An integrated treatment system for recovering sulphur and water from wastewater and a method therefor

Abstract

The present invention relates to an integrated treatment system for recovering sulphur and water from wastewater with high sulphur and salinity. Said treatment system comprises at least one membrane bioreactor with one or more filtering units having at least one reactor in which sulphur compounds dissolved in the fed wastewater are converted into zero-valent elemental sulphur, and at least one membrane to filter and separate the converted zero valent elemental sulphur, and at least one electrodeionization unit. Further, the present invention describes a treatment method for use in such a treatment system.

Description

[0001] AN INTEGRATED TREATMENT SYSTEM FOR RECOVERING SULPHUR AND WATER FROM WASTEWATER AND A METHOD THEREFOR

[0002] Technical Field of the Invention

[0003] The present invention relates to an integrated treatment system for recovering sulphur and water from wastewater with high sulphur and salinity, and a treatment method for use in such system. Particularly, the present invention relates to a treatment system and a method for recovering sulphur and water from green liquor wastewater resulting from paper and pulp production.

[0004] Background of the Invention

[0005] In paper and pulp production processes, high amounts of waste are generated. It is known that about 60 m3of water is consumed to produce a ton of paper, and nearly 10-50 m3of wastewater is released.

[0006] In the production of paper pulp from wood logs, Kraft Process is preferably employed for pulping the high fibrous content of the wood. In the Kraft process, wood chips are processed with high-pH and sulphur compounds, resulting in a strong sulphur-rich wastewater. The wastewater discharged into the environment after the production, which is called green liquor water, comprises high amounts of various pollutants that can cause serious damage to the soil and living organisms. The pH value of the said green liquor wastewater is above 12.5, and it is also known that this value can even reach up to 14. In view of the dangers it presents for the environment, the wastewater generated in the pulp production process must be treated to render it harmless. In the prior art, the treatment of the resulting strong wastewater is performed by chemical methods. It is important to reduce the consumption of chemicals used in the treatment process both in terms of environmental impacts and cost. Furthermore, in the state of the art, the recovery of sulphur and water used in the Kraft process is important in order to provide a sustainable solution.

[0007] In the prior art, there are no studies available wherein biological sulphur recovery is performed from green liquor wastewater due to the pH value, salinity and high concentration of chemical content of the green liquor wastewater resulting from the Kraft process.

[0008] In the state of the art, it is known to use membrane bioreactors (MBR), a technology based on biological treatment processes, in various industries and processes (wastewater treatment, drinking water treatment, food industry, pharmaceutical production, bioenergy production, etc.). Like conventional bioreactors, membrane bioreactors are also based on microorganisms (bacteria, fungi, etc.) breaking down and removing organic matter from the water. In membrane bioreactors, however, the microorganisms that perform the biological treatment process are maintained in a chamber separated by a special membrane. The electrodeionization (EDI) systems, which are currently used in the state of the art, are used to remove ions from water to increase the purity thereof by means of ion exchange membranes and electrodes, especially in industries and application areas where high-purity water is required (food and beverage industry, power plants, semiconductor industry, hemodialysis, chemical industry, etc.). However, in prior art, it is not known an integrated system in which membrane bioreactors and electrodeionization systems are used together and a biological sulphur production is performed using sulphur bacteria in order to recover sulphur and water from wastewater and, particularly, to recover sulphur and water from green liquor wastewater generated in paper and pulp production, and a method developed to be used in such system.

[0009] Objects of the Invention

[0010] A main object of the present invention is to provide a solution to the technical problems of the prior art. Another object of the present invention is to provide an integrated and innovative treatment system that recovers sulphur and water from paper industry wastewater, so making contribution to sustainable production.

[0011] Another object of the present invention is to provide an integrated treatment system that stabilizes paper industry wastewater, thereby preventing it from posing risks and harms to the environment.

[0012] Another object of the present invention is to provide an integrated treatment system in which a problem of permanent clogging in the membrane bioreactor is prevented or reduced, and an increase in flux is achieved.

[0013] Another object of the present invention is to provide an integrated treatment system that provides energy savings.

[0014] Still another object of the present invention is to provide an integrated treatment system which reduces consumption of chemicals used in the treatment of wastewater generated in paper and pulp production processes, and thus provides a cost advantage.

[0015] Summary of the Invention

[0016] The present invention relates to an integrated treatment system for recovering sulphur and water from wastewater with high sulphur and salinity, comprising at least one membrane bioreactor with one or more filtering units having at least one reactor in which sulphur compounds dissolved in the wastewater fed into the said treatment system are converted into zero-valent elemental sulphur, and at least one membrane to filter and separate the converted zero-valent elemental sulphur; and at least one electrodeionization unit.

[0017] In an embodiment of the invention, the reactor of the said membrane bioreactor comprises bacteria capable of oxidizing sulphur under halophilic conditions. Said reactor optionally comprises one of the bacteria of the species Thioalkalivibrio versutus AL2, Thioalkalivibrio denitrificans, Thiomicrospira sp., or Thioa / ka / imicrobium sp. In a preferred embodiment of the invention, said reactor comprises bacteria of the species Thioalkalivibrio versutus AL2.

[0018] In an embodiment of the invention, said electrodeionization unit comprises at least one selective ionic membrane. Alternatively, said electrodeionization unit comprises an adjustable DC power supply to convert alternating current into direct current and supply it to the said electrodeionization unit in a controlled manner.

[0019] In an embodiment of the invention, said electrodeionization unit comprises a solution of NaCI, H2SO4, NaOH, or HNO3 as an electrolyte for conducting electric current. Said electrodeionization unit alternatively comprises a NaCI solution as an electrolyte for conducting electric current. As a different alternative, said electrodeionization unit comprises a NaCI solution in the range of 0.5 M to 1 M as an electrolyte.

[0020] In an embodiment of the invention, said electrodeionization unit comprises Pt / Ir-coated titanium as an anode material, V4A Steel as a cathode material, and polypropylene as an electrode housing material.

[0021] In an embodiment of the invention, the membrane provided in the said filtering unit is a ceramic membrane. Said membrane is a ceramic membrane optionally coated with polydopamine. Said membrane is a ceramic membrane optionally coated with polydopamine by dip coating.

[0022] The present invention also describes a treatment method for use in the treatment system of the invention, comprising the following method steps: (a) feeding the wastewater to be treated into a membrane bioreactor; (b) converting the dissolved sulphur compounds in the wastewater into zero-valent elemental sulphur in the reactor of the membrane bioreactor; (c) filtering the partially precipitated and partially suspended elemental sulphur obtained in the previous step and performing sulphur-water separation; (d) feeding the concentrated high-ion water obtained in the previous step into the electrodeionization unit; and (e) removing ions from the water in order to recover water in the said electrodeionization unit. In an embodiment of the invention, said treatment method comprises a step of performing said conversion process in step (b) by bacteria capable of oxidizing sulphur under halophilic conditions. In another embodiment of the invention, said treatment method comprises a step of performing said conversion process in step (b) by means of bacteria of the species Thioalkalivibrio versutus AL2, Thioalkalivibrio denitrificans, Thiomicrospira sp., or Thioalkalimicrobium sp. In another embodiment of the invention, said treatment method comprises a step of performing said conversion process in step (b) by means of bacteria of the species Thioalkalivibrio versutus AL2.

[0023] In an embodiment of the invention, in the said treatment method, the filtering process in step (c) is performed by means of at least one membrane provided in the filtering unit of the membrane bioreactor. In another embodiment of the invention, the filtering process in step (c) is performed by means of at least one ceramic membrane provided in the filtering unit of the membrane bioreactor. In another embodiment of the invention, the filtering process in step (c) is performed by means of at least one polydopamine-coated ceramic membrane provided in the filtering unit of the membrane bioreactor.

[0024] In an embodiment of the invention, said treatment method comprises a step of drying the elemental sulphur obtained from the filtering process in step (c) at a temperature of 40 and 80 °C in order to remove the moisture contained therein.

[0025] In an embodiment of the invention, said treatment method comprises a step of removing ions from water by means of at least one selective ionic membrane and direct current, and recovering water in step (e). Said treatment method alternatively comprises a step of removing ions from water by converting alternating current to direct current via an adjustable DC power supply and supplying it to the said electrodeionization unit in a controlled manner.

[0026] In an embodiment of the invention, said treatment method comprises a step of feeding the concentrated high-ion water obtained in step (c) into the electrodeionization unit containing a solution of NaCI, H2SO4, NaOH or HNO3 as an electrolyte for conducting electric current. In an embodiment of the invention, said treatment method comprises a step of feeding the concentrated high-ion water obtained in step (c) into the electrodeionization unit containing a NaCI solution -optionally in the range of 0.5 M to 1 M- as an electrolyte for conducting electric current.

[0027] In an embodiment of the invention, said treatment method comprises a step of feeding clean water into the medium in step (e) for separating ions removed from the high-ion filtrate.

[0028] In an embodiment of the invention, said treatment method comprises the steps of diluting and aerating the wastewater to be treated before feeding it into the membrane bioreactor.

[0029] Brief Description of the Drawings

[0030] Fig. 1 shows the process steps of a production process called the Kraft process, which is conducted to obtain pulp from wood chips, along with the method steps of the present invention for recovering sulphur and water from green liquor wastewater.

[0031] Detailed Description of the Invention

[0032] With reference to the figures outlined above, the present invention is described in detail below. The reference numbers used in the figures are listed below:

[0033] 1 paper production plant

[0034] 2 storage tank

[0035] 3 pump

[0036] 4 treatment system

[0037] 4.1 membrane bioreactor

[0038] 4.2 electrodeionization unit

[0039] 4.3 DC power supply

[0040] 4.4 selective ionic membrane 10 paper pulp

[0041] 11 wood chips

[0042] 12 white liquor

[0043] 13 weak black liquor

[0044] 14 strong black liquor

[0045] 15 green liquor

[0046] 111 cooking unit

[0047] 112 washing unit

[0048] 113 bleaching unit

[0049] 114 drying unit

[0050] 115 vaporization unit

[0051] 116 recycling boiler

[0052] 117 causticizing boiler

[0053] The present invention relates to an integrated treatment system (4) for recovering sulphur and water from wastewater with high sulphur and salinity. Said treatment system (4) is mainly operated by a sulphur oxidation process, thereby enabling the treatment of wastewater containing dissolved sulphur compounds - which, without limitation, is generated in the production of the paper production plants (1) - and allowing the recovery of sulphur and water from the wastewater. Said treatment system (4) comprises at least one membrane bioreactor (MBR) (4.1) with one or more filtering units having at least one reactor in which sulphur compounds dissolved in the fed wastewater are converted into zero-valent elemental sulphur, and at least one membrane to filter and separate the converted zero-valent elemental sulphur, and at least one electrodeionization unit (EDI) (4.2).

[0054] The reactor of the membrane bioreactor (4.1) of the present invention comprises bacteria capable of oxidizing sulphur under halophilic conditions. The bacteria capable of oxidizing sulphur under halophilic conditions are generally characterized by their ability to adapt to extreme environmental conditions. The pH value of the wastewater to be treated with the treatment system (4) of the present invention can be 12.5 and more, which can sometimes even reach up to 14. In this respect, the use of bacteria capable of oxidizing sulphur under halophilic conditions in the said reactor allows an effective and sustainable treatment in the treatment system (4) of the invention. In an embodiment of the invention, the bacteria capable of oxidizing sulphur under halophilic conditions present in the said reactor are one of the following species: Thioalkalivibrio versutus AL2, Thioalkalivibrio denitrificans, Thiomicrospira sp., or Thioalkalimicrobium sp. In their studies, the inventors have found that the bacteria of the species Thioalkalivibrio versutus AL2 exhibit high resistance against high sulphur and salinity and are highly tolerant to extreme conditions. Due to these advantages, in a preferred embodiment of the invention, said reactor comprises bacteria of the species Thioalkalivibrio versutus AL2.

[0055] Said electrodeionization unit (EDI) (4.2) of the treatment system (4) described in the invention comprises at least one selective ionic membrane (4.4). These membranes have a specialized structure in that they allow the passage of certain types of ions while blocking others. Said electrodeionization unit (4.2) also alternatively comprises an adjustable DC power supply (4.3) to convert alternating current to direct current and supply it to the said electrodeionization unit (4.2) in a controlled manner. Said electrodeionization unit (4.2) comprises an electrolyte for conducting electric current, which can optionally be a solution of NaCI, H2SO4, NaOH, or HNO3. In an embodiment of the invention, said electrodeionization unit (4.2) according to the invention comprises a NaCI solution as an electrolyte, given its availability and cost advantage. Said electrodeionization unit (4.2) preferably comprises a NaCI solution in the range of 0.5 M to 1 M, more preferably 0.5 M NaCI, as an electrolyte. In an embodiment of the invention, said electrodeionization unit (4.2) comprises Pt / Ir- coated titanium as an anode material, V4A Steel as a cathode material, and polypropylene as an electrode housing material. With the platinum and iridium coatings in this embodiment, the corrosion resistance of the corrosion-resistant titanium is further enhanced, thereby contributing to the extension of the life of the anode. Thus, its resistance to various chemical environments is increased. Besides, platinum and iridium provide an advantage in terms of their high electrical conductivity. V4A steel, on the other hand, is advantageous in that it is a material having low maintenance requirements and exhibiting high corrosion resistance. Furthermore, the membrane provided in the said filtering unit of the invention may be a metallic membrane, a ceramic membrane, or an organic membrane (such as PES (polyethersulfone), PVDF (polyvinylidenedifluoride), and PAN (polyacrylonitrile)). However, a metallic membrane is disadvantageous in that it is highly possible to observe surface poisoning thereon and it is difficult to provide hydrophilic properties whereas an organic membrane is highly possible to be damaged in highly acidic and alkaline conditions. A ceramic membrane is preferred in the present invention as it has the advantages of being resistant to high acidity and alkalinity and not being damaged by ambient conditions. The membrane of the said filtering unit can optionally be coated with Polyvinyl Alcohol (PVA), Silica Gels, Protein, polydopamine (PDA), ZnO, or TiCh in order to provide hydrophilic properties. Said membrane is preferably a ceramic membrane coated with polydopamine (PDA). In the studies, it has been found that polydopamine (PDA) is more easily coated on the ceramic membrane -compared to other options, resulting in a more durable coating. In addition, it has been found that the hydrophilic properties are significantly increased by reducing a contact angle of the ceramic membrane and the polydopamine (PDA) coating. The polydopamine coating of the said ceramic membrane can be carried out by one of the following methods: vacuum plasma, electrospinning, spin coating, spray coating, or dip coating. The polydopamine coating of the said ceramic membrane is preferably carried out by dip coating. The dip coating is advantageous in terms of ease of application and the fact that no additional devices or equipment are needed during the coating. In addition, when the surfaces of the membranes coated with this method are examined by electron microscopy in relation with the contact angle experiments, it is determined that the coating material is homogeneously coated on the entire surface. As a result of the studies carried out by the inventors, it has been found that the permanent clogging problem experienced in the membrane can be prevented and an increase in the flux is achieved, given that the membrane provided in the inventive filtering unit is a polydopamine-coated ceramic membrane.

[0056] Fig. 1, as devised according to an embodiment of the present invention, shows the process steps of the production process called the Kraft process, which is conducted to obtain paper pulp (10) from wood chips (11), along with the elements and method steps of the treatment system (4) of the present invention for recovering sulphur and water from green liquor (15) wastewater. Within the scope of the current Kraft process, wood chips (11) obtained by grinding the wood are cooked in a cooking unit (111) with a cooking solution containing sodium hydroxide (NaOH) and sodium sulfate (Na2SO4), and called white liquor (12). A cellulose obtained from washing of the mixture that has been introduced into a washing unit (112) after the cooking step, is exposed to the relevant bleaching chemicals in a bleaching unit (113). Once the cellulose exiting from the bleaching unit (113) is introduced into a drying unit (114) and dried, paper pulp (10) is obtained.

[0057] In this process, a waste cooking solution called as weak black liquor (13) is also obtained as a result of the washing process carried out in the washing unit (112). The weak black liquor (13) generally has a low (<20% SM) solids content. In order to increase the solids content, it is concentrated in an evaporation unit (115) until the solids content is more than 65% and a strong black liquor (14) is obtained. The resulting strong black liquor (14) is introduced into a recycling boiler (116), and sodium and sulphur compounds are recovered by the addition of sulphur (S) (Na2SO4Na2S; Na2COs + 2 Na2S + 4 SO2 3 Na2S2O3 + CO2). A melt coming from the recycling boiler (116) and called as green liquor (15) generally comprises sodium sulfite (Na2S) and sodium carbonate (N32CO3). Green liquor (15) is causticized by adding lime in a causticizing boiler (117) (CaO + H2O Ca(OH)2+ Heat; Ca(OH)2+ Na2CO3NaOH + CaCOs; CaCCh + Heat CaO + CO2), and white liquor (12) (NaOH + Na2S) is obtained. Thus, the weak black liquor (13) discharged from the washing unit (112) is converted into white liquor (12) and reused in the Kraft process.

[0058] Fig. 1 also shows that the wastewater with high sulphur and salinity, as received from a paper mill or paper production plant (1), is introduced into a storage tank (2) and then, optionally, fed by one or more pumps (3) into the integrated treatment system (4) of the present invention. In the treatment method developed for use in the treatment system (4) of the present invention, the method steps as described below are followed: a. feeding the wastewater to be treated into the membrane bioreactor (4.1); b. converting the dissolved sulphur compounds in the wastewater into zero-valent elemental sulphur in the reactor of the membrane bioreactor (4.1); c. filtering the partially precipitated and partially suspended elemental sulphur obtained in step (b) and performing sulphur-water separation; d. feeding the concentrated high-ion water obtained in step (c) into the electrodeionization unit (4.2); and e. removing ions from the water to recover water in the said electrodeionization unit (4.2).

[0059] Since a large amount of water is consumed in the Kraft process, the water obtained at the end of step (e) of the above treatment method is used in the Kraft process, so water is recovered for the process.

[0060] The conversion process mentioned in step (b) of the treatment method is performed by bacteria capable of oxidizing sulphur under halophilic conditions. As a matter of fact, the pH value of the wastewater to be treated can be 12.5 and above, and sometimes can even reach up to 14. Due to the high pH and salinity in the wastewater, it has been found that it is not possible for any bacteria to perform the conversion process in the reactor and / or provide effective and sustainable treatment. This problem has been overcome by using those bacteria capable of oxidizing sulphur under halophilic conditions in said reactor. In an embodiment of the invention, the conversion process in step (b) of the treatment method is performed by bacteria of the species Thioalkalivibrio versutus AL2, Thioalkalivibrio denitrificans, Thiomicrospira sp., or Thioalkalimicrobium sp. In a preferred embodiment of the invention, the conversion process in step (b) of the said treatment method is performed by bacteria of the species Thioalkalivibrio versutus AL2. It has been found that the bacteria of the species T hioaikaiivibrio versutus AL2 are highly resistant to high sulphur and salinity and are highly tolerant to extreme conditions. In this way, a highly effective and sustainable treatment method is achieved.

[0061] For example, the theoretical reactions for the conversion of the dissolved sulphur compounds in the paper industry wastewater into zero-valent elemental sulphur in the reactor (4.1) of the membrane bioreactor are as follows:

[0062] S2O32+ 2 o2+ H2O -> 2 SO2+ 2 H+ S2O;2+ 0.5

[0063] S° + 0.5 O2

[0064] The filtering process in step (c) of the disclosed treatment method is optionally carried out by means of at least one membrane provided in the filtering unit of the membrane bioreactor (4.1). In an embodiment of the invention, the filtering process in step (c) of the said treatment method is performed by means of a ceramic membrane provided in the filtering unit of the membrane bioreactor (4.1). The fact that said membrane is a ceramic membrane, it is resistant to high acidity and alkalinity, and is not damaged by ambient conditions has some advantages. The treatment method including step (c) according to this embodiment has the advantage of providing a method that can be operated interruptedly. However, in another embodiment of the invention, the filtering process in step (c) of the said treatment method is performed by means of a polydopamine (PDA)-coated ceramic membrane provided in the filtering unit of the membrane bioreactor (4.1). With the polydopamine coating of the said ceramic membrane, a durable coating is obtained, and advantageously, it has been found that the hydrophilic properties of the membrane are enhanced. Accordingly, the treatment method including step (c) according to this embodiment is advantageous in terms of providing a method in which the problem of a possible permanent clogging of the membrane is eliminated.

[0065] In an embodiment of the invention, said treatment method comprises a drying step in which the elemental sulphur obtained from the filtering process in step (c) is exposed to a temperature in the range of 40 to 80 °C in order to remove the moisture contained therein (to evaporate water). In a preferred embodiment, the temperature exposed is approximately 50 °C. In fact, since the elemental sulphur that is filtered does not contain a large amount of water, it does not require a lot of energy to remove the moisture therein. In addition, such operation of the system also provides energy savings. It is possible to reuse the produced sulphur in the Kraft process.

[0066] The step (e) of the inventive method optionally comprises a step of removing ions from water by means of at least one selective ionic membrane (4.4) and direct current, and recovering the water. In the method step according to this embodiment, the step of removing ions from water can also be performed by converting alternating current to direct current by means of an adjustable DC power supply (4.3) and supplying it to the said electrodeionization unit (4.2) in a controlled manner.

[0067] The step (d) of the treatment method of the present invention optionally comprises a step of feeding the concentrated high-ion water obtained in step (c) into the electrodeionization unit (4.2) containing a solution of NaCI, H2SO4, NaOH, or HNO3 as an electrolyte. In a preferred embodiment of the invention, step (d) of the treatment method comprises a step of feeding the concentrated high-ion water obtained in step (c) into the electrodeionization unit (4.2) containing a NaCI solution, optionally in the range of 0.5 M to 1 M, as an electrolyte.

[0068] Optionally, said treatment method comprises a step of feeding clean water into the medium in step (e) for separating ions removed from the high-ion filtrate.

[0069] Furthermore, in order to increase efficiency, said treatment method may comprise the steps of diluting and aerating the wastewater to be treated before it is fed into the membrane bioreactor (4.1). For example, the pH and the salinity of the green liquor (15) wastewater, being a paper mill wastewater, are very high. In the halophilic conditions mentioned in the invention, the bacteria capable of oxidizing sulphur can survive but cannot oxidize sulphur at the desired extend. In this respect, the pH value of the wastewater must be reduced. However, given that this is not possible with the addition of acid, the wastewater is diluted. In the studies, it has been found that the highest elemental sulphur production is realized when the green liquor (15) wastewater, being a paper mill wastewater, is diluted at a rate of 25%.

[0070] The present invention provides a good alternative to reduce chemical consumption and costs for the treatment of wastewater, while at the same time providing a sustainable solution by recovering the sulphur and water required for the Kraft process.

Claims

CLAIMS1. An integrated treatment system (4) for recovering sulphur and water from wastewater with high sulphur and salinity, comprising:- at least one membrane bioreactor (4.1) with one or more filtering units having at least one reactor in which sulphur compounds dissolved in the wastewater fed into the treatment system (4) are converted into zero-valent elemental sulphur, and at least one membrane to filter and separate the converted zero-valent elemental sulphur;- at least one electrodeionization unit (4.2).

2. The treatment system (4) according to claim 1, wherein the reactor of the said membrane bioreactor (4.1) comprises bacteria capable of oxidizing sulphur under halophilic conditions.

3. The treatment system (4) according to claim 2, wherein said reactor comprises one of the bacteria of the species Thioalkalivibrio versutus AL2, Thioalkalivibrio denitrificans, Thiomicrospira sp., or Thioalkalimicrobium sp.

4. The treatment system (4) according to claim 3, wherein said reactor comprises bacteria of the species Thioalkalivibrio versutus AL2.

5. The treatment system (4) according to any one of the preceding claims, wherein said electrodeionization unit (4.2) comprises at least one selective ionic membrane (4.4).

6. The treatment system (4) according to any one of the preceding claims, wherein said electrodeionization unit (4.2) comprises an adjustable DC power supply (4.3) to convert alternating current to direct current and supply it to the said electrodeionization unit (4.2) in a controlled manner.

7. The treatment system (4) according to any one of the preceding claims, wherein said electrodeionization unit (4.2) comprises a solution of NaCI, H2SO4, NaOH, or HNO3 as an electrolyte for conducting electric current.

8. The treatment system (4) according to claim 7, wherein said electrodeionization unit (4.2) comprises a NaCI solution as an electrolyte for conducting electric current.

9. The treatment system (4) according to claim 8, wherein said electrodeionization unit (4.2) comprises a NaCI solution in the range of 0.5 M to 1 M as an electrolyte.

10. The treatment system (4) according to any one of the preceding claims, wherein said electrodeionization unit (4.2) comprises Pt / Ir-coated titanium as an anode material, V4A Steel as a cathode material, and polypropylene as an electrode housing material.

11. The treatment system (4) according to any one of the preceding claims, wherein the membrane provided in the said filtering unit is a ceramic membrane.

12. The treatment system (4) according to claim 11, wherein said membrane is a polydopamine-coated ceramic membrane.

13. The treatment system (4) according to claim 12, wherein said membrane is a ceramic membrane coated with polydopamine by dip coating.

14. A treatment method for use in the treatment system (4) according to any one of the preceding claims, comprising the following method steps:(a) feeding the wastewater to be treated into the membrane bioreactor (4.1);(b) converting the dissolved sulphur compounds in the wastewater into zero-valent elemental sulphur in the reactor of the membrane bioreactor (4.1);(c) filtering the partially precipitated and partially suspended elemental sulphur obtained in the previous step and performing sulphur-water separation;(d) feeding the concentrated high-ion water obtained in the previous step into the electrodeionization unit (4.2); and(e) removing ions from the water to recover water in the said electrodeionization unit (4.2).

15. The treatment method according to claim 14, comprising a step of performing said conversion process in step (b) by bacteria capable of oxidizing sulphur under halophilic conditions.

16. The treatment method according to claim 15, comprising a step of performing said conversion process in step (b) by bacteria of the species Thioalkalivibrio versutus AL2, Thioalkalivibrio denitrificans, Thiomicrospira s ., or Thioalkalimicrobium sp.

17. The treatment method according to claim 16, comprising a step of performing said conversion process in step (b) by bacteria of the species Thioalkalivibrio versutus AL2.

18. The treatment method according to any one of claims 14 to 17, wherein the filtering process in step (c) is performed by means of at least one membrane provided in the filtering unit of the membrane bioreactor (4.1).

19. The treatment method according to claim 18, wherein the filtering process in step (c) is performed by means of at least one ceramic membrane provided in the filtering unit of the membrane bioreactor (4.1).

20. The treatment method according to claim 19, wherein the filtering process in step (c) is performed by means of at least one polydopamine-coated ceramic membrane provided in the filtering unit of the membrane bioreactor (4.1).

21. The treatment method according to any one of claims 14 to 20, comprising a step of drying the elemental sulphur obtained from the filtering process in step (c) at a temperature of 40 and 80 °C in order to remove the moisture contained therein.

22. The treatment method according to any one of claims 14 to 21, comprising a step of removing ions from water by means of at least one selective ionic membrane (4.4) and direct current, and recovering water in step (e).

23. The treatment method according to claim 22, comprising a step of removing ions from water by converting alternating current to direct current by means of the adjustable DC power supply (4.3) and supplying it to the said electrodeionization unit (4.2) in a controlled manner.

24. The treatment method according to any one of claims 14 to 23, comprising a step of feeding the concentrated high-ion water obtained in step (c) into the electrodeionization unit (4.2) containing a solution of NaCI, H2SO4, NaOH, or HNO3 as an electrolyte for conducting electric current.

25. The treatment method according to claim 24, comprising a step of feeding the concentrated high-ion water obtained in step (c) into the electrodeionization unit (4.2) containing a NaCI solution as an electrolyte for conducting electric current.

26. The treatment method according to claim 25, comprising a step of feeding the concentrated high-ion water obtained in step (c) into the electrodeionization unit (4.2) containing a NaCI solution in the range of 0.5 M to 1 M as an electrolyte for conducting electric current.

27. The treatment method according to any one of claims 14 to 26, comprising a step of feeding clean water into the medium in step (e) for separating ions removed from the high-ion filtrate.

28. The treatment method according to any one of claims 14 to 1 , comprising the steps of diluting and aerating the wastewater to be treated before it is fed into the membrane bioreactor (4.1).

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