Polyethylene microplastics increase extracellular polymeric substances production in aerobic granular sludge

Low-intensity ultrasound combined with inert particles to improve denitrifying flocculated sludge performance and resulting granulation mechanism

To enhance the understanding of flocculated sludge granulation, this study focused on a bacterial denitrification system using low-intensity ultrasound and inert particles to stimulate cell activity and facilitate flocculated sludge granulation. After 75 days, the activated carbon, activated carbon + ultrasonication, and microplastic + ultrasonication groups showed partial pelletization. Both ultrasound and inert particles promoted extracellular polymeric substance secretion and enhanced electron transport system activity. Low-intensity ultrasound improved denitrification performance and enhanced denitrifying bacteria. The addition of inert materials facilitated denitrifying flocculated sludge granulation. Low-intensity ultrasound combined with microplastics obtained the highest activity and enrichment of denitrifying bacteria in granular sludge. This study provides new ideas for optimizing anaerobic sludge granulation.

The crucial factor for microplastics removal in large-scale subsurface-flow constructed wetlands

Constructed wetlands (CWs) are an effective method for removing microplastics (MPs). Nevertheless, the understanding of the impact of various parameters on MPs removal within CWs remains incomplete. Through field investigations of large-scale CWs and the application of machine learning methods with an interpretable attribution technique (the Shapley Additive Explanation), we investigated the critical factors influencing MPs removal within CWs. The MPs abundance in the influent and the inlet of Z-CW (400.1 ± 20.8 items/L and 699.6 ± 50.6 items/kg) was significantly higher compared to that in M-CW (138.8 ± 20.5 items/L and 166.5 ± 36.8 items/kg), with no significant difference observed in the effluent. The primary characteristic of MPs is their fibrous and transparent appearance. The MPs removal range from 87.9% to 95.5 %, influenced by the types and characteristics of MPs, physical and chemical parameters, biofilms, and different processes. Among these factors, dissolved organic carbon with high humic content, aromaticity, and carboxyl abundance may serve as a crucial factor in MPs removal. The results of this study highlight the significance of physical and chemical parameters for the MPs removal in CWs, providing the necessary theoretical data for the construction of future large-scale engineering applications.

Exploring the effects of polyethylene and polyester microplastics on biofilm formation, membrane Fouling, and microbial communities in Modified Ludzack-Ettinger-Reciprocation membrane bioreactors

Microplastics (MPs) inevitably enter wastewater treatment plants (WWTPs), yet their impacts remain poorly understood. This study investigates the effects of MPs on system performance and membrane fouling in a Modified Ludzack-Ettinger (MLE)-Reciprocation Membrane Bioreactor (rMBR), an energy-efficient alternative to conventional membrane bioreactors. Additionally, the study examines changes in microbial community induced by different types and shapes of MPs-polyethylene (PE) pellets and polyester (PES) fibers- as well as biofilm formation on MPs, using next-generation sequencing. Results revealed that transmembrane pressure (TMP) increased 2-3 times faster in the presence of PE pellets, while TMP remained stable during the PES stage, implying that MP type and shape could influence biofouling behaviors. Furthermore, enhanced nitrate removal was observed in the aerobic tank due to denitrifying biofilm formation on MPs. However, PES MPs reduced nitrate removal efficiency from 99.6 ± 0.3 % to 90.9 ± 7.9 % and decreased the relative abundance of denitrifying bacteria. Numerous taxa showed affinity to PE pellets, including some pathogens, e.g., Norcadia and Mycobacterium. Notably, an uncultured phylum Candidatus Saccharibacteria dominated in membrane biofilm and MPs, reaching up to 37 % relative abundance. This study is the first to explore how different types and shapes of MPs affect membrane bioreactor systems, particularly with respect to microbial community structure and biofilm formation. The findings offer new insights into the influence of MPs on wastewater treatment processes and highlight the significance of the uncultured phylumCandidatus Saccharibacteriain membrane fouling.

Bacillus subtilis, a promising bacterial candidate for trapping nanoplastics during water treatment

As a probiotic, Bacillus subtilis (B. subtilis) has a wide range of application values. In this study, the trap by B. subtilis and the effect of NPs on its growth physiology were studied. Confocal laser scanning microscopy (LCSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that PS-NPs were trapped by B. subtilis when they were exposed to PS-NPs. At this point, most of the PS-NPs are clustered around B. subtilis. Flow cytometry showed that at 10 mg/L, 73.7 % of PS-NPs' environmental state changed. The complexity of 9.73 %, 23.77 %, 43.27 %, and 65.13 % of B. subtilis increased at PS-NP concentrations of 10, 20, 50, and 200 mg/L, respectively. The increase in overall EPS secretion ranged from 0.51 ∼ 7.13 μg/mL after adding different concentrations of PS-NPs. The effect of different concentrations of PS-NPs on NAR activity ranged from -11.38 ∼ 16.2 %, on NIR activity from -17.90 ∼ 7.22 %, on NOR activity from -15.10 ∼ 7.69 % and on NO2R activity from -14.01 ∼ 17.03 %. These results indicated that B. subtilis can process nitrogen compounds in water while capturing NPs in the environment. They have the potential to be candidate bacteria in the water treatment process, and specific applications are needed to research further.

Sustainable control of microplastics in wastewater using the electrochemically enhanced living membrane bioreactor

Wastewater treatment plant (WWTP) discharges are major contributors to the release of microplastics (MPs) into the environment. This research work aimed to assess the performance of the novel living membrane bioreactor (LMBR), which utilizes a biological layer as a membrane filter for the removal of polyethylene (PE) MPs from wastewater. The impact of an intermittently applied low current density (0.5 mA/cm2) on the reduction of MPs in the electrochemically enhanced LMBR (e-LMBR) has also been examined. The reactors were also compared to a conventional membrane bioreactor (MBR) and an electro-MBR (e-MBR). 1H nuclear magnetic resonance spectroscopy (1H NMR) was implemented for the MPs detection and quantification in terms of mass per volume of sample. The LMBR and MBR achieved comparable mean PE MPs reduction at 95% and 96%, respectively. The MPs mass reduction in the e-LMBR slightly decreased by 2% compared to that achieved in the LMBR. This potentially indicated the partial breakdown of the MPs due to electrochemical processes. Decreasing and inconsistent NH4-N and PO4-P removal efficiencies were observed over time due to the addition of PE MPs in the MBR and LMBR. In contrast, the integration of electric field in the e-MBR and e-LMBR resulted in consistently high values of conventional contaminant removals of COD (99.72-99.77 %), NH4-N (97.96-98.67%), and PO4-P (98.44-100.00%), despite the MPs accumulation. Integrating electrochemical processes in the e-LMBR led to the development of a stable living membrane (LM) layer, as manifested in the consistently low effluent turbidity 0.49 ± 0.33 NTU. Despite the increasing MPs concentration in the mixed liquor, applying electrochemical processes reduced the fouling rates in the e-LMBR. The e-LMBR achieved comparable efficiencies in contaminant reductions as those observed in the e-MBR, while using a low-cost membrane material.

Microplastics in granular sequencing batch reactors: Effects on pollutant removal dynamics and the microbial community

This study investigated the relationship between microplastic (MP) presence and pollutant removal in granular sludge sequencing batch reactors (GSBRs). Two types of MPs, polyethylene (PE) and polyethylene terephthalate (PET), were introduced in varying concentrations to assess their effects on microbial community dynamics and rates of nitrogen, phosphorus, and organic compound removal. The study revealed type-dependent variations in the deposition of MPs within the biomass, with PET-MPs exhibiting a stronger affinity for accumulation in biomass. A 50 mg/L dose of PET-MP decreased COD removal efficiency by approximately 4 % while increasing P-PO4 removal efficiency by around 7 % compared to the control reactor. The rate of nitrogen compounds removal decreased with higher PET-MP dosages but increased with higher PE-MP dosages. An analysis of microbial activity and gene abundance highlighted the influence of MPs on the expression of the nosZ and ppk1 genes, which code enzymes responsible for nitrogen and phosphorus transformations. The study also explored shifts in microbial community structure, revealing alterations with changes in MP dose and type. This research contributes valuable insights into the complex interactions between MP, microbial communities, and pollutant removal processes in GSBR systems, with implications for the sustainable management of wastewater treatment in the presence of MP.

A review of microplastics on anammox: Influences and mechanisms

Microplastics (MPs) are prevalent in diverse environmental settings, posing a threat to plants and animals in the water and soil and even human health, and eventually converged in wastewater treatment plants (WWTPs), threatening the stable operation of anaerobic ammonium oxidation (anammox). Consequently, a comprehensive summary of their impacts on anammox and the underlying mechanisms must be provided. This article reviews the sources and removal efficiency of MPs in WWTPs, as well as the influencing factors and mechanisms on anammox systems. Numerous studies have demonstrated that MPs in the environment can enter WWTPs via domestic wastewater, rainwater, and industrial wastewater discharges. More than 90% of these MPs are found to accumulate in the sludge following their passage through the treatment units of the WWTPs, affecting the characteristics of the sludge and the efficiency of the microorganisms treating the wastewater. The key parameters of MPs, encompassing concentration, particle size, and type, exert a notable influence on the nitrogen removal efficiency, physicochemical characteristics of sludge, and microbial community structure in anammox systems. It is noteworthy that extracellular polymer secretion (EPS) and reactive oxygen stress (ROS) are important impact mechanisms by which MPs exposure affects anammox systems. In addition, the influence of MPs exposure on the microbial community structure of anammox cells represents a crucial mechanism that demands attention. Future research endeavors will delve into additional crucial parameters of MPs, such as shape and aging, to investigate their effects and mechanisms on anammox. Furthermore, the effective mitigation strategies will also be developed. The paper provides a fresh insight to reveal the influences of MPs exposure on the anammox process and its influence mechanisms, and lays the groundwork for further exploration into the influence of MPs on anammox and potential mitigation strategies.

Nanoplastic Contamination in Freshwater Biofilms Using Gel Permeation Chromatography and Plasmonic Nanogold Sensor Approaches

The worldwide contamination of aquatic ecosystems by plastics is raising concern, including their potential impacts on the base of the food chain, which has been poorly documented. This study sought to examine, for the first time, the presence of nanoplastics (NPs) in biofilms from freshwater streams/rivers. They were collected at selected polluted sites, such as the industrial sector for plastic recycling and production, miscellaneous industries, agriculture, municipal wastewaters/effluents and road runoffs. In parallel, the functional properties of sampled biofilms were determined by proteins, lipids, esterase (lipase), viscosity and oxidative stress. The results revealed that biofilms collected at the plastic industries and road runoffs contained the highest NP levels based on size exclusion chromatography, fluorescence detection and a new nanogold sensor visualization method. Examination of the chromatographic elution profiles showed increased abundance and size of NPs in the 10-150 nm size range at the polluted sites. Biofilms from the plastic industry site had elevated levels of aldehydes (oxidative stress) and lipids compared to the other sites. Biofilms collected at the municipal sites had elevated levels of proteins and esterases/lipases, with a decrease in total lipids. Biofilms collected at agriculture sites had the lowest levels of NPs in this campaign, but more samples would be needed to confirm these trends. In conclusion, biofilms represent an important sink for plastics in freshwater environments and display signs of distress upon oxidative stress.

Insight into effect of polyethylene microplastic on nitrogen removal in moving bed biofilm reactor: Focusing on microbial community and species interactions

Microplastics (MPs) pollution has emerged as a global concern, and wastewater treatment plants (WWTPs) are one of the potential sources of MPs in the environment. However, the effect of polyethylene MPs (PE) on nitrogen (N) removal in moving bed biofilm reactor (MBBR) remains unclear. We hypothesized that PE would affect N removal in MBBR by influencing its microbial community. In this study, we investigated the impacts of different PE concentrations (100, 500, and 1000 μg/L) on N removal, enzyme activities, and microbial community in MBBR. Folin-phenol and anthrone colorimetric methods, oxidative stress and enzyme activity tests, and high-throughput sequencing combined with bioinformation analysis were used to decipher the potential mechanisms. The results demonstrated that 1000 μg/L PE had the greatest effect on NH4+-N and TN removal, with a decrease of 33.5 % and 35.2 %, and nitrifying and denitrifying enzyme activities were restrained by 29.5-39.6 % and 24.6-47.4 %. Polysaccharide and protein contents were enhanced by PE, except for 1000 μg/L PE, which decreased protein content by 65.4 mg/g VSS. The positive links of species interactions under 1000 μg/L PE exposure was 52.07 %, higher than under 500 μg/L (51.05 %) and 100 μg/L PE (50.35 %). Relative abundance of some metabolism pathways like carbohydrate metabolism and energy metabolism were restrained by 0.07-0.11 % and 0.27-0.4 %. Moreover, the total abundance of nitrification and denitrification genes both decreased under PE exposure. Overall, PE reduced N removal by affecting microbial community structure and species interactions, inhibiting some key metabolic pathways, and suppressing key enzyme activity and functional gene abundance. This paper provides new insights into assessing the risk of MPs to WWTPs, contributing to ensuring the health of aquatic ecosystems.

Microplastics removal in wastewater treatment plants: A review of the different approaches to limit their release in the environment

In last 10 years, the interest about the presence of microplastics (MPs) in the environment has strongly grown. Wastewaters function as a carrier for MPs contamination from source to the aquatic environment, so the knowledge of the fate of this emerging contaminant in wastewater treatment plants (WWTPs) is a priority. This work aims to review the presence of MPs in the influent wastewater (WW) and the effectiveness of the treatments of conventional WWTPs. Moreover, the negative impacts of MPs on the management of the processes have been also discussed. The work also focuses on the possible approaches to tackle MPs contamination enhancing the effectiveness of the WWTPs. Based on literature results, despite WWTPs are not designed for MPs removal from WW, they can effectively remove the MPs (up to 99 % in some references). Nevertheless, they normally act as "hotspots" of MPs contamination considering the remaining concentration of MPs in WWTPs' effluents can be several orders of magnitude higher than receiving waters. Moreover, MPs removed from WW are concentrated in sewage sludge (potentially >65 % of MPs entering the WWTP) posing a concern in case of the potential reuse as a soil improver. This work aims to present a paradigm shift intending WWTPs as key barriers for environmental protection. Approaches for increasing effectiveness against MPs have been discussed in order to define the optimal point(s) of the WWTP in which these technologies should be located. The need of a future legislation about MPs in water and sludge is discussed.

The impacts of biodegradable and non-biodegradable microplastic on the performance and microbial community characterization of aerobic granular sludge

Introduction

Microplastics (MPs), identified as emerging contaminants, have been detected across diverse environmental media. Their enduring presence and small size facilitate the adsorption of organic pollutants and heavy metals, leading to combined pollution effects. MPs also accumulate in the food chain thus pose risks to animals, plants, and human health, garnering significant scholarly attention in recent years. Aerobic granular sludge (AGS) technology emerges as an innovative approach to wastewater treatment. However, the impacts of MPs on the operational efficiency and microbial characteristics of AGS systems has been insufficiently explored.

Methods

This study investigated the effects of varying concentration (10, 50, and 100 mg/L) of biodegradable MPs (Polylactic Acid, PLA) and non-biodegradable MPs (Polyethylene Terephthalate, PET) on the properties of AGS and explored the underlying mechanisms.

Results and discussions

It was discovered that low and medium concentration of MPs (10 and 50 mg/L) showed no significant effects on COD removal by AGS, but high concentration (100 mg/L) of MPs markedly diminished the ability to remove COD of AGS, by blocking most of the nutrient transport channels of AGS. However, both PLA and PE promoted the nitrogen and phosphorus removal ability of AGS, and significantly increased the removal efficiency of total inorganic nitrogen (TIN) and total phosphorus (TP) at stages II and III (P < 0.05). High concentration of MPs inhibited the growth of sludge. PET noticeably deteriorate the sedimentation performance of AGS, while 50 mg/L PLA proved to be beneficial to sludge sedimentation at stage II. The addition of MPs promoted the abundance of Candidatus_Competibacter and Acinetobacter in AGS, thereby promoting the phosphorus removal capacity of AGS. Both 50 mg/L PET and 100 mg/L PLA caused large amount of white Thiothrix filamentous bacteria forming on the surface of AGS, leading to deterioration of the sludge settling performance and affecting the normal operation of the reactor. Comparing with PET, AGS proved to be more resistant to PLA, so more attention should be paid to the effect of non-biodegradable MPs on AGS in the future.

Effects of photoaging on structure and characteristics of biofilms on microplastic in soil: Biomass and microbial community

Understanding of the environmental behaviors of microplastics is limited by a lack of knowledge about how photoaging influences biofilm formation on microplastics in soil. Here, original microplastics (OMPs) and photoaged-microplastics (AMPs) were incubated in soil to study the effect of photoaging on formation and characteristics of biofilm on the poly (butylene succinate) microplastics. Because photoaging decreased the hydrophobicity of the microplastic, the biomass of biofilm on the OMPs was nearly twice that on the AMPs in the early stage of incubation. However, the significance of the substrate on biomass in the biofilm declined as the plastisphere developed. The bacterial communities in the plastisphere were distinct from, and less diverse than, those in surrounding soil. The dominant genera in the OMPs and AMPs plastispheres were Achromobacter and Burkholderia, respectively, indicating that photoaging changed the composition of the bacterial community of biofilm at the genus level. Meantime, photoaging decreased the complexity and stability of the plastisphere bacterial community network. Results of Biolog ECO-microplate assays and functional prediction from amplicons showed that photoaging treatment enhanced the carbon metabolic capacity of the microplastic biofilm. This study provides new insights into the formation of plastispheres in soil.

The critical role of microplastics in the fate and transformation of sulfamethoxazole and antibiotic resistance genes within vertical subsurface-flow constructed wetlands

Constructed wetlands (CWs) are reservoirs of microplastics (MPs) in the environment. However, knowledge about the impact of MPs on antibiotic removal and the fate of antibiotic resistance genes (ARGs) is limited. We focused on sulfamethoxazole (SMX) as a representative compound to examine the effects of MPs on SMX removal and the proliferation and dissemination of two SMX-related ARGs (sul1 and sul2) in vertical subsurface-flow CW (VFCW) microcosm. The presence of MPs in the substrate was found to enhance the proliferation of microorganisms owing to the large specific surface area of the MPs and the release of dissolved organic carbon (DOC) on MP surfaces, which resulted in a high SMX removal ranging from 97.80 % to 99.80 %. However, the presence of MPs promoted microbial interactions and the horizontal gene transfer (HGT) of ARGs, which led to a significant increase in the abundances of sul1 and sul2 of 68.47 % and 17.20 %, respectively. It is thus imperative to implement rigorous monitoring strategies for MPs to mitigate their potential ecological hazards.

Tire materials disturb transformations of nitrogen compounds and affect the structure of biomass in aerobic granular sludge reactors

Tire materials (TMs) present a notable hazard due to their potential to release harmful chemicals and microplastics into the environment. They can infiltrate wastewater treatment plants, where their effects remain inadequately understood, raising concerns regarding their influence on treatment procedures. Thus, this study investigated the impact of TMs in wastewater (10, 25, 50 mg/L) on wastewater treatment efficiency, biomass morphology, and microbial composition in aerobic granular sludge (AGS) reactors. TM dosage negatively correlated with nitrification and denitrification efficiencies, reducing overall nitrogen removal, but did not affect the efficiency of chemical-oxygen-demand removal. The presence of TMs increased the diameter of the granules due to TM incorporation into the biomass. The most frequently leached additives from TMs were N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine, benzothiazole (BTH), and 2-hydroxybenzothiazole. In the treated wastewater, only BTH and aniline were detected in higher concentrations, which indicates that tire additives were biodegraded by AGS. The microbial community within the AGS adapted to TMs and their chemicals, highlighting the potential for efficient degradation of tire additives by bacteria belonging to the genera Rubrivivax, Ferruginibacter, and Xanthomonas. Additionally, our research underscores AGS's ability to incorporate TMs into biomass and effectively biodegrade tire additives, offering a promising solution for addressing environmental concerns related to TMs.

Insights into the role of extracellular polymeric substances (EPS) in the spread of antibiotic resistance genes

Antibiotic resistance genes (ARG) are prevalent in aquatic environments. Discharge from wastewater treatment plants is an important point source of ARG release into the environment. It has been reported that biological treatment processes may enhance rather than remove ARG because of their presence in sludge. Attenuation of ARG in biotechnological processes has been studied in depth, showing that many microorganisms can secrete complex extracellular polymeric substances (EPS). These EPS can serve as multifunctional elements of microbial communities, involving aspects, such as protection, structure, recognition, adhesion, and physiology. These aspects can influence the interaction between microbial cells and extracellular ARG, as well as the uptake of extracellular ARG by microbial cells, thus changing the transformative capability of extracellular ARG. However, it remains unclear whether EPS can affect horizontal ARG transfer, which is one of the main processes of ARG dissemination. In light of this knowledge gap, this review provides insight into the role of EPS in the transmission of ARGs; furthermore, the mechanism of ARG spread is analyzed, and the molecular compositions and functional properties of EPS are summarized; also, how EPS influence ARG mitigation is addressed, and factors impacting how EPS facilitate ARG during wastewater treatment are summarized. This review provides comprehensive insights into the role of EPS in controlling the transport and fate of ARG during biodegradation processes at the mechanistic level.

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.

Soil protists are more resilient to the combined effect of microplastics and heavy metals than bacterial communities

Heavy metals and micro-/nanoplastic pollution seriously threaten the environment and ecosystems. While many studies investigated their effects on diverse microbes, few studies have focused on soil protists, and it is unclear how soil protists respond to the combined effect of micro-/nanoplastics and heavy metals. This study investigated how soil protistan and bacterial communities respond to single or combined copper and micro-/nanoplastics. The bacterial community exhibited an instantaneous response to single copper pollution, whereas the combined pollution resulted in a hysteresis effect on the protistan community. Single and combined pollution inhibited the predation of protists and changed the construction of ecological networks. Though single and combined pollution did not significantly affect the overall community structure, the exposure experiment indicated that combined pollution harmed soil amoeba's fitness. These findings offer valuable new insights into the toxic effects of single and combined pollution of copper and plastics on soil protistan and bacterial communities. Additionally, this study shows that sequencing-based analyses cannot fully reflect pollutants' adverse effects, and both culture-independent and dependent methods are needed to reveal the impact of pollutants on soil microbes.

Effects of microplastics on the properties of different types of sewage sludge and strategies to overcome the inhibition: A review

Microplastics have been identified as an emerging pollutant. When microplastics enter wastewater treatment plants, the plant traps most of the microplastics in the sludge during sewage treatment. Therefore, the effects of microplastics on sludge removal performance, and on the physical and chemical properties and microbial communities in sludge, have attracted extensive attention. This review mainly describes the presence of microplastics in wastewater treatment plants, and the effects of microplastics on the decontamination efficiency and physicochemical properties of activated sludge, aerobic granular sludge, anaerobic granular sludge and anaerobic ammonium oxidation sludge. Further, the review summarizes the effects of microplastics on microbial activity and microbial community dynamics in various sludges in terms of type, concentration, and contact time. The mechanisms used to strengthen the reduction of microplastics, such as biochar and hydrochar, are also discussed. This review summarizes the mechanism by which microplastics influence the performance of different types of sludge, and proposes effective strategies to mitigate the inhibitive effect of microplastics on sludge and discusses removal technologies of microplastics in sewage. Biochar and hydrochar are one of the effective measures to overcome the inhibition of microplastics on sludge. Meanwhile, constructed wetland may be one of the important choice for the future removal of microplastics from sewage. The goal is to provide theoretical support and insights for ensuring the stable operation of wastewater treatment plants and reducing the impact of microplastics on the environment.

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.

Synergistic analysis of performance, microbial community, and metabolism in aerobic granular sludge under polyacrylonitrile microplastics stress

Aerobic granular sludge (AGS) has proved to be a promising biotechnology for microplastics wastewater treatment. However, polyacrylonitrile microplastics (PAN MPs), the most widely used plastic in textile materials, have not been investigated. Therefore, the effect of the neglected PAN MPs on AGS at different concentrations (1, 10, and 100 mg/L) was evaluated. The results indicated that PAN MPs with 1 and 10 mg/L concentrations had no obvious effect on granular stability and nutrient removal performance, but greatly promoted the secretion of EPS. Remarkably, the granule structure was severely damaged under 100 mg/L PAN MPs. Moreover, microbial community analysis showed that phylum Proteobacteria played a dominant role in resistance to PAN MPs. Metabolic analysis further revealed that genes related to denitrification pathway (nasA, nirK, nirS and norB) and membrane transport were significantly inhibited under PAN MPs stress. This study may provide additional information on the treatment of microplastics wastewater using AGS.

Phototransformation of extracellular polymeric substances in activated sludge and their interaction with microplastics

Substantial amounts of extracellular polymeric substances (EPS) are present in sludge from wastewater treatment plants (WWTP), and EPS can significantly affect the fate, bioavailability, and toxicity of microplastics (MPs) that coexist in the effluent, however, the mechanism of action between EPS and microplastics remains unclear. In addition, ultraviolet (UV) disinfection is indispensable in the wastewater treatment process in WWTP, which can significantly affect the characteristics of EPS. Therefore, it is of great significance to study the photochemical characteristics of EPS and the effect on binding MPs. In this study, using multispectral technology and two-dimensional correlation spectroscopy analysis, indicates that the molecular weight and aromaticity of EPS after phototransformation were reduced. The results showed that the adsorption of EPS on PSMPs was in the order of TB-EPS > LB-EPS > S-EPS, which was positively correlated with the SUVA254, but negatively correlated with O/C of EPS. This indicates that the main adsorption mechanisms of PSMPs on EPS were π-π and hydrophobicity. The adsorption capacity of S-EPS, LB-EPS and TB-EPS to PSMPs decreased with the increasing of illumination time. After phototransformation, the adsorption sensitivity and reaction sequence of EPS and PSMPs did not change much. This research provides a theoretical basis for understanding the photochemical transformation of extracellular polymers and the morphology and migration of microplastics in sewage treatment, and evaluating the impact of microplastics on ecosystems.

Insight into response characteristics and inhibition mechanisms of anammox granular sludge to polyethylene terephthalate microplastics exposure

Currently, in-depth understanding of response characteristics and mechanisms of anammox process under microplastics (MPs) stress remains quite limited. This study investigated the influence of 0.1-1.0 g/L polyethylene terephthalate (PET) on anammox granular sludge (AnGS). Compared with the control, 0.1-0.2 g/L PET did not significantly affect the anammox efficiency, while the anammox activity decreased by 16.2% at 1.0 g/L PET. Integrity coefficient and transmission electron microscopy analysis demonstrated that the strength and structural stability of the AnGS became weaken following exposure to 1.0 g/L PET. With the PET increasing, the abundance of anammox genera and genes related to energy metabolism and cofactors and vitamins metabolism decreased. The reactive oxygen species generated in the interaction between microbial cells and PET resulting in cellular oxidative stress was responsible for inhibiting anammox. These findings give novel insights into the anammox behavior in biological nitrogen removal systems treating PET-loaded nitrogenous wastewater.

Coagulation and Flocculation before Primary Clarification as Efficient Solutions for Low-Density Microplastic Removal from Wastewater

Microplastic (MP) removal from wastewater was investigated using various types and doses of commercial coagulants (PIX, PAX) and flocculants (FPM, PEL, FCT) before primary clarification in a wastewater treatment plant (WWTP). Dosing with FPM, PIX, and PEL caused small MPs (180-212 µm) to be transferred mainly to the settled sludge (up to 86.4% of MP at a dose of 5 mL FMP/m³), while dosing of FCT and PAX caused these MPs to be transferred to the floated sludge (up to 64% MP at a dose of 5 mL PAX/m³). The efficiency of MP removal from wastewater was the highest (90%) with 2.5 mL PAX/m³; the generated primary sludge had a low MP content and could be safely managed in subsequent stages of sludge treatment. At the highest doses, PIX significantly increased the removal of P-PO₄ (up to 94%) and COD (up to 73%). FPM and FCT resulted in over 40% efficiency of ammonium removal-such disturbance in wastewater composition may negatively affect further biological treatment. Effective removal of MP in the mechanical part of WWTP resulting from coagulation and flocculation enables the safe use of the excess sludge for agricultural purposes.