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.

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.

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.

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.

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.

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.

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.

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.

Fouling comparisons of the organic fractions in surface and algae-laden waters make it possible to determine the main compounds responsible for the fouling of ultrafiltration (UF) membranes. This study examined the fouling of UF membranes and its relationship to the characteristics of the organic fractions found in drinking-water supply. Four types of water were prepared by combining natural organic matter (NOM) from lake water with algal organic matter (AOM) from four algae species commonly found in freshwater. Liquid chromatography-organic carbon detection (LC-OCD) and a fluorescence excitation-emission matrix (FEEM) were used to analyze the feed water and permeate to assess the interactions between and fouling behavior of the organic fractions. The results showed that the interaction of large-molecular-weight AOMs on the membrane surfaces and their transport through the membrane pores were the main fouling mechanisms. Polysaccharides followed by protein-like substances were the organic compounds responsible for the fouling of the UF membranes. The fouling affinity of these substances was attributed to two processes, the adsorption of their carboxyl, hydroxyl and cationic groups on the membrane surfaces, and the molecular complexation of their organic groups. The humic substances\' retention was marginal and attributed to the synergetic effects of the polysaccharides and proteins.

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), β-cyclocitral (β-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 β-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.