Impact of permanganate with polyaluminium chloride on algae-laden karst water: Behaviors and disinfection by-products control.

The removal of algal organic matter (AOM) through water treatment processes is a major approach of reducing the formation of disinfection by-products (DBP). Here, the formation of DBP from AOM in karst water under different combination of potassium permanganate (KMnO4) and polyaluminium chloride (PACl) was investigated. The effect of divalent ions (Ca2+ and Mg2+) on DBP formation was traced by AOM chemistry variations. For DBP formation after KMnO4 preoxidation, total carbonaceous DBPs (C-DBPs) decreased by 12.9% but nitrogen-containing DBPs (N-DBPs) increased by 18.8%. Conversely, the C-DBPs further increased by 3.3% but N-DBPs reduced by 10.7% after the addition of PACl besides KMnO4 preoxidation. The variations of aromatic protein-like, soluble microbial products-like compounds and ultraviolet absorbance at 254 nm (UV254) were highly correlated with the formation of DBPs, which suggest aromatic substances strongly affect DBP behaviors at different treatment conditions. In the presence of divalent ions (Ca2+ = 135.86 mg/L, Mg2+ = 18.51 mg/L), the combination of KMnO4 and PACl was more effective in controlling DBP formation compared to the situation without Ca2+ and Mg2+. Specifically, trichloromethane formation was largely inhibited compared to the other tested DBPs, which may refer to complexation of electron-donating groups via divalent ions. While Ca2+ and Mg2+ may not affect the nature of α-carbon and amine groups, so the variation of haloacetonitriles (HANs) was not obvious. The study enhances the understanding of the DBP formation patterns, transformation of carbon and nitrogen by preoxidation-coagulation (KMnO4-PACl) treatment in algae-laden karst water.

The adsorption of biogenetic odorants onto activated carbon: Adsorption characteristics and impacts of algal organic matter.

Powdered activated carbon (PAC) adsorption is regarded as an efficient method for removing odorants from drinking water. However, in eutrophic aquatic environments, the presence of algal organic matter (AOM) produced by cyanobacteria considerably impedes the adsorption of odorous compounds by activated carbon. This study focused on investigating the adsorption characteristics of three representative odorants: 2-methylisoborneol (2-MIB), ß-cyclocitral (ß-cyclo), and butyl sulfide (BS) by PAC and the effects of AOM on the PAC adsorption of odorants. The removal of the three odorants reached 83.5-97.5% at a PAC dosage of 10 mg/L after 12 h of exposure in a competition-free scenario. The adsorption kinetics demonstrated higher conformity (R2 > 0.9) with the pseudo-second-order model, whereas the adsorption capacity exhibited stronger conformity (R2 > 0.9) with the Freundlich model. The presence of AOM resulted in varying levels of competition for PAC for the adsorption of the three odorants. As the concentration of AOM increased from 0 to 5 mg C/L, the removal of 2-MIB was the most affected (from 83.5% to 10.0%), followed by ß-cyclo (from 86.6% to 55.0%), and BS (from 97.5% to 92.0%). The competitive adsorption of AOM at the molecular level was studied using density functional theory (DFT). The DFT results suggested that odorants with higher and more uniformly distributed electrostatic potentials exhibited a heightened affinity for PAC adsorption and a diminished susceptibility to disruption caused by AOM. This study provides valuable insights into the mitigation of odorous compounds during drinking water purification.

Molecular complexation properties of Cd2+ by algal organic matter from Scenedesmus obliquus.

A detailed understanding the metals binding with algal organic matter (AOM) is essential to gain a deeper insight into the toxicity and migration of metals in algae cell. However, the molecular complexation mechanism of the metals binding with AOM remains unclear. In this study, cadmium ion (Cd2+) binding properties of AOMs from Scenedesmus obliquus, which included extracellular organic matter (EOM) and intracellular organic matter (IOM), were screened. When Cd2+ < 0.5 mg/L, the accumulation of Cd2+ could reach 40%, while Cd2+ > 0.5 mg/L, the accumulation of Cd2+ was only about 10%. EOM decreased gradually (from 8.51 to 3.98 mg/L), while IOM increased gradually (from 9.62 to 21.00 mg/L). The spectral characteristics revealed that IOM was richer in peptides/proteins and had more hydrophilic than EOM. Both EOM and IOM contained three protein-like components (containing tryptophan and tyrosine) and one humic-like component, and their contents in IOM were higher than that in EOM. The tryptophan protein-like substances changed greatly during Cd2+ binding, and that the tryptophan protein-like substances complexed to Cd2+ before tyrosine protein-like substances in IOM was identified. Moreover, the functional groups of N-H, O-H, and CO in AOM played an important role, and the N-H group was priority to interacts with Cd2+ in the complexing process. More functional groups (such as C-O and C-N) were involved in the metals complexing in EOM than in IOM. It could be concluded that Cd2+ stress promoted the secretion of AOM in Scenedesmus obliquus, and proteins in AOM could complex Cd2+ and alleviate its toxicity to algal cell. These findings provided deep insights into the interaction mechanism of AOM with Cd2+ in aquatic environments.

Formation of regulated and unregulated disinfection byproducts during chlorination and chloramination: Roles of dissolved organic matter type, bromide, and iodide.

Algal blooms and wastewater effluents can introduce algal organic matter (AOM) and effluent organic matter (EfOM) into surface waters, respectively. In this study, the impact of bromide and iodide on the formation of halogenated disinfection byproducts (DBPs) during chlorination and chloramination from various types of dissolved organic matter (DOM, e.g., natural organic matter (NOM), AOM, and EfOM) were investigated based on the data collected from literature. In general, higher formation of trihalomethanes (THMs) and haloacetic acids (HAAs) was observed in NOM than AOM and EfOM, indicating high reactivities of phenolic moieties with both chlorine and monochloramine. The formation of haloacetaldehydes (HALs), haloacetonitriles (HANs) and haloacetamides (HAMs) was much lower than THMs and HAAs. Increasing initial bromide concentrations increased the formation of THMs, HAAs, HANs, and HAMs, but not HALs. Bromine substitution factor (BSF) values of DBPs formed in chlorination decreased as specific ultraviolet absorbance (SUVA) increased. AOM favored the formation of iodinated THMs (I-THMs) during chloramination using preformed chloramines and chlorination-chloramination processes. Increasing prechlorination time can reduce the I-THM concentrations because of the conversion of iodide to iodate, but this increased the formation of chlorinated and brominated DBPs. In an analogous way, iodine substitution factor (ISF) values of I-THMs formed in chloramination decreased as SUVA values of DOM increased. Compared to chlorination, the formation of noniodinated DBPs is low in chloramination.

Characterization of algal organic matter as precursors for carbonaceous and nitrogenous disinfection byproducts formation: Comparison with natural organic matter.

Algal organic matter (AOM) and natural organic matter (NOM) from a typical eutrophic lake were comprehensively investigated in terms of their physico-chemical property, components and disinfection byproduct formation potentials (DBPFPs). The relationships between specific chemical properties of AOM and NOM with their corresponding DBPFPs were further evaluated during chlorination. Results indicated that AOM had lower specific UV absorbance (SUVA) but richer organic nitrogen contents than NOM. Fluorescence excitation emission matrix spectroscopy further demonstrated that AOM were chiefly composed of aromatic protein-like and soluble microbial byproduct-like matters, while NOM were mainly contributed from humic acid-like and soluble microbial byproduct-like substances. Although the molecular weight (MW) distribution of AOM and NOM showed no significant difference, size-exclusion chromatography with organic carbon as well as organic nitrogen detection (LC-OCD-OND) revealed that AOM were concentrated with the fraction of building blocks and NOM had higher concentrations of biopolymers and humics (HS). Moreover, AOM displayed higher DBPFPs than NOM, especially for nitrogenous DBPFP (N-DBPFP). MW < 1 kDa fractions both in AOM and NOM contributed the largest proportion to the formation of carbonaceous disinfection byproducts (C-DBPs). In addition, Pearson correlation analysis showed that bulk parameter SUVA was significantly relevant to the formation potentials of trihalomethane both in AOM and NOM, but was ineffective for carbonaceous DBPFP (C-DBPFP) prediction. Dissolved organic nitrogen contents in biopolymer and HS characterized by LC-OCD-OND had strong correlations with N-DBPFPs from AOM and NOM, indicating that LC-OCD-OND quantitative analysis could improve the prediction accuracy of the DBP formation than bulk parameters during NOM and AOM chlorination.

The impact of preozonation on the coagulation of cellular organic matter produced by Microcystis aeruginosa and its toxin degradation.

Ozonation pretreatment is typically implemented to improve algal cell coagulation. However, knowledge on the effect of ozonation on the characteristics and coagulation of associated algal organic matter, particularly cellular organic matter (COM), which is extensively released during algal bloom decay, is limited. Hence, this study aimed to elucidate the impact of ozonation applied before the coagulation of dissolved COM from the cyanobacteria Microcystis aeruginosa. Additionally, the degradation of microcystins (MCs) naturally present in the COM matrix was investigated. A range of ozone doses (0.1-1.0 mg O3/mg of dissolved organic carbon - DOC) and ozonation pH values (pH 5, 7 and 9) were tested, while aluminium and ferric sulphate coagulants were used for subsequent coagulation. Despite negligible COM removal, ozonation itself eliminated MCs, and a lower ozone dose was required when performing ozonation at acidic or neutral pH (0.4 mg O3/mg DOC at pH 5 and 7 compared to 0.8 mg O3/mg DOC at pH 9). Enhanced MC degradation and a similar pattern of pH dependence were observed after preozonation-coagulation, whereas coagulation alone did not sufficiently remove MCs. In contrast to the benefits of MC depletion, preozonation using ≥ 0.4 mg O3/mg DOC decreased the coagulation efficiency (from 42%/48% to 28%-38%/41%-44% using Al/Fe-based coagulants), which was more severe with increasing ozone dosage. Coagulation was also influenced by the preozonation pH, where pH 9 caused the lowest reduction in COM removal. The results indicate that ozonation efficiently removes MCs, but its employment before COM coagulation is disputable due to the deterioration of coagulation.

Influence of COM-peptides/proteins on the properties of flocs formed at different shear rates.

Coagulation followed by floc separation is a key process for the removal of algal organic matter (AOM) in water treatment. Besides optimizing coagulation parameters, knowledge of the properties of AOM-flocs is essential to maximizing AOM removal. However, the impact of AOM on the floc properties remains unclear. This study investigated how peptides/proteins derived from the cellular organic matter (COM) of the cyanobacterium Microcystis aeruginosa influenced the size, structure, and shape of flocs formed at different shear rates (G). Flocs formed by kaolinite, COM-peptides/proteins and a mixture of the same were studied, and the effect of intermolecular interactions between floc components on floc properties was assessed. The coagulation experiments were performed in a Taylor-Couette reactor, with aluminum (Al) or ferric sulphate (Fe) utilized as coagulants. Image analysis was performed to gauge floc size and obtain data on fractal dimension. It was found that floc properties were affected by the presence of the COM-peptides/proteins and the coagulant used. COM-peptides/proteins increased floc size and porosity and widened floc size distributions. The Fe coagulant produced larger and less compact flocs than Al coagulant. Moreover, the decrease in floc size that occurred in parallel with increase in shear rate was not smooth in progress. A rapid change for the kaolinite-coagulant suspension and two rapid changes for the suspensions containing COM were observed. These were attributed to various intermolecular interactions between floc components participating in coagulation at different G. Based on the results obtained, shear rates suitable for efficient separation of flocs containing COM were suggested.

Investigating the coagulation of non-proteinaceous algal organic matter: Optimizing coagulation performance and identification of removal mechanisms.

The removal of algal organic matter (AOM) is a growing concern for the water treatment industry worldwide. The current study investigates coagulation of non-proteinaceous AOM (AOM after protein separation), which has been minimally explored compared with proteinaceous fractions. Jar tests with either aluminum sulphate (alum) or polyaluminium chloride (PACl) were performed at doses of 0.2-3.0 mg Al per 1 mg of dissolved organic carbon in the pH range 3.0-10.5. Additionally, non-proteinaceous matter was characterized in terms of charge, molecular weight and carbohydrate content to assess the treatability of its different fractions. Results showed that only up to 25% of non-proteinaceous AOM can be removed by coagulation under optimized conditions. The optimal coagulation pH (6.6-8.0 for alum and 7.5-9.0 for PACl) and low surface charge of the removed fraction indicated that the prevailing coagulation mechanism was adsorption of non-proteinaceous matter onto aluminum hydroxide precipitates. The lowest residual Al concentrations were achieved in very narrow pH ranges, especially in the case of PACl. High-molecular weight saccharide-like organics were amenable to coagulation compared to low-molecular weight (<3 kDa) substances. Their high content in non-proteinaceous matter (about 67%) was the reason for its low removal. Comparison with our previous studies implies that proteinaceous and non-proteinaceous matter is coagulated under different conditions due to the employment of diverse coagulation mechanisms. The study suggests that further research should focus on the removal of low-molecular weight AOM, reluctant to coagulate, with other treatment processes to minimize its detrimental effect on water safety.

Performance of titanium salts compared to conventional FeCl3 for the removal of algal organic matter (AOM) in synthetic seawater: Coagulation performance, organic fraction removal and floc characteristics.

During algal bloom periods, operation of seawater reverse osmosis (SWRO) pretreatment processes (e.g. ultrafiltration (UF)) has been hindered due to the high concentration of algal cells and algal organic matter (AOM). The present study evaluated for the first time the performance of titanium salts (i.e. titanium tetrachloride (TiCl4) and polytitanium tetrachloride (PTC)) for the removal of AOM in seawater and results were compared with the conventional FeCl3 coagulant. Previous studies already demonstrated that titanium salts not only provide a cost-effective alternative to conventional coagulants by producing a valuable by-product but also minimise the environmental impact of sludge production. Results from this study showed that both TiCl4 and PTC achieved better performance than FeCl3 in terms of turbidity, UV254 and dissolved organic carbon (DOC) removal at similar coagulant dose. Liquid chromatography - organic carbon detection (LC-OCD) was used to determine the removal of AOM compounds based on their molecular weight (MW). This investigation revealed that both humic substances and low MW organics were preferentially removed (i.e. up to 93% removal) while all three coagulants showed poorer performance for the removal of high MW biopolymers (i.e. less than 50% removal). The detailed characterization of flocs indicated that both titanium coagulants can grow faster, reach larger size and present a more compact structure, which is highly advantageous for the design of smaller and more compact mixing and sedimentation tanks. Both titanium coagulants also presented a higher ability to withstand shear force, which was related to the higher amount of DOC adsorbed with the aggregated flocs. Finally, TiCl4 had a better recovery after breakage suggesting that charge neutralization may be the dominant mechanism for this coagulant, while the lower recovery of both PTC and FeCl3 indicated that sweep flocculation is also a contributing mechanism for the coagulation of AOM.

Impact of pre-ozonation on disinfection by-product formation and speciation from chlor(am)ination of algal organic matter of Microcystis aeruginosa.

The increasing use of algal-impacted source waters is increasing concerns over exposure to disinfection byproducts (DBPs) in drinking water disinfection, due to the higher concentrations of DBP precursors in these waters. The impact of pre-ozonation on the formation and speciation of DBPs during subsequent chlorination and chloramination of algal organic matter (AOM), including extracellular organic matter (EOM) and intracellular organic matter (IOM), was investigated. During subsequent chlorination, ozonation pretreatment reduced the formation of haloacetonitriles from EOM, but increased the yields of trihalomethanes, dihaloacetic acid and trichloronitromethane from both EOM and IOM. While in chloramination, pre-ozonation remarkably enhanced the yields of several carbonaceous DBPs from IOM, and significantly minimized the nitrogenous DBP precursors. Also, the yield of 1,1-dichloro-2-propanone from IOM was decreased by 24.0% after pre-ozonation during chloramination. Both increases and decreases in the bromine substitution factors (BSF) of AOM were observed with ozone pretreatment at the low bromide level (50µg/L). However, pre-ozonation played little impact on the bromide substitution in DBPs at the high bromide level (500µg/L). This information was used to guide the design and practical operation of pre-ozonation in drinking water treatment plants using algae-rich waters.

The interaction mechanisms of algal organic matter (AOM) and various types and aging degrees of microplastics.

Algal blooms can produce substantial amounts of algal organic matter (AOM). Microplastics (MPs) in aquatic environments inevitably interact with AOM. Meanwhile, the aging and type of MPs may increase the uncertainty surrounding interaction. This study focused on polyethylene (PE) and polylactic acid (PLA) to investigate their interaction with AOM before and after aging. The results shw that PLA has a stronger adsorption capacity for AOM than PE. Meanwhile, aging enhanced and weakened the adsorption of PE and PLA for AOM. Compared to unaged PE (UPE) and aged PLA (APLA), aged PE (APE) and unaged PLA (UPLA) more significantly promote the humification of AOM and alter its functional groups. 2D-IR-COS analysis reveals that the sequence of functional group changes in AOM interacting with MPs is influenced by the type and aging of MPs. After interacting with AOM, surface roughness increased for all MPs. FTIR and XPS analyses show that the addition of AOM accelerated the oxidation of MPs surfaces, especially for UPE and APLA, with oxygen content increasing by 9.32 % and 1 %. Aging enhances the interaction between PE and AOM, while weakening the interaction between PLA and AOM. These findings provide new insights into understanding the interplay between AOM and MPs.

Algae removal and algal organic matter chemistry modulated by KMnO4-PAC in simulated karst water.

In this study, we examined the modulation of algae removal and algal organic matter (AOM) chemistry by potassium permanganate and poly-aluminum chloride (KMnO4-PAC) in simulated karst water. Specifically, we verified the compositional changes of AOM sourcing from Chlorella sp. and Pseudanabaena sp. in response to the presence of divalent ions (Ca2+ and Mg2+). Aromatic protein and soluble microbial products were identified as the primary AOM components. Divalent ions accelerated dissolved organic carbon (DOC) and UV254 removal, particularly with Pseudanabaena sp. greater than Chlorella sp. (P < 0.05). Surface morphology analysis manifested that the removal of filamentous Pseudanabaena sp. was more feasible in comparison to globular Chlorella sp.. Our results highlight the significance of divalent ions in governing chemical behaviors and subsequent removal of both algae and AOM. This study upscales the understanding of the interactions among divalent ions, algae and AOM during preoxidation and coagulation process in algae-laden karst water.

Effects of algal organic matters on microporous ceramic emitters clogging in agricultural water distribution systems: Experiment and molecular simulation investigations.

The mechanism by which algal organic matter (AOM) affects the clogging of ceramic emitters remains unclear, which partially reduces the operational life of agricultural water distribution systems. This paper systematically investigated the clogging phenomenon of ceramic emitters under three different AOM concentrations. The results of irrigation tests revealed that the AOM significantly affects the degree of clogging of ceramic emitters, with higher AOM concentrations leading to faster flow reduction. By analyzing the original irrigation water and effluent and characterizing the clogged emitter surface, it was demonstrated that AOM was intercepted by the ceramic emitter, forming a dense biofilm. Infrared spectroscopy analysis revealed that polysaccharides and humic substances were the main clogging components. The clogging kinetics showed that as the AOM concentration increased, the clogging of the filter cake layer gradually become dominant. Further, the mechanism of interaction between AOM and silica ceramic emitters was explored from a microscopic perspective using molecular dynamics (MD) simulation with bovine serum albumin (BSA), sodium alginate (SA), and humic acid (HA) as model clogging substances in AOM. The simulation results indicated a strong interaction between AOM molecules and silica molecules dominated by electrostatic attraction, with the strength of the interaction as SA > HA > BSA. It was hypothesized that early clogging was mainly formed by polysaccharides and humic substances combining with silica molecules, while BSA was retained later by combining with organics on the clogging layer or through size exclusion. This study provides insights into bio-clogging in microporous ceramic emitters and may offer a theoretical basis for developing measures to control emitter clogging.

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.

The Biophysical Properties of Microalgal Cell Surfaces Govern Their Interactions with an Amphiphilic Chitosan Derivative Used for Flocculation and Flotation.

Microalgae show great promise for producing valuable molecules like biofuels, but their large-scale production faces challenges, with harvesting being particularly expensive due to their low concentration in water, necessitating extensive treatment. While methods such as centrifugation and filtration have been proposed, their efficiency and cost-effectiveness are limited. Flotation, involving air-bubbles lifting microalgae to the surface, offers a viable alternative, yet the repulsive interaction between bubbles and cells can hinder its effectiveness. Previous research from our group proposed using an amphiphilic chitosan derivative, polyoctyl chitosan (PO-chitosan), to functionalize bubbles used in dissolved air flotation (DAF). Molecular-scale studies performed using atomic force microscopy (AFM) revealed that PO-chitosan's efficiency correlates with cell surface properties, particularly hydrophobic ones, raising the question of whether this molecule can in fact be used more generally to harvest different microalgae. Evaluating this, we used a different strain of Chlorella vulgaris and first characterized its surface properties using AFM. Results showed that cells were hydrophilic but could still interact with PO-chitosan on bubble surfaces through a different mechanism based on specific interactions. Although force levels were low, flotation resulted in 84% separation, which could be explained by the presence of AOM (algal organic matter) that also interacts with functionalized bubbles, enhancing the overall separation. Finally, flocculation was also shown to be efficient and pH-independent, demonstrating the potential of PO-chitosan for harvesting microalgae with different cell surface properties and thus for further sustainable large-scale applications.

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.

Impact of organic matter molecular weight on hexavalent chromium enrichment in green microalgae.

In lightly polluted water containing heavy metals, organic matter, and green microalgae, the molecular weight of organic matter may influence both the growth of green microalgae and the concentration of heavy metals. This study elucidates the effects and mechanisms by which different molecular weight fractions of fulvic acid (FA), a model dissolved organic matter component, facilitate the bioaccumulation of hexavalent chromium (Cr(VI)) in a typical green alga, Chlorella vulgaris. Findings show that the addition of FA fractions with molecular weights greater than 10 kDa significantly enhances the enrichment of total chromium and Cr(VI) in algal cells, reaching 21.58%-31.09 % and 16.17 %-22.63 %, respectively. Conversely, the efficiency of chromium enrichment in algal cells was found to decrease with decreasing molecular weight of FA. FA molecular weight within the range of 0.22 µm-30 kDa facilitated chromium enrichment primarily through the algal organic matter (AOM) pathway, with minor contributions from the algal cell proliferation and extracellular polymeric substances (EPS) pathways. However, with decreasing FA molecular weight, the AOM and EPS pathways become less prominent, whereas the algal cell proliferation pathway becomes dominant. These findings provide new insights into the mechanism of chromium enrichment in green algae enhanced by medium molecular weight FA.

Insights into how characteristics of dissolved algal organic matter affect the efficiency of modified clay in controlling harmful algal blooms.

Dissolved algal organic matter (dAOM) originating from harmful algal blooms (HABs) can deteriorate the quality of municipal water supplies, threaten the health of aquatic environments, and interfere with modified clay (MC)-based HABs control measures. In this study, we explored the composition of dAOM from Prorocentrum donghaiense, a typical HAB organism, and assessed the influence of dAOM on MC flocculation. Our results suggested that dAOM composition was complex and had a wide molecular weight (MW) distribution. MW and electrical properties were important dAOM characteristics affecting flocculation and algal removal efficiency of MC. Negatively charged high-MW components (>50 kDa) critically affected algal removal efficiency, reducing the zeta potential of MC particles and leading to small and weak flocs. However, the effect of dAOM depended on its concentration. When the cell density of P. donghaiense reached HAB levels, the high-MW dAOM strongly decreased the algal removal efficiency of MC.

Insights from colony formation: The necessity to consider morphotype when assessing the effect of antibiotics on cyanobacteria.

Colonial cyanobacteria have been identified as the primary contributor to the global occurrence of cyanobacterial harmful algal blooms (cyanoHABs), which are further intensified by the presence of "pseudo-persistent" antibiotics. Nevertheless, the impact of antibiotics on the growth and size of colonial cyanobacteria remains unclear. In this study, the response of cyanobacterium Microcystis to varying doses of antibiotics was assessed (0, 0.1, 0.5, 1, 10, and 50 µg L-1) by comparing the unicellular and colonial morphotypes. Interestingly, the morphological structure of cyanobacteria plays a significant role in their reaction to antibiotics. In comparison to the unicellular morphotype, the colonial morphotype exhibited a greater promotion in growth rate (11 %-22 %) to low doses of antibiotics and was less inhibited (-121 %--62 %) under high doses. Furthermore, antibiotics may affect the size of cyanobacterial colonies by disrupting the secretion of algal organic matter, which also exhibited a two-phase pattern. This work sheds light on the significance of methodology research involving both unicellular and colonial cyanobacteria. Future research and lake management should prioritize studying the morphological traits of cyanobacteria under different levels of antibiotic exposure. This approach may lead to novel strategies for predicting cyanoHABs under antibiotic pollution more effectively.

Application of fluorescence spectra and molecular weight analysis in the identification of algal organic matter-based disinfection by-product precursors.

Algal organic matter (AOM) is considered to be threatening for the consumption of disinfectants and the formation of disinfection by-products (DBPs) during the disinfection process. Incompatible parameters in the conventional pretreatment of algal-laden water will lead to counterproductive results, such as AOM release. Therefore, the generation of AOM and its conversion to DBPs during pretreatment should be observed. The characteristics of DBPs from extracellular organic matter (EOM) and intracellular organic matter (IOM) were epitomized and simulation experiments were conducted in deionized (DI) water and source water under pretreatment conditions. Differences in DBP formation between the different backgrounds during chlorination and powdered activated carbon (PAC) treatment were investigated. Instead of monotonous excitation-emission matrix (EEM) spectra, molecular weight (MW) fractionation was simultaneously applied to elucidate the mechanisms of chlorination and PAC adsorption on AOM-based DBPs. The fluorescence regional integration (FRI) EEM results showed a clear correlation between the fluorescent properties and MW distribution of AOM. A decreasing trend was observed after a rapid increase in fluorescence intensity during the chlorination and PAC treatment of water samples in the simulation experiments in deionized (DI) water and source water. The DBP formation potential (FP) in the source water was consistent with the change in AOM during chlorination and PAC adsorption. In addition, EEM showed decent predictability of AOM-based trihalomethanes (THM) FPs (R2 = 0.77-0.99) invoking a combination with MW fractionation. Macromolecular protein compounds were highly correlated with the formation of dichloroacetonitrile (DCAN) (R2 = 0.89-0.98). These post-mortems results imply that EEM spectra are a useful tool for identifying AOM-based precursors to reveal the accurate environmental fate and risk assessments of AOM.