Aerobic granular sludge formation and stability in enhanced biological phosphorus removal system under antibiotics pressure: Performance, granulation mechanism, and microbial successions

Unraveling stress responses of microalgal-bacterial granular sludge when treating ciprofloxacin-laden wastewater

Unraveling the potential of microalgal-bacterial granular sludge (MBGS) technology for sustainable treatment of ciprofloxacin (CIP)-laden wastewater and mitigation of antibiotic resistance genes (ARGs) remains limited. This study evaluated the performance of bacterial granular sludge (BGS) and MBGS systems in terms of nutrient and CIP removal, granular stability, and ARG attenuation under long-term exposure to CIP for the first time. While both systems achieved effective pollutant removal at low CIP concentrations (0.1 and 0.5 mg/L), MBGS demonstrated superior resilience and efficiency under high CIP loads (10 mg/L). Notably, MBGS improved phosphorus removal by 32.71 %, achieved a 70.42 μg/(g-SS)/d greater CIP removal and maintained structural integrity, unlike BGS, which disintegrated under oxidative stress. The microalgae species (Pseudoneochloris and Chlamydopodium) could effectively resist various concentrations of CIP. Additionally, the relative abundance of ARGs in MBGS was 30.91 % lower than that in BGS, suggesting that microalgae in MBGS system could reduce ARG production. Overall, these findings improve our understanding of the role of microalgae in enhancing CIP remediation and controlling ARG propagation in MBGS systems.

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.

Effect of pre-chlorination on bioelectricity production and stabilization of excess sludge by microbial fuel cell

Microbial fuel cell (MFC) is a technology that can generate electricity while degrading excess sludge. However, the complex components, intricate biological structures, and inhibitory compounds in sludge limit the application of MFC. Therefore, this study utilized chlorination as a sludge pretreatment method to improve the comprehensive performance of MFC in sludge treatment. Results showed that pre-chlorination at a dose of 0.2 mg/L increased output voltage of MFC by 500 % from approximately 100 mV to around 600 mV, and power density by 15.60 % from 3.15 W/m³ to 3.64 W/m³, and simultaneously increased the degradation of sludge MLSS (mixed liquor suspended solids), MLVSS (mixed liquor volatile suspended solids), EPS (extracellular polymeric substances) polysaccharide and protein by 9.64 %, 47.07 %, 18.63 % and 16.26 %, respectively. Molecular composition analysis of EPS in sludge by three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM), Fourier transform infrared spectroscopy (FTIR) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) indicated pre-chlorination significantly promoted the molecular transformation in MFC. The microbiome analysis of anode biofilm in MFC by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), metagenomics and metametabolomics revealed that pre-chlorination facilitated the development of biomass, enrichment of electricity-producing bacteria (EPB), enhancement of electricity-producing activity and metabolic activity. Moreover, the sludge EPS was the importance source for the microbial metabolites in MFC was validated by the joint analysis of FT-ICR-MS and metametabolomics.

Removal of mixed antibiotics from saline wastewater under intermittent electrical stimulation and alterations of microbial communities and resistance genes

Antibiotics and antibiotic resistance genes (ARGs) are severe refractory pollutants in water. However, the effect of an intermittent electrical stimulation on the removal of antibiotics and ARGs from saline wastewater remains unclear. An anaerobic-aerobic-coupled upflow bioelectrochemical reactors (AO-UBERs) was used to treat tetracyclines (TCs) and quinolones (QNs) in saline wastewater. In an aerobic cathode-anaerobic anode reactor at an intermittent voltage of 0.9 V, antibiotic wastewater with a salinity of 15 g/L was treated. The removal rates of oxytetracycline, tetracycline, norfloxacin, and ciprofloxacin were 29.30%, 35.14%, 15.49%, and 15.84% higher, respectively, than those in reactors without voltage application. Compared with non-saline wastewater, the removal of TCs and QNs from saline wastewater was improved significantly by intermittent electrical stimulation. The contribution of the anaerobic region was significantly higher than that of the aerobic region. Intermittent electrical stimulation enriches and degrades Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Dysgonomonas, Hydrogenophaga, Terrimonas, and Methyloversatilis related functional microorganisms. The anaerobic anode reactor with an aerobic cathode was advantageous for the removal of ARGs in general. However, it showed enrichment for certain targeted genes. Therefore, AO-UBERs is an effective method for antibiotic removal. However, its effect on the removal of ARGs needs further 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 Wastewater Treatment with Aerobic Granular Sludge: Impacts of Tetracycline Pressure on Microbial Dynamics and Structural Stability

This study evaluated the efficiency of aerobic granular sludge (AGS) technology in treating wastewater contaminated with tetracycline (TC), a common antibiotic. AGS was cultivated under a TC pressure gradient ranging from 5 mg/L to 15 mg/L and compared with conventional wastewater conditions. The results demonstrated that AGS achieved high removal efficiencies and exhibited robust sedimentation performance, with significant differences in average particle sizes observed under both conditions (618.6 μm in TC conditions vs. 456.4 μm in conventional conditions). Importantly, exposure to TC was found to alter the composition and production of extracellular polymeric substances (EPSs), thereby enhancing the structural integrity and functional stability of the AGS. Additionally, the selective pressure of TC induced shifts in the microbial community composition; Rhodanobacter played a crucial role in EPS production and biological aggregation, enhancing the structural integrity and metabolic stability of AGS, while Candida tropicalis demonstrated remarkable resilience and efficiency in nutrient removal under stressful environmental conditions. These findings underscore the potential of AGS technology as a promising solution for advancing wastewater treatment methods, thus contributing to environmental protection and sustainability amid growing concerns over antibiotic contamination.

Mechanism Involved in Polyvinyl Chloride Nanoplastics Induced Anaerobic Granular Sludge Disintegration: Microbial Interaction Energy, EPS Molecular Structure, and Metabolism Functions

Nanoplastics (NPs) are emerging pollutants and have been reported to cause the disintegration of anaerobic granular sludge (AnGS). However, the mechanism involved in AnGS disintegration was not clear. In this study, polyvinyl chloride nanoplastics (PVC-NPs) were chosen as target NPs and their long-term impact on AnGS structure was investigated. Results showed that increasing PVC-NPs concentration resulted in the inhibition of acetoclastic methanogens, syntrophic propionate, and butyrate degradation, as well as AnGS disintegration. At the presence of 50 μg·L-1 PVC-NPs, the hydrophobic interaction was weakened with a higher energy barrier due to the relatively higher hydrophilic functional groups in extracellular polymeric substances (EPS). PVC-NPs-induced ROS inhibited quorum sensing, significantly downregulated hydrophobic amino acid synthesis, whereas it highly upregulated the genes related to the synthesis of four hydrophilic amino acids (Cys, Glu, Gly, and Lys), resulting in a higher hydrophily degree of protein secondary structure in EPS. The differential expression of genes involved in EPS biosynthesis and the resulting protein secondary structure contributed to the greater hydrophilic interaction, reducing microbial aggregation ability. The findings provided new insight into the long-term impact of PVC-NPs on AnGS when treating wastewater containing NPs and filled the knowledge gap on the mechanism involved in AnGS disintegration by PVC-NPs.

When antibiotics encounter microplastics in aquatic environments: Interaction, combined toxicity, and risk assessments

Antibiotics and microplastics (MPs), known as emerging pollutants, are bound to coexist in aquatic environments due to their widespread distribution and prolonged persistence. To date, few systematic summaries are available for the interaction between MPs and antibiotics in aquatic ecosystems, and a comprehensive reanalysis of their combined toxicity is also needed. Based on the collected published data, we have analyzed the source and distribution of MPs and antibiotics in global aquatic environments, finding their coexistence occurs in a lot of study sites. Accordingly, the presence of MPs can directly alter the environmental behavior of antibiotics. The main influencing factors of interaction between antibiotics and MPs have been summarized in terms of the characteristics of MPs and antibiotics, as well as the environmental factors. Then, we have conducted a meta-analysis to evaluate the combined toxicity of antibiotics and MPs on aquatic organisms and the related toxicity indicators, suggesting a significant adverse effect on algae, and inapparent on fish and daphnia. Finally, the environmental risk assessments for antibiotics and MPs were discussed, but unfortunately the standardized methodology for the risk assessment of MPs is still challenging, let alone assessment for their combined toxicity. This review provides insights into the interactions and environment risks of antibiotics and MPs in the aquatic environment, and suggests perspectives for future research.

Characteristics, Performance and Microbial Response of Aerobic Granular Sludge for Treating Tetracycline Hypersaline Pharmaceutical Wastewater

Salt-tolerant aerobic granular sludge(AGS) was successfully cultivated under the dual stress of tetracycline and 2.5% salinity, resulting in an average particle size of 435.0 ± 0.5 and exhibiting a chemical oxygen demand(COD) removal rate exceeding 80%, as well as excellent sedimentation performance. The analysis of metagenomics technology revealed a significant pattern of succession in the development of AGS. The proportion of Oleiagrimonas, a type of salt-tolerant bacteria, exhibited a gradual increase and reached 38.07% after 42 days, which indicated that an AGS system based on moderate halophilic bacteria was successfully constructed. The expression levels of targeted genes were found to be reduced across the entire AGS process and formation, as evidenced by qPCR analysis. The presence of int1 (7.67 log10 gene copies g-1 in 0 d sludge sample) enabled microbes to horizontally transfer ARGs genes along the AGS formation under the double pressure of TC and 2.5% salinity. These findings will enhance our understanding of ARG profiles and the development in AGS under tetracycline pressure, providing a foundation for guiding the use of AGS to treat hypersaline pharmaceutical wastewater.

Electroactive properties of EABs in response to long-term exposure to polystyrene microplastics/nanoplastics and the underlying adaptive mechanisms

Given widespread presence of polystyrene (PS) microplastics/nanoplastics (MPs/NPs), the electroactive responses and adaptation mechanisms of electroactive biofilms (EABs) exposed long-term to PS-containing aquatic environments remain unclear. Therefore, this study investigated the impacts of PS MPs/NPs on electroactivity of EABs. Results found that EABs exhibited delayed formation upon initially exposure but displayed an increased maximum current density (Imax) after subsequent exposure for up to 55 days. Notably, EABs exposure to NH2PS NPs (EAB-NH2PSNPs) demonstrated a 50% higher Imax than the control, along with a 17.84% increase in viability and a 58.10% increase in biomass. The cytochrome c (c-Cyts) content in EAB-NH2PSNPs rose by 178.35%, benefiting the extracellular electron transfer (EET) of EABs. Moreover, bacterial community assembly indicated the relative abundance of electroactive bacteria increased to 87.56% in EAB-NH2PSNPs. The adaptability mechanisms of EABs under prolonged exposure to PS MPs/NPs predominantly operate by adjusting viability, EET, and bacterial community assembly, which were further confirmed a positive correlation with Imax through structural equation model. These findings provide deeper insights into long-term effects and mechanisms of MPs/NPs on the electroactive properties of EABs and even functional microorganisms in aquatic ecosystems.

Advanced treatment of antibiotic-polluted wastewater by a consortium composed of bacteria and mixed cyanobacteria

This study constructed a cyanobacteria-bacteria consortium using a mixture of non-toxic cyanobacteria (Synechococcus sp. and Chroococcus sp.) immobilized in calcium alginate and native bacteria in wastewater. The consortium was used for the advanced treatment of sulfamethoxazole-polluted wastewater and the production of cyanobacterial lipid. Mixed cyanobacteria increased the abundances of denitrifying bacteria and phosphorus-accumulating bacteria as well as stimulated various functional enzymes in the wastewater bacterial community, which efficiently removed 70.01-71.86% of TN, 91.45-97.04% of TP and 70.72-76.85% of COD from the wastewater. The removal efficiency of 55.29-69.90% for sulfamethoxazole was mainly attributed to the upregulation of genes encoding oxidases, reductases, oxidoreductases and transferases in two cyanobacterial species as well as the increased abundances of Stenotrophomonas, Sediminibacterium, Arenimonas, Novosphingobium, Flavobacterium and Hydrogenophaga in wastewater bacterial community. Transcriptomic responses proved that mixed cyanobacteria presented an elevated lipid productivity of 33.90 mg/L/day as an adaptive stress response to sulfamethoxazole. Sediminibacterium, Flavobacterium and Exiguobacterium in the wastewater bacterial community may also promote cyanobacterial lipid synthesis through symbiosis. Results of this study proved that the mixed cyanobacteria-bacteria consortium was a promising approach for advanced wastewater treatment coupled to cyanobacterial lipid production.

Ascorbic acid reduction pretreatment enhancing metal regulation to improve methane production from anaerobic digestion of waste activated sludge

Conversion of waste activated sludge (WAS) to methane by anaerobic digestion (AD) is often limited by the slow rate of hydrolysis, and the presence of metal ions in sludge is regarded as a critical factor hindering sludge hydrolysis. This study developed a novel strategy to remove Fe from WAS by using ascorbic acid (VC) as a reducing agent under acidic conditions. The feasibility of reduction pretreatment in improving methane production of AD and its intrinsic mechanism were investigated. Results indicate that, under VC doses of 100 mmol/L and pH of 3.50, pretreatment removed 47.60 % of Fe, 59.88 % of Ca, and 51.86 % of Mg contained in the sludge. The removal of metal ions facilitated the disruption of sludge flocculation structure and extracellular polymeric substance (EPS) layers, leading to a 14.78 % increase in cell lysis and a decrease in fractal dimension values to 2.08. Batch AD experiments showed that VC pretreatment improved methane production, with an optimized net methane yield of 190.22 mL/g·VS, an increase of 134.75 % compared to raw WAS. The pretreatment affected the interfacial interaction energy of the sludge, leading to a transformation in the sludge surfaces from hydrophilic to hydrophobic, reducing the interaction between sludge molecules and increasing the number of binding sites available for enzymatic reactions. According to a study of microbial communities, it was found that VC pretreatment caused an increase in the presence of essential functional microbes responsible for hydrolysis, acidification, and methanation. This increase in acetoclastic and hydrogenotrophic methanogens resulted in a substantial enhancement in methane production. These results can be used to develop better pretreatment methods to enhance AD performance.

When aerobic granular sludge faces emerging contaminants: A review

The evolution of emerging contaminants (ECs) has caused greater requirements and challenges to the current biological wastewater treatment technology. As one of the most promising biological treatment technologies, the aerobic granular sludge (AGS) process also faces the challenge of ECs. This study summarizes the recent progress and characteristics of several representative ECs (persistent organic pollutants, endocrine disrupting chemicals, antibiotics, and microplastics) in AGS systems that have garnered widespread attention. Additionally, the biodegradation and adsorption mechanisms of ECs were discussed, and the interactions between various ECs and AGS was elucidated. The importance of extracellular polymeric substances for the stabilization of AGS and the removal of ECs is also discussed. Knowledge gaps and future research directions that may enable the practical application of AGS are highlighted. Overall, AGS processes show great application potential and this review provides guidance for the future implementation of AGS technology as well as elucidating the mechanism of its interaction with ECs.

Anticancer drugs drive changes in the performance, abundance, diversity, and composition of eukaryotic communities of an aerobic granular sludge system

Anticancer drugs are emerging contaminants that are being increasingly detected in urban wastewater. However, there is limited knowledge on the use of biological wastewater treatments, such as granular sludge systems (AGSs), to remove these substances and on their impacts on the general performance of the system and the eukaryotic communities in the granules. We investigated the impacts of three anticancer drugs commonly found in wastewater treatment plants and applied at three different concentrations on the removal efficiency of anticancer drugs, physicochemical parameters, and the eukaryotic microbiome of an AGS operated in a sequential batch reactor (SBR). Anticancer drugs applied at medium and high concentrations significantly decreased the removal efficiency of total nitrogen, the granular biomass concentration, and the size and setting velocity of granules. However, these effects disappeared after not adding the drugs for about a month thus showing the plasticity of the system to return to original levels. Regardless of the concentration of anticancer drugs tested, the AGS technology was effective in removing these substances, with removal rates in the range of 68.5%-100%. The presence of anticancer drugs at medium and high concentrations significantly decreased the abundance of total fungi, an effect that was linked to changes in the physicochemical parameters. Anticancer drugs also induced decreases in the diversity of the eukaryotic community, altered the community composition, and reduced the network complexity when applied at medium and high concentrations. Taxa responsive to the presence of anticancer drugs were identified. The diversity and composition of the eukaryotic microbiome returned to original diversity levels after not adding the drugs for about a month. Overall, this study increases our understanding of the impacts of anticancer drugs on the performance and eukaryotic microbiome of an AGS and highlights the need for monitoring these substances.

Potential of aerobic granular sludge membrane bioreactor (AGMBR) in wastewater treatment

This investigation is a review of the potential of aerobic granular sludge membrane bioreactor (AGMBR) in wastewater treatment due to the advantage of combination of membrane and aerobic granules for reducing membrane fouling and enhancing removal performance. The AGMBR is the same as the membrane bioreactor (MBR), but the activated sludge is replaced by aerobic granular sludge. This technology combines the advantages of aerobic granular sludge, such as good settleability, strong ability to withstand shock-loadings and high organic loading rate, and capacity of simultaneous chemical oxygen demand (COD) and nitrogen removal, and advantages of membrane bioreactor (MBR) such as excellent effluent quality, high biomass content, low excess sludge production, and small land requirement. Therefore, it can be considered a promising option for efficient wastewater treatment. Most studies have shown that aerobic granules could control membrane fouling, which often occurs in MBR. The main fouling mechanism was determined to be surface fouling by floccular sludge in MBR but pore fouling by colloids and solutes in AGMBR. Aerobic granular sludge also removed COD and nitrogen simultaneously, with more than 60% total nitrogen removal efficiency. The formation and stability of aerobic granules in AGMBR with various operational modes are discussed in this study.

Effect of food-to-microorganisms ratio on aerobic granular sludge settleability: Microbial community, potential roles and sequential responses of extracellular proteins and polysaccharides

The food-to-microorganism ratio (F/M) is an important parameter in wastewater biotreatment that significantly affects the granulation and settleability of aerobic granular sludge (AGS). Hence, understanding the long-term effects and internal mechanisms of F/M on AGS settling performance is essential. This study investigated the relationship between F/M and the sludge volume index (SVI) within a range of 0.23-2.50 kgCOD/(kgMLVSS·d). Thiothrix and Candidatus_Competibacter were identified as two dominant bacterial genera influencing AGS settling performance. With F/M increased from 0.27 kgCOD/(kgMLVSS·d) to 1.53 kgCOD/(kgMLVSS·d), the abundance of Thiothrix significantly increased from 0.20% to 27.02%, and the hydrophobicity of extracellular proteins (PN) decreased, which collectively reduced AGS settling performance. However, under high-F/M conditions, the gel-like polysaccharides (PS) effectively retained the granular biomass by binding to the highly abundant Thiothrix (53.65%). The progressive increment in biomass led to a concomitant reduction in F/M, resulting in the recovery of AGS settleability. In addition, two-dimensional correlation infrared spectroscopy analysis revealed the preferential responses of PN and PS to the increase and decrease of F/M, and the content and characteristics of PN and PS played important roles in granular settling. The study provides insight into the microbial composition and the potential role of extracellular polymer substances in the AGS sedimentation behavior, offering valuable theoretical support for stable AGS operation.

The shock of benzalkonium chloride on aerobic granular sludge system and its microbiological mechanism

Quaternary ammonium compounds (QACs) are a kind of biocides and surfactants widely used around the world and wastewater treatment systems were identified as its largest pool. QACs could significantly inhibit microbial activity in biological treatment. Aerobic granular sludge (AGS) is an emerging wastewater biological treatment technology with high efficiency and resistance, but it is still unclear if AGS system could tolerate QACs shock. In this study, a typical QAC (benzalkonium chloride (BACC12)) was selected to investigate its effect on AGS system. Results indicate that BAC could inhibit the pollutants removal performance of AGS system, including COD, NH4+-N and PO43- in the short term and the inhibition ratio had positive correlation with BAC concentration. However, AGS system could gradually adapt to the BAC stress and recover its original performance. BAC shock could destroy AGS structure by decreasing its particle size and finally leading to particle disintegration. Although AGS could secret more EPS to resist the stress, BAC still had significant inhibition on cell activity. Microbial community analysis illustrated that after high BAC concentration shock in short term, Thauera decreased significantly while Flavobacterium became the dominant genus. However, after the performance of AGS system recovered the dominant genus returned to Thauera and relevant denitrifiers Phaeodactylibacter, Nitrosomonas and Pseudofulvimonas also increased. The typical phosphorous removal microorganism Rubrivivax and Leadbetterella also showed the similar trend. The variation of denitrification and phosphorus removal microbial community was consistent with AGS system performance indicating the change of functional microorganism played key role in the AGS response to BAC stress.