Release Of Extracellular Polymeric Substances Research Articles

Effects of aggregation and settling of photoactive TiO2 nanoparticles on Microcystis aeruginosa and extracellular matters release

Owing to their diverse applications, TiO2-nanoparticles have been extensively discharged into the aquatic environment, posing serious threats to aquatic life and human health. Meanwhile, the aquatic organisms such as cyanobacteria affect the mobility and fate of the nanoparticles, in turn, these aquatic organisms also may be influenced by the nanoparticles, and which further elicits more hazard to ecosystem. In this study, the different concentration of TiO2 nanoparticles were added into the algal solution to observe the status of TiO2 nanoparticles and assess their influences, especially for photocatalytic toxicity on algal growth. The results demonstrated that algal cells and extracellular polymeric substances (EPS) simultaneously affected the TiO2 aggregation and settling in algae culture. In addition, TiO2 NPs inhibited the growth of algal cells through the multiple effects on the light adsorption, photosynthetic activity, oxidative stress and lipid peroxidation. Particularly, the reactive oxygen species generated by photoactive TiO2 NPs caused the changes of EPS and microcystin-LR (MC-LR) release, and these extracellular matters were crucial intermediate to the state of TiO2 NPs and algal cells growth. This study will not only be significant for understanding TiO2 behavior in the real aquatic environment but also be helpful for exploring the effects of TiO2 nanoparticles on cyanobacteria, especially for the released extracellular matters.

The cumulative impact of temperature and nitrogen availability on the potential nitrogen fixation and extracellular polymeric substances secretion by Dolichospermum

Nitrogen-fixing cyanobacteria not only cause severe blooms but also play an important role in the nitrogen input processes of lakes. The production of extracellular polymeric substances (EPS) and the ability to fix nitrogen from the atmosphere provide nitrogen-fixing cyanobacteria with a competitive advantage over other organisms. Temperature and nitrogen availability are key environmental factors in regulating the growth of cyanobacteria. In this study, Dolichospermum (formerly known as Anabaena) was cultivated at three different temperatures (10 °C, 20 °C, and 30 °C) to examine the impact of temperature and nitrogen availability on nitrogen fixation capacity and the release of EPS. Initially, confocal laser scanning microscopy (CLSM) and the quantification of heterocysts at different temperatures revealed that lower temperatures (10 °C) hindered the differentiation of heterocysts under nitrogen-deprived conditions. Additionally, while heterocysts inhibited the photosynthetic activity of Dolichospermum, the secretion of EPS was notably affected by nitrogen limitation, particularly at 30 °C. Finally, real-time quantitative polymerase chain reaction (qPCR) was used to measure the expression of nitrogen-utilizing genes (ntcA and nifH) and EPS synthesis-related genes (wzb and wzc). The results indicated that under nitrogen-deprived conditions, the expression of each gene was upregulated, and there was a significant correlation between the upregulation of nitrogen-utilizing and EPS synthesis genes (P < 0.05). Our findings suggested that Dolichospermum responded to temperature variation by affecting the formation of heterocysts, impacting its potential nitrogen fixation capacity. Furthermore, the quantity of EPS released was more influenced by nitrogen availability than temperature. This research enhances our comprehension of interconnections between nitrogen deprivation and EPS production under the different temperatures.

Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

The creation of large amounts of excess sludge and residual nitrogen are critical issues in wastewater biotreatment. This study introduced Fe(II) into an oligotrophic anaerobic reactor (OARFe) that was implemented to modify an anoxic-oxic process to motivate in-situ sludge reduction and enhance denitrification under an effective electron shuttle among organic matter, nitrogen, and Fe. The addition of 15 mg L−1 Fe(II) resulted in a sludge reduction efficiency reached 32.0% with a decreased effluent nitrate concentration of 33.3%. This was mostly attributed to the electron transfer from Fe(II) to organic matters and nitrogen species in OARFe. The participation of Fe(II) led to the upregulation of Geothrix and Terrimonas, which caused active organic matter hydrolysis and cell lysis to stimulate the release of extracellular polymeric substances (EPS) and substance transfer between each layer of EPS. The higher utilization of released bioavailable dissolved organic matter improved endogenous denitrification, which can be combined with iron autotrophic denitrification to realize multiple electron donor-based nitrogen removal pathways, resulting in an increased nitrate removal rate of 58.2% in the absence of external carbon sources. These functional bacteria associated with the transformation of nitrogen and carbon and cycling between ferrous and ferric ions were enriched in OARFe, which contributed to efficient electron transport occurred both inside and outside the cell and increased 2,3,5-triphenyltetrazolium chloride electronic transport system activity by 46.9%. This contributed to the potential operational costs of chemical addition and sludge disposal of Fe-AO being 1.9 times lower than those of conventional A2O processes. These results imply that the addition of ferrous ions to an oligotrophic anaerobic zone for wastewater treatment has the potential for low-cost pollution control.

Diatom-derived extracellular polymeric substances form eco-corona and enhance stability of silver nanoparticles.

Silver nanoparticles (nAg) are extensively used across various fields and are frequently introduced into aquatic environments, where their behavior depends on environmental conditions. Extracellular polymeric substances (EPS) derived from aquatic organisms, such as diatoms, could play an important yet to be explored role in shaping the fate of nAg in aquatic environments. This study investigates the interactions between EPS, particularly those from the diatom Cyclotella meneghiniana, and citrate-coated nAg. The main objective is to understand how EPS influence the behaviours of nAg in freshwater settings, in terms of modulation of the nAg surface properties, colloidal stability and dissolution. To achieve these objectives a combination of the state-of-the-art spectroscopic and imaging techniques was employed. nAg was incubated with EPS isolated from an axenic C. meneghiniana culture, and their interactions were explored in a simulated freshwater environment over both short-term (0-2 h) and long-term (0-72 h) periods. The study focused on the changes in nAg, examining surface modulation, colloidal stability, dissolution, EPS adsorption on nAg, and the resulting eco-corona formation. The results indicate that EPS enhance the colloidal stability of nAg and decrease their dissolution in synthetic freshwater by adsorbing onto their surface and inducing steric repulsion between nAg particles. Visualization of the eco-corona formed by diatom EPS on nAg and its impact on aggregation processes is achieved through transmission electron microscopy. The formation of the EPS corona is attributed to the presence of diverse biopolymers within EPS, particularly proteins and polysaccharides. Fluorescence quenching studies on protein fluorophores demonstrate the formation, through hydrophobic interactions, of protein-nAg complex, further confirmed by AF4-DAD-FLD-ICP-MS. In a broader context, the results of this mechanistic study imply that diatoms, through the release of EPS, may significantly influence the destiny and possibly the bioavailability of nAg in EPS-abundant aquatic environments.

A noteworthy response process of Microcystis aeruginosa induced by exogenous reactive oxygen species in algae-laden water treatment

The effectiveness of reactive oxygen species (ROS) generated by advanced oxidation processes (AOPs) in inactivating harmful algae in drinking water varies considerably. Therefore, the physiological and biochemical reactions of algae need to be considered to clarify the underlying mechanisms. Herein, we studied the response mechanisms of Microcystis aeruginosa to exogenous ROS. Increased CAT, SOD, and GSH levels indicated oxidative stress damage, and increased MDA levels indicated lipid peroxidation in the treatment group. SEM images and fluorescence spectrogram revealed that these reactions promote the release of extracellular polymeric substances (EPS), which increase by ≥ 1.2 mg/L for proteins and ≥ 0.89 mg/L for polysaccharides. The phycobiliprotein content decreased, in which phycocyanin content decreased by approximately 77.41 %. Changes in differential metabolites, including increased regulation of protein and polysaccharide synthesis, enhanced cell membrane fluidity, and increased intracellular microcystin-LR levels were significantly associated with these results. Increased alkaloid levels, reduced vitamin levels, and ATP imbalances also affect cellular activity. These results provide new insights into the response mechanisms of algae and facilitate the practical and sustainable applications of AOPs-treated algae-laden water.

Performance evaluation of the effect of humic acid on Anammox granular sludge: Apparent morphology, nitrogen removal and microbial community

Humic acid (HA) is a typical refractory organic matter, so it is of great significance to investigate its effect on the performance of Anammox granular sludge. When the dosage of HA ≤ 50 mg/L, HA promotes the total nitrogen removal rate (NRR) to 1.45 kg/(m3·day). When HA was between 50 and 100 mg/L, the NRR of Anammox was stable. At this time, the adsorption of HA causes the sludge to gradually turn from red to brown, but the activities of heme and enzymes showed that its capacity was not affected. When HA levels reached 250 mg/L, the NRR dropped to 0.11 kg/(m3·day). Moderate HA levels promoted the release of extracellular polymeric substance (EPS), but excessive HA levels lead to a decrease in EPS concentrations. HA inhibited Anammox activity, which indirectly hindered the transmission of substrate and accumulated substrate toxicity. Although HA promoted the increase of heterotrophic microbial abundance in Anammox system, the microbial diversity decreased gradually. With the increase of HA concentration, the abundance of Candidatus_Brocadia, the main functional microorganism of Anammox system, decreased gradually, while the abundance of Candidatus_Kuenenia increased gradually.

Unraveling the role of polymeric ferric sulfate in promoting propionic acid in anaerobic sludge hydrogen production fermentation

Polymerized ferric sulfate (PFS) is widely employed in the pretreatment of industrial wastewater and sludge dewatering. Its widespread use results in its accumulation in waste activated sludge (WAS) and may impact anaerobic fermentation (AF). This work fills the gap in the effects and mechanisms of PFS on hydrogen (H2) production from AF under mesophilic and thermophilic conditions. PFS (40 g/kg total solids, TS) reduced cumulative H2 production by 59.2% (mesophilic conditions) and 52.6% (thermophilic conditions) (p < 0.001), whereas propionic acid production increased by 299.2% and 192.0%, respectively. Model-based analysis showed that PFS inhibited solubilization, hydrolysis, and acidification below 10 g/kg TS but promoted them above 10 g/kg TS. Changes in the ratio of the two forms of nicotinamide adenine dinucleotide (NADH/NAD+) and hydrogenase activity led to unfavorable pathways for H2 production. Thermophilic fermentation exhibited strong tolerance to PFS due to the increased release of extracellular polymeric substances (EPSs). By analyzing 16S-rRNA gene operational taxonomic units (OTUs), the effects of environmental factors on microbial communities and microbial interactions under the combined effects of PFS and temperature were identified, revealing the important factors affecting H2 production. Sludge containing PFS was not conducive to anaerobic H2 production; however, mesophilic fermentation with PFS may be a potential way to recover propionic acid with low energy consumption. This study provided insights into the effects of potential contaminants in WAS on AF for H2 production and information for the effective disposal and resource utilization of WAS.

Effect and mechanism of perfluorooctanoic acid (PFOA) on anaerobic digestion sludge dewaterability

Perfluorooctanoic acid (PFOA) as nonbiodegradable organic pollutant, its presence and risks in wastewater treatment system has aroused wide concern. This study investigated the effect and underlying mechanism of PFOA on anaerobic digestion sludge (ADS) dewaterability. Long-term exposure experiments were set up to investigate the effect with various concentration of PFOA dosed. Experimental results suggested that the existence of high concentration PFOA (over 1000 μg/L) could deteriorate ADS dewaterability. The long-term exposure to 100,000 μg/L PFOA of ADS increased specific resistance filtration (SRF) by 81.57%. It was found that PFOA promoted the release of extracellular polymeric substances (EPS), which was strongly associated with sludge dewaterability. The fluorescence analysis revealed that the high PFOA concentration could significantly improve the percentage of protein-like substances and soluble microbial by-product-like content, and then further deteriorated the dewaterability. The FTIR results showed that long-term exposure of PFOA caused loose protein structure in sludge EPS, which led to loose sludge floc structure. The loose sludge floc structure aggravated the deterioration of sludge dewaterability. The solids-water distribution coefficient (Kd) decreased with the increase of initial PFOA concentration. Moreover, PFOA significantly affected microbial community structure. Metabolic function prediction results showed significant decrease of fermentation function exposed to PFOA. This study revealed that the PFOA with high concentration could deteriorated sludge dewaterability, which should be highly concerned.

Investigation of the role of cell hydrophobicity and EPS production in the aggregation of the marine diatom Cylindrotheca closterium under hypo-saline conditions

Aggregation of diatoms is of global importance to understand settling of particulate organic carbon in aquatic systems. In this study, we investigate the aggregation of the marine diatom Cylindrotheca closterium during the exponential growth phase under hypo-saline conditions. The results of the flocculation/flotation experiments show that the aggregation of the diatom depends on the salinity. In favorable growth conditions for marine diatoms (salinity of 35), the highest aggregation is achieved. To explain these observations, we used a surface approach combining atomic force microscopy (AFM) and electrochemical methods to characterize both the cell surface properties and the structure of the extracellular polymeric substances (EPS) cell produce, and to quantify the amount of surface-active organic matter released. At a salinity of 35, the results showed that diatoms are soft, hydrophobic and release only small amounts of EPS organized into individual short fibrils. In contrast, diatoms adapt to a salinity of 5 by becoming much stiffer and more hydrophilic, producing larger amounts of EPS that structurally form an EPS network. Both adaptation responses of diatoms, the hydrophobic properties of diatoms and the release of EPS, appear to play an important role in diatom aggregation and explain the behavior observed at different salinities. This biophysical study provides important evidence allowing to get a deep insight into diatom interactions at the nanoscale, which may contribute to a better understanding of large-scale aggregation phenomena in aquatic systems.

Treatment of industrial etching terminal wastewater using ZnFe2O4/g-C3N4 heterojunctions photo-assisted cathodes in single-chamber microbial electrolysis cells

Cost-effective, semiconductor ZnFe2O4/g-C3N4 heterojunction cathodes were investigated to achieve efficient treatment of industrial etching terminal wastewater in photo-assisted, single-chamber, microbial electrolysis cells (PS-MECs). The PS-MECs performance progressively increased over time, reaching significant Ni(II) removal (4.4 mg/L/h), recalcitrant organics mineralization (11.3 mg/L/h), hydrogen production (0.55 m3/m3/d) and solar-to-hydrogen conversion efficiency (6.7%) after 12 days fed-batch operation. The progressive deposition of Ni over the cathodes and the physiological release of extracellular polymeric substances (EPS) dynamically influenced the proportions of reactive oxidative species. Triplet 3EPS* (78%) on both electrodes and cathodic holes (22%) contributed to recalcitrant organics mineralization during the 12th fed-batch operational cycle, while cathodic holes (65%) exceeded anodic 3EPS* (35%) during the 1st-cycle. Significantly different bacterial communities were observed over the cathodes (Acinetobacter (17.7%) and Staphylococcus (16.8%) and anodes (Novosphingobium (42.9%)) after the 12th-cycle, as confirmed by KEGG PICRUSt analysis. This study broadens the application of cost-effective PS-MECs for industrial wastewater treatment.

Sensitive and Accurate Differentiation of Extracellular Polymeric Substance Hydrolysis Using Flow Cytometry during Biofilm Extracellular Polymeric Substance Extraction

Extracellular polymeric substances (EPS) affect the formation, properties, and function of biofilms. Understanding the roles of EPS in biofilm-related processes depends on reliable extraction and evaluation methods. However, differentiating true EPS from intracellular organic polymers released by cell lysis has proven to be difficult during EPS extraction. In this study, thermal and cation exchange resin (CER) treatments were used to extract biofilm EPS. SYTOX Green (SG) dye was used to stain nucleic acid (NA), and the enhanced fluorescence signal (FS) from the NA-SG complex was sensitively recorded by flow cytometry (FC). Results showed that thermal extraction could achieve effective EPS release, but a higher temperature and longer time caused a significant cell activity decline, protein denaturation, and cell lysis. In contrast, CER extraction had no effects on cell activity and organics denaturation, and it only caused minor cell lysis at a high CER dose. Combining all the results indicates that CER extraction using 70 g-CER/g-VSS for 2 h provided reliable and efficient extraction of biofilm EPS: high EPS extraction efficiency with minimal EPS denaturation, cell lysis, and loss of cell activity. FC combined with SG staining should be applicable for evaluating the effectiveness of EPS extraction from any microbial aggregates.

Impacts of floc breakage on dewaterability of chemically conditioned sludges and implications on practical conditioning strategies

While chemical conditioning is the most commonly used conditioning process for sludge dewatering, the dewaterability of chemically conditioned sludge is found to be significantly affected by shear force. However, relevant studies are still lacked, which obstructed an in-depth understanding on sludge conditioning. In this study, we systematically investigated the impacts of floc breakage induced by shearing on the sludges conditioned with polyacrylamides (PAMs)/inorganic salts. Although PAM-conditioned sludges had better structural strength and dewaterability than the ones conditioned with inorganic salts, they exhibited a drastically deteriorated dewaterability upon floc breakage after shearing. Further analysis revealed that the PAM-conditioned flocs were mainly wrapped by polymer chains and thus floc breakage would lead to a substantial release of extracellular polymeric substance (EPS) and exposure of massive non-neutralized negative charge. In comparison, the coagulation by inorganic salts was mainly completed by charge neutralization and compression of EPS, which resulted in a conditioned sludge with a much less deteriorated dewaterability after shearing. Accordingly, PAMs are suggested as the chemical agents if screw pump is used for the sludge conditioning, while extra shearing should be minimized in the conditioning process. Inorganic salts are more applicable for the conditioning layout with a flexibly located equalization tank due to their relatively low coagulation kinetics but well-maintained sludge dewaterability. This study fills some critical knowledge gaps in the fundamental understandings on chemical conditioning process and offers a guideline for the selection of practical conditioning strategy.

Anti-biofilm activity of biochanin A against Staphylococcus aureus.

Biofilm-forming Staphylococcus aureus can easily accumulate on various food contact surfaces which induce cross-contamination and are difficult to eliminate in the food industry. This study aimed to evaluate the anti-biofilm effects of natural product biochanin A against S. aureus. Results showed that biochanin A effectively eradicated established S. aureus biofilms on different food-contact materials. Fluorescence microscopic analyses suggested that biochanin A disintegrated the established biofilms by dissociate extracellular polymeric substance (EPS) in matrix. In addition, biochanin A at the sub-MIC concentration also effectively inhibited the biofilm formation by regulating the expression of biofilm-related genes (icaA, srtA, eno) and suppressing the release of EPS in biofilm matrix. Molecular docking also demonstrated that biochanin A conducted strong interactions with biofilm-related proteins (Ica A, Sortase A, and Enolase). These findings demonstrated that biochanin A has the potential to be developed as a potent agent against S. aureus biofilm in food industries. KEY POINTS: • Anti-biofilm effect of biochanin A against S. aureus was revealed for the first time. • Biofilm of S. aureus on various food-contact surfaces were efficiently eradicated. • Biochanin A prevented S. aureus biofilm formation via reducing EPS production.

Physiological response of electroactive bacteria via secretion of extracellular polymeric substances in microbial electrochemical processes: A review

Microbial electrochemical processes involving microbial catalyzed electrochemical reactions are directly/indirectly related to the electroactive bacteria (EAB) physiological secretion of extracellular polymeric substances (EPS) with favorable biofilm dispersion. EPS harbor cytochrome-like substances, and thus accelerate extracellular electron transfer (EET) processes resulting in the simultaneous removal of environmental contaminants or in the conversion of dissolved CO 2 to key-block chemicals. This review holistically documents case-studies in the last five years focusing on EAB and their physiological release of EPS in response to external stimuli. The important role played by EPS in the performance of microbial electrochemical systems and the relationship of the EPS compositional diversity with the process parameters is reviewed. Targeting the physiological response of electroactive bacteria towards the release of EPS with precise compositional diversity provides tremendous opportunities for optimizing microbial electrochemical processes. This review provides kernels, quantitative approaches and promising advanced techniques guiding further research directions in this exciting field. [ ]

Polydopamine-copper spacers improve longevity and prevent biofouling in reverse osmosis

Abstract Reverse Osmosis (RO) is a promising technology that will increase access to clean and safe water sources throughout the world. However, the impact of RO filtration of natural waters is severely hindered by biofouling. Formation of complex biofilms on RO membranes dramatically decreases output due to release of extracellular polymeric substances (EPS) by the microorganisms. We present a polydopamine-copper (PD-Cu) coating for RO feed spacer materials to prevent biofouling and enhance longevity of Cu ions. The following spacers were tested in a continuous flow bench scale RO system: (1) Polypropylene (PP) feed spacers coated with PD-Cu, (2) a pristine PP, control spacer, (3), a PD control spacer and (4) a Cu control spacer. Results showed the PD-Cu spacers exhibited higher Cu ion chelation, retaining 71 ± 2% more Cu ions compared to a Cu-only spacer after 13 h. In a stirring beaker, PD-Cu spacers lost loosely attached Cu ions until the optimum Cu concentration was achieved, approximately 30.6 ± 0.3% of total composition, within 6 h, and the remaining Cu ions bonded with PD covalently. In addition, PD-Cu spacers showed a 17.5% higher permeate flux and a 58% biofilm biovolume decrease as compared to a pristine spacer over 24 h.

Enhancing microbial electrosynthesis by releasing extracellular polymeric substances: Novel strategy through extracellular electron transfer improvement

Microbial electrosynthesis (MES) is a promising process in which microbes obtain electrons from electrodes, producing high value-added chemicals from CO2. Electrons from the cathode are the only energy source for reducing CO2; thus, the electron transfer rate is the key to the conversion efficiency of the entire MES system. Here, we report a strategy that promotes the release of extracellular polymeric substances (EPSs) by adding a surfactant to enhance microbial extracellular electron transfer (EET) in an MES system. The addition of the nonionic surfactant Tween 80 not only enables the cathode biofilm to secrete more EPSs, and thus, improve its electrochemical activity, but it also adjusts the composition of the mixed microbial community to promote the enrichment of the primary acetogen, namely, Acetobacterium. Consequently, the acetate production rate of the MES system with 80 mg/L Tween 80 addition was 1.42 times higher than that of the control, and its coulombic efficiency increased from 47.12 ± 2.71 % to 76.33 ± 1.08 %. This new strategy for releasing EPSs via surfactant treatment improves EET, and consequently, enhances MES efficiency.

Enriched sewage sludge from anaerobic pre-treatment in spurring valorization potential of black soldier fly larvae

The valorization of sewage sludge by black soldier fly larvae (BSFL) has gained attentions for sewage sludge management since the sludge can be reduced securely as well as larval biomass can be used for biorefineries application. Nevertheless, the BSFL growth was impeded while assimilating nutrition from sewage sludge due to the presence of extracellular polymeric substances (EPS) that had entrapped the essential nutrients inside. Accordingly, the pre-treatment of sewage sludge via anaerobic digestion at different pH was employed in this work to rupture the EPS structure and release more nutrients for larval growth. The results showed that larvae fed with raw sewage sludge had attained the lowest final larval weight (2.05 ± 0.38 mg/larva) as opposed to batches fed with pre-treated sewage sludges. This was because the soluble carbohydrate (more than 6.81 ± 1.31 mg of glucose/g sewage sludge) in EPS was released after anaerobic pre-treatment, facilitating larval assimilation for growth. Furthermore, it was observed that further increasing of pH for sewage sludge pre-treatment had led to lower final larval weight gained due to the inhibitory effect stemming from ammonia production at higher pH. The anaerobic pre-treatment of sewage sludge being executed at pH 3 for 8 days had achieved the highest final larval weight at 7.34 ± 0.97 mg/larva. The still low quality of sewage sludges after the pre-treatment also offered benefit, where high sewage sludge reduction and waste reduction index were recorded due to the necessity of BSFL to consume more sewage sludge in compensating the nutrients destitution in sludge. Lastly, the possibility of predicting final larval weight was successfully materialized via a statistical model derived from the multiple linear regression method. The derived model incorporated the interactive parameters of anaerobic pre-treated pH and durations at various combinations could predict the final larval weight.

Reinterpretation of the mechanism of coagulation and its effects in waste activated sludge treatment

Previous studies suggest that the coagulation mechanisms in wastewater and sludge treatment are the same. However, this study found that changes of COD in wastewater and sludge supernatant after the addition of coagulants (Fe3+ and Al3+) were opposite, indicating that the mechanisms of coagulation in these two systems were not the same. The dose of coagulant efficiently reduced the pH of sludge, the higher the dosage, the lower the pH, indicating hydrolytic acidification exists in the sludge coagulation process. Coagulation proved superior to acid conditioning in reducing negative charge and improving the floc size of sludge, demonstrating that the mechanisms of double layer compression, charge neutralization, intraparticle bridging and colloid entrapment are suitable for sludge coagulation. Furthermore, the addition of Fe3+ and Al3+ promoted the exchange of Ca2+ and Mg2+ in extracellular polymeric substances (EPS), which weakened cross-linking between EPS and cells, and further accelerated the disintegration and release of EPS. Due to the mechanisms of hydrolytic acidification and ion exchange, the solid organic matter in sludge was dissolved and released as liquid, resulting in a significant increase of COD in the supernatant of sludge coagulation. In addition, changes in sludge extracellular substances do not reflect changes in intracellular substances well. This study contributes an improved understanding of the mechanism of coagulation in the sludge dewatering treatment.

A unified operating procedure is crucial to evaluate sludge dewaterability, taking the setup of refrigerated storage time as an example

Although extensive efforts have been carried out to study sludge dewatering mechanism, the lack of universal operating procedures makes it never be satisfactorily explained. This study evaluated the impact of a unified operating procedure on waste activated sludge (WAS) dewaterability by taking the setup of refrigerated storage time as an example. It was found that storage time played an important role in determining WAS dewaterability and sampled WAS should be refrigerated within 2 days. The results showed that after 2-d storage, sludge filterability was deteriorated significantly while the extent of dewatering efficiency had little change. Meanwhile, increasing storage time greatly increased the release of extracellular polymeric substances (EPS) and heavy metals, decreased sludge viscosity and weakened its network strength, but had little impact on the floc size and zeta potential of the sludge samples. It can hardly reveal the mechanism of storage time on sludge dewaterability due to the non-uniformity of operating procedures in literatures, which is normally ignored. This study emphasizes a unified operating procedure is crucial to evaluate WAS dewaterability. Therefore, more efforts shall be focused on establishing the uniform operating procedure while advancing applied research in the field of sludge dewatering.

Toxicity mechanism of Nylon microplastics on Microcystis aeruginosa through three pathways: Photosynthesis, oxidative stress and energy metabolism

Nylon has been widely used all over the world, and most of it eventually enters the aquatic environment in the form of microplastics (MPs). However, the impact of Nylon MPs on aquatic ecosystem remains largely unknown. Thus, the long-term biological effects and toxicity mechanism of Nylon MPs on Microcystis aeruginosa (M. aeruginosa) were explored in this study. Results demonstrated that Nylon MPs had a dose-dependent growth inhibition of M. aeruginosa at the initial stage, and the maximum inhibition rate reached to 47.62% at the concentration of 100 mg/L. Meanwhile, Nylon MPs could obstruct photosynthesis electron transfer, reduce phycobiliproteins synthesis, destroy algal cell membrane, enhance the release of extracellular polymeric substances, and induce oxidative stress. Furthermore, transcriptomic analysis indicated that Nylon MPs dysregulated the expression of genes involved in tricarboxylic acid cycle, photosynthesis, photosynthesis-antenna proteins, oxidative phosphorylation, carbon fixation in photosynthetic organisms, and porphyrin and chlorophyll metabolism. According to the results of transcriptomic and biochemical analysis, the growth inhibition of M. aeruginosa is inferred to be regulated by three pathways: photosynthesis, oxidative stress, and energy metabolism. Our findings provide new insights into the toxicity mechanism of Nylon MPs on freshwater microalgae and valuable data for risk assessment of MPs.