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      Laboratory-scale simulations with hydrated lime and organic polymer to evaluate the effect of pre-chlorination on motile Ceratium hirundinella cells during conventional water treatment

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          Abstract

          Algal genera such as Carteria, Chlamydomonas, Chlorogonium, Cryptomonas, Ceratium, Peridinium and Euglena are motile and may disrupt unit processes and cause water treatment problems. Algal species belonging to these motile algal genera are known to interfere with coagulation and flocculation unit processes which are the main processes for algal removal. These cells are well adapted, by means of their motile structures, morphological shapes and storage products, to remain in the supernatant (by swimming or floating) until it is carried over to sand filters, where cells may cause filter-clogging problems. When organic material is released from algal cells as a result of physical-chemical impacts on the cells, it may result in taste-and odour-related problems or the formation of harmful organic products such as trihalomethanes (THM). The aims of this study were to: (i) determine chlorine concentrations required to immobilise C. hirundinella cells; (ii) determine the removal efficiencies of pre-chlorination; (iii) investigate the integrity of C. hirundinella cells; and (iv) identify trihalomethanes that are formed. Source water samples enriched with C. hirundinella cells were exposed to a pre-determined chlorine concentration range (0.05-0.45 mg/L). This study found that the half-maximal inhibitory concentration (IC50-values) for chlorine < 0.20 mg/L is sufficient to render C. hirundinella cells immobile, while cells remain intact. Pre-chlorination did not have an impact on C. hirundinella removal when hydrated lime was used as a coagulant or coagulant aid. However, when organic polymer only was used as coagulant, removal efficiencies were improved by 20%. Chlorine by-products were measured, but posed no specific health risks to drinking water consumers due to the low concentration levels measured. Algal removal challenges that occur in water treatment plants when dosing organic polymers can be resolved by implementation of effective pre-chlorination strategies.

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          Computational tools for fitting the Hill equation to dose-response curves.

          Many biological response curves commonly assume a sigmoidal shape that can be approximated well by means of the 4-parameter nonlinear logistic equation, also called the Hill equation. However, estimation of the Hill equation parameters requires access to commercial software or the ability to write computer code. Here we present two user-friendly and freely available computer programs to fit the Hill equation - a Solver-based Microsoft Excel template and a stand-alone GUI-based "point and click" program, called HEPB.
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            Standard methods for the examination of water and waste water

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              Oxidation of Microcystis aeruginosa and Anabaena flos-aquae by ozone: Impacts on cell integrity and chlorination by-product formation

              Pre-ozonation of cyanobacterial (CB) cells in raw water and inter-ozonation of settled water can cause CB cell damage. However, there is limited information about the level of lysis or changes in cell properties after ozonation, release of intracellular compounds and their contribution to the formation of disinfection by-products (DBPs). This study aims to: (1) assess the extent of the pre-ozonation effects on CB cell properties; (2) determine the CT (ozone concentration × detention time) values required for complete loss of cell viability; and (3) study the DBPs formation associated with the pre-ozonation of cyanobacterial cells in laboratorial suspensions. To these ends, both Microcystis aeruginosa and Anabaena flos-aquae suspensions were prepared at concentrations of 250,000 cells mL(-1) and 1,500,000 cells mL(-1) and were subjected to ozone dosages of 0.5, 2.0 and 4.0 mg L(-1) at pH 6 and pH 8. A quick and complete loss of viability was achieved for both CB species after exposure (CT) to ozone of <0.2 mg min L(-1), although no significant decrease in total cell numbers was observed. Maximum dissolved organic carbon (DOC) releases of 0.96 mg L(-1) and 1.63 mg L(-1) were measured after ozonation of 250,000 cells mL(-1) of M. aeruginosa and A. flos-aquae, respectively. DOC release was found to be pH and ozone dose dependent. Ozonation of CB cells increased formation of trihalomethanes (THM) and haloacetic acids (HAA), mainly for suspensions of A. flos-aquae at pH 8 (by 174% and 65% for THM and HAA respectively). Utilities considering using ozone for oxidising CB cells should weigh out the benefit of CB control with the potential increased formation of chlorinated DBPs.
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                wsa
                Water SA
                Water SA
                Water Research Commission (WRC)
                1816-7950
                April 2016
                : 42
                : 2
                : 270-278
                Affiliations
                [1 ] North-West University South Africa
                [2 ] Rand Water Analytical Services South Africa
                Article
                S1816-79502016000200011
                10.4314/wsa.v42i2.11

                This work is licensed under a Creative Commons Attribution 4.0 International License.

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                Categories
                Water Resources

                Oceanography & Hydrology

                algae, coagulation, dinoflagellate, pre-treatment, trihalomethanes (THM)

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