Extracellular Organic Matter Research Articles

Contribution of specific extracellular organic matter on membrane fouling in ultrafiltration and coagulation-ultrafiltration of algae-laden water

This study explores the specific impact of bound and dissolved extracellular organic matter (bEOM and dEOM), and their collective influence with algal cells on membrane fouling during ultrafiltration (UF) and coagulation-UF of algae-laden water. By characterizing the organic properties and adsorptive behaviors of bEOM and dEOM, and analyzing their subsequent impacts, we clarify their roles and contributions to membrane fouling. Our analyses revealed that bEOM, characterized by its higher molecular weight (MW) and hydrophobic nature, contains more protein-like substances compared to dEOM. Quartz Crystal Microbalance with Dissipation (QCM-D) analysis highlights significant differences in their adsorption behaviors, with bEOM demonstrating greater adhesion and higher adsorptive fouling potential. Despite bEOM's lower concentration relative to dEOM, at a ratio of 0.12–1, their contributions to irreversible membrane resistance are nearly identical, at 30.7% and 30.9% respectively, in the UF of algae-laden water. Coagulation pretreatment effectively reduces bEOM's fouling potential by forming larger flocs, thus minimizing its contact with the membrane. In terms of irreversible membrane resistance, the contributions are 6.5% from cells, 24.8% from bEOM, and 68.6% from dEOM. The presence of dEOM complicates coagulation efficiency due to its low MW components and high hydrophilicity. Using the Hermia model, atomic force microscopy (AFM), and scanning electron microscopy (SEM), we demonstrated how bEOM and dEOM modify membrane fouling mechanisms, particularly by influencing cake layer formation. These insights emphasize the distinct and significant contributions of bEOM and dEOM to membrane fouling, necessitating targeted strategies for their management to enhance the efficiency and sustainability of UF systems in water treatment facilities.

Intracellular and extracellular organic matter removal by BT/C heterogeneous interface under visible light photodriven

Algae-derived organic matter (AOM) limits the effectiveness of conventional water treatment processes, affects the normal operation of water treatment plants, and causes water quality deterioration. Efficient elimination of AOM is an urgent issue in the advanced treatment of drinking water. In this study, A heterogeneous interface for AOM removal was established based on BT/C, which can be driven by visible light. The removal efficiencies of extracellular organic matter (EOM), intracellular organic matter (IOM), and AOM by BT/C reached the optimal levels at 30 min, 60 min, and 90 min, respectively, reaching 48.5 %, 81.8 %, and 74.0 %. BT/C can oxidize and break down a large amount of high-molecular-weight organic matter in EOM into medium- and low-molecular-weight organic substances, and effectively remove the low-molecular-weight organic matter in EOM. In addition, BT/C can efficiently remove humic acids(HS) and aromatic protein organic matter in IOM, directly mineralize or decompose high-molecular-weight biopolymers into small-molecular-weight acidic and neutral organic matter; electron paramagnetic resonance spectroscopy and reactive oxygen species trapping experiments verified that hydroxyl radical (·OH) have play most important role on the degradation of various molecular weight organic matters. Superoxide radical (·O2–) plays a dominant role in the oxidation process of soluble microbial metabolites and HS, and ·OH plays a significant role in the oxidation process of amino acid-like proteins. This study provides new ideas and technical support for the complete removal of algae-derived organic matter and the protection of drinking water safety.

Toxicological and mechanistic insights into organic contaminants released from on-line membrane cleaning during ultrafiltration of algal-containing waters

Eutrophication has significantly challenged the treatment of algae-contaminated water. Ultrafiltration has become an essential method for water purification, though frequent on-line chemical cleaning is necessary to maintain membrane permeability. This study aims to systematically investigate the impact of various chemical cleaning agents on the release of dissolved organic matters and toxic by-products, particularly from algal cells. Through a series of controlled experiments, Microcystis aeruginosa cells were exposed to different cleaning agents (HCl, NaOH, NaClO), and the resulting DOM and by-products were characterized. Special attention was paid to the release of intracellular organic matter (IOM) and extracellular organic matter (EOM). Results revealed that NaClO significantly oxidized IOM, leading to the formation of humic-like substances and halogenated organic compounds (TOX), including 15 types of halogenated by-products detected by UPLC/ESI-tqMS. Furthermore, the release of toxic microcystin LR (MC-LR) was traced primarily to IOM. The removability of these contaminants by UF and reverse osmosis (RO) membranes was analyzed, revealing that over 50% of the toxic by-products passed through UF membranes, and 10% still penetrated RO membranes, raising significant concerns for downstream water quality and drinking water safety.

Understanding the fouling characteristics in ultrafiltration membrane for marine algae-laden seawater pretreatment: Focus on the role of algal extracellular organic matter

The increasing frequency and extent of harmful algal blooms (HABs) due to global warming and environmental pollution pose significant challenges to the ultrafiltration (UF)-seawater reverse osmosis (SWRO) desalination process. The UF process is a dominant pretreatment method to reduce HAB fouling potential in subsequent SWRO processes. Herein, we systematically evaluate the UF membrane fouling characteristics at different growth phases of HAB algae in terms of reversible/irreversible fouling and pinpoint the fouling mechanisms on UF membranes in the real seawater matrix. We employed Prorocentrum donghaiense as a model marine HAB specie to characterize algal derivatives, including extracellular organic matter (EOM) and granule particles. LC-OCD, MFIs, 3D-EEM, and GPC were used to analyze algae-derived matters. Results from the multiple fouling model revealed that algal solution in both stationary and decline phases exhibit severe membrane fouling, characterized by rapid cake layer formation, swift flux decline, and high membrane resistance. Soluble EOM (S-EOM) was the primary contributor to membrane fouling, linked to its elevated concentrations of dissolved organic matters, polysaccharides, proteins, and humic substances, which are predominantly hydrophobic. Additionally, granule particles mitigated organic membrane fouling, as evidenced by the smaller permeate volume required for S-EOM cake layer formation (<5 mL), resulting in a faster initial flux decline. These results revealed a shift in released organic matter from protein-centric to humic substance-centric during the transition from exponential growth to the decline phase, with correlation analysis further underscoring the substantial contribution of humic substances to membrane resistance. This research highlights the distinct UF membrane fouling characteristics at different marine algal growth stages, offering theoretical support for predicting and managing HABs.

Control ultrafiltration membrane fouling in Chlorella-laden water treatment by integrated heat-activated peroxydisulfate pre-oxidation and coagulation treatment

The membrane fouling induced by algal extracellular organic matter (EOM) remain a bottleneck in restricting ultrafiltration (UF) application during harmful algal-water treatment. In current study, the application of heat-activated peroxydisulfate (PMS) and coagulation (Aluminum chlorohydrate, PACI) on membrane fouling behavior during Chlorella-laden water treatment was investigated. The membrane fouling mechanism was analyzed using the extended Derjaguin-Landau-Verwey-Over-beek (XDLVO) theory. The results revealed that separated heat-activated PMS could enhance the filtration flux of EOM at high PMS does >0.2 mM, whereas the membrane fouling was further alleviated by combined heat-activated PMS (0.2–1.0 mM) and PACI (20 mg/L) treatment, especially at low PMS dose. Combined heat-activated PMS and PACI pretreatment could effectively increase the adhesive repulsion between membrane and foulants and reduce the cohesion free energies between organic foulants than those by separated heat-activated PMS treatment, making the initial filtration flux reduced and the cake layer looser. Moreover, the organic foulants of proteins, polysaccharides, and humic-like organics were removed. Cake formation was the major fouling mechanism when EOM was treated with/without separated heat-activated PMS treatment, whereas the membrane fouling mechanism was changed from cake layer formation to pore blocking after combined heat-activated PMS and PACI treatment. Overall, this research provided a feasible method in membrane fouling control during Chlorella -laden water treatment.

The photodegradation of carbamazepine and theophylline in the presence of EOM: The effect of growth period and molecular weight

This study confirmed the discrepancy of growth period and molecular weight (MW) of extracellular organic matter (EOM) on the photodegradation of carbamazepine (CBZ) and theophylline (TF). Comparing to high MW EOM (100 kDa), low MW components (<100 kDa) acted as stronger competitors to photons and free radicals, which restrained the photodegradation of CBZ and TF. 3EOM* played an important role in the degradation of CBZ and TF. Lignin was considered as a new precursor of 3EOM*, which was highly depended on the MW of EOM. The high MW 3EOM* was derived from the CHON compound, while the low MW 3EOM* was derived from the CHONS compound. The results demonstrated that the discrepancy of EOM properties in algae growth period might play a non-negligible influence in the migration and transformation of CECs in the true natural water system.

Abatement of algal extracellular organic matter by vacuum ultraviolet: Effect of dissolved oxygen and role of in-situ formed reactive oxygen species

Algal extracellular organic matter (EOM) in water produced during the outbreak of algal blooms is difficult to be effectively removed by conventional water treatment processes. Compared with ultraviolet (UV), vacuum ultraviolet (VUV) can additionally radiate 185 nm photons, and VUV can split water to produce reactive oxygen species (ROS) in-situ. Herein, abatement and characteristic variation of EOM under VUV irradiation and the mechanism were investigated. Results indicated that EOM abatement by VUV irradiation were significantly higher than that by UV irradiation. The mineralization rate constant of EOM under VUV was 2.25 times of that under UV. Besides, under VUV irradiation, the abatement efficiency of EOM was promoted with the increased dissolved oxygen (DO), and EOM with a lower initial concentration had a higher abatement efficiency. Intensities of characteristic fluorescence peaks of EOM decreased obviously after VUV irradiation, and removal rates of specific fluorescent organic components were ≥ 74.4%. Under VUV irradiation, organic matter in EOM with higher molecular weight was transformed into that with lower molecular weight. Moreover, hydroxyl radical (•OH) generated in-situ by VUV dissociating water with different DO was directly identified by fluorescence molecular probe technology, and the higher DO caused the higher production of •OH. Furthermore, the mechanism of EOM abatement by VUV was proposed. DO and the produced ROS enhanced the abatement efficiency of EOM, and they played important roles in EOM abatement. This study disclosed abatement characteristics of EOM under VUV irradiation and provided great value for expanding the utilization of VUV in water treatment.

Enhanced Coagulation for Algae Removal Using Composite Al-Based Coagulants: Collaborative Optimization Mechanism of Aluminum Morphology

The main purpose of this paper was to reveal the effect of aluminum (Al)-based coagulants on enhanced coagulation for the removal of algae and the synergistic optimization mechanism among different Al species. The formation, breakage, and regrowth processes of algal coagulation flocs formed by a series of monomeric Al-based coagulants (Al2(SO4)3, Al13, and Al30), Al13/Al30 composite coagulant and poly(diallyldimethylammonium chloride)/Al13 (PDADMAC/Al13) composite coagulant were studied. Results indicated that Al13 mainly employed a charge neutralization mechanism, which was conducive to the destabilization of algae and the regeneration of flocs, while Al30 mainly employed a sweep flocculation mechanism, which was conducive to the formation of algae and the strength of flocs. Meanwhile, the charge neutralization was the main mechanism during the algae coagulation process because it could effectively remove the soluble microbial products (SMP) component in the extracellular organic matter (EOM). Therefore, Al13 could achieve a higher coagulation performance than other monomeric Al-based coagulants. The Al13/Al30 composite coagulant could make up for the deficiency of the sweep flocculation mechanism in Al13 and charge neutralization mechanism in Al30, and achieve the best synergistic optimization performance at Al13:Al30-7:3. Additionally, PDADMAC, as a polymer, could further enhance the charge neutralization ability of Al13 at low dosages and the sweep flocculation ability of Al13 at high dosages, respectively. However, an excessive dosage would lead to charge reversal and thus reduce the coagulation effect. Therefore, controlling the dosage was key when using Al-composite coagulants. The findings of our research could offer a certain theoretical foundation for the development of inorganic polymer flocculants.

Enhanced removing of cyanobacterium by NZVI coupled with H2O2: Influencing factors and removal mechanisms

AbstractAs advanced oxidation processes (AOPs) is considered to be a highly effective approach for degrading organic pollutants, the simultaneous coagulation and oxidation process by the Fenton‐like reaction of nanoscale zero‐valent iron (NZVI) and hydrogen peroxide (H2O2) is investigated to eliminate the harmful cyanobacterium Microcystis aeruginosa in this study, and the process conditions are optimized using the central composite design of response surface methodology (RSM); in addition, the removal efficiency of M. aeruginosa (in terms of chlorophyll a, Chl a) and the verifications of the antioxidant abilities, as well as extracellular organic matters (EOM) and intracellular organic matters (IOM) are investigated under the optimized conditions. Results indicate that H2O2 concentration is the key factor affecting the Chl a removal efficiency, and the maximum Chl a removal reaches 98.10% under the optimized conditions: NZVI concentration 62.82 mg L−1, H2O2 concentration 54.2 mmol L−1, pH 4.38 and rotating speed 67 rpm. The high correlation coefficient (R2 &gt; 0.80) of analysis of variance (ANOVA) demonstrates the RSM model is extremely significant and suitable for experimental results. Moreover, the total organic carbon (TOC) and fluorescent substances (soluble cyanobacteria metabolic byproducts, aromatic proteins II, humic and fulvic acid‐like compounds) for both EOM and IOM are enhanced removal. It is speculated the removal mechanisms of the Fenton‐like process of NZVI/H2O2 for cyanobacterium belongs to the combined actions of the oxidation of Fe(II)/H2O2 and the coagulation of Fe(III), which destroy the defense system and result in the removal of M. aeruginosa.

Phytic acid metal complex as precursor for fabrication of superhydrophilic membrane with photo-Fenton self-cleaning property for microalgae dewatering and oil/water emulsion separation

Membrane technology is regarded as one of the most effective approaches for microalgae dewatering in the biofuel production industrial and oil/water emulsion separation. However, it inherently suffers from the issue of membrane fouling, particularly irreversible membrane fouling, which is hard to remove by physical methods. Herein, a robust superhydrophilic membrane combined with photo-Fenton self-cleaning property was developed for microalgae dewatering and oil/water emulsion separation. Phytic acid (PA) and FeIII formed a hydrophilic PA-FeIII complex on the polyethersulfone (PES) membrane as the precursor for the in situ growth of β-FeOOH nanorods. When used for microalgae filtration, the irreversible fouling that blocked membrane pores could be degraded by the photo-Fenton reaction. Hence, the obtained PES/PA@β-FeOOH membrane possessed a flux recovery rate (FRR) of 90.2 % (within 30 min), which was significantly higher than that of the PES membrane (32.9 %). The proteins and polysaccharides (extracellular organic matter) attached on the PES/PA@β-FeOOH membrane with photo-Fenton cleaning were 11.2 and 9.1 mg/m2, which was considerably lower than that of PES after hydraulic cleaning (184.1 and 334.9 mg/m2). Moreover, due to the superhydrophilic, the prepared PES/PA@β-FeOOH membrane also exhibited excellent oil/water emulsion separation ability. This work presents a facile and mild strategy to design an anti-fouling coating with superhydrophilic and photo-Fenton activity, which can be used in membrane technology for microorganism filtration and wastewater treatment.

Formation and toxicity alteration of halonitromethanes from Chlorella vulgaris during UV/chloramination process involving bromide ion

Frequent algal blooms cause algal cells and their algal organic matter (AOM) to become critical precursors of disinfection by-products (DBPs) during water treatment. The presence of bromide ion (Br−) in water has been demonstrated to affect the formation laws and species distribution of DBPs. However, few researchers have addressed the formation and toxicity alteration of halonitromethanes (HNMs) from algae during disinfection in the presence of Br−. Therefore, in this work, Chlorella vulgaris was selected as a representative algal precursor to investigate the formation and toxicity alteration of HNMs during UV/chloramination involving Br−. The results showed that the formation concentration of HNMs increased and then decreased during UV/chloramination. The intracellular organic matter of Chlorella vulgaris was more susceptible to form HNMs than the extracellular organic matter. When the Br−: Cl2 mass ratio was raised from 0.004 to 0.08, the peak of HNMs total concentration increased 33.99%, and the cytotoxicity index and genotoxicity index of HNMs increased 67.94% and 22.80%. Besides, the formation concentration and toxicity of HNMs increased with increasing Chlorella vulgaris concentration but decreased with increasing solution pH. Possible formation pathways of HNMs from Chlorella vulgaris during UV/chloramination involving Br− were proposed based on the alteration of nitrogen species and fluorescence spectrum analysis. Furthermore, the formation laws of HNMs from Chlorella vulgaris in real water samples were similar to those in deionized water samples. This study contributes to a better comprehension of HNMs formation from Chlorella vulgaris and provides valuable information for water managers to reduce hazards associated with the formation of HNMs.

Mechanisms of hormetic effects of ofloxacin on Chlorella pyrenoidosa under environmental-relevant concentration and long-term exposure

Antibiotics are frequently detected in surface water and pose potential threats to organisms in aquatic ecosystem such as microalgae. The occurrence of biphasic dose responses raised the possibility of stimulation of microalgal biomass by antibiotics at environmental-relevant concentration and caused potential ecological risk such as algal bloom. However, the underlying mechanisms of low concentration-induced hormetic effects are not well understood. In this study, we evaluated the hormesis of ofloxacin on Chlorella pyrenoidosa under environmental-relevant concentration and long-term exposure. Results showed the hormetic effects of ofloxacin on cell density and carbon fixation rate (RC). The predicted maximum promotion was 17.45 % by 16.84 μg/L and 20.08 % by 15.78 μg/L at 21 d, respectively. The predicted maximum concentration of non-effect on cell density and RC at 21 d was 3.24 mg/L and 1.44 mg/L, respectively. Ofloxacin induced the mobilization of pigments and antioxidant enzymes to deal with oxidative stress. PCA analysis revealed Chl-a/Chl-b could act as a more sensitive biomarker under acute exposure while chlorophyll fluorescence parameters were in favor of monitoring long-term implication. The hormesis in increased secretion of extracellular organic matters was regarded as a defensive mechanism and accelerated indirect photodegradation of ofloxacin. Bioremoval was dominant and related to biomass accumulation in the total dissipation while abiotic removal appeared slight contributions. This study provided new insights into the understanding of hormesis of microalgae induced by antibiotics.

Environment-specific virocell metabolic reprogramming.

Viruses impact microbial systems through killing hosts, horizontal gene transfer, and altering cellular metabolism, consequently impacting nutrient cycles. A virus-infected cell, a "virocell," is distinct from its uninfected sister cell as the virus commandeers cellular machinery to produce viruses rather than replicate cells. Problematically, virocell responses to the nutrient-limited conditions that abound in nature are poorly understood. Here we used a systems biology approach to investigate virocell metabolic reprogramming under nutrient limitation. Using transcriptomics, proteomics, lipidomics, and endo- and exo-metabolomics, we assessed how low phosphate (low-P) conditions impacted virocells of a marine Pseudoalteromonas host when independently infected by two unrelated phages (HP1 and HS2). With the combined stresses of infection and nutrient limitation, a set of nested responses were observed. First, low-P imposed common cellular responses on all cells (virocells and uninfected cells), including activating the canonical P-stress response, and decreasing transcription, translation, and extracellular organic matter consumption. Second, low-P imposed infection-specific responses (for both virocells), including enhancing nitrogen assimilation and fatty acid degradation, and decreasing extracellular lipid relative abundance. Third, low-P suggested virocell-specific strategies. Specifically, HS2-virocells regulated gene expression by increasing transcription and ribosomal protein production, whereas HP1-virocells accumulated host proteins, decreased extracellular peptide relative abundance, and invested in broader energy and resource acquisition. These results suggest that although environmental conditions shape metabolism in common ways regardless of infection, virocell-specific strategies exist to support viral replication during nutrient limitation, and a framework now exists for identifying metabolic strategies of nutrient-limited virocells in nature.

Algal Extracellular Organic Matter Induced Photochemical Oxidation of Mn(II) to Solid Mn Oxide: Role of Mn(III)-EOM Complex and Its Ability to Remove 17α-Ethinylestradiol.

Photosensitizer-mediated abiotic oxidation of Mn(II) can yield soluble reactive Mn(III) and solid Mn oxides. In eutrophic water systems, the ubiquitous algal extracellular organic matter (EOM) is a potential photosensitizer and may have a substantial impact on the oxidation of Mn(II). Herein, we focused on investigating the photochemical oxidation process from Mn(II) to solid Mn oxide driven by EOM. The results of irradiation experiments demonstrated that the generation of Mn(III) intermediate was crucial for the successful photo oxidization of Mn(II) to solid Mn oxide mediated by EOM. EOM can serve as both a photosensitizer and a ligand, facilitating the formation of the Mn(III)-EOM complex. The complex exhibited excellent efficiency in removing 17α-ethinylestradiol. Furthermore, the complex underwent decomposition as a result of reactions with reactive intermediates, forming a solid Mn oxide. The presence of nitrate can enhance the photochemical oxidation process, facilitating the conversion of Mn(II) to Mn(III) and then to solid Mn oxide. This study deepens our grasp of Mn(II) geochemical processes in eutrophic water and its impact on organic micropollutant fate.

Toxic effects and action mechanism of metal-organic framework UiO-66-NH2 in Microcystisaeruginosa

The zirconium metal-organic framework UiO-66-NH2 has garnered considerable attention for their potentials of removing environmental contaminants from water. The production and application of UiO-66-NH2 make their releases into the aquatic environment inevitable. Nevertheless, little information is available regarding its potential risk to the environment and aquatic organisms, thus limiting the evaluation of its safe and sustainable use. In this study, the ecotoxicity of UiO-66-NH2 was evaluated, specifically its impacts on growth, extracellular organic matter release, and metabolomic changes of the model phytoplankton Microcystis aeruginosa (M. aeruginosa). UiO-66-NH2 exhibited moderate effects on algal physiology including growth, viability, and photosynthetic system. At concentrations below 20 mg/L, UiO-66-NH2 induced negligible inhibition of algal growth, algal viability, and photosynthesis. In contrast, UiO-66-NH2 boosted the release of extracellular organic matter even at concentration as low as 0.02 mg/L. These findings indicated that, while no evident damage to algal cells was observed, UiO-66-NH2 was hazardous to the aquatic environment as it stimulated the release of algal toxins. Moreover, UiO-66-NH2 entered algal cells rather than adhering to the surface of M. aeruginosa as observed by the fluorescence imaging. Based on metabolic analysis, UiO-66-NH2 influenced the cyanobacteria mainly through interference with purine metabolism and ABC transporter. This study sheds light on the potential threat UiO-66-NH2 posing to microalgae, and has potential implications for its safe utilization in the environmental field.

Compensatory growth of Microcystis aeruginosa after copper stress and the characteristics of algal extracellular organic matter (EOM)

Cyanobacterial blooms can impair drinking water quality due to the concomitant extracellular organic matter (EOM). As copper is often applied as an algicide, cyanobacteria may experience copper stress. However, it remains uncertain whether algal growth compensation occurs and how EOM characteristics change in response to copper stress. This study investigated the changes in growth conditions, photosynthetic capacity, and EOM characteristics of M. aeruginosa under copper stress. In all copper treatments, M. aeruginosa experienced a growth inhibition stage followed by a growth compensation stage. Notably, although chlorophyll-a fluorescence parameters dropped to zero immediately following high-intensity copper stress (0.2 and 0.5 mg/L), they later recovered to levels exceeding those of the control, indicating that photosystem II was not destroyed by copper stress. Copper stress influenced the dissolved organic carbon (DOC) content, polysaccharides, proteins, excitation–emission matrix spectra, hydrophobicity, and molecular weight (MW) distribution of EOM, with the effects varying based on stress intensity and growth stage. Principal component analysis revealed a correlation between the chlorophyll-a fluorescence parameters and EOM characteristics. These results imply that copper may not be an ideal algicide. Further research is needed to explore the dynamic response of EOM characteristics to environmental stress.

Effect of extracellular organic matter (EOM) accumulation on algal proliferation and disinfection by-product precursors during cyclic cultivation

Algal blooms, driven by nutrient enrichment from nitrogen and phosphorus, pose significant challenges to water treatment processes, particularly due to the accumulation of extracellular organic matter (EOM).

Simultaneous removing algal and its extracellular organic matters by Mg/Al-layered double hydroxide /La-montmorillonite

ABSTRACT Rapid and effective simultaneous removal of algal and extracellular organic matter (EOM) is essential for algal blooms water emergency treatment. In this study, a composite material was prepared by physical and chemical interaction between La-montmorillonite (La-MMT) and Mg/Al-layered double hydroxide (LDHs), and its removal effect of algal and extracellular organic matters (EOM) was investigated. The results showed that the removal rate of chlorophyll a (chl-a) was 96.8% within 2 h when the LDHs/La-MMT2:1 dosage was 1.0 g/L. Three-dimensional fluorescence characteristic spectra and parallel factor analysis showed that the removal of EOM by composite material mainly reflected in the removal of humus-like substances. The reaction heat of composite material for the algal solution was −32.7 J/g. Zeta potential changed from −25.7 mV to −16.9 mV, the main treatment mechanisms of composite material were surface adsorption, complexation precipitation, charge neutralisation, and ion exchange. These findings herein proposed that composite material was a potential and proper treating agent for removing algal cells and EOM from algal blooms water.

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.

Cell viability changes coagulation efficiency of polyaluminium chloride for cyanobacteria-laden source water treatment

Cyanobacterial blooms challenge drinking water safety, and polyaluminium chloride (PACl) coagulation is crucial in treating algal-laden source water in drinking water treatment plants (DWTPs). The cell viability of cyanobacteria declines at the bloom decay stage, which may affect the coagulation process. Most studies have focused on high-viability cells, not low-viability cells. Herein, PACl coagulation experiments were conducted to compare the removal efficiencies of high- and low-viability Microcystis, and the effects of cellular properties and extracellular organic matter (dEOM) on their removal efficiency were discussed. The removal efficiency of low-viability cells (38.3–99.3 %) was higher than that of high-viability cells (14.5–85.9 %) after coagulation-sedimentation, owing to the declining cellular buoyancy and enhanced adsorptive interaction with Al(OH)3(am) via increased aromatics/peptides containing functional groups of aromatic, OH, NH, CN on their hydrophobic cellular surface. By contrast, together with in situ dEOM, the removal efficiency of low-viability cells (1.3–90.5 %) became much lower than that of high-viability cells (2.2–98.2 %) even with a higher ratio of [PACl: DOC], due to elevated low molecular weight (MW) peptides of <10 kDa in dEOM impeding the coagulation removal of low-viability cells via chelation and negative charge supply. Additionally, a decrease in the removal ratio of dEOM was observed, and peptides (<10 kDa) in the residual dEOM increased by 93–100 %. Overall, this study demonstrated that the declining cell viability could strongly affect the coagulation efficiency of algal-laden source water, and the optimization of the coagulation process by water managers should depend on the cell viability of cyanobacteria.