Algal Extracellular Organic Matter Research Articles

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.

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

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

Characterizing photochemical production carboxyl content of dissolved organic matters using absorbance spectroscopy combined with FT-ICR MS

Irradiation can significantly impact the structure, reactivity and environmental behavior of dissolved organic matter (DOM). The extent of these processes remains to be ascertained in more detail but the heterogeneity and site-specificity of DOM, and the lack of methods to characterize DOM at its environmentally-relevant concentrations make it a challenge. In this study, the differences of DOM response to photodegradation in four typical origins (i.e., surface water, sediment and intracellular and extracellular algal DOM) were tracked on the molecular-level using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). Changes of the carboxyl and phenolic DOM moieties induced by irradiation were quantified by spectroscopic titrations, and the mechanism of functional groups affecting the changes of specific molecular composition was qualitatively proposed. The results demonstrated that intracellular algal organic matter (I-DOM) was most susceptible to photodegradation (ca. 63% DOM loss), then came extracellular algal organic matter (E-DOM) and surface water DOM (W-DOM) (ca. 15% DOM loss). Sediment DOM (S-DOM) was most resistant to irradiation, with a very small level of its mineralization. Lipids, lignin-like compounds and tannin-like compounds in I-DOM and E-DOM were relatively photo-labile. The photodegradation of lipids was related to the decarboxylation of carboxyl functional groups, while the photodegradation of tannin-like compounds was related to the rupture of phenolic functional groups. In comparison, the molecular composition of W-DOM and S-DOM was less affected by irradiation, which was also reflected in the fact that the carboxyl and phenolic functional groups were highly photo-resistant. This study showed that the photoactivity of DOM in surface water was closely related to the abundance of algae, so controlling the excessive reproduction of algae may have a positive effect on stability of quality and quantity of organic matter in surface water.

In situ extracellular algal organic matter beneficial to the coagulation removal of Microcystis aeruginosa at the stationary growth phase

Cyanobacterial blooms in source water deteriorate drinking water quality. Coagulation process is the first barrier to treat cyanobacteria-laden source water in drinking water treatment plants (DWTPs). The changed growth phase of exponential-stationary of cyanobacteria might affect their coagulation efficiency. However, previous studies mainly conducted coagulation tests using one growth phase of exponential or stationary, and the comparative study is limited. Herein, coagulation tests to remove M. aeruginosa at the exponential and stationary phase were compared using a coagulant of polyaluminum chloride, and factors and mechanisms to differ the coagulation efficiency of M. aeruginosa at the two phases were also investigated. Results showed that the removal efficiency of M. aeruginosa at the stationary phase became higher (3.5–98.4 %) than that at the exponential phase (1.2–94.5 %) with in situ bEOM (binding extracellular organic matter)/dEOM (dissolved extracellular organic matter). The larger and looser flocs were formed at the stationary phase than that at the exponential phase. It could be ascribed to their stronger adsorption inter-bridge and sweeping flocculation via more aromatic/N-containing functional groups in bEOM and molecular-weight of dEOM (>30 kDa) interacted with elevated Al(OH)3(am). These findings provide a deep insight into the coagulation removal of cyanobacterial cells at the two phases. Moreover, this study reveals that these in situ bEOM/dEOM biosynthesized by M. aeruginosa at the stationary phase might be promising bio-flocculants to assist cyanobacterial control at a high efficiency in DWTPs.

Effect of Electrochemical Pre-Oxidation for Mitigating Ultrafiltration Membrane Fouling Caused by Extracellular Organic Matter

Algal extracellular organic matter (EOM) will cause grievous membrane fouling during the filtration of algae-laden water; hence, boron-doped diamond (BDD) anodizing was selected as the pretreatment process before the ultrafiltration, and the EOM fouling mitigation mechanism and the purification efficiency were systematically investigated. The results showed that BDD oxidation could significantly alleviate the decline of membrane flux and reduce membrane fouling, and the effect was more notable with an increase in oxidation time. Less than 10% flux loss happened when oxidation duration was 100 min. The dominant fouling model was gradually replaced by standard blocking. BDD anodizing preferentially oxidizes hydrophobic organic matter and significantly reduces the DOC concentration in EOM. The effluent DOC was reduced to less than 1 mg/L when 100 min of BDD anodizing was applied. After the pre-oxidation of BDD, the zeta potential and interfacial free energy, including the cohesive and adhesive free energy, were all constantly increasing, which implied that the pollutants would agglomerate and deposit, and the repulsion between foulants and the ultrafiltration membrane was augmented with the extensive oxidation time. This further confirms the control of BDD on membrane fouling. In addition, the BDD anodizing coupled ultrafiltration process also showed excellent performance in removing disinfection by-product precursors.

Visible light photocatalysis alleviates ceramic membrane fouling caused by intracellular organic matter of Microcystis aeruginosa

Ultrafiltration (UF) is an effective technology for treating algae-containing water. The algal intracellular organic matter (IOM) released by dead algae during an excessive algae growth phase causes more serious membrane fouling than viable algal cells and algal extracellular organic matter (EOM), which seriously restricts stable operation of UF. This paper studied the removal of IOM by a Bi2O3–TiO2/PAC (Bi-doped TiO2 nano-composites supported by powdered activated carbon) photocatalytic oxidation-ceramic ultrafiltration membrane, the inhibitory effect of membrane fouling at different photocatalytic oxidation times, and the fouling mechanism. The results show that both the adsorption and photocatalytic oxidation of Bi2O3–TiO2/PAC can significantly remove proteinoids and humic acid-like fluorescent components present in IOM, with removals of UV254 and DOC reaching up to 81.8% and 44.0%. The generated superoxide radicals and hydroxyl radicals positively affect the degradation of organic compounds of various molecular weights, and holes mainly degrade acidic low-molecular weight organic compounds. When the photocatalytic oxidation time was extended to 60 min, the membrane flux increased by 70.7% and the reversible resistance and irreversible resistance decreased by 83.4% and 90.1%, respectively. Under these conditions, the fouling mechanism changed from complete blockage to intermediate blockage. In the late stage of photocatalytic oxidation (90–120min), part of the high and medium molecular weight organic components were oxidized to produce low-molecular weight organic compounds (LMW acidic and neutral organic compounds), and blockage of filter cake became the main fouling mechanism. After photocatalysis, the zeta potential decreases significantly and the interaction forces between pollutants and pollutants are transformed into repulsive forces. Application of an appropriate photocatalytic oxidation time can alleviate the ultrafiltration membrane fouling caused by algal-derived organics.

Algal organic matter and dissolved Mn cooperatively accelerate 17α-ethinylestradiol photodegradation: Role of photogenerated reactive Mn(III)

Algal extracellular organic matter (EOM), a major fraction of the dissolved organic matter found in eutrophic plateau lakes, can act as a photosensitizer to drive the abiotic oxidation of Mn(II). This process has the potential to generate reactive Mn(III) and influence the fate of organic pollutants. In this study, the photodegradation of 17α-ethinylestradiol (EE2) in the presence of Mn(II) and EOM was investigated with emphasis on the photogeneration mechanism of Mn(III). The results indicated that Mn(II) can accelerate EE2 photodegradation in EOM solution owing to the photogeneration of reactive Mn(III), and the enhancement was greater at higher Mn(II) concentrations. The generation of reactive Mn(III) was mainly attributable to the action of superoxide radical generated by photosensitization of EOM. In addition, the photodegradation of EE2 was slower at higher pH, possibly because of the deactivation of Mn(III) under alkaline conditions. Single-electron transfer was an indispensable process in the photodegradation. The differences in fluorophore content, pH, and NO3− concentrations are all important determinants for EE2 photodegradation in natural waters. The information obtained in this research would contribute to the understanding of reactions between Mn(II) and EOM, and provide new insights into the behaviors of reactive Mn(III) in eutrophic water irradiated by sunlight.

Compositional variations in algal organic matter during distinct growth phases in karst water

Inland surface water plays an important role in global carbon cycling, which responds to transformation between dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). Studies have shown that algae in karst lakes and reservoirs can convert DIC to organic matter (OM) and form stable carbon sinks via photosynthesis. However, the pathways of conversion of inorganic carbon to organic carbon during algal growth remain unclear and need further investigation. In this study, spectroscopic techniques were applied to investigate the variations in algal organic matter (AOM) composition in the growth metabolism of Chlorella vulgaris and Scenedesmus obliquus under simulated karst water condition. The results showed that algal extracellular organic matter (EOM) contained high DIC concentration during the adaptation phase, which formed the carbon source for algal photosynthesis. In addition, DOC in algae increased after entering the stationary phase, while more OM was released into water. As algal growth proceeded, the amino groups in EOM were consumed to produce more aromatic protein-like material, while more lipid material was produced in intracellular organic matter (IOM). The spectral characterization results could intuitively determine AOM dynamics in different growth stages of algae, which can be used for establishing effective approaches for detecting organic carbon variations and responding to regional carbon cycling in karst water.

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.

Membrane fouling during algal blooms: Impact of extracellular algal organic matter feed and membrane surface properties

Extracellular organic matter (EOM) released by algae during algal blooms have been reported to present significant challenges for ultrafiltration (UF) fouling management. However, current understanding of the impact of complex interactions between biopolymers in EOM and the impact of membrane surface properties including pore size and roughness on subsequent fouling behaviour is limited. In this study, EOM from Dolichospermum circinale (DC), two strains of Microcystis aeruginosa (MA555 and MA564), and Chlorella vulgaris (CV), were characterised and filtered with three polyvinylidene fluoride (PVDF) UF membranes. Fouling rate across algal species was found to decrease in the order MA564 > DC > CV > MA555. The high fouling rate of MA564 was attributed to complex carbohydrate aggregation and covalent protein-carbohydrate interactions forming glycoproteins. The biopolymer networks present in MA564 also enhanced fouling reversibility, potentially through electrostatic repulsion interactions with the membrane surface. For DC and MA555, the behaviour of short-term fouling was observed to depend on biopolymer content. Membrane surface roughness influenced the fouling behaviour of DC and MA555, while smaller pore size generally resulted in lower irreversible fouling for all species due to reduced impact of pore blocking. Biopolymers and low molecular weight neutrals (LMWN) were observed to bind to membrane surfaces and pore walls leading to greater chemical cleaning demand for DC and CV, respectively. This study demonstrated the significance of complex biopolymeric interactions elucidated by detailed characterisation methods and the role of membrane pore size and roughness on EOM fouling behaviour towards more effective UF management during algal blooms.

Effect of peroxydisulfate oxidation catalyzed with ordered mesoporous carbons on controlling ultrafiltration membrane fouling by algal organic matter.

As typical ordered mesoporous carbons (OMCs) materials, CMK-3 and CMK-8 were proposed for catalyzing peroxydisulfate (PDS), and the OMCs/PDS process was combined with membrane filtration to remove algal extracellular organic matter and mitigate membrane fouling. The CMK-3/PDS process achieved substantial reduction of dissolved organic carbon and UV254, followed by CMK-8/PDS. The degradation behavior of fluorescent organics demonstrated the superior performance of OMCs/PDS, while the decomposition of high molecular weight (MW) compounds and generation of lower MW organics were observed. Generally, CMK-3 possessed higher catalytic activity on PDS compared with CMK-8 and powdered activated carbon. The CMK-3/PDS process distinctly decreased the fouling resistances for polyether sulfone and polyvinylidene fluoride membranes, with the reversible resistance reduced by 59.5-83.2% and irreversible resistance declined by 71.7-73.0%. In the meanwhile, CMK-3/PDS prolonged the volumes to the transition period, and postponed the cake layer's generation. The characterization of the membrane morphologies and chemical compositions also showed effective alleviation of fouling. The generated SO4-, OH, O2- and 1O2 as major active oxidation species provided radical as well as non-radical reaction ways for pollutants removal. Overall, our study provides some new ideas for membrane-based combined water purification processes.

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.

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.

The adsorption of endocrine-disrupting compounds (EDCs) on carbon nanotubes: effects of algal extracellular organic matter (EOM)

The adsorption of endocrine-disrupting compounds (EDCs) on carbon nanotubes: effects of algal extracellular organic matter (EOM)

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 (17β-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.

Effect of ferrate pre-oxidation on algae-laden water ultrafiltration: Attenuating membrane fouling and decreasing formation potential of disinfection byproducts

Effect of ferrate [Fe(VI)] pre-oxidation on improving FeCl3/ultrafiltration (UF) of algae-laden source water was investigated. Fe(VI) disrupted algae cells and the in situ formed ferric (hydr)oxides aggregated with cell debris. Particle size and zeta potential of algae increased by 20% and 55% on average, respectively, after treatment with 0.02 mM of Fe(VI). These variations facilitated the formation of algae-ferric floc. Fe(VI) degraded algal extracellular organic matter into lower molecular weight products (fulvic-like and humic-like substances). Membrane flux, reversible membrane resistance (Rr) and irreversible membrane resistance (Rir) were improved by 51%, 61%, and 52% in Fe(VI) (0.02 mM)/FeCl3/UF treatment group compared with FeCl3/UF treatment after three filtration cycles. Fe(VI)/FeCl3/UF removed more than 10% ~ 34% of the dissolved organic compounds (DOC) and 6% ~ 17% of the total nitrogen (TN) compared with FeCl3/UF. Due to the enhanced removal of DOC and TN, formation potential of 12 kinds of carbonaceous-disinfection byproducts (C-DBPs) and 7 kinds of nitrogenous-disinfection byproducts (N-DBPs) decreased by 32.5% and 22.5%, respectively. Fe(VI) pre-oxidant was effective for alleviating membrane fouling and reducing formation potential of DBPs in algal laden water treatment.

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.

Detailed algal extracellular carbohydrate-protein characterisation lends insight into algal solid-liquid separation process outcomes

The effectiveness of algal solid-liquid separation processes has been impacted by the strong influence of algal extracellular organic matter (EOM), where the composition of proteins and carbohydrates and their associated interactions have been implicated. However, despite this, no studies have analysed the detailed protein and carbohydrate composition in EOM in relation to their impacts on separation. Hence, the aim of this study was to explore the relationship between the variety of carbohydrates and proteins present in the EOM of select algal and cyanobacterial samples and the associated separation performance to better understand the influence of specific biopolymers. The protein and carbohydrate composition of the EOM of three species - Microcystis aeruginosa CS-555/1, Chlorella vulgaris CS-42/7 and Microcystis aeruginosa CS-564/01, previously observed to result in variable treatment performance were investigated. The carbohydrates were analysed via high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) while the proteins were analysed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) combined with liquid chromatography-mass spectrometry (LC-MS). Ten unique monosaccharides were identified; of these, the greatest proportion of charged uronic acid carbohydrates were present in the EOM of M.aeruginosa CS-564/01. The protein profiling revealed that M.aeruginosa CS-564/01 had a greater proportion and concentration of proteins >75kDa when compared to M.aeruginosa CS-555/1 or C.vulgaris CS-42/7. It was determined that three serine- and two threonine-based proteins, detected in greater concentrations in M.aeruginosa CS-564/01 than CS-555/1, could covalently interact with carbohydrates (OHenderson etal., 2010a, 2010b-linked glycosylation). These proteins have the ability to form numerous localised networks with carbohydrates and cells in the presence of coagulant molecules, thereby providing a good hypothesis to explain the excellent treatment performance observed for M.aeruginosa CS-564/01 previously. It is proposed that the uronic acids in M.aeruginosa CS-564/01 could interact with proteins via glycosylation, explaining why the coagulant demand for this strain remained low despite the high charged carbohydrate concentration. Overall, it is proposed that process performance could be impacted by: (a) physicochemical characteristics and (b) carbohydrate-protein interactions.

Influence of algal organic matter of Microcystis aeruginosa on ferrate decay and MS2 bacteriophage inactivation

Surface water contaminated with algae and with enteric viruses is a global problem. When surface water is used as a drinking water source, it is important to know the influence of algal organic matter on the disinfection of viruses. In this work, we studied the disinfection efficacy of ferrate and the influence of algal organic matter on the disinfection. We determined the MS2 inactivation kinetics by ferrate under three pH conditions (7, 8, and 8.7). The experimental results and pH-dependent calculation suggest that H2FeO4 and HFeO4− are 1935 and 8 times as effective as FeO42− in MS2 inactivation. We also found that intracellular algal organic matter (IAOM) had a stronger effect on MS2 inactivation kinetics than extracellular algal organic matter (EAOM) suggesting that IAOM led to higher consumption of Fe(VI) compared to EAOM. At pH 8.7, while significant consumption of FeO42− by as low as 8 mg C/L of EAOM and 2 mg C/L of IAOM was detected, MS2 inactivation was negatively influenced only when 13 mg C/L of IAOM present. This study showed that it is important to control pH and to determine the concentration of algal organic matter if ferrate is used for disinfection of surface water contaminated with algae.

Organic matter removal and membrane fouling mitigation during algae-rich surface water treatment by powdered activated carbon adsorption pretreatment: Enhanced by UV and UV/chlorine oxidation

In this work, UV and UV/chlorine (UV/Cl) were employed to enhance powdered activated carbon (PAC) adsorption pretreatment prior to ultrafiltration process for algae-contaminated surface water treatment. Their performance on membrane fouling mitigation and organic pollutant rejection was systematically evaluated. A comparative experiment was conducted under varying pollution degrees of algal extracellular organic matter (EOM) contamination in surface river water. The results indicated that UV/PAC and UV/Cl/PAC pretreatment effectively enhanced the removal of dissolved organic carbon (DOC) and UV-absorbing at 254 nm (UV254). The characteristics of feed water after pretreatments were investigated through apparent molecular-weight (MW) distribution and fluorescence parallel factor analysis (PARAFAC). In regard to membrane fouling mitigation, UV/Cl/PAC noticeably decreased reversible and irreversible fouling resistance simultaneously and UV/PAC preferred reducing reversible membrane fouling. Combined fouling modeling was operated to scrutinize the fouling mitigation mechanisms and standard pore blocking was proved to be dominant during the filtration process. Moreover, the UV/Cl and UV/Cl/PAC pretreatments were proved positive for emerging micropollutants degradation and disinfection by-products formation potential reduction. The results suggested that UV and UV/Cl are likely strategies to enhance the efficiency of PAC adsorption pretreatments prior to ultrafiltration during algae-contaminated water treatment.