Algal-derived organic matter as precursors of disinfection by-products and mutagens upon chlorination
Croucher Institute for Environmental Sciences and Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong, PR China.Water Research (Impact Factor: 5.53). 01/2011; 45(3):1454-62. DOI: 10.1016/j.watres.2010.11.007
Algal-derived organic materials (including algal cells, hydrophilic and hydrophobic proteins) from Chlamydomonas sp. (a common green alga in local reservoirs), were chlorinated in the laboratory (20 °C, pH 7, Cl(2)/DOC ratio of 20 mg Cl(2) mg(-1)). Levels of disinfection by-products and mutagenicity (via Salmonella T100 mutation assay, -S9) over 2 h of chlorination time were determined. The hydrophilic proteins were more effective precursors of chloroform (35.9 μmol L(-1) at 120 min), 35 times greater than that from the hydrophobic proteins; whereas the hydrophobic proteins were more potent precursors of direct-acting mutagens (maximum level of 50.1 rev μL(-1) at 30 s) than the hydrophilic proteins (maximum level of 3.38 rev μL(-1) at 60 min). The mutagenicity of the chlorinated solutions generally reached a peak level shortly after chlorination and then declined afterwards, a pattern different from that of chloroform generation. The results indicate that algal hydrophilic proteins, containing low aromaticity and difficult to be removed via coagulation/flocculation, are important chloroform precursors. It is also suggested that hydrophobic organic intermediates with low molecular weight formed during chlorination may serve as the direct-acting mutagens.
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- "Natural organic matter (NOM) which occurs in water reservoirs is mainly present in two forms: (i) allochthonous NOM of terrestrial origin dominated by humic substances (HS, mostly humic and fulvic acids) and (ii) autochthonous NOM, including mainly compounds derived from algae and cyanobacteria, i.e. algal organic matter (AOM). As well as HS, AOM has received increasing attention as it can cause either aesthetic concerns (i.e., colour, taste and odour) or undesirable health effects associated with disinfection by-products (DBPs) (Lui et al., 2011; Li et al., 2012), cyanobacterial toxins (Harada, 2004) and other toxic compounds contained in NOM (Ghernaut et al., 2011). Moreover, AOM may instigate serious problems in drinking water treatment processes, especially during the decline phase of an algal bloom, when high concentrations of cellular organic matter, consisting mainly of saccharide-like and protein-like substances, are released into the source water (Zhang et al., 2010; Nicolau et al., 2015). "
ABSTRACT: This study focuses on the effects of molecular interactions between two natural organic matter (NOM) fractions, peptides/proteins derived from cyanobacterium Microcystis aeruginosa (MA proteins) and peat humic substances (HS), on their removal by coagulation. Coagulation behaviour was studied by the jar tests with MA protein/HS mixtures and with single compounds (MA proteins or HS). Aluminium sulphate was used as a coagulant. Besides MA proteins, bovine serum albumin (BSA) was used as a model protein. For the MA protein/HS mixture, the removal rates were higher (80% versus 65%) and the dose of coagulant substantially lower (2.8 versus 5.5 mg L(-1) Al) than for coagulation of single HS, indicating the positive effect of protein-HS interactions on the coagulation process. The optimum coagulation pH was 5.2-6.7 for MA proteins and 5.5-6 for HS by alum. The optimum pH for the removal of MA protein/HS mixture ranged between pH 5.5-6.2, where the charge neutralization of negatively charged acidic functional groups of organic molecules by positively charged coagulant hydroxopolymers lead to coagulation. MA proteins interacted with HS, probably through hydrophobic, dipole-dipole and electrostatic interactions, even in the absence the coagulant. These interactions are likely to occur within a wide pH range, but they result in coagulation only at low pH values (pH < 4). At this pH, the negative charge of both MA proteins and HS was suppressed due to the protonation of acidic functional groups and thus the molecules could approach and combine forming aggregates. Virtually the same trends were observed in the experiments with HS and BSA, indicating that BSA is a suitable model for MA proteins under experimental conditions used in this study. The study showed that increases in organic content in source water due to the release of algae products may not necessarily entail deterioration of the coagulation process and a rise in coagulant demand.Water Research 07/2015; 84:278-285. DOI:10.1016/j.watres.2015.07.047 · 5.53 Impact Factor
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ABSTRACT: This study was performed to illustrate the effects of preoxidation by potassium permanganate on the fluorescence spectrum of Microcysis aeruginosa, a kind of blue-green algae. The results showed there were four dominate excitation/emission (Ex/Em) wavelength pairs, 230/334, 280/312, 280/334 and 620/642 nm/nm in the fluorescence spectra of algae and their derived organic matters (AOM). Coagulation resulted in desorption of the organic matter adsorbed in algae cells and produced two new fluorophores centered at 275/460 and 400/460 nm/nm. Potassium permanganate preoxidation could reduce the fluorescence intensity of algae and dissolved algal organic matters effectively and the descent rate increased with increasing potassium permanganate dosage.07/2011; 71-78. DOI:10.4028/www.scientific.net/AMM.71-78.2920
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ABSTRACT: Cells and proteins of Chlamydomonas sp. (a common green alga in local reservoirs) were separated by ultrafiltration respectively into 3 fractions with variable molecular weights (MW: >100, 10-3 and <3 kDa). After chlorination (20°C, pH 7, Cl(2)/DOC ratio of 20 mg Cl(2)mg(-1), 120 h), levels of disinfection by-products (DBPs) and mutagenicity (via Salmonella T100 mutation assay, -S9) were analyzed. The highest yields of chloroform (2571 μmol mol C(-1)), DCAA (19,083 μmol mol C(-1)) and TCAA (4939 μmol mol C(-1)) were observed from the fraction of MW>100 kDa, while the fraction of 3-10 kDa was potent DCAN precursor. In contrast, the chlorinated MW 3-10 kDa cell fraction showed high mutagenicity (maximum level of 93 rev μL(-1) at 2 min), while the MW>100 kDa cell fraction showed low mutagenicity (maximum level of 16.6 rev μL(-1) at 7200 min) after chlorination. This indicated that unmeasured DBPs or possible interactions among the DBPs contributed to the mutagenicity. Comparing between the cell and protein fractions, the former was more potent in forming chloroform, DCAA, TCAA, DCAN and TCAN. This is the first study that fractionated algal cells and proteins were examined for DBP formation and mutagenicity.Journal of hazardous materials 03/2012; 209-210:278-84. DOI:10.1016/j.jhazmat.2012.01.023 · 4.53 Impact Factor
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