Method of dosing biocide into a fluid system
A method and apparatus are provided for dosing biocide into fluid. A biofilm sensor configured to measure an amount of biofilm on the biofilm sensor is used. A method identifies, if present, in a data set representing measurement over time by the biofilm sensor a minimum and an inflection point and, if identified. According to some embodiments, dosing of biocide is determined to be effectuated when an inflection point has been identified occurring time wise after an identified minimum.
1 . A method of dosing biocide into a fluid system, the method comprising:
providing a control unit, a biofilm sensor arranged in the fluid system and a dosing pump arranged in the fluid system to dose biocide into the fluid system, the biofilm sensor having a sensing surface configured to be exposed to a flow of fluid in the fluid system, the sensor being configured to measure an amount of biofilm on said sensing surface of the biofilm sensor, said control unit being configured to obtain and store data representing measurements of the amount of biofilm on said biofilm sensor from said biofilm sensor, said dosing pump being controlled by said control unit to dose biocide into the fluid system;
controlling said pump by the control unit to provide a dose of biocide into the fluid system;
after said initial dose of biocide, obtaining and storing data from said biofilm sensor via said control unit, said data representing measurements of a first amount of biofilm on said biofilm sensor measured by said biofilm sensor after said initial dose of biocide;
determining a minimum in said data via said control unit, wherein said minimum represents a maximum obtainable biofilm removal from said sensor based on said initial dose of biocide;
determining an inflection point in said data via said control unit, the inflection point occurring after said minimum in said data, and recording the inflection point via said control unit, wherein said inflection point represents a point in time at which measurements of a second amount of biofilm begin to go towards a plateau, wherein said plateau represents that said biofilm sensor is no longer capable measuring biofilm growth on said sensing surface;
determining the point in time based on said data via said control unit to provide a subsequent dosing of biocide into the fluid system via said control unit after said inflection point and said minimum are determined, wherein said point in time is determined to occur after said inflection point and before said plateau in said data is reached; and
controlling said pump by the control unit to provide said subsequent dosing into the fluid system via said dosing pump at said point in time.
2 . A method according to claim 1 , wherein the subsequent dosing of biocide is based on a dosing criteria to be fulfilled comprising a magnitude of measurements in the data asymptotically going towards a constant value.
3 . A method according to claim 2 , where the subsequent dosing of biocide is provided based on a slope or an angle in the data corresponding to a post-inflection slope in the data after an occurrence of the inflection point and initiating the subsequent dosing of biocide is based on changes in the slope or the angle in the data corresponding to the post-inflection slope.
4 . A method according to claim 3 , wherein the subsequent dosing of biocide is provided based on the angle corresponding to the slope in the data passing a predefined threshold based on a tangent of the angle being less than 40 .
5 . A method according to claim 3 , wherein the subsequent dosing of biocide is provided based on the angle corresponding to the slope in the data passing a predefined threshold, where the threshold is selected from between a tangent of angles (y, A) greater than 40 and less than 60.
6 . A method according to claim 3 , wherein the subsequent dosing of biocide is provided when the angle corresponding to the slope passes a predefined threshold, where the threshold is selected from between a tangent of angles (y, A) more than 50 and less than 70 degrees, or more than 70 and less than 90.
7 . A method according to claim 2 , wherein the subsequent dosing of biocide is provided when a correlation coefficient is greater than a preselected number, the correlation coefficient being determined based on a linear line fitted to at least a subset of the data.
8 . A method according to claim 2 , wherein the subsequent dosing of biocide is provided based on the magnitude of measurements of the amount of biofilm in the data being above a predefined reference magnitude.
9 . A method according to claim 2 , wherein an amount of the subsequent dosing of biocide is increased if the magnitude of measurements increase over time, the magnitude of measurements being based on minima in the data after the inflection point is identified.
10 . A method according to claim 2 , wherein an amount of a further subsequent dosing of biocide is equal to the subsequent dosing of biocide if the magnitude of measurements decrease over time, the magnitude of measurements being based on minima in the data after the inflection point is identified.
11 . A method according to claim 2 , wherein an amount of a further subsequent dosing of biocide is decreased if the magnitude of measurements are constant over time, the magnitude of measurements being based on minima in the data after the inflection point is identified.
12 . A method according to claim 9 , wherein an increase or decrease in magnitude of a subsequently identified minima is determined based on fitting a straight line through the subsequently identified minima considered and if the correlation coefficient is greater than predefined number the slope of this fitted line is used to determine whether the subsequently identified minima are decreasing or increasing.
13 . A method according to claim 2 , wherein the data representing measurements of the amount of biofilm is obtained by filtering read-outs from the sensor and by applying moving mean algorithm having a predefined window size on the filtered read-outs.
14 . A method according to claim 2 , wherein the minimum is identified as a change in slope from smaller than zero to larger than zero, the slope is zero, or an angle corresponding to the slope, evaluated as tan to slope, changes sign from negative to positive.
15 . A method according to claim 2 , wherein the inflection point is determined as a rate of change in slope or the inflection point is determined as an angle corresponding to the slope from increasing to decreasing.
16 . A method according to claim 2 , wherein the method is carried out synchronized with an occurrence of data, such that a sequence is based on a data set comprising most recent available data.
17 . A method of dosing biocide into a fluid system, the method comprising:
providing a control unit, a biofilm sensor arranged in the fluid system and a dosing pump arranged in the fluid system to dose biocide into the fluid system, the biofilm sensor having a sensing surface configured to be exposed to a flow of fluid in the fluid system, the sensor being configured to measure an amount of biofilm on said sensing surface of the biofilm sensor, said dosing pump being controlled by said control unit to dose biocide into the fluid system;
controlling said pump by the control unit to provide an initial dose of biocide into the fluid system;
after providing said initial dose of biocide, measuring the amount of biofilm on said biofilm sensor via said biofilm sensor to provide biofilm data;
transmitting said biofilm data to said control unit, said control unit storing said biofilm data;
determining a minimum in said biofilm data via said control unit, wherein said minimum represents a maximum obtainable biofilm removal from said sensor based on said initial dose of biocide;
determining an inflection point in said biofilm data via said control unit, the inflection point occurring after said minimum in said data, and recording the inflection point via said control unit, wherein said inflection point represents a point in time at which said measurements of a second amount of biofilm begin to go towards a plateau, wherein the plateau represents that the biofilm sensor is no longer capable of measuring biofilm growth on the sensing surface;
determining the point in time based on said data via said control unit to provide a subsequent dosing of biocide into the fluid system via said control unit after said inflection point and said minimum are determined, wherein said point in time is determined to occur after said inflection point and before said point in time is reached at which said biofilm sensor is no longer capable of measuring biofilm growth on said sensor surface;
controlling said pump by the control unit to provide said subsequent dosing into the fluid system via said dosing pump at said point in time.
18 . A method according to claim 17 , wherein the subsequent dosing of biocide is based on a dosing criteria to be fulfilled comprising a magnitude of measurements in the data asymptotically going towards a constant value.
19 . A method according to claim 18 , where the subsequent dosing of biocide is provided based on a slope or an angle corresponding to a post-inflection slope in the data after an occurrence of the inflection point and initiating the subsequent dosing of biocide is based on changes in a subsequent slope or angle in the data corresponding to the post-inflection slope.
20 . A method according to claim 19 , wherein the subsequent dosing of biocide is provided based on the angle corresponding to the slope in the data passing a predefined threshold, and wherein a tangent of the angle is less than 40.