Algogenic Organic Matter Research Articles

Nanobubble-enabled foam fractionation to remove algogenic odorous micropollutants

Due to climate change and environmental pollution, natural lakes and reservoir water suffer increasingly serious algal blooms and associated water quality problems due to the presence of algal or algogenic organic matter (AOM) such as algal odour and toxins. Effective removal of these micropollutants, especially in the event of algal blooms, is critical to aesthetic values of water bodies, drinking water security and human health. The study investigated the removal efficiency of two common odorous compounds, trans-1,10-dimethyl-trans-9-decalol (geosmin) and 2-Methylisoborneol (2-MIB), using foam fractionation enabled by air nanobubbles with addition of two common cationic and anionic surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), to enhance foaming ability and stability. The results showed that the cationic surfactant (i.e., CTAB), a low pH, and high ionic strength significantly promoted the removal of geosmin and 2-MIB. For example, the removal tests using the synthetic water determined that the conditions of pH = 7, [CTAB] = 20 mg·L−1 and IS = 10 mM as NaCl resulted in both the highest geosmin removal rate of 91.81% and highest 2-MIB removal rate of 85.0%. The removal of two odorous compounds in real lake water was evaluated, which yielded removal rates of 83.2% for geosmin and 48.1% for 2-MIB, highlighting the minor inhibition from water matrixes on the removal performances. Compared to microbubbles, nanobubbles enabled greater surface areas of foam and higher removal efficiencies. The study provided new insights into the use of foam fractionation with air nanobubbles to enhance the removal of odorous compounds from impaired water and mitigate the negative environmental and health impacts of harmful algal blooms (HABs).

Synergies of pH-induced calcium phosphate precipitation and magnetic separation for energy-efficient harvesting of freshwater microalgae

Energy- and time-consuming concentration steps currently limit the industrial application of microalgae. Compared to state-of-the-art technologies, magnetic separation shows a high potential for efficient harvesting of microalgae. This study presents a novel approach to combine pH-induced calcium phosphate precipitation with cheap natural magnetite microparticles for magnetic separation of the freshwater microalgae Chlorella vulgaris. Harvesting efficiencies up to 98% were achieved at moderate pH and low particle and calcium phosphate concentrations in a model medium. However, cultivation-dependent high loads of algogenic organic matter can severely inhibit flocculation and particle/algae interactions, requiring higher salt concentrations or pH. Harvesting efficiencies above 90% were still attainable at moderate pH with increased calcium phosphate concentrations of 10mM. Acidification of the suspension to pH 5 allows for simple and reversible particle recycling. The presented process provides a promising path to universal and cost-effective harvesting, advancing the utilization of microalgae as a sustainable bioresource.

Surface regeneration of templated PVDF membrane for efficient microalgae-rich high saline aquaculture wastewater treatment in membrane distillation

This study investigated the use of templated PVDF membranes with intermediate flushing to revive fouled membrane during membrane distillation (MD) for sustainable high saline seawater aquaculture wastewater treatment. Results showed that superhydrophobic templated membrane with intermediate physical flushing was highly effective in reducing fouling, even after 5 cleaning cycles, when treating microalgae-rich feed with algogenic organic matter and high salinity aquaculture wastewater. Specifically, the membrane restoring flux performance by up to 97.2 %, compared to only 75.6 % for pristine membranes. In this study, intermediate flushing effectively restored the advancing and reducing contact angles of fouled templated membranes, enhancing membrane regeneration and reducing surface adhesion properties. In long-term 82-h MD tests, the superhydrophobic templated membrane still demonstrated excellent separation, achieving 99.84 % rejection rate for all components and maintaining average water permeation flux of 21.4 kg/m2.h when treating microalgae-rich feed. The study suggests that the use of superhydrophobic templated membrane with surface reviving capability holds immense potential in overcoming the challenges of membrane fouling in MD, providing a sustainable treatment solution for microalgae-rich and high salinity wastewater treatment.

Effects of Long-Term Exposure of Pharmaceuticals and Personal Care Products on Algogenic Organic Matter Characteristics

Algal organic matter (AOM) released from microalgae has high potential effects for water treatment. In response to the complex problem of algal-laden water treatment, this study investigated the characteristics of AOM of Microcystis aeruginosa under long-term exposure to pharmaceuticals and personal care products (PPCPs). The results indicated that algae under low carbamazepine (<10 µg/L), high naproxen (>10 µg/L), and/or diclofenac at any concentration treatment promoted the release of total organic matter, whereas they were inhibited at high carbamazepine and low naproxen exposure. Macromolecular organics of AOM were inhibited when algae were subjected to long-term exposure to carbamazepine at any concentration (0.25–1000 µg/L), and the higher the carbamazepine concentration was, the more seriously macromolecular organics were inhibited. For naproxen and diclofenac treatment, macro- and medium-molecular-weight organics were promoted under high concentration treatment (>1 µg/L), yet they were inhibited under low concentration <10 µg/L. The fluorescent organics of AOM were also changed by fluorescence excitation-emission matrices-parallel factor analysis, with the fluorescent intensity of humic-like and protein-like substances inhabited under carbamazepine of any concentration, whereas they were promoted under high naproxen treatment (>10 µg/L). This research had significant effects on algal-laden water treatment containing various PPCPs concentrations as well as the risk assessment of PPCPs in water.

Gravity-driven membrane coupled with oxidation technology to modify the surface properties and biofilm formation: Biofouling mitigation

Biofilms caused by biological fouling play an essential role in gravity-driven membranes’ (GDMs) flux decline and rejection rate. The effects of ozone, permanganate, and ferrate (VI) in-situ pretreatment on membrane properties and biofilm formation were systematically studied. Due to the selective retention and adsorption of algal organic matter by biofilms and oxidative degradation, the rejection efficiency of dissolved organic carbon (DOC) in algae-laden water pretreated with permanganate by GDM was up to 23.63%. Pre-oxidation extraordinarily postponed flux decline and biofilm formation of GDM and reduced membrane fouling. The total membrane resistance decreased by 87.22%–90.30% within 72 h after pre-ozonation. Permanganate was more effective than ozone and ferrate (VI) in alleviating secondary membrane fouling caused by algal cells destroyed by pre-oxidation. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory revealed that the distribution of electrostatic force (EL), acid-base (AB), and Lifshitz-van der Waals forces (LW) interactions between M. aeruginosa and the released intracellular algogenic organic matter (IOM) and ceramic membrane surface was similar. The membrane and foulants are always attracted to each other by LW interaction at different separation distances. The dominant fouling mechanism of GDM combined with pre-oxidation technology shifts from complete pore blocking to cake layer filtration during operation. After pre-oxidation of algae-laden water by ozone, permanganate, and ferrate (VI), GDM can treat at least 131.8%, 37.0%, and 61.5% more feed solution before forming a complete cake layer. This study provides new insights into the biological fouling control strategies and mechanisms for GDM coupled with oxidation technology, which is expected to alleviate membrane fouling and optimize the feed liquid pretreatment procedure.

Harvesting of microcells from cyanobacteria-laden water by energy-efficient electro-flocculation-flotation with aluminum hydrates

Electrocoagulation-flotation (ECF) is able to effectively harvest microcells from eutrophicated drinking water reservoirs to reduce algogenic organic matter (AOM) during cyanobacteria blooming. However, ECF needs high current density (CD) and prolonged reaction time with inevitable high-energy consumption. This study aimed to investigate a novel electrocoagulation-flocculation-flotation (EFF) process, with 10 min EC reaction and 15 min flocculation followed by 10 min flotation, for Microcystis aeruginosa (MA) cell harvesting from water as well as AOM reduction with Al hydrates at various CD and pH conditions. The results have shown that significant MA cell separation and dissolved organic carbon (DOC) reduction by EFF occurred at pH 8 with 5 mA/cm2, accounting for 95 % and 56 %, respectively. At such a condition, the formation of dominant colloidal Al species (Alc) governed the EFF to promote cells and AOM destabilization by strong sweep flocculation along with weak charge neutralization by polymeric Al species (Alb). Moreover, the pronounced reduction in soluble microbial product-like (SMPL) substances could be further improved by up to 60 % with EFF. It was also found that EFF required only 2.07 × 10−2 kWh/kg in energy input and served energy saving ~63 % less than that by prolonged ECF at similar MA cell separations. It concluded that EFF was an energy-efficient technique to fast separate and harvest microcells from MA-laden water and AOM reduction with low energy input for practical application in drinking water treatment.

Removal of Microcystis aeruginosa and microcystin-LR using chitosan (CTS)-modified cellulose fibers and ferric chloride

The occurrences of harmful algae blooms (HABs) and cyanotoxins such as microcystin-LR (MC-LR) are increasing in water reservoirs and compromise drinking water security. In this study, chitosan (CTS) modified cellulose fibers (CF) were developed as a green adsorbent for the simultaneous removal of a model algae cell, Microcystis aeruginosa, and MC-LR. The results showed that the CTS modification could render amine groups (−NH2) on CF and increased the adsorption affinity toward algae. In the absence of algogenic organic matter (AOM), the algae removal reached 100% at a dosage of 26.7 g-NH2-CF/g-algae (dry weight); however, at the same CF dosage, the presence of AOM (8.13 mg‑carbon·L−1) strongly reduced the adsorption by NH2-CF and removal rate of algae cells reached only 3.2 ± 3.0%. When adding FeCl3 or Fe3+ at a concentration of 11.2 mg-Fe·L−1, the inhibitory effect of AOM was dramatically reduced as indicated by the improved algae removal up to 95% at an NH2-CF dosage of 20.45 g·g−1, because of the reduced energy barrier between NH2-CF and cells. Moreover, when the Fe3+ concentration was increased to 16.8 mg·L−1, 79% of MC-LR was simultaneously removed. Thus, combining Fe3+ with NH2-CF is proven effective to enhance the adsorption and removal of Microcystis aeruginosa and MC-LR and achieve a sustainable mitigation of HABs.

Insights on free radical oxidation and in-situ coagulation in PMS/Fe(II) process for the removal of algogenic organic matter precursors

Algogenic organic matter (AOM) is unwelcome in raw water as it is a major precursor of carcinogenic disinfection byproducts (DBPs). Unfortunately, conventional coagulation is ineffective against AOM, raising the need for a better alternative for AOM and AOM-derived-DBP removal. This study examined the effectiveness and underlying mechanisms of a novel hybrid oxidation-coagulation PMS/Fe(II) process for effective removal of AOM-DBP precursors. Under optimal conditions, only PMS/Fe(II) or combined PMS/Fe(II) with Al/Fe coagulation removed significant amounts of dissolved organic carbon (DOC) (45–52%) and 50–65% AOM-fluorescent components. These values were much better than conventional Al/Fe coagulations (e.g. 15–19% DOC and < 40% fluorescent components at [Fe3+] = [Al3+] = 100 μM, pH 5.5–6). AOM-derived DBPs were thus significantly eliminated (>80% of total DBP levels) after PMS/Fe(II) related processes, which markedly outperformed Al/Fe coagulations (of only 20–30%). PMS/Fe(II) presented its strongest oxidative ability at pH 4 (with [SO4•−] = 2.16 × 10−12 and [•OH] = 1.26 × 10−12 M), rather than at pH 7 or 9. Acidic conditions rapidly increased oxidized-carbon contents (e.g. %ketone + %carbonyl increased from 10% to 25%) in AOM structure after PMS/Fe(II) treatment. By contrast, pH 7 and 9 were the favorable conditions for in-situ coagulation with faster floc aggregation and growth rates than pH 4. Regardless, PMS/Fe(II) process performed best in effectively removing AOM-DBP precursor only under neutral pH of 6–7 by gaining the synergistic benefits of free radical oxidation and in-situ coagulation. Our findings are a significant contribution to filling the knowledge gap in the study of PMS/Fe(II) and highlight the possibilities of this novel hybrid process as an alternative to conventional coagulation for sustainable water treatment.

Harvesting of Microcystis flos-aquae using dissolved air flotation: The inhibitory effect of carboxyl groups in uronic acid-containing carbohydrates

Harvesting algal biomass reduces nutrient loading in eutrophicated lakes and the protein-rich microalgal biomass could be recycled as feedstocks of feed and fertilizer. Due to the complexity of algogenic organic matter (AOM), the key components and functional groups in AOM that inhibit coagulation-based microalgal harvesting have not been disclosed thus far. This study quantitatively analysed the responsive compositions and functional groups of AOM involved in the dissolved air flotation (DAF) harvesting of M. flos-aquae with 1 × 109 cell L−1 density at coagulation pH 6.2. The results showed that harvesting efficiency dropped drastically from 95.5 ± 0.7% to 43 ± 0.7% in the presence of AOM (26.77 mg L−1) at the coagulant dosage of 0.75 mg L−1 and further deteriorated with increasing AOM concentration. Carbohydrates contributed 81% of the total composition of substances involved in the DAF, while the contribution of protein and humic-like substances were only 18% and 1%, respectively. Stoichiometric analysis of functional groups in carbohydrates, proteins, and humic-like substances using model components revealed that carboxyl groups in uronic acid-containing carbohydrates accounted for 76% of the total reduction in carboxyl groups, which was much higher than that in proteins (23%) and humic-like substances (1%), indicating that carboxyl groups in uronic acids containing carbohydrates were the major inhibitors. A conceptual model of charge competition was proposed to explain the inhibition mechanism of carboxyl functional groups in uronic acid-containing carbohydrates on microalgal DAF. Strategies such as preventing carboxyl deprotonation by pH reduction and employment of sweeping/bridging polymeric coagulants/flocculants were proposed for the to reduce the inhibitory effect of carboxyl functional groups.

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

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

Removal of cyanobacteria using novel pre-pressurized coagulation: The effect of cellular properties and algogenic organic matter characteristics

• Pre-pressurized coagulation reduces coagulant dosage for M. flos-aquae removal. • Changes in cell properties/AOM characteristics after pre-pressurization is studied. • Pre-pressurization ruptures mucilaginous sheath and raises coagulation efficiency. • Exposure to more electronegative functional groups promotes the cell-CPAM binding. Pressurization pretreatment is reported as a novel pretreatment method for the coagulation removal of Microcystis sp . from eutrophicated water, as less coagulant is required than without pressurization. However, how cellular properties and algogenic organic matter (AOM) characteristics change with pressurization pretreatment and thus reduce the coagulant dose are still not understood. Using Microcystis flos-aquae in Lake Taihu, this study analyzed the changes in cellular morphology, size distribution, and charge density, as well as the changes in concentration and composition of cell-based protonated functional groups. Coagulation experiments using different combinations of cells and AOM with/without pressurization pretreatment showed that the changes in cell surface properties played a bigger role in coagulation enhancement than AOM. The enhancement of the coagulation efficiency of M. flos-aquae with pressurization pretreatment is related to the rupture of the mucilaginous sheath and subsequent exposure of cells with more active functional groups, the content of phosphodiester, carboxyl and phosphoryl functional groups on the surface of M. flos-aquae cells increased by 55%, 29% and 203%, respectively. Thus increasing the binding sites between M. flos-aquae cells and cationic polyacrylamide (CPAM). As a result, with pressurization pretreatment, the dose of CPAM was reduced from 5 mg L −1 to 0.8 mg L −1 for the same removal efficiency of 90%. These results may help us understand the mechanism by which pressurization treatment impacts M. flos-aquae coagulation and thus provide a new perspective for the low-cost and sustainable removal of cyanobacterial blooms.

Effect of Al hydrates on minimization of disinfection-by-products precursors by coagulation with intensified pre-oxidation towards cyanobacteria-laden water

Pre-oxidation is warranted to improve cyanobacteria removal and minimize disinfection by-products (DBPs) precursors for subsequent coagulation with polyaluminum chloride (PACl) in drinking water treatment. However, the reduction in DBP precursors strongly depends on the Al hydrates for PACl coagulation. This study aimed to investigate the effects of intensified NaOCl and ClO2 pre-oxidation on the removal of Microcystis aeruginosa (MA) and the corresponding halogenated DBP precursors by PACl coagulation with different Al hydrates. Two PACl coagulants, namely PACl-W with 51% monomeric Al and PACl-H with 71% polymeric Al, were used for FlocCAM jar test. The results have shown that the reductions in MA cell and algogenic organic matter (AOM) are more pronounced by sweep flocculation in PACl-W coagulation coupled with NaOCl pre-oxidation. In contrast, ClO2 pre-oxidation with PACl-H coagulation outperforms the floc formation and the reduction in each fluorescent DOM substance, especially for humic acid-like (HAL) substances reduction in response to charge neutralization. Regardless of pre-oxidation approach, PACl-H coagulation exhibits a superior reduction in carbonaceous DBP formation potential (C-DBPFP) comparative PACl-W coagulation, especially for intensified pre-oxidation (Cl2:DOC = 3:1). Intensified NaOCl pre-oxidation is effective to enhance DBPFP reduction in a similar way to ClO2 oxidation by coagulation with both PACl coagulants. In addition, it clearly demonstrates that the halogenated DBP precursors are well-correlated with UV254 absorbance on the basis of principal component analysis (PCA) inference. It is concluded that intensified NaOCl pre-oxidation is an alternative approach to ClO2 pre-oxidation for the minimization of DBP precursors in oxidation-coagulation processes for cyanobacteria-laden water treatment.

The effect of coagulation on the removal of algogenic organic matter and the optical parameters for predicting disinfection byproducts

Algae-derived disinfection byproducts (DBPs) are receiving increasing attention. Coagulation is the first water treatment section in removing algogenic organic matter (AOM). However, there is a significant knowledge gap in the effects of coagulation on DBPs produced from AOM. In this study, in view of the multi-component AOM, several analysis methods were combined to investigate the changes in AOM of Microcystic aeruginosa during the coagulation treatment, including ultraviolet–visible absorbance, multi-peaks Gaussian fitting method based on differential absorption spectroscopy, Excitation-emission matrix, and Fourier transform infrared spectroscopic analysis. To identify the characteristic parameters that could indicate the formation of DBPs, the yields of twenty-one DBP species produced from the residual AOM after the coagulation treatment were investigated. The correlations between DBPs and the spectral parameters were also analyzed. The results showed that aluminum salt coagulant could significantly remove protein-like compounds, chlorophyll, and phycocyanin in AOM, but it had a limited ability to precipitate AOM. With the increase of aluminum sulfate coagulant, the yields of DBPs produced from the residual extracellular organic matter decreased, while those produced from the residual intracellular organic matter decreased firstly and then gradually increased. The Pearson’s correlation results showed that the combination of fluorescent regions of protein-like and humic acid-like could be used as an optical surrogate for predicting the formation of DBPs.

Algogenic organic matter fouling alleviation in membrane distillation by peroxymonosulfate (PMS): Role of PMS concentration and activation temperature

Membrane distillation (MD) has attracted significant attention in recent years; however, MD membrane fouling is still a big issue. For the first time, this study explored the performance of a standalone direct contact membrane distillation (DCMD) and an integrated peroxymonosulfate (PMS)/DCMD for the treatment of surface water mainly containing algogenic organic matter (AOM) to elucidate pollutant removal as well as fouling propensity and mitigation. The results indicated that the overall conductivity and dissolved organic carbon (DOC) removals by the standalone DCMD and PMS/DCMD were comparable (98–99.8%). However, permeate flux of the standalone DCMD reduced by 62% due to severe membrane fouling. After pre-treatment at 60 °C, flux reduction of 27–40% and no flux decline were observed at PMS concentrations of 1–5 mM and 10–15 mM, respectively. The optimum PMS concentration of 10 mM was also demonstrated to be effective for membrane fouling mitigation at 40 and 50 °C. Characterisation of AOM indicated the presence of protein-like and high MW (≥10 kDa) compounds, which were readily degraded by the reactive species (OH and 1O2) generated by heat-activated PMS. Characterisation of fouled MD membrane confirmed that fouling was mainly caused by protein-like compounds, consequently affecting permeate flux and membrane properties.

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.

Sustainable production of microalgae biomass for biofuel and chemicals through recycling of water and nutrient within the biorefinery context: A review

AbstractCommercial‐scale production of microalgae biomass for biofuel and biochemicals requires a substantial amount of water and nutrients. Many studies are conducted to explore the potential of various aqueous streams originating from harvesting stage and different energy recovery steps as an alternative for water and nutrient supply. Presence of toxic organic compounds, unassimilated ions, particulate matter, and high alkalinity in post‐harvest water limit its recyclability. Nutrient recovery from biomass via anaerobic digestion (AD) and various hydrothermal processes is being explored. So, there is a need to understand the impact of harvesting methods, nature and impact of organic compounds, buildup of algogenic organic matter (OM), amount of unused nutrients, and salinity on water recycling. Optimum conditions for maximum nutrient recovery from AD and hydrothermal processes are discussed for effective nutrient recycling. This review is an attempt to understand the challenges associated with the recycling of aqueous streams for water and nutrient requirement for sustainable microalgae cultivation. The effectiveness of a recycling stream is defined here as “biomass ratio.” Possible growth inhibiting factors are identified, and their solutions are suggested along with potential directions for future research. Large‐scale sustainable cultivation of microalgae through recycling of different streams depends on better understanding of biological activity of algal OM through detailed characterization and in‐depth understanding of physiochemical properties.

Disinfection by-product formation potential of algogenic organic matter from Microcystis aeruginosa: Effects of growth phases and powdered activated carbon adsorption

Algae can exhibit different disinfection by-product formation potential (DBPFP) depending on the characteristics of the algogenic organic matter (AOM) released during growth. In this study, the amount of AOM released by Microcystis aeruginosa and its DBPFP were compared between the exponential growth phase and the death phase. Moreover, the efficiency of DBPFP removal through powdered activated carbon (PAC) adsorption was evaluated. The correlations between DBPFPs and dissolved organic carbon concentration or ultraviolet absorbance at 254 nm (UV254) were also investigated to predict DBPFPs. Among DBPFPs, which were higher at the death phase, the formation potential (FP) of haloacetic acid was the highest. In addition, the high relative haloacetonitrile FP at the death phase indicated that a relevant portion of the intracellular organic matter derived from cell autolysis was converted into a large amount of haloacetonitriles. Furthermore, PAC addition reduced all DBPFPs at both growth phases. PAC was found to selectively adsorb dichloroacetic acid precursors at the death phase and dichloroacetonitrile precursors at both growth phases. Finally, UV254 showed greater correlations with the three DBPFPs at all growth phases. These results highlight the possible use of UV254 as an alternative analytical tool for fast determination of M. aeruginosa DBPFPs.

Harvesting of Microcystis aeruginosa using membrane filtration: Influence of pore structure on fouling kinetics, algogenic organic matter retention and cake formation

Different membrane pore structures can affect filtration characteristics and membrane fouling during membrane harvesting of algae suspensions. In this study, four membrane materials with different pore structures (MC-5, PC-3, PVDF-5, and PVDF-100KDa) were employed to filter Microcystis aeruginosa suspensions to compare their filtration characteristics, retention of algogenic organic matter and membrane fouling. The correlation between membrane performance and pore structure characteristics, such as pore size, porosity, surface free energy, zeta potential, and surface pore area, were analyzed by a redundancy analysis method. The results revealed that PVDF-100KDa had the lowest deionized water flux compared with the microfiltration membranes due to its smaller pore size, and its high retention of organic matter aggravated membrane fouling. In addition, the track-etched single-pore PC-3 membrane exhibited fast flux decline and the highest cake layer resistance. PVDF-5 had strong adsorption capacity for aromatic protein-like compounds, which can increase irreversible fouling. Overall, MC-5 exhibited the best average flux and better flux recovery with a lower retention of organic matter and the maximum roughness observed by optical coherence tomography. For further insight, a conceptual model was proposed, which clarifies the effect of pore structure on fouling kinetics, algogenic organic matter retention and cake formation and thus provides valuable guidance for the development of membrane harvesting of algae suspensions.

Harvesting of Microcystis flos-aquae using chitosan coagulation: Influence of proton-active functional groups originating from extracellular and intracellular organic matter

Algogenic organic matter (AOM) produced by Microcystis cells inhibits coagulation harvesting; however, the harvesting inhibitory mechanisms at the functional groups level remain to be determined. This study fractionated extracellular organic matter (EOM) and intercellular organic matter (IOM) from Microcystis flos-aquae into five different hydrophilic and hydrophobic fractions and investigated their inhibition of chitosan coagulation harvesting. The proton-active functional groups in the inhibitory fractions were further analysed by potentiometric titration, and the interaction between these functional groups and chitosan was elucidated. The results showed that the harvesting inhibition of M. flos-aquae cells was dominated by HPI in AOM due to its high charge density, which resulted in greater consumption of coagulant. Potentiometric titration results suggested that the proton-active functional groups of both HPIEOM and HPIIOM consist mainly of phosphodiester, carboxylic, phosphoryl and amine/hydroxyl functional groups, and the harvesting inhibition of HPI on M. flos-aquae cells at pH 6.5 was mainly due to the deprotonation of phosphodiester and carboxylic functional groups. Moreover, carboxylic functional groups with stronger polarity could enhance the intermolecular interaction between HPI and chitosan more effectively than phosphodiester at pH 6.5. Preventing the deprotonation of carboxylic functional groups by adjusting the pH to 4.3 could effectively alleviate the harvesting inhibition caused by HPI. These findings revealed the inhibition mechanism of AOM on the coagulation harvesting of M. flos-aquae cells from the perspective of deprotonation of proton-active functional groups, which may provide important insights for assessing the role of AOM in the coagulation harvesting of Microcystis cells.

NOM removal and residual Al minimization by enhanced coagulation: roles of sequence dosing with PACl–FeCl3

Abstract To remove higher proportions of natural organic matter (NOM) in water treatment plants, over dosing of Al-based coagulant is frequently applied. However, this leads to the risk of an excess of coagulant residue in the clean water. In this study, sequential coagulation with polyaluminum chloride (PACl) and FeCl3 was proposed to improve the removal of NOM as well as to minimize residual Al. Single dosing with either PACl or FeCl3 in particular was compared with sequential coagulation, with different dosing sequences of PACl–FeCl3 (P–F) or FeCl3–PACl (F–P). At optimum dosage, sequential coagulation P–F showed twice as much dissolved organic carbon (DOC) removal from water containing algogenic organic matter, compared to single dosing of PACl and sequential coagulation F–P. However, sequential coagulation F–P was the most effective approach for humic substance removal that improved DOC removal up to &amp;gt;70% compared to other dosing approaches (&amp;lt;60%). Practical treatment with real water also showed the advantages of sequential coagulation with P–F in improving the removal of low SUVA NOM by 18% compared to the traditional single dosing of PACl. As expected, the Al residues found in both sequential coagulation (0.07 mg/L) were significantly reduced compared to single dosing with PACl (0.15 mg/L), indicating the promising application of sequential coagulation for future safe water treatment.