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Merle de KREUK, et al.

Waste Water Treatment

Eurekalert.com

26-Jun-2006

Contact: Frank Nuijens, Science Information [email protected] University of Technology

Delft Water-Purification Method Promises Radical Improvement

Delft University of Technology research has discovered a method that could drastically change the waywe purify water within a few years. Delft, in partnership with DHV engineering bureau, has developed acompact and environmentally-friendly purification method, in which aerobic bacteria form granules that

sink quickly. An important part of the project's success was the work of Delft researcher Merle deKreuk, who, on Tuesday, 27 June, will receive her PhD degree based on this research subject.

With the new aerobic granular sludge technology (Nereda TM), aerobic (thus oxygen using) bacterialgranules are formed in the water that is to be purified. The great advantage of these granules is thatthey sink quickly and that all the required biological purifying processes occur within thesegranules.

The technology therefore offers important advantages when compared to conventional water purificationprocesses. For example, all the processes can occur in one reactor. Moreover, there is no need to uselarge re-sinking tanks, such as those used for conventional purification. Such large tanks are needed forthis because the bacteria clusters that are formed take much longer to sink than the aerobic granulesludge.

According to Delft PhD researcher Merle de Kreuk, a Nereda TM purification installation needs only aquarter of the space required by conventional installations. Moreover, Nereda TM uses 30% lessenergy than the normal purification process. This Nereda TM purification process is suitable for bothdomestic and industrial waste water.

Delft University of Technology has a long tradition in researching the possibilities of water purificationwith aerobic granular sludge. The maturation of the technology is largely due to the research conductedby De Kreuk. During her PhD research with Prof. Mark van Loosdrecht, De Kreuk working togetherwith DHV engineering bureau and supported by STOWA and STW grants solved varioustechnological bottlenecks and expanded the capacity of the test installation from 3 litres per hour to1,500 litres per hour. DHV now has the final design, which is ready for practical implementation.

The aerobic granular sludge technology is very promising, and has been nominated for the DutchProcess Innovation Award 2006. The technology is now in the commercialisation phase. In the coming

Page 1 of 13Delft University -- Loosdrecht, et al -- water purifaction method

06.01.2010http://www.rexresearch.com/dekreuk/dekreuk.htm


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years, De Kreuk will continue to contribute to the project's trajectory as a Delft researcher. DHV iscurrently negotiating with water purification companies to test this purification method on a larger scale.The first installations are already in use in the industrial sector.

US 2006032815Method for the Treatment of Waste Water with Sludge Granules

2006-02-16VAN LOOSDRECHT MARINUS C (NL); KREUK MERLE K D (NL)Applicant: STICHTING VOOR DE TECH (NL)Also published as: WO2004024638 // EP1542932 // CN1705618 // CA2498747 / AU2003271227 (A1)

Abstract: The invention relates to a method for the treatment of waste water comprising an organicnutrient. According to the invention, the waste water is in a first step fed to sludge granules, after thesupply of the waste water to be treated the sludge granules are fluidised in the presence of an oxygen-comprising gas, and in a third step, the sludge granules are allowed to settle in a settling step. Thismakes it possible to effectively remove not only organic nutrients but optionally also nitrogen

compounds and phosphate.

US 6,566,119

Method for Acquiring Grain-Shaped Growth of a Microorganism in a Reactor

2003-05-20HEIJNEN JOSEPH JOHANNES (NL); VAN LOOSDRECHT MARINUS CORNELI (NL)Applicant: UNIV DELFT TECH (NL)Also published as: WO9837027 / EP0964831 / EP0964831 / EP0964831 / NL1005345C (C2)




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Abstract: The invention relates to a method of acquiring granular growth of a microorganism in areactor containing a liquid medium. Surprisingly, according to the invention, aerobic microorganismsalso can be induced to granular growth by maintaining specific culture conditions. During a first step anoxygen-containing gas is supplied and the reactor contents are kept in turbulence. In a second step, after

a short settling period, the top part of the reactor medium is discharged.

Description

FIELD OF THE INVENTION

The present invention relates to a method of acquiring granular growth of a microorganism in a reactorcontaining a liquid phase which comprises a substrate, wherein in a first step said substrate is convertedby the microorganism resulting in the formation of and growth on a phase comprising the organismwhile the liquid phase is being mixed, in a second step mixing in the reactor is stopped to allow part ofthe solid phase to settle, and in a third step the reactor is partly emptied by discharging the top part of thereactor contents, which reactor is subsequently replenished with substrate-comprising liquid, to repeatsteps 1 to 3.

BACKGROUND OF THE INVENTION

Such a method has been described by Sung S. et al. (Laboratory studies of the anaerobic sequencingbatch reactor, in Water Environment Research, 67 (3), p. 294, 1995). In this method an anaerobicconversion is carried out, the contents of the reactor are then clarified in characteristically 10-30 minutesafter which the top part of the reactor contents is discharged. According to this publication work withanaerobically activated sludge has long been known, although it was not recognized in the beginning(1966) that what was occurring was "granulation" of the biomass. Granulation under methanogenicconditions (that is to say in the absence of oxygen) is often explained by the specific need of therespective organisms to exchange substrates the so-called "interspecies hydrogen transfer", or to reducethe toxicity of oxygen.

SUMMARY OF THE INVENTION

Surprisingly, applicant has found that granulation can also occur under aerobic and turbulent conditions.




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The method according to the invention is therefore characterized in that the microorganism is an aerobicmicroorganism, in that at least during the first step a third phase is present, which third phase comprisesoxygen-containing gas being fed to the reactor during the first step while the contents of the reactor arekept in turbulence, and in that settling occurs in the second step and takes less time than the height ofliquid in the reactor at the end of the first step divided by a settling velocity of at least 5 meters per hour.

The formation of granules under turbulent aerobic conditions is unexpected, because organisms in agranule are under very great stress as due to the size of the granule, nutrients have to diffuse over largedistances before reaching the interior of a granule. The fact that in addition aerobic organisms requireoxygen, increases the stress still more so that one would expect such aerobic organisms only toflocculate. In addition, the expert would expect the granules to disintegrate due to the great shearingforces caused by the turbulence.

In the present application an aerobic microorganism is understood to be both an obligate and afacultative aerobic microorganism.

Preferably the compound is fed to the reactor in pulses. This causes the organisms in a granule to beflooded with compound. As the organisms at the outside of the granule are unable to process such asupply of compound, the compound gets the opportunity to diffuse into the interior of the granule. Thisis especially important if the compound to be converted is a nutrient. An example of this is carbohydratefermentation for the preparation of lactic acid.

In accordance with a favourable embodiment the contents of the reactor are substantially continuouslymixed during the first step.

To promote the formation of aggregates, Sung et al. prefer periodical mixing during which only slightshearing forces occur. According to the invention, however, continuous turbulent mixing subjects flocsto mixing forces, allowing them to be discharged more easily in the third step. In addition, applicant hasestablished by experimentation that if microorganisms are subjected to great shearing forces, the result isa more robust granule. Thus according to the invention the organisms in the reactor form into granulesmore quickly.

Turbulent mixing is conveniently carried out by feeding oxygen-containing gas into, for instance, anairlift-reactor or bubbling-bed reactor.

An interesting application of the method according to the invention is characterized in that theconversion is a nitrification-denitrification-conversion in which the oxygen-containing gas is onlysupplied during the first part of the first step for the completion of the nitrification, and that the reactoroperates during the remainder of the first step under substantially anaerobic conditions for thecompletion of the denitrification. If desired, the gas may during this first step be recirculated over thereactor. Due to recirculation all oxygen is used up and turbulence is maintained.

When applying the method according to the invention, the organism-comprising granules must be

present, or at least conditions promoting the formation of granules must be provided before starting upthe reactor. It is useful, for instance, to feed the reactor with carrier particles to which organisms adhere,or are able to adhere. It has been shown that a mycelium-forming fungus can also be used as carrier.

According to a very favourable embodiment settling occurs in the second step, taking less time than theheight of liquid in the reactor at the end of the first step divided by a settling velocity of at least 10meters per hour, preferably at least 15 meters per hour. Thus the presence of granules in the reactor isstrongly favoured in comparison with the presence of flocs. As mentioned above, Sung et al. describe aclarification step taking characteristically 10 to 30 minutes. The settling velocity is then only 1 meter perhour, and applied to aerobic organisms such a method will not result in granulation. While underanaerobic conditions the clarification step merely serves to separate organisms and treated water, is alsothe clarification step in the method according to the invention of essential importance for the induction

of granulation.

BRIEF DESCRIPTION OF THE DRAWINGS




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The invention will now be explained with reference to an exemplary embodiment and with reference tothe drawing, in which

FIG. 1 is a graphical representation of the carbon dioxide percentage in gas discharged from a bubbling-bed reactor during a cycle of the method according to the invention; and

FIG. 2 is an illustration of a granule composed of aerobic organisms.

EXAMPLE 1

A bubbling-bed reactor (2.5 liters; height/diameter 20) was fed with 1.25 liters of a solution serving asmodel for waste water, comprising 8.7 mM ethanol, 5 mM ammonium chloride, 4.7 mM potassiumphosphate, 2.4 mM magnesium sulphate, 0.48 calcium chloride and per liter solution 1.5 ml of astandard solution of trace elements. The solution was inoculated with aerobically active sludge from awater treatment plant. The model waste water in the bubbling bed reactor was subjected to a cyclictreatment at pH 6-8 and a temperature of 20.degree. C. The treatment consisted of i) aerating for 4 hoursat a flow rate of 1.5 liters air per minute (FIG. 1 shows the carbon dioxide percentage in the gasdischarged from a bubbling-bed reactor during this phase. This percentage is a measure of theconversion of the ethanol), ii) the one-minute stoppage of aeration, and iii) draining model waste waterfrom the bubbling-bed reactor at the half-way point of the column of liquid. Any biomass present duringdraining in the top half of the solution, was discharged together with the effluent. Finally, iv) thebubbling-bed reactor was replenished with a volume of model waste water equal to that of thedischarged effluent. The cycle was then resumed with four hours aeration of the solution.

FIG. 2 shows the granules comprised of aerobic microorganisms, obtained by the method according tothe invention. The average size is 3 mm.

US 6,183,642Biological Treatment of Wastewater

2001-02-06HEIJNEN JOSEPH JOHANNES (NL); VAN LOOSDRECHT MARINUS CORNELI (NL)Applicant: GRONTMIJ ADVIES & TECHNIEK BV (US)




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Abstract: A method is described for the biological treatment of ammonium-rich wastewater in at leastone reactor which has a temperature of at least 25 DEG C., which involves the wastewater being passedthrough the said reactor(s) with a population, obtained by natural selection in the absence of sludgeretention, in the suspended state of nitrifying and denitrifying bacteria to form, in a first stage with theinfeed of oxygen, a nitrite-rich wastewater and by the nitrite-rich wastewater thus obtained beingsubjected, in a second stage without the infeed of oxygen, to denitrification in the presence of an electon

donor of inorganic or organic nature, in such a way that the contact time between the ammonium-richwastewater and the nitrifying bacteria is at most about two days, and the pH of the medium is controlledbetween 6.0 and 8.5 and the excess, formed by growth, of nitrifying and denitrifying bacteria and theeffluent formed by the denitrification are extracted. In addition the growth rate of the nitrifying anddenitrifying bacteria is expediently controlled by means of the retention time, in the reactor, of thewastewater to be treated which is fed in.

US 5,863,435Biological Treatment of Wastewater

1999-01-26HEIJNEN JOSEPH JOHANNES (NL); VAN LOOSDRECHT MARINUS CORNELI (NL)Applicant: GRONTMIJ ADVIES & TECHNIEK BV (NL)Also published as: EP0826639 / EP0826639 / NL1003866C (C2)




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Abstract: A method is described for the biological treatment of ammonium-rich wastewater in at leastone reactor which has a temperature of at least 25 DEG C., which involves the wastewater being passedthrough the said reactor(s) with a population, obtained by natural selection in the absence of sludgeretention, in the suspended state of nitrifying and denitrifying bacteria to form, in a first stage with theinfeed of oxygen, a nitrite-rich wastewater and by the nitrite-rich wastewater thus obtained beingsubjected, if required, in a second stage without the infeed of oxygen, to denitrification in the presence

of a carbon source such as methanol, in such a way that the contact time between the ammonium-richwastewater and the nitrifying bacteria is at most about two days, and the pH of the medium is controlledbetween 6.5 and 8.5 by the infeed of the said carbon source, and the excess, formed by growth, ofnitrifying and denitrifying bacteria and the effluent formed by the denitrification are extracted, thedemand for the said carbon source during the treatment being controlled as a function of the amount ofheat produced in the reactor. In addition the growth rate of the nitrifying and denitrifying bacteria isexpediently controlled by means of the retention time, in the reactor, of the wastewater to be treatedwhich is fed in.

Description

BACKGROUND OF THE INVENTION

The invention relates to a method for the biological treatment of ammonium-rich wastewater in at leastone reactor which has a temperature of at least 25.degree. C., by the wastewater being passed through




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the said reactor(s) with a population, obtained by natural selection in the absence of sludge retention, inthe suspended state of nitrifying and denitrifying bacteria to form, in a first stage with the infeed ofoxygen, a nitrite-rich wastewater and by the nitrite-rich wastewater thus obtained being subjected, ifrequired, in a second stage without the infeed of oxygen, to denitrification in the presence of a carbonsource such as methanol, in such a way that the retention time of the ammonium-rich wastewater is atmost about three days, and the pH of the medium is controlled between 6.5 and 8.5 by the infeed of thesaid carbon source, and the excess, formed by growth, of nitrifying and denitrifying bacteria and the

effluent formed by the denitrification are extracted.

Such a method is known from a publication in Delft Outlook, 95.2, pp. 14-17. However, the researchreported in this publication was carried out on a laboratory scale and does not provide any suggestionwhatsoever on the measures required for using such a process in practice to achieve adequate cleaning ofthe wastewater in question.

As a result of discharge standards having become more stringent, in particular for nitrogen, there is aneed for efficient, cost-effective purification systems for the treatment of wastewater. Examples of theseconcentrated industrial wastewater streams are, wastewater streams like those released with off-gastreatment etc. Another example of the concentrated nitrogen-rich wastewater stream is the so-calledrejection water. This rejection water stream is formed after dewatering of fully digested sewage sludgeand has not only a high ammonium concentration (about 1000 mg of NH.sub.4 -N per litre) but also ahigh temperature (usually about 30.degree. C.). The ammonium in the rejection water may account foras much as 15% of the total nitrogen loading of a wastewater treatment installation, while the volumeflow of the rejection water is only less than 1% of the wastewater volume flow to be processed. Thisrejection water therefore makes a considerable contribution to the nitrogen loading of the treatmentinstallation.

The biological treatment of such wastewater streams normally makes use of treatment processes inwhich the high sludge concentrations required are obtained by employing a form of sludge retentionsuch as settling, membrane filtration, attachment to filter media, etc. In that context it is worth drawingattention to the STOWA report 95-08, which relates to the treatment of nitrogen-rich return streams insewage plants, and to the Proc. 18th IAWQ Biennial, Water Quality International '96, 23-28 June 1996,Singapore, pp. 321-328.

An, as it happens, frequently used treatment process is known as the activated-sludge system. Such asystem is characterized on the one hand by employing sludge retention by sludge settling and, on theother hand, by the bacteria mainly being present in so-called activated-sludge flocculae. Such flocculaeusually have a size of 0.1-2 mm.

SUMMARY OF THE INVENTION

It should be noted that the present process of biological nitrogen removal preferably proceeds in twosuccessive stages, an aerobic and an anoxic stage. Both stages can, in the present invention, take place inone reactor, separated in time, or in separate reactors which may or may not involve a return stream tothe first stage. In the first stage the nitrogen present as ammonium is largely converted into nitrite, with

the aid of oxygen and nitrifying bacteria. The second stage comprises the conversion of nitrite intomolecular nitrogen, said conversion being anoxic and taking place with the aid of denitrifying bacteria.These denitrifying bacteria require a carbon source such as methanol, to carry out the said conversion.

We have now found, surprisingly, that the method as set forth in the preamble can be carried out on anindustrial scale, with an ammonium removal efficiency of more than 90% being achieved, by controllingthe demand of the denitrifying bacteria for a carbon source, in this case methanol.

More in particular we have found that the methanol demand during the treatment can be controlled as afunction of the amount of heat produced in the reactor. These parameters proved to be directlyproportional to one another. As will be explained hereinafter, the pH of the medium is controlled at thesame time by means of the methanol being metered.

It should be noted that during the nitrification two moles of protons are produced per oxidized mole ofammonium. The pH drops as a result. The pH is usually controlled by feeding alkali and/or acid into thereactor. During denitrification, on the other hand, protons are consumed. Denitrification furthermore




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takes place under anoxic conditions, nitrite being used as an electron acceptor. For denitrification to bepossible, the presence of not only an electron acceptor, but also of an electron donor is required.Methanol, for example, is indeed added at the same time in the present process as an electron donor.

In addition, the following may be noted with respect to the present process. For the purpose of nitrogenremoval, the ammonium present in the wastewater is not nitrified to nitrate but only to nitrite. Indeed,the term of nitritifying bacteria is sometimes used, to indicate more clearly that what takes place

predominantly is the formation of nitrite. The denitrifying bacteria which are capable of anoxicconversion of both the nitrate and the nitrite into molecular nitrogen, consume a carbon source such asmethanol, as explained above. The conversion of nitrite into molecular nitrogen requires on its own,however, about 40% less methanol than the conversion of nitrate into nitrogen. Moreover, the oxidationof nitrite to nitrate costs oxygen. Indeed, direct conversion of nitrite into nitrogen provides another(approximately) 25% savings on the oxygen account. The conversion via nitrite instead of nitrate istherefore very advantageous in economic terms.

If, under certain circumstances, the conversion via nitrate is more attractive, however, than theconversion via nitrite, this can obviously be achieved by extending the retention time, of the wastewaterto be treated, in the present process.

In an expedient variation of the present process in addition the growth rate of the nitrifying anddenitrifying bacteria is controlled by means of the retention time, in the reactor, of the wastewater to betreated which is fed in. This retention time is an important parameter, since the stability of the nitrifyingprocess may be put at risk as a result of the maximum growth rate of the biomass decreasing as thetemperature decreases. This therefore requires a higher temperature than with known, more conventionalprocesses. In practical trials the influent of the reactor was found to have a temperature of 30.degree. C.The biological conversion such as the nitrification will cause the temperature to rise by about 15.degree.C. per gram of nitrogen per litre removed. Increasing the process control temperature beyond 40.degree.C., however, is not advantageous to the stability of the present process. By controlling the amount to befed in of wastewater to be treated it is therefore possible to control the growth rate of the biomass; thetemperature in the system and consequently the heat production therein then reflects the conversion inthe system.

It was found that a retention time of the amount of wastewater to be fed in of 0.5-2.5 days, preferably of1.3-2.0 days, affords optimum results, i.e. an overall removal efficiency of more than 90%.

Expediently, the retention time in the aerobic phase is from 0.5 to 2 days and in the anoxic phase from0.4 to 1 day. A reduction in the retention time in the aerobic phase may lead to an improvement in theammonium conversion ratio. This is caused by a longer retention time for the denitrifying bacteria thenbeing achieved with an identical cycle time of the aerobic and anoxic period. This produces a higheraverage pH, as a result of which the ammonium conversion rate is increased. If the retention time in theaerobic phase is extended at the expense of the retention time in the anoxic phase, the pH is notsufficiently stabilized by the denitrifying bacteria and the conversion ratio drops again. However, if theretention time in the aerobic phase is reduced too far, the nitrifying bacteria will be flushed out and as aresult the conversion ratio again drops.

Although control of the pH of the process according to the invention is effected by methanol beingmetered as a function of the amount of heat produced by the biological treatment, monitoring of the pHis obviously possible by the pH of the medium being measured directly. As explained above, protons (oracid ions) are produced during the nitrification process, as a result of which the pH of the medium dropsin accordance with the equation

The nitrification rate is therefore pH-dependent, so that conversely the pH can be regarded as a relevantprocess parameter. It was found, incidentally, that during the nitrification buffering may take place bybicarbonate (HCO.sub.3.sup.-) which is present in the rejection water fed into the reactor or is added, inaccordance with the equation

For an optimum effect it is important, in this context, that the carbon dioxide is transported (stripped)from the liquid phase to the gas phase. With respect to dimensioning the reactor to be used in the methodaccording to the invention it was indeed found, in this context, that in the case of a ratio of volume tobottom area of the reactor in the range of 2-10 very beneficial results are achieved in terms of the




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nitrification-denitrification process according to the invention.

The characteristic feature of the invention is that the process takes place without sludge retention beingemployed, i.e. the sludge retention time is equal to the liquid retention time. To achieve this, both themixing and the discharge of the treated water need to be effective. Good mixing can be obtained byemploying, for example, aeration in the aerobic phase, and in the anoxic phase, for example, byemploying mechanical agitators, liquid injection, introduction of low-oxygen or oxygen-free gases etc.

As a result of these measures a very active bacterial population is obtained, which is mainly present inthe liquid phase as free cells and/or very small clusters of a limited number of cells, rather thanactivated-sludge flocculae.

It should further be noted that the denitrification in the reactor is carried out under essentially oxygen-free conditions. Such conditions can be formed spontaneously as a result of denitrifying bacteriaconsuming the oxygen present, the environment consequently automatically becoming anoxic.Expediently, and to accelerate the process if required, the denitrification is carried out, however, withrecycling of the nitrogen already formed previously by denitrification. An additional advantage of this isthat the nitrogen stream through the reactor at the same time strips the carbon dioxide from the reactor.

As indicated above, the excess, formed by growth, of nitrifying and denitrifying bacteria is extracted. Inpractice this involves these bacteria being entrained by the effluent from the reactor and being added tothe main stream of the wastewater treatment process, after which the further removal of residualammonium is carried out.

It should be noted that the effluent from the reactor is preferably withdrawn therefrom at a point belowthe liquid level prevailing in the reactor, expediently with local intensive mixing. While at the momentthis cannot be stated with certainty, this measure may be essential for a process without sludge retention.

According to an attractive variation of the method according to the invention, the nitrite-rich, acidiceffluent formed by nitrification is used, at least in part, for the neutralization of ammonia. This ammoniacan be present both in the rejection water to be treated and, alternatively, in a process stream of whateverorigin. The treatment can be carried out, for example, in a gas scrubbing installation known per se,whereas the effluent obtained after treatment can be recycled, for further treatment, to the nitrification

reactor according to the invention.

SURVEY OF THE DRAWINGS

The accompanying FIGS. 1 and 2 schematically show the progress of the nitrification/denitrificationprocess according to the invention. More in particular, FIG. 1 provides a sketch of the pH profile in thereactor, the pH being controlled between 8 and 7 with the addition of methanol.

FIG. 2 also represents the change in time, produced by methanol being fed in, of the nitrite concentrationand ammonium concentration for one cycle.

It should be noted that if it is undesirable or less desirable for the bacteria present in the effluent to reach

the main stream of the wastewater treatment process when the effluent is recycled to said main stream,said effluent, according to a very expedient embodiment of the method according to the invention, isfirst subjected to a treatment with protozoa. Such a variation is of interest, in particular, if the influent ofthe reactor is a COD-containing wastewater. The term COD refers, as usual, to chemical oxygendemand; the component relevant thereto in solution is primarily formed by carbon bound in organiccompounds. This material acts as a nutrient for the bacteria present in the reactor. By subjecting theeffluent of the biological treatment to a treatment with protozoa it proved possible to largely remove thebacteria suspended in the effluent and entrained from the reactor.

It should also be noted that the principle, employed in the method according to the invention, of theabsence of sludge retention can also expediently be employed in the treatment of COD-containingwastewater. More in particular this then means replacing the present nitrite route by the COD route, in

which case an overall removal efficiency of more than 50% was obtained.

The invention is explained in more detail with reference to an exemplary embodiment.




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EXAMPLE

In this example a continuous flow reactor without sludge retention was employed. Such a reactor makesit possible for the bacterial population having the lowest maximum growth rate to be flushed from thesystem selectively.

The reason for this is that a retention time can be used which is lower than the maximum reciprocal

growth rate of the one bacterial population (in this case the nitrite oxidizers which oxidize the nitritepresent to nitrate), but is higher than the maximum reciprocal growth rate of the other bacterialpopulation (in this case the ammonium oxidizers). Flushing out the nitrite oxidizers therefore leads to abuild-up of nitrite in the reactor.

The reactor used had a diameter of about 20 m and a height of 6 m and therefore an effective volume ofabout 1150 m.sup.3.

The influent for the reactor, the so-called rejection water, had a temperature of about 30.degree. C. andan ammonia concentration of about 1000 mg of N/l, while the total amount of rejection water fed in wasabout 760 m.sup.3 per day.

For the purpose of converting ammonia into nitrite, followed by the conversion into nitrogen, the reactorcontained about 120 kg of biomass.

The treatment of the rejection water took place in the reactor with a cycle configuration as shown inFIG. 2, i.e. a cycle time of about 2 hours consisting of an aeration period of .+-.80 min, followed by aperiod involving recycling of the nitrogen gas formed in a first period of bout 40 min.

In the steady state of the process the amount of rejection water fed to the reactor was such that theretention time was about 1.5 days. The infeed of methanol was about 1 kg per kg of nitrogen bound asammonium and was effected in such a way, while the temperature difference between the input and theoutput of the reactor was being measured, that the pH of the medium could be kept between about 7.2and 7.7.

The rejection water thus treated had a nitrogen concentration of as little as about 80 mg of totalN.multidot.l.sup.-1, which could be recycled for treatment to the main stream of the treatmentinstallation. The result of the treatment of this rejection water was therefore a purification efficiency ofabout 90%.

US 6,383,390Method of Treating Ammonia Comprising Waste Water

2002-05-07

VAN LOOSDRECHT MARINUS CORNELI (NL); JETTEN MICHAEL SILVESTER MARIAAlso published as: WO9807664 / EP0931023 / EP0931023 / EP0931023 / PL187475




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Abstract: The invention relates to a method of treating ammonia-comprising waste water in which thebicarbonate ion is the counter ion of the ammonium ion present in the waste water. According to theinvention half the ammonium is converted into nitrite, yielding an ammonia and nitrite-containingsolution, and in the second step the nitrite is used as oxidant for the ammonia. In the method accordingto the invention the conversion of half the ammonia into nitrite occurs automatically, providing a methodwhich requires fewer controls. Also, the method according to the invention requires no external additive.

NL 1003860C

Ammonia-Containing Waste Water Treatment

1998-02-26




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LOOSDRECHT MARINUS CORNELIS MA (NL); JETTEN MICHAEL SILVESTER MARIA(NL)Applicant: UNIV DELFT TECH (NL)


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