Characterization of dissolved extracellular organic matter (dEOM) and bound extracellular organic matter (bEOM) of Microcystis aeruginosa and their impacts on UF membrane fouling

Harvesting of cyanobacteria and phosphorus by electrocoagulation-flocculation-flotation: Role of phosphorus precipitation in cell separations and organics destabilization

A high level of phosphate triggers the excretion of algogenic organic matter (AOM) during algae blooming, leading to disinfection by-products (DBPs) formation. The presence of phosphate could impact cyanobacteria harvesting and AOM separations by electrocoagulation. This study aims to investigate the role of phosphate in cell separations and AOM destabilization by Al-based electrocoagulation-flocculation-flotation (EFF) for harvesting of cyanobacteria and phosphate. The Al-based EFF was conducted to harvest Microcystis aeruginosa (MA) with varied phosphate (0-10 mg/L) at 5 mA/cm2 and pH 8. Fluorescent organic fractions, molecular weight distributions, the properties of flocs and DBPs formation potential were fully investigated. The results showed that the EFF at a low level of phosphate (1 mg/L) effectively improves the harvesting of MA cells, phosphate and the reduction in dissolved organic matter (DOC) up to 99.5 %, 95 % and 50 %, respectively. However, the presence of concentrated phosphate (10 mg/L) alleviates cell harvesting and worsens AOM separations due to ineffective floc formation induced by the fast formation of inactive AlPO4 precipitates along with limited Al(OH)3. At such a condition, it worsens DBPs precursors minimization owing to AOM release from MA cells. The increase in the current density during EFF can compensate for cell harvesting efficiency even though at concentrated phosphate, but it further induces AOM release. It is concluded that Al-based EFF demonstrates an efficient harvesting of cyanobacteria, phosphorus and AOM separations from algae-laden water under phosphate impact.

Comprehensive strategies for microcystin degradation: A review of the physical, chemical, and biological methods and genetic engineering

Addressing the threat of harmful cyanobacterial blooms (CyanoHABs) and their associated microcystins (MCs) is crucial for global drinking water safety. In this review, we comprehensively analyze and compares the physical, chemical, and biological methods and genetic engineering for MCs degradation in aquatic environments. Physical methods, such as UV treatments and photocatalytic reactions, have a high efficiency in breaking down MCs, with the potential for further enhancement in performance and reduction of hazardous byproducts. Chemical treatments using chlorine dioxide and potassium permanganate can reduce MC levels but require careful dosage management to avoid toxic by-products and protect aquatic ecosystems. Biological methods, including microbial degradation and phytoremediation techniques, show promise for the biodegradation of MCs, offering reduced environmental impact and increased sustainability. Genetic engineering, such as immobilization of microcystinase A (MlrA) in Escherichia coli and its expression in Synechocystis sp., has proven effective in decomposing MCs such as MC-LR. However, challenges related to specific environmental conditions such as temperature variations, pH levels, presence of other contaminants, nutrient availability, oxygen levels, and light exposure, as well as scalability of biological systems, necessitate further exploration. We provide a comprehensive evaluation of MCs degradation techniques, delving into their practicality, assessing the environmental impacts, and scrutinizing their efficiency to offer crucial insights into the multifaceted nature of these methods in various environmental contexts. The integration of various methodologies to enhance degradation efficiency is vital in the field of water safety, underscoring the need for ongoing innovation.

Deciphering the Role of Microbial Extracellular and Intracellular Organic Matter in Antibiotic Photodissipation: Molecular and Fluorescent Profiling under Natural Radiation

This study addresses existing gaps in understanding the specific involvement of dissolved organic matter (DOM) fractions in antibiotic photolysis, particularly under natural conditions and during DOM photobleaching. Employing fluorescent, chemical, and molecular analysis techniques, it explores the impact of extracellular and intracellular organic matter (EOM and IOM) on the photodissipation of multiclass antibiotics, coupled with DOM photobleaching under natural solar radiation. Key findings underscore the selective photobleaching of DOM fractions, propelled by distinct chemical profiles, influencing DOM-mediated antibiotic photolysis. Notably, lipid-like substances dominate in the IOM, while lignin-like substances prevail in the EOM, each uniquely responding to sunlight and exhibiting selective photobleaching. Sunlight primarily targets fulvic acid-like lignin components in EOM, contrasting the initial changes observed in tryptophan-like lipid substances in IOM. The lower photolability of EOM, attributed to its rich unsaturated compounds, contributes to an enhanced rate of indirect antibiotic photolysis (0.339-1.402 h-1) through reactive intermediates. Conversely, the abundance of aliphatic compounds in IOM, despite it being highly photolabile, exhibits a lower mediation of antibiotic photolysis (0.067-1.111 h-1). The triplet state excited 3DOM* plays a pivotal role in the phototransformation and toxicity decrease of antibiotics, highlighting microbial EOM's essential role as a natural aquatic photosensitizer for water self-purification. These findings enhance our understanding of DOM dynamics in aquatic systems, particularly in mitigating antibiotic risks, and introduce innovative strategies in environmental management and water treatment technologies.

Preferential adsorption of medium molecular weight proteins in extracellular polymeric substance alleviates toxicity of small-sized microplastics to Skeletonema costatum

Extracellular polymeric substances (EPS) secreted by organisms tend to encapsulate microplastics (MPs), forming an EPS-corona that affects the fate of MPs in marine ecosystems. However, the impact of the EPS-corona on the biotoxicity of MPs to marine organisms remains poorly understood. Herein, the effect of the EPS-corona on the toxicity of polystyrene (PS) MPs of different sizes (0.1 and 1 µm) to Skeletonema costatum (S. costatum) was investigated. The preferential adsorption of medium molecule weight (∼55 kDa) proteins onto PS MPs mainly contributed to the EPS-corona formation, decreasing the surface charge negativity of small-sized PS MPs (0.1 µm) by 72.4 %. Nitrogen (N) and oxygen (O) moieties in polysaccharides and proteins were identified as the preferential adsorption sites in the EPS-PS MPs interaction. Density functional theory (DFT) calculations confirmed the nuclear magnetic resonance spectroscopy (NMR) results, revealing that the binding mode between EPS and PS MPs was mainly hydrogen bonding. In addition, EPS-corona increased the cell density of S. costatum by 35.5-36.0 % when exposed to small-sized PS MPs (0.1 µm, 25-50 mg/L). These findings provide new insights into how EPS-corona affects the environmental fate and ecological risks associated with micro- and nano-sized plastics in marine ecosystems.

Attached indigenous microalgal-bacterial consortium with greater stress-resistance facilitated recovery of integrated fixed-film system after experiencing short-term stagnation inhibition

Stability of integrated fixed-film indigenous microalgal-bacterial consortium (IF-IMBC) requires further investigation. This study focused on the influence of short-term stagnation (STS), caused by influent variations or equipment maintenance, on IF-IMBC. Results showed that the IF-IMBC system experienced initial inhibition followed by subsequent recovery during STS treatment. Enhanced organics utilization was believed to contribute to system recovery. It is proposed that the attached IMBC possessed greater stress resistance. On the one hand, a higher increase in bacteria potentially participating in organic degradation was observed. Moreover, the dominant eukaryotic species significantly decreased in suspended IMBC while its abundance remained stable in the attached state. On the other hand, increased abundance for most functional enzymes was primarily observed in the attached bacteria. This fundamental research aims to bridge the knowledge gap regarding the response of IMBC to variations in operational conditions.

A new concern raised from algal bloom: Organic chloramines in chlorination

Algal blooms have become a significant challenge in water treatment all over the world. In chlorination of drinking water, algal organic matter (AOM) leads to the formation of organic chloramines. The objectives of this review are to comprehensively summarize and discuss the up-to-date researches on AOM-derived organic chloramines and their chemical activities and toxicity, thereby drawing attention to the potentially chemical and hygienic risks of organic chloramines. The predominant algal species in water sources varied with location and season. AOM from cyanobacteria, green algae, and diatoms are composed of diverse composition. AOM-derived amino acids take a low portion of the precursors of organic chloramines. Both experimental kinetic data and quantum chemical calculation demonstrate the preferential formation of organic chloramines in the chlorination of model compounds (amino acids and peptides). Organic chloramines are persistent in water and can transform into dichloro- and trichloro-organic chloramines, unknown low-molecular-weight organic chloramines, and nitrogenous disinfection byproducts with the excess of free chlorine. The active chlorine (Cl+) in organic chloramines can lead to the formation of chlorinated phenolic compounds. Organic chloramines influence the generation and species of radicals and subsequent products in UV disinfection. Theoretical predictions and toxicological tests suggest that organic chloramines may cause oxidative or toxic pressure to bacteria or cells. Overall, organic chloramines, as one group of high-molecular-weight disinfection byproducts, have relatively long lifetimes, moderate chemical activities, and high hygienic risks to the public. Future perspectives of organic chloramines are suggested in terms of quantitative detection methods, the precursors from various predominant algal species, chemical activities of organic chloramines, and toxicity/impact.

Role of low-proportion, hydrophobic dissolved organic matter components in inhibiting methylmercury uptake by phytoplankton

Uptake of methylmercury (MeHg), a potent neurotoxin, by phytoplankton is a major concern due to its role as the primary pathway for MeHg entry into aquatic food webs, thereby posing a significant risk to human health. While it is widely believed that the MeHg uptake by plankton is negatively correlated with the concentrations of dissolved organic matter (DOM) in the water, ongoing debates continue regarding the specific components of DOM that exerts the dominant influence on this process. In this study, we employed a widely-used resin fractionation approach to separate and classify DOM derived from algae (AOM) and natural rivers (NOM) into distinct components: strongly hydrophobic, weakly hydrophobic, and hydrophilic fractions. We conduct a comparative analysis of different DOM components using a combination of spectroscopy and mass spectrometry techniques, aiming to identify their impact on MeHg uptake by Microcystis elabens, a prevalent alga in freshwater environments. We found that the hydrophobic components had exhibited more pronounced spectral characteristics associated with the protein structures while protein-like compounds between hydrophobic and hydrophilic components displayed significant variations in both distributions and the values of m/z (mass-to-charge ratio) of the molecules. Regardless of DOM sources, the low-proportion hydrophobic components usually dominated inhibition of MeHg uptake by Microcystis elabens. Results inferred from the correlation analysis suggest that the uptake of MeHg by the phytoplankton was most strongly and negatively correlated with the presence of protein-like components. Our findings underscore the importance of considering the diverse impacts of different DOM fractions on inhibition of phytoplankton MeHg uptake. This information should be considered in future assessments and modeling endeavors aimed at understanding and predicting risks associated with aquatic Hg contamination.

Effects of different oxidants on the behaviour of microplastic hetero-aggregates

Microplastic hetero-aggregates are stable forms of microplastics in the aqueous environment. However, when disinfecting water containing microplastic hetero-aggregates, the response of them in water to different oxidizing agents and the effect on water quality have not been reported. Our results showed that Ca(ClO)2, K2S2O8, and sodium percarbonate (SPC) treatment could lead to the disaggregation of microplastic hetero-aggregates as well as a rise in cell membrane permeability, which caused a large amount of organic matter to be released. When the amount of oxidant dosing is insufficient, the oxidant cannot completely degrade the released organic matter, resulting in DOC, DTN, DTP and other indicators being higher than before oxidation, thus causing secondary pollution of the water body. In comparison, K2FeO4 can purify the water body stably without destroying the microplastic hetero-aggregates, but it only weakly inhibits the toxic cyanobacteria Microcystis and Pseudanabaena, which may cause cyanobacterial bloom as well as algal toxin and odorant contamination in practical application. Compared with the other oxidizers, K2S2O8 provides better inhibition of toxic cyanobacteria and has better ecological safety. Therefore, when treating microplastic-containing water bodies, we should consider both water purification and ecological safety, and select appropriate oxidant types and dosages to optimize the water treatment.

Physico-chemical treatments for the removal of cyanotoxins from drinking water: Current challenges and future trends

Cyanobacteria are highly prevalent blue-green algae that grow in stagnant and nutrient-rich water bodies. Environmental conditions, such as eutrophication and human activities, increased the cyanobacterial blooms in freshwater resources worldwide. The excessive bloom formation has also resulted in an alarming surge of cyanobacterial toxins. Prolonged exposure to cyanotoxins is a potential threat to natural ecosystems, animal and human health by the spoilage of the quality of bathing and drinking water. Various molecular and analytical methods have been proposed to monitor their occurrence and understand their global distribution. Moreover, different physical, chemical, and biological approaches have been employed to control cyanobacterial blooms and their toxins to mitigate their occurrence. Numerous strategies have been engaged in drinking water treatment plants (DWTPs). However, the degree of treatment varies greatly and is primarily determined by the source, water properties, and operating parameters such as temperature, pH, and cyanotoxin variants and levels. A comprehensive compilation of methods, from traditional approaches to more advanced oxidation processes (AOPs), are presented for the removal of intracellular and extracellular cyanotoxins. This review discusses the effectiveness of various physicochemical operations and their limitations in a DWTP, for the removal of various cyanotoxins. These operations span from simple to advanced treatment levels with varying degrees of effectiveness and differing costs of implementation. Furthermore, mitigation measures applied in other toxin systems have been considered as alternative strategies.

Spatial gradients and molecular transformations of DOM, DON and DOS in human-impacted estuarine sediments

Dissolved organic matter (DOM) constitutes the most active fraction in global carbon pools, with estuarine sediments serving as significant repositories, where DOM is susceptible to dynamic transformations. Anthropogenic nitrogen (N) and sulfur (S) inputs further complicate DOM by creating N-bearing DOM (DON) and S-bearing DOM (DOS). This study delves into the spatial gradients and transformation mechanisms of DOM, DON, and DOS in Pearl River Estuary (PRE) sediments, China, using combined techniques of UV-visible spectroscopy, Excitation-emission matrix (EEM) fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and microbial high-throughput sequencing. Results uncovered a distinct spatial gradient in DOM concentration, aromaticity (SUVA254), hydrophobicity (SUVA260), the content of substituent groups including carboxyl, carbonyl, hydroxyl and ester groups (A253/A203) of chromophoric DOM (CDOM), and the abundances of tyrosine/tryptophan-like protein and humic-like substances in fluorophoric DOM (FDOM). These all decreased from upper to lower PRE, accompanied by a decrease in O3S and O5S components, indicating seaward reduction in the contribution of terrestrial OM, especially anthropogenic inputs. Additionally, sediments exhibited a reduction in molecular diversity (number of formulas) of DOM, DON, and DOS from upper to lower PRE, with molecules tending towards a lower nominal oxidation state of carbon (NOSC) and higher bio-reactivity (MLBL), molecular weight (m/z) and saturation (H/C). While molecular composition of DOM remained similar in PRE sediments, the relative abundance of lignin-like substances decreased, with a concurrent increase in protein-like and lipid-like substances in DON and DOS from upper to lower PRE. Mechanistic analysis identified the joint influence of terrestrial OM, anthropogenic N/S inputs, and microbial processes in shaping the spatial gradients of DOM, DON, and DOS in PRE estuarine sediments. This study contributes valuable insights into the intricate spatial gradients and transformations of DOM, DON, and DOS within human-impacted estuarine sediments.

Antibiotics soil-solution chemistry: A review of environmental behavior and uptake and transformation by plants

The increased use of antibiotics by humans for various purposes has left the environment polluted. Antibiotic pollution remediation is challenging because antibiotics exist in trace amounts and only highly sensitive detection techniques could be used to quantify them. Nevertheless, their trace quantity is not a hindrance to their transfer along the food chain, causing sensitization and the development of antibiotic resistance. Despite an increase in the literature on antibiotic pollution and the development and transfer of antibiotic-resistant genes (ARGs), little attention has been given to the behavior of antibiotics at the soil-solution interface and how this affects antibiotic adsorption-desorption interactions and subsequent uptake and transformation by plants. Thus, this review critically examines the interactions and possible degradation mechanisms of antibiotics in soil and the link between antibiotic soil-solution chemistry and uptake by plants. Also, different factors influencing antibiotic mobility in soil and the transfer of ARGs from one organism to another were considered. The mechanistic and critical analyses revealed that: (a) the charge characteristics of antibiotics at the soil-root interface determine whether they are adsorbed to soil or taken up by plants; (b) antibiotics that avoid soil colloids and reach soil pore water can be absorbed by plant roots, but their translocation to the stem and leaves depends on the ionic state of the molecule; (c) few studies have explored how plants adapt to antibiotic pollution and the transformation of antibiotics in plants; and (d) the persistence of antibiotics in cropland soils can be influenced by the content of soil organic matter, coexisting ions, and fertilization practices. Future research should focus on the soil/solution-antibiotic-plant interactions to reveal detailed mechanisms of antibiotic transformation by plants and whether plant-transformed antibiotics could be of environmental risk.

Insight into coagulation/flocculation mechanisms on microalgae harvesting by ferric chloride and polyacrylamide in different growth phases

FeCl3 and polyacrylamide (PAM) had been used to investigate the effect of coagulation, flocculation, and their combination on algae cells and extracellular organic matter (EOM) at different phases. PAM tended to aggregate particle-like substances, while FeCl3 could interact with EOM. The content of EOM kept rising during the algae growth cycle, while OD680 peaked at about 3.0. At stationary phase Ⅰ, the removal efficiencies of UV254, turbidity and OD680 of the suspension conditioned with FeCl3 + PAM reached (88.08 ± 0.89)%, (89.72 ± 0.36)% and (93.99 ± 0.05)%, respectively. Nevertheless, PAM + FeCl3 exhibited the worst efficiency because of the release of EOM caused by the turbulence. The results suggested that algal cells served as a coagulation aid to facilitate floc formation, while excessive EOM deteriorated harvesting performance. The process of FeCl3 + PAM at stationary phase Ⅰ appears to be a promising technology for microalgae harvesting.

EPS-corona formation on graphene family nanomaterials (GO, rGO and graphene) and its role in mitigating their toxic effects in the marine alga Chlorella sp

GFNs have widespread applications but can harm marine systems due to excessive use and improper disposal. Algae-secreted EPS can mitigate nanomaterial harm, but their impact on GFN toxicity is understudied. Hence, in the present study, we investigated the toxicity of three GFNs, graphene oxide (GO), reduced graphene oxide (rGO), and graphene, in pristine and EPS-adsorbed forms in the marine alga Chlorella sp. At an environmentally relevant concentration of 1 mgL-1, all three GFNs induced considerable oxidative stress and impeded growth and photosynthetic activity of the algae. The order of the toxic potential followed GO > rGO > graphene. The various facets of adsorption of EPS (1:1 mixture of loosely bound, and tightly bound EPS) on GFNs were investigated through microscopy, surface chemical analyses, fluorescence quenching studies, and isotherm and kinetics studies. Amongst the pristine GFNs treated with algal cells, GO was found to exert the maximum negative effects on algal growth. Upon adsorption of EPS over the GFNs, a significant decline in growth inhibition was observed compared to the respective pristine forms which strongly correlated with reduced oxidative stress and enhanced photosynthetic parameters in the cells. The formation of a layer of eco-corona after interaction of GFNs with EPS possibly caused a barrier effect which in turn diminished their toxic potential. The findings from the present investigation offer valuable insights into the environmental toxicity of GFNs and show that the eco-corona formation may lessen the risk posed by these materials in the marine environment.

Al and Mn speciation changes during the pre-oxidation with potassium permanganate and coagulation removing natural organic matter and its membrane fouling behavior

In this study, we systematically explore coagulation behavior, ultrafiltration membrane fouling behavior and the mechanism involved in during the process of pre-oxidation of potassium permanganate and coagulation of aluminum chloride at different condition to treat model pollutants (humic acid, HA) and natural water. The KMnO4 pre-oxidation significantly enhances flocs formation, and for HA artificial water the flocs size increases from 82 to 122 μm at pH 5.5, from 63 to 185 μm at pH 7.0 and from 0 to 75 μm at pH 8.5, respectively, as for natural water it increases from 72 to 139 μm. The enhanced coagulation at pH 5.5 is attributed to the increased polymeric Al speciation after pre-oxidation along with the generated Mn2+ damaging the electric double layer structure. And for pH 8.5 it is mainly caused by the in-situ MnO2 as combination nuclei during pre-oxidation. Besides, for pH 7.0, the combined effect of in-situ MnO2 and the increased polymeric Al speciation both contribute to improvement of the coagulation. What's more, the enhanced Al coagulation by pre-oxidation of KMnO4 also helps alleviate the membrane fouling for both HA artificial water and natural water, and a much rougher surface with larger flocs forms after KMnO4-aided Al coagulation filtration. This study provides an alternative perspective on the mechanism of pre-oxidation coagulation process.

Unveiling the enhancement mechanisms of algogenic extracellular organic matters on chlortetracycline photodegradation: Constitutive relationships of compound components and reactive oxygen species generation

Algogenic extracellular organic matters (EOMs) have been found to play a crucial role in the photodegradation of antibiotics. However, the specific molecular structure compositions of EOMs have not been fully characterized, and the intrinsic association between the structure and the production of ROS remains unclear. In this study, EOMs from Chlorella Vulgaris were characterized using FT-ICR-MS. Based on the FT-ICR-MS results, nine representative model compounds (MCs, i.e., benzene, naphthalene, anthracene, phenanthrene, glucose, l-glutamic, triglyceride, tannic and lignin) were applied to investigate the physicochemical properties of EOMs and the ROS changes induced by the photoreaction of chlortetracycline (CTC). With the help of quenching assays, nine MCs were classified into prone-ROS and non-prone-ROS fractions. Prone-ROS compounds generate O2- upon electron transfer to 3O2, which then produces ·OH after disproportionation to generate hydrogen peroxide. The formation of 1O2 is attributed to energy transfer from prone-ROS to 3O2. Density functional theory revealed that prone-ROS exhibited higher reactivity compared to non-prone-ROS, this finding is as well supported by the result of steady-state photolysis measurement. Our study gives a new insight into photochemical fate of CTC in aquatic environments, providing theoretical basis for assessing antibiotics' ecological risk accurately.

Bio-coatings in permeated cultivation systems: Unprecedented impacts on microalgal monoculture growth and organic matter yield

Bio-coating, a recent and promising approach in attached microalgal cultivation systems, has garnered attention due to its efficiency in enhancing immobilized algal growth, particularly in submerged cultivation systems. However, when the cells are cultured on thin solid microporous substrates that physically separate them from the nutrient medium, it remains unclear whether the applied bio-coatings still have a significant impact on algal growth or the subsequent rates of algal organic matter (AOM) release. Therefore, this current work investigated the role of bio-coatings on the microalgal monoculture growth of one freshwater species, Chlorella vulgaris ESP 31, and one marine species, Cylindrotheca fusiformis on a hydrophilic substrate, polyvinylidene fluoride membrane in a permeated cultivation system. Wide range of bio-coating sources were adapted, with the result demonstrating that bacteria-derived coating promoted algal growth by as high as 140% when compared with the control group for both species. Interestingly, two distinct adaptation mechanisms were observed between the species, with only C. fusiformis demonstrating a positive correlation between cell growth and AOM productivity, particularly in its extracellularly bound fractions. It is worth noting that despite this specific fraction exhibiting the lowest content among all; it displayed significant relevance in terms of AOM productivity. High extracellular protein-to-polysaccharide ratio (>5.7 fold) quantified on bacterial intracellular exudate-coated membranes indirectly revealed an underlying symbiotic microalgal-bacterial interaction. This is the first study showing how bio-coating influenced AOM yield without any physical interaction between microalgae and bacteria. It further confirms the practical benefits of bio-coating in attached cultivation systems.

Evaluation of Front-Face Fluorescence for Assessing Cyanobacteria Fouling in Ultrafiltration

Cyanobacteria fouling in ultrafiltration (UF) drinking water treatment poses a significant threat to the stability and sustainability of the process. Both phycocyanin found in cyanobacteria and the polymer membrane exhibit strong fluorescence, which could be readily detected using front-face excitation-emission matrix (FF-EEM) spectroscopy. In this study, FF-EEM was employed for the nondestructive and in situ characterization of algae fouling evolution in UF, while also analyzing fouling mechanisms and reversibility. The results indicated that phycocyanin fluorescence on the membrane surface showed a linear correlation with the specific algal cell count on the membrane surface before reaching saturation. As fouling progressed, membrane fluorescence decreased, which was associated with the extent of the surface coverage on the membrane. The plateau in membrane fluorescence indicated full coverage, coinciding with the cake filtration mechanism, cake compression, and deterioration of fouling reversibility. These findings highlight the promise of FF-EEM as a valuable tool for monitoring and evaluating fouling of cyanobacteria in UF systems.

Gravity-driven membrane coupled with oxidation technology to modify the surface properties and biofilm formation: Biofouling mitigation

Biofilms caused by biological fouling play an essential role in gravity-driven membranes' (GDMs) flux decline and rejection rate. The effects of ozone, permanganate, and ferrate (VI) in-situ pretreatment on membrane properties and biofilm formation were systematically studied. Due to the selective retention and adsorption of algal organic matter by biofilms and oxidative degradation, the rejection efficiency of dissolved organic carbon (DOC) in algae-laden water pretreated with permanganate by GDM was up to 23.63%. Pre-oxidation extraordinarily postponed flux decline and biofilm formation of GDM and reduced membrane fouling. The total membrane resistance decreased by 87.22%-90.30% within 72 h after pre-ozonation. Permanganate was more effective than ozone and ferrate (VI) in alleviating secondary membrane fouling caused by algal cells destroyed by pre-oxidation. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory revealed that the distribution of electrostatic force (EL), acid-base (AB), and Lifshitz-van der Waals forces (LW) interactions between M. aeruginosa and the released intracellular algogenic organic matter (IOM) and ceramic membrane surface was similar. The membrane and foulants are always attracted to each other by LW interaction at different separation distances. The dominant fouling mechanism of GDM combined with pre-oxidation technology shifts from complete pore blocking to cake layer filtration during operation. After pre-oxidation of algae-laden water by ozone, permanganate, and ferrate (VI), GDM can treat at least 131.8%, 37.0%, and 61.5% more feed solution before forming a complete cake layer. This study provides new insights into the biological fouling control strategies and mechanisms for GDM coupled with oxidation technology, which is expected to alleviate membrane fouling and optimize the feed liquid pretreatment procedure.

Impact of salinity on anaerobic ceramic membrane bioreactor for textile wastewater treatment: Process performance, membrane fouling and machine learning models

Anaerobic membrane bioreactor (AnMBR) shows great potential for textile wastewater treatment, but high salinity in the influent may undermine its performance. This study evaluated the impact of salinity on the treatment performance of an upflow anaerobic sludge blanket (UASB) configured AnMBR using a flat sheet ceramic membrane. The salinity was stepwise increased (0, 5, 10 and 20 g/L) in four phases of the AnMBR operation. Results indicated that increased salinity jeopardized the COD removal efficiency of AnMBR from 92% to 73%, but had a marginal effect on dye removal efficacy (90-96%). Low salinity (5 g/L) boosted the biogas production whilst high salinity (>10 g/L) had a negative impact. Additionally, the increase of salinity resulted in the soluble microbial production (SMP) concentration soar and membrane fouling rate increase, peaking at a salinity of 10 g/L (Phase III) and recovering back to a lower level at a salinity of 20 g/L (Phase IV). This indicated a transition occurrence at a salinity of 10 g/L (Phase III). The microbial diversity analyses further suggested a transition from salinity-sensitive microbes (Aminiphilus, Caldatribacterium, Mesotoga, Methanobrevibacter, Methanobacterium, Methanosaeta) to salinity-tolerant microbes (Longilinea, Ignavibacterium, Rhodovarius, Bosea and Flexilinea). This transition can be associated with the increase SMP concentration and more severe membrane fouling in Phase III, which were mitigated after a new equilibrium was reached when the microbial consortium acclimatized to the high salinity. Finally, a machine learning model of the Adaboost algorithm was established to predict COD removal under different salinities. Importantly, this study revealed that AnMBR process performance and membrane operation can be maintained for high salinity textile wastewater treatment with a halophilic microbial community growth under high-salinity selection pressure.

Regulation and role of extracellular polymeric substances in the defensive responses of Dictyosphaerium sp. to enrofloxacin stress

Algae are susceptible to enrofloxacin (ENR), an antibiotic frequently detected in aquatic environments. However, algal responses, especially the secretion and roles of extracellular polymeric substances (EPS), under ENR exposure remain unknown. This study is the first to elucidate the variation in algal EPS triggered by ENR at both the physiological and molecular levels. The results showed that EPS were significantly (P < 0.05) overproduced along with increased polysaccharide and protein contents in algae exposed to 0.05, 0.5, and 5 mg/L ENR. Secretion of aromatic proteins, especially tryptophan-like substances with more functional groups or aromatic rings, was specifically stimulated. Furthermore, the genes with upregulated expression related to carbon fixation, aromatic protein biosynthesis, and carbohydrate metabolism are direct causes of enhanced EPS secretion. Improved EPS levels increased the cell surface hydrophobicity and provided more adsorption sites for ENR, which strengthened the van der Waals interaction and reduced ENR internalization. The hormesis effects of ENR were alleviated, as illustrated by the less affected cell density, chlorophyll a/b, and carotenoids biosynthesis in algae with EPS. These findings demonstrate the involvement of EPS in algal ENR resistance and promote a deeper understanding of the ecological effects of ENR in aquatic environments.

Toxicity and tolerance mechanism of binary zinc oxide nanoparticles and tetrabromobisphenol A regulated by humic acid in Chlorella vulgaris

Recent studies have reported that nanoparticles (NPs) released into the aquatic environment may interact with persistent organic pollutants such as brominated flame retardants, whereas the environmental processes and toxicological impacts induced by such binary NPs require further specification. This study investigated the ultrastructural damage of Chlorella vulgaris triggered by exposure to zinc oxide (ZnO) NPs, tetrabromobisphenol A (TBBPA), ZnO-TBBPA, and ZnO-TBBPA-humic acid (HA), clarified the uptake and distribution of ZnO NPs in cells, and explored the physiological toxicity and tolerance mechanism. The results demonstrated that ZnO NPs induced irregular morphology in algal cells, and the disruption of the cellular ultrastructure by binary ZnO-TBBPA was also extremely severe due to the excessive uptake of ZnO NPs, which resulted in strong oxidative stress responses. In particular, the accumulation of reactive oxygen species further exacerbated the reduction of total chlorophyll content and algal density. Moreover, the cluster heat map and correlation analysis revealed that superoxide dismutase activity played a critical role in alleviating lipid peroxidation damage and enhancing the tolerance of algal cells to the stress of binary ZnO NPs. More notably, the existence of HA intensified the dispersion stability of NP suspensions and significantly mitigated the synergistic toxicity of binary ZnO-TBBPA. This study provides new insights into the environmental behavior and biological impacts of binary NPs in the natural environment.

Photobleaching-induced changes in the optical and photochemical properties of algal organic matter

Algal organic matter (AOM), a significant source of endogenous dissolved organic matter (DOM) is released in high concentrations during cyanobacterial blooms, along with cyanotoxins. Subsequent photobleaching of AOM is an important phenomenon to investigate. In this study, intracellular organic matter (IOM) and extracellular organic matter (EOM) were extracted from cultured cyanobacteria taken from Taihu Lake in China. The formation of photochemically produced reactive intermediates in different stages of IOM and EOM photobleaching was compared to Suwannee River DOM (SRDOM, reference standard DOM). Results revealed notable differences influenced by the pigment component among IOM, EOM, and SRDOM. The pigment in IOM contributed to a triplet state pool with strong energy-transfer but limited electron-transfer capabilities. Notably, IOM exhibited the highest triplets state quantum yield value in the visible region, suggesting its potential significance in pollutant degradation in deeper water layers. For EOM, one of the pools exhibits photolability and remarkable electron-transfer capability, indicating it as a high-energy triplet state component. Moreover, three cyanotoxins (MC-LR, ACA, and ATX-a) were detected in the extracted AOM, and their photodegradation was monitored during the AOM photobleaching process. This highlights the potential role of AOM as a photosensitizer in the natural self-cleaning mechanisms of water bodies, facilitating the degradation of organic pollutants through photochemical reactions. The findings of this study contribute to understanding the dynamic nature of AOM and its implications in environmental processes.

Distinct seasonal variations of dissolved organic matter across two large freshwater lakes in China: Lability profiles and predictive modeling

Biological lability of dissolved organic matter (DOM) is a crucial indicator of carbon cycle and contaminant attenuation in freshwater lakes. In this study, we employed a multi-stage plug-flow bioreactor and spectrofluorometric indices to characterize the seasonal variations in DOM composition and lability across Poyang Lake (PY) and Lake Taihu (TH), two large freshwater lakes in China with distinct hydrological seasonality. Our findings showed that the export of floodplain-derived organics and river-lake interaction led to a remarkable increase in terrestrial aromatic and humic-like DOM with high molecular weights and long turnover times in PY. Consequently, the labile fraction was extremely low (average LDOC% of 3%) during the rising-to-flood season (spring and summer). Conversely, autochthonous production in TH considerably enriched semi-labile (average SDOC% of 26%) and biodegradable DOM (average BDOC% of 34%) during the phytoplankton bloom to post-bloom season (summer and autumn). This was reflected by the accumulation of low-light-absorbing and protein-like components with high biological and fluorescence indices. In the dry and non-bloom season (winter), the better preservation of humic substances maintained the high molecular weight and humic degree of DOM in PY, while the decay of aquatic plants strengthened autochthonous production, resulting in a similar BDOC% of PY samples (23%-34%) to TH samples (18%-33%). We further applied partial least squares regression using DOM optical indices as predictive proxies, which generated a greater prediction strength for BDOC% (R² = 0.80) compared to SDOC% (R² = 0.57) and LDOC% (R² = 0.28). The regression model identified aromaticity (SUVA₂₅₄) as the most effective and negative predictor and low molecular weight (A₂₅₀/A₃₆₅) as the highly and positively influential factor. Our study provides new evidence that the seasonality of DOM lability profiles is regulated by the trade-off between flow-related variation and phytoplankton production, and presents an approach to describe and predict DOM lability across freshwater lakes.

Autochthonous DOM had solar disinfection effect but nitrate counteracted with them

Pathogens in natural water can pose great threat to public health and challenge water quality. In sunlit surface water, dissolved organic matters (DOMs) can inactivate pathogens due to their photochemical activity. However, the photoreactivity of autochthonous DOM derived from different source and their interaction with nitrate on photo-inactivation remained limited understood. In this study, the composition and photoreactivity of DOM extracted from Microcystis (ADOM), submerged aquatic plant (PDOM) and river water (RDOM) were studied. Results revealed that lignin and tannin-like polyphenols and polymeric aromatic compounds negatively correlated with quantum yield of ³DOM*, whilst lignin like molecules positively correlated with •OH generation. ADOM had highest photoinactivation efficiency of E. coli, followed by RDOM and PDOM. Both the photogenerated •OH and low energy ³DOM* could inactivate bacteria damaging cell membrane and causing increase of intracellular reactive species. PDOM with more phenolic or polyphenols compounds not only weaken its photoreactivity, also increase regrowth potential of bacteria after photodisinfection. The presence of nitrate counteracted with autochthonous DOMs on photogeneration of •OH and photodisinfection activity, as well as increased the reactivation rate of PDOM and ADOM, which might be attributed to the increase of survival bacteria and more bioavailable fractions provided in systems.

Pre-oxidation coupled with charged covalent organic framework membranes for highly efficient removal of organic chloramines precursors in algae-containing water treatment

Organic chloramines in water would pose both chemical and microbiological risks. It is essential to remove the precursors of organic chloramine (amino acids and decomposed peptides/proteins) to limit its formation in disinfection. In our work, nanofiltration was chosen to remove organic chloramines precursors. To solve the "trade-off" effect and low rejection of small molecules in algae organic matter, we synthesized a thin film composite (TFC) nanofiltration (NF) membrane with a crumpled polyamide (PA) layer via interfacial polymerization on polyacrylonitrile (PAN) composite support loaded with covalent organic framework (COF) nanoparticles (TpPa-SO₃H). The obtained NF membrane (PA-TpPa-SO₃H/PAN) increased the permeance from 10.2 to 28.2 L m^-2 h^-1 bar^-1 and the amino acid rejection from 24% to 69% compared to the control NF membrane. The addition of TpPa-SO₃H nanoparticles decreased the thickness of PA layers, increased the hydrophilicity of the membrane, and increased the transition energy barrier for amino acids transferring through the membrane, which was identified by scanning electron microscope, contact angle test, and density functional theory computations, respectively. Finally, pre-oxidation coupled with PA-TpPa-SO₃H/PAN membrane nanofiltration on the limitation of organic chloramines formation was evaluated. We found that the combined application of KMnO₄ pre-oxidation and PA-TpPa-SO₃H/PAN membranes nanofiltration in algae-containing water treatment could minimize the formation of organic chloramines in subsequent chlorination and maintain a high flux during filtration. Our work provides an effective way for algae-containing water treatment and organic chloramines control.

Fluorescence and molecular weight dependence of disinfection by-products formation from extracellular organic matter after ultrasound irradiation

Algal blooms have a negative impact on the safety of drinking water. Ultrasonic radiation technology is an "environment-friendly" technology that is widely used in algae removal. However, this technology leads to the release of intracellular organic matter (IOM), which is an important precursor of disinfection by-products (DBPs). This study investigated the relationship between the release of IOM in Microcystis aeruginosa and the generation of DBPs after ultrasonic radiation as well as analyzed the generation mechanism of DBPs. Results showed that the content of extracellular organic matter (EOM) in M. aeruginosa increased in the order of 740 kHz >1120 kHz >20 kHz after 2 min of ultrasonic radiation. Organic matter with a molecular weight (MW) greater than 30 kDa increased the most, including protein-like, phycocyanin (PC) and chlorophyll a, followed by small-molecule organic matter less than 3 kDa, mainly humic-like substances and protein-like. DBPs with an organic MW range of less than 30 kDa were dominated by trichloroacetic acid (TCAA), while those with an MW greater than 30 kDa had the highest trichloromethane (TCM) content. Ultrasonic irradiation changed the organic structure of EOM, affected the amount and type of DBPs, and tended to generate TCM.

Treatment of micro-polluted water with low C/N ratio by immobilized bioreactor using PVA/sintered ores@sponge cube: Performance effects and potential removal pathways

The widespread use of industrial products containing lead (Pb²⁺) and tetracycline (TC) medications led to the combined pollution of nitrate, Pb²⁺, and TC in water. A novel biomaterial containing polyvinyl alcohol (PVA) and sponge cube with sintered ores (PVA/sintered ores@sponge cube) was prepared to ensure the maximum NO₃^--N removal efficiency (96.21 %) of the bioreactor under the hydraulic retention time (HRT) of 7.0 h, pH of 6.0, and the carbon to nitrogen (C/N) of 1.5 that had the ability to remove TC and Pb²⁺ synergistically. Composite pollutants slightly decreased denitrification performance in the combined pollution system on account of the addition of sintered ores. Results of scanning electron microscopy (SEM) showed that the sintered ores in the biocarrier induced denitrification and the adsorption of bio‑iron oxides were involved in the removal of TC and Pb²⁺. The simultaneous removal of composite pollutants during denitrification was facilitated by extracellular polymeric substances (EPS) as revealed by Fourier transform infrared spectroscopy (FTIR) and fluorescence excitation-emission matrix (EEM). In addition, high-throughput sequencing results showed that Zoogloea had the highest proportion in the bioreactor.

Metabolites of extracellular organic matter from Microcystis and Dolichospermum drive distinct modes of carbon, nitrogen, and phosphorus recycling

Algal extracellular organic matter (EOM) metabolites exert considerable impact on the carbon (C), nitrogen (N), and phosphorus (P) cycles mediated by attached bacteria. Field investigations were conducted in two ponds to explore the relationship among EOM metabolites from Microcystis and Dolichospermum, co-occurring microbes, and nutrient recycling from April 2021 to December 2021. Microcystis blooms primarily produced more complex bound EOM (bEOM) metabolites with many amino acid components, which facilitated bacterial colonization and provided sufficient substrates for ammonification. Meanwhile, high abundances of dissimilatory nitrate reduction to ammonium genes from co-occurring microbes such as Rhodobacter have demonstrated their strong N retention ability. Metabolic products of bEOM from Microcystis comprise a large number of organic acids that can solubilize non-bioavailable P. All these factors have collectively resulted in the increase of all fractions of N and P, except for nitrate (NO₃^--N) in the water column. In contrast, the EOM metabolite from Dolichospermum was simple, coupled with high abundance of functional genes of α-glucosidase, and produced small molecular substances fueling denitrification. The metabolic products of EOM from Dolichospermum include abundant N-containing substances dominated by heterocyclic substances, suggesting that the metabolic products of Dolichospermum are not conducive to N regeneration and retention. Therefore, the metabolic products of EOM from Microcystis triggered a shift in the attached microbial community and function toward C, N, and P recycling with close mutual coupling. Acquisition of N and P in Dolichospermum is dependent on itself based on N fixation and organic P hydrolysis capacity. This study provides a new understanding of the contribution of algal EOM to the nutrient cycle.

Microalgal wastewater recycling: Suitability of harvesting methods and influence on growth mechanisms

Wastewater recycling helps address the challenge of microalgae biomass commercialization by allowing for efficient resource recovery. In this study, three conventional harvesting methods, including centrifugation, microfiltration, and flocculation sedimentation, were investigated to explore the effects of harvesting methods on the characteristics of recycled wastewater and the growth of microalgae to select a suitable harvesting method for the microalgal wastewater recycling system. During the wastewater recycling process, the least amount of accumulated substances was exhibited in the wastewater recycled by microfiltration, followed by centrifugation, and the most by flocculation sedimentation. After 4 batches of cultivation, microalgal biomass harvested from centrifugation wastewater and microfiltration wastewater was 21.26 % and 13.54 % higher than that from flocculation wastewater, respectively. Lipids, carbohydrates and pigments were all increased by varying degrees. Additionally, flocculation sedimentation was not suitable for the microalgal wastewater recycling process since the low residual nutrients, high salinity, and excessive algal organic matter severely inhibited the growth of microalgae. Under the regulation of phytohormones, microalgae increased their energy reserves, enhanced photosynthesis, and improved their defense capability to resist the increasing abiotic stress. This study provides scientific support for the selection of suitable harvesting technology during the microalgal wastewater recycling process.

Extracellular polymeric substances enhance dissolution and microbial methylation of mercury sulfide minerals

Due to the extremely low solubility, mercury sulfide minerals, as the major environmental mercury sinks, are generally considered to be inert mercury species with minimal bioavailability. Here, we demonstrate that extracellular polymeric substances (EPS), continuously secreted and released by anaerobic methylating bacteria, enhance the dissolution processes of cinnabar (α-HgS) minerals. The enhancing effects of EPS occur to a greater extent in the dissolution of nanoparticulate α-HgS compared to the bulk-scale counterpart. The released EPS-Hg(II) species are available for microbial methylation to produce bioaccumulative neurotoxin, methylmercury. This is probably due to the abundant aromatic proteins in EPS that strongly interact with surface Hg(II) via inner-sphere complexation as well as cation-π interaction. Our study discovers the potential environmental risks of "inert" mercury sulfide minerals in natural microbial habitats, particularly benthic biofilms with abundant microbial EPS, transformed to the severely toxic methylmercury. The mechanistic findings will facilitate an accurate understanding of the interactions between soft and transition metals and microorganism-derived organics, which may dictate the environmental fate and impact of these elements.

Positive effects of magnetic Fe3O4@polyaniline on aerobic granular sludge: Aerobic granulation, granule stability and pollutants removal performance

The magnetic material has been determined to have a positive effect on sludge granulation and wastewater treatment performance. In this study, the effect of magnetic Fe₃O₄@polyaniline (Fe₃O₄@PANI) on aerobic granulation, granule stability, and pollutants removal performance was evaluated by adding it into a sequencing batch reactor to cultivate aerobic granular sludge (AGS). The results indicated that the composite combined the advantages of PANI and Fe₃O₄ to promote the formation of AGS during the granulation period. The Fe₃O₄@PANI stimulated the granules to secrete extracellular polymeric substances with a higher proteins/polysaccharides ratio, thus enhancing the stability of the AGS. In addition, microbial community analysis revealed that the great performance of the AGS on denitrification and phosphorus removal could be attributed to the enrichment of denitrifying bacteria, phosphorus accumulating organisms (PAO), and denitrifying PAO by Fe₃O₄@PANI. Thus, Fe₃O₄@PANI has been demonstrated to have a positive effect on the formation and stability of AGS.

Evaluation of membrane fouling at elevated temperature impacted by algal organic matter

Membrane distillation (MD) is a thermally driven technology applied in desalination and water reuse with utilisation of sustainable energy. However, algal organic matter (AOM) could foul membrane critically and plague MD's long-term operational stability. In this study, the soluble extracellular polymeric substance (sEPS) and intracellular organic matter with bound extracellular polymeric substance (IOM + bEPS) of two algal species (Amphora coffeaeformis and Navicula incerta) were exposed to 60 °C, 70 °C and 80 °C for 8 h with polypropylene hydrophobic membrane, simulating heated AOMs contacted with membrane inside MD unit, to study the temperature effect on membrane fouling. The dissolved carbohydrate and protein in the sEPS and IOM + bEPS samples generally increased after being heated. Heating caused cell lysis and the release and dissolution of carbohydrate and protein from sEPS, IOM and bEPS into water. As heating temperature increased, the carbohydrate release from the AOM usually increased. The contact angle of membrane contacted with sEPS and IOM + bEPS reduced significantly after heat treatment. The reduction in IOM + bEPS was larger than sEPS, in line with SEM analysis, indicating membrane surfaces and pores with IOM + bEPS fouled more severely than sEPS. It is due to higher hydrophobicity in IOM + bEPS causing adherence to membrane and presence of amphiphiles. High protein, lipid, and saturated fats proportions also cause severe fouling. SEM-EDX analysis indicated presence of O, Na, Cl and Mg elements, pointing to carbohydrate and lipids, and salt trapped in foulants. AOM heating and composition had direct effect to the membrane integrity, dictating severity of fouling in MD operations.

Impacts of algal organic matter and humic substances on microcystin-LR removal and their biotransformation during the biodegradation process

The application of bioaugmentation (i.e., injection of contaminant-degrading microorganisms) has shown its potential to remove harmful cyanotoxins like microcystin-LR (MC-LR) from drinking water sources. However, the natural organic matter (NOM) present in both natural and engineered water systems might affect the bacterial biodegradation of MC-LR. Therefore, for the successful application of bioaugmentation for MC-LR removal in water treatment, it is important to understand NOM effects on MC-LR biodegradation. In this study, the impact of NOM [algal organic matter (AOM) and humic substances (HS)] on MC-LR biodegradation was evaluated in the presence of varying concentrations of NOM by monitoring MC-LR biodegradation kinetics. The changes in NOM composition during MC-LR biodegradation were also characterized by a five-component Parallel factor (PARAFAC) model using 336 excitation-emission matrix (EEM) spectra collected at different sampling points. Our results showed decreases in MC-LR biodegradation rate of 1.6-and 3.4-fold in the presence of AOM and HS, respectively. The expression of the functional mlrA gene exhibited a similar trend to the MC-LR degradation rate at different NOM concentrations. EEM-PARAFAC analyses and NOM molecular size fractionation results indicated a relatively greater production of terrestrial humic-like components (57%) and a decrease of protein-like components. Two-dimensional correlation spectroscopy (2D-COS) analyses further confirmed that low molecular weight protein-like components were initially utilized by bacteria, followed by the formation of higher molecular weight humic-like components, likely due to microbial metabolism.

Reduction mechanisms of V5+ by vanadium-reducing bacteria in aqueous environments: Role of different molecular weight fractionated extracellular polymeric substances

Extracellular polymeric substances (EPS) are high-molecular polymers secreted by microbes and play essential roles in metallic biogeochemical cycling. Previous studies demonstrated the reducing capacity of the functional groups on EPS for metal reduction. However, the roles of different EPS components in vanadium speciation and their responsible reducing substances for vanadium reduction are still unknown. In this study, the EPS of Bacillus sp. PFYN01 was fractionated via ultrafiltration into six components with different kDa (EPS_>100, EPS_100-50, EPS_50-30, EPS_30-10, EPS_10-3, and EPS_<3). Batch reduction experiments of the intact cells, EPS-free cells, the pristine and fractionated EPS with V⁵⁺ were conducted and characterized. The results demonstrated that the extracellular reduction of V⁵⁺ into V⁴⁺ by EPS was the major reduction process. Among the functional groups in EPS, C=O/C-N of amide in protein/polypeptide and CO of carboxyl in fulvic acid-like substances might act as the reductants for V⁵⁺, while CO in polysaccharide molecules and PO in phosphodiester played a key role in the adsorption process. The intracellular reduction was via translocating V⁵⁺ into the cells and releasing V⁴⁺ by the intracellular reductases. The reducing capacity of the fractionated EPS followed a sequence of EPS_<3 > EPS_10-3 > EPS_50-30 > EPS_100-50 > EPS_30-10 > EPS_>100. The small molecules of fulvic acid-like substances and amino acids were responsible for the high reducing capacity of EPS_<3. EPS_>100 had the lowest reducing capacity due to its macromolecular structure decreasing the exposure of the reactive sites. In addition to reduction, those intermediate EPS components may also have supporting functions, such as connecting protein skeletons and increasing the specific surface area of EPS. Therefore, the diverse effects of the EPS components cannot be neglected in vanadium biogeochemical cycling.

Production of Fluorescent Dissolved Organic Matter by Microalgae Strains from the Ob and Yenisei Gulfs (Siberia)

Dissolved organic matter (DOM) is an important component of aquatic environments; it plays a key role in the biogeochemical cycles of many chemical elements. Using excitation-emission matrix fluorescence spectroscopy, we examined the fluorescent fraction of DOM (FDOM) produced at the stationary phase of growth of five strains of microalgae sampled and isolated from the Ob and Yenisei gulfs. Based on the morphological and molecular descriptions, the strains were identified as diatoms (Asterionella formosa, Fragilaria cf. crotonensis, and Stephanodiscus hantzschii), green microalgae (Desmodesmus armatus), and yellow-green microalgae (Tribonema cf. minus). Three fluorescent components were validated in parallel factor analysis (PARAFAC): one of them was characterized by protein-like fluorescence (similar to peak T), two others, by humic-like fluorescence (peaks A and C). The portion of fluorescence intensity of humic compounds (peak A) to the total fluorescence intensity was the lowest (27 ± 5%) and showed little variation between species. Protein-like fluorescence was most intense (45 ± 16%), but along with humic-like fluorescence with emission maximum at 470 nm (28 ± 14%), varied considerably for different algae strains. The direct optical investigation of FDOM produced during the cultivation of the studied algae strains confirms the possibility of autochthonous production of humic-like FDOM in the Arctic shelf regions.

In-situ enrichment and application of heterotrophic nitrification-aerobic denitrification bacteria in membrane aerated biofilm reactor

In order to reduce the resource and energy consumption of traditional biological nitrogen removal (BNR) process, heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was in situ enriched in membrane aerated biofilm reactor (MABR) by inoculating conventional activated sludge. Contaminants removal performance, EPS composition and microbial community were explored. The results indicated that the average removal efficiency of COD and TN under optimal condition reached 84.13% and 91.54%, respectively, which demonstrated that the reactor possessed excellent contaminants removal capacity. EPS analysis suggested that abundant protein especially tryptophan protein-like substance played a vital role in maintaining the microbial stability of biofilms. Multiple HN-AD genera, mainly Paracoccus, were detected with the highest relative abundance of 54.70%, which confirmed the successful enrichment of the HN-AD bacteria. Conventional nitrifiers and denitrifiers also thrived in biofilm, which demonstrated the synergistic nitrogen removal of multiple microorganisms. This study provided important insights into application of HN-AD bacteria and synergistic nitrogen removal in BNR system.

A novel gravity sedimentation - Forward osmosis hybrid technology for microalgal dewatering

A novel gravity sedimentation - forward osmosis (G-FO) hybrid reactor was built up for separating and concentrating the biomass from the algal-rich water (microalgal dewatering). The extracellular organic matter (EOM) from Chlorella vulgaris (C. vulgaris) was divided into dissolved EOM (dEOM) and bound EOM (bEOM). Water flux, flux recovery rate and moisture content (MC) were investigated. Through sedimentation rate, zeta potential and hydrophilicity/hydrophobicity to analyze the experimental results. Scanning electronic microscopy (SEM) was used to observe the different morphologies of accumulated algae cells and EOM on the surface of the membrane. The results showed that cell + bEOM solution had the fastest sedimentation rate and fewest negative charge, so the pollutants accumulated more easily on the membrane surface, resulting in the highest flux decline. Its algal cake layer was the densest from the view of SEM. Cell + bEOM + dEOM solution had the lowest flux decline and the cake layer was the loosest. Cell + bEOM solution had the most severe irreversible fouling and the lowest flux recovery rate (FRR). The membrane fouling of cell solution was lower than that of cell + bEOM + dEOM solution, and the FRR of cell solution was almost 100%. According to the nonionic macro-porous resin fraction results of EOM, cell + bEOM + dEOM solution contained more hydrophilic components, resulting in the lowest MC. On the contrary, cell + bEOM solution showed the highest MC, which contained more hydrophobic components. Effects of bEOM and dEOM on microalgae dewatering performance of a novel gravity sedimentation - forward osmosis (G-FO) hybrid system were investigated, which provided a theoretical basis for large-scale application of FO technology for microalgae dewatering.

Enhancing ultrafiltration of algal-rich water using ferrate activated with sodium percarbonate: Foulants variation, membrane fouling alleviation, and collaborative mechanism

Ultrafiltration (UF) is a reliable method to treat algal-rich water, whereas severe membrane fouling has impeded its actual application. To improve UF performance and alleviate membrane fouling resulted by algal foulants, a novel strategy coupling ferrate (Fe(VI)) and sodium percarbonate (SPC) was proposed. During the coupling process, Fe(VI) was activated by SPC to generate high-valent Fe intermediates (Fe(V) and Fe(IV)), which played a crucial role in high-efficiency oxidation for algal foulants, and the in-situ formed Fe(III) particles decomposed by Fe(VI) also enhanced the coagulation and adsorption capacity to the coupling system. Under the triple effects of coagulation, adsorption and oxidation, the algal foulants were efficiently eliminated. The zeta potential increased from -32.70 mV to -6.56 mV at most, the particle size was significantly enlarged, and the generated flocs possessed a great settleability. The morphology, viability, and integrity of algae cells were effectively maintained. The dissolved organic matters and fluorescent organics were efficiently removed, as well as macromolecular organics were reduced into lower molecular weight components. With the collaborative effect of Fe(VI) and SPC, the terminal specific flux was increased from 0.29 to 0.92, and the reversible and irreversible fouling resistances were reduced by 98.5% and 69.4%, individually. The surface functional groups were changed, and the dominant mechanisms were also converted to pore blocking from cake layer filtration. Overall, the experimental results would provide some new thoughts in actual production for algal-rich water treatment and UF membrane fouling alleviation.

Toxicity alleviation and metabolism enhancement of nonylphenol in green algae Dictyosphaerium sp. by NaHCO3

Nonylphenol (NP) toxicity limits the improvements in its algal remediation efficiency. This study comprehensively investigated the performance and mechanism of NaHCO₃-driving effects on NP-exposed algae. The results showed that NaHCO₃ enhanced algal resistance to NP and the corresponding EC₅₀ values increased 1.31-4.25 times. Further, the toxicological effects of NP reduced with increasing pyrenoid volume and chlorophyll and carotenoids production, and decreasing cellular damage degree. Moreover, the concentration of extracellular polymeric substances was enhanced and more NP adsorption sites were formed. Consistently, RNA-seq demonstrated significant expression alterations in genes related to energy metabolism, cellular synthesis, photosynthesis, and carbon fixation. Besides, NP biodegradation rate was increased by 15.2 % and 11.1 % in the 1, and 4 mg/L NP treatments, respectively. Identification of degradation intermediates and their toxicity via Ecological Structure Activity Relationship program showed that NaHCO₃ accelerated sequential α-C removal from NP in algae with faster generation of less toxic metabolites, namely, 4-ethylphenol, 4-cresol and 4-hydroxybenzoic acid. This study provides new insights into the role of NaHCO₃ in toxicity alleviation and metabolism enhancement of NP in algae and can assist NP bioremediation efforts in aquatic environment.

Enhancing Effects of Sludge Biochar on Aerobic Granular Sludge for Wastewater Treatment

Sludge biochar can be used as bio-carrier to enhance aerobic granular sludge, however, its impact on the formation and especially long-term stability of aerobic granules has not been fully investigated. In this paper, aerobic granular sludge was cultivated in two parallel sequencing batch reactors (SBRs), R1 and R2, with and without sludge biochar addition in the activated sludge inoculum, respectively. The sludge characteristics, wastewater treatment performance, and microbial community structure of granular sludge were examined on a 240-day operation, during which aerobic granular sludge in the two reactors experienced dynamic changes including granule formation, maturation, breakage, filamentous proliferation, and recovery. Aerobic granules in R1 with biochar formed two weeks earlier than that in R2, presenting a larger mean size, and higher settling ability and biomass retention in the granule maturation period. Concurrently, aerobic granules in R1 showed higher denitrification ability with over 80% removal efficiency throughout the whole operation period. During the maturation period, the ratio of food to biomass (F/M) in R1 was below 0.5 gCOD/gVSS d while it ranged between 0.5 and 1.0 gCOD/gVSS d in R2 due to lower biomass retention. The elemental analysis showed more Ca and P accumulation in aerobic granular sludge from R1, with 3% Ca and 2.75% P in sludge from R1 and 0.91% Ca and 0.75% P in sludge from R2, respectively. The microbial community in R1 had higher richness, diversity, excretion of extracellular polymer substances (EPSs) and abundance of denitrifying genera than that in R2, supporting its higher stability and denitrification performance. These results demonstrated that aerobic granular sludge formed by using sludge biochar as a carrier for granulation can speed up granule formation, improve denitrification performance, and enhance the long-term stability of aerobic granules. The findings disclosed the enhancing effects of biochar for wastewater treatment by aerobic granular sludge, suggesting the potential of practical application of biochar in aerobic granular sludge-based reactors.

The binding effect and photooxidation on oxytetracycline with algal extracellular polymeric substances and natural organic matter

Surface water contains a large amount of dissolved organic matter (DOM). Interactions between DOM and micropollutants have a significant impact on micropollutant degradation. In this study, algal extracellular polymeric substances (EPS) and natural organic matter (NOM) were selected as two DOM sources and oxytetracycline (OTC) as a representative micropollutant. EPS was mainly composed of tryptophan and protein-like organics, while NOM was mainly composed of fulvic acid-like, humic acid-like, and hydrophobic acid components. In addition, OTC degradation significantly decreased when bound with EPS and the C=O and C-H bonds of CH₂ or CH₃ groups may be involved in binding EPS and OTC, respectively, while -COOH may be involved in the binding of NOM and OTC. Furthermore, triplet intermediates were found to play a major role in OTC photodegradation in both EPS and NOM, with the contribution calculated as 49.96% and 44.61%, respectively. Steady-state concentrations of ³EPS* in EPS and ³NOM* in NOM were 3.59 × 10^-14 mol L^-1 and 5.54 × 10^-15 mol L^-1, respectively. These results provide new insights into the degradation of antibiotic-containing wastewater in the natural environment or engineering applications.

Algal extracellular organic matter pre-treatment enhances microalgal biofilm adhesion onto microporous substrate

Adhesive biocoating has microstructure composed of biomolecules to entrap viable cells in a stabilized matrix over exposed surfaces. Although marine benthic diatoms are a common group of algae excreting substantial amount of extracellular polymeric substances (EPS), studies regarding the utilization of these EPS are scarce. Using the soluble EPS derived from Navicula incerta and pre-deposition of it as a thin conditioning layer on microporous polyvinylidene fluoride (PVDF) membranes, the pre-coated surface was used to investigate the cell binding affinity of three marine microalgae, namely Amphora coffeaeformis, Cylindrotheca fusiformis and Navicula incerta. Microalgae actively engaged themselves on the pre-coated membranes which was 10 times greater than the initial cell adhesion degree. Soluble EPS is mainly comprised of polysaccharide while bounded EPS is mainly comprised of protein. On EPS pre-coated membranes, N. incerta released the least amount of bounded polysaccharides (<100 mg m^-2) and vice versa for the other two because EPS production is usually maximized to assist cell adhesion onto unfavorable substrates. In stark contrast, when the adaptation period (first 6 h) ended, cells began to secrete more bounded protein for cell growth, and an increasing trend of protein content found in N. incerta has verified its optimal adaptation onto the biocoating itself. On pristine PVDF membranes, the adhesion degree was ranked in ascending order: C. fusiformis, N. incerta and A. coffeaeformis. Interestingly, after the pre-coating process, the order was reported as: A. coffeaeformis, N. incerta and C. fusiformis, but it should be noted that C. fusiformis demonstrated fluctuating cell colonization degree and bounded EPS production over time. In other words, the biofilm's susceptibility was confirmed since the cells latched loosely on the membranes rather than in a biofilm matrix. Biocoating enables uniform cell distribution and firmer biofilm growth, opening the door to vast future applications in environmental bioremediation and sensing.

Effect of free ammonia shock on Chlorella sp. in wastewater: Concentration-dependent activity response and enhanced settleability

The unstable microbial activity and unsatisfactory settling performance impede the development and implementation of microalgal wastewater treatment, especially in high-ammonium wastewater in the presence of free ammonia (FA). The shock of FA due to the nutrient fluctuation in wastewater was demonstrated as the primary stress factor suppressing microalgal activities. Recent study has clearly revealed the inhibition mechanism of FA at a specific high level (110.97 mg/L) by inhibiting the genetic information processing, photosynthesis, and nutrient metabolism. However, the effects of various FA shock concentrations on microalgal activities and settling performance remain unknown, limiting the wastewater bioremediation efficiencies improvement and the process development. Herein, a concentration-dependent shock FA (that was employed on microalgae during their exponential growth stages) effect on microalgal growth and photosynthesis was observed. Results showed that the studied five FA shock concentrations ranging from 25 to 125 mg/L significantly inhibited biomass production by 14.7-57.0%, but sharp reductions in photosynthesis with the 36.0-49.0% decreased Fv/Fm values were only observed when FA concentration was above 75.0 mg/L. On the other hand, FA shock enhanced microalgal settling efficiency by 12.8-fold, which was believed to be due to the stimulated intra- and extracellular protein contents and thereby the enhanced extracellular polymer substances (EPS) secretion. Specifically, FA shock induced 40.2 ± 2.3% higher cellular protein content at the cost of the decreased carbohydrates (22.6 ± 1.3%) and fatty acid (39.0 ± 0.8%) contents, further improving the protein secretion by 1.21-fold and the EPS production by 40.2 ± 2.3%. These FA shock-induced variations in intra- and extracellular biomolecules were supported by the up-regulated protein processing and export at the assistance of excessive energy generated from fatty acid degradation and carbohydrates consumption. In addition, FA shock significantly decreased the biomass nutritional value as indicated by the 1.86-fold lower essential amino acid score and nearly 50% reduced essential to non-essential amino acids ratio, while slightly decreased the biodiesel quality. This study is expected to enrich the knowledge of microalgal activities and settling performance in response to fluctuant ammonium concentrations in wastewater and to promote the development of microalgal wastewater treatment.

Effect of vacuum ultraviolet/ozone pretreatment on alleviation of ultrafiltration membrane fouling caused by algal extracellular and intracellular organic matter

Algal blooms in source water can cause algal organic matter (AOM)-related membrane fouling in drinking water treatment. Herein, the effects of vacuum ultraviolet/ozone (VUV/O₃) pretreatment on alleviating ultrafiltration membrane fouling caused by AOM, including extracellular organic matter (EOM) and intracellular organic matter (IOM), were investigated systematically. Compared to its sub-processes (UV/O₃, O₃, VUV, and UV), VUV/O₃ pretreatment showed the best performance on AOM removal and membrane fouling mitigation. After VUV/O₃ pretreatment, the DOC of EOM and IOM in feed decreased by 51.1% and 26.7%, respectively, and fluorescence components and UV₂₅₄ of EOM and IOM in feed decreased obviously. Hence, the final specific fluxes of the membranes increased significantly under the impacts of VUV/O₃, and VUV/O₃ achieved 89.5% and 97.2% mitigation of reversible fouling caused by EOM and IOM, respectively. VUV/O₃ pretreatment also reduced the foulants on membrane surface and surface roughness. Moreover, under the effects of reactive oxygen species oxidation, VUV photolysis, and direct O₃ oxidation, VUV/O₃ decreased organic load and changed the molecular weight distribution, hydrophilicity, and interaction-free energy of AOM, thus mitigating membrane fouling. Furthermore, the effects of O₃ dosage and molecular weight cut-off of ultrafiltration membrane on membrane fouling mitigation by VUV/O₃ were also investigated. All results highlighted that VUV/O₃ pretreatment had huge potential in mitigating AOM-induced membrane fouling.

Using molecular weight-based fluorescent detector to characterize dissolved effluent organic matter in oxidation ditch with algae

Implementation of microalgae has been considered for enhancing effluent wastewater quality. However, it can cause environmental issues due to the release of extracellular and algal organic matter in the biological process. This study aimed to investigate the characteristics of dissolved effluent as algae- and bacteria-derived organic matter during the oxidation ditch process. Furthermore, experiments were conducted under three combinations filled by Spirulina platensis, Chlorella vulgaris, and without microalgae. The results showed that dissolved effluent organic matter was more aromatic and hydrophobic than before treatment. Fluorescence spectroscopy identified two components-aromatic protein-like and soluble microbial product-like components-at excitation/emission of 230/345 nm and 320/345 nm after treatment, instead of fulvic acid-like at 230/420 nm and humic acid-like at 320/420 nm in raw wastewater. These components were fractionated based on the average of molecular weight cut-offs (MWCOs), and high (MWCOs > 50,000 Da), medium (MWCOs 50,000-1650 Da), and low molecular weights (MWCOs < 1650 Da) were reported. Biological oxidation ditch under symbiosis algal bacteria generated humic and fulvic acid with a higher MWCOs than the process without algal. The quality and quantity of dissolved effluent organic matter in an oxidation ditch reactor were significantly affected by algal-bacteria symbiotic.

Optimization of Air Flotation and the Combination of Air Flotation and Membrane Filtration in Microalgae Harvesting

On account of its small size and poor sedimentation performance, microalgae harvesting is restricted from a wider application. Air flotation is an efficient and fast solid–liquid separation technology, which has the potential to overcome the impediments of microalgae harvesting. In this study, factors influencing microalgae harvesting by air flotation were investigated. The results illustrated that bound extracellular organic matter (bEOM) had a greater effect on microalgae harvesting by air flotation, compared with dissolved extracellular organic matter (dEOM). Microalgae harvesting by air flotation in different growth stages proceeded, and the effect of air flotation in the heterotrophic stage was better than the autotrophic stage. The molecular weight distributions demonstrated that after air flotation, the proportion of high MW substance increased, while the proportion of low MW substance decreased, regardless of whether dEOM or bEOM. Membrane filtration was carried out for the algal solutions before and after air flotation. The membrane of pre-flotation algal solution had a higher critical flux of 51 L/m2·h than that of no-pre-flotation (24 L/m2·h), and, thus, pre-flotation had an active effect on membrane filtration in microalgae harvesting. Moreover, the combination of air flotation and membrane filtration provided an efficient technology for microalgae harvesting.

Laboratory-scale study of a biodegradable microplastic polylactic acid stabilizing aerobic granular sludge system

The effects of microplastics on aerobic granular sludge technology are an emerging issue, although the impact of degradable microplastics (DMPs) on the aerobic granular system is still unexplored. In this study, degradable microplastic polylactic acid (DMP-PLA) was added at three concentrations (5, 15, 40 mg/L), which strengthened the granular stability and consequently stabilized pollutant removal compared to the control (without DMP-PLA). The experiment showed that adding DMP-PLA made cells secrete more extracellular polymeric substances [64.8 mg/g MLVSS (mixed liquor suspended solids)], particularly retaining β-D-glucopyranose polysaccharides in experimental group. In addition, abundant hydrogen bonds were also maintained. The reactor under the stress of DMP-PLA exhibited high pollutant removal efficiency (COD>88%, TP>91%, TIN>86%), indicating high performance of the microbes. Microbial analysis at the genus level indicated that Defuviicoccus and Candidatus_Competibacter were dominant after DMP-PLA addition, which identified denitrifying glycogen-accumulating organisms as beneficial for nitrogenous compound removal. Redundancy analysis showed that the abundance of Candidatus_Competibacter was positively related to the addition of DMP-PLA. This study demonstrated that DMP-PLA was feasibly employed in the aerobic granular water treatment process, and presents a new method to optimize the stability and extracellular secretion of the microbial community.