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    19 Abstract The present invention relates to a method and as apparatus for simultaneous removal ofthiosalt and nitrogen compounds in waste water, wherein the amount of thiosalt in the wastewater is lager than the stoichiometric demand for the autotrophic nitrogen removal. Theapparatus comprises a bioreactor (1) including an autotrophic bacteria culture carrying out adenitrification process using the thiosalt as an electron donor, having an inlet (3) for receivingthe waste water, and an outlet (4) for discharging the purified water. The apparatus comprisesan oxygen supply device (6) arranged to supply oxygen to the water in the reactor and a controlunit (10) arranged to control the content of dissolved oxygen in the reactor such that the excessof thiosalt is oxidized by the oxygen at the same time as the denitrification process ismaintained. (Figure 1)
    公开号:SE1251085A1
    申请号:SE1251085
    申请日:2012-09-25
    公开日:2014-03-26
    发明作者:Jan-Eric Sundkvist；Amang Saleh
    申请人:Boliden Mineral Ab；
    IPC主号:
    专利说明:

    A method and an apparatus for simultaneous removal of thiosalt and nitrogen compounds inwaste water Field of the invention The present invention relates to a bacteria assisted method and an apparatus for treating waterincluding thiosalt, such as thiosulphate and tetrathionate, and nitrogen compounds, such asnitrite, nitrate and ammonia, wherein the amount of thiosalt in the waste water is larger thanthe stoichiometric demand for the autotrophic nitrogen removal. The water is treated with anautotrophic denitrification process using the thiosalt as electron donor.
    Prior Art Water from mines and ore dressing plants includes large amounts of sulphur compounds, suchas thiosalt, and nitrogen compounds, such as nitrite, nitrate and ammonia. lf the water isdischarged directly into the nature without any treatment it will cause acidification andeutrophication. lncreasing demand on the removal of the thiosalt and nitrogen compounds hasbeen raised from the authorities. Today, the thiosalts and nitrogen compounds are oftenremoved to a minor extent by natural degradation in the large tailings ponds. However, thereare examples where chemical methods, such as the Fenton process, are applied for thiosaltsremoval. There are also examples where the nitrogen compounds are actively removed inseveral steps including nitrification and denitrification using a heterotrophic bacteria culture.
    Biological denitrification using bacteria cultures is a cost efficient method for nitrate and nitriteremoval from most wastewater types. From an article ”Denitrification by new strains ofthiobacillus denitrificans under non-standard physicochemical conditions, effects oftemperature, pH, and sulphur source", written by C. Trouve, P.M. Chazal, B. Gueroux and N.Saouvaitre, in Environmental Technology, vol 19, pp 601 - 610, in March 1998, it is known toremove nitrates from water by means of by biological denitrification using Thiobacillusdenitrificans as bacteria culture and using a sulphur compounds, for example thiosulphate, asan energy source. The following reaction was suggested to describe the stoichiometry when the bacteria are growing:0.844 82032' + N03" + 0.347 C02 + 0.0865 C032' + 0.0865 NHÄ + 0.434 H20==> 0.0865 C5H702N + 0.5 NZ + 1.689 S042' + 0.697 HT As seen from the above formula, carbon dioxide has to be supplied to the process. This processis carried out anaerobically.
    From an article ”|V|ethabolic changes of Thiobacillus denitrificans accompanying the transitionfrom Aerobic to Anaerobic growth in continuous chemostate culture" by Pauline Justin and D.
    P. Kelly, in Journal of General Microbiology 107, 131 - 137, in March 1978, it is known thatThiobacillus denitrificans is capable of rapid growth on thiosulphate both aerobically andanaerobically with nitrate or nitrite as oxidant. The denitrification of nitrate is an anaerobicprocess and depends strongly on the oxygen concentration in the water. This is disclosed inTable 1 of the article, which exemplifies how the nitrate consumption depends on theconcentration of dissolved oxygen. The table shows that the nitrate consumption ceases whenthe oxygen content in the water exceeds IZuIVI/l. The conclusion is that denitrification withthiosulphate as deoxidizing agent ceases when the oxygen content in the water exceeds a lowlevel.
    ”Combined Denitrification in Bioaugmented Activated Sludge System” written by I. Manconi, A. Carucci, ln an article removal of Sulfur Compounds and Nitrate by Autotrophicand P. Lens, published online 9 March 2007 in Wiley Inter Sience (vvwwintersciencewiley.com)it is proposed to simultaneously remove reduced sulfur compounds and nitrate from wastewater by growth of autotrophic sulfur bacteria, such as Thiobacillius Denitrificans, underanaerobic conditions. The reduced sulphur compounds are used for reducing the nitrate andthe nitrate is used to oxidize the reduced sulphur compounds. lf the amount of sulphurcompound and the amount of nitrate in the waste water corresponds to the stoichiometricdemand for the nitrogen removal, it is possible to simultaneously remove the reduced sulfurcompounds and the nitrate. From the reaction formula described above it is clear that themolar ratio between the amount of reduced sulphur compound and the nitrate must be about0,84 in order to achieve a complete removal of the sulphur compound and the nitrate.
    This is a quotation from the article: ”Thus, to allow maximum N03' removal without N02'accumulation, the reactor has to be operated in a nitrate limiting mode by addition of electrondonor (sulfide or thiosulfate) in excess. However, a careful control of the required electrondonor excess is also necessary, since both thiosulfate and sulfide have a chemical oxygendemand (COD), and because below N/S =0.6 elemental sulfur was likely formed during sulfideoxidation. lncomplete oxidation of thiosulfate or sulfide to elemental sulfur would require aseparation step of the insoluble elemental sulfur from the wastewater, increasing the processcomplexity." However, in waste water from mines and ore dressing plants the amount of thiosalt in thewaste water is normally significantly larger than the stoichiometric demand for the nitrogenremoval. For example, the molar ratio between the thiosalt and the nitrogen compounds in thewater can be in the order of 10 - 20. This can be compared with 0.84, which is thestoichiometric demand for nitrogen removal when the culture is growing. Although the abovedescribed method can be used for complete removal the nitrate in the water, it will onlyremove a minor part of the thiosalt. Thus, a problem with treating this type of waste water with the above described method is that a mayor part of the thiosalt will still remain in the waterafter the treatment.
    Object and summary of the invention One object of the present invention is to provide a method for simultaneous removal of thiosaltand nitrogen compounds in waste water where the amount of thiosalt is significantly largerthan the stoichiometric demand for the nitrogen removal. This means that the molar ratiobetween the thiosalt and the nitrogen compounds in the waste water is significantly larger thanthe ration required for the denitrification process, i.e. larger than 0.84.
    This object is achieved with a method as defined in claim 1.
    The method comprises supplying oxygen to the water and controlling the content of dissolvedoxygen in the water such that the excess of thiosalt is oxidized by the oxygen at the same timeas the denitrification process is maintained.
    According to the invention, the water is treated using an autotroph culture, for exampleThiobacillius Denitrificans, while adding oxygen to the water. A part of the thiosalt is oxidized bythe nitrogen compound at the same time as the nitrogen compound is reduced to nitrogen gasby the thiosalt. The excess of thiosalt is oxidized by the added oxygen. The content of dissolvedoxygen in the water is controlled so that it does not exceed the level where the denitrificationprocess ceases. The oxygen content is preferably kept within a range of 0.3 - 1mg/l, and morepreferably within a range of 0.35 - 0.6mg/l. The oxygen is added to the water in such a rate thatthe oxygen content in the water never exceeds the content at which the denitrification ceases.This means that the oxygen is added to the water at about the same rate as it is consumed bythe oxidation of the thiosalt. The oxygen can be added to the water, for example, by aeration orinjection of oxygen gas. The invention makes it possible to carry out simultaneouslydenitrification of the nitrogen compound and oxidation of the thiosalt of waste water in whichthe molar ratio between the thiosalt and the nitrogen compounds is significantly lager than theratio required for the denitrification process. Thus, an efficient removal of both nitrogencompounds and thiosalt is achieved. lt has also been shown that a significant part of theammonium content of the water is removed according to the above equation, since ammoniumis the preferred nitrogen species for biomass growth.
    The following advantages are achieved with the method according to the invention:- Denitrification and oxidation of thiosalt is made in one step.
    - The method is environmentally friendly since is only requires supply of oxygen and a carbondioxide source. No supply of organic compounds, such as methanol, ethanol, or acetate, isneeded.
    - The method is carried out at a neutral pH, which means that the process is less sensitive formetals, fluorine etc. compared to bacterial oxidation of thiosalt carried out at a low pH.- The method according to the invention can be used for treatment of water at temperaturesfrom down to temperatures close to O°C. Thus, denitrification can be carried out efficiently at alower temperature compared to conventional methods using organic reduction agents. This isadvantageous in cold countries, such as the Nordic countries.
    - Low costs regarding operating economy as well as investments costs, since only one reactor isneeded.
    According to an embodiment of the invention, the method comprises measuring the content ofdissolved oxygen in the water and controlling supply of oxygen to the water so that the contentof dissolved oxygen in the water is kept within a certain range, preferably in a range of 0.3 -1mg/l, and more preferably within a range of 0.35 - O.6mg/l.
    According to an embodiment of the invention, the method further comprises measuring the UVabsorption in the purified water, preferable at a wave length close to the maximum UVabsorption of the thiosalt and nitrogen compounds, measuring the content of dissolved oxygenin the water, and controlling the supply of oxygen to the water based on the measured UVabsorption and the measured oxygen content so that the measured UV absorption isminimized. To achieve a high rate of the removal of both thiosalt and nitrogen compounds, it isimportant that the control of the oxygen supply is optimized. lf the oxygen content in the wateris too low, the rate of the oxidation of the thiosalt becomes low, and if the oxygen content inthe water is too high, the rate of the denitrification process becomes low. This embodimentimproves the control of the oxygen supply to the water and accordingly improves the efficiencyof the removal of the thiosalt and the nitrogen compounds in the water. The UV measurementis a measurement of the actual content of thiosalt and nitrogen compounds in the water. lf theUV absorption is high, the content of thiosalt and/or nitrogen compounds is high. lf the UVabsorption is low, the content of thiosalt and/or nitrogen compounds is low. By controlling thesupply of oxygen to the water such that the UV absorption of the thiosalt and nitrogencompounds is minimized, an optimal rate of removal of the thiosalt and nitrogen compounds isachieved.
    According to an embodiment of the invention, the UV absorption is preferably measured at awave length in a range of 190 - 225nm. The wave length of the maximum UV absorption ofthiosalt and nitrogen compounds, such as nitrate, nitrite and ammonium, is about 214nm. Byon-line-measuring in an interval around 214nm it is possible to decide whether the remainingcontent of thiosalt and nitrogen compounds in the purified water is minimized.
    According to an embodiment of the invention, the method comprises decreasing the supply ofoxygen if the measured UV absorption is high and the content of oxygen is high, e.g. above a limit value, increasing the supply of oxygen if the content of oxygen is low, e.g. below a limitvalue, and the UV absorption is high, and otherwise maintaining the oxygen supply. Bymeasuring the UV absorption in the purified water at a wave length close to the maximum UVabsorption of the thiosalt and nitrogen compounds, it is possible to decide whether the totalcontent of thiosalt and nitrogen compounds in the purified water is minimized. However, it isnot possible to decide which one of the thiosalt and nitrogen compounds remains, andaccordingly it is not possible to decide whether the oxygen supply is to be increased ordecreased. By measuring the oxygen content and comparing it with one or more limit values, itis possible to determine whether the oxygen content is too high or too low, and accordinglydetermine whether the oxygen content is to be increased or decreased. lf the oxygen content istoo low the rate of oxidation of the thiosalt is too slow, and if the oxygen content is high, therate of the nitrification is too slow. Thus, by adjusting the supply of oxygen to the water in thatway until the absorption is minimize, the rate of removal of the thiosalt and nitrogencompounds is optimized.
    According to an embodiment of the invention, the waste water is fed to a bioreactor and theUV absorption at a wave length close to the maximum UV absorption of the thiosalt andnitrogen compounds is measured in the waste water fed to the reactor as well as in the purifiedwater discharged from the reactor, and the supply of oxygen to the water is controlled independence of the ratio between the measured UV absorption of the feed and dischargedwater. This embodiment improves the measurement of the UV absorption, by minimizing theeffect of changes in background UV absorption from other species in the solution than thiosaltsand nitrogen compounds. For process control, it is preferred that the measured UV absorptionis on regular basis compared to measured concentration of thiosalts and nitrogen speciesdetermined by standard analytical procedures.
    According to an embodiment of the invention, the method comprises measuring the pH valuein the water and supplying a suitable pH regulator to the water to maintain the pH within arange 6 - 8, and preferably in the range of 6.5 - 7.5. To avoid further acidification downstreamin case of residual thiosalts and nitrogen species, the additional pH regulators such as sodiumcarbonate may be added to buffer the water before the purified water is discharged into thenature.
    According to another embodiment of the invention, the autotrophic denitrification process iscarried out by a Thiobacillius Denitrificans strain. Preferably, the autotrophic denitrificationprocess is preferably carried out by a psychrophilic or psychrotolerant strain of ThiobacilliusDenitrificans. Thiobacillius Denitrificans has been proven to be very suitable to carry out thisprocess since it is active close to O°C, producing biofilm and active sludge.
    Another object of the present invention is to provide an apparatus for simultaneous removal ofthiosalt and nitrogen compounds in waste water where the amount of thiosalt is larger than thestoichiometric demand for the nitrogen removal.
    This object is achieved with a method as defined in claim 10.
    The apparatus comprises a bioreactor including an autotrophic bacteria culture carrying out adenitrification process using the thiosalt as an electron donor, having an inlet for receiving thewaste water, and an outlet for discharging the purified water. The apparatus further comprisesan oxygen supply device arranged to supply oxygen to the water in the reactor and a controlunit arranged to control the content of dissolved oxygen in the reactor such that such that theexcess of thiosalt is oxidized by the oxygen at the same time as the denitrification process ismaintained.
    According to an embodiment of the invention, the apparatus further comprises a device formeasuring the content of dissolved oxygen in the reactor and a spectrometer arranged tomeasure the UV absorption in the purified water at a wave length close to the maximum UVabsorption of the thiosalt and nitrogen compounds, and the control unit is arranged to controlthe supply of oxygen to the water based on the measured UV absorption and the measuredoxygen content so that the measured UV absorption is minimized.
    According to an embodiment of the invention, the control unit is arranged to control the supplyof oxygen to the reactor by decreasing the supply of oxygen is if the measured UV absorption ishigh and the content of dissolved oxygen is above a limit value, and increasing the supply ofoxygen is if the UV absorption is high and the content of dissolved oxygen is below a limit value,and maintaining the present supply of oxygen is if the measured UV absorption is low.
    According to an embodiment of the invention, the apparatus comprises devices to retain thebiomass, e.g. biofilm carriers or/and downstream facilities to recover and recycle the biomass.
    The present invention also relates to the use of the method according to the invention and theapparatus according to the invention for treating waste water from mines and ore dressingplants. The invention is particularly suitable for treatment of waste water from mines and oredressing plants since the amount of thiosalt usually is significantly larger than the stoichiometricdemand for the nitrogen removal in waste water from mines and ore dressing plants.
    Brief description of the drawings The invention will now be explained more closely by the description of different embodimentsof the invention and with reference to the appended figures.
    Fig. 1 shows an apparatus for simultaneous removal ofthiosalt and nitrogen compounds inwaste water according to an embodiment of the invention.
    Fig. 2 shows a diagram with examples of UV measurements on waters including differentamounts of nitrate and thiosulphate ions.
    Detailed description of preferred embodiments of the invention ln the following an example is described on how the method according to the invention can beused to remove nitrogen species and thiosalt in waste water. ln this example, the thiosaltincludes thiosulfate and tetrathionate.
    The waste water is added to a reactor including an autotroph bacteria culture capable ofcarrying out a denitrification process. ln this example the bacteria culture is ThiobacilliusDenitrificans strain. Preferably, the autotrophic denitrification process is carried out by apsychrophilic or psychrotolerant strain of Thiobacillius Denitrificans, or a combination of both.Thiobacillius Denitrificans has been proven to be very suitable to carry out this process since itis active close to O°C, producing biofilm and active sludge. However, molecular phylogeny of theused culture has been investigated and it shows that other species are also present andidentified as being related to Lysobacter brunescens and but also to unknown species.
    The following reaction has been suggested to describe the stoichiometry when bacteria aregrowing: 0.844 S3032' + N03' + 0.347 C03 + 0.0865 C032' + 0.0865 NHÄ + 0.434 H30 (1)==> 0.0865 C3H703N + 0.5 N; + 1.689 S042' + 0.697 Hl Thus, the expected molar consumption ratio between 83032' and N03' is 0.844 when bacteriaare growing.
    As seen from formula 1 a carbon dioxide source should be added to the reactor is order tomaintain the reaction.
    The nitrification process can be carried out even when the biomass is not growing, due toenzymes which are active also without bacterial growth. The following reaction has beensuggested to describe the stoichiometry without bacterial growth: 5 S203” + s Nog + H20 ==> 10 S042- + 4N2 + 2 H* (2) Thus, the expected molar consumption ratio between 83032' and N03' is 0.625 without bacterialgrowths. However, in waste water from mines and ore dressing plants the molar ratio betweenthiosalt and nitrate often is significantly lager than the molar consumption ratio described with the above formulas 1 and 2. Typically, the molar ratio is in the interval of 10 - 20. Accordinglythere the amount of thiosalt in the waste water is significantly lager than the stoichiometricdemand for the nitrate removal. ln order to remove the excess of thiosalt oxygen is added to the water. The oxygen can beadded to the water, for example, by aeration or injection of oxygen gas.
    The thiosulfate and tetrathionate are oxidized by the added oxygen according to the followingstoichiometric reactions. szoå' + 2 oz + Hzo -> 2 sof' + 2 H* (s)S406” + 3.5 oz + 3 Hzo ==> 4 sof' + 6 H* (4) The oxidation converts the thiosulfate and tetrathionate into sulfuric acid. ln order to neutralizethe sulfuric acid, a pH regulator is added to the water. A suitable pH regulator is carbonate,such as CaC03. cof- + H* ==> Hcog (s)This is a part of the reaction described in formula 1.
    However, other carbon dioxide sources can be used to neutralize the produced acid, such asC02. An advantage with supplying carbonate is that besides the neutralizing effect, it becomes acarbon dioxide source for maintaining the reaction described in formula 1 above. lt is alsopossible to use other types of pH regulators, such as Na0H in combination with carbon dioxidesupply. At low biomass growth rate, the carbon dioxide supplied by added air may be sufficient.Typically, air contains 300 - 400ppm C02.
    The pH in the water is controlled so that it is maintained within a range of 6 - 8, and morepreferably within the range of 6.5 - 7.5. The method may comprise the steps of measuring thepH value in the water, and supplying additional alkali or acid (compared to the stoichiometricdemand) if the feed water is too acidic or too alkaline in order to obtain the optimal pH forprocess.
    The content of dissolved oxygen in the water is controlled such that the excess of thiosalt isoxidized by the oxygen at the same time as the denitrification process, as described by formula1, is maintained. Experimental work has shown that the content of dissolved oxygen iscontrolled so that it preferably is kept within a range of 0.3 - 1mg/l, and more preferably is keptwithin a range of 0.35 - 0.6mg/l. However, the content of dissolved oxygen which leads to theceasing of the denitrification process may vary due to the water content and other conditionssuch as the reactor design with respect to fluid dynamics etc. Preferably, the content of dissolved oxygen which leads to ceasing of the denitrification process is determined for thecurrent water by experiments and optimization.
    Figure 1 shows an example of an apparatus for simultaneous removal of thiosalt and nitrogencompounds in waste water according to the invention. The apparatus includes a reactor 1 in theform of a vessel including an autotrophic bacteria culture capable of carrying out adenitrification process using thiosalt as an electron donor. ln this embodiment ofthe invention,the reactor is a moving bed bio reactor (MBBR) which includes biofilm carriers 5. By usage ofthe MBBR technique, only one reactor is needed.
    The apparatus has an inlet 3 for receiving waste water, and an outlet 4 for discharging thepurified water. The apparatus comprises an oxygen supply device 6 arranged to supply oxygenor air to the water in the reactor. The oxygen supply device 6 includes air spargers 7 arranged inthe bottom of the reactor and a device 8 for adjusting the oxygen supply to the reactor, such asa valve. However, the air sparger may also be installed at a higher level. The apparatus furtherincludes a control unit 10 arranged to control the content of dissolved oxygen in the reactorsuch that the excess of thiosalt is oxidized by the oxygen at the same time as the denitrificationprocess is maintained. Preferably, several probes for measuring dissolved oxygen are installedat different levels to monitor the dissolved oxygen profile in the reactor. The control unit 10 is,for example, a computer or any other programmable logical device suitable for controlling theprocess.
    To achieve a high rate of the removal of both thiosalt and nitrogen compounds, it is importantthat the control of the oxygen supply is optimized. lf the oxygen content in the water is too low,the rate of the oxidation of the thiosalt becomes low, and if the oxygen content in the water istoo high, the rate of the denitrification process becomes low.
    The apparatus comprises a measuring device 12, such as a D.O. probe, for measuring thecontent of dissolved oxygen in the reactor. The measuring device 10 is connected to the controlunit 10. The control unit 10 is adapted to receive the measurements of the oxygen content inthe reactor and to control the supply of oxygen to the reactor by controlling the valve 8. Theapparatus further comprises a spectrometer 14 arranged to measurer the UV absorption in thepurified water at the outlet 4 of the reactor. The UV absorption is measured at a wave lengthclose to the maximum UV absorption of the thiosalt and nitrogen compounds, i.e. at a wavelength close to 214nm. The spectrometer 14 is connected to the control unit 10. The controlunit 10 is arranged to receive the measurements of the UV absorption from the spectrometer14 and to control the supply of oxygen to the water based on the measured UV absorption andthe measured oxygen content so that the measured UV absorption is minimized. The UVmeasurement is a measurement of the actual content of thiosalt and nitrogen compounds in the water. lf the UV absorption is high, the content of thiosalt and/or nitrogen compounds ishigh. lf the UV absorption is low, the content of thiosalt and/or nitrogen compounds is low. Byon-line-measuring in an interval around 214nm it is possible to decide whether the remainingcontent of thiosalt and nitrogen compounds in the purified water is minimized.
    Figure 2 shows examples of UV measurements on four different solutions. A first solutioncontains 1 mg NOg-/l and a second solution contains 20mg NO3'/l. From the diagram it is shownthat the UV absorption is significantly lower in the solution containing 1mg NO3'/l than in thesolution containing 20mg NOg-/L The UV absorption in the solution containing 20 mg NO3'/l hasa peak in the wavelength between 200 - 220 nm. A third solution contains 5mg S2O32'/l and afourth solution contains 50mg SZOf/l. From the diagram it is shown that the UV absorption issignificantly lower in the solution containing 5mg S2O32'/l than in the solution containing 50mgSZOf/l. The UV absorption in the solution containing 50mg SZOf/l has a peak in thewavelength between 210 - 220nm.
    However, since both nitrate and thiosulphate have a peak at about 214nm it is not possible todecide from the UV measurements which one of the thiosalt and nitrogen compounds remains,and accordingly it is not possible to decide whether the oxygen supply is to be increased ordecreased. ln order to be able to decide whether the oxygen supply is to be increased ordecreased the amount of dissolved oxygen in the water is measured. By comparing themeasured oxygen content with a limit value, it is possible to determine whether the oxygencontent is too high or too low, and accordingly to determine whether the oxygen content is tobe increased or decreased. lf the oxygen content is too low the rate of oxidation of the thiosaltis too slow, and if the oxygen content is high, the rate of the nitrification is too slow.
    The control unit 10 is arranged to control the supply of oxygen to the reactor by decreasing thesupply of oxygen is if the measured UV absorption is high, i.e. above a first limit value, and themeasured content of dissolved oxygen is above a second limit value, and increasing the supplyof oxygen is if the UV absorption is high and the content of dissolved oxygen is below thesecond limit value, and maintaining the present supply of oxygen is if the measured UVabsorption is low, i.e. below the first limit value. By adjusting the supply of oxygen to the waterin that way until the absorption is minimize, the rate of removal of the thiosalt and nitrogencompounds is optimized.
    The table below shows an example of control of the oxygen supply based on measured UVabsorption and measured dissolved oxygen content in the water. 11 UV absorption Oxygen content Action Decrease oxygen supply as long More than 0,5 More than 0.4mg/l as the UV absorption decreases Increase oxygen supply as long More than 0,5 Less than 0.4mg/l as the UV absorption decreases Maintain the oxygen supply aslong as the UV absorption islow and stable Less than 0,5 Independent The control unit 10 includes a UV controller adapted to control the UV absorption in thereactor. The control of the oxygen supply is, for example, done by setting a desired value forthe UV absorption as a control point for the UV regulator. The content of dissolved oxygen inthe reactor becomes an operating range for the UV controller, in which the UV controllersearches for an optimal oxygen supply. The oxygen supply is reduced if the oxygen content inthe water is high, and the oxygen supply is increased if the oxygen content in the water is low.Thus, the oxygen supply is tuned within the operating range in dependence on the UVresponse. ln this embodiment of the invention, the UV absorption at a wave length close to the maximumUV absorption of the thiosalt and nitrogen compounds is also measured in the waste water fedto the reactor. The apparatus comprises a second spectrometer 16 arranged to measurer theUV absorption in the water at the inlet 4 of the reactor. The second spectrometer 16 isconnected to the control unit 10, and the control unit 10 is arranged to receive themeasurements of the UV absorption from the first and second spectrometers and to controlthe supply of oxygen to the water based on the ratio between the measured UV absorption ofthe feed and discharged water. This improves the measurement of the UV absorption, byminimizing the effect of changes in background UV absorption from other species in thesolution than thiosalts and nitrogen compounds. For process control, it is preferred that themeasured UV absorption is on regular basis compared to measured concentration of thiosaltsand nitrogen species determined by standard analytical procedures.
    The apparatus further comprises a pH control device adapted measure the pH level in thereactor, and to control the pH level in the reactor by supplying a suitable pH regulator to thewater in order to maintain a neutral pH value. The pH-control device includes a pH measuringdevice, such as a pH electrode 18, a source of pH regulator, a device 20 for adjusting the oxygensupply to the reactor, such as a valve 22 connected to the source of pH regulator, and a 12 controller adapted to determine the amount of pH regulator to be supplied to the reactor inorder to maintain a neutral pH value in the reactor. Preferably, the pH in the reactor iscontrolled within a range 6 - 8, and preferably in the range of 6.5 - 7.5. ln this example, the pHregulator is sodium carbonate (NazCOg), which also functions as a C02 source. Alternatively, 5 carbon dioxide (C02) in combination with sodium hydroxide (NaOH) or lime can be supplied tothe water. ln the embodiment disclosed in figure 1, the pH controller is implemented in thesame control unit 10 as the control the supply of oxygen to the reactor. ln an alternativeembodiment a separate pH controller can be implemented.
    The apparatus may downstream contain a device for recycling biomass to the bioreactor. 10 The nitrogen and thiosalt removal rate of the process depends on the temperature in thereactor. The process has been proven to work within a temperature interval of 0-20°C.However, the removal rate is higher at a temperature close to 20°C than close to 0°C. lt is likelythat other strains can be found to demonstrate the process at higher temperatures. 15 The following four examples show tests during different conditions and the test results. A Pilotscale 1-stage with 500 liter reactor volume and 60 % filling volume of Biocarrier-Anox KaldnesKl is used in all examples. HRT stands for the hydraulic retention time.
    Example 1 Process conditionsTem rature Aeration D.O°C YES/No mg oz/i1.5 YES 0.60 Feed anal esNH.. N02' 52032' 54062'm m m m1.13 5.92 119.7 0.00Residual anal esNH.. N02' S203 S406m m m m2.67 2.8Removal N02' S203 + + 2- 2- + 2- Nog' N H4% % % %98.9 96.2 54.9 20 Molar ratio S2O32'/NO3' removal = 2.46 13 Low temperature, balanced oxygen supply ==> high removal rate of both thiosalts and nitrate The first example shows that no accumulation of nitrite occurs at optimal conditions.
    Example 2 Process conditionsTem rature Aeration D.O°C YE5/N0 mg 04/|3.1 YES 0.19 Feed anal esN06' NH4 N04' 54062' 54062'm m m m m 61.6 2.52 7.6 270.3 5.02Residual anal es N04' 54062' 54062' + + N06' N H4m m m m mo. 24 0.91 o. 39 102. 5 2. 32Removal N04' 54062' 54062' % % % % % 99.6 63.9 94.9 62.1 53.8 + N06' NH4 Molar ratio S2O32'/NO3' removal = 1.51 5 Low temperature, low oxygen supply ==> low D.O ==> low residual concentration of nitrate andnitrite, but high residual concentration of thiosalts Example 3 Process conditions rature°c4.6 Tem Feed anal esN03' NH4 N02'm m m68 2.42 4.1Residual anal esN03' NH4 N02'm m m16.40 0.95 4.84RemovalN03' NH4 N02'% % %75.9 60.7 + + + Molar ratio S2032'/N03' removal = 1.69 Minor formation 14 AerationYES/N0YES 52032' m265. 5 52032'm107.8 52032'%59.4 Low temperature, low retention time, balanced oxygen supply ==> lowering the removal of thiosalts and nitrate. Minor accumulation of nitrite occurs.
    Example4 Process conditionsTem rature Aeration°C YES/No13 YES Feed anal esNog NH. No¿ goå'm m m m 48.3 5.01 9.11 152.0Residual anal es No¿ gof' + + N03' NH4m m m m2.10 3.48 9. 83 4.6RemovalN02'% % %95.7 30.5 Minor formation + Nog NH.
    Molar ratio SzOgzi/NOg' removal = 1.77 Medium temperature, balanced oxygen supply => high removal rate of both thiosalts andnitrate. Minor accumulation of nitrite occurs.
    With a method according to the invention, the removal of thiosalt and nitrogen compounds inwaste water is made in one step by a balanced oxygen supply.
    The present invention is not limited to the embodiments disclosed but may be varied andmodified within the scope of the following claims. For example, the method is not limited toMBBR technology. Other methods such as activated sludge process and fix bed reactor are alsoapplicable in order to retain and to control the biomass concentration in the system.
    权利要求:
    Claims (16)
    [1] 1. A method for simultaneous removal of thiosalt and nitrogen compounds in waste waterwith an autotrophic denitrification process using the thiosalt as an electron donor,wherein the amount of thiosalt in the waste water is larger than the stoichiometricdemand for the autotrophic nitrogen removal, characterized in that the methodcomprises supplying oxygen to the water and controlling the content of dissolvedoxygen in the water such that the excess of thiosalt is oxidized by the oxygen at thesame time as the denitrification process is maintained.
    [2] 2. The method according to claim 1, wherein the content of dissolved oxygen is controlledso that it is kept within a range of 0.3 - 1mg/l.
    [3] 3. The method according to claim 1, wherein the content of dissolved oxygen is controlledso that it is kept within a range of 0.35 - O.6mg/l.
    [4] 4. The method according to any of the previous claims, wherein the method comprises: - measuring the UV absorption in the water at a wave length close to the Maximum UVabsorption of the thiosalt and nitrogen compounds, - measuring the content of dissolved oxygen in the water, and - controlling the supply of oxygen to the water based on the measured UV absorptionand the measured oxygen content so that the measured UV absorption is minimized.
    [5] 5. The method according to claim 4, wherein the UV absorption is measured at a wavelength in a range of 190 - 225nm.
    [6] 6. The method according to claim 4 or 5, wherein the method comprises: - decreasing the supply of oxygen if the measured UV absorption is high and thecontent of oxygen is high, - increasing the supply of oxygen if the UV absorption is high and the content of oxygenlow, and - otherwise maintaining the oxygen supply.
    [7] 7. The method according to any of the claims 4 - 6, wherein the waste water is fed to abioreactor and the UV absorption at a wave length close to the maximum UV absorptionof the thiosalt and nitrogen compounds is measured in the waste water fed to thereactor as well as in the purified water discharged from the reactor, and the supply of
    [8] 8.
    [9] 9.
    [10] 10.
    [11] 11.
    [12] 12.
    [13] 13. 17 oxygen to the water is controlled in dependence of the ratio between the measured UVabsorption of the feed and discharged water. The method according to any of the previous claims, wherein the method comprisesmeasuring the pH value in the water and supplying a suitable pH regulator to the waterto maintain the pH within a range 6 - 8, and preferably in the range of 6,5 - 7,5. The method according to claim 1, wherein the autotrophic denitrification process iscarried out by a culture containing a psychrophilic and/or psychrotolerant ThiobacilliusDenitrificans strain. An apparatus for simultaneous removal of thiosalt and nitrogen compounds in wastewater, wherein the amount of thiosalt in the waste water is lager than thestoichiometric demand for the autotrophic nitrogen removal, the apparatus comprises abioreactor (1) including an autotrophic bacteria culture carrying out a denitrificationprocess using the thiosalt as an electron donor, having an inlet (3) for receiving thewaste water, and an outlet (4) for discharging the purified water, characterized in thatthe apparatus comprises an oxygen supply device (7) arranged to supply oxygen to thewater in the reactor and a control unit (10) arranged to control the content of dissolvedoxygen in the reactor such that the excess of thiosalt is oxidized by the oxygen at thesame time as the denitrification process is maintained. The apparatus according to claim 10, wherein control unit (10) is arranged to control thecontent of dissolved oxygen in the reactor so that it is kept within a range of 0.3 -1mg/l, preferably within a range of 0.35 - 0.6mg/l. The apparatus according to claim 10 or 11, wherein the apparatus comprises a device(12) for measuring the content of dissolved oxygen in the reactor (1) and a device(14,16) arranged to measurer the UV absorption in the purified water at a wave lengthclose to the Maximum UV absorption of the thiosalt and nitrogen compounds, and thecontrol unit (10) is arranged to control the supply of oxygen to the water based on themeasured UV absorption and the measured oxygen content so that the measured UVabsorption is minimized. The apparatus according to claim 12, wherein the control unit (10) is arranged to controlthe supply of oxygen to the reactor by decreasing the supply of oxygen if the measuredUV absorption is high and the content of dissolved oxygen is high, and increasing the
    [14] 14.
    [15] 15.
    [16] 16. 18 supply of oxygen if the UV absorption is high and the content of dissolved oxygen is low,and maintaining the present supply of oxygen is if the measured UV absorption is low. The apparatus according to any of the claims 10 - 13, wherein the apparatus comprises apH-control device (10,18,22) adapted measure the pH level in the reactor and to controlthe pH level in the reactor by supplying a suitable pH regulator to the water to maintainthe pH within a range 6 - 8, and preferably in the range of 6,5 - 7,5. The apparatus according to any ofthe claims 10 - 14, wherein the bioreactor (1) is amoving bed bio reactor which includes biofilm carriers (5). Use of the method according to any of the claims 1 - 9 and the apparatus according toany of the claims 10 - 15 for treating waste water from mines and ore dressing plants.
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    同族专利:
    公开号 | 公开日
    EP2900608A1|2015-08-05|
    SE536972C2|2014-11-18|
    CA2881911A1|2014-04-03|
    FI127135B|2017-12-15|
    US20150251937A1|2015-09-10|
    FI20155210A|2015-03-24|
    WO2014048844A1|2014-04-03|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    FR2921917B1|2007-10-09|2011-04-08|Degremont|METHOD AND PLANT FOR TREATING EFFLUENTS CONTAINING NITROGEN IN A SEQUENTIAL BIOLOGICAL REACTOR|
    FR2962051B1|2010-07-02|2015-01-16|Suez Environnement|METHOD FOR REMOVING THE POLLUTION OF A CHARGED GAS OF HYDROGEN SULFIDE AND AMMONIA, AND INSTALLATION FOR CARRYING OUT SAID METHOD|CN110818093A|2019-11-04|2020-02-21|北京恩菲环保技术有限公司|Method for culturing obligate denitrobacillus|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    SE1251085A|SE536972C2|2012-09-25|2012-09-25|A method and apparatus for the simultaneous removal of thiosalt and nitrogen compounds in wastewater|SE1251085A| SE536972C2|2012-09-25|2012-09-25|A method and apparatus for the simultaneous removal of thiosalt and nitrogen compounds in wastewater|
    EP13773647.6A| EP2900608A1|2012-09-25|2013-09-20|A method and an apparatus for simultaneous removal of thiosalt and nitrogen compounds in waste water|
    CA 2881911| CA2881911A1|2012-09-25|2013-09-20|A method and an apparatus for simultaneous removal of thiosalt and nitrogen compounds in waste water|
    US14/430,916| US20150251937A1|2012-09-25|2013-09-20|Method and an apparatus for simultaneous removal of thiosalts and nitrogen compounds in waste water|
    PCT/EP2013/069541| WO2014048844A1|2012-09-25|2013-09-20|A method and an apparatus for simultaneous removal of thiosalt and nitrogen compounds in waste water|
    FI20155210A| FI127135B|2012-09-25|2015-03-24|A method and apparatus for the simultaneous removal of thiosalt and nitrogen compounds in wastewater|
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