Algal Organic Matter Removal Research Articles

Simultaneous removal of cyanobacteria and algal organic matter (AOM) by CaCO3 precipitation combined with Polyaluminum chloride (PACl) flocculation

Simultaneous removal of cyanobacteria and algal organic matter (AOM) is still a difficult task for drinking water treatment plants (DWTPs) during cyanobacteria blooms. CaCO3 precipitation, an environment-friendly drinking water treatment technique, has been recommended to removal cyanobacteria or AOM from drinking water. However, knowledge of simultaneous removal performance by CaCO3 precipitation is limited. Here, the simultaneous removal performance to cells and AOM of CaCO3 precipitation, combined with polyaluminum chloride (PACl) flocculation, was investigated, as well as the underlying mechanisms. The results showed that CaCO3 precipitation strategy significantly improved the simultaneous removal performance of PACl, with removal efficiency up to 98 % for cells and 48 % for AOM. CaCO3 precipitation exhibited reliable simultaneous removal effects at various initial cells densities and AOM concentrations. Scanning electron microscope (SEM), transmission electron microscope (TEM) and zeta potential results suggested that mutual flocculation between positively charged CaCO3 crystalline particles and negatively charged cells is the main responsible mechanism for cells removal. Despite that the adsorption of AOM on CaCO3 nuclei surface delays its precipitation, co-precipitation removal mechanism of AOM is realized during CaCO3 nucleation. Moreover, further AOM removal can be obtained by CaCO3 crystalline particles via chemisorption between organic molecules and the particles surface.

Impact of permanganate with polyaluminium chloride on algae-laden karst water: Behaviors and disinfection by-products control

The removal of algal organic matter (AOM) through water treatment processes is a major approach of reducing the formation of disinfection by-products (DBP). Here, the formation of DBP from AOM in karst water under different combination of potassium permanganate (KMnO4) and polyaluminium chloride (PACl) was investigated. The effect of divalent ions (Ca2+ and Mg2+) on DBP formation was traced by AOM chemistry variations. For DBP formation after KMnO4 preoxidation, total carbonaceous DBPs (C-DBPs) decreased by 12.9% but nitrogen-containing DBPs (N-DBPs) increased by 18.8%. Conversely, the C-DBPs further increased by 3.3% but N-DBPs reduced by 10.7% after the addition of PACl besides KMnO4 preoxidation. The variations of aromatic protein-like, soluble microbial products-like compounds and ultraviolet absorbance at 254 nm (UV254) were highly correlated with the formation of DBPs, which suggest aromatic substances strongly affect DBP behaviors at different treatment conditions. In the presence of divalent ions (Ca2+ = 135.86 mg/L, Mg2+ = 18.51 mg/L), the combination of KMnO4 and PACl was more effective in controlling DBP formation compared to the situation without Ca2+ and Mg2+. Specifically, trichloromethane formation was largely inhibited compared to the other tested DBPs, which may refer to complexation of electron-donating groups via divalent ions. While Ca2+ and Mg2+ may not affect the nature of α-carbon and amine groups, so the variation of haloacetonitriles (HANs) was not obvious. The study enhances the understanding of the DBP formation patterns, transformation of carbon and nitrogen by preoxidation-coagulation (KMnO4-PACl) treatment in algae-laden karst water.

Photocatalytic Degradation of Algal Organic Matter Using TiO2/UV and Persulfate/UV

Eutrophication in water reservoirs releases algal organic matter (AOM), a key precursor to the formation of disinfection by-products (DBPs) during the disinfection process. Typical drinking water treatment is not efficient for AOM removal, and advanced treatments are necessary for the removal of residual AOM before chlorination. UV-based technology with PS and TiO2 is widely used as a pre-oxidation step in water treatment; however, no publications have focused on them for AOM degradation. In this context, this work investigated the effect of oxidant concentration (0.1 to 0.5 g∙L−1) and pH (6 to 10) on AOM degradation with TiO2/UV and persulfate (PS)/UV using response surface methodology. In general, PS/UV was more effective in removing protein, while TiO2/UV was more effective in carbohydrate degradation. TiO2/UV removals varied from 27 to 57% for protein and from 48 to 86% for carbohydrates. The optimal condition (57% for protein and 86% for carbohydrates) was obtained using 0.5 g∙L−1 TiO2 at pH 10. PS/UV removals varied from 33 to 81% for protein and from 24 to 53% for carbohydrates. The optimal condition (81% for protein and 53% for carbohydrates) was obtained using 0.5 g∙L−1 PS concentration at pH 8. Degradation kinetics showed a good fit to the pseudo-first-order model (R2 > 95%) for both processes. The DBP formation reductions observed with TiO2/UV—trihalomethane (THM) (85 to 86%) and chloral hydrate (CH) (94 to 96%)—were similar to the efficiencies observed for PS/UV—THM (87 to 89%) and CH (83 to 88%). These results show the efficiency of UV-based technology for AOM degradation and the control of DBP formation.

Is Electrocoagulation a Promising Technology for Algal Organic Matter Removal? Current Knowledge and Open Questions

AbstractElectrocoagulation (EC) is a practical alternative to chemical coagulation for the treatment of drinking water that contains various pollutants, including humic substances. Nevertheless, the performance of EC for removal of algal organic matter (AOM) is still largely unexplored. In this review, the properties of AOM, the principles of chemical coagulation and EC, and the current state of knowledge on the coagulation of AOM have been outlined. The limited available literature on the EC of AOM is critically reviewed and let conclude that this is a promising technology for AOM removal. However, the studies on EC are inconsistent in their approaches, and they lack thorough optimization of operating conditions (resultant pH, coagulant dosing) and reports of residual metal concentrations. Some of the identified needs for future research include the complete optimization of EC for AOM removal, its direct comparison with chemical coagulation, and EC testing for the elimination of mixtures of AOM, humic substances, and inorganic particles.

A molecular-level mechanism analysis of PFS coagulation behaviors: Differences in natural organic matter and algal organic matter

Coagulation is generally considered as the key process to remove dissolved organic matters in water treatment plants, of which natural organic matter (NOM) and algal organic matter (AOM) are two commonly seen species. However, the removal efficiency of NOM and AOM by coagulation varies a lot. Here we unraveled the possible reasons for the different performance on NOM and AOM removal from molecule-level insights. With van Krevelen diagram, we observed that removed components in NOM and AOM were located in similar areas (high O/C and low H/C), indicating that polyferric sulfate (PFS) coagulation is prone to remove oxygen-containing and unsaturated components. Further, the results showed that NOM components are mainly composed of C, H, and O, with high O/C and low H/C, which therefore are easier to be removed (51%). However, ∼50% AOM components are N-containing, which mainly located in areas of low O/C and high H/C, leading to the relatively poor coagulation performance (19%). With further data processing of the Fourier transform ion cyclotron resonance (FT-ICR) results, we found that molecules with higher oxidized state or more carboxyl groups were preferentially removed by PFS coagulation. This study reveals the PFS coagulation mechanism of NOM and AOM, and provides theoretical foundations for enhanced coagulation in practical applications.

Fouling control in SWRO desalination during harmful algal blooms: A historical review and future developments

Harmful algal blooms (HABs) are a major barrier to the stable and efficient operation of seawater reverse osmosis (SWRO) desalination plants. Although the intensity varies regionally, the occurrence of HABs impairs plant operation through severe particulate, organic, and biological fouling of both pretreatment and RO systems. As a result, considerable effort has been put into developing and optimizing pre-treatment techniques to mitigate these problems. This study reviews the historical changes and current status of pretreatment applications based on >110 datasets for large SWRO desalination plants. Chronological analysis underscores the increasing trend in the operation of dissolved air flotation and ultrafiltration systems since severe HABs in the Middle East from 2008 to 2009. The impact of HAB characteristics on system performance was also analyzed, and the efficiency of current pretreatment systems for the removal of HABs was evaluated, along with proposals for operational guidelines. Finally, future strategies for i) intelligent monitoring and prediction of HABs, ii) improvement of unit processes for the removal of algal organic matter, and iii) utilization of algal biomass to alleviate environmental impact were systematically delineated for smarter, safer, and greener operation of future SWRO desalination plants in response to the occurrence of HABs.

Screening of new adsorbents to remove algal organic matter from aqueous solutions: kinetic analyses and reduction of disinfection by-products formation.

The algal organic matter (AOM) is a problem in water treatment. Although the adsorption process is extensively applied to drinking water treatment, little information is known about the potential of new adsorbents to remove AOM. Herein, this work evaluated the removal of AOM and its main compounds (dissolved organic carbon (DOC), carbohydrate, and protein) by new adsorbents-mesoporous silica (SBA-16), graphene oxide material from citric acid (CA), and sugar (SU), and a composite of CA immobilized on sand (GSC). In general, the removal efficiencies followed the order of SBA-16 > CA > SU or GSC for DOC, carbohydrate, and protein. At environmental condition (5mg DOC·L-1 and pH 8), high removals were reported for SBA-16 (88.8% DOC, 80.0% carbohydrate, and 99.6% protein) and CA (70.0% DOC, 66.7% carbohydrate, and 89.7% protein), while moderate removals were found for SU (60.5% DOC, 47.9% carbohydrate, and 66.5% protein) and GSC (67.4% DOC, 60.8% carbohydrate, and 57.4% protein). Based on these results, further analyses were done with SBA-16 and CA. Both adsorbents' efficiencies decayed with the pH increment of the test water. Disinfection by-products reductions found using SBA-16 - trihalomethanes (58.2 to 94.7%) and chloral hydrate (48.7 to 78.8%) - were higher than the ones using CA-trihalomethanes (45.2 to 82.4%) and chloral hydrate (40.1 to 70.8%). This study showed the potential of applying these adsorbents for AOM removal, and further investigations are suggested to increase the adsorption capacity of these adsorbents.

Effect of vacuum ultraviolet/ozone pretreatment on alleviation of ultrafiltration membrane fouling caused by algal extracellular and intracellular organic matter

Algal blooms in source water can cause algal organic matter (AOM)-related membrane fouling in drinking water treatment. Herein, the effects of vacuum ultraviolet/ozone (VUV/O3) pretreatment on alleviating ultrafiltration membrane fouling caused by AOM, including extracellular organic matter (EOM) and intracellular organic matter (IOM), were investigated systematically. Compared to its sub-processes (UV/O3, O3, VUV, and UV), VUV/O3 pretreatment showed the best performance on AOM removal and membrane fouling mitigation. After VUV/O3 pretreatment, the DOC of EOM and IOM in feed decreased by 51.1% and 26.7%, respectively, and fluorescence components and UV254 of EOM and IOM in feed decreased obviously. Hence, the final specific fluxes of the membranes increased significantly under the impacts of VUV/O3, and VUV/O3 achieved 89.5% and 97.2% mitigation of reversible fouling caused by EOM and IOM, respectively. VUV/O3 pretreatment also reduced the foulants on membrane surface and surface roughness. Moreover, under the effects of reactive oxygen species oxidation, VUV photolysis, and direct O3 oxidation, VUV/O3 decreased organic load and changed the molecular weight distribution, hydrophilicity, and interaction-free energy of AOM, thus mitigating membrane fouling. Furthermore, the effects of O3 dosage and molecular weight cut-off of ultrafiltration membrane on membrane fouling mitigation by VUV/O3 were also investigated. All results highlighted that VUV/O3 pretreatment had huge potential in mitigating AOM-induced membrane fouling.

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.

Release and removal of algal organic matter during prechlorination and coagulation treatment of cyanobacteria-laden water: Are we on track?

A better understanding of the physicochemical properties and fate of algae-derived organic matter (AOM) in water treatments significantly benefits the control of algae-derived disinfection byprodcuts and process parameter optimization. In this study, we conducted a comprehensive investigation of the release and treatability of dissolved organic matter during prechlorination and postcoagulation treatments of cyanobacteria-laden source water via size-exclusion chromatography-tandem diode array detector, fluorescence detector and organic carbon detector. The results revealed that the allochthonous humic substances could protect algal cell membrane from damage during prechlorination at a low level of chlorine dose. Due to the release and oxidation of biopterins during prechlorination of M. aeruginosa cells, the variation of the humic-like fluorescence can be used to indicate the chlorine dose for a sufficient membrane damage of algae cells. The prechlorination of M. aeruginosa cells induced minimal release of large MW biopolymer fractions but much more release of low MW fractions E1 and E2 (i.e., unknown carbonaceous substances and fluorescent nitrogenous biopterins). The physically extracted AOM contained a large proportion of biopolymers and could not well represent those released during prechlorination treatment. During coagulation, the negative effect of humic substances on the coagulant demand to achieve algae removal was more remarkable than AOM released by prechlorination. The high-MW biopolymers and humic substances can be removed over 50% by coagulation. Among the low-MW carbonaceous fractions, E1 released by prechlorination can also be effectively removed via coagulation while fractions C, D (possibly oligopeptides or secondary aromatic metabolites & low MW acids) and nitrogenous biopterins were recalcitrant to coagulation. This study highlights the differences of AOM properties between physical extraction and prechlorination and provides a basis for drinking water treatment plants to give more attention to the recalcitrant low MW fractions in coagulation when treating algae-laden source water.

Adsorption of algal organic matter on activated carbons from alternative sources: Influence of physico-chemical parameters

The algal organic matter (AOM) is a concern for water treatment due to its low removal by traditional technologies. Granular activated carbon (GAC) is used extensively in drinking water treatment in various roles; however, there is little information about GAC performance for AOM removal. In this context, this study investigated the AOM removal by alternative (bovine bone (BO), babassu coconut (BA), and dende coconut (DE)) and traditional (bituminous (BI)) activated carbons in different testing conditions (pH, ionic strength, and adsorbent dosage). Freundlich model fitted better to predict the isotherm data than the Langmuir model for all GACs (R2 > 0.99). High removals were found for BI (86.3 to 99.5%), BA (82.9 to 95.5%), BO (67.2 to 88.2%), and DE (58.0 to 78.8%). The AOM removal followed the order of BI > BA > BO > DE for all conditions tested. The traditional BI showed the best performance for AOM removal; however, BA was also effective and showed efficiencies close to BI. Trihalomethanes formation potential (THMFP) after the adsorption was assessed and high reductions were obtained for BI (86.3 to 99.5%), BA (82.9 to 94.3%), BO (67.2 to 88.2%), and DE (58.0 to 78.8%). The competition between AOM with dissolved humic acid (HA) for sorption sites was also evaluated. The presence of HA in a lower concentration than AOM can increase the AOM removal significantly for all GACs, making their efficiencies very similar. Our findings will allow a better design to improve the affinity of these GACs for AOM removal in water treatment facilities.

Adsorption isotherms and kinetics for the removal of algal organic matter by granular activated carbon

Seasonal algal blooms in surface water release a significant amount of algal organic matter (AOM), which alters the composition of dissolved organic matter (DOM). AOM affects the drinking water treatment processes and finished water quality. In this study, the relative removal efficiency of AOM and humic acid by granular activated carbon (GAC) adsorption was determined. Batch experiments were conducted to evaluate the adsorption capacity of GAC, which varied from 4.235–31.45 mg/g for AOM originated from different algae. Freundlich isotherm models fitted the adsorption equilibrium data, and the adsorption kinetics data were fitted well using a pseudo-second order kinetic model. The calculated thermodynamics parameters (∆G0, ∆H0 and ∆S0) indicated that GAC adsorption for DOM removal was endothermic and spontaneous in nature.

Removal of Microcystis Aeruginosa by oxidation-assisted coagulation: Effect of algogenic organic matter fraction changes on algae destabilization with Al hydrates

Oxidation-assisted coagulation has been widely applied to destabilize algae and improve algae removal through a flocculation-sedimentation process in drinking water treatment plants (DWTPs). However, oxidation poses a potential threat to drinking water safety with increasing algal organic matter (AOM) in the algae-polluted surface water. This study investigated the effect of sodium hypochlorite (NaOCl) oxidation-assisted polyaluminum chloride (PACl) coagulation on algae removal, along with the identification of the optical properties for AOM fractions. The results have demonstrated that the increased NaOCl oxidant dose coupled with PACl coagulation induced by sweep flocculation is more effective in Microcystis aeruginosa (MA) cells destabilization and removal, where the highest algae removal rate around 99 %. However, NaOCl oxidation coupled with PACl coagulation fails to reduce the dissolved organic carbon (DOC) in MA suspension attributed to the released AOM. Strong free chlorine destroys MA cells in response to the increases in humic acid-like (HAL) and fulvic acid-like (FAL) substances, while it is sufficient to degrade soluble microbial product-like (SMPL) and aromatic protein-like (APL) substances. In oxidation-assisted coagulation, bigger diameter (483–640 μm) with lower fractal dimension (1.31–1.39) of M. aeruginosa flocs are formed at low chlorine dosing ratio (Cl2:DOC = 1:1), while higher fractal dimension (2.39–2.75) with smaller diameter (143–395 μm) is reached at high chlorine dosing ratio (Cl2:DOC = 3:1). It is concluded that the changes in fluorescent organic matter fraction during chlorination dominantly affect coagulation performance for AOM removal in oxidation-coagulation process.

Investigating adsorption of model low-MW AOM components onto different types of activated carbon – influence of temperature and pH value

ABSTRACT Low molecular weight algal organic matter (AOM), as a frequent water contaminant with poor coagulation efficiency, adversely affects the quality of produced water and serves as a source of potentially carcinogenic disinfection by-products. AOM removal from water is inevitable to eliminate the negative health and environmental impacts. This research evaluates the removal of arginine, phenylalanine and aspartic acid, which are amino acids abundant in AOM. Adsorption experiments were performed at 10, 18 and 25 °C and pH 5, 7 and 9 using two different activated carbons (FTL, PIC). Amino acids showed endothermic adsorption behaviour, with a higher removal at higher temperature. Higher temperature increased the diffusion of amino acid molecules, reduced the solution viscosity, or enhanced the hydrophobic interactions contributing to adsorption. The effect of temperature manifested differently during experiments depending on the chemical nature of the amino acids, the pH value and the surface properties of the carbon. Phenylalanine isotherms showed specific waves (Langmuir type 4). pH had a greater effect on arginine adsorption than did temperature. Aspartic acid isotherms exhibited a decrease in adsorption at higher pH values and higher temperatures. The principal mechanisms involved in amino acid adsorption were hydrophobic interactions, electrostatic interactions or hydrogen bonds.

Improving energy efficiency of pretreatment for seawater desalination during algal blooms using a novel meshed tube filtration process

A new meshed tube filtration (MTF) process was developed and assessed as a low energy-consuming pretreatment process that withstands algal blooms (i.e., red tide). This process can potentially replace the dissolved air flotation (DAF) process in typical seawater reverse osmosis (SWRO) desalination plants. Two marine microalgae species, namely C. polykrikoides and T. suecica, were first cultivated and then utilized to simulate algal bloom conditions in the lab-scale filtration experiments. The algal matter was coagulated and circulated by aeration in the MTF system that was filled with cylindrical polypropylene meshed tubes with ciliary ends and had the ability to capture coagulated algae in an effective manner. The efficiency of the MTF process to remove algal cells was significantly enhanced by optimizing the coagulant dose and the aeration rate. In order to further verify the MTF performance, DAF experiments were conducted, under similar conditions, for the comparison of algal removal effectiveness and energy consumption rates. The results showed high removal rates of algal cells as well as turbidity for MTF, although only a limited reduction of algal organic matter (AOM) was observed. When DAF was operated at energy consumption levels equivalent to MTF, its algae removal rate was lower than that of MTF. Furthermore, under optimal operating conditions, MTF consumed approximately one-third of the energy needed for DAF operation, mainly due to the fact that MTF requires less aeration. For future improvements in the AOM removal process, an energy-efficient pretreatment process could be realized for SWRO desalination facilities facing potential algal blooms.

Study of Algal Organic Matter Removal Efficiency Using a Newly Developed Removal System

Water sources are currently facing great challenges from rapid population growth and industrial developments. Investigations into how to remove algal organic matter (AOM) are thus of great importance from an environmental point of view because most lakes and reservoirs in South Korea suffer from algae problems, especially in the summer. Many efforts have been made to remove AOM from the aquatic environment in South Korea. In this study, we focus on development of a new AOM removal system, utilizing waste oyster shells and ferrihydrite as the media of the filtration system. Using this system, the removal rate of AOM was investigated regarding the concentrations of chlorophyll a, total phosphorus, and alginate. It was found that about 92% of the total phosphorus was removed through this system when raw oyster shell powders were heated at 900°C to convert them into calcium oxide powders. The use of a continuous system also led to a reduction of 94.2% in total phosphorus, 78.8% in chlorophyll a, and 43.6% in alginate.

Influence of COM-peptides/proteins on the properties of flocs formed at different shear rates

Coagulation followed by floc separation is a key process for the removal of algal organic matter (AOM) in water treatment. Besides optimizing coagulation parameters, knowledge of the properties of AOM-flocs is essential to maximizing AOM removal. However, the impact of AOM on the floc properties remains unclear. This study investigated how peptides/proteins derived from the cellular organic matter (COM) of the cyanobacterium Microcystis aeruginosa influenced the size, structure, and shape of flocs formed at different shear rates (G). Flocs formed by kaolinite, COM-peptides/proteins and a mixture of the same were studied, and the effect of intermolecular interactions between floc components on floc properties was assessed. The coagulation experiments were performed in a Taylor–Couette reactor, with aluminum (Al) or ferric sulphate (Fe) utilized as coagulants. Image analysis was performed to gauge floc size and obtain data on fractal dimension. It was found that floc properties were affected by the presence of the COM-peptides/proteins and the coagulant used. COM-peptides/proteins increased floc size and porosity and widened floc size distributions. The Fe coagulant produced larger and less compact flocs than Al coagulant. Moreover, the decrease in floc size that occurred in parallel with increase in shear rate was not smooth in progress. A rapid change for the kaolinite-coagulant suspension and two rapid changes for the suspensions containing COM were observed. These were attributed to various intermolecular interactions between floc components participating in coagulation at different G. Based on the results obtained, shear rates suitable for efficient separation of flocs containing COM were suggested.

Investigating the coagulation of non-proteinaceous algal organic matter: Optimizing coagulation performance and identification of removal mechanisms

The removal of algal organic matter (AOM) is a growing concern for the water treatment industry worldwide. The current study investigates coagulation of non-proteinaceous AOM (AOM after protein separation), which has been minimally explored compared with proteinaceous fractions. Jar tests with either aluminum sulphate (alum) or polyaluminium chloride (PACl) were performed at doses of 0.2–3.0 mg Al per 1 mg of dissolved organic carbon in the pH range 3.0–10.5. Additionally, non-proteinaceous matter was characterized in terms of charge, molecular weight and carbohydrate content to assess the treatability of its different fractions. Results showed that only up to 25% of non-proteinaceous AOM can be removed by coagulation under optimized conditions. The optimal coagulation pH (6.6–8.0 for alum and 7.5–9.0 for PACl) and low surface charge of the removed fraction indicated that the prevailing coagulation mechanism was adsorption of non-proteinaceous matter onto aluminum hydroxide precipitates. The lowest residual Al concentrations were achieved in very narrow pH ranges, especially in the case of PACl. High-molecular weight saccharide-like organics were amenable to coagulation compared to low-molecular weight (<3 kDa) substances. Their high content in non-proteinaceous matter (about 67%) was the reason for its low removal. Comparison with our previous studies implies that proteinaceous and non-proteinaceous matter is coagulated under different conditions due to the employment of diverse coagulation mechanisms. The study suggests that further research should focus on the removal of low-molecular weight AOM, reluctant to coagulate, with other treatment processes to minimize its detrimental effect on water safety.

Mitigation of algal organic matter released from Chaetoceros affinis and Hymenomonas by in situ generated ferrate

This study demonstrates the application of in situ ferrate (Fe(VI)) for the efficient removal of dissolved algal organic matter (AOM) from seawater. Sodium hypochlorite (NaOCl) and ferric (Fe(III)) were used to produce in situ Fe(VI) by wet chemical oxidation. First, the removal efficiencies of two model AOM compounds, humic acid (HA) and sodium alginate (SA), were evaluated in the presence of sodium chloride with an initial influent dissolved organic carbon (DOC) concentration of 5.0 mg C L−1 at different pH levels to establish the optimal doses for in situ Fe(VI) generation. The concentration of Fe(VI) was determined by the 2,2-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) ultraviolet–visible spectrophotometry method. In the case of HA, 72% DOC removal was recorded when applied with 1.5 mg L−1 of Fe(III) and 1.5 mg L−1 of NaOCl (in situ Fe(VI) concentration of 1.46 mg L−1) while 42% DOC removal was observed for SA. Subsequently, the removal of AOM extracted from two bloom-forming algal species, Chaetoceros affinis (CA) and Hymenomonas (Hym), cultivated in seawater from the Red Sea, were tested with in situ generated Fe(VI) at the established optimum condition. In situ Fe(VI) recorded superior performance in removing AOM extracted from CA and Hym, showing 83% and 92% DOC removal when the influent DOC concentrations were 2.48 and 2.63 mg L−1, respectively. A detailed AOM characterization was conducted using liquid chromatography–organic carbon detection.

Removal of Algal Organic Matter and Control of Disinfection By-products by Powder Activated Carbon

The removal efficiencies of algal organic matter (AOM) and typical nitrogenous and non-nitrogenous disinfection by-products (DBPs) through adsorption with powder activated carbon (PAC) were investigated. Three-dimensional fluorescence spectroscopy confirmed that PAC adsorption changed the composition of AOM. PAC adsorption showed high removal efficiency for humus-like substances in AOM, but limited removal efficiency for aromatic protein-like substances. When the dosage of PAC was 20 mg·L-1 and the adsorption time ranged from 10 to 30 min, the removal rates of 3.30 mg·L-1 dissolved organic carbon were 20.7%-31.9% for intracellular organic matter (IOM) and 12.6%-19.0% for extracellular organic matter (EOM). The highest removal rates of trihalomethanes by PAC in the chlorination of IOM and EOM were 26.6% and 35.8%, respectively. The highest removal rates of haloacetonitriles were 49.6% and 53.6% in the chlorination of IOM and EOM. The removal of dibromoacetonitrile precursors by PAC was significant. In summary, the PAC had a higher efficiency in reducing the generation of DBPs in EOM chlorination than in IOM chlorination.