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.

Solicola gregarius gen. nov., sp. nov., a soil actinobacterium isolated after enhanced cultivation with Micrococcus luteus culture supernatant.

An actinobacterial strain, designated A5X3R13T, was isolated from a compost soil suspension supplemented with extracellular material from a Micrococcus luteus-culture supernatant. The strain was cultured on tenfold-diluted reasoner's 2A agar. The cells were ovoid-to-rod shaped, non-motile, Gram-stain-positive, oxidase-negative, catalase-positive and had a width of 0.5 µm and a length of 0.8-1.2 µm. The results of both 16S rRNA-based phylogenetic and whole-genome analyses indicate that A5X3R13T forms a distinct lineage within the family Nocardioidaceae (order Propionibacteriales). On the basis of the 16S rRNA gene sequence, A5X3R13T was closely related to Aeromicrobium terrae CC-CFT486T (96.2 %), Nocardioides iriomotensis IR27-S3T (96.2 %), Nocardioides guangzhouensis 130T (95.6 %), Marmoricola caldifontis YIM 730233T (95.5 %), Aeromicrobium alkaliterrae KSL-107T (95.4 %), Aeromicrobium choanae 9H-4T (95.4 %), Aeromicrobium panaciterrae Gsoil 161T (95.3 %), and Nocardioides jensenii NBRC 14755T (95.2 %). The genome had a length of 4 915 757 bp, and its DNA G+C content was 68.5 mol %. The main fatty acids were 10-methyl C17 : 0, C16 : 0, C15 : 0, C18 : 0, C17 : 0 and iso-C16 : 0. The main polar lipids were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol and two unidentified phospholipids. MK-9(H4) was the predominant respiratory quinone. The peptidoglycan type was A3γ (A41.1) and contained alanine, glycine, glutamic acid and ll-diaminopimelic acid in a molar ratio of 1.2 : 0.9 : 1.0 : 0.8. On the basis of the results of the phylogenetic and phenotypic analyses and comparisons with other members of the family Nocardioidaceae, strain A5X3R13T is proposed to represent a novel species within a novel genus, for which the name Solicola gregarius gen. nov., sp. nov. is proposed. The type strain is A5X3R13T (=DSM 112953T=NCCB 100840T).

Pedomonas mirosovicensis gen. nov., sp. nov., a bacterium isolated from soil with the aid of Micrococcus luteus culture supernatant containing resuscitation-promoting factor.

An orange-golden iridescent culture, designated A1X5R2T, was isolated from a compost soil suspension which was amended with Micrococcus luteus NCTC 2665T culture supernatant. The cells were non-motile, Gram-stain-negative, 0.4-0.5 µm wide and 0.7-1.4 µm long. The 16S rRNA-based phylogenetic and whole-genome analyses revealed that strain A1X5R2T forms a distinct lineage within the family Sphingosinicellaceae and is closely related to members of the genus Sphingoaurantiacus (S. capsulatus, 93.04 % similarity, and S. polygranulatus, 92.77 %). The organism grew at 22-47 °C (optimal at 37 °C), salinity <3 % (optimal at 1.5 %) and at pH 7. The major respiratory quinone was ubiquinone-10, but a small quantity of ubiquinone-9 was also detected The major polyamine was homospermidine, but a small quantity of putrescine was also detected. The strain contained C18  :  1ω7c, C16 : 0, C16 : 1 ω7c and C18 : 0 as the major fatty acids. The main polar lipids were phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, sphingoglycolipid, diphosphatidylglycerol, two unidentified phospholipids and three unidentified amino lipids. The DNA G+C content was 64.9 mol%. According to the results of phylogenetic and phylogenomic analyses, as well as its physiological characteristics, strain A2X5R2T represents the type species of a novel genus within the family Sphingosinicellaceae. The name Pedomonas mirosovicensis gen. nov., sp. nov. is proposed, with the type strain being A1X5R2T (=NCCB 100839T=DSM 112829T).

Investigation of membrane fouling and mechanism induced by extracellular organic matter during long-term exposure to pharmaceuticals and personal care products.

This study investigated ultrafiltration membrane fouling by extracellular organic matter (EOM) and the mechanism operating during long-term exposure to pharmaceuticals and personal care products. The results indicated that carbamazepine and diclofenac in algal-laden water altered the filtration flux and membrane fouling by EOM. Exposure to low-concentration carbamazepine (0.25 µg/L) improved the filtration flux and the total (Rtot) and reversible fouling resistance (Rc), whereas the filtration flux and Rtot and Rc were reduced when EOM was used during long-term exposure to high carbamazepine concentrations (>1 µg/L). Both Rtot and Rc were increased when algae were exposed to 0.25 µg/L diclofenac, whereas the filtration flux and Rtot and Rc were alleviated when algae were exposed to >1 µg/L diclofenac. Moreover, carbamazepine and diclofenac (0.25 µg/L - 1000 µg/L) in water enhanced the irreversible fouling resistance (Rb) when ultrafiltration was used to treat algal-laden waters. The mechanism indicated that membrane fouling induced by standard blocking was transformed to complete blocking when EOM was exposed to high levels of carbamazepine (>0.25 µg/L) in the initial filtration process, whereas cake layer formation played an important role during the later filtration process; with low carbamazepine levels (0.25 µg/L), standard blocking of EOM was dominant during the entire filtration process. The membrane fouling mechanism also changed when algal-laden waters were exposed to diclofenac, the membrane fouling was transformed from complete blocking to standard blocking when DFC was present in the initial filtration process, whereas cake layer formation exerted an important role during the late filtration process. This research provides important information on the long-term risks caused by pharmaceutical and personal care products and potential threats to membrane treatment.

Algal extracellular organic matter mediated photocatalytic degradation of estrogens.

Estrogens are among the most concerned emerging contaminants in the wastewater treatment effluent due to their sexual disruption in aquatic wildlife. The use of microalgae for secondary wastewater effluent polishing is a promising approach due to the economic benefit and value-added products. In this study, three microalgae species, including Selenastrum capricornutum, Scenedesmus quadricauda and Chlorella vulgaris were selected to conduct batch experiments to examine important mechanisms, especially the role of algal extracellular organic matter (AEOM) on two selected estrogens (17ß-estradiol, E2 and 17α-ethynylestradiol, EE2) removal. Results showed that estrogens could not be significantly degraded under visible light irradiation and adsorption of estrogens by microalgae was negligible. All three living microalgae cultures have ability to remove E2 and EE2, and Selenastrum capricornutum showed the highest E2 and EE2 removal efficiency of 91% and 83%, respectively, corresponding to the reduction of predicted estrogenic activity of 86%. AEOM from three microalgae cultures could induce photodegradation of estrogens, and AEOM from Selenastrum capricornutum and Chlorella vulgaris achieved 100% of E2 and EE2 removal under visible light irradiation. Fluorescence excitation-emission matrix spectroscopy identified humic/fulvic-like substances in AEOM from three microalgae cultures, which might be responsible for inducing the indirect photolysis of E2 and EE2. Therefore, in the living microalgae cultures, the major estrogens removal mechanisms should include biotransformation as well as AEOM meditated photocatalytic degradation. Since removal rates through photodegradation could be faster than biotransformation, the AEOM mediated photocatalytic degradation can play a potential role to remove emerging contaminants when using microalgae technology for wastewater effluent treatment.

The role of extracellular organic matter on the cyanobacteria ultrafiltration process.

The membrane fouling caused by extracellular organic matter (EOM) and algal cells and organic matter removal of two typical cyanobacteria (M. aeruginosa and Pseudoanabaena sp.) during ultrafiltration (UF) process were studied in this work. The results showed that EOM had a broad molecular weight (Mw) distribution and the irreversible membrane fouling was basically caused by EOM. Moreover, humic acid and microbial metabolites were major components of EOM of two typical cyanobacteria. Since EOM could fill the voids of cake layers formed by the algal cells, EOM and algal cells played synergistic roles in membrane fouling. Fourier transform infrared spectroscopy analysis indicated that the CH2 and CH3 chemical bonds may play an important role in membrane fouling caused by EOM. Interestingly, the cake layer formed by the algal cells could trap the organic matter produced by algae and alleviate some irreversible membrane fouling. The results also showed that although the cake layer formed by the algal cells cause severe permeate flux decline, it could play a double interception role with UF membrane and increase organic matter removal efficiency. Therefore, when using UF to treat algae-laden water, the balance of membrane fouling and organic matter removal should be considered to meet the needs of practical applications.

Enhanced nitrogen removal of aerobic denitrifier using extracellular algal organic matter as carbon source: application to actual reservoir water.

Man-made organic matter acting as carbon source for oligotrophic aerobic denitrification has been studied extensively, while less attention has been paid to the actual organic matter derived from drinking water reservoir. In this study, the effect of extracellular organic matter (EOM) released from Microcystis aeruginosa and Chlorella sp. and organic matter in actual reservoir water on aerobic denitrification performance of Acinetobacter johnsonii strain WGX-9 has been investigated, by measuring nitrogen removal and determining changes in the properties of organic matter. Results indicated that the Acinetobacter johnsonii strain WGX-9 showed effective nitrogen removal efficiency when cultural conditions were low C/N of 5, pH of 5-11, and low temperature of 8 °C. The nitrate removal efficiency with EOM as the sole carbon source was relatively higher than that with intracellular organic matter or natural organic matter as the sole carbon source. This is probably due to that EOM exerts a lower molecular weight and better ability of donating electrons. Besides, the findings can elucidate that nitrate and total organic matter removal efficiency with actual high-density algal water as the carbon source was higher than that with actual low-density algal water as the carbon source. This was attributed to that more EOM was released in high-density algal water, which highlighted the aerobic denitrification performance of Acinetobacter johnsonii strain WGX-9. This study will provide a reference for the application of aerobic denitrifier in drinking water reservoirs.

Extracellular organic matter (EOM) distribution characteristic in algae electro-dewatering process.

The work evaluated the influence of different operating conditions (voltage, ionic strength and mechanical pressure) on algae electro-osmotic dewatering effect and extracellular organic matter (EOM) regionalization. It was found that the algae electro-dewatering effect became better as the voltage and ionic strength increased, but electro-dewatering effect was decreased when ionic strength was more than 0.006gNaCl/gTSS, this indicated that too high ionic strength will reduce algae electro-dewatering effect. In addition, electro-osmosis effect first increases and then weakens when the pressure was increased. The content of dissolved organic materials (DOM) in the filtrate of both electrodes was increased when the voltage and ionic strength enhanced, the DOM content of filtrate at cathode and anode were increased from 42.9 mg/L, 36.7 mg/L to 68.2 mg/L, 85.3 mg/L when ionic strength raised from 0gNaCl/gTSS to 0.01gNaCl/gTSS, this indicated that a large amount of EOM dissolution as the voltage and ionic strength increased. The DOM content of both electrodes did not change significantly when mechanical pressure changed, anodic oxidation can oxidize and decompose macromolecular weight substances into mid-molecular weight and low molecular weight substances.

Effect of nitrogen/phosphorus concentration on algal organic matter generation of the diatom Nitzschia palea: Total indicators and spectroscopic characterization.

Critical algal blooms in great lakes increase the level of algal organic matters (AOMs), significantly altering the composition of natural organic matters (NOMs) in freshwater of lake. This study examined the AOM's characteristics of Nitzschia palea (N. palea), one kind of the predominant diatom and an important biomarker of water quality in the great lakes of China, to investigate the effect of AOMs on the variation of NOMs in lakes and the process of algal energy. Excitation-emission matrix fluorescence (EEM) spectroscopy, synchronous fluorescence (SF) spectroscopy and deconvolution UV-vis (D-UV) spectroscopy were utilized to characterize AOMs to study the effects of nutrient loading on the composition change of AOMs. From results, it was revealed that the phosphorus is the limiting factor for N. palea's growth and the generation of both total organic carbon and amino acids but the nitrogen is more important for the generation of carbohydrates and proteins. EEM spectra revealed differences in the composition of extracellular organic matter and intracellular organic matter. Regardless of the nitrogen and phosphorus concentrations, aromatic proteins and soluble microbial products were the main components, but the nitrogen concentration had a significant impact on their composition. The SF spectra were used to study the AOMs for the first time and identified that the protein-like substances were the major component of AOMs, creating as a result of aromatic group condensation. The D-UV spectra showed carboxylic acid and esters were the main functional groups in the EOMs, with -OCH3, -SO2NH2, -CN, -NH2, -O- and -COCH3 functional groups substituting into benzene rings.

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.

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.

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.

UV/Fe(II)/S(IV) Pretreatment for Ultrafiltration of Microcystis aeruginosa-Laden Water: Fe(II)/Fe(III) Triggered Synergistic Oxidation and Coagulation.

Ultrafiltration (UF) has been proven effective in removing algae during seasonal algal blooms, but the algal cells and the metabolites can induce severe membrane fouling, which undermines the performance and stability of the UF. Ultraviolet-activated sulfite with iron (UV/Fe(II)/S(IV)) could enable an oxidation-reduction coupling circulation and exert synergistic effects of moderate oxidation and coagulation, which would be highly preferred in fouling control. For the first time, the UV/Fe(II)/S(IV) was systematically investigated as a pretreatment of UF for treating Microcystis aeruginosa-laden water. The results showed that the UV/Fe(II)/S(IV) pretreatment significantly improved the removal of organic matter and alleviated membrane fouling. Specifically, the organic matter removal increased by 32.1% and 66.6% with UV/Fe(II)/S(IV) pretreatment for UF of extracellular organic matter (EOM) solution and algae-laden water, respectively, while the final normalized flux increased by 12.0-29.0%, and reversible fouling was mitigated by 35.3-72.5%. The oxysulfur radicals generated in the UV/S(IV) degraded the organic matter and ruptured the algal cells, and the low-molecular-weight organic matter generated in the oxidation penetrated the UF and deteriorated the effluent. The over-oxidation did not happen in the UV/Fe(II)/S(IV) pretreatment, which may be attributed to the cyclic redox Fe(II)/Fe(III) coagulation triggered by the Fe(II). The UV-activated sulfate radicals in the UV/Fe(II)/S(IV) enabled satisfactory organic removal and fouling control without over-oxidation and effluent deterioration. The UV/Fe(II)/S(IV) promoted the aggregation of algal foulants and postponed the shift of the fouling mechanisms from standard pore blocking to cake filtration. The UV/Fe(II)/S(IV) pretreatment proved effective in enhancing the UF for algae-laden water treatment.

Variations in trihalomethane formation potential of Microcystis aeruginosa under different growth conditions: Phenomenon and mechanism.

Cyanobacteria and their metabolites are one of the primary precursors of disinfection by-products (DBPs) in natural water environments. However, few studies have investigated whether the production of DBPs by cyanobacteria changes under complex environmental conditions and possible mechanisms underlying these changes. Therefore, we investigated the effects of algal growth phase, water temperature, pH, illumination and nutrients on the production of trihalomethane formation potential (THMFPs) by Microcystis aeruginosa in four algal metabolic fractions, that is, hydrophilic extracellular organic matter (HPI-EOM), hydrophobic EOM (HPO-EOM), hydrophilic intracellular organic matter (HPI-IOM) and hydrophobic IOM (HPO-IOM). Additionally, correlations between THMFPs and some typical algal metabolite surrogates were analyzed. The results showed that the productivity of THMFPs by M. aeruginosa in EOM could be affected significantly by the algal growth phase and incubation conditions, while the IOM productivity varied insignificantly. M. aeruginosa in the death phase could secrete more EOM and have a higher THMFP productivity than those in the exponential or stationary phases. Cyanobacteria grown under harsh conditions could have increased THMFP productivity in EOM by increasing the reactivity of algal metabolites with chlorine, for example, under low pH conditions, and secreting more metabolites in EOM, for example, under low temperature or nutrient limitation conditions. Polysaccharides were responsible for the enhanced THMFP productivity in HPI-EOM fraction, and a significant linear correlation was found between the concentration of polysaccharides and THMFPs (r = 0.8307). However, THMFPs in HPO-EOM did not correlate with dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254), specific UV absorbance (SUVA) and cell density. Thus, we could not specify the kind of algal metabolites that contribute to the increased THMFPs in the HPO-EOM fraction under harsh growth conditions. Compared with the case in EOM, the THMFPs in IOM were more stable and correlated with the cell density and total amount of IOM. The results implied that the THMFPs in the EOM were sensitive to growth conditions and were independent of algal density. Considering the fact that traditional water treatment plants cannot remove dissolved organics as efficiently as algal cells, the increased THMFP productivity in EOM by M. aeruginosa under harsh growth conditions could be a potentially serious threat to the safety of the water supply.

Effects of chlorination on the nitrosamines formation from two algae species in drinking water source-M. aeruginosa and C. meneghiniana.

The effects of chlorine dosage, reaction time, algae concentration, and cell components, including extracellular organic matter (EOM), intracellular organic matter (IOM) and cell debris (CD), were evaluated on the formation of nitrosamines (NAs), including N-Nitrosodimethylamine (NDMA), -Nitrosomethylethylamine (NMEA), N-Nitrosodi-n-propylamine (NDPA), N-nitrosodi-n-butylamine (NDBA), N-Nitrosopyrollidine (NPyr), during the chlorination of Microcystis aeruginosa (M. aeruginosa) and Cyclotella meneghiniana (C. meneghiniana) in drinking water treatment. In addition, the NAs formation from Chlorophyll-a and Microcystin-LR (MC-LR) chlorination was investigated. The results showed that NDMA was the most dominant product of two algae, while only a small yield of NPyr, NMEA and NDBA was generated with NDPA as the least. The nitrosamines formation potential (NAsFP) of M. aeruginosa was positively correlated with the chlorine concentration, while the highest NAsFP of C. meneghiniana was observed at 10 mg/L chlorine. With the increase of reaction time, the NAsFP from C. meneghiniana was higher than M. aeruginosa. The NAs formation enhanced with the increase of cell concentration. Moreover, the impacts of cellular components on the NAsFP followed the order of CD > IOM > EOM and IOM > EOM > CD for M. aeruginosa and C. meneghiniana, respectively. The results indicated that proteins and soluble microbial products (SMPs) were the main cellular components to contribute to NAs formation and IOM was the primary source of NAs precursor for both algae. Chlorination of Chlorophyll-a and MC-LR showed that chlorophyll-a formed only a small yield of NDMA and NDBA, while MC-LR made a more significant contribution to the types of NAs.

Characteristics of extracellular organic matters and the formation potential of disinfection by-products during the growth phases of M. aeruginosa and Synedra sp.

Extracellular organic matter (EOM) is an important precursor of disinfection by-products (DBPs). Nowadays, little is known about changes in molecular weight (MW) and hydrophilic (HPI)/hydrophobic (HPO) fractions of EOM during the entire algal growth phase. In this study, a combined approach of fractionation procedure and parallel factor (PARAFAC) analysis was applied to characterize the EOM during the entire growth phase of two algal species (M. aeruginosa and Synedra sp.), and investigated the relationships between fluorescent component and the DBP formation potential (FP) in MW and HPI/HPO fractions. Thereinto, three components (including one protein-like component (C1), one humic-like component (C2), and one fulvic acid-like component (C3)) were identified by the PARAFAC model. For two algae, the HPI and high MW (> 100 kDa) fractions were both the main components of algal EOM in the three growth phases in terms of the dissolved organic carbon. The high MW fraction had more C1 compared with other MW fractions, especially for M. aeruginosa. Besides, the formation risk of EOM-derived DBPs from M. aeruginosa was lower than that from Synedra sp. The result of this study showed the FP of DBPs varied with fluorescent components of algal EOM fractions and also indicated that the humic-like substances were tended to form trichloromethane and the tryptophan-like substances were associated with dichloroacetic acid by canonical correspondence analysis for both two algae.

Comparison of the formation of N-nitrosodimethylamine (NDMA) from algae organic matter by chlor(am)ination and UV irradiation.

Microcystis aeruginosa (M. aeruginosa, blue-green algae) blooms frequently in drinking water reservoirs and subsequently causes the formation of disinfection by-products (DBPs) after disinfection, which may pose a potential health risk. In this study, the formation of N-nitrosodimethylamine (NDMA) was evaluated from algal organic matter (AOM) including extracellular organic matter (EOM) and intracellular organic matter (IOM) during the disinfection process of chlorination, chloramination, or ultraviolet (UV) irradiation. The effects of a variety of factors, including reaction times, disinfectant dosages and pH, on the NDMA formation by three different disinfection methods were investigated. Additionally, this study evaluated the nitrogen sources involved in NDMA formation during chloramination of EOM and IOM using 15N-labeled monochloramine. The results showed that the NDMA formation by three different disinfection methods were ranked in the order of chlorination > UV irradiation ≈ chloramination and the specific yield from EOM was greater than that from IOM regardless of disinfection method. The yields of NDMA firstly increased and then plateaued as time prolonged during the chlorination and chloramination of AOM. Similarly, the NDMA formation from EOM was firstly increased and then remained constant with the increase of the disinfectant dosage, while it was gradually increased for IOM. The solution pH highly influenced the NDMA formation during chlorination and chloramination, while exhibited a little impact under UV irradiation. Moreover, fluorescence excitation-emission (EEM) analysis confirmed that soluble microbial by-product-like (SMPs) in EOM and IOM were the major precursors in algal-derived organic matter that contributed to the NDMA formation. Chloramination of EOM and IOM using isotope 15N-labeled monochloramine indicated that the nitroso group of the formed NDMA originates mainly from EOM and IOM of algal cells.

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.

Mineralization, characteristics variation, and removal mechanism of algal extracellular organic matter during vacuum ultraviolet/ozone process.

Extracellular organic matter (EOM) produced by algal blooms in source water is detrimental to drinking water treatment processes and supplied water quality. Ozonation has been used to treat algal EOM, but it could not mineralize EOM effectively. In this study, mineralization and characteristics variation of EOM by vacuum ultraviolet/ozone (VUV/O3) and its sub-processes were comprehensively investigated. Results showed that EOM removal in different processes followed the order of VUV/O3 > UV/O3 > O3 > VUV > UV. For VUV/O3 process, removal efficiencies of dissolved organic carbon (DOC), UV254, protein, and polysaccharide at 50 min were 75.6%, 80.8%, 80.1%, and 78.0%, respectively, and fluorescence components received very high removal rates (≥92.8%, at 10 min). The yield of trichloromethane dropped from 102.0 to 30.1 µg/L after treating for 50 min by VUV/O3. Besides, effects of O3 dosage, initial pH, and water matrices on EOM removal in VUV/O3 process were investigated. Moreover, fluorescent molecular probe experiments confirmed that hydroxyl radical and superoxide radical were the main reactive oxygen species (ROS) in VUV/O3 process, and the transformation of ROS was proposed. The mechanism of EOM removal by VUV/O3 included VUV photolysis, direct O3 oxidation, and ROS oxidation. Furthermore, the removal of EOM in filtered water by VUV/O3 was satisfactory. All results indicated that VUV/O3 process had great application potential in treating EOM-rich filtered water.

Identification of the key biochemical component contributing to disinfection byproducts in chlorinating algogenic organic matter.

Disinfection byproducts (DBPs) remains an ongoing issue because of their widespread occurrence and toxicity. Various organic substances in Algogenic organic matter (AOM) can produce DBPs in the chlorination process. To provide specific suggestions for the targeted removal of DBP precursors in AOM, the main biochemical components in AOM were qualitatively and quantitatively analyzed. An accurate model for predicting the DBP formation potentials (DBPFPs) of AOM was herein developed based on the dissolved organic carbon of the five main biochemical components in AOM and the DBPFPs of their corresponding surrogates. The contributions of each biochemical component to the three DBP species were evaluated, and the key components were identified. The results showed that lipids, proteins, carbohydrates, humic acid-like substances, and fulvic acid-like substances were the main biochemical components in AOM. Thereof, proteins (71.2 ± 2.1%) and carbohydrates (53.1 ± 2.1%) were the major contributor to the carbon content in intracellular organic matter and extracellular organic matter, respectively. The contribution results of biochemical components to the formation of DBPs showed that proteins were the key contributor to DBPs, suggesting that the targeted removal of proteins before the chlorination process would effectively reduce DBPs from AOM.