A METHOD FOR CYANOBACTERIA AND/OR CYANOBACTERIA METABOLITES REMOVAL IN AN AQUEOUS SOLUTION

Abstract

A method for cyanobacteria removal in an aqueous solution, includes a first main step of determining a percentage of coagulable dissolved aromatic organic matter to remove corresponding to a cyanobacteria percentage concentration to remove, a second main step of determining an optimal coagulant dose corresponding to the determined percentage of coagulable dissolved aromatic organic matter to remove and a third main step of applying the optimal coagulant dose as the adjusted coagulant dose for cyanobacteria removal. The invention may comprise an evaluation of cyanobacteria concentration in the aqueous solution. The invention may comprise a metabolite removal step adapted for removing dissolved cyanobacteria metabolites, comprising applying a powdered activated carbon dose/contact time couple as by determining at least one Freundlich coefficient for each metabolite type in the aqueous solution.

Claims

1. A method for cyanobacteria removal in an aqueous solution, comprising the following main steps: a first main step of determining a percentage of coagulable dissolved aromatic organic matter to remove corresponding to a cyanobacteria percentage concentration to remove; a second main step of determining an optimal coagulant dose corresponding to the determined percentage of coagulable dissolved aromatic organic matter to remove and; a third main step of applying said optimal coagulant dose as the adjusted coagulant dose for cyanobacteria removal.

2. The method as claimed in claim 1 comprising, prior to the main steps, the following preliminary steps: a first preliminary step of determining the cyanobacteria concentration percentage to remove; a second preliminary step of measuring the turbidity of the aqueous solution; a third preliminary step of measuring the dissolved aromatic organic matter of the aqueous solution; a fourth preliminary step of identifying for the aqueous solution a category among at least two categories of water according to the measured turbidity and dissolved aromatic organic matter of the aqueous solution, each category of water providing a relation between the percentage of cyanobacteria concentration to remove and the percentage of coagulable dissolved aromatic organic matter to remove; the first main step using said relation and the determined cyanobacteria concentration percentage to remove.

3. The method as claimed in claim 2, the first preliminary step of determining the cyanobacteria concentration percentage to remove comprising: a first initial step of determining the initial cyanobacteria concentration in the aqueous solution; a second initial step of determining an objective of final cyanobacteria concentration in the aqueous solution.

4. The method as claimed in claim 1, comprising, prior to the main steps, the following steps: a first initial step of determining the initial cyanobacteria concentration in the aqueous solution; and a third initial step of alerting on the need of eliminating cyanobacteria, if the determined cyanobacteria concentration is at least 2 000 cells/ml for metabolites producing cyanobacteria and at least 10 000 cells/ml for others cyanobacteria.

5. The method as claimed in claim 3, the first initial step of determining the initial cyanobacteria concentration in the aqueous solution comprising the steps: a step of measuring all or part of the quantity of pigments present in the aqueous solution, chosen among cyanobacteria pigments; a step of determining the quantity of pigments for at least a cyanobacteria cell species using a first database; a step of determining a cell number of cyanobacteria in the aqueous solution using the measured quantity of pigments and the determined quantity of pigments per cyanobacteria cell species; a step of evaluating the cyanobacteria concentration in the aqueous solution according to the determined cell number of cyanobacteria and the aqueous solution volume.

6. The method as claimed in claim 3, the first initial step of determining the initial cyanobacteria concentration in the aqueous solution consisting in evaluating the most likely dominant cyanobacteria species concentration in the aqueous solution and comprising the following steps: a step of determining at least a most likely dominant cyanobacteria species for the aqueous solution using a second database; a step of determining the quantity of pigments for each of the determined most likely dominant cyanobacteria species using a first database; a step of determining a cell number for each of the most likely dominant cyanobacteria species in the aqueous solution using the measured quantity of pigments present in the aqueous solution and the determined quantity of pigments for each most likely dominant cyanobacteria species; a step of evaluating the most likely dominant cyanobacteria species concentrations in the aqueous solution using the deducted cell number for all most likely dominant cyanobacteria species, and the aqueous solution volume.

7. The method as claimed in claim 1, further comprising a metabolite removal step adapted for removing dissolved cyanobacteria metabolites, said metabolite removal step comprising: a first sub-step of determining the dissolved organic carbon of the aqueous solution; a second sub-step of evaluating the concentration of each cyanobacteria metabolite type in the aqueous solution; a third sub-step of determining at least one Freundlich coefficient for each metabolite type in the aqueous solution using the determined dissolved organic matter of the aqueous solution and the closest determined dissolved organic matter of a third database; a fourth sub-step of determining a powdered activated carbon dose/contact time couple to be used in the aqueous solution for the removal of the evaluated concentration of each cyanobacteria metabolite type, using the determined Freundlich coefficients; a fifth sub-step of applying said powdered activated carbon dose/contact time couple as the adjusted powdered activated carbon dose/contact time.

8. The method as claimed in claim 7, the second sub-step of evaluating the concentration of the cyanobacteria metabolite types in the aqueous solution comprising the following steps: a step of determining the concentration of the cyanobacteria species in the aqueous solution; a step of evaluating the cyanobacteria metabolite types quota for each cyanobacteria species cells using a fourth database; a step of evaluating the concentration of the cyanobacteria metabolites types using the determined concentration of the cyanobacteria species in the aqueous solution and the evaluated cyanobacteria metabolites quota for each cyanobacteria species.

9. The method as claimed in claim 8, the step of determining the concentration of the cyanobacteria species in the aqueous solution comprising using the evaluated most likely dominant cyanobacteria species concentration in the aqueous solution as claimed in claim 6.

10. A computer implemented method for cyanobacteria removal in water comprising the steps of a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] The invention will be better understood and its various characteristics and advantages will emerge from the following description of a number of exemplary embodiments and its appended figures in which:

[0100] FIG. 1 displays a graph exposing the relation between the coagulant dose, the residual cyanobacteria or cylindrospermopsis concentration and the residual dissolved aromatic organic matter (“UV absorbance”) in a settled aqueous solution.

[0101] FIG. 2 displays the main steps of a method for cyanobacteria removal in an aqueous solution.

[0102] FIG. 3 displays a method for cyanobacteria removal in an aqueous solution with main and preliminary steps.

[0103] FIG. 4 displays a method for cyanobacteria removal in an aqueous solution with main, preliminary and initial steps.

[0104] FIG. 5A displays a first embodiment of the step of evaluating the cyanobacteria concentration in an aqueous solution.

[0105] FIG. 5B displays a first embodiment of the method for cyanobacteria removal including the first embodiment of the step of determining the initial cyanobacteria concentration in an aqueous solution.

[0106] FIG. 6A displays a second embodiment for evaluating the most likely dominant cyanobacteria species concentration in an aqueous solution.

[0107] FIG. 6B displays a second embodiment of the method for cyanobacteria removal including the second embodiment of the step of evaluating the cyanobacteria concentration in an aqueous solution.

[0108] FIG. 7 displays a first embodiment for applying a powdered activated carbon dose to an aqueous solution in order to remove cyanobacteria metabolites by taking into account each metabolite type.

[0109] FIG. 8 displays a second particular embodiment for applying a powdered activated carbon dose to an aqueous solution including evaluating the concentration of the cyanobacteria metabolites types.

[0110] FIG. 9 displays both the second particular embodiment for applying a powdered activated carbon dose to an aqueous solution and the second embodiment of the step of evaluating cyanobacteria concentration in an aqueous solution method for cyanobacteria removal.

[0111] FIG. 10 displays a graph describing the difference between cyanobacteria removal and cylindrospermopsis removal in settling process according to the coagulable UV removal percentage.

[0112] FIG. 11 displays a graph describing the relationship between coagulant dose and coagulable UV removal.

[0113] FIG. 12 displays the second embodiment of a global method for cyanobacteria and/or cyanobacteria metabolites removal in an aqueous solution.

DETAILED DESCRIPTION OF THE INVENTION

[0114] FIG. 1 displays a graph exposing the relation between the coagulant dose to be used, the residual cyanobacteria (graph a) or the residual cylindrospermopsis concentration (graph b) after coagulation and the residual dissolved aromatic organic matter “UV absorbance” (graph c) after coagulation in a settled aqueous solution. The residual “UV absorbance” is equivalent to the residual coagulable dissolved aromatic organic matter.

[0115] It is important to note that the residual cyanobacteria and the cylindrospermopsis concentration graphs follow the residual coagulable dissolved aromatic organic matter graph.

[0116] FIG. 2 displays a method 10 for cyanobacteria removal in an aqueous solution, comprising the following main steps: [0117] a first main step 200 of determining a percentage of coagulable dissolved aromatic organic matter to remove corresponding to a cyanobacteria percentage concentration to remove, using a relation between the percentage of cyanobacteria concentration to remove and the percentage of coagulable dissolved aromatic organic matter to remove; [0118] a second main step 210 of determining an optimal coagulant dose corresponding to the predetermined to use to carry out the coagulation of the determined percentage of coagulable dissolved aromatic organic matter to remove and; [0119] a third main step 220 of applying said optimal coagulant dose as the adjusted coagulant dose for cyanobacteria removal.

[0120] FIG. 3 displays a method for cyanobacteria removal in an aqueous solution further including preliminary steps.

[0121] The preliminary steps are prior to the main steps 200, 210, 220 and comprise: [0122] a first preliminary step 140 of determining the cyanobacteria concentration percentage to remove; [0123] a second preliminary step 150 of measuring the turbidity of the aqueous solution; [0124] a third preliminary step 160 of measuring the dissolved aromatic organic matter of the aqueous solution; [0125] a fourth preliminary step 170 of identifying for the aqueous solution a category among at least two categories 171, 172 of water according to the measured turbidity and dissolved aromatic organic matter of the aqueous solution, each category of water providing a relation between the percentage of cyanobacteria concentration to remove and the percentage of coagulable dissolved aromatic organic matter to remove; [0126] the first main step 200 using said relation and the determined cyanobacteria concentration percentage to remove.

[0127] The fourth preliminary step 170 of identifying for the aqueous solution a category among at least two categories 171, 172, requires the second preliminary step 150 of measuring the turbidity of the aqueous solution and the third preliminary step 160 of measuring the dissolved aromatic organic matter of the aqueous solution, preferably by measuring the UV absorbance, preferentially at 254 nm. Each pair of data obtained from turbidity expressed in Nephelometric Turbidity Units (NTU) and UV absorbance expressed in m.sup.−1 of the aqueous solution corresponds to a category.

[0128] For instance, a first category of water could be a high turbidity and high dissolved aromatic organic matter water, corresponding to aqueous solutions whose turbidity is superior to a first value and whose dissolved aromatic organic matter is superior to a second value. A second category could be a low turbidity and a low dissolved aromatic organic matter water, corresponding to aqueous solutions whose turbidity is inferior to the first value and whose dissolved aromatic organic matter is inferior to the second value.

[0129] Each category provides a relation between the percentage of cyanobacteria concentration to remove and the percentage of coagulable dissolved aromatic organic matter (“UV absorbance”) to remove.

[0130] Using the relation between the percentage of cyanobacteria concentration to remove and a the percentage of coagulable dissolved aromatic organic matter (“UV absorbance”) to remove in one category, the fourth preliminary step 170 allows retrieving from the determined cyanobacteria concentration percentage to remove the percentage of coagulable dissolved aromatic organic matter to remove.

[0131] Similarly, when focusing the method on the cylindrospermopsis removal, each category gives a relation between the percentage of cylindrospermopsis concentration to remove and the percentage of coagulable dissolved aromatic organic matter to remove.

[0132] The relation between the percentage of cylindrospermopsis concentration to remove and the percentage of coagulable dissolved aromatic organic matter to remove allows retrieving from the cylindrospermopsis concentration percentage to remove a percentage of coagulable dissolved aromatic organic matter to remove.

[0133] The second main step 210 allows determining an optimal coagulant dose. This optimal coagulant dose will also be the optimal coagulant dose to be used in order to remove a percentage of cylindrospermopsis.

[0134] The optimal coagulant dose to be used in order to remove a given percentage of coagulable dissolved aromatic organic matter may be established by prior lab tests with increasing coagulant dose according to the pH of the aqueous solution. Any water treatment plant may adapt its own database of lab tests, or may use other tests giving a relation between the optimal coagulant dose and a given percentage of coagulable dissolved aromatic organic matter to remove.

[0135] FIG. 4 displays a method for cyanobacteria removal in an aqueous solution further including main, preliminary.

[0136] Furthermore, the first preliminary step 140 comprises the following steps: [0137] a first initial step 110 of determining the initial cyanobacteria concentration in the aqueous solution and; [0138] a second initial step 120 of determining an objective of final cyanobacteria concentration in the aqueous solution.

[0139] The cyanobacteria concentration percentage to remove may be calculated from initial steps 110 and 120, that is the difference between a determined initial cyanobacteria concentration and a determined objective of final cyanobacteria concentration, depending on the water quality required after the treatment. For instance, the cyanobacteria concentration percentage to remove from an aqueous solution may depend on the capacity of filters which may be used after the treatment of the present invention. For instance, a threshold concentration is targeted in order to prevent filters from clogging due to the cyanobacteria concentration.

[0140] Alternatively, the cyanobacteria concentration percentage to remove may be determined directly, without steps 110 and 120.

[0141] In a particular embodiment, the method 10 comprises prior to the main steps 200, 210, 220, a first initial step 110 of determining the initial cyanobacteria concentration in the aqueous solution and a third initial step 130 of alerting on the need of eliminating cyanobacteria, if the determined cyanobacteria concentration is at least 2 000 cells/ml for metabolites producing cyanobacteria and at least 10 000 cells/ml for others cyanobacteria.

[0142] FIG. 5A displays a first embodiment 110 of a first initial step of determining the cyanobacteria concentration in an aqueous solution, said first initial step comprising: [0143] a step 111 of measuring all or part of the quantity of pigments present in an aqueous solution; [0144] a step 112 of determining the quantity of pigments for at least a cyanobacteria cell species using a first database 11; [0145] a step 113 of determining a cell number of cyanobacteria in the aqueous solution using the measured quantity of pigments and the determined quantity of pigments per cyanobacteria cell species; [0146] a step 114 of evaluating the cyanobacteria concentration in the aqueous solution according to the determined cell number of cyanobacteria and the aqueous solution volume 15.

[0147] The first database 11 comprises at least the cell quota estimates for chlorophyll or phycocyanin for different cyanobacteria species. For instance, the measurement of the pigments may be carried out by a phycocyanin or chlorophyll-a probe.

[0148] Chlorophyll-a or phycocyanin concentration are standard measures of algal or cyanobacterial biomass, and cell chlorophyll-a or phycocyanin quotas are published. For instance, the first database may comprise data according to the chlorophyll-a content of Anabaena circinalis and the chlorophyll-a content of Microcystis aeruginosa. For instance, the chlorophyll-a content of Anabaena circinalis may be 0.72 pg per cell and the chlorophyll-a content of Microcysits aeruginosa is 0.36 pg per cell. This may be used to determine the number of cells.Math.mL.sup.−1 from the chlorophyll-a concentration. Multiple database have been published and disclose chlorophyll-a or phycocyanin concentration. For example, such data have been disclosed by Water Quality Research Australia, published in Research report 74, Management Strategies for Cyanobacteria (blue-green algae): a Guide for Water Utilities.

[0149] By dividing the quantity of pigments present in a specific aqueous solution by the quantity of pigments in a cyanobacteria cell species, step 103 allows the determination of a cell number of cyanobacteria in the aqueous solution. Therefore, knowing the cyanobacteria cell number and the volume 15 of an aqueous solution, step 104 allows the evaluation of a cyanobacteria concentration in the aqueous solution.

[0150] In a mixture of species, the ability to apply a single division of the quantity of pigments by the quantity of pigments in a single cyanobacteria cell species may not be relevant due to the different species cell quotas. It is preferred to evaluate the most likely dominant cyanobacteria species concentration in an aqueous solution.

[0151] FIG. 5B displays a first embodiment of the method 10 for cyanobacteria removal including the first embodiment of the first initial step 110 of determining the initial cyanobacteria concentration in an aqueous solution.

[0152] FIG. 6A displays a second embodiment 110′ of a first initial step for determining the cyanobacteria concentration in an aqueous solution consisting in evaluating the most likely dominant cyanobacteria species concentration in an aqueous solution. More precisely, said second embodiment 110′ of the initial step 110′ comprises: [0153] a step 111′ for determining at least a most likely dominant cyanobacteria species for the aqueous solution using a second database 12; [0154] a step 112′ of determining a quantity of pigments for each of the determined most likely dominant cyanobacteria species using the first database 11; [0155] a step 113′ of determining a cell number for each of the most likely dominant cyanobacteria species in the aqueous solution using the measured quantity of pigments present in the aqueous solution and the determined quantity of pigments for each most likely dominant cyanobacteria species; [0156] a step 114′ of evaluating the most likely dominant cyanobacteria species concentrations in the aqueous solution using the deduced cell number for all most likely dominant cyanobacteria species, and the aqueous solution volume 15.

[0157] The second database 12 is an extensive database associating the different cyanobacteria species distribution according to different types and/or parameters of waters, therefore allowing determining the cyanobacteria species distribution, depending on the water subject to the method.

[0158] The distribution of cyanobacteria species according to a particular type of water can be easily defined using classic analysis of such water type. Multiple data have been published regarding the cyanobacteria species distribution in different types of water. For instance, a percentage of cyanobacteria cells of a particular species in an aqueous solution which exceeds 50% may be considered as a most likely dominant cyanobacteria species for an aqueous solution. For example, lists of cyanobacteria and methods for identifying them have been disclosed by the Afssa (Agence française de sécurité sanitaire des aliments) in a report («Rapport sur l'évaluation des risques liés à la présence de cyanobactéries et de leurs toxines dans les eaux destinées à l'alimentation, à la baignade et autres activités récréatives»).

[0159] In this calculation, another complexity is the determination of the species specific cell quotas of phycocyanin fluorescence. Parameters derived from laboratory analyses may provide estimates of quotas for known species in controlled conditions, however these observation may differ significantly to those found in an environmental context due to, light history, nutrient status and physiological state. These same conditions vary from waterbody to waterbody and therefore site specific, species specific parameters will be preferred to reduce the error of predictions as much as possible. Therefore a process to derive site specific, species specific parameters from monitoring program data is defined as follows:

[00001]$x_t=\underset{i}{\overset{n}{.Math.}}{c}_{i,t}.Math.p_i+c+\mathrm{.Math.}$

Where x.sub.t is the phycocyanin at time t, c.sub.i,t is the cell density of the ith species at time t, p.sub.i is the cell quota parameter of the ith species, c is the background concentration of x and ε is the residual error of the equation, fitted to observations of cell density and phycocyanin fluorescence using an advanced Monte Carlo Markov Chain approach. This approach defines posterior probability distributions for the parameters allowing the characterization of the uncertainty in the predictions made on the basis of the fluorescence probe outputs. The prediction of cell density is then used to predict the range of concentrations of metabolites that may be present in the water. This is based on lab and field observations of the cell quota of metabolite concentration and the proportion of the metabolite found in the extracellular space. Metabolites are described in terms of the potential range of their concentration by considering best, worst and median metabolite characteristics (cell quota and proportion extracellular) and the range of cyanobacterial predictions.

[0160] FIG. 6B displays a second embodiment of the method 10′ for cyanobacteria removal including the second embodiment of the step 110′ of evaluating the cyanobacteria concentration in an aqueous solution.

[0161] FIG. 7 displays a first embodiment 300 of a metabolite removal step consisting in applying a powdered activated carbon dose to an aqueous solution in order to remove cyanobacteria metabolites, taking into account each metabolite type.

[0162] The embodiment 300 of a metabolite removal step comprises: [0163] a first sub-step 310 of determining the dissolved organic carbon of the aqueous solution; [0164] a second sub-step 320 of evaluating the concentration of each cyanobacteria metabolite type in the aqueous solution; [0165] a third sub-step 330 of determining at least one Freundlich coefficient for each metabolite type in the aqueous solution using the determined dissolved organic matter of the aqueous solution and the closest determined dissolved organic matter of a third database 31; [0166] a fourth sub-step 340 of determining a powdered activated carbon dose/contact time couple to be used in the aqueous solution for the removal of the evaluated concentration of each cyanobacteria metabolite type, using the determined Freundlich coefficients; [0167] a fifth sub-step 350 of applying said powdered activated carbon dose/contact time couple as the adjusted powdered activated dose/contact time.

[0168] The Freundlich coefficients of the third database can be obtained according to the published research and analysis for different powdered activated carbon types, different metabolites and for different aqueous solution. The application of the Freundlich equation to the adsorption of organic chemicals onto carbons is common. For instance, in “Simulation of saxitoxins adsorption in full-scale GAC filter using HSDM”, Jose Capelo-Neto et al. is disclosed methods for determining and using such Freundlich coefficients.

[0169] Cellular content or “cell quota” ranges for metabolites are classic measures which are applied to estimate the likely yield of the cyanobacteria metabolites under a type/category of water. Such measures are published or can be obtained by classic analysis. For instance, the fourth database may comprise data according to the proportion of extracellular or dissolved geosmin for a population of a particular cyanobacteria species, i. e. a ratio of geosmin to Anabaena circinalis of 100 ng.Math.μg.sup.−1, or a ratio of microcystin to Microcystis of 0.12 ng.Math.μg.sup.−1. Relationships between metabolites and chlorophyll concentration have been used to define cell quota and have been published. For instance, the relationship between geosmin and chlorophyll concentrations in culture samples has shown a fairly consistent correlation. For example, in “Physiology of geosmin production by Anabaena circinalis isolated from the murrumbidgee river, Australia”, K. H. Bowmer et al. data are given regarding ratio of metabolites to the producing cyanobacteria.

[0170] FIG. 8 displays a second particular embodiment 300′ of a metabolite removal step consisting in applying a powdered activated carbon dose to an aqueous solution further including evaluating the concentration of the cyanobacteria metabolites types.

[0171] In this second particular embodiment 300′, the second sub-step of evaluating the concentration of each cyanobacteria metabolite type in the aqueous solution comprises: [0172] a step (321) of determining the concentration of the cyanobacteria species in the aqueous solution; [0173] a step (322) of evaluating the cyanobacteria metabolite types quota for each cyanobacteria species cells using a fourth database (41); [0174] a step (323) of evaluating the concentration of the cyanobacteria metabolites types using the determined concentration of the cyanobacteria species in the aqueous solution and the evaluated cyanobacteria metabolites quota for each cyanobacteria species.

[0175] FIG. 9 displays both the second particular embodiment of metabolite removal and the first embodiment of the step of evaluating cyanobacteria concentration in an aqueous solution method for cyanobacteria removal.

[0176] In FIG. 9 the step 321 of determining the concentration of the cyanobacteria species in the aqueous solution uses the second embodiment 110′ of the initial step of determining the initial cyanobacteria concentration in the aqueous solution as the method described at FIG. 6A.

[0177] FIG. 10 display a graph exposing the relation between the cyanobacteria percentage removal or the cylindrospermopsis percentage removal and the “coagulable UV” removal according to a category considering the raw water turbidity and dissolved aromatic organic matter.

[0178] Especially, the difference between cylindrospermopsis percentage removal exposes the specific difficulty to remove such a cyanobacteria species from an aqueous solution using coagulant for certain types of water. Hence, for certain types of water, the “coagulable UV” removal percentage for cylindrospermopsis is equal or inferior to the “coagulable UV” removal percentage for cyanobacteria.

[0179] As an example, FIG. 11 displays a graph exposing a relation between the optimal coagulant dose and a given percentage of coagulable dissolved aromatic organic matter to remove. This relation may be easily used to determine an optimal coagulant dose. The graph represents the coagulant dose in ppm required to coagulate a specific percentage of dissolved aromatic organic matter. Such a relation allows obtaining an optimal coagulant dose required for cyanobacteria, for instance cylindrospermopsis, removal by coagulation when a relation is set up between the cyanobacteria, for instance the cylindrospermopsis, concentration to remove and a percentage of the dissolved aromatic organic matter to remove.

[0180] Such an obtained optimal coagulant dose may be added to the aqueous solution depending on the already added dose.

[0181] FIG. 12 displays the second embodiment 10′ of a global method for cyanobacteria and/or cyanobacteria metabolites removal in an aqueous solution further including the third particular embodiment of a metabolite removal. The global method described is constituted of multiple parts which may be performed independently or successively.

[0182] This embodiment comprises: evaluating 114′ the most likely dominant cyanobacteria species concentrations in the aqueous solution, determining according to a first preliminary step 140 the cyanobacteria concentration percentage to remove, determining according to a first main step 200 a coagulable dissolved aromatic organic matter to remove and according to a second and third main step 210 and 220 determining and applying an optimal coagulant dose for cyanobacteria removal.

[0183] In parallel or further, the evaluated most likely dominant cyanobacteria species concentrations in the aqueous solution from step 114 allows evaluating according to step 323 the concentration of the cyanobacteria metabolites types. Then, the evaluated concentration of the cyanobacteria metabolite types allows determining allows, using the determined dissolved organic matter and a third database, to determine according to the third sub-step 330 at least one Freundlich coefficient for each metabolite type in the aqueous solution and further, according to the fourth and the fifth sub-step 340 and 350 to determine a powdered activated carbon dose/contact time couple to apply as the adjusted powdered activated carbon.