Algogenic Organic Matter Research Articles

Performance of PAC treatments on MF membrane fouling behavior and mechanism by various algogenic organic matter

Performance of PAC treatments on MF membrane fouling behavior and mechanism by various algogenic organic matter

Minimization of halogenated DBP precursors by enhanced PACl coagulation: The impact of organic molecule fraction changes on DBP precursors destabilization with Al hydrates

The destabilization of halogenated disinfection-by-product (DBP) precursors by coagulation are mostly subjected to Al speciation of polyaluminum chloride (PACl) and the fraction of dissolved organic matter (DOM), which significantly affect the minimization of halogenated DBP precursors, such as trihalomethane (THM) and haloacetic acids (HAA), in post-chlorination. In this study, the destabilization of DOM in the solution of humic acid (HA) with and without algogenic organic matter (AOM) using two PACl coagulants with different Al speciation was investigated, along with the identification of optical properties for DOM fractions. Additionally, total THM and HAA formation potential of the supernatant before and after coagulation-sedimentation were determined. The results showed that high polymeric Al-containing PACl (PACl-H, 66% Al13) outcompetes in destabilizing HA than commercial PACl (PACl-C, 29% Al13, 32% Al(OH)3). However, the removal of DOM in HA/AOM mixture by both PACl coagulants are significantly suppressed with greater removal of humic-like and fulvic-like substances than aromatic protein-like substances after coagulation-sedimentation, where PACl-C shows superiority in the removal of hydrophobic and hydrophilic substances with MW around 1 kDa than PACl-H. In the absence of AOM, total THM and HAA formation potential were effectively reduced for HA coagulation by both PACl, but vice versa with the presence of AOM, especially for cellular organic matter (COM). Minimization of halogenated DPB precursors by coagulation are predominated by destabilized hydrophilic molecule fractions with Al hydrates. It is concluded that PACl-H favors charge neutralization to destabilize total carbonaceous DBP (C-DBP) precursors in HA or HA/AOM mixture and the corresponding C-DBP formation potential is lower compared to PACl-C that predominates adsorption and co-precipitation in destabilizing C-DBP precursors.

The inhibition effect of recycled Scenedesmus acuminatus culture media: Influence of growth phase, inhibitor identification and removal

Existing research shows that the presence of algogenic organic matter (AOM) in recycled media can inhibit the growth of algae. However, the characteristics and occurrence of the inhibitors are not well understood. In this study, changes in the algogenic organic matter present in culture media and the influence of these changes on the recultivation of Scenedesmus acuminatus were investigated. A hydrophobic humic substance was then extracted from the recycled medium, and its inhibitory effects on the growth of Scenedesmus acuminatus were assessed. The efficiency of the removal of the humic substance from the recycled media using granular activated carbon (GAC) treatment was evaluated. The results showed that the later the growth phase at which the recycled media was harvested, the stronger the growth inhibition was. In addition, it was found that the percentage of total carbohydrates, fatty acids, and proteins in the algogenic organic matter decreased with the prolongation of growth phase, while the percentage of the hydrophobic humic substance in algogenic organic matter increased as the algae gradually went into the declining phase. Furthermore, an inhibitory effect of the hydrophobic humic substances on the growth of Scenedesmus acuminatus was identified. The effectiveness of inhibitor removal using granular activated carbon column adsorption was confirmed. The results of this study can be applied to the sustainable utilization of water and nutrients in the mass production of microalgal biomass.

Harvesting of Isochrysis zhanjiangensis using ultrafiltration: Changes in the contribution ratios of cells and algogenic organic matter to membrane fouling under different cross-flow velocities

Increasing the cross-flow velocity can improve the permeate flux to a certain extent during cross-flow ultrafiltration harvesting of microalgae. In this study, the effect of cross-flow velocity on the fouling mechanisms of Isochrysis zhanjiangensis suspension, fragile algogenic organic matter-free cells and cell-free algogenic organic matter was investigated using different cross-flow velocities of 0.13, 0.26, 0.51 and 0.63 m·s−1. The fouling mechanism of algogenic organic matter and algae cells was analyzed by Hermia's model; in particular, the changes in their fouling ratios under different cross-flow velocities were further elucidated based on the criteria importance through intercriteria correlation. The results revealed that cake formation by algogenic organic matter and cells mainly induced membrane fouling at different cross-flow velocities. Notably, the contribution of algogenic organic matter and algae cells to membrane fouling varied with cross-flow velocity. The objective weight of fouling caused by algae cells decreased from 0.758 to 0.279, then increased to 0.560 after cell disruption and finally reached 0.946. This result suggested that the cell disruption significantly aggravated cellular fouling. In contrast, the objective weight of fouling caused by algogenic organic matter increased with cross-flow velocity, and cell disruption reversed the trend. For further insight, a model was developed based on the fouling contributions of algogenic organic matter and cells to cake formation; the model was capable of predicting fluxes under different cross-flow velocities. These findings not only clarify the fouling mechanism of I. zhanjiangensis cells and algogenic organic matter but also provide a valuable model that is instructive for the development of membrane filtration of fragile microorganisms.

Influences of cellular characteristics and media properties on membrane microalgal harvesting: a comparative study using Scenedesmus acuminatus cultivated at a pilot scale

AbstractBACKGROUNDIn order to reveal the influence of cellular characteristics and media properties on membrane microalgal harvesting, changes in the cellular characteristics and media properties of Scenedesmus acuminatus culture contaminated by microzooplankton were characterized, and their influences on membrane harvesting were compared with the control culture. Cells and algogenic organic matter (AOM) in the contaminated and control cultures were fractionated to evaluate the membrane fouling potential.RESULTSThe contaminated culture had a 32% lower average flux than control culture. Both the fractionated cells and AOM in the contaminated culture with or without concentration adjustment had higher membrane fouling potentials. Microzooplankton contamination caused more cell aggregates and transparent exopolymer particles, which formed less permeable cake layer. Increased AOM in contaminated culture contained more carbohydrates and humic/fulvic acid‐like substances, which caused a 15.5‐fold higher adhesion force between AOM and the membrane surface, and thus resulted in higher flux declining rates and lower backwashing recovery rates.CONCLUSIONMicrozooplankton contamination caused the formation of cell aggregates and high concentration of AOM in S. acuminatus culture. AOM played a more important role than microalgal cells in flux declining and backwashing recovery. It is necessary to develop cultivation practice and culture pretreatment techniques to improve membrane harvesting efficiency. © 2019 Society of Chemical Industry

Influence of growth phase on the harvesting of Scenedesmus acuminatus using ultrafiltration

Cellular characteristics and algogenic organic matter (AOM) properties change with culture time. This study aims to understand the changes throughout the growth phase, and their effect on Scenedesmus acuminatus harvesting using ultrafiltration. The variations in cellular particle size distribution, cellular EPS content, and the biochemical composition and molecular weight of AOM were analyzed, followed by the membrane harvesting of the original S. acuminatus suspension, AOM-free cells and cell-free AOM. The results showed that the average flux for the original suspension increased with growth phase and reached an increase of 36.3% in the declining phase. AOM played a greater role than S. acuminatus cells in flux decline for all growth phases. Exponential-phase AOM contained a greater high-MW fraction and more carbohydrates, and the exponential cells were smaller cells and had a higher EPS content; these characteristics resulted in a reduced average flux.

Using fluorescence surrogates to track algogenic dissolved organic matter (AOM) during growth and coagulation/flocculation processes of green algae

Tracking the variation of the algogenic organic matter (AOM) released during the proliferation of green algae and subsequent treatment processes is crucial for constructing and optimizing control strategies. In this study, the potential of the spectroscopic tool was fully explored as a surrogate of AOM upon the cultivation of green algae and subsequent coagulation/flocculation (C/F) treatment processes using ZrCl4 and Al2(SO4)3. Fluorescence excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC) identified the presence of three independent fluorescent components in AOM, including protein-like (C1), fulvic-like (C2) and humic-like components (C3). Size exclusion chromatography (SEC) revealed that C1 in AOM was composed of large-sized proteins and aromatic amino acids. The individual components exhibited their unique characteristics with respect to the dynamic changes. C1 showed the highest correlation with AOM concentrations (R2 = 0.843) upon the C/F processes. C1 could also be suggested as an optical predictor for the formation of trihalomethanes upon the C/F processes. This study sheds a light for the potential application of the protein-like component (C1) as a practical surrogate to track the evolution of AOM in water treatment or wastewater reclamation systems involving Chlorella vulgaris green algae.

Fluorescent and molecular weight dependence of THM and HAA formation from intracellular algogenic organic matter (IOM)

This study (i) examined the formation of two major carbonaceous disinfection by-products (C-DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), during the chlorination of intracellular algogenic organic matter (IOM) extracted from two commonly blooming algae M. aeruginosa (MA) and Chlorella sp. (CH), and (ii) investigated the roles and relationships of fluorescent and molecular weight (MW) properties on/with IOM-derived THMs and HAAs. The extracted IOM samples were separated into different MW fractions by centrifugal devices with membrane support with MW cut-offs of 100, 30, 10, 3, and 1 kDa. We observed an overall reduction of C-DBPs with a decrease of IOM-MW from >100 kDa to <1 kDa. Of six fractionated IOM, a large fraction (>100 kDa) contributed the largest amount to the MW distribution of IOM, accounting for 33 and 42% of the total dissolved organic carbon (DOC) of MA and CH, respectively. It also had the highest-yielding potential to produce significant levels of THMs and HAAs, and total C-DBPs over other small MW fractions. Although small MW fractions (>10 kDa) contributed around 50% of the total DOC, they made an insignificant contribution (>20%) to the THMs, HAAs, and overall C-DBPs. Furthermore, the decrease of IOM MW caused a shift from the domination of HAA formation to THM formation, especially when MW was <10 kDa. By canonical correspondent analysis, the relationship of IOM-derived THMs and HAAs with IOM properties was examined. In particular, large fractions of IOM, exhibiting aromatic protein- (AP) and soluble microbial product- (SMP) like fluorescence, are favorable for the formation of HAAs, whereas small MW fractions of IOM with HA- and FA-like fluorescence preferentially tends to form THMs. Our findings evidently show the strong dependence of IOM-derived THMs and HAAs on the fluorescent and MW properties. Therefore, the characterization of MW and fluorescent properties can provide the advantages in the control of algae-derived DBPs upon the chlorination of eutrophic water.

Effects of water temperature and light intensity on the performance of gravity-driven membrane system

The selection of favorable environmental conditions for gravity-driven membrane (GDM) systems is crucial to their widespread application. In this study, GDM systems operated under different light intensities (illuminance levels of 0, 200, and 3000 Lux) and water temperatures (10, 20, and 30 °C) were investigated for their performance and fouling layer characteristics. The results showed that indoor light (200 Lux) had limited effects on the performance of the GDM system. However, full daylight (3000 Lux) led to algal growth; these algae increased fouling resistance and deteriorated permeate water by releasing algogenic organic matter, although they could also enhance the heterogeneity of the biofouling layer by increasing the microbial activity. Water temperature rarely influenced the total organic matter removal. The fouling layers had different thicknesses and heterogeneity, but the same level of EPS; therefore, the hydraulic resistances of these fouling layer were almost the same at different water temperatures. These findings suggest that GDM system could be operated at low water temperature and indoor light conditions, and that strong light should be avoided during the operation of GDM systems.

Yield of trihalomethane, haloacetic acid and chloral upon chlorinating algae after coagulation-filtration: Is pre-oxidation necessarily negative for disinfection by-product control?

Effect of pre-chlorination and pre-ozonation on Microcystis aeruginosa (MA) and Coccomyxa subellipsoidea (CS) as disinfection by-products (DBPs) precursors was investigated after coagulation-filtration. Pre-chlorination considerably decreased the autofluorescence of algae cells but barely influenced cell granularity. In comparison, after pre-ozonation more algae cells were associated with decreased cell size; yet less reduction in the autofluorescence was observed. In MA case, pre-chlorination increased the residual algae density after coagulation-filtration by 132%-146% while pre-ozonation enhanced the algae removal by 26%-28%. In CS case, algae removal was improved by pre-chlorination (32%-45%) and pre-ozonation (7%-45%). Pre-chlorination enhanced the removal of algogenic organic matters (AOM) by coagulation-filtration, especially for tryptophan-like and soluble microbial products. Effect of pre-ozonation on the fluorescence intensity of AOM after coauglation-filtration depended on AOM species and the ratio of [ozone dose]:[algae density]. In both MA and CS cases, chlorine increased the yields of trihalomethane (THM, 25%-78% and 51%-103%), haloacetic acid (HAA, 140%-360% and 167%-233%) and chloral (50%-161% and 68%-108%), respectively. Pre-ozonation decreased the total DBPs yields. For MA-added suspensions, ozone decreased the production of THM, HAA and chloral by 15%-37%, 28%-39% and 60%, respectively. In CS case, chloral yield was decreased by 12%-31% while THM formation was largely unchanged. HAA production varied by ± 1.5 μg/L.

Probing algogenic organic matter (AOM) by size-exclusion chromatography to predict AOM-derived disinfection by-product formation

High-performance size exclusion chromatography (HPSEC) coupled with peak-fitting technique was used to probe molecular weight (MW) properties of algogenic organic matter (AOM). The qualitative and quantitative MW information derived was used to predict AOM-derived disinfection by-product (DBP) formation. We resolved overlapping HPSEC chromatograms of all AOM samples into six major peaks with R2 > 0.996. This study gave significant insight into the HPSEC profiles of AOM, in which resolved peaks A and B (biopolymers) and peak C (humic substances) showed a strong correlation with the formation of carbonaceous-DBPs (C-DBPs). This likely resulted from the abundance of aromatic structures and conjugated CC double bonds in their chemical nature. Our results also indicated the importance of algal cells, including intra-cellular and cell-bound organic matter, over extra-cellular organic matter as precursors to C-DBP formation. The application of the information extracted from HPSEC profiles associated with the fluorescent components of AOM showed great improvements in the predictability of THMs, HAAs, and C-DBPs with R2 > 0.7 and p < 0.05. The outcome of this study will significantly benefit effective control of AOM-derived DBP formation by the chlorination of eutrophic waters.

Characteristics of intracellular algogenic organic matter and its reactivity with hydroxyl radicals

The aim of this study was to investigate the reactivity of intracellular algogenic organic matter (IOM) with hydroxyl radicals (·OH), a key reaction species in advanced oxidation processes. IOM was extracted from two green algae, Chlamydomonas reinhardtii and Scenedesmus sp., and two blue-green algae, Anabaena sp. and Microcystis aeruginosa using a freeze–thaw method. The second-order rate constants of the extracted IOM with ·OH were determined as 7.95 × 108 MC−1 s−1 (Chlamydomonas reinhardtii), 6.71 × 108 MC−1 s−1 (Scenedesmus sp.), 4.02 × 108 MC−1 s−1 (Anabaena sp.), and 4.45 × 108 MC−1 s−1 (Microcystis aeruginosa). These rate constants were significantly higher than values reported for dissolved organic matter in various water sources. This implies that IOM formation during algal bloom season could change the ·OH water matrix demand and adversely affect the performance of advanced oxidation processes. To investigate the physical and chemical composition characteristics of IOM and their relationship to the rate constants determined for the reaction between IOM and ·OH, liquid chromatography-organic carbon detection (LC-OCD) and fluorescence excitation-emission matrix & parallel factor analysis (FEEM-PARAFAC) were used. The IOM mainly consisted of low molecular weight (LMW) matter and protein-related compounds, as evidenced LMW neutrals (38–65%), biopolymers (7–19%), and tryptophan-like compounds (74–94%). Based on the composition characteristics of IOM, it was concluded that the molecular weight and the presence of nitrogen-containing compounds are influential parameters for determining the reactivity of IOM with ·OH.

Algal fouling of microfiltration and ultrafiltration membranes and control strategies: A review

Abstract Microalgae are ubiquitous in aquatic systems and are a highly diversified group of uni- and multicellular microorganisms. In low pressure-driven membrane systems, these cells and their secretions have a strong tendency to foul membranes and lead to a very low filtration efficiency. A significant amount of investigation on algal fouling of microfiltration (MF) and ultrafiltration (UF) membranes has been conducted in recent years. In this paper, recent knowledge of both MF and UF membrane fouling by microalgal suspensions, including the mechanisms and factors influencing algal fouling control strategies, is reviewed. The main components and properties of microalgae suspension are summarized. As algal cells and algogenic organic matter (AOM) are major foulants in microalgae suspension, their roles in algal fouling are compared and critically assessed. Based on the fouling mechanisms of these cells and AOM, strategies for mitigation of algal fouling are provided in detail, including pretreating feedwater, changing membrane properties, and enhancing hydrodynamic conditions. The breakup and growth of cells and their consequential influences on fouling receive special attention. Finally, useful directions for further work on MF and UF algal fouling are indicated.

Microalgal dewatering using a polyamide thin film composite forward osmosis membrane and fouling mitigation

In this study, the dewatering of Scenedesmus acuminatus suspensions using a polyamide thin film composite (TFC) forward osmosis (FO) membrane with enhanced surface shearing was investigated. The influence of the draw solution (DS) concentration and microalgal properties were studied, and a fouling mitigation method using mechanical shearing was developed. S. acuminatus suspension dewatering by the same FO membrane was repeated 8 times to test the membrane's recoverability and durability. The results showed that the membrane flux and the concentration of magnesium chloride DS presented a non-linear relationship. In addition, membrane flux did not increase once the DS concentration increased to 2 mol L−1, when serious fouling occurred. However, the membrane flux was significantly improved by mechanical shearing across the membrane surface. At shear rate of 4 (1000 rpm), a 2 mol L−1 MgCl2 solution resulted in an average flux as high as 25.9 L m−2 h−1 during the dewatering of a 1.0 g L−1 microalgal suspension. Microalgal cells and algogenic organic matter (AOM) were tested to determine the membrane fouling mechanism. The results showed that the microalgal cells and AOM resulted in 15.4% and 9.4% water flux loss in 1 h, respectively, whereas the combination of microalgal cells and AOM resulted in 24.7% water flux loss. After dewatering for 8 h, microalgal suspensions were concentrated 20 times, and the average membrane flux was 23.3 L m−2 h−1. In addition, most of the membrane fouling was reversible by simple hydraulic flushing; the pure water flux remained more than 97% of original pure water flux after 8 repeated dewatering processes, which demonstrated the potential application of FO in microalgal dewatering.

Optical properties of algogenic organic matter within the growth period of Chlorella sp. and predicting their disinfection by-product formation

Algogenic organic matter (AOM) in eutrophic waters is a well-known precursor to disinfection by-product (DBP) formation in drinking water. This purpose of this study is (i) to characterize the optical properties of AOM origins, including intra- (IOM) and extra-cellular organic matter (EOM), derived from Chlorella sp. growth as precursors to two major carbonaceous DBPs (C-DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs) and (ii) to correlate these optical properties with THM and HAA formation potential (FP) in order to predict DBP formation. The results show that both EOM and IOM had low UV254 and UV280 absorbance during their entire growth phase. While IOM chiefly comprised of aromatic proteins and soluble microbial products-like substances (80% of average fluorescent intensity–AFI), EOM spectra were rich in humic- and fulvic-like substances (60% AFI). However, its chemical nature likely differed from terrestrial humics. In DBPFP tests, IOM was a higher-yielding precursor of THMs and HAAs compared to EOM, regardless its growth status. Consequently, C-DBPFP of IOM was always higher than EOM during four growth phases. Results from DBP tests also showed insignificant variation of EOM-derived THMFP and HAAFP during the algal growth phase, while the algal growth status strongly influenced the yields of IOM-derived THMFP and HAAFP. From correlation analysis, our results showed no correlation between UV absorbance with THMFP and HAAFP. Conversely, the regional AFI showed a good correlation with HAAFP and C-DBPFP. Predicting models based on AFI for the formation of HAAs and C-DBPs consequently yielded great predictability for laboratory AOM-containing water samples, with a coefficient of determination R2=0.879, p<0.01 and R2=0.846, p<0.01. This study indicates a promising application of fluorescent spectra for predicting DBPs derived from algae-rich water sources.

Chemical structures of extra- and intra-cellular algogenic organic matters as precursors to the formation of carbonaceous disinfection byproducts

Algal eutrophication in reservoirs is frequently accompanied by a remarkable increase in the concentration of algogenic organic matter (AOM). Because AOM is well-known as an important precursor to disinfection byproducts (DBPs) in drinking water, algal eutrophication poses severe concerns for public health. This study aimed to characterize the chemical properties of AOM from two major origins, i.e. extra- (EOM) and intra-cellular organic matter (IOM), of a commonly found green alga Chlorella sp. as precursors to trihalomethanes (THMs) and haloacetic acids (HAAs). Particularly, the corresponding relation between the chemical functional structure of EOM and IOM and their THM and HAA formation potential (THMFP and HAAFP) was comprehensively investigated. Results show that IOM chiefly comprised of aromatic and other aliphatic protein-like materials (high organic nitrogen content) those have high activity for chlorine substitution (high UV253/UV203 value) due to the high hydroxyl and amide contents in its chemical structures. EOM alternatively exhibited the characteristics of humic- and fulvic-like materials accompanying with high DOC/DON ratio and aromaticity. However, the chemical structure of EOM had a low tendency for chlorine substitution (low UV253/UV203 value); it was also accompanied by a considerable content of carboxylic moisture, which likely resulted in an unfavorable substitution reaction of EOM with chlorine. As a result, the carbonaceous DBP formation potential (C-DBPFP) showed that IOM yielded higher levels of both THMFP and HAAFP than that yielded by EOM.

Interfacial interactions between Skeletonema costatum extracellular organic matter and metal oxides: Implications for ceramic membrane filtration

In the current study, the interfacial interactions between the high molecular weight (HMW) compounds of Skeletonema costatum (SKC) extracellular organic matter (EOM) and ZrO2 or Al2O3, were investigated by atomic force microscopy (AFM). HMW SKC-EOM was rigorously characterized and described as a hydrophilic organic compound mainly comprised of polysaccharide-like structures. Lipids and proteins were also observed, although in lower abundance. HMW SKC-EOM displayed attractive forces during approaching (i.e., leading to jump-to-contact events) and adhesion forces during retracting regime to both metal oxides at all solution conditions tested, where electrostatics and hydrogen bonding were suggested as dominant interacting mechanisms. However, the magnitude of these forces was significantly higher on ZrO2 surfaces, irrespective of cation type (Na+ or Ca2+) or concentration. Interestingly, while HMW SKC-EOM interacting forces to Al2O3 were practically insensitive to solution chemistry, the interactions between ZrO2 and HMW SKC-EOM increased with increasing cation concentration in solution. The structure, and lower charge, hydrophilicity, and density of hydroxyl groups on ZrO2 surface would play a key role on favoring zirconia associations with HMW SKC-EOM. The current results contribute to advance our fundamental understanding of Algogenic Organic Matter (AOM) interfacial interactions with metal oxides (i.e., AOM membrane fouling), and would highly assist in the proper selection of membrane material during episodic algal blooms.

Algal removal from cyanobacteria-rich waters by preoxidation-assisted coagulation–flotation: Effect of algogenic organic matter release on algal removal and trihalomethane formation

The cyanobacteria-bloom in raw waters frequently causes an unpredictable chemical dosing of preoxidation and coagulation for an effective removal of algal cells in water treatment plants. This study investigated the effects of preoxidation with NaOCl and ClO2 on the coagulation–flotation effectiveness in the removal of two commonly blooming cyanobacteria species, Microcystis aeruginosa (MA) and Cylindrospermopsis raciborskii (CR), and their corresponding trihalomethane (THM) formation potential. The results showed that dual dosing with NaOCl plus ClO2 was more effective in enhancing the deformation of cyanobacterial cells compared to single dosing with NaOCl, especially for CR-rich water. Both preoxidation approaches for CR-rich water effectively reduced the CR cell count with less remained dissolved organic carbon (DOC), which benefited subsequent coagulation–flotation. However, preoxidation led to an adverse release of algogenic organic matter (AOM) in the case of MA-rich water. The release of AOM resulted in a poor removal in MA cells and a large amount of THM formation after oxidation-assisted coagulation–flotation process. The reduction in THM formation potential of CR-rich waters is responsible for effective algae and DOC removal by alum coagulation. It is concluded that the species-specific characteristic of cyanobacteria and their AOM released during chlorination significantly influences the performance of coagulation–flotation for AOM removal and corresponding THM formation.

Fouling and Cake Behavior of Algal Organic Foulants on Microfiltration Membranes in Various Growth Phases

This study investigated the fouling behavior of algal organic foulants in various growth phases during microfiltration. The characteristics of the algogenic organic matter (AOM) in various growth phases were also determined to identify the membrane foulants on fouled membranes. The results indicated the stationary phase of the Aphanizomenon flos‐aquae and Anabaena flos‐aquae AOMs resulted in the most serious filtration flux, followed by their late exponential and primary exponential phases. The amounts of protein/protein‐like substances, the neutral hydrophilic fraction, and the macromolecular organics (including molecular weight) increased with cultivation time, potentially attributed to increasing membrane fouling. Analysis of organic hydrophobicity, molecular weight distribution and fluorescence excitation–emission matrix indicated that algal organic accumulation is a dynamic process of algal activity, biopolymers such as protein‐like and polysaccharides‐like substances were the major components of membrane foulants for the three algal growth phases. Moreover, pore plugging and cake layer formation were the dominant fouling mechanisms in membrane filtration. Timely monitoring of algal growth in water can be important for effectively predicting membrane fouling in microfiltration.

Effects on cyanobacterial growth and water quality after harvesting accumulated cyanobacteria in autumn: an &lt;i&gt;in-situ&lt;/i&gt; experiment in Lake Chaohu

An in-situ enclosure experiment was conducted to study the effect of harvesting of algae on cyanobacteria growth and water quality in the northwestern Lake Chaohu in autumn. The gill type filter was used to harvest cyanobacteria in two enclosures and no treatment was conducted in control enclosure. The growth rates of cyanobacteria and the concentrations of nutrients and organic matters were investigated after harvesting compared with that in the control. The initial concentrations of chlorophyll-a,total nitrogen and total phosphorus reached 309. 5 ± 3. 7 μg / L,3. 32 ± 0. 14 mg / L and 0. 30 ± 0. 04 mg / L,respectively. Algogenic organic matter became a major source of dissolved organic matter in the enclosures,and fluorescent dissolved organic matter was dominated by proteinoid materials. Harvesting reduced the cyanobacterial biomass by 41. 7%,which relieved the "density dependence of growth"of cyanobacteria,and then resulted in an increase in diel frequency of dividing cells and the in-situ growth rates of cyaobacteria. Algogenic organic matters were reduced due to harvesting increased the viability of cyanobacterial cells in a short term.What's more,cyanobacteria tended to decline in autumn and chlorophyll-a concentration dropped gradually in the enclosures,which testified that harvesting in autumn would not cause a second outbreak of algal bloom. Primary productivity,nitrogen and phosphorus nutrients,Potassium permanganate index were controlled significantly in the harvesting enclosures due to the reduction of cyanobacterial biomass. Furthermore,the release of algogenic organic matters was controlled and macromolecular organic compound was degraded easily to low-molecular-weight organics. Therefore,harvesting the accumulated cyanobacteria shoreside in autumn could control the amount of algae,nitrogen and phosphorus nutrients as well as the release of algogenic organic matters,which could reduce the ecological risk in lakes.