Treatment Of Algae-laden Water Research Articles

Suitability of inorganic coagulants for algae-laden water treatment: Trade-off between algae removal and cell viability, aggregate properties and coagulant residue

Inorganic coagulants could effectively precipitate algae cells but might increase the potential risks of cell damage and coagulant residue. This study was conducted to critically investigate the suitability of polyaluminum (PAC), FeCl3 and TiCl4 for algae-laden water treatment in terms of the trade-off between algal substance removal, cell viability, and coagulant residue. The results showed that an appropriate increase in coagulant dosage contributed to better coagulation performance but severe cell damage and a higher risk of intracellular organic matter (IOM) release. TiCl4 was the most destructive, resulting in 60.85% of the algal cells presenting membrane damage after coagulation. Intense hydrolysis reaction of Ti salts was favorable for the formation of larger and more elongated, dendritic structured flocs than Al and Fe coagulants. TiCl4 exhibited the lowest residue level and remained in the effluents mainly in colloidal form. The study also identified charge neutralization, chemisorption, enmeshment, and complexation as the dominant mechanisms for algae water coagulation by metal coagulants. Overall, this study provides the trade-off analyses between maximizing algae substance removal and minimizing potential damage to cell integrity and is practically valuable to develop the most suitable and feasible technique for algae-laden water treatment.

Can we reversely filtrate the catalytic membrane when treating algae-laden water?

During catalytic membrane filtration, algal cells and macromolecules in environmental aqueous conditions load on the surface of the catalytic material, leading to progressive deactivation of the catalytic membrane. Here, we synthesized catalytic membranes with outstanding water flux by anchoring catalyst (δ-MnO2 and sulfur-doped g-C3N4) on homoporous base membranes and immobilizing them by PIP-TMC interfacial polymerization. And the reverse filtration was used to pre-remove the hard-to-degrade foulings such as algal cells to enhance the degradation performance and antifouling performance of the catalyst membrane. The presence of reverse pre-filtration endowed the catalytic membrane to obtain 1.5 times higher water flux than normal filtration, reducing the contact of foulings with the catalyst and improving the catalytic efficiency and stability. Therefore, the operating conditions of the catalytic layer were optimized to obtain higher degradation rates and maintain long-term catalytic activity compared to normal filtration. Also, in the treatment of algae-laden water, reverse filtration allowed algal cells to be separated due to pore size sieving and catalytic material space, avoiding cell fragmentation and release of extracellular polymers caused by activated generated reactive oxygen species. In the catalytic removal of the refractory pollutants (APAP and SMX), the SK25 membrane was able to remove 100 % of the performance with degradation rates up to 0.36 mol·L−1·s−1. This study proposes a novel strategy for catalytic membrane filtration and promotes the application of catalytic membrane filtration technology in practical environmental problems.

Synchronous Photooxidation–Coagulation for the Efficient Treatment of Algae-Laden Water by Utilizing Titanium Xerogel Coagulant

Synchronous Photooxidation–Coagulation for the Efficient Treatment of Algae-Laden Water by Utilizing Titanium Xerogel Coagulant

Biofouling metallic membranes in algae-laden water treatment: Performance, mechanism, and the role of the pre-coated layer

Biofouling is the primary factor limiting the performance of ultrafiltration membrane systems in drinking water treatment. This study systematically investigated the application effect and biofouling behavior of metallic membranes in the treatment of algae-laden water and evaluated the mitigation effect and mechanism of the pre-coated layer on biofouling. The findings demonstrate that the metallic membrane can almost completely remove algal cells (>99.99 %) and macromolecular organics in EOM (Extracellular Organic Matter) but has limited effects on micromolecules, such as humic acid and fulvic acid, in EOM (47.29 % and 17.72 % for TOC (Total Organic Carbon) and UV254, respectively). During direct filtration, algal cells can form a cake layer in front of the metallic membrane to reduce the membrane flux, whereas the presence of EOM makes the cake layer denser and hastens the decline in flux. In addition, irreversible membrane fouling is exasperated in acidic or Ca2+-rich solutions, whereas an increase in algal cell particles exacerbates reversible membrane fouling, causing a faster decline in flux. According to the membrane mechanism analysis, the fouling mechanism ranges from complete pore blocking to standard and intermediate blocking throughout the direct filtration process. In contrast, the application of a pre-coated kaolin layer significantly decreases membrane fouling compared with direct filtration. The pre-coated layer can prevent direct contact between the foulants and the membrane surface during the early stages of filtration, resulting in a delayed complete pore blockage stage. On the other hand, XDLVO (Derjaguin-Landau-Verwey-Overbeek) data reveals that the force between kaolinite and algae (−102.323 mJ/m2) is greater than that between kaolinite and metallic membranes (−61.424 mJ/m2), resulting in better backwashing efficacy. These findings support the use of metallic membranes in drinking water treatment.

Novel calcium hypochlorite/ferrous iron as an ultrafiltration membrane pretreatment process for purifying algae-laden water

Algal fouling has become one of the most critical factors hindering the large-scale development of membrane processes in algae-laden water treatment. Herein, novel calcium hypochlorite (Ca(ClO)2)/ferrous iron (Fe(II)) process was proposed as an ultrafiltration (UF) membrane pretreatment technology, and its effects on membrane fouling and water properties were systematically studied. Results showed that the terminal specific fluxes were significantly elevated to 0.925 and 0.933, with the maximum removal ratios of reversible resistance reaching 99.65% and 96.99% for algae-laden water and extracellular organic matter (EOM), respectively. The formation of cake filtration was dramatically delayed, accompanied by a significant reduction of the adhesion free energy, and the contaminants attached to the membrane surface were effectively decomposed. With respect to water quality, the removal ratios of OD685 and turbidity achieved 81.25–95.31% and 90.16–97.72%, individually. The maximum removal rates of DOC, UV254 and fluorescent organics in influent water reached 46.14%, 55.17% and 75.77%, respectively. Furthermore, the generated reactive species (e.g., •OH, Cl•, Cl2•- and ClO•) could efficiently degrade EOM, which appreciably reduced the electrostatic repulsion between the algal foulants while ensuring the integrity of algal cells. At the Ca(ClO)2/Fe(II) dosage of 0.04/0.24 mM, the zeta potential changed from −32.9 mV to −10.8 mV, and a large range of aggregates was formed. The macromolecules in the algal solution were significantly removed, and the proportion of micromolecular organics was increased to some extent. Coagulation of in-situ formed Fe(III) dominated the membrane fouling mitigation, and the reactive species also contributed to the improvement of filtration performance. Overall, Ca(ClO)2/Fe(II) pretreatment has an exceptional prospect for efficient degradation of algal pollutants and enhancement of UF capability.

Effective removal of algae and phosphate by CaO2-modified carbon nanotube-polyvinylidene fluoride pellets: Performance investigation and mechanistic insights

Simultaneous removal of toxic algae and phosphate nutrient is crucial to remediate algae-contaminated waters. Herein, we report the approach for synthesis of CaO2-modified carbon nanotube-polyvinylidene fluoride (CaO2-CNT-PVDF) pellets for the remediation. The pellets were prepared by an in-situ co-precipitation approach and optimized for the best performance through such key parameters as content of CNT, concentrations of CaCl2 and H2O2 and times. The pellet prepared by 1% of CNT, 0.25-M of H2O2 and CaCl2 with an incubation time of 8-h (termed as CHAT-1228) exhibited the best performance in terms of inhibition of cyanobacteria growth at least for 40-d and uptake of phosphate of 3.6 mg/g CHAT-1228 (270.7 mg-phosphate per gram-CaO2). Our mechanistic studies showed that the cyanobacteria are inactivated by the slow and long-lasting H2O2 release and phosphate is removed via its chemical reactions with calcium species (mainly CaO2). Furthermore, CHAT-1228 can easily collected from water and reused. It works well in the removal of phosphate with a wider pH range (from 3.4 to 10.9) and in the presence of chloride, fluoride, nitrate, bicarbonate, and sulphate ions. This study demonstrates that the optimized CaO2-CNT-PVDF pellet has a great potential for industrial applications in algae-laden water treatment.

Moderate pre-photocatalysis-enhanced coagulation alleviates ultrafiltration membrane fouling of algae-laden water

Moderate chemical pre-oxidation of coagulation to remove algae without breakage of the algae cells and release of algal organic matter has been well reported, while little was known about moderate pre-photocatalysis followed by coagulation on the ultrafiltration performance and membrane fouling control during algae-laden water treatment. Herein, three pretreatment methods (photocatalysis, coagulation and moderate pre-photocatalysis-enhanced coagulation (PC)) were investigated to reduce membrane fouling during ultrafiltration of algae-laden water. Moderate photocatalysis by a composite of Bi2O3-TiO2/PAC (Bi-doped TiO2 nano-composites supported by powdered activated carbon) not only avoided algae cell breakage and controlled the release of intracellular organic matter, but also halved the aluminum sulphate (AS) coagulant dosage, since Bi2O3-TiO2/PAC acted as both a photocatalyst and flocculation core. Under optimal conditions (1.2 g/L Bi2O3-TiO2/PAC irradiated under visible light for 20 min and 0.1 mM AS), the removal of OD680, DOC and UV254 were 83.8 %, 60.3 % and 77.3 % respectively. Moderate photocatalysis degraded medium and high molecular weight organics (biopolymers, humic substances and building blocks) to low MW acidic and neutral organics, resulting in effective removals of humic substances and microbial metabolites typically present in algal-derived pollutant. Following PC pre-treatment with ultrafiltration, 87.5 % increase in the final specific flux, 96.1 % reduction in irreversible resistance, and a change in the fouling mechanism from cake layer blockage to intermediate blockage. In addition, the zeta potential was reduced and the interaction force between pollutant-pollutant/membrane became a repulsive force. This work demonstrates the potential benefits of moderate pre-photocatalysis-enhanced coagulation to remove algal contaminants and mitigate ultrafiltration membrane fouling.

A noteworthy response process of Microcystis aeruginosa induced by exogenous reactive oxygen species in algae-laden water treatment

The effectiveness of reactive oxygen species (ROS) generated by advanced oxidation processes (AOPs) in inactivating harmful algae in drinking water varies considerably. Therefore, the physiological and biochemical reactions of algae need to be considered to clarify the underlying mechanisms. Herein, we studied the response mechanisms of Microcystis aeruginosa to exogenous ROS. Increased CAT, SOD, and GSH levels indicated oxidative stress damage, and increased MDA levels indicated lipid peroxidation in the treatment group. SEM images and fluorescence spectrogram revealed that these reactions promote the release of extracellular polymeric substances (EPS), which increase by ≥ 1.2 mg/L for proteins and ≥ 0.89 mg/L for polysaccharides. The phycobiliprotein content decreased, in which phycocyanin content decreased by approximately 77.41 %. Changes in differential metabolites, including increased regulation of protein and polysaccharide synthesis, enhanced cell membrane fluidity, and increased intracellular microcystin-LR levels were significantly associated with these results. Increased alkaloid levels, reduced vitamin levels, and ATP imbalances also affect cellular activity. These results provide new insights into the response mechanisms of algae and facilitate the practical and sustainable applications of AOPs-treated algae-laden water.

Salt tide affecting algae-laden micropolluted surface water treatment and membrane performance based on BDD electro-oxidation coupled with ceramic membrane process

Harmful algal blooms pose an emerging threat to freshwater ecological security and human health, necessitating further study in offshore areas. In this work, boron-doped diamond electro-oxidation (BDD/EO) coupled with a ceramic membrane filtration was employed aiming to assess the salt tide affecting algae-laden water treatment involving with various natural organic matters (e.g., HA, SA, and BSA). The results have demonstrated that BDD/EO remove chlorophyll from the algae-laden water effectively due to the inactivation of algal cells. Moreover, considering the influence of salt tide, NH3–N would be mainly oxidized through the in-situ generated active chlorine at the electrode-liquid interface. In addition, in three kinds of salt tide affecting algae-laden water, TOC content in BSA group was decreasing remarkably after BDD/EO with TOC removal efficiency above 80%; while those in HA and SA groups had no obvious reducing due to the more algae cells breakage synchronous with HA and SA removal. Based on the fluorescent characteristics and particle size distribution, the generated small molecular organics after electro-oxidation might raise the pore blockage probability and the hydrophobic organic and fluorescent substances were preferentially oxidized in BDD/EO process being beneficial to reducing membrane fouling. Besides, the membrane special flux in three groups were decreasing significantly and the irreversible fouling resistance in SA group accounted for a larger proportion of the total resistance than those of HA and BSA. At last, in BDD/EO-CM process, macromolecular substances degradation rate was greater than that of small molecules based on the molecular weight distribution in three groups of salt tide affected algae-laden water treatment. In a word, this work provides effective and innovative strategies for the harmful algal bloom control and contributes interesting insights of membrane fouling performance of electrochemical coupled ultrafiltration membrane process.

Anion exchange resin/quartz sand bi-layer composite dynamic membranes in ultrafiltration for algae-laden water treatment

Ultrafiltration treatment of algae-laden water is the biggest challenge of membrane fouling. In this study, a bi-layer composite dynamic membrane was constructed by depositing anion exchange resin (AER) and quartz sand on the surface of UF membrane to enhance the separation performance and reduce membrane fouling. AER deposition layers improve contaminants removal and reduce membrane fouling based on retention and ion exchange effect, however, the large porosity results in less than optimal efficiency gains. Deposition of quartz sand on the AER deposit layer significantly enhanced pollutants removal rate and reduced the fouling resistance of the membrane. Compared to AER deposition alone, the bi-layer significantly improved the removal of DOC (20%), UV254 (22%), protein (18%), polysaccharide (13%), MC-LR (11%), GSM (18%) and 2-MIB (3%) and slowed down the development of fouling resistance when the amount of quartz sand deposited reached 68.6 g/m2. As the quartz sand deposition increased to 91.4 g/m2, the presence of a critical value was found, and although the pollutants retention rate increased further, reversible fouling appeared to increase. SEM image analysis of the dense sediment layer traps too much contaminants, resulting in a gel-like layer of contamination that increases membrane fouling.

Calcium sulfite oxidation activated by ferrous iron integrated with membrane filtration for removal of typical algal contaminants

Oxidation treatment of algae-laden water may cause cells rupture and emission of intracellular organics, thus restricting its further popularization. As a moderate oxidant, calcium sulfite could be slowly released in the liquid phase, thus exhibiting a potential to maintain the cells integrity. To this end, calcium sulfite oxidation activated by ferrous iron was proposed integrated with ultrafiltration (UF) for removal of Microcystis aeruginosa, Chlorella vulgaris and Scenedesmus quadricauda. The organic pollutants were significantly eliminated, and the repulsion between algal cells was obviously weakened. Through fluorescent components extraction and molecular weights distribution analyses, the degradation of fluorescent substances and the generation of micromolecular organics were verified. Moreover, the algal cells were dramatically agglomerated and formed larger flocs under the premise of maintaining high cell integrity. The terminal normalized flux was ascended from 0.048–0.072 to 0.711–0.956, and the fouling resistances were extraordinarily decreased. Due to the distinctive spiny structure and minimal electrostatic repulsion, Scenedesmus quadricauda was easier to form flocs, and its fouling was more readily mitigated. The fouling mechanism was remarkably altered through postponing the formation of cake filtration. The membrane interface characteristics including microstructures and functional groups firmly proved the fouling control efficiency. The reactive oxygen species (i.e., SO4•− and 1O2) generated through the principal reactions and Fe–Ca composite flocs played dominant roles in alleviating membrane fouling. Overall, the proposed pretreatment exhibits a brilliant application potential for enhancing UF in algal removal.

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.

Moderate KMnO4/Fe(II) pre-oxidation for membrane fouling mitigation in algae-laden water treatment

Moderate KMnO4/Fe(II) pre-oxidation is a promising technique to mitigate membrane fouling and avoid the environmental risk brought by the breakage of algae cells, which often happens in the practical application of pre-oxidation techniques. Various components, i.e., KMnO4, in-situ formed MnO2 and in-situ formed Fe(III), are involved in this technique, and how they mitigate membrane fouling is still unclear. In this work, we investigated their performances on the mitigation of membrane fouling and their influences on the physiochemical characteristics of the organic foulants and fouling layers individually. It was found that Fe(III) formed in situ showed the best performance in controlling membrane fouling among the various components, and the total fouling resistance was reduced by 87.6%. MnO2 formed in situ was most effective in enhancing the organic matter removal performance of ultrafiltration, and the removal rate of the dissolved organic matter reached 39.9%. In addition, after the KMnO4/Fe(II) pretreatment, the electrostatic repulsion between algal foulants was decreased, facilitating the aggregation of foulants. Based on the physicochemical changes of the characteristics of foulants and fouling layers on the membrane surface, we concluded that KMnO4/Fe(II) alleviated the algae-derived membrane fouling mainly in two ways: (1) enhancing the interception effect of ultrafiltration membrane on hydrophobic organic matter, which reduced the blockage of membrane pores; (2) enhancing the sparseness of the cake layer on the membrane surface, which reduced the cake fouling resistance. Our work not only shows that the KMnO4/Fe(II) pretreatment technique has considerable applicative potential in alleviating the membrane fouling caused by algae-laden water, but also gives a comprehensive understanding of the fouling mitigation mechanisms.

Comparison of peracetic acid and sodium hypochlorite enhanced Fe(Ⅱ) coagulation on algae-laden water treatment

In this study, Fe(Ⅱ)/peracetic acid (PAA) and Fe(Ⅱ)/sodium hypochlorite (NaClO) systems were applied as the combined preoxidation and coagulation process to enhance algae removal. A high removal rate of algae and turbidity could be achieved, with most algal cells keeping intact when adding reasonable concentrations of PAA and NaClO to enhance Fe(Ⅱ) coagulation. The variations of chlorophyll a, malondialdehyde, and intracellular reactive oxygen species suggested that moderate oxidation with only destroying surface-adsorbed organic matter rather than cell integrity was realized. The generated organic radicals, Fe(Ⅳ), and hydroxy radical played the major roles in the Fe(Ⅱ)/PAA system for the moderate oxidation of algal cells, but direct oxidation by NaClO rather than producing reactive species in the Fe(Ⅱ)/NaClO process contributed to the preoxidation. Concurrently, the in-situ formed Fe(Ⅲ) greatly promoted the agglomerating and settling of algae. The analysis of cell integrity, biochemical compositions, and fluorescence excitation-emission matrices spectra demonstrated that excess NaClO but not PAA would seriously damage the algal cells. This might be because that NaClO would directly oxidize the cell wall/membrane, while PAA mainly permeates into the cell to inactivate algae. These results suggest that Fe(Ⅱ)/PAA is an efficient strategy for algae-laden water treatment without serious algae lysis.

Effect of ferrous-activated calcium peroxide oxidation on forward osmosis treatment of algae-laden water: Membrane fouling mitigation and mechanism

Forward osmosis (FO) is a high-efficiency and low-energy consumption way for algae-laden water treatment, whereas membrane fouling is still an unavoidable problem in its practical application. In this work, a strategy of ferrous-activated calcium peroxide (Fe(II)/CaO2) was proposed to control FO membrane fouling in the purification of algae-laden water. With the treatment of Fe(II)/CaO2, the aggregation of algal contaminants was promoted, the cell viability and integrity were well preserved, and the fluorescent organics were efficiently removed. With respect to the fouling of FO membrane, the flux decline was generally alleviated, and the flux recovery was promoted to varying degrees under different process conditions. It could be revealed through the extended Derjaguin-Landau-Verwey-Overbeek theory that the adhesion of contaminants and membrane surfaces was reduced by Fe(II)/CaO2 treatment. The interface morphologies and functional groups of membrane verified that Fe(II)/CaO2 could mitigate the fouling by reducing the amount of algal contaminants adhering to the FO membrane. The co-coagulation of in-situ Fe(III) together with Ca(OH)2, as well as the oxidation of •OH were the main mechanisms for fouling mitigation. In sum, the Fe(II)/CaO2 process could effectively improve the efficiency of FO for algae-laden water treatment, and has broad application prospects.

Mechanism study on the effect of peracetic acid (PAA), UV/PAA and ultrasonic/PAA oxidation on ultrafiltration performance during algae-laden water treatment

In this work, peracetic acid (PAA), ultraviolet (UV)/PAA and ultrasonic (US)/PAA pre-oxidation were applied to enhance ultrafiltration (UF) performance during algae-laden water treatment. The results showed that 10 mg/L PAA, exhibiting an optimal performance with membrane fouling resistance reduced by 76.26%. Low dosage of UV/PAA can effectively control fouling by enhancing the degradation of dissolved organics. Though more radicals were generated with the increasing dosage of PAA during the UV/PAA process, flux deterioration was occurred when PAA dosage over 10 mg/L, owing to a negative correlation between fouling resistance and algal integrity loss. Compared with UV, US exhibited a worse activation effect on PAA with less reactive radicals produced. Even worse, US can stimulate the stress metabolism of algal cells with slightly integrity loss, which then resulted in an exacerbation of permeate quality. Fouling mechanism analysis revealed that the delay formation of cake layer with membrane fouling alleviation mainly through efficient degradation of macromolecular organics. The investigation of synergistic and individual effect of EOM degradation, algae rupture and IOM release on the filtration performance revealed that EOM degradation was the primary mechanism for fouling control while algae rupture rather than IOM release was crucial for membrane fouling aggravation. This indicates that moderate oxidation, with property of high organic degradation and low cell rupture, was the working principal and objectives for algae-laden water treatment. Additionally, it was found that the ·OH radicals produced during UV/PAA process can efficiently degrade representative odors. In general, pretreatments of PAA and low dosages of UV/PAA showed promising prospects in improving the UF performance of algae-laden water and treating algal secretions.

FT-ICR/MS deciphers formation of unknown macromolecular disinfection byproducts from algal organic matters after plasma oxidation

Algal organic matter (AOM) is a potential precursor of disinfection byproducts (DBPs) in water treatment. It is a major challenge to identify macromolecular DBPs due to the diversity of AOM. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) was applied to diagnose the AOM diversity after algae removal by plasma oxidation and to recognize the macromolecular DBPs in subsequent chlorination. Significant removal of AOM released by M. aeruginosa, C. raciborskii, and A. spiroies was achieved by plasma oxidation, accompanied by decrease in the proportion of CHNO formulas and increase in CHO formulas. Without plasma treatment, chlorination generated approximately 2486 macromolecular carbonaceous DBPs (C-DBPs) and 1984 nitrogenous DBPs (N-DBPs), with C11HnOmClx and C18HnNmOzClx as the most abundant DBPs. The numbers of C-DBPs and N-DBPs decreased by 63.3% and 62.9%, respectively, if plasma treatment was applied prior to chlorination. Network computational analysis revealed that Cl substitution was the main formation pathway of AOM-derived DBP formation rather than HOCl addition. The precursors of macromolecular DBPs contained a characteristic atomic number of C and O (7 ≤ C ≤ 18; 3 ≤ O ≤ 11). This study firstly disclosed the relationship between AOM diversity and novel macromolecular DBPs during algae-laden water treatment.

TiCl3 coagulation for algae-laden water treatment: Performance, control of algal organic matters release and mechanism

TiCl3 coagulation for algae-laden water treatment: Performance, control of algal organic matters release and mechanism

A moderate activated sulfite pre-oxidation on ultrafiltration treatment of algae-laden water: Fouling mitigation, organic rejection, cell integrity and cake layer property

In this study, a moderate oxidation strategy, in-situ pretreatment with ferrous activated sulfite (Fe(II)/S(IV)), was employed to mitigate membrane fouling during the filtration of algae-laden water and to improve the rejection of organic matter. It was worth noting that the moderate oxidant can avoid serious cells breakage and control the release of intracellular organic matter. Besides, sulfite-based pretreatment had an excellent removal effect DBPs, including chloroform (TCM), dichloroacetonirile (DCAN) and trichloronitromethane (TCNM). Fe(II)/S(IV) pretreatment also improved the removal of DOC and UV254 and the proportion of hydrophilic substances was increased to 91.4% which was conductive to membrane fouling alleviation. With the increase in Fe(II) dosage, both the Rr and Rir were declined since the macromolecular organic transforming to micromolecular organic and the coagulation effect by the in-situ generation of Fe(III). Meanwhile, permeable channels formed on the loose and porous cake layer due to the in-situ Fe(III) could enhance the specific flux. When the ratio of Fe(II)/S(IV) was 2:1, the fouling mechanism was inferred to cake filtration which showed a great discrepancy with other condition.

Separation performance of ultrafiltration during the treatment of algae-laden water in the presence of an anionic surfactant

Ultrafiltration was demonstrated to be an effective and efficient method to treat algae-laden water. However, the presence of compounds such as surfactants can act as a stimulus for algae outbreak and change the characteristics of algae cells and derived organics. Therefore, it is necessary to investigate the filtration and separation performance of ultrafiltration during the treatment of algae-laden water in the presence of anionic surfactants (the most widely used surfactant type). In this study, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (LAS) were employed respectively to simulate the presence of a low concentration of an anionic surfactant in eutrophicated water. It was found that surfactants present in natural waters could enhance the hydrophilicity of the algae interface and the stability of the algae-laden water system with mitigated algae aggregation. During the initial filtration process, membrane fouling was aggravated related to the more serious pore blocking induced by the present SDS or LAS; however, during the next stage, membrane fouling was alleviated due to the formation of a looser cake layer in the presence of SDS or LAS. The pore blocking at the earlier stage contributes more to the decrease of total flux when surfactants are involved. Furthermore, the disinfection byproduct formation potential was reduced with SDS or LAS mainly due to the degradation of free available chlorine by the surfactants. While the concentration of algal toxins was ascended in the ultrafiltration effluent, which indicates that the separation performance was highly impacted by the presence of anionic surfactant.