals to contribute to the dissemination of antibiotic resistance, offering a critical foundation for further research into the environmental and public health implications of such compounds.

Response characteristics of the microbial community, metabolic pathways, and anti-resistance genes under high nitrate and sulfamethoxazole stress in a fluidized sulfur autotrophic denitrification process

The adaptability and microbial response mechanism of a sulfur autotrophic denitrification (SADN) biofilm under high nitrate (NO3--N) and sulfamethoxazole (SMX) stress through long-term operation of a fluidized bioreactor was evaluated. The SADN biofilm adapted to nitrate contents of up to 150 mg/L, and at 1 mg/L SMX, the nitrogen removal efficiency and SMX removal efficiency were as high as 85 % and 64 %, respectively. Microbial adaptation was driven by upregulated secretion of acyl-homoserine lactone (AHL) signal molecules, specifically 3OC6-HSL and 3OC8-HSL, which stabilized at concentrations of 575.7 ng/L and 579.9 ng/L, respectively. These molecules dynamically regulated the composition of extracellular polymeric substances, with total EPS content increasing from 113.37 mg/gVSS in the initial phase to 456.85 mg/gVSS under early SMX exposure, ensuring biofilm structural integrity. Under prolonged SMX stress, Simplicispira emerged as a key genus with a relative abundance of 21.20 %, utilizing apoptotic autotrophic denitrifiers and EPS metabolites as carbon sources for heterotrophic denitrification. This genus harbored critical nitrate reductase genes, including NarG, which accounted for 28.5 % of total functional gene abundance. In addition, SMX stress reduced the abundance of total anti-resistance genes (ARGs), with resistance mechanisms dominated by antibiotic efflux pumps, with the contribution increased from 63 % to 67 %. The relevance of this pump continuously increased, which hindered binding of SMX to cells and effectively reduced its toxicity. The results of this study provide scientific evidence for the application of SADN technology in a high-nitrate and antibiotically stressed environment. The results can further guide practical operations and provide technical support for increasing denitrification efficiency and antibiotic removal capacity in the SADN process.

Role of biogas stirring in alleviating acidification and promoting methanogenesis during the anaerobic digestion of food waste: Macroscale and microscale perspectives

Anaerobic digestion (AD) represents an important solution for reducing the annual increase in global food waste, by facilitating the recycling of food resources. In the present study, we introduce a biogas stirring reactor (RB) to address the over-acidification in AD systems, enhancing methanogenic efficiency. Compared with the mechanical stirring reactor (RM), the RB exhibited higher methane yields (219 ± 17 mL CH4/g volatile solids (VS)added/d) and stable pH values (7.0 ± 0.2) during the steady-state phase. Computational fluid dynamics analysis highlighted the superior vertical mixing and flow velocity in RB, which reduced the sludge particle size (359 μm in RM vs. 100 μm in RB) and extracellular polymeric substance content (283 mg/g VS in RM vs. 126 mg/g VS in RB), thereby enhancing microorganism interactions and AD efficiency. Notably, biogas stirring enriched hydrogenotrophic methanogens, particularly, Methanobacterium, rebalancing the AD process. Microbial community analysis confirmed the positive impact of biogas stirring on hydrogen utilization by microorganisms. Our findings highlight the effectiveness of biogas stirring in enhancing the methane yield and present a viable approach for managing over-acidification in AD systems.

The inhibition of anammox system under Cu2 + stress and mechanisms of biochar-mediated recovery

Copper (Cu2+)-containing wastewater has proven difficult to effectively treat using the anammox process. In this study, the nitrogen removal efficiency (NRE), sludge characteristics, microbial community and recovery mechanisms of biochar-mediated anammox under Cu2+ stress were elucidated. At a Cu2+stress of 5 mg/L, a 73.52 % decrease in NRE (from 99 % to 25.48 %) was observed within the control setup (no biochar). The highest average NH4+-N removal for 36.28 % was observed at a reduced Cu2+ concentration of 3 mg/L with biochar addition compared to only 16.63 % in control reactor. The differences in the protein/polysaccharide (PN/PS) content in sludge from different biochar systems under long-term Cu2+ stress was a key factor influencing overall nitrogen removal performance, with the sludge predominantly displaying tightly bound extracellular polymeric substances (TB-EPS). The relative abundance of Candidatus Brocadia increased from 2.61 % to 15.28 % in the nitric acid-modified bamboo biochar group following cessation Cu2+ addition, while the control group only recovered to 0.76 %. The Cu2+ inhibition alleviation effect of biochar, facilitated via enhanced EPS secretion and selective proliferation of key functional microorganisms, has thus been demonstrated.

Elucidating the complex hydrolysis and conversion network of xanthan-like extracellular heteropolysaccharides in waste activated sludge fermentation

The hydrolysis of structural extracellular polymeric substances (St-EPS) is considered a major limiting step in the anaerobic fermentation of waste activated sludge (WAS). However, the degradation of heteropolysaccharides, characterized by complex monomers of uronic acids and neutral saccharides in St-EPS, has rarely been reported. In this study, microbial-produced xanthan-like heteropolysaccharides, characterized by a blue filamentary film, were identified. The xanthan-producing bacteria comprised ∼7.2% of total genera present in WAS. An xanthan-degrading consortium (XDC) was enriched in an anaerobic batch reactor. This consortium could degrade Xanthan for over 90% and disrupt the gel structure of xanthan while promoting methane production from WAS by 29%. The xanthan degradation network consisting of extracellular enzymes and bacteria was elucidated by combining high-throughput sequencing, metagenomic, and metaproteomic analyses. Five enzymes were identified as responsible for hydrolyzing xanthan to monomers, including xanthan lyase, β-d-glucosidase, β-d-glucanase, α-d-mannosidase, and unsaturated glucuronyl hydrolase. Seven genera, including Paenibacillus (0.2%) and Clostridium (3.1%), were identified as key bacteria excreting one to five of the aforementioned enzymes. This study thus provides insights into the complex conversions in anaerobic digestion of WAS and gives a foundation for future optimization of this process.

Application of atmospheric pressure plasma jet in membrane bioreactor for membrane fouling control: Performance evaluation and mechanism exploration

The plasma plume generated by atmospheric pressure plasma jet (APPJ) can directly oxidize and decompose the sludge on the membrane surface in membrane bioreactor (MBR), and simultaneously modify the membrane surface, thus achieving the objective of membrane cleaning. Compared with NaClO cleaning, APPJ cleaning showed stronger performance in reducing membrane fouling. Furthermore, the average membrane fouling period using NaClO cleaning was 2.5 days, while that of APPJ cleaning increased to 3 days. The average total flux recovery ratio of the membrane after APPJ cleaning reached 85.6 %, which was higher than the 73.4 % after NaClO cleaning. The atmospheric pressure plasma plume could directly blow away the sludge on the membrane surface. Plasma generated reactive species, such as free radicals (•OH), H2O2 and O3 to destroy cells and decompose extracellular polymers into small molecules. Meanwhile, the reactive species degraded β-D-glucose polysaccharide and caused the cake layer on the membrane to be looser. APPJ cleaning could degrade signal molecules C6-HSL in the cake layer, thereby maintaining C8-HSL at low levels. In addition, the direct scanning of the plasma jet to the membrane resulted in a more hydrophilic, smoother, and more electronegative surface, which increased the anti-fouling performance of the membrane.

Fluoride-induced stress shapes partial denitrification granules to sustain microbial metabolism

The presence of fluoride ions (F-) in nitrogen-rich wastewater from photovoltaic and semiconductor industries introduces a significant challenge to biological treatment processes, particularly for the innovative partial denitrification (PD) process, which supplies nitrite for anaerobic ammonium oxidation (Anammox). This study provides the first comprehensive and systematic investigation of the effects of F- stress on the granule-based PD process through batch tests and long-term operation. Results indicate that PD activity remains resilient to F- shock up to 1.5 g/L but is markedly impaired at concentrations of 2.0-3.0 g/L, despite maintaining a nitrate-to-nitrite transformation ratio (NTR) of approximately 80 %. Under long-term F- stress at 0.5 g/L, NTR gradually reduces to 50 %, but subsequently recovers to and maintains at 70 %. The increased secretion of loosely bound extracellular polymeric substances and proteins likely enhances the resistance of PD granules to F- stress, though excessive amounts degrade their settling properties. F--induced microbial community succession shapes a predominance of medium granules (1.0 < d < 2.0 mm of 60.2 %) by enhancing aggregation of smaller granules and disintegration of larger ones. This enhances the mechanical strength and microbial activity of PD granules, aiding in resistance to F- stress to sustain microbial metabolism. Thauera is selectively enriched under long-term F- stress, with upregulated nirBDS genes contributing to the reduced NTR. Additionally, increased electron metabolism activity and a robust antioxidative response help to maintain higher microbial metabolic activity, mitigating F--induced oxidative stress. These findings advance our understanding of the resilience and adaptability of the PD process under F- stress, providing critical insights for optimizing biological wastewater treatment systems in challenging environments.

Unravelling the mechanism of residual sludge promoting rapid formation of microalgal-bacterial granular sludge: Enhancement of extracellular polymers substances and electron transfer efficiency

Microalgal-bacterial granular sludge (MBGS) is a sustainable biotechnology that has attracted increasing attention, but there remains limited knowledge about the utilization of residual sludge generated from MBGS. This present work proposed a promising approach to rapidly construct the MBGS system from activated sludge by inoculating residual microalgal-bacterial sludge. Compared with inoculated activated sludge, the newly formed MBGS maintained a stable structure, higher biomass content (4.51 g/L), better settleability (42 mL/g), and higher pollutant removal. The results indicated that inoculation of residual sludge resulted in higher extracellular polymeric substances (EPS) content and promoted the microbial aggregation. Besides, this increase effectively improved the electron transfer efficiency within the particle, which facilitated the granulation of MBGS. Microbial community analysis revealed that the dominant bacteria (Pseudofulvimonas and Thauera) were mainly responsible for the secretion of EPS. Furthermore, the nitrogen and phosphorus metabolic pathways were also promoted to some certain extent. In conclusion, the inoculation of residual sludge can achieve an effective reduction in granulation period. This study provides a novel insight and fills the gap in the utilization of residual sludge generated by MBGS.

Adhesion behavior of dewatered sewage sludge during indirect thermal drying

We comprehensively investigated the factors influencing sludge adhesion during indirect thermal drying. We analyzed sludge properties and assessed adhesion during thermal drying using peel and shear tests at temperatures ranging from 100 to 180 °C. We conducted a comparative analysis of sludge properties and adhesion, exploring their correlations. Additionally, we examined the relationship between sludge adhesion and changes in extracellular polymeric substances (EPSs) throughout the drying process. The results indicate that factors leading to increased sludge adhesiveness include higher drying temperatures and the initial soluble EPS (S-EPS) concentration (R > 0.88). Only the S-EPS concentration showed an initial increase during thermal drying, followed by a decrease. Sludge with higher initial S-EPS concentrations released more S-EPS during the early stages of thermal drying. Sludge adhesion tended to increase after the S-EPS concentration began to decline. These observations suggest that the adhesive properties of sludge are not directly related to S-EPS but rather to the heat-induced release and transformation of organic content into substances that enhance adhesion. Potential technical solutions to mitigate sludge adhesion include lowering the drying temperature or reducing the S-EPS concentration through anaerobic digestion.

Cumulative inhibitory effect of 6:2 chlorinated polyfluorooctane ether sulfonate in anaerobic digestion processes

Microbial anaerobic metabolism is crucial for biogeochemical cycles, impacting both natural and engineered ecosystems. However, the increasing emissions of 6:2 Cl-PFESA, an alternative to PFOS, pose significant risks. In this study, long-term high 6:2 Cl-PFESA concentration level of 10 µg/g TS exposure led to a substantial decrease in methane production from 204.8 ± 4.8 mL/g VS to 143.6 ± 3.5 mL/g VS, indicating a cumulative inhibitory effect on carbohydrate-related anaerobic digestion. Key processes such as polysaccharide release, hydrolysis, acetogenesis, and acetoclastic methanogenesis were contributed by 28.6 %, 9.3 %, 8.9 %, and 11.7 % of significant reduction, respectively, correlating with inhibition in relevant enzymatic activities and gene expressions. Hydrolytic bacteria such as Rectinema and Defluviitoga declined to 11.7 % from 14.3 % and 20.9 % from 23.9 %, reflecting decreased hydrolysis efficiency. Reduced transcription levels of acetogenesis- and acidogenesis-related genes further inhibited these processes. Conversely, methanogens Methanolinea and Methanothrix increased from 35.8 % to 55.7 % and 10.9-40.8 %, suggesting enzyme inhibition rather than methanogen abundance reduction. Additionally, 6:2 Cl-PFESA partially biotransformed into 6:2H-PFESA, facilitated by species like Dechloromonas, unclassified Xanthomonadales, and Betaproteobacteria. These findings confirm that the limited degradation and cumulative inhibitory effects of 6:2 Cl-PFESA during anaerobic digestion highlight its significant disruption to carbon cycling stability within ecosystems.

Aerobic biofilm systems outperform anaerobic and anoxic regimes in 2,4-dimethylphenol degradation: Microbial synergy and metabolic mechanisms

The efficient biodegradation of 2,4-dimethylphenol (2,4-DMP), a toxic and recalcitrant phenolic pollutant, remains a critical challenge in wastewater treatment, with ongoing debate regarding the optimal dissolved oxygen (DO) regime for biofilm-based systems. To resolve this, four biofilm reactors-anaerobic (R1), anoxic (R2), microaerobic (R3), and aerobic (R4)-were operated under a DO gradient (0.3-8.0 mg/L). When influent 2,4-DMP concentrations increased from 25 to 300 mg/L, removal efficiencies declined significantly in R1-R3 (9.0 %, 44.8 %, and 58.8 %, respectively), whereas R4 maintained 100 % removal regardless of loading. Rapid degradation occurred within 8-16 h in R4, correlating with DO consumption from 8.0 to 5.0 mg/L. Aerobic conditions eliminated dependence on extracellular polymeric substances (EPS) for pollutant sequestration, as complete mineralization negated intermediate accumulation. Microbial analysis revealed Zoogloea (18.92 % abundance), Prosthecobacter, and Ferruginibacter as keystone aerobic bacteria, encoding aromatic ring-hydroxylating dioxygenases (RHDs) for 2,4-DMP hydroxylation and β-ketoadipate pathway activation. Concurrently, fungal genera Cutaneotrichosporon (74.50 %) and Kalenjinia were enriched in R4, contributing laccase-mediated ring cleavage. Synergy between bacterial oxidative pathways and fungal ligninolytic systems enabled sustained COD removal (95.54 %) without biofilm destabilization. These findings conclusively demonstrate aerobic biofilms' superiority in 2,4-DMP treatment, driven by metabolic completeness, energy-efficient respiration, and cross-kingdom functional partitioning.

A synergistic approach integrating potassium ferrate oxidation with polyacrylamide flocculation to enhance sludge dewatering and its mechanisms

Sludge dewatering is a critical phase in sludge treatment and disposal, significantly impacting storage, transportation, and subsequent handling. This study introduces an innovative approach combining potassium ferrate (PF) oxidation and polyacrylamide (PAM) flocculation to synergistically enhance sludge dewatering efficiency. PF disrupts EPS and releases bound water, while PAM restores floc structure, addressing the limitations of standalone oxidation. Initial PF conditioning significantly reduced sludge water content (Wc) to 75.18 %, attributed to the oxidative breakdown of extracellular polymeric substances (EPS) and the release of bound water. However, higher PF doses increased specific filtration resistance (SFR) and capillary suction time (CST), indicating deteriorated filterability. The subsequent addition of PAM mitigated these issues, further reducing Wc to 73.64 %, SFR from 12.75 × 1012 m/kg to 3.62 × 1012 m/kg, and reduced CST from 88.95 s to 32.3 s, demonstrating marked improvements in dewatering performance. Characterization studies revealed the underlying mechanisms: PF-induced sludge fragmentation and EPS degradation, followed by PAM-mediated re-flocculation and structural reorganization. Further, applying XDLVO theory and Flory-Huggins lattice theory revealed changes in the sludge's surface hydrophilicity and the system's chemical potential, improving SFR and enhancing dewatering efficiency while reducing moisture content. This investigation not only offers an innovative dewatering approach but also underpins the mechanism of improved dewaterability.

Why the disinfection efficiency of ultraviolet radiation may become unsatisfactory at low suspended solid concentrations: The mechanism of extracellular polymeric substances secretion induced by different particles

Due to the global outbreaks caused by pathogens, disinfection has attracted widespread attention, especially as the final inactivation step in wastewater treatment plants (WWTPs). Ultraviolet (UV) radiation is regarded as one of low carbon disinfection methods without chemical agents, but in practice, the effects are sometimes unsatisfactory, e.g., Escherichia coli (E. coli) still stay alive excessively at low concentrations of suspended solids (SS) that meets the discharge standards (<10 mg l-1). WWTPs focus on each process's efficiency, while the particle influence of different upstream processes on UV radiation is ignored. This study investigated the changes in extracellular polymeric substances (EPS) structure and biofilm from the perspective of single cell and cell-to-cell interactions at low SS concentrations before and after UV radiation. We disclosed that the effective characteristics of effluent SS particles were mainly related to some specific operation units, like coagulation sedimentation or sand filtration, which induced EPS secretion and biofilm formation, and subsequently caused the different responses of cells within the biofilm to UV radiation. Compared with filtrating sand particles, the magnetic coagulant induced more polysaccharide secretion and expanded the EPS structure, leading to a thicker and more effective protective layer to weaken UV intensity and reduce reactive oxygen species levels inside cells. The microbial community analysis of a real WWTP confirmed the survival of microorganisms with abilities of EPS secretion and sheltering others. Therefore, considering the potential positive effect of particles (such as metal particles) in the upstream process on the microbial aggregation in the subsequent process, it is recommended that the UV disinfection requires a lower SS concentration standard or a higher UV radiation dose. This study provides a basis for effective UV disinfection at the present application standards.

Recyclable cation exchange resin-driven fermentation of waste activated sludge in sequential batch-parallel pattern: long-term resin/regenerant recycle stability and triple driving mechanisms

Anaerobic acidogenic fermentation has been posited as a preferable technology for waste activated sludge management, whereas the inefficient hydrolysis, inadequate metabolism and disordered microbiota still existed as three fermentability limitations. The existing solutions addressed single limitation while consuming substantial chemicals/energy, thereby restraining technological dissemination. Innovatively, the recyclable cation exchange resin (CER) is a promising approach for synchronously overcoming these fermentability limitations and reducing chemicals/energy costs from sludge-native metal removal perspective; however, it has been rarely reported. This study pioneered a recyclable CER-driven sludge fermentation in continuous CER and regenerant reuse scene, taking comprehensive insights into long-term performance and multiple mechanisms. The CER induced speciation conversion and stepwise removal of structural metals from sludge, especially organic-binding and residual Ca&Mg, which played triple driving contributions: (1) breaking metal-bridging sites and hydrogen bonds disentangled protein molecules for raising electronegative repulsion and flocculation energy barrier, causing synergic extracellular and intracellular hydrolysis (up to 30.05 %); (2) liberating endogenous redox mediators from metal-complexations for assisting electron shuttle and extracellular respiration, which metabolic electron transfer activity by 1.58 times; (3) triggering "bacteria screening" through sensitive methanogen inhibition and tolerant acidogens growth towards maximum acidogenic eco-functions. Such fermentability breakthroughs greatly promoted short-chain fatty acids (superior carbon sources) accumulation by average 2.52 folds while declining sludge solid by 55.87 %. The NaCl regeneration thoroughly restored CER active sites and eluted pollutant blockages, with negligible capability loss ≤ 3.53 % in 18-cycle operations, which stabilized acidogenic performances during 72-day fermentation (RSD ≤ 7.88 %). The fermentative products presented as high-quality carbon sources with abundant carbon and absent nitrogen, owing to CER-mediated NH4+ exchange. Innovative batch-parallel operation was established in engineering strategy, offering 409.49 CNY/ton SS income. The findings provided mechanism framework linking sludge fermentability with native metal functions.

Quorum sensing-mediated microecological homeostasis in anammox consortia

Quorum sensing (QS) mediated by signal molecules regulates bacterial communication and further affects the performance and microbial physiological characteristics of anaerobic ammonium oxidation (anammox) process. The potential application of low concentrations of typical exogenous signal molecules into maintaining the long-term homeostasis of anammox consortia were evaluated in this study. The results of 150-d continuous-flow experiment showed that 30 μg L-1N-hexanoyl-homoserine lactone (C6-HSL) and diffusible signaling factor (DSF) could maintain the stable nitrogen removal efficiency of anammox systems (90.3 ± 3.6 % and 90.2 ± 3.8 %). C6-HSL and DSF also significantly promoted the anammox activity and the production of extracellular polymeric substances (EPS). Microbial community analysis indicated that the relative abundance of Candidatus Kuenenia fluctuated and finally maintained at 27.0 % and 39.3 %, which was still significantly higher than that of initial phase. Meanwhile, the abundances of functional genes related to anammox process (hzsA, hdh and nirS) increased significantly. Metagenomic analysis revealed that the abundances of main functional genes involved in nitrogen metabolism, amino acid metabolism and QS were significantly upregulated. The interspecies interactions were also enhanced through QS-mediated intercellular communication, which was beneficial to microecological homeostasis in anammox systems. In contrast, DSF exhibited the more significant and longer-lasting promotion impact, while the effect of C6-HSL was rapid. These findings reveal the potential regulatory mechanism of exogenous signaling molecules on anammox consortia and drive the potential application of signaling molecules in the anammox process to treat real wastewater.

Enhancing sulfide mitigation via the synergistic dosing of calcium peroxide and ferrous ions in gravity sewers: Efficiency and mechanism

Chemical dosing constitutes an effective strategy for sulfide control in sewers; however, its efficacy requires further optimization and enhancement. In this study, a novel dosing strategy using the synergistic dosing of calcium peroxide (CaO2) and ferrous ions (Fe2+) for sulfide control was proposed, and its efficacy in controlling sulfides was evaluated using a long-term laboratory-scale reactor. The results showed that adding CaO2-Fe2+ improves the effect of sulfide control. When the ratio of the agent to the sewage (w/v) was 0.30 %, the RT50 of sulfide production rate was 8.34 days. The analysis of microbial communities in sewage biofilm revealed that the relative abundances of sulfate-reducing bacteria (SRB) and sulfide-oxidizing bacteria (SOB) demonstrated an overall downward tendency, suggesting that the potent oxidizing •OH generated by the synergism of CaO2 and Fe2+ could indiscriminately restrain the growth of microorganisms. Additionally, intracellular metabolic pathways, along with enzyme activities and the relative abundances of genes associated with sulfide metabolism, were significantly impaired. The cost of CaO2-Fe2+ synergistic dosing is 31.3 % of CaO2 and 63.4 % of Fe2+ alone addition. It can be reasonably proposed that the addition of CaO2-Fe2+ may provide an efficacious and cost-effective method for the mitigation of sulfide in sewer systems.

Unignorable environmental risks: Insight into differential responses between biofilm and plastisphere in sulfur autotrophic denitrification system upon exposure to quaternary ammonium compounds

Concerns of quaternary ammonium compounds (QACs) and microplastics (MPs) as emerging containments accumulating in wastewater treatment plants (WWTPs) have attracted much attention. Plastisphere with distinctive microbial communities might also be the repository for pathogens and resistance genes (RGs). Thus, the effects of three representative QACs with different concentrations on biofilm and plastisphere were studied in sulfur autotrophic denitrification (SAD) system. Over 100 days, 1-5 mg/L QACs exerted few impacts on system stability, whereas 15 mg/L QACs seriously lowered the microbial activity and the inhibitory effects ranked: benzylalkyldimethylethyl ammonium compound > dialkyldimethyl ammonium compound > alkyltrimethyl ammonium compound. Dosing of QACs in SAD system not only altered the microbial community structure and assembly, but also induced higher levels of intracellular RGs and extracellular RGs in plastisphere than in biofilm. Although the free RGs abundances in water slightly lowered, they might also pose great ecological risks. Pathogens identified as the potential hosts of RGs were more prone to colocalizing in plastisphere. Mobile genetic elements directly contributed to the three-fraction RGs transmission in SAD system. This study offered new insights into the differential responses of biofilm and plastisphere under QACs stress and guided for the disinfectants and MPs pollution containment in WWTPs.

Elucidation of the stress mechanisms on activated sludge stability induced by yttrium oxide nanoparticles with cytotoxicity: Performance deterioration, biointerface variation and microbial response

As technoscience advances, widespread use of nanoparticles (NPs) has resulted in environmental risks. This study focuses on the potential stress of 0-200 mg/L yttrium oxide (Y2O3) NPs on the activated sludge stability. Y2O3 NPs progressively suppressed nitrification, caused significant NO2- accumulation (200 mg/L) and diminished activities of key functional enzymes. Deteriorated flocculation corroborates the Y2O3 NPs' destruction. Extracellular polymeric substances were lessened, yet amplified microbial metabolites prove the microbial counteraction coping with Y2O3 NPs' cytotoxicity. Plausible blockage of different protein channels contributed to the wane in biological nitrogen-removal capacity. Plus, 50 mg/L Y2O3 NPs stimulated the β-glucan production. When exceeding 100 mg/L, plentiful Y2O3 NPs aggregate on sludge-surface, which inhibits nutrients transfer and metabolism. Furthermore, ammonia-oxidizing bacteria shifted from Nitrosomonas to Nitrosospira with Y2O3 NPs increase. Reduction in Nitrospira, Saccharimonada-genera, and Microlunatus further corroborates the impairment of pollutants removal. PICRUSt2 prediction demonstrates Y2O3 NPs impedes nitrogen and glycolytic metabolic pathway.

Enhancing concurrent production of volatile fatty acids and phosphorus minerals from waste activated sludge via magnesium ferrate pre-oxidation

This study investigated the strategy of magnesium ferrate (MF) pre-oxidation to enhance acidogenic fermentation of waste activated sludge (WAS), targeting the simultaneous production of volatile fatty acids (VFAs) and phosphorus-minerals (struvite and vivianite). Results showed that such fermentation produced a high-value liquid within four days, achieving a peak VFA content of 241 ± 4 mg COD/ g VSfeed, ammonia nitrogen levels below 350 mg/L of and PO43-P under 3 mg/L. Further investigation revealed that the MF pre-oxidation raised the pH, enhanced key hydrolases activity, enriched acidogens and iron-reducing bacteria for driving the concurrent production of VFAs and phosphorus-minerals. The MF pre-oxidation promoted VFAs and phosphorus-minerals formation by enhancing the cooperation among the hydrolyzing bacteria of Acinetobacter and Proteocatella, acidogens of Fusibacter and Tissierella_Soehngenia, and iron-reducing bacteria of Dechloromonas and Thauera. This study provided an effective strategy for realizing concurrent production of high-purity VFAs along with struvite and vivianite from WAS.

Effective role and mechanism of scrap iron filings in controlling hydrogen sulfide production in septic tanks

Long-term anaerobic conditions in septic tanks exacerbate the release of hazardous gases, such as hydrogen sulfide (H2S), which degrades urban air quality. While traditional iron salt addition effectively inhibits H2S production, its large-scale application imposes economic burdens and challenges for low-carbon emission reduction. To address this issue, this study proposes the use of scrap iron filings (SIFs) as a source of Fe2+ and Fe3+ ions and evaluates their efficacy in sulfide control through a long-term laboratory-scale septic tank reactor. Experimental results demonstrated that the addition of SIFs reduced the average concentration of dissolved sulfides by 45.6 % and gaseous H2S by 92.6 %. Microbial community analysis of septic tank sediments revealed a significant decrease in sulfate-reducing bacteria (SRB) and an increase in sulfur-oxidizing bacteria (SOB), indicating that SIFs influence microbial activity by suppressing sulfide generation while enhancing sulfide oxidation. Furthermore, the addition of SIFs slightly increased the carbon-to-nitrogen (C/N) and carbon-to-phosphorus (C/P) ratios in the effluent, potentially improving subsequent nitrogen and phosphorus removal in wastewater treatment. These findings suggest a promising strategy for reducing hydrogen sulfide emissions and corrosion in septic tanks.

Simultaneously enhance nutrient removal and sludge settleability through hydrocyclone-based technology in a full-scale high-inert containing activated sludge process

Sludge densification technology through hydrocyclone is a promising solution to address the challenge related to increasing loading rate in existing municipal wastewater treatment plants (WWTPs). Although previous studies have investigated the positive effects of hydrocyclone on improving nutrient removal and sludge settleability, little is known if sludge densification technology is still function into the high inert containing activated sludge process in China. This study investigated technical feasibility and revealed underlying mechanisms to simultaneously enhance nitrogen and phosphorus removal and sludge settleability through installing a hydrocyclone-based sludge densification module in a full-scale WWTP with a designed capacity of 4 × 104 m3/d. Compared to the control line without hydrocyclone, the hydrocyclone installation helped improve total nitrogen and total phosphorus removal efficiency by 16.9 % and 29.4 % (p < 0.05), with the effluent concentrations of 4.86 ± 1.08 mg/L and 0.077 ± 0.035 mg/L, respectively. The strategy of "hydrocyclone treating only half of the wasted activated sludge (WAS) to produce densified activated sludge (DAS)" successfully prevented the accumulation of inerts in the mainstream. Meanwhile, sludge settleability after densification was improved, as evidenced by a reduced sludge volume index (SVI30) by 7.6 mL/g (53.2 ± 7.30 mL/g) and an increased settling velocity by 2 m/h (4.04 ± 0.60 m/h) compared to control line. Beyond selecting few large-sized DAS, the hydrocyclone also targeted small, densified flocs containing ballasting inerts (primarily Fe/Al-based hydroxides and phosphates) within high-inert containing activated sludge, further enhancing sludge settleability. The hydraulic shear forces of the hydrocyclone promoted the release of active sites from metal hydroxides, further enhancing phosphorus removal in mainstream. Meanwhile, shear forces lead to the disruption of DAS and ordinary flocs but also promoted the binding of flocs and inerts, forming densified flocs. The anoxic zones formed within DAS enabled denitrifying phosphorus-accumulating organisms (DPAOs) and denitrifiers to preferentially utilize polysaccharides of extracellular polymeric substances (EPS) for nutrient removal, thereby enhancing functional enzyme activity. These findings provide an important basis for the application of sludge densification technology in high-inert containing activated sludge process.

Siderophore-Mediated Cooperation in Anammox Consortia

It has been widely accepted that iron plays an important role in stimulating the activity of anammox bacteria, which contain many iron clusters for electron transport in cells. However, whether anammox bacteria could directly use and how to uptake Fe(III) have been long-time ignored. Here, we found that micrometer-scale magnetite with the size of 10-20 μm significantly promoted the anammox bacterial activity by iron core and iron uptake. Anammox bacteria cannot utilize Fe(III) directly as they are unable to secrete siderophore for the extracellular Fe(III) transfer to intracellular. In anaerobic anammox consortia at the presence of magnetite, siderophore synthesis bacteria belonging to Alphaproteobacteria, Candidate phylum, and Chloroflexi secreted abundant siderophores, which combined with Fe(III) ionized from magnetite to form siderophore-Fe(III) complexes. These complexes were then used by anammox bacteria via a specific outer membrane receptor and transported by the transporter protein to the periplasm, further releasing Fe(III). Cytochrome c was then formed by the siderophore-Fe(III) complex reduction, for assimilation and synthesis of Fe-S protein and heme B in anammox bacteria to increase electron transfer capability. This study reveals the siderophore-mediated bacterial cooperation in anammox consortia for Fe(III) assimilation and implies the important role of siderophore-mediated cooperation in driving nitrogen conversion in the artificial or natural system.

Behavior of carbon source type on the construction of aerobic granular sludge system and its removal of quinoline: A tortoise and hare race between starch and phenol

Coal chemical wastewater contains high concentrations of toxic organic pollutants such as quinoline and phenol. Microorganisms in aerobic granular sludge (AGS) are known to efficiently degrade organic matter. This study systematically compared the cultivation characteristics of quinoline-degrading aerobic granular sludge using starch (R1), a common carbon source, and phenol (R2), a toxic carbon source, as co-metabolizing substrates. The results indicated that R2 was more conducive to improving sludge settleability, biomass retention, and the growth of quinoline-degrading bacteria when a low quinoline concentration (30 mg/L) was applied. However, as the quinoline concentration increased, the granular sludge cultured with starch eventually outperformed phenol as a co-metabolizing substrate in terms of settling performance, biomass, and pollutant removal. Analysis of the pollutant degradation characteristics during a typical operation cycle revealed that the time required to degrade quinoline to approximately 5.5 mg/L was 150 min in R1 and 420 min in R2, indicating a higher reaction rate in R1. Acidovorax was identified as the dominant quinoline-degrading bacterium in both reactors. In addition, microbial differential analysis and functional genes indicated more pronounced bacterial differentiation in R1, enriched in Firmicutes and Deinococcaceae. the relative abundance of enzymes associated with quinoline degradation was higher in R1.

Analysis of microbial methane oxidation capacity of landfill soil cover using quorum sensing

Landfill gas (LFG) has become the second-largest anthropogenic source of methane (CH4) emissions globally. CH4 is the second most significant greenhouse gas after carbon dioxide (CO2), thus it is crucial to mitigate the methane emission of landfills. The soil in landfill cover layers is rich in methane-oxidizing bacteria (MOB), which use CH4 as their sole carbon and energy source. However, during the microbial methane oxidation process, the oxidation rate tends to decrease over time. It is anticipated that extracellular polymeric substance (EPS) is one of the key factors governing the reduction in the methane oxidation rate. Furthermore, the quorum sensing (QS) is responsible to regulate the production of EPS in the microbial system. To clarify the mechanism of QS in controlling the microbial methane oxidation rate, laboratory experiments were conducted to study the correlations between the oxidation rate of MOB, the EPS content and the concentration of AHLs signaling molecules and to elucidate the regulatory mechanism of the QS on the microbial methane oxidation rate. The following conclusions were drawn: It is observed that the EPS produced by MOB can inhibit their methane oxidation rate. The addition of AHLs increases the EPS content produced by MOB. It is postulated that in the QS system of MOB, AHLs signaling molecules stimulate production of EPS, and its accumulation inhibits methane oxidation rate of MOB. Thus, the QS would provide a new perspective for the mitigation measures for methane emission in landfills.

Extracellular polymeric substances (EPS) in sewage sludge management: A call for methodological standardization

Extracellular polymeric substances (EPS) are crucial in sewage sludge management, influencing key processes such as sedimentation, dewatering, and drying. Despite their importance, the lack of standardized methods for EPS extraction and analysis has led to inconsistent research findings, hindering a thorough understanding of EPS's role in sludge treatment. This review paper addresses this issue by critically comparing various EPS extraction and analysis methods, emphasizing the urgent need for standardization in the field. Standardized methodologies will enable researchers to compare studies more accurately and derive meaningful insights into EPS's role across different stages of sludge treatment, ultimately advancing EPS knowledge and application in sludge management. Additionally, this paper summarizes findings from numerous studies on EPS impact in sedimentation, dewatering, and drying, offering a holistic view of their significance in sludge management. Moreover, it explores the potential EPS applications, highlighting both the future directions and the challenges associated with their production.

Salinity stress and recovery of the algal-bacterial granular sludge (ABGS) system under the influence of different N-acyl-homoserine lactones (AHLs)

The algal-bacterial granular sludge (ABGS) system was established to explore the effect of 1% salinity condition, determine the recovery process following salinity disturbance, and probe the impacts of two N-acyl-homoserine lactones (AHLs) on the system. Exposure to 1% salinity led to the reduction of filaments and an increase in TB-EPS contents within the ABGS system. The phosphorus removal performance of the ABGS system severely decreased at 1% salinity and did not restore fully during the subsequent recovery stage, demonstrating that salinity stress induced long-term inhibition. Oligotrophic bacteria were found to be enriched at 1% salinity, indicating the self-adaptation of the ABGS system against salinity stress. The addition of AHLs helped mitigate the inhibitory effect of salinity stress. Specifically, C6-HSL slowed down the decline in microbial diversity, while 3-oxo-C12-HSL weakened the inhibition on microalgae growth. This study provided novel insights into the effects of salinity stress and AHLs on ABGS systems.

Achieving stable partial nitrification by exploiting lag phase of NOB recovery for selective washout

Stable inhibition of nitrite-oxidizing bacteria (NOB) is a significant challenge in achieving partial nitrification (PN) and partial nitrification-anaerobic ammonia oxidation (PNA). Growing evidence suggested that NOB can develop resistance to suppression over time, leading to the re-enrichment of NOB within reactors. To address these issues, this study aimed to achieve stable PN by regulating SRT to selectively washout NOB during the lag phase of activity recovery following FA/FNA exposure. The effects of this new strategy on nitrifying bacteria, sludge characteristics, and microbial interspecies relationships were investigated over a 150-day trial. Under the new strategy operation, the effluent ammonia, nitrite, and nitrate concentrations were 4.72 mg/L, 51.81 mg/L, and 3.30 mg/L, respectively, at a dissolved oxygen (DO) concentration of 0.18 mg/L, with a nitrite accumulation rate (NAR) remaining above 95%. This was attributed to the increasing relative abundance of ammonia-oxidizing bacteria (AOB) (Nitrosomonas) up to 25.86% and the decreasing relative abundance of NOB (Nitrospira, Nitrobacter and Candidatus Nitrotoga) to below the detection limit (1%) during the stabilization period. Analysis of the PN sludge characteristics revealed a tendency for sludge to form loosely structured aggregates, facilitating the potential rapid start-up of the PNA biofilm system or granular sludge. These findings suggest that the new strategy is a straightforward and effective method for achieving PN.

Upflow blanket filter anammox (UBFA) system treating low-nitrogen wastewater: high-efficient nitrogen removal, granules formation, N2O emission, and microbial succession

This research provides an important approach for low-nitrogen wastewater treatment through anaerobic ammonium oxidation (Anammox), and Anammox granule sludge (AnGS) in the Upflow. Blanket Filter Anammox (UBFA) system through shortening the hydraulic retention time was successfully cultivated. The percentage of medium granules (1.0-2.0 mm) with the highest Anammox activity increased from 0 to 28.5%, and the proportion of flocs (0-200 μm) reduced from 84.5% to 17.6%. Through the multidimensional analysis of AnGS, the relationship between AnGS and EPS secretion, low SVI, high PN/PS, multiple filamentous bacteria, and AnAOB were explored. Microelectrode tracing tests demonstrated that the main anammox reaction active layer was 0-1500 μm, and the highest activity was observed at 200-400 μm, whereas denitrification activity and N2O production were mainly distributed in the granules deep layer of 1500-2500 μm. The research showed that Candidatus Brocadia and Candidatus Kuenenia were the predominant anammox species in the UBFA system, while the abundance of AnAOB was higher in medium granules.

Responses of microbial communities in coastal sediments exposed to triclocarban and triclosan

Triclocarban (TCC) and triclosan (TCS) are applied in a wide range of pharmaceutical and personal care products to prevent or reduce bacterial growth. Due to their extensive application, they are frequently detected in marine environments. In this study, marine sediment systems exposed to different concentrations of TCC and TCS were established to evaluate their effects on microbial communities. It was found that TCC and TCS increased catalase and protease activities on Day 1, but inhibited after 15 days. Microbial activity, as indicated by increased dehydrogenase activity and polysaccharide production, should be enhanced after a 15-day adaptation period. High-throughput sequencing revealed resilient α-diversity but significant shifts in community structures were observed, particularly on Day 15. Function prediction analysis confirmed that most functional profiles remained stable, and network analysis indicated that TCC and TCS enhanced the complexity of the microbial community. This study provides new insights into the impacts and risks of TCC and TCS on the marine environment.

Proteomic and spectral analysis reveals the role of extracellular polymeric substances in mercury biosorption by activated sludge under high-altitude conditions

In high-altitude regions, elevated mercury (Hg) levels in wastewater treatment plants (WWTPs) influent raise concerns about treatment efficiency and environmental impact. This study investigated the Hg biosorption capacity of activated sludge under high-altitude conditions, focusing on the binding mechanisms between EPS and Hg, and variations in EPS secretion. Low pressure, oxygen, and temperature at high altitudes increase EPS secretion, enhancing Hg biosorption. EPS provides numerous binding sites for Hg, forming nonfluorescent complexes with tryptophan-like and aromatic proteins, while hydrocarbon and oxygen-containing groups limit Hg entry into microbial cells. Proteomic analysis revealed the upregulation of transporters, stress-resistance, and binding proteins, along with those involved in carbon and amino acid metabolism, which enhance microbial resilience and EPS production, leading to increased Hg biosorption. These insights reveal adaptive mechanisms that optimize pollutant removal in high-altitude environments.

Microplastics Settling in Turbid Water: Impacts of Sediments-Induced Flow Patterns on Particle Deposition Rates

When microplastics (MPs) enter water bodies, they undergo various transport processes, including sedimentation, which can be influenced by factors such as particle size, density, and interactions with other particles. Surface waters contain suspended natural particles (e.g., clay and silt), which may impact MP settling rates. Here, we investigated how the presence of suspended sediments (SS) influenced the deposition patterns and rates of MPs in turbid waters. We systematically analyzed the settling velocities of particles, including different MP sizes and SS concentrations, in a plexiglass column with a camera array. For each experimental variant, we collected data on thousands of individual MPs, strengthening the statistical analysis of the particles' velocities. Simultaneous measurements of the SS flow and MPs trajectories revealed that the SS induced complex flow patterns, with MPs spending more time in downwelling flow regions, thereby accelerating MPs sedimentation. This effect was more pronounced when SS were aggregated. Additionally, we found that smaller MP fragments were more affected by the fluctuations than spheres or larger fragments. Collectively, our results provide valuable data for future MP fate models and help to understand the sedimentation processes of MPs in natural waters, which is crucial for assessing their environmental transport and impact.

Harnessing the rhizosphere sponge to smooth pH fluctuations and stabilize contaminant retention in biofiltration system

Fluctuating pH conditions can affect heavy metal mobility, thereby limiting the efficiency of biofiltration systems (BS). To address this, we developed an innovative rhizosphere sponge, biochar-based bioreactor (RBB), designed to stabilize Cd2+ removal across a pH range of 5 to 9. RBB consistently outperformed the control, achieving a notable 91.3 % Cd2+ removal at pH 5. By creating optimized oxygen and redox zoning, the rhizosphere sponge enhanced both biochar surface reactions and microbial activity. Under acidic conditions, biochar facilitated Fe2+/Mn2+ precipitation into stable (oxy)hydroxides, a process further driven by microbial oxidation. Consequently, RBB accumulated 1.54 times more Fe-Mn oxide-bound Cd than the control, effectively reducing Cd2+ mobility. Additionally, loosely bound extracellular polymeric substances claimed preferential Cd2+ sequestration after acidification. The stabilized microecology and increased ecological niches, allowing RBB to better buffer against pH fluctuations, presenting it as a robust solution for sustainable heavy metal remediation in variable environments.

Combining quorum quenching by Rhodococcus sp. BH4 and Acinetobacter sp. DKY-1 to control biofouling in membrane bioreactors

This study investigates a novel approach to mitigate biofouling in membrane bioreactors (MBRs) using a combinational quorum quenching (QQ) strategy. Rhodococcus sp. BH4 and Acinetobacter sp. DKY-1 were employed to disrupt intraspecies N-acyl-homoserine lactones (AHL) and interspecies autoinducer-2 (AI-2) quorum sensing, respectively. BH4 and DKY-1 were immobilized independently and the antibiofouling effects of single QQ beads and 1: 1 mixed QQ beads, both with the same final doses, were compared. While both bead types exhibited high QQ activity, the mixed QQ beads more effectively inhibited microbial biofilm formation, delaying biofouling by two times compared to 1.5 and 1.7 times for the single species beads. Additionally, the mixed QQ MBR demonstrated significantly lower extracellular polymeric substances and a notable reduction in the genus Nitrospira. This combined QQ strategy presents a promising method for enhancing antibiofouling performance in MBRs through targeted disruption of microbial communication.

Evaluation of the shear stability of aerobic granular sludge from a pilot-scale membrane bioreactor: Establishment of a quantitative method

This work established a quantitative method to access the shear stability of aerobic granular sludge (AGS) and validated its feasibility by using the mature AGS from a pilot-scale (50 tons/day) membrane bioreactor (MBR) for treating real municipal wastewater. The results showed that the changing rate (ΔS) of the peak area (S) of granule size distribution (GSD) exhibited an exponential relationship (R2≥0.76) with the shear time (y=a-b·cx), which was a suitable indicative index to reflect the shear stability of different AGS samples. The limiting granule size (LGS) was defined and proposed to characterize the equilibrium size for AGS after being sheared for a period of time, whose value in terms of Dv50 showed high correlation (R2=0.92) with the parameter a. The free Ca2+ (28.44-34.21 mg/L) in the influent specifically interacted with polysaccharides (PS) in the granule's extracellular polymeric substance (EPS) as a nucleation site, thereby inducing the formation of Ca precipitation to enhance its Young's modulus, while Ca2+ primarily interacted with PS in soluble metabolic product (SMP) during the initial granulation process. Furthermore, the Young's modulus significantly affected the parameter a related to shear stability (R2=0.99). Since the parameter a was more closely related (R2=1.00) to ΔS than that of the parameter b or c, the excellent correlation (R2=0.99) between the parameter a and the wet density further verified the feasibility of this method.

Effects of different quaternary ammonium compounds on intracellular and extracellular resistance genes in nitrification systems under the pre-contamination of benzalkyl dimethylammonium compounds

As the harm of benzalkyl dimethylammonium compounds (BACs) on human health and environment was discovered, alkyltrimethyl ammonium compound (ATMAC) and dialkyldimethyl ammonium compound (DADMAC), which belong to quaternary ammonium compounds (QACs), were likely to replace BACs as the main disinfectants. This study simulated the iterative use of QACs to explore their impact on resistance genes (RGs) in nitrification systems pre-contaminated by BACs. ATMAC could initiate and maintain partial nitrification. DADMAC generated higher levels of reactive oxygen species and lactate dehydrogenase, leading to increased biological toxicity in bacteria. The abundance of intracellular RGs of sludge was higher with the stress of QACs. DADMAC also induced higher extracellular polymeric substance secretion. Moreover, it facilitated the transfer of RGs from sludge to water, with ATMAC disseminating RGs through si-tnpA-04 and DADMAC through si-intI1. Sediminibacterium might be potential hosts for RGs. This study offered insights into disinfectant usage in the post-COVID-19 era.

Coupling Thiosulfate-Driven denitrification and anammox to remove nitrogen from actual wastewater

A coupled thiosulfate-driven denitrification and anammox (TDDA) process was established to remove nitrogen from wastewater. It was optimized in an up-flow anaerobic sludge blanket reactor using synthetic wastewater, and its reliability was then verified with actual wastewater. The results demonstrated that nitrate, nitrite, and ammonium could be synergistically removed, and the highest total nitrogen removal efficiency reached 97.8% at a loading of 1.39 kgN/(m3·d). Anammox bacteria, primarily Candidatus_Brocadia, were the main contributors to nitrogen removal, while sulfur-oxidizing bacteria such as Thiobacillus and Rhodanobacter played a supportive role. By optimizing substrate conditions to enhance the anammox process, the coupled system attained higher abundances of functional genes such as napA, nirS, hzs, soxXA, and soxYZ, along with the corresponding microbial species. The data suggested that microbial cross-feeding and self-adaptation strategies were key to efficient nitrogen removal by TDDA.

Effects of granule disintegration and re-granulation on the physiological characteristics and microbial diversity of anammox granules

The impact of artificial disintegration and re-granulation of anammox granules on the granule size, Extra-cellular Polymeric Substances (EPS) composition, microbial community characteristics, and the performance of the anammox process was investigated. Before the granule disintegration, the Dv50 and Granulation Index (GI) were 1280 μm and 54.62%, respectively. Following two cycles of disintegration and re-granulation process, these values shifted to 463 μm and 81.53%, respectively. This indicates that the disintegration and re-granulation process helped to form denser particles. The reduction in total EPS content and the increase in the PS/PN ratio of EPS well reflect these particle characteristics. Additionally, the disintegration and re-granulation process increased the dominance of Kuenenia Stuttgartiensis, which is well adapted to high salinity (2%) conditions, from 11.2% to 68.1%. By artificially disintegrating the granules and inducing re-granulation, it was possible to increase the dominance of specific anammox microorganisms with enhanced resilience of the anammox process.

Effect of inoculated sludge concentration on start-up of anammox reactor: Nitrogen removal performance and metabolic pathways

The anammox process is efficient for nitrogen removal but faces challenges due to slow bacterial growth and limited inoculated sludge supply. This study examined the effects of different inoculated sludge concentrations (3.5, 7, and 14 g/L) on start-up and nitrogen metabolism in anammox reactors. Three identical reactors were operated under controlled conditions, with comprehensive analysis of nitrogen removal efficiency, sludge characteristics, and microbial community dynamics through metagenomic and transcriptomic approaches. Results demonstrated that higher inoculated sludge concentrations accelerated reactor start-up, with the 14 g/L reactor achieving stable operation in 13 days compared to 44 days for the 3.5 g/L reactor. However, the improvement in nitrogen removal rate showed a boundary effect, not proportional to the increase in sludge concentration. Notably, reactors with higher inoculated sludge concentrations exhibited lower sludge loads but higher sludge yield coefficients. Metagenomic analysis revealed Candidatus Kuenenia as the dominant anammox bacteria, with decreasing hydrazine dehydrogenase (hdh) gene expression levels observed at higher sludge concentrations, suggesting hydrazine synthesis as a potential rate-limiting step. This study provides novel insights into the optimal range of inoculated sludge concentration for anammox reactor start-up and elucidates the underlying metabolic mechanisms, offering valuable guidance for practical engineering applications.

Enhancement of dewatering performance and effective degradation of petroleum hydrocarbons in biological oily sludge using atmospheric pressure plasma jet

The presence of petroleum hydrocarbon components (PHCs) in biological oily sludge increases the toxicity of the sludge and makes dewatering even more difficult. In this study, an atmospheric pressure plasma jet (APPJ) technology was used for treating biological oily sludge. The results showed that under specific conditions-a sludge/water ratio of 1:100, a discharge power of 440 W, and a 60-min treatment-the degradation rate of PHCs reached 36.3 %. APPJ can convert larger molecule PHCs and extracellular polymeric substances, thereby reducing the particle size and viscosity of the sludge. Meanwhile, the sludge volume was reduced and the sludge dewatering efficiency was improved. The hydroxyl radical and superoxide radical generated by APPJ were the main active species involved in the degradation process. This work provides a novel strategy for the reduction of biological oily sludge and the synergistic removal of PHCs along with the sludge.

Studies on the treatment of anaerobically digested sludge by white-rot fungi: evaluation of the effect of Phanerochaete chrysosporium and Trametes versicolor

BACKGROUND

The composition of anaerobically digested sludge is inherently complex, enriched with structurally complex organic compounds and nitrogenous constituents, which are refractory to biodegradation. These characteristics limit the subsequent rational utilization of resources from anaerobically digested sludge. White-rot fungi (WRF) have garnered significant research interest due to their exceptional capacity to degrade complex and recalcitrant organic pollutants. However, the exploration of WRF in the context of sludge treatment remains an under-investigated area within the scientific community. The present investigation explores the application of WRF in the treatment of anaerobically digested sludge, offering a novel approach for the valorization of sludge resources.

RESULTS

In this study, WRF enzymes, manganese peroxidase (MnP) and lignin peroxidase (LiP), exhibited sustained high activities of approximately 102 U/L and 26 U/L, respectively, within the anaerobically digested sludge under a controlled pH of 5.5 within the growth system. These conditions were found to significantly enhance the treatment efficacy of the anaerobic sludge. The removal of soluble chemical oxygen demand (COD) and Total COD by Trametes versicolor powder was better than that of Phanerochaete chrysosporium powder. The treatment of sludge samples with WRF, specifically Phanerochaete chrysosporium powder, resulted in a significant reduction of ultraviolet radiation (UV254). Fourier-transform infrared spectroscopy (FTIR) analysis revealed that the application of Trametes versicolor powder exerted a notably pronounced impact on the functional groups present in sludge samples. Specifically, there was a significant decrease in the peak intensities corresponding to the C-O bonds, indicative of saccharide degradation, alongside an observable increase in the intensities of amide peaks, which is suggestive of protein synthesis enhancement. Microbial community analysis demonstrated that Phanerochaete chrysosporium was the predominant fungal species, exerting a significant regulatory role within the sludge ecosystem.

CONCLUSION

In conclusion, this research furnishes a robust scientific foundation for the utilization of WRF in the treatment of anaerobic digestion sludge. It elucidates the fungi's capacity to ameliorate the physicochemical attributes and microbial community composition within the sludge. Furthermore, the study offers a certain reference for the subsequent use of WRF in the treatment of other types of sludge.

Enhancement of microalgae co-cultivation self-settling performance and water purificationcapacity of microalgae biofilm

Cultivating microalgae for the remediation of aquaculture wastewater provides a promising solution for pollution control. However, the economic viability of this approach faces challenges due to the high costs associated with microalgal biomass harvesting. This study aims to address this issue by immobilizing microalgae onto coral velvet carriers, enhancing the efficiency of biomass recovery. Four types of microalgae were screened: Chlorella sp., Isochrysis galbana, Chaetoceros sp., and Nannochloropsis sp. Among them, Isochrysis galbana exhibited the best self sedimentation rate, achieving a self sedimentation rate of 94.36%. Chlorella sp. demonstrated the best denitrification rate, with a nitrate removal rate of 100% and an inorganic nitrogen removal rate of 79.13%. In addition, this study found that extracellular polymeric substances(EPS) affects the self-settling performance of microalgae, and the results emphasize the key role of tightly-bound EPS(TB-EPS) content in determining self settling efficiency. Furthermore,the assessments of the purification of simulated aquaculture wastewater were conducted, comparing the outcomes of co-cultivation with mono-culture. The co-cultivation strategy showed exceptional efficacy, achieving a 100% removal rate for NO3--N by the 5th day. In contrast, mono-cultures of Chlorella sp. and Isochrysis galbana showed removal rates of 77.76% and 45.72%, respectively, at the same interval. Applying of the co-cultivation microalgal biofilm to treat the actual aquaculture wastewater showed remarkable denitrification performance, attaining a 100% removal rate for NO3--N by the 7th day. The study proposes the co-cultivation of Chlorella sp. and Isochrysis galbana for treating aquaculture wastewater and explores the potential application of immobilization technology to remove nitrogen-containing pollutants.

Critical evaluation of extracellular polymeric substances extraction methods: Extraction efficiency, molecular characteristics, and heavy metals binding properties

Extracellular polymeric substances (EPS) significantly influence the properties and performance of waste activated sludge. Various pretreatment protocols with different extraction efficiency and characteristics of EPS have been reported, which markedly impact subsequent treatment and disposal of sewage sludge. This study systematically assesses the EPS properties from twelve extraction pretreatment methods. The organic and inorganic matters content, cell lysis, basic physicochemical property, molecular weight distribution, and fluorescence properties of extracted EPS were determined. Physical extraction methods (Centrifugation, Heat, and Ultrasound) were relatively mild, resulting in lower extraction of organic matter contents from EPS (< 6 mg total organic carbon /g volatile solids). Biological extraction methods (Enzyme and Enzyme-NaOH) exhibited high EPS extraction efficiency however led to significant cell lysis, thereby contaminating the extracted EPS with intracellular substances. In addition, heating and biological extraction methods excessively degraded EPS, resulting in a large amount of small molecular weight matters (≤ 103 Da) generation. Chemical extraction methods offered efficient EPS extraction with the different degrees of cell lysis, but it would introduce chemical reagent residues in EPS. Among those extraction methods, EPS extracted by cation exchange resin (CER) method had uniform and abundant molecular weight matters and fluorescence matters distribution. After dialysis, the residual Na and other metal elements could be significantly removed. Then, the fluorescence quenching effect of Cu(II) and Zn(II) at 400 μM on the Bound-EPS after dialysis increased up to the maximum value of 65 % and 30 %, respectively, compared to that without dialysis. It indicates that dialysis coupled with CER extracted EPS has a well extraction efficiency and can maintain the original state of EPS for the subsequent investigation.

Microelectricity enhances aerobic granular sludge granulation and sulfamethazine degradation: Performance, mechanism, antibiotic resistance genes and microbial community

With the widespread use of typical antibiotics such as sulfamethazine (SMT), it leads to their accumulation in the environment, increasing the risk of the spread of antibiotic resistance genes (ARGs). Aerobic granular sludge (AGS) has shown great potential in treating antibiotic wastewater. However, the long cultivation period of AGS, the easy disintegration of particles and the poor stability of degradation efficiency for highly concentrated antibiotic wastewater are still urgent problems that need to be solved, and it is important to explore the migration and changes of ARGs and microbial diversity in AGS systems. In this study, a microelectrically enhanced pelletizing reactor (MEPR) was innovatively constructed using a microbial electrolysis cell (MEC) coupled with an AGS system, and a comparative study was carried out using a conventional sequential batch reactor (SBR). The results showed that the AGS obtained from MEPR culture was smooth white spherical, with rich internal microbial phase and good sludge activity. The microelectric condition shortened the AGS culture cycle by 10 days, with smaller AGS particle size, denser structure, and better pollutant degradation ability, and the average removal rate of SMT by MEPR (74.3 %) was much higher than that of SBR (3.13 %). The microelectrical properties reduced the sludge pressure to a certain extent, induced the reasonable secretion of extracellular polymeric substances (EPS), and kept the MEPR in a strong stable state. High-throughput sequencing and detection of ARGs indicated that MEPR had a richer microbial community structure, which significantly controlled the enrichment of ARGs. This study provides a theoretical reference for enhanced sludge granulation and biological treatment of high concentration antibiotic wastewater.

Enhancing performance in gravity-driven membrane systems through pre-coating with aluminum-based flocs: Mechanism and energy saving analysis

The gravity-driven membrane (GDM) system is an energy-efficient and environmentally sustainable water purification process; however, after prolonged operation, its membrane flux remains relatively low, making it necessary to adopt effective strategies for improving system performance. In this study, the effects of hydrostatic pressure (60, 100, 200 mbar) and pre-coating with aluminum-based flocs (ABF) on GDM flux and organic matter removal were investigated, and the regulatory mechanisms of the bio-cake layer were explored through interactions between morphological structure, composition and microbes. The results showed that the stable flux of the GDM-ABF system at a hydrostatic pressure of 60 mbar was almost equal to that at 100 mbar, and it outperformed higher hydrostatic pressure in organic matter removal, resulting in a more porous bio-cake layer structure. GDM-ABF system at 60 mbar achieved 38.51% energy saving compared to that at 100 mbar. Increased hydrostatic pressure led to a denser biofouling layer and higher EPS concentrations, whereas pre-coating reduced the EPS concentration and resulted in a looser biofouling layer. Hydrostatic stress and pre-coating determined membrane fouling by regulating microbial communities and key metabolites. Increasing hydrostatic pressure down-regulated arginine and proline metabolism and aggravated membrane fouling, while pre-coating ABF up-regulated arginine and proline metabolism, down-regulated galactose metabolism, and alleviated the membrane fouling. Hydrostatic stress and pre-coating altered the abundance of keystone species involved in extracellular polymeric substances (EPS) formation within the bio-cake layer. Pre-coating with ABF at low hydrostatic pressure can achieve stable flux and effective water purification in GDM systems, similar to high hydrostatic pressure conditions, with the added benefits of being more environmentally friendly and low-carbon. This study proposes a strategy to balance flux and energy consumption in GDM systems, providing theoretical and technical support for the efficient application of GDM technology in membrane water treatment processes.

Unraveling the resistance mechanism of anammox granular sludge to iron nanoparticles

Iron nanoparticles (FeNPs) generated from industrial activities could end up into the sewer system, and potentially affect wastewater treatment processes. The impact of FeNPs on anammox process is getting increasing attention. However, the resistance mechanism of anammox granular sludge (AnGS) to FeNPs has not been fully elucidated. The current study investigated the metabolic and morphological response of AnGS to acute and chronic FeNPs exposure. Results showed that nitrogen removal efficiencies were elevated at 1-4 mM FeNPs concentrations compared to 0-0.5 mM FeNPs. Extracellular protein and tyrosine-like and tryptophan-like fluorophore secretions of AnGS were stimulated by FeNPs, which largely contributed to the adsorption of FeNPs on AnGS surface. FeNPs exposure triggered higher necrotic fraction of AnGS compared with no FeNPs condition. Highly absorbed particles appeared inside the bacterial cells of AnGS, soft X-ray imaging illustrated that anammox bacteria maintained intact cellular and anammoxosome structures whereas non-anammox bacterial structures were damaged under FeNPs exposure. Anammox bacterial abundance increased from 4.84% to 20.64%, when FeNPs concentrations increased from 0 mM to 4 mM, and anammoxosome membrane ensured anammox bacterial metabolism under FeNPs exposure. This study extended fundamental understanding of AnGS resistance mechanisms to FeNPs.

A critical review of in-situ moisture distribution detection and characterization techniques utilizing deep dewatering for organic waste

Deep dewatering is crucial for effectively reducing the volume of organic waste and facilitating its downstream transportation and disposal. An in-depth understanding of the occurrence states, composition, and morphological characteristics of moisture in organic waste is the basis for optimizing the dewatering process, improving dewatering efficiency, and reducing energy consumption. Given the common problems of time-consuming, low sensitivity, and poor parallelism of traditional methods, this work reviews the advanced in-situ analysis methods for moisture distribution of organic waste. The Raman microscopy imaging technique is highlighted to provide a new approach for visualizing the spatial distribution of moisture with different binding strengths in solid flocs. Various physical, chemical, and biological characteristics and characterization methods of organic waste related to deep dewatering are introduced, and they are correlated with conditioning methods. Almost all conditioning will cause changes in the physical characteristics of organic waste, while the improvement of dewatering performance is actually caused by changes in the chemical composition and biological characteristics of the matrix, and these characteristics are intrinsically related to the moisture distribution. The characterization and in-situ moisture detection methods presented in this work aim to support future studies in understanding changes in material composition related to improving dewatering performance and further clarifying the mechanisms of deep dewatering of organic wastes.

Solids retention time (SRT) control in the co-treatment of leachate with domestic sewage in aerobic granular sludge systems: Impacts on system performance, operational stability, and bioresource production

This study investigates the co-treatment of leachate and domestic sewage in municipal wastewater treatment plants using aerobic granular sludge (AGS) systems, focusing on granule formation, system stability, and resource production in two units (R1 and R2). In R2, solids retention time (SRT) was controlled between 10 and 25 days, while R1 maintained approximately 9 days. The results show that low leachate proportions (5 %) did not affect system performance or stability. However, increasing the leachate to 10 % reduced the structural stability of extracellular polymeric substances (EPS), leading to a significant decrease in alginate-like exopolysaccharides (ALE) production in R1 (216 mgALE/gVSS) and R2 (125 mgALE/gVSS). Principal component analysis revealed that SRT was crucial for optimizing biopolymer synthesis. Furthermore, SRT control in R2 improved filamentous control, biomass retention, and total nitrogen removal. Thus, selective biomass discharge is essential for maintaining granule stability, enhancing treatment efficiency, and supporting resource production.