Denitrificarea Apei

8/13/2019 Denitrificarea Apei

1/10

Analele Universit ii Constantin Brncui din Trgu Jiu, Seria Inginerie, Nr. 1/2009

Annals of the Constantin Brncui University of Trgu Jiu, Engineering Series, No. 1/2009

85

STUDIU ASUPRA UNOR TEHNOLOGII

DE DENITRIFICARE A APEI

POTABILE

Conf. univ. dr. Daniela Crn,

Universitatea Constantin Brncui dinTrgu-Jiu

Rezumat

Concentraiile crescute de azotai n apasubteranau fcut inutilizabile unele acvifere ca sursde appotabil. n comunitile care utilizau foraje deap poluat cu azotai i care din acest motiv au fostnchise, se confrunt n prezent cu nevoia regenerriiresurselor de ap. Pe de altparte, apele de suprafa

prezint depiri sezoniere ale concentraiilor deazotai. Ca urmare, interesul pentru ndeprtareaazotailor din apa brut a devenit unul important.Obiectivul prezentei lucrri este de a evidenia i acompara diverse tehnologii de tratare disponibile

pentru ndeprtarea azotailor din ap, urmrite dinpunct de vedere al eficienei, uurinei de exploatare ia costurilor lor.

Cuvinte cheie: ape subterane, azotati, regenerarearesurselor de apa, ape de suprafata, indepartareaazotatilor din apa bruta.

1. IntroducereConcentraiile ridicate de azotai n

sursele de ap potabil prezint un riscpotenial pentru sntatea public.Concentraiile de fond ale azotailor n apelede suprafasunt n general sub 5 mg/l NO3

--N, n apele subterane ns se constat adeseaconcentraii mai mari.

Apele uzate oreneti ar putea scontribuie cu pn la 40% din coninutul deazotai prezeni n apele de suprafa.Concentraiile acestora au crescut n urmafolosirii mai intense a ngrmintelor cuazot, a modificrilor n structura folosiriiterenurilor agricole, precum i n urmarecirculrii sporite a apelor uzate menajere.Dei se consider c azotaii sunt relativnetoxici pentru aduli, fiind eliminai repede

prin rinichi, concentraiile de peste 10 mg/l

STUDY ON SOME TECHNOLOGIES OF

DENITRIFICATION OF DRINKABLE

WATER

Assoc. Prof. PhD. Daniela Crn,Constantin Brncui University of Trgu-

Jiu

Abstract

Increased nitrates densities in the undergroundwaters made unusable some water-bearing as source ofdrinkable water. In the communities that used drilling

of water polluted with nitrates and which, for thisreason, have been closed, faces today the necessity ofregeneration of water resources. On the other side,

surface waters present seasonal exceeding of nitratesdensities. As a result, the interest for nitratesalienation from raw water becomes an important one.The objective of the present paper is to underline andcompare different treatment technologies that areavailable for the alienation of the nitrates from thewater, followed from the point of view of efficiency,ease of exploitation and their costs.

Key words: underground waters, nitrates, regeneration ofwater resources, surface waters, alienation of nitratesfrom raw water.

1. IntroductionThe increased densities of nitrates in

drinkable water sources present a potentialrisk for public health. The basic densities ofthe nitrates in the surface waters are generallyunder 5 mg/l NO3

--N, but in the undergroundwaters, often can be seen higher densities.

Municipal used waters mightcontribute with up to 40% at the content ofnitrates that are present in the surface waters.Their densities increased as a result of themore intense usage of nitrate fertilizers, of themodification in the structure of usage ofagricultural fields, as well as a result ofincreased recirculation of domestic usedwaters. Even if it is considered that nitrates arerelatively not toxic for adults, being fasteliminated trough kidneys, densities over 10

mg/l NO3-

-N can be lethal for children that


2/10



86

NO3--N pot fi fatale pentru copiii mai mici de

ase luni. n organismul copiilor mici, NO3-

este redus la NO2-, care se combin cu

hemoglobina din snge formnd

methemoglobina. Aceasta conduce la o starecunoscut sub numele de boala albastr saumethemoglobinemie.

n literatura de specialitate existnumeroase informaii privind gradul de poluarecu azotai al surselor de apbrut, neeexistndnsun studiu detaliat al diverselor tehnologiide ndeprtare a azotailor din ap. Azotatuleste un ion stabil i foarte solubil, cu un

potenial sczut de coprecipitare sau deadsorbie. Aceste proprieti l fac dificil de

ndeprtat prin tehnologii clasice de tratare aapei, precum dedurizarea cu var i filtrarea[1,2].

Legislaia Comunitii EconomiceEuropene pentru azotai n apa de butstabilete un nivel maxim admisibil de 1,3mg/l exprimat ca azot (5,7 mg/l ca NO3

-) iun nivel orientativ de 5,65 mg/l ca azot (25mg/l ca NO3

-). Se cunosc mai multetehnologii care s-au dovedit a fi adecvate

pentru rezolvarea problemei de a aduce

nivelul azotailor la acela al standardelorComunitii Europene dintre care pot fimenionate ndeosebi schimbul ionic,epurarea biologic i osmoza invers.Osmoza invers devine tot mai eficienteconomic pentru tratarea apelor cu coninutsczut de silice, totui cheltuielile deexploatare sunt ncdestul de ridicate pentrua-i descuraja pe cei mai muli utilizatori

poteniali [3].Epurarea biologicfolosete bacteriile

denitrificatoare care reduc azotaii la azotgazos. Ea comport adugarea unei surse decarbon cum ar fi metanolul sau acidul acetic.Doza de substanorganictrebuie controlatatent, deoarece n caz de exces apa devinenecorespunztoare pentru consum uman. Apatratat biologic ar putea, de asemenea, sconinspori ai microorganismelor anaerobe,astfel nct ea trebuie reaerat, sterilizat, iarsuspensiile prezente trebuie ndeprtate prin

flocu1are i filtrare. Pe de alt parte reacia

are less than six months. In the organism ofsmall children, NO3

- is reduced to NO2-,

which combines with the hemoglobin in theblood, forming methemoglobin. This leads to

a status that is known with the name of bluedisease or methemoglobinemia.In the specialty literature there are

numerous information regarding the nitratespollution degree of the raw water sources, notexisting a detailed study of the diversetechnologies of alienation of nitrates from thewater. Nitrate is a stable and very soluble ion,with a low potential of co-precipitation orabsorption. These properties make him hard toalienate by classical technologies of water

treatment, as purification with lime andfiltration [1,2].

The legislation of the EuropeanEconomic Community for nitrates in thedrinking water establishes a maximumadmissible level of 1,3 mg/l expressed asnitrogen (5,7 mg/l as NO3

-) and a guidinglevel of 5,65 mg/l as nitrogen (25 mg/l as

NO3-). There are known several technologies

that proved to be adequate to solve theproblem and bring the level of nitrates to that

of the standards of the European Communityfrom which can be mentioned especially theionic exchange, biological purification andreverse osmosis. The reverse osmosis

becomes more and more efficient from theeconomic point of view for the treatment ofwaters with low content of silica; still theexploitation expenses are high enough todiscourage most of the potential users [3].

Biological purification usesdenitrification bacteria that reduce the nitratesat the gaseous nitrogen. It conducts to addinga carbon source as methanol or acetic acid.The dose of organic substance must becontrolled in an attentive manner, because incase of excess, water becomes unsatisfactoryfor human consumption. Biological treatedwater might, also, contain spores of theanaerobic microorganisms, so that it should

be re-aerated, sterilized and the presentsuspensions must be alienated by flocculation

and filtration. On the other side, the


3/10



87

biologic este lent, mai ales la temperaturisczute, astfel nct eficiena este greu de

prevzut [4].Tehnologia bazat pe schimb ionic

poate fi o soluie adecvat i eficienteconomic pentru problema azotatilor dinsursele de ap potabil. Denitrificarea prinschimb ionic utilizeaz rini anionice

puternic bazice n forma clorur pentru andeprta azotaii din ap. n timpulschimbului, rina pune n libertate ionii declorur i absoarbe ionii liberi de azotat,sulfat i bicarbonat din apa brut. Schimbulionic este considerat adesea c ar aveadezavantajul de a mari concentraia de cloruri

n apa tratat. Fiecare mg/l de azotatndeprtat va duce la o cretere aconcentraiei de cloruri cu 0,57 mg/l, iar acelei de sulfat cu 0,74 mg/l, astfel c apatratat devine mai coroziv, iar n unelecazuri neadecvat pentru consum uman [5].n continuare sunt prezentate n detaliu unele

procedee de denitrificare aplicate n scopulndeprtrii azotului din apa potabil.

2. Tehnologii dendeprtare anitrailor prin denitrificare

Denitrificarea biologic este folositcurent pentru tratarea apelor uzate oreneti iindustriale. Acumularea de cunotine iexperien a fcut posibil aplicarea cueficien a denitrificrii biologice i landeprtarea azotailor din apa potabil.Transferul lent al tehnologiei de la tratareaapelor uzate la tratarea apei potabile s-a

datorat n principal problemelor legate de oposibilcontaminare bacteriana apei tratate,de prezena unor substane organice remanenten apa tratat precum i de cretereanecesarului de clor al apei tratate. Principiulde baz al denitrificrii biologice const nreducerea azotailor la azot gazos care are locn condiii anoxice printr-o serie de etape,astfel:

NO3- NO2

- NO N2O

biological reaction is lent, especially at lowtemperatures, so that the efficiency canhardly be seen [4].

The technology based on ionic

exchange can be an adequate solution andeconomical efficient for the problem ofnitrates from drinkable water sources.Denitrification through ions exchange usesanionic resins that are powerfully basic in theform of chloride to alienate nitrates from thewater. During the exchange, the resin releaseschloride ions and absorbs free ions of nitrate,sulphate and bicarbonate from raw water. Theionic exchange is often considered as havingthe disadvantage to increase the density of

chloride in the treated water. Each mg/l ofalienated nitrate will lead to the increase ofchloride densities with 0,57 mg/l, and of thesulphate one with 0,74 mg/l, so that thetreated water becomes more corrosive, and insome case is not adequate for humanconsumption [5]. As follows are presented, indetail, some procedures of denitrification thatare applied with the purpose of nitrogenalienation from drinkable water.

2. Technologies of nitrates

alienation through denitrification

Biological denitrificationis frequentlypracticed for the treatment of municipal andindustrial used waters. The accumulation ofknowledge and experience made possible theefficient application of biologicaldenitrification and the alienation of nitratesfrom drinkable water. The lent transfer of thetechnology from the treatment of used watersto the treatment of drinkable water was mainlydue to problems connected to a possible

bacterial contamination of treated water, by thepresence of some residual organic substancesin the treated water as well as the increase ofthe chlorine necessary of the treated water.The basic principle of biological denitrificationresides in the reduction of nitrates to gaseousnitrogen, that takes place in anoxic conditionsthrough a series of stages, so that:

NO3-

NO2-

NO N2O N2


4/10



88

N2 (1)S-a constatat c oxigenul n

concentraii de 0,1-0,2 mg/l are efecteinhibitoare asupra denitrificrii.

Denitrificarea poate fi realizatatt de bacteriiheterotrofe ct i de bacterii autotrofe. ncondiii anoxice, bacteriile heterotrofeutilizeaz substanele organice cum suntmetanolul, etanolul i acidul acetic pentruconversia azotailor n azot. Raportul (C/N)

pentru substanele menionate este de 0,93;1,05 i respectiv 1,32, metanolul fiind decicel mai eficient din punct de vedere al acestuiraport. De asemenea, substanele organicegazoase ca metanul i monoxidul de carbon

pot servi ca substrate pentru denitrificareaapei.

n 1986 Roennefahrt a elaborat unprocedeu de denitrificare heterotrof(procedeul Denipor) prezentat schematic nfig.1, care a fost aplicat n scopul ndeprtriiazotailor din apele subterane.

(1)

It was observed that the oxygen indensities over 0,1-0,2 mg/l has inhibitor

effects on denitrification. Denitrification canbe used by heterotrophic bacteria as well asby autotrophe bacteria. In anoxic conditions,heterotrophic bacteria use organic substanceslike methanol, ethanol and acetic acid for theconversion of nitrates in nitrogen. The ratio(C/N) for the mentioned substances is of0,93; 1,05 namely 1,32, so, methanol beingthe most efficient from the point of view ofthis ratio. Also, organic gaseous substances asmethane and white damp can serve as

substratum for water denitrification.In 1986 Roennefahrt elaborated aprocedure of heterotrophic denitrification(Denipor procedure) that is conceptual

presented in fig.1, that was applied with thepurpose of alienation of nitrates fromunderground waters.

Fig.1. Schema instalaiei de denitrificare heterotrofprin procedeul Denipor. / Thescheme of the heterotrophic denitrification through Denipor procedure.

Procedeul folosete microorganismeheterotrofe prezente n acvifer. Pentrureactoarele cu pat fix s-a folosit ca materialsuport pentru biomasun material sintetic subformde sfere plutitoare realizat din polistiren

The procedure uses heterotrophicmicroorganisms that are present in the water

bearings. For reactors with fix layer, it wasused as a support material for biomass, asynthetic material, with the form of floating


5/10



89

expandat care nltur problemele legate decolmatare; biomasa n exces a fost ndeprtatcu uurindin materialul suport prin splaren curent descendent. Ca substrat s-a folosit

etanol i s-a adugat fosfat ca nutrient.Rezultatele experimentrilor au artat c la oncrcare de 0,7-1,0 kgN/m3.zi s-au ndeprtat

peste 95% din azotai. Apa denitrificata fosttratat n continuare n dou filtre aerobe.Carbonul organic total (COT) al efluentului la10C a fost de 1 mg/l. Procedeul a fost aplicatcu succes n Germania i n Frana n instalaiila scarindustrial.

n denitrificarea autotrof, pot fifolosite bacterii de tipul Thiobacillus

denitrificanspentru a reduce concentraiile deazotai de la 24 la 1 mg/l, n reactoare cu patfix, folosind ca surs de electroni, sulf sausulfuri. Folosirea unor particule de sulf maifine a condus la un timp de retenie hidraulicmai sczut. Pentru asigurarea alcalinitii s-afolosit calcar fapt care a dus la cretereasrurilor dizolvate n efluent. Denitrificarea cusulf/calcar a fost utilizat pentru regenerareaacviferelor poluate cu azotai. n fig.2 se

prezinto schema sistemului de denitrificare

cu sulf/calcar.

spheres realized from expanded polystyrenethat alienates problems connected to plugging;the excess biomass was easily alienated fromthe support material, by washing in descendant

current. As a substratum it was used ethanoland as a nutrient it was used phosphate. Theresults of the experiments showed that at aloading of 0,7-1,0 kgN/m3/ day have beenalienated over 95% from nitrates. Denitrifiedwater was continuously treated in two aerobefilters. The total organic carbon (COT) of theeffluent at 10C was of 1 mg/l. The procedurewas successfully applied in Germany andFrance, in installations on industrial scale.In autotrophic denitrification, can be used

bacteria of the Thiobacillus denitrificans typeto reduce nitrates density from 24 la 1 mg/l, inreactors with fix layer, using as electronssource, sulphur or sulphides. The use of somefine particles of sulphur leads to a lowerhydraulic retention time. To ensure alkalinityit was used limestone, fact that lead to theincrease of salts dissolved in the effluent. Thedenitrification with sulphur/ limestone wasused to regeneration of water bearings pollutedwith nitrates. In fig.2 it is presented a scheme

of the system of detrinification with sulphur/limestone.

Fig.2. Schema procedeului de denitrificare autotrofcu sulf/calcar. / The scheme of theautotrophic denitrification procedure with sulphur/ limestone

Sistemul de tratare a constat dintr-undegazificator sub vid pentru ndeprtarazotului i oxigenului din ap. Patul filtrant a

fost format din granule de sulf i calcar n

The treatment system was realizedfrom a decontaminator under vacuum for thealienation of the nitrogen and the oxygen from

the water. The filtering layer was formed of


6/10



90

raport de 1/1. Dupfiltrare, apa a fost aerati lsat s se infiltreze n sol n vederea

post-tratrii. Sistemul de tratare a fostexploatat cu succes timp de 800 de zile cu

nivele ale azotailor n efluent sub 25 mg/l.Pe baza acestor studii, n Olanda, a fostconstruito instalaie la scarindustrial.

Procedeul cu sulf/calcar mreteconinutul de sulfai i duritatea apei finisatei de aceea este adecvat pentru ape srace icu duritate mic.

ntr-un procedeu n care denitrificatoriiautotrofi au fost ncapsulai n bile (perle) dealginat de calciu care conineau sulf icarbonat de calciu, concentraiile de azotai

au fost reduse n decurs de apte ore de la 27la 6 mg/l.

Combinarea schimbului ionic cu

denitrificarea biologicProcesul de schimb ionic comport

trecerea apei ncrcate cu azotai printr-unpat granular de rin care necesit pentruregenerare cantiti mari de soluieconcentratde NaCl (50-100 g/l). De regul,saramura uzat are un coninut ridicat de

azotai, sulfai i cloruri; eliminarea satrebuie fcut cu grij i contribuie lacosturile de exploatare. Apa tratat ntr-un

proces de denitrificare necesit post-tratarepentru ndeprtarea microorganismelor i asubstratului organic. Combinarea schimbuluiionic cu denitrificarea biologic poateelimina unele din problemele ce apar ncazul proceselor individuale. ntr-un

procedeu combinat (fig.3) schimbul ioniceste folosit pentru a ndeprta azotaii dinapele subterane iar denitrificarea biologiceste folosit pentru a trata soluia deregenerare bogat n azotai rezultat dinrina schimbtoare anionic.

particles of sulphur and limestone in ratio of1/1. After filtering, water was aerated andallowed to enter the soil for after-treatment.The treatment system was successfully

exploited for 800 days with level of thenitrates in the effluent, under 25 mg/l. Basedon these studies, in Holland, was realized aninstallation at industrial scale.

The procedure with sulphur / limestoneincreases the content of sulphates and thehardness of the finished water and that is whyit is adequate for poor waters and which areless hard.

In a procedure in which autotrophicdenitrificators have been encapsulated into

balls (pearls) of calcium alginate thatcontained sulphur and limestone, the nitratesdensities have been reduced in seven hoursfrom 27 to 6 mg/l.

The combination of the ionic

exchange with biological denitrificationThe process of ionic exchange leads to

the passage of the water loaded with nitratesthrough a granular layer of resin that requiredfor the regeneration, great quantities of

concentrated solution of NaCl (50-100 g/l).As a rule, the brine used has a high content ofnitrates, sulphates and chloride; itselimination must carefully be done andcontributes to exploitation costs. Watertreated in a process of denitrification requires

post-treatment for alienation ofmicroorganisms and of organic substratum.The combination of ionic exchange with

biological denitrification can eliminate someof the problems that appear in the case ofindividual processes. In a combined

procedure (fig.3) the ionic exchange is used toalienate nitrates from underground waters and

biological denitrification is used to treat theregeneration solution that is rich in nitratesand results from the anionic exchanging resin.


7/10



91

Fig.3. Schema procedeului combinat de schimb ionic/denitrificare biologic. / Thescheme of the combined procedure of ionic exchange/ biological denitrification.

Sistemul combinat evit contactuldirect dintre denitrificatori i apa de tratat.Pentru denitrificarea soluiei de regenerarese folosete un reactor cu pat de nmol cucurgere ascendent. Reactorul biologic estecapabil s denitrifice soluii cu salinitatemare coninnd 25-30 g/l NaHCO

3i 10-15

g/l NaCl. Procedeul este indicat pentrutratarea apelor cu coninut ridicat de sulfai.Saramura produs reprezint 13-20% dincantitatea produs la coloanele cuschimbtori de ioni. Se recomandintercalarea ntre reactorul biologic icoloana de schimbtori de ioni a unui filtrude nisip i dezinfecia rinii cu acid aceticadugat n cursul splrii. Procedeulcombinat a fost aplicat i pentru ape

subterane folosind rini sulfat-selective iazotat-selective. n comparaie cu schimbulionic clasic, procedeul combinat a condus lao reducere de circa 90% a saramuriireziduale.

Denitrificarea chimic

ndeprtarea azotailor se poate realizai cu ajutorul procedeelor chimice. ncondiii de pH bazic, reducerea poate avealoc conform reaciei urmtoare:

NO3-

+ 8Fe(OH)2 + 6H2O NH3 +

The combined system avoids directcontact between denitrificators and treatmentwaters. For the denitrification of theregeneration solution will be used a reactorwith layer of mud with ascendant flowing.The biological reactor is capable of denitrifysolutions with high salinity, containing 25-30g/l NaHCO3 and 10-15 g/l NaCl. The

procedure is indicated for the treatment ofwaters with a high content of sulphates. The

brine produced represents 13-20% from thequantity produced at the columns of ionsexchangers. It is recommended theinterpolation between the biological reactorand the column of ions exchanger of a sandfilter and the disinfection of the resin withacetic acid, added during washing. The

combined procedure was also applied onunderground waters using sulphate-selectiveand nitrate selective resins. In comparisonwith the classical ionic exchange, thecombined procedure leads to a reduction ofabout 90% of the residual brine.

Chemical denitrification

The alienation of the nitrates can berealized also with the aid of the chemical

procedures. In the conditions of a basic pH,

the reduction can take place according to the


8/10



92

8Fe(OH)3 + OH- (2)

Pentru ca reacia s aib loc estenecesar un raport Fe2+/NO3

-de aproximativ

15/1, n prezena unui catalizator de cupru.Acest proces genereaz cantiti mari denmol de fier i duce la formarea deamoniac care trebuie stripat cu aer.

Denitrificarea chimicse poate realizai cu pulbere de aluminiu. S-a constatat c

produsul principal este amoniacul (60-95%)care poate fi ndeprtat prin stripare.ndeprtarea optim a azotailor prin acest

procedeu s-a obinut la pH= 10,25.Denitrificarea a fost pus pe seama

urmtoarelor reacii:3NO3

- + 2Al + 3H2O 3NO2- +

2Al(OH)3 (3)

NO2- + 2Al + 5H2O NH3+

2Al(OH)3+ OH- (4)

2NO2- + 2Al + 4H2O N2+

2Al(OH)3+ 2OH- (5)

Procedeul poate fi folosit la staiile de

tratare a apei care folosesc var pentrudedurizarea apei. n mod obinuit, pH-uleste ridicat la 9,1 sau peste, cu var, astfelnct cheltuielile pentru a spori pH-ul lavaloarea optimsunt mici.

Aluminiul reacioneazcu apa conformreaciei urmtoare:

2Al + 6H2O 2A1(OH)3+ 3H2 (6)

Pierderea de aluminiu datorit reacieide mai sus (la pH= 9,1-9,3) s-a constatat a fisub 2%. S-a stabilit cpentru reducerea a 1gde azot este nevoie de 1, 16 g de aluminiu.n domeniul de pH de 9-10,5 a fost posibilreducerea selectiv a azotailor n raport cusulfaii.

Concluzii

following reaction:NO3

- + 8Fe(OH)2 + 6H2O NH3 +8Fe(OH)3 + OH

- (2)

As for the reaction to be realized, it isnecessary a ratio Fe2+/NO3- of about 15/1, in

the presence of a copper catalyst. This processgenerates great quantities of iron mud andleads to the formation of ammonia that must

be purified with air.The chemical denitrification can be also

realized with aluminum powder. It wasobserved that the main products is theammonia (60-95%) that can be alienated by

purification. The optimal alienation of the

nitrates through this procedure was obtained atpH= 10,25. The denitrification was ascribed tothe following reactions:

3NO3-+ 2Al + 3H2O 3NO2

- +2Al(OH)3 (3)

NO2- + 2Al + 5H2O NH3+

2Al(OH)3+ OH- (4)

2NO2- + 2Al + 4H2O N2+

2Al(OH)3+ 2OH- (5)

The procedure can be used at the watertreatment plants that used limes for water

purification. Commonly, pH is increased to9,1 or over, with lime, so that expenses toincrease pH at optimal value are lower.

Aluminum reacts with water accordingto the following reaction:

2Al + 6H2O 2A1(OH)3+ 3H2 (6)

The loss of the aluminum due to theabove reaction (at pH= 9,1-9,3) was observedto be under 2%. It was established that for thereduction of 1g of nitrogen are necessary 1, 16g of aluminum. In the field of pH of 9-10,5 itwas possible the selective reduction of thenitrates in relation with sulphates.


9/10



93

Denitrificarea biologic pentru apapotabil are o larg aplicare n variantadenitrificrii heterotrofe n comparaie cu

cea autotrof, mai ales la scar industrial.Denitrificarea heterotrof este caracterizatprin rate specifice volumetrice dedenitrificare mai mari (0,4-24 kg/m3.zi NO3

-

-N) dect denitrificarea autotrof (0,5-1,3kg/m3.zi NO3

--N). Fezabilitatea tehnic ieconomic a denitrificrii heterotrofe a fostconfirmat la scarindustrial n mai multeri europene. Viteza reaciei autotrofe estemic i de aceea pentru a asigura timpi deretenie suficieni pentru denitrificare este

nevoie de volume mari ale reactorului, faptcare duce la creterea costurilor de investiie.

Pe de alt parte denitrificareaheterotrofpoate ndeprta i micropoluaniorganici cum ar fi tetraclorura de carbon itricloretilena. Denitrificarea biologic nreactoare cu pat fluidizat este preferatfade cea n reactoare cu pat fix. Astfel,

problemele cum sunt colmatarea iformarea de curgeri prefereniale care aparde obicei la reactoarele cu pat fix sunt

nlturate. Mai mult la reactoarele cu patfluidizat s-au observat rate mai mari dendeprtare a azotailor. ntruct reactoarelecu pat fluidizat necesit recirculareaefluenilor pentru o ndeprtare eficient aazotailor, aceste instalaii impun oconducere mai atenta procesului.

Denitrificarea biologic esteaplicabilapelor de suprafadat fiind faptulcprocesul se poate adapta uor la variaiilede calitate a apei cum sunt coninutul dematerii organice naturale, de sruridizolvate, suspensii, azotai i sulfai.

Principalele probleme legate defolosirea denitrificrii biologice sunt:

monitorizarea sporit n caz deexploatare intermitent;

ratele de denitrificare reduse latemperaturi mai sczute, cnd nivelulazotailor n apele de suprafa tind screasc;

post-tratarea apei denitrificate pentru

3. ConclusionsThe biological denitrification for

drinkable water has a large application in thevariant of heterotrophic denitrification in

comparison with the autotrophic one,especially at industrial scale. Theheterotrophic denitrification is characterized

by specific volumetric higher rates ofdenitrification (0,4-24 kg/m3.zi NO3

--N) thanthe autotrophic denitrification (0,5-1,3kg/m3.zi NO3

--N). The technical and economicfeasibility of heterotrophic denitrification wasconfirmed at industrial scale in severalEuropean countries. The speed of theautotrophic reaction is smaller and that is why,

to ensure sufficient retention periods fordenitrification, there are necessary greatvolumes of the reactor, fact that leads to theincrease of the investment costs.

On the other side, heterotrophicdenitrification can alienate organicmicropolluters like carbon tetrachloride andtrichlorideethylene. The biologicaldenitrification in reactors with fluidized layeris preferred in comparison with the one inreactors with fix layer. So, problems like

plugging and formation of preferentialflowing that commonly appear at reactorswith fix layer are alienated. More, at reactorswith fluidized layer, have been observedgreater rates of nitrates alienation. As reactorswith fluidized layer require the recirculationof effluents for an efficient alienation ofnitrates, theses installations impose a moreattentive administration of the process.

The biological denitrification isapplied to surface waters due to the fact thatthe process can be easily adapted to thewaters quality variations as are the content ofnatural organic materials, undissolved salts,suspensions, nitrates and sulphates.

The main problems connected to theuse of biological denitrification are:- Increased monitoring in case of

intermittent exploitation;- Rates of denitrification reduced at low

temperatures, when the level of nitrates in

the surface waters tend to increase;


10/10



94

ndeprtarea substratului organic folositpentru denitrificare i ndeprtareamicroorganismelor.

ndeprtarea azotailor din apa

potabil este un domeniu important decercetare n care au fost dezvoltatetehnologii noi, dar este necesaroptimizareai perfecionarea n continuare a acestora.Un studiu detaliat al exploatrii reactorului

biologic cu privire la concentraia de substrati de nutrient, pH i temperatur, poatestabili n mod clar efectele acestor parametriiasupra eficienei de eliminare a azotailor.De asemenea, trebuie precizat faptul cefectul compuilor organici toxici asupra

performanelor reactorului nc nu estecunoscut. O atenie deosebit trebuieacordat determinrii caracteristicilormicrobiologice ale apei denitrificate pentrucare nu exist o monitorizare a rezultatelor

pe termen lung.

Bibliografie

Ianculescu, O., Ionescu, Gh., Racovieanu,

R. Epurarea apelor uzate, Ed. MatrixRom, Bucureti, 2001.Constantinescu, G. C. - Chimia mediului -

Hidrochimia, Ed. UNI-PRESS C-68,Bucureti, 2001.Ciocan, V., Traist, E., Podariu, M. Tratamentul apelor reziduale, Ed.Universitas, Petroani, 2000.Rojanschi, V., Bran, F., Diaconu, G.

Protecia i Ingineria Mediului, Ed.Economic, Bucureti, 1997Negulescu, M., Antoniu, R., Rusu, G.,Cua, E. Protecia calitii apelor, Ed.Tehnic, Bucureti, 1982

- Post-treatment of the denitrified water forthe alienation of the organic substratumused for the denitrification and alienationof the microorganisms.

The alienation of the nitrates fromdrinkable water is an important research fieldin which have been developed newtechnologies, but it is necessary theircontinuous optimization and perfectioing. Adetailed study of exploration of the biologicalreactor, regarding the densities of substratumand nutrient, pH and temperature, canestablish in an exact manner the effects ofthese parameters on the efficiency ofelimination of nitrates. Also, it must be

mentioned the fact that the effect of the toxicorganic compounds on the performances ofthe reactor is not yet known. A specialattention must be granted to the determinationof the microbiological characteristics of thedenitrified water for which does not exist amonitoring of the results on long term.

Bibliography

1.Ianculescu, O., Ionescu, Gh., Racovieanu,R. Purification of used waters, MatrixRom Publishing House, Bucharest, 2001.

2.Constantinescu, G. C. - Chemistry of theenvironment - Hydro chemistry, UNI-PRESS C-68 Publishing House, Bucharest,2001.

3.Ciocan, V., Traist, E., Podariu, M. Thetreatments of residual waters, UniversitasPublishing House, Petroani, 2000.

4.Rojanschi, V., Bran, F., Diaconu, G. Protection and Engineering of the

Environment , Economic Publishing House,Bucharest, 19975.Negulescu, M., Antoniu, R., Rusu, G.,

Cua, E. Protection of the water quality,Technical Publishing House, Bucharest,1982.

Denitrificarea Apei

Documents

Transcript of Denitrificarea Apei