Abstract

JUAREZ, Ivan et al. Modelling of chlorophyll-a and Microcystis aeruginosa decay under the effect of different oxidants in culture media. Water SA [online]. 2020, vol.46, n.3, pp.523-533. ISSN 1816-7950.  http://dx.doi.org/10.17159/wsa/2020.v46.i3.8663.

Blooms of the cyanobacterium Microcystis aeruginosa are common in many eutrophic freshwater bodies and pose a serious threat to water quality, potentially giving rise to high turbidity, food web alterations, increased production of toxic microcystin (MC-LR) and odorous compounds. The comparative effectiveness of oxidant treatment of M. aeruginosa cells in culture media was evaluated by applying a mathematical model of chlorophyll-a (Chl-a), cells and MC removal. The oxidants were chlorine (1-5 mg∙L^-1), hydrogen peroxide (HP: 50-150 mg∙L^-1), percitric acid (PCA: 10-50 mg∙L^-1), and peracetic acid (PAA: 1.5-7.5 mg∙L^-1). The Weibull distribution model was applied to assess the degree of inactivation of M. aeruginosa viability under different oxidant treatments. First-order kinetics was successfully applied to the experimental data for Chl-a decay. Using the Weibull model, it was possible to predict the required exposure time (T_r) for oxidants to achieve a 99.9% reduction in viable M. aeruginosa cells with respect to the initial value. 5 mg∙L^-1 chlorine produced a 81% degradation of [D-Leu¹] MC-LR after 72 h, with an exposure time (T_r) of 141 h. Among the peroxide treatments (HP, PCA and PAA), PCA (10-50 mg∙L^-1) produced the highest level of [D-Leu¹] MC-LR degradation (39-79%), with low exposure times (T_r = 119-125 h). Chl-a concentration and M. aeruginosa counts for each oxidant treatment were highly correlated and successfully linked by a cubic polynomial. This is the first modelling report of M. aeruginosa decay by oxidant treatments.

Keywords : Microcystis aeruginosa; microcystin; mathematical model; oxidants; chlorophyll-a decay; Weibull model.

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