Evaluating Adsorption and Biodegradation Mechanisms during the Removal of Microcystin-RR by Periphyton

Microcystin-RR (MCRR) is among the cyanobacterial toxins of significant concern due to their negative effects on water quality and human health. In this study, periphyton dominated by bacteria and diatoms was applied to remove MCRR from water. The maximum removal rate of MCRR by periphyton was observed in the first day (the latent adaptation period). Within this period, 85.2%, 73.3%, 83.5%, and 86.5% of the total MCRR removed (through adsorption and biodegradation) was by the adsorption of periphyton when the periphyton biomasses were 1.32 g, 3.96 g, 6.60 g, and 9.24 g, respectively. The amount of MCRR adsorbed increased with the increasing ratio of periphyton biomass to MCRR in solution. The adsorption process fitted well to the Freundlich, Langmuir, and Dubinin−Radushkevich (D-R) models, implying that the bioadsorption process has mechanistic relevance. The MCRR adsorption by periphyton is physical in nature and thermodynamically spontaneous. This study provided strong evidence that adsorption was the main mechanism for the removal of MCRR and other microcystins by periphyton and similar microbial aggregates in the latent adaptation period. Thereafter, biodegradation of periphyton dominated the toxin removal process. These results show that periphyton can be employed for an environmentally benign and effective solution for MCRR removal

The kinetic parameters of P_org transformation by the periphyton.

<p>The kinetic parameters of P_org transformation by the periphyton.</p

The removal process of P_org by the periphyton. P_total means total phosphorus content and P_inorg means inorganic phosphorus content.

<p>The removal process of P_org by the periphyton. P_total means total phosphorus content and P_inorg means inorganic phosphorus content.</p

Adsorption kinetic analysis, (a d) the pseudo first-order kinetic and (b e) the pseudo second-order kinetic and (c f) the intra-particle diffusion kinetic of the periphyton biofilm for the P_org with different biomass content at different temperatures.

<p>Adsorption kinetic analysis, (a d) the pseudo first-order kinetic and (b e) the pseudo second-order kinetic and (c f) the intra-particle diffusion kinetic of the periphyton biofilm for the P_org with different biomass content at different temperatures.</p

Phosphatase activity of the periphyton under different P_org concentrations.

<p>Phosphatase activity of the periphyton under different P_org concentrations.</p

Kinetic parameters for P_org removal by the periphyton.

<p>Kinetic parameters for P_org removal by the periphyton.</p

The conversion process of P_org (a) the change of the P_total and P_inorg over the time (b) the change of q_c over the time (experiment conditions: light intensity = 12000 Lux, temperature = 25°C).

<p>The conversion process of P_org (a) the change of the P_total and P_inorg over the time (b) the change of q_c over the time (experiment conditions: light intensity  = 12000 Lux, temperature  = 25°C).</p

The P_org removal rate under different treatments.

<p>The P_org removal rate under different treatments.</p

Characteristics of the the periphyton.

<p>The photo of the periphyton employed for the experiments (a), the periphyton observed under OM (b, ×2000), CLSM (c, ×2000), and SEM (d, ×2000); the microbial community diversities of the periphyton based on Biolog analyses (e).</p

The <i>in vitro</i> kinetic parameters of <i>E. equisetina</i> extract removing cyanobacteria (<i>M. aeruginosa</i>) from eutrophic water.

*<p>One-way ANOVA was performed for each treatment. <i>w</i> represents the rate constant for the applied <i>E. equisetina</i> extract dose. <i>p</i> values were determined using one-way ANOVA. Half-life  =  (ln (2))/<i>w</i>.</p