REDUCTION OF THE AMOUNT OF SULPHUR COMPOUNDS IN A SULPHUR COMPOUNDS CONTAMINATED WASTEWATER STREAM USING A GRANULAR SLUDGE TREATMENT SYSTEM

Abstract

The invention relates to a process for reducing the amount of sulphur compounds in a sulphur compounds contaminated wastewater stream, using a granular sludge treatment system (10) comprising anaerobic microorganisms, wherein the process comprises the steps of adding an aqueous nitrate solution to the wastewater stream, contacting the wastewater stream with the anaerobic microorganisms, and anoxic oxidation of at least part of the sulphur compounds in the sulphur compounds contaminated wastewater stream by the anaerobic microorganisms, resulting in a sulphur compounds depleted wastewater stream. The invention furthermore relates to such a granular sludge treatment system (10).

Claims

1-16. (canceled)

17. Process for reducing the amount of sulphur compounds in a sulphur compounds contaminated wastewater stream, using a granular sludge treatment system (10) comprising anaerobic microorganisms, wherein the process comprises the steps of contacting the sulphur compounds contaminated wastewater stream with the anaerobic microorganisms; and oxidation of at least part of the sulphur compounds in the sulphur compounds contaminated wastewater stream by the anaerobic microorganisms, CHARACTERIZED IN THAT the process further comprises the step of adding an aqueous nitrate solution to the sulphur compounds contaminated wastewater stream prior to being contacted with the anaerobic microorganisms, enabling the anaerobic microorganisms to oxidize the sulphur compounds without the presence of oxygen.

18. The process according to claim 17, wherein the aqueous nitrate solution is chosen from an ammonium, calcium, potassium or sodium nitrate solution or any combination thereof.

19. The process according to claim 18, wherein the aqueous nutrient solution comprises a phosphor source.

20. The process according to claim 19, wherein the phosphor source is an aqueous phosphoric acid solution.

21. The process according to claim 18, wherein the process comprises the step of automatically adjusting the dosage of the nutrients solution added to the wastewater stream in relation to the sulphur compound content in the sulphur compounds contaminated wastewater stream at an inlet of the granular sludge treatment system.

22. The process according to claim 17, wherein the sulphur compounds comprise hydrogen sulphide.

23. The process according to claim 17, wherein the wastewater stream is an industrial wastewater stream.

24. Granular sludge treatment system (10) arranged to reduce the amount of sulphur compounds in a sulphur compounds contaminated wastewater stream, the granular sludge treatment system (10) comprising anaerobic microorganisms capable of oxidizing the sulphur compounds, these anaerobic microorganisms being arranged to be contacted with the sulphur compounds and being arranged to oxidize at least part of the sulphur compounds in the sulphur compounds contaminated wastewater stream, resulting in a sulphur compounds depleted wastewater stream, CHARACTERIZED IN THAT the granular sludge treatment system comprises a dosage system (6) for adding an aqueous nitrate solution to the sulphur compounds contaminated wastewater stream before being contacted with the anaerobic microorganisms, enabling the anaerobic microorganisms to oxidize the sulphur compounds without the presence of oxygen.

25. Granular sludge treatment system (10) according to claim 24, wherein the granular sludge treatment system (10) comprises a controller (5) that is arranged to monitor one or more signals from loads of sulphur compounds at an inlet (1) of a granular sludge reactor (11) forming part of the granular sludge treatment system (10); calculate the demand of the nitrogen and/or the phosphor source in the nutrient solution for the anaerobic microorganisms; and adjust the dosage of the nitrogen and/or the phosphor source in the nutrient solution based on the demand of the nitrogen and/or the phosphor source equalling to a ratio of sulphur compound, nitrogen and phosphor source of 20:10:1 based on weight.

26. Granular sludge treatment system (10) according to claim 25, wherein the controller (5) is arranged to simultaneously adapt the dosage of the nitrogen and the phosphor source in the nutrient solution.

27. Granular sludge treatment system (10) according to claim 26, wherein the controller (5) is arranged to adapt the dosage of the nitrogen and the phosphor source in the nutrient solution separately.

28. Granular sludge treatment system (10) according to claim 24, wherein the system (10) comprises a supersonic probe (7) arranged to measure the flow volume stream at the inlet (1) of the granular sludge reactor (11).

29. Granular sludge treatment system (10) according to claim 24, wherein the system (10) comprises a headspace (3) arranged to allow the produced off-gas to leave the granular sludge reactor (11).

30. Use of a granular sludge treatment system (10) according to claim 24 for reducing the amount of sulphur compounds in a sulphur compounds contaminated wastewater stream.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0062] FIG. 1 shows a scheme of a granular sludge reactor according to the invention

DETAILED DESCRIPTION OF THE INVENTION

[0063] The process according to the invention for removing sulphur compounds, more specifically inorganic sulphur compounds and most specifically hydrogen sulphide (H.sub.2S), out of a sulphur compound contaminated wastewater stream, more specifically industrial wastewater, and most specifically a wastewater stream from the petrochemical industry, uses a granular sludge treatment system 10 comprising anaerobic microorganisms that are able to, without the presence of oxygen, oxidize the sulphur compounds using an aqueous nitrate solution as the source of nitrate serving as the electron acceptor for the oxidation of the sulphur compounds into elemental sulphur and/or sulphates. It is herewith remarked that the exact type of microorganisms is not critical to the invention, as long as these anaerobic microorganisms are able to use the nitrate source to oxidize the sulphur compounds.

[0064] The process according to the invention comprises the steps of [0065] adding an aqueous nitrate solution to the sulphur compounds contaminated wastewater stream; [0066] contacting the sulphur compounds contaminated wastewater stream with the anaerobic microorganisms; and [0067] anoxic oxidation of at least part of the sulphur compounds in the sulphur compounds contaminated wastewater stream by the anaerobic microorganisms, resulting in a sulphur compounds depleted wastewater stream.

[0068] The aqueous nitrate solution is chosen from an ammonium, calcium, potassium or sodium nitrate solution or any combination thereof.

[0069] The process according to the invention also comprises the step of adding an aqueous nutrient solution to the wastewater stream for the anaerobic microorganisms. The aqueous nutrient solution that is added to the wastewater stream as an electron acceptor for anoxic oxidation of the sulphur compounds in the wastewater stream, also serves as a nitrogen source for the anaerobic microorganisms. In wastewater conditions for anoxic oxidation of for instance H.sub.2S, about 2 g NO.sub.3.sup. is needed to oxidize 1 g H.sub.2S. The nutrient solution furthermore preferably comprises a phosphor source, more preferably in the form of an aqueous phosphoric acid solution.

[0070] The process preferably comprises the step of automatically adjusting the dosage of the nutrients solution added to the wastewater stream in relation to the sulphur compound content in the sulphur compounds contaminated wastewater stream at an inlet of the granular sludge treatment system 10. In order to enable this automatic adjustment of the dosage of the nutrients solution as mentioned before, the granular sludge treatment system 10 comprises a controller that is arranged to [0071] monitor one or more signals from loads of sulphur compounds at an inlet 1 of the granular sludge reactor 11; [0072] calculate the demand of the nitrogen and/or the phosphor source in the nutrient solution for the anaerobic microorganisms; and [0073] adjust the dosage of the nitrogen and/or the phosphor source in the nutrient solution based on the demand of the nitrogen and/or the phosphor source equalling to a ratio of sulphur compound, nitrogen and phosphor source of 20:10:1 based on the weight.

[0074] The controller can be arranged either to simultaneously adapt the dosage of the nitrogen and the phosphor source in the nutrient solution, either to adapt the dosage of the nitrogen and the phosphor source in the nutrient solution separately.

[0075] The invention is herewith illustrated with the scheme as shown in FIG. 1 which illustrates a non-limiting exemplary embodiment of a granular sludge treatment system for reducing the amount of hydrogen sulphide out of a hydrogen sulphide contaminated wastewater according to the invention.

[0076] The wastewater enters the granular sludge reactor 11 at the inlet 1 thereof, where the flow volume stream is preferably measured by a supersonic probe 7 and the temperature is preferably measured by an industrial sensor such as a PT-100. The treated wastewater then leaves the granular sludge reactor 11 at the effluent 2. The produced off-gas leaves the granular sludge reactor 11 at the headspace 3. The off-gas can contain some methane, but mostly CO.sub.2, so it will be released to the atmosphere without further use.

[0077] In the granular sludge reactor 11, granular sludge 9 in water 4 is present. The granular sludge 9 consists of aggregates of anaerobic microorganisms (without using carrier material). The microorganisms oxidize hydrogen sulphide, in the wastewater without the presence of oxygen using an aqueous nitrate solution. This aqueous nitrate solution forms part of the nutrient solution for the microorganisms. The supply of the nitrate solution is calculated and controlled by a controller 5. This calculation is based on the inlet flow that is measured by the supersonic probe 7 and the remaining concentration of the hydrogen sulphide, as preferably measured by an industrial metal oxide sensor 8. The nitrate solution is applied via a dosage system 5 to the granular sludge reactor 11. Also the aqueous phosphoric acid is preferably applied by this dosage system 5. They can be applied simultaneously or separately. Also the supply of the amount of aqueous phosphoric acid is preferably calculated and controlled by the controller 5.

EXAMPLE

[0078] A laboratory scale setup of a granular sludge treatment system according to the invention was loaded with sulphide concentrations up to 500 g S.sup.2/m.sup.3/h. The amount of aqueous nitrate solution added was controlled to be sufficient to act as an electron acceptor for the oxidation of the sulphide in the treated wastewater. The ratio S.sup.2:N based on weight was kept at approximately 2:1.

TABLE-US-00001 TABLE 1 Sulphide Retention Initial Sulphide Removal Load Time concentration Efficiency [g S.sup.2/m.sup.3/h] [h] [mg/L] [%] 21 12 313 99.56 42 12 625 99.36 167 12 2500 99.99 250 12 3750 99.95 500 6 3750 25.07

[0079] Out of table 1, it can be seen that up to 250 g S.sup.2, the removal efficiency was satisfying.