Process to convert bisulphide to elemental sulphur
The invention is directed to a control method for a process to convert bisulphide to elemental sulphur in an aqueous solution comprising sulphide-oxidising bacteria wherein the process is controlled by applying a potential between the anode electrode and the cathode electrode or between the anode electrode and the reference electrode of an electrochemical cell resulting in a current between the cathode electrode and the anode electrode, measuring a current as measured by an electrochemical cell and adapting the process in response to the measured current. The process to convert bisulphide may comprise the following steps: (a) contacting bisulphide with oxidised sulphide-oxidising bacteria in the aqueous solution and elemental sulphur, (b) oxidizing the reduced sulphide-oxidising bacteria, (c) using the oxidised sulphide-oxidising bacteria obtained in step (b) in step (a) and (d) isolating elemental sulphur from the aqueous solution obtained in step (a) and/or step (b).
1. A control method for a process to convert bisulphide to elemental sulphur in an aqueous solution comprising sulphide-oxidising bacteria wherein the control method comprises
providing an electrochemical cell comprising a cathode electrode, an anode electrode and a reference electrode,
wherein the electrodes are in contact with the aqueous solution,
wherein a potential is applied, the applied potential, between the anode electrode and the cathode electrode or between the anode electrode and the reference electrode resulting in a current between the cathode electrode and the anode electrode and wherein reduced sulphide-oxidising bacteria transfer electrons to the anode electrode,
wherein the current is measured running between the cathode electrode and the anode electrode at anaerobic conditions while maintaining a constant potential between the anode electrode and the cathode electrode or while maintaining a constant potential between the anode electrode and the reference electrode,
wherein the measured current is a measure of the bioactivity of the sulphide-oxidising bacteria to convert bisulphide to elemental Sulphur, and
adapting the process in response to the measured current.
2. The control method according to claim 1 , wherein the applied potential is between −0.6 V and 0.4 V expressed as the anode potential versus a Ag/AgCl reference.
3. The control method according to claim 1 , wherein the current is measured while varying the applied potential between the anode and cathode electrode.
4. The control method according to claim 3 , wherein the current as measured for at least one value of the varying applied potential is greater than 0.01 A/m 2 .
5. The control method according to claim 1 , wherein the electrochemical cell is controlled by a potentiostat, a resistance and/or and external power source.
6. The control method according to claim 1 , wherein the process to convert bisulphide to elemental sulphur comprises at least the following steps:
(a) contacting bisulphide with oxidised sulphide-oxidising bacteria in the aqueous solution to obtain reduced sulphide-oxidising bacteria and elemental sulphur,
(b) oxidizing the reduced sulphide-oxidising bacteria to obtain oxidised sulphide-oxidising bacteria,
(c) using the oxidised sulphide-oxidising bacteria obtained in step (b) in step (a) and
(d) isolating elemental sulphur from the aqueous solution obtained in step (a) and/or step (b).
7. The control method according to claim 6 , wherein in step (a) an aqueous solution comprising oxidised sulphide-oxidising bacteria is contacted with a gas comprising hydrogen sulphide.
8. The control method according to claim 7 , wherein step (a) is performed in a gas absorber in which the aqueous solution comprising oxidised sulphide-oxidising bacteria is contacted with a gas comprising hydrogen sulphide to obtain a loaded aqueous solution and in a bio-reactor to which the loaded aqueous solution is provided.
9. The control method according to claim 6 , wherein step (a) is performed under anaerobic conditions.
10. The control method according to claim 6 , wherein the current as measured by the electrochemical cell is measured by contacting the electrodes of the electrochemical cell with an aqueous solution comprising oxidised sulphide-oxidising bacteria as obtained in step (b).
11. The control method according to claim 8 , wherein the current as measured by an electrochemical cell is measured by contacting the electrodes of the electrochemical cell with the loaded aqueous solution.
12. The control method according to claim 11 , wherein in addition a current is measured by an electrochemical cell by contacting the electrodes of the electrochemical cell with the loaded aqueous solution from which the sulphide-oxidising bacteria have been removed and wherein this current is subtracted from the current measured for the loaded aqueous solution and wherein the resulting current is used as a measure for the ability of the sulphide-oxidising bacteria to convert bisulphide into elemental sulphur.
13. The control method according to claim 1 , wherein in addition to measuring a current the concentration of bacteria is also measured and wherein in response to the to the measured current and measured bacteria concentration the process is adapted by adapting the amount of nutrients added to the process.
14. The control method according to claim 6 , wherein step (b) is performed by contacting the reduced sulphide-oxidising bacteria with an oxidant.
15. The control method according to claim 14 , wherein the oxidant is oxygen or nitrate.
16. The control method according to claim 6 , wherein the current as measured by the electrochemical cell is measured by contacting the electrodes of the electrochemical cell with the aqueous solution obtained in step (b) and wherein the process is adapted in response of the measured current by adjusting the rate of oxidation in step (b).