LT3624B - Process for the treatment of water containing sulphur compounds - Google Patents

Abstract

Water contg. sulphides is purified by oxidising in a reactor using sludge contg. aerobic bacteria. The sludge load (w.r.t. the sulphide oxidising part of the sludge) is at least 10 mg sulphide per Mg N in the sludge per hr.. Pref. the sludge load is at least 20 mg (at least 35 mg) sulphide per mg N. The sludge is in the form of biofilms bound to a carrier. The O2 concn. in the reactor is 0.1-9.0 (4) mg/l. The sulphide concn. in the effluent is kept at 0.5-30 mg/l. The sulphide surface load is at least 10 g/sq. m. The sulphide load is at least 50 (at least 100) mg S/l.h. In a two-stage process sulphide is (partially) oxidised to S and then, in a second reactor S and remaining sulphide oxidised to sulphate. The first oxidn. pref. uses a sulphide load of at least 26 mg S/l.h. (at least 50) (100-1000) mg S/l.h. S cpds. may first be anaerobically reduced to sulphide. The S cpds. are esp. sulphates, sulphites or thiosulphate. Purified water may be recycled to keep the S content below 800 (below 350) mg/l during anaerobic treatment.

Description

The present invention relates to the field of waste water recycling. In particular, the present invention relates to a process for the processing of water containing sulfur compounds or higher oxidation sulfur compounds such as sulfate, sulfide or thiosulfate, and may also contain organic matter.

According to the process of the present invention, sulfur compounds are oxidized in a pulp (biomass) reactor containing aerobic bacteria. The invention further relates to the removal of heavy metals from sewage by precipitation of these heavy metals in the form of sulfides.

The presence of sulfur compounds such as sulfide in wastewater has many negative consequences, such as:

- corrosive effects on steel and concrete;

- a high chemical demand for oxygen (CHPD), which results in a reduction of effluent run-off into the oxygen receiving water basin, in addition to environmental pollution and / or high environmental pollution charges;

- Toxic effects in humans and animals;

- strong unpleasant odor.

Although sulfide can be removed from wastewater by chemical oxidation, desorption and precipitation, biological treatment methods have become more significant. Biologically, sulfide can be removed by using phototropic sulfur bacteria (also producing sulfur) as well as by denitrifying bacteria. Also, sulfide can be converted into sulfate-activated pulp by bacteria that use oxygen. The formation of sulfur using oxygen consuming bacteria has advantages over the use of phototropic bacteria paLT 3624 B, since aerobic conversion is much faster than anaerobic (phototropic) conversion, and providing light to a dense gaseous sulfur reactor is not an easy task, whereas oxygen can to be supplied to an aerobic reactor in a simple manner without problems. For denitrifying bacteria, nitrate is required.

Advantages of converting sulfide to sulfur instead of sulfate:

- Significantly less oxygen consumption and, at the same time, significantly lower energy consumption;

- the process is much faster;

- reduced biological pulp production;

- no sulphate or thiosulphate is formed;

- sulfur recovery is possible.

A method for removing sulfide from wastewater by oxidizing sulfide to elemental sulfur is known (Dutch Patent Application No. 8801009), where sulfur formation can be accelerated by supplying less oxygen than is necessary for sulfate formation. Although this known process produces significant amounts of sulfur, it is necessary to improve this process to minimize the formation of soluble sulfur compounds such as sulfide and sulfate.

Another problem with biological wastewater recycling systems is that sulphate adversely affects treatment efficiency and pulp retention by aerobic treatment of wastewater based on activated pulp application. One reason is that oxidizing sulfide can initiate the proliferation of fibrous bacteria, such as Thiothrix and Beggiatoa, in the digestion plant 3624 B. These fibrous bacteria do not allow the pulp to settle efficiently, causing the pulp to be washed (volume reduced). This phenomenon has two negative consequences:

a: reduces the efficiency of the waste water treatment plant and thus the efficiency of the treatment;

b: Increases in charges due to an increase in the charge of compounds with high oxygen demand after leaching the pulp.

High levels of other sulfur compounds, such as more than 350-500 mg / l sulfur or less than 10 sulfur to waste water oxygen demand (CHPD / S), cause difficulties in anaerobic digestion of wastewater because the sulfide formed inhibits metal bacteria. However, anaerobic wastewater treatment has the overall advantages over aerobic treatment: low energy consumption, low pulp growth, methane recovery, etc. Thus, there is a need for anaerobic treatment of organic sewage, even at high sulfur content.

A method of recycling anaerobic wastewater containing sulfur compounds is known (European Patent Application No. 0241999, wherein wastewater containing sulphate is purified by anaerobic reduction of sulphate to sulphide. The sulphide is then removed from the wastewater ₂ S) The disadvantages of this method are that it is necessary to measure (adjust) the pH by removing the sulfide from the water to a sufficient degree, and that the hydrogen sulphide must then be separated from the methane and any other gas, thereby forming a brine, which can not be easily applied, moreover, if the sulfide charge is high, anaerobic bacteria can be poisoned.

It is common knowledge that heavy metals are present even in very low concentrations. undesirable because of their high toxicity to humans and animals. Conventional removal methods such as hydroxide formation and separation, reversible osmosis, and ion exchange are complex and do not produce the desired result.

The method for removing sulfur compounds and heavy metal ions is known (International Patent Application

WO80 / 02281).

In this method, sulfate-reducing bacteria are grown in fermentors in the presence of a nutrient solution and a portion of the recycled sewage, and the aqueous solution of the resulting sulfide is fed to the settler along with the remaining volume of the effluent. The sulphides of metals are deposited in the form of flakes in the precipitator, especially when iron (III) ions are present in the effluent.

The metals which can be deposited include lead, mercury, cadmium, iron, copper, nickel, zinc, cobalt, manganese and silver. However, sulfate and / or sulfide cannot be completely eliminated in this way.

It has been found that sulfur formation can be accelerated by a method for purifying sulfur-containing water, wherein the sulfide is oxidized in the reactor using a slurry of aerobic bacteria and the sulfide charge is kept to a minimum in the aerobic reactor.

In a first aspect of the present invention, the process is characterized in that the pulp charge in the reactor is at least 10 mg sulfide / mg nitrogen per hour in the pulp, the pulp charge being calculated as a fraction of the sulfide oxidizing biomass.

In another aspect, the process is carried out in two steps, the first step comprising at least a portion of the sulfide to elemental sulfur in the first aerobic reactor with minimal sulfide loading, and in the second step further oxidizing to the sulfate in the second aerobic reactor.

In another aspect of the invention, the process is applicable to the recycling of high sulfur compounds, wherein the sulfur compounds are initially reduced to sulfide anaerobically and the resulting sulfide is then oxidized in an aerobic reactor with a minimal sulfide charge.

In yet another aspect of the invention, the method is used for the removal of heavy metal ions, wherein water containing sulfide ions reacts with heavy metal ions to form metal sulfides, and then precipitated sulfide is oxidized to elemental sulfur in an aerobic reactor with minimal sulfide aerobic reactor charge.

The required minimum sulfide charge according to the process of the invention is better expressed as the sulfide pulp charges, i. y. ratio of the amount of sulfide present in the aerobic reactor per unit time to the mass of the bacterial pulp that oxidizes the sulfide. The pulp charge shall be at least 10 mg S / mg N per hour. Here the bacterial content (biomass) is determined by the nitrogen content. It has been found that when the sulphide pulp charge is less than 10 mg S / mg N per hour, almost exclusively sulphate is produced, which is generally undesirable, because sulphate cannot be separated in an appropriate way from the effluent recycled, whereas elemental sulfur is formed. can be easily separated at higher pulp loads. Preferably, the pulp loading is at least 20 mg S / mg N per hour, and more preferably at least 30 mg S / mg N per hour. In most cases, with a pulp charge of about 35 mg S / mg N per hour. and more, only elemental sulfur is obtained.

The present invention includes all the sulfide sulfur divalent ionic and non-ionic organic compounds, such as sulphide (S ^2), hydrosulfide (HS ^_), hydrogen sulfide (H ₂ S) and the corresponding polysulphide material.

Waste water is any liquid based on water that has at least one component such as a sulfur compound that must be removed from it.

The aerobic reactor pulp contains sulfur-oxidizing species such as Thiobacillus and Thiomicrospira.

The pulp charge used in this process may be obtained by selecting the time of retention of the respective effluent in the aerobic reactor or other parameters such as pulp volume in the reactor, sulfide concentration or oxygen concentration in the effluent.

Oxygen concentration has been found not to be a critical parameter of the present invention. It may be in a wide range and is preferably in the range of 0.1 to 9.0 mg O ₂ , more preferably about 4 mg O ₂ per liter of material present in the reactor.

In the method of the present invention, the pulp loading is unexpectedly high compared to known methods. This is shown in Table A. In normal aerobic processes, the pulp charge is less than 0.1 mg S / mg per hour.

Table A

Sulphide pulp loading (mg S / mg per hour) Sulfur yield as a percentage of total sulfide charge 0-10 0 10-20 0-75 -20-30 75-95 30-35 95-100 > 35 100

LT 3824 B

The pulp content (biomass) in Table A is expressed as the nitrogen content of the bacteria. To calculate the dry mass content of this expression, multiply that number by a factor of 8.3. Table A clearly shows that the pulp loading must be greater than 35 mg S / mg N per hour in order to convert all sulfide to sulfur.

In the process of the present invention, the biomass used in the reactor is in the form of biofilms which are bonded to a carrier. Suitable carriers for this purpose include any polymeric or other material such as polyurethane, polyethylene, polypropylene, polychlorinyl and the like.

Preferably, the elemental sulfur is formed as the only or practically only sulfur product in the process. This product can be separated from the effluent by filtration, centrifugation, precipitation and the like.

To avoid the formation of more oxidized sulfur compounds, the sulfide concentration in the effluent from the reactor stream is kept to a minimum; preferably at a concentration of 0.5-30 mg S per liter of effluent.

The values given in Table A are only applicable to waste water streams which do not contain organic material.

The presence of organic matter in wastewater increases additional biomass that does not oxidize to sulfide, which results in an increase in the total nitrogen content of the biomass compared to Table A. In the case of organic substances in the effluent, a specific parameter for the conversion of sulfide into elemental sulfur may be the surface charge of sulfide (it is understood that the surface is the surface of the biofilm). The values of this parameter are given in Table B.

Table B

Surface charge of sulphide (g S / m ² , day) Sulfur yield as a percentage of total sulfide charge 0-10 0-80 10-20 80-95 20-25 95-100 25th 100

Thus, the process of the present invention is preferably carried out at a surface sulfide charge of at least 10 g S / m · day, and more preferably

20-25 g S / nf · para. Where no organics are available, the values given in Table A may be used.

It has been found that in the process of the present invention the pH value in the aerobic reactor should not exceed 9.0. The lower limit of pH is not a critical parameter; it can be significantly less than 5, since sulfur oxidizing bacteria are known to grow at pH values below 0.5.

The minimum reactor sulfide charge required for efficient sulfide conversion can also be used in a two-step process where

(a) at least part of the sulfide is oxidised to elemental sulfur in the first aerobic reactor;

b) The resulting liquid of step (a), which contains elemental sulfur and may contain sulfide and other components, is fed to a second aerobic reactor in which the sulfur and sulfide are oxidized to sulfate. The separation step may be between steps (a) and (b) in which the major elemental sulfur is removed.

This has particular advantages when the water to be treated is one where, under normal processing conditions, undesirable fibrous bacteria of the species Thiothrix and Beggiotoa are grown. This can happen when cleaning water containing sulfide that is heavily contaminated with organic pollutants.

The minimum sulfide charge can be expressed as the minimum sulfide content per unit biomass per hour as above. It may also be expressed as the minimum amount of sulfide per liter of material present in the first aerobic reactor per hour. In this case, the minimum sulfide charge is 25 mg S / l. or.

The increase in sulfide charge in the first aerobic reactor, i. y. Increasing sulfide concentration, reducing processing time and / or reducing processing volume would improve the efficiency of sulfur removal and secondary aerobic recycling of other contaminants.

In general, the present invention improves pulp retention in the second stage of aerobic purification. This is illustrated in Table C, which shows the test results obtained with the reactor described in Dutch patent no. No. 8801009 (for the conversion of sulfide to sulfur).

Table C

Results after two weeks

CHDS efficiency Volume decrease Two-step approach (invention) 76 very slight One-step mode strong (normal)

io

Table D shows the effect of the change of process parameters on sulfide removal efficiency and growth of fibrous bacteria.

Table D

Consumption (1 / hr) Hydraulic retention time (or.) Sulfide concentric ration When entering (mg / i) Sulphide Charge (mg S ² '/ l per hour. Sulphide concentration at discharge (mgS ² '/ l) Thiothrix / Beggiatoa growth 75 0.3 140 525 14th - 15th 1.3 140 105 25th - 1.5 13.3 140 10, 5 0, 5 ++ 15th 1.3 25th 18, 8 2, 0 ++ 71 0.3 3.0 10.5 0, 0 ++

It follows from Table D that only hydraulic retention time and sulfide concentration in effluents alone have no direct effect on the efficiency of primary aerobic treatment.

Conversely, significant growth of unwanted fibrous bacteria that oxidize sulfur occurs with a sulphide charge of less than about 20 mg S / l per hour. Thus, the minimum sulfide loading in this process should be 25 mg S / l per hour. Preferably, the sulfide loading is at least 25 mg S / l per hour, and more preferably at least 100 mg S / l per hour. Sulphide Load greater than 1000 mg S / l. per or. will not be used at all because of unacceptable costs. Thus, high concentrations of effluent streams must be diluted prior to treatment.

The sulfide can be oxidized to sulfur and / or sulfate in a two-step process, depending on retention time and oxygen concentration. In most cases, it is preferable to add sulfur to sulfur oxyXL 3624 B since it is more convenient to remove it by precipitation, centrifugation or filtration. A limited amount of oxygen is used for this purpose. The sulfide is oxidized in the first, relatively small, high-cost aerobic reactor (residence time from several tens of minutes to several hours), and the other oxidized components are then removed in a relatively large reactor with a long residence time (for example, 24 hours).

The elemental sulfur separator may be located between two reactors. The outflow of recycled waste water is largely or completely free of sulfur compounds.

This method of the invention can also be applied to anaerobic treatment of wastewater, even if it contains large amounts of sulfur compounds, which makes them highly purified from sulfur compounds. The sulfur compounds as described above are reduced to sulfide in an anaerobic reactor and the sulfide is then removed by oxidation to elemental sulfur. When the concentration of sulfur compounds in the recycled water is very high, part of the purified water is better recirculated to the water to be treated. Preferably, it is circulated into the water to be treated. Preferably, the repeatability of the recirculation (the ratio of the amount of water circulated to the anaerobic reactor to the amount of purified water discharged) is chosen so that the sulfur concentration in the anaerobic reactor is less than 800 mg S / l, and even less 350 mg S / l. .

The method can be applied to the treatment of wastewater containing different sulfur compounds in almost any concentration. These may include inorganic sulfur compounds such as sulfate, sulLT 3624 B phyt, thiosulfate, tetrathionate, elemental sulfur and the like, as well as organic compounds such as carbon disulfide, dialkyl sulfides, dialkyl disulfides, mercaptans, sultans, sulfoxides, sulfuric acids and the like. The process is particularly suitable for the processing of water containing sulphates, sulphites and thiosulphates.

Bacteria suitable for the reduction of sulfur compounds to sulfide include the major groups of species that reduce sulfur and sulfate such as Desulfovibrio, Desulfotomaculum, Desulfomonas, Desulfobulbus, Desulfobacter, Desulfococcus, Desulfoneme, Desulfosarcina, Deculfobacterium and Desulforomas. Collectively, these bacteria can be obtained from anaerobic cultures and / or self-grow in anaerobic reactors.

Recirculation of part of the purified effluent stream to the inlet water reduces the sulfide concentration by anaerobic digestion so that the anaerobic flora (mainly bacteria producing methane) is not inhibited.

A further advantage of the present invention is that sulfide removal does not require lowering the pH of the partially treated wastewater. In addition, there is no need for gas scrubbers, which in turn provide secondary wastewater.

Any type of wastewater with any sulfur concentration can be recycled by selecting the appropriate recirculation repeatability. The recurrence repeatability can vary within wide limits and can be, for example, 1-10. When recycling waste water has a high sulfur load, a relatively small proportion of the treated water is recirculated. In this way, wastewater containing 30 g / l of material having a high CHDC (calculated as sulfur) can be efficiently recycled by the present invention.

The treatment plant comprises an anaerobic digestion reactor coupled to a reactor for sulfide oxidation to elemental sulfur, a separator for separating elemental sulfur, and a tube through which a portion of the effluent from the separator is fed to the anaerobic reactor.

The method of removing the sulfur compounds can be carried out, for example, in processing plants, as shown schematically in Fig. 1. According to Fig. 1. the waste water stream 1 is fed to an anaerobic reactor 2 where organic pollutants are mainly converted to methane and sulfur compounds are converted to sulfide. The resulting gas is removed from the anaerobic reactor 2 by a tube (not shown). The anaerobic reactor is connected by a tube 3 to an oxidizing reactor 4 where the sulfides entering are converted into elemental sulfur by bacteria oxidizing the sulfur under conditions (minimal sulfur charge, oxygen concentration) that necessarily produce sulfur. An appropriate amount of oxygen is supplied through Inlet 5. The reactor does not necessarily contain a carrier for sulfur oxidizing bacteria. The residence time in reactor 4 is relatively short (e.g. less than 20 minutes). In reactor 4, the recycled water is fed through a conduit 6 to a separator 7 where the sulfur formed is separated through outlet 8. The recycled effluent is then discharged into a final stream 10 and a recirculating stream 11, the ratio of these flows being controlled at input 1 depending on the effluent to be recycled , properties.

In order to remove heavy metal ions from water which also contains sulfur compounds, the present invention artificially introduces sulfide ions into the water which react with metal ions to form metal sulfides and the remaining sulfide is oxidized to elemental sulfur in an aerobic reactor with a minimal sulfide charge, as described above.

The sulfide ions, which are necessary for the production of metal sulfides, can be added to the stream at the reactor inlet. Preferably, the sulphide ions are generated in water, anaerobic reduction of sulfur compounds that can be recycled water, and ^z or can be added. If sulfur compounds are to be added, it is preferable that it be elemental sulfur.

Preferably, in the anaerobic sulfur stage, the metal ratio is sufficient for complete deposition of heavy metals. In this way, sulfide traps all heavy metal ions.

Preferably, the metal sulfides and elemental sulfur formed in the cleaning process are removed together, for example by precipitation, filtration, centrifugation or flotation.

A nutrient medium (electron donor) can be added to reduce sulfur compounds to sulfide. Such an electron donor is required for the recycling of water free from organic pollutants. The specific application will determine the medium to be added: hydrogen, carbon monoxide and organic compounds such as formic acid, sugar, fatty acids, alcohols and starch. Nutrients such as nitrogen, phosphate and trace elements may also be added if necessary.

Examples of wastewater containing heavy metals that can be recycled by the present invention include groundwater, mining sewage, industrial wastewater such as the photographic industry and metallurgy, and sewage scrubber wastewater.

Heavy metals that can be removed by the process of the present invention include all metals with low sulfide solubility. These include lead, tin, bismuth, cadmium, mercury, silver, zinc, copper, nickel, cobalt, iron, manganese, chromium, vanadium and titanium.

Retention of metal sulphides at the aerobic stage must be significantly shorter in order to avoid excessive oxidation, because when sulphide is completely oxidized, metal sulphides cannot remain in the sediment.

By maintaining a low residual sulfide concentration in the aerobic stage (micro-aerophilic sulfide oxidation) and in the separation stage, where elemental sulfur and the grown biomass are separated from the water stream, we avoid re-melting of the metals.

This concentration may vary over a very wide range and may be, for example, 0.1 to 50 mg / l, preferably 1 to 10 mg sulfide / l. The maintenance of the required sulfide concentration can, for example, be controlled by measuring the sulfide concentration or oxidation-reduction potential in an aerobic reactor or separator. The oxidation-reduction potential should be better negative during sulfide oxidation and separation, for example below 100 mV. It is observed that the oxidation-reduction potential during the first stage, i. y. during anaerobic sulfur reduction should be within the range - 200 - - 400 mV.

Any sulfide ions, after the separation step, can be oxidized, for example, to the sulfate in any known manner (e.g., by aeration or by addition of peroxide) prior to their emission.

The method for removing heavy metals according to the present invention may be carried out, for example, in a device schematically illustrated in the accompanying drawing. 2. According to Fig. 2 recyclable effluent stream (inlet) 1 fed to buffer / agitator vessel 12. Feed media and electron donors can be added via inlet 13.

The solution is removed from the buffer vessel through outlet 14 and fed to anaerobic reactor 2 where the sulfur compounds are reduced to sulfide to form metal sulfides. The metal sulfides are deposited on the bottom of reactor 2 (not shown). During the anaerobic process, the gas is discharged through a tube 15 to a gas processing unit 16, where combustion and H ₂ S can occur. The liquid obtained in the reducer 2 containing the sulfide is transported by tube 3 to the aerobic reactor 4 where the sulfide is oxidized to elemental sulfur. The air into the aerobic reactor 4 is fed through an inlet 5. The gas is conveyed through a conduit 17 to an odor remover 18.

The sulfur-containing liquid is removed from the aerobic reactor 4 via outlet 6 and fed to a separator 7 for sulfur separation. The sulfur is separated through the outlet 8, while the purified stream flows from the separator 7 through the outlet 10.

Tables E and F summarize the measurement results of the recycling system operating in accordance with the method of the present invention.

Table E

Concentration of major components in the removal of heavy metals

Stage Zinc Fig. 2 (mg / l) Sulphate (mg / l) Sulfide (mg / l) Cheese (mg / l) Ethanol (mg / l) Oxidac. -re · in the fog. potential (mV) Incoming 145 (D · 960 0 0 0 150 a (3) 0.5 10th 245 0 10th -410 b (6) <0.1 15th 4 205 <1 -300 outflow (10) <0.1 15th 3 5 <1 -200

a = after anaerobic stage; b = after aerobic stage. Ethanol was added to the inlet stream; also about 350 mg / l of metal sulfide precipitate is formed.

Table F

Concentration of other metals in the inlet and outlet streams

Metal Inbound (mg / 1) Outflow (mg / 1) cadmium 0, 95 <0, 01 iron in general 25th 0, 05 lead 46th <0, 01 copper 0, 57 <0.02 cobalt 0.10 <0.015 nickel 0.10 <0.015 manganese 7.0 3, 5 calcium 410 275 aluminum 10th 1

An example

By estimating the ratio of sulfur and / or sulfate formation to sulfide pulp charge reduction at the sulfide removal plant, sulfur formation is measured for many stationary situations.

In the experiment, only sulfide and nutrient-free media are fed to the reactor, so N content is determined only by sulfide oxidizing biomass.

The results are shown in Fig. 3. Less. 10 S / mg N per hour, only sulphate is formed. When the pulp charge is more than 10 mg S / mg N per hour, the sulfur output increases.

The nitrogen content of bacteria oxidizing sulfur is measured according to the modified Kjeldahl method developed by Novozamsky et al. (1983) Comm. Soil Science Plant Anai.

Claims (23)

DEFINITION OF INVENTION 1. A process for purifying sulfur-containing water by oxidizing the sulfide in a reactor with a slurry of aerobic bacteria, characterized in that the reactor contains at least 10 mg of sulfide / mg of nitrogen in the slurry per hour, and the pulp charge is calculated by the sulfide-oxidizing pulp. part. 2. The method of claim 1, wherein the pulp charge is at least 20 mg of sulfide / mg of nitrogen per pulp per hour. 3. A process according to claim 1, wherein the pulp charge is at least 35 mg of sulfide / mg of nitrogen per pulp per hour. Method according to any one of claims 1 to 3, characterized in that the pulp is in the form of biofilms which are combined with a carrier. The process according to any one of claims 1 to 4, wherein the oxygen concentration in the reactor is controlled within the range of 0.1 to 9.0 mg / l, preferably 4 mg / l. A process according to any one of claims 1 to 5, characterized in that it oxidizes substantially to elemental sulfur. 7. A process according to any one of claims 1 to 6, wherein the concentration of sulfide in the effluent from the aerobic reactor is 0.5 to 30 mg / l. 8. A process according to any one of claims 1 to 7, wherein the surface loading is at least 10 mg / m / day. 9. A process as claimed in any one of claims 1 to 8 wherein the sulfide charge is at least 50 mg S / l per hour. 10. The method of 9 in that sulfide an hour. point, charge bes consists of i s k i r at least 100 i a n t i s per mg S / l 11. Method according to any of 1 - 10 points, b e s i - distinguishing s that that (a) oxidizes at least part of the sulfide to elemental sulfur in the first aerobic reactor, b) Feeding the resulting liquid, which may contain sulfide and other components in addition to elemental sulfur, to a second aerobic reactor where the sulfur and sulfide are oxidized to sulfate. 12. A process for purifying sulfide-containing water, characterized in that (a) at least part of the sulfide is oxidised to elemental sulfur in the first aerobic reactor and the sulfide charge is at least 25 mg S / l per hour, b) the liquid obtained in step a), which may contain sulfide and other components in addition to elemental sulfur, is fed to an aerobic reactor where the sulfur and sulfide are oxidized to sulfate. 13. A process according to claim 11 or 12, wherein the sulfide charge in step a) is at least 50 mg S / l per hour. 14. The process of claim 11 or 12, wherein the sulfide charge in step a) is 100 to 1000 mg S / l per hour. 15. A process for recycling anaerobic wastewater rich in sulfur compounds, wherein the sulfur compounds are reduced to sulfide during anaerobic digestion and the sulfide is subsequently removed by the process of any one of claims 1 to 14. 16. A process according to claim 15 wherein after purification of the sulfide some of the purified water is recirculated to the effluent to be recycled. 17. A process according to claim 16, wherein the sulfur concentration in the purified recirculated water during anaerobic processing is less than 800 mg S / l, preferably less than 350 mg S / l. Use of the process according to any one of claims 15 to 17 for the recycling of water containing sulfate. Use of a process according to any one of claims 15 to 17 for the recycling of water containing sulfite. Use of a process according to any one of claims 15 to 17 for the recycling of water containing thiosulfate. 21. A method of removing heavy metal ions from water, which may also contain sulfur compounds, wherein the sulfide ions introduced into the water react with the metal ions to form metal sulfides, wherein the remaining sulfide is oxidized in an aerobic step to elemental sulfur by a method according to any one of claims 1 to 14. 22. The method of claim 21, wherein the water, after anaerobic reduction of sulfur compounds, has sulfide ions present and / or added thereto. 23. A process according to any one of claims 21 to 23, wherein the anaerobic reduction has a sulfur / metal ratio sufficient for the complete precipitation of heavy metal ions. 24. A process according to any one of claims 21 to 23, wherein the aerobic stage has a negative oxidation-reduction potential of below 100 mV. 25. A process according to any one of claims 21 to 24, wherein the concentration in the aerobic stage is 0.1 to 50 mg / L, preferably 1-10 mg / L.