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Influence of calcining parametersof FeP04 and CaO compositionson the solubility of phosphorus

compoundsZbigniew Wzorek and Katarzyna GorazdaInstitute oj Chemistry and Inorganic Technology,

Kraków University oj Technology, Kraków, PolandJoanna Kulczycka

Minerał and Energy Economy Researcli Institute oj the Polish Academy ojSciences, Kraków, Poland, and

Tadeusz RzepeckiTarnoto Waterworks, Tarnów, Poland

AbstractPurpose - To deterrnine the influence of alkali components (especially Ca compounds) on thehernatite phase forrnation during therrnal processing of sewage sJudge and the observation oftransforrnations proceecling at different ratios of Ca to FeP04•

Design/methodology/approach - The model compositions were heated to ternperatures of 600°Cand 950°C, then calcined within 3 hours without mixing. Cooled products were subjected chemicalanalysis regarding the eontent of phosphorus that was soluble in cold water, 0.4 per cent HCI,2 percentcitric acid and aqua regia as well as crystallographic identification.Findings - On calcining at 600°C, Cao reacts with FeP04, forrning hydroxylapatite. The hematitephase which is insoluble in mineral acids crystallizes above 600°C. Further increasing the calciningtemperature leads to transforrnations resulting in CagFe(P04l7 and hematite formation, Molar ratios otCao to FeP04· 2H20 ot 1.0 and 2.0 lead to hernatite phase forrnation and increase the availability otphosphorus compounds (characterized by phosphate solubility in 0.4 percent HCI and 2 percent citricacid) in compositions after calcining.Practical implications - The addition ot Cao to sewage sludge before the combustion processshould be beneficial from the point ot view of further extraction ot phosphorus compounds from theash obtained Suitable Cao addition favours iron binding into the hematite phase and raises thesolubility of the phosphorus compounds in the ashes forrnedOriginality/value - This paper is a new source of information which complements existingknowledge about phosphorus recovery frorn sewa e sludge.Keywords Waste management, SewagePaper type Research paper

IntroductionPhosphorus is a ehemical element with great biological importanee. It is a eomponentof some proteins, enzymes and vitamins, as well as a basie inorganie bone eomponent(hydroxyl apatite). Phosphorus is a basie eomponent of nucleie aeids, i.e.

This study was supported in part by research grant KB J 4 T09B 068 24.

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Management of EnvironmentalOualitv: An International Journal

Vol. 16 No. 6. 2005pp. 627·638

C>Emerald Group Publishing Limited1477·7835

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deoxyribonucJeic acid (D A) and ribonucJeic acid (RNA), which play a decisive role inthe processes of heredity, and storing and transmitting genetic information (Chmiel,1998). Phosphorus is also a fundamental ingredient of the energy carriers ATP, ADPand AMP.

Another aspect of phosphorus is the threat it poses to the environment. Increasedphosphorus and nitrogen concentrations in surface water favour eutrophication.Hence, phosphorus has to be removed from industrial, stock-farming and municipalwaste waters to minimize that threat. According to Polish regulations, from 2003, thetotal admissible phosphorus eontent in treated sewage should not exceed lmg Pzdrrr',or 10 percent of the general phosphorus charge in raw sewage (RozporzędzenieMinistra Ochrony Środowiska, 2002). European Union regulations specify phosphorusconcentrations of l mg P/dm3 and 80 percent phosphorus reduction (DyrektywaWspólnot Europejskich, 1991).

Sewage treatment methods can be divided into three main methods (see Figure 1),taking into consideration phosphorus removal:

(1) chemical methods;(2) biological methods; and(3) mixed methods (Miksch and Czerska 1997; Kurbiel and Rybicki, 1997; Bemacka

et al, 1995; Kurbiel and Bartoszewski, 2002).

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628

Figurę LCharacteristics ofphosphorus removalmethods

Nowadays, most European sewage treatment plants use simple and effectiveprecipitation methods, in which water-insoluble iron and aluminium phosphate areprecipitated by the addition of Fe2(S04h. FeCh (sometimes, but rarely, FeSOJ,AI2(S04h'14H20 and Ca in the form of lime milko Nevertheless, the amount of sewagesludge after treatment processes is increased.

METHODS OF PHOSPHORUS REMOVAL FROM SEWAGE

CHEMICAL

MIXEO METHOOSIntegrated systems with high efficiency ot

phosphorus removal

TECHNOLOGIES:Phostrip BIOLOGICAL

- initial precipitation at mechanical stage- pre-precipitation belore further biological

treatment- simultaneous precipilation. reagents addition at

lIle final part ol !he activated sludge reactor- final precipitation

Puritication rnelllods wHh !he use ot bacterialstrains (eg. Acinetobacter). which accumulatephosphorus (in excess to its metaboli<: needs) inlIle torm ot połyphosphates at variable oxygenconditions

AOVANTAGES:- deerease of energy expenditure of aerating

systems beeause of signlflcant 8005ellmination at oxygen-free eonditlons

- limHation or ełimination ot chemical precipitation- improvernent ol sedimentation properties ot

sewage sludge due to appłication ot anaerobiezone belore aerobic

PRECIPITATING AGENTS:Salts ot trivalent metais: Fe and Al

Fe2(S04lJ, FeC13,Al2(SO.b 14Hp, cso

AOVANTAGES:

Rate, tacility, efficiency

OISAOVANTAGES:

- generation ot large Quantities ol sewage sludge- deficiency ot sewage sludge usage because ot

unavailabilHy ot FeP04 by plants- high exploitation costs

OISAOVANTAGES:- posslblllty ot phosphorus secondary

release from bacleńa cells

TECHNOLOGIES:Bardenpho, UCT, Biodenipho, SBR, NO, A210

From the available methods of phosphorus removal, BPRPhostrip (biologicalphosphorus removal) must be mentioned as the process in which the conditions forbacterial growth, which accumulates phosphorus in excess to its metabolic needs, arecreated. This group also comprises modified biological methods enabling simultaneousnitrogen and phosphorus removal (Bardenpho, Johannesburg Proces s) by introducingpreliminary aerobic reactors for nitrification processes and anoxic reactors fordenitrification processes iPhosphorus & Potassium, 1998; Kijkowska et al., 1999; Brettet al., 1997; Klimuk and łebkowska, 2003). The final products of treatment are purified --------sewage and sewage sludge, where phosphorus is accumulated in the form of insolublephosphates or elements of live matter (bacteria).

The high costs of the preliminary processing and storage of sewage sludge, the banon the storing of sewage sludge containing more than 5 percent of organie matter (validfrom the year 2005), along with the new modification of Directive UE 86/278, haveresulted result in a systematic increase of the importance of the thermal processing ofsewage sludge. Thermal treatment of sewage sludge causes a significant massreduction and the concentration of inorganic fractions as ash. The combustingproducts should be treated as a potential raw material for the production ofphosphorus compounds. However, ash processing technologies are still developingand, most of them are at the laboratory stage. The Combi/Krepro'P' process should bementioned here (Dulley, 2001). It is the best known and advanced system, acombination of the earlier systems Combi and Kemira/Alfa Laval and the Bio-Conprocess (Takahashi et al, 2001), which use sewage sludge combustion at 950°C and ashtreatment with sulphuric acid. The Japanese EBPR process proposes intensive ashwashing with demineralised water at 53°C or sulphuric acid (Andersen, 2003).

The main problem associated with the recovery of phosphorus compounds from ashis the form in which phosphorus occurs. During the treatment process usingphosphorus from the popular precipitation method with Fe2(S04h or FeCls, thephosphorus from such sewage sludge will be bound as iron phosphate, whicheliminates the usage of extraction methods for phosphorus recovery.

The research carried out by the authors reveals that the presence of alkalicomponents such as Ca, Mg and Na in analysed sewage sludge can influence thetransformation that takes place during combustion processes, especially in ironbinding in the insoluble hematite phase (Fe203) and the formation of differentconnections between phosphorus, calcium and iron (Rzepecki, 2003; Gorazda, 2004).The addition of Ca, Mg and Na can also beneficially affect the decrease in humidity ofthe sewage sludge before the combustion processes, thereby reducing energy use.

Influence ofcalcining

parameters

629

ExperimentalDuring previous research (Rzepecki, 2003; Gorazda, 2004) it was found that the basiesolid phases identified in the ash after sewage sludge combustion at 950°C (P95Osr) werequartz, anhydrite, hematite and Ca9Fe(p04h. The combustion research was carried outon sewage sludge sampIes from Municipal Sewage Treatment Plant "Kujawy" inKraków-Pleszów. The presence of the hematite phase significantly infiuences theselectivity, in relation to iron, of the leaching of phosphorus compounds from ash. Theintensity of the highest hematite peak (Inet from X-ray analysis), increases withincreasing ash calcination temperature, and results in a decrease of Fe concentrationsin extracts after ash leaching with nitric acid.

630

The goal of the present research was to determine the influence of alkalicomponents (especially Ca compounds) on the hematite phase formation duringthermal processing of sewage sludge, and the observation of transformationsproceeding at different ratios of Ca to FeP04. Sewage sludge containingphosphorus bound as insoluble iron phosphate, precipitated after chemicalphosphorus removal during sewage treatment processes, was analysed.

In order to examine the processes between sewage sludge components like P, Ca andFe during its combustion, caJcining tests of model compositions made fromanalytically pure FeP04 ·2H20 and CaO roasted at 1000°C were carried out. Thecomponents ratio at compositions corresponded to a mol ar ratio of Ca:P04 and Ca:Fe,respectively, for Ca9Fe(p04h, ash Pg50srand Ca3(P04)z. The model compositions (beforecaJcining processes were analysed with the use of thermal analyses) were sintered in achamber kiln at 600°C and caJcined at that temperature for a further 3h. The sampIeswere cooled, analysed and then caJcined again to 950°C for another 3 h. The modelcomposition sarnples after caJcination at both temperatures were submitted for X-rayanalyses for the identification of crystalline phases. The scheme of experimentsconducted is presented in Table I.

The results of the thermal analysis of the chosen model compositions andanalytically pure FeP04 .2H20 and CaO roasted at lOOO°Care shown in Figure 2.

The thermal analysis (TA) results indicate three types of changes during caJciningof the model compositions. The first is observed at a temperature of 170°C, and isconnected with a decrease in moisture eontent and crystallization water fromFeP04 . 2H20. The second smali er effect observed at CaO corresponds to caJciumhydroxide decomposition. The third change - which is exothermic - occurred at600°C, and can be related to caJcium carbonate decomposition. The X-ray analysis ofmodel compositions after caJcining at 600°C and 950°C for experiments 1-5 arecompared in Table II (taking into account the three main crystalline phases) and areshown in Figure 3.

Analysis of above results indicates that during the caJcination process of al!compositions at a temperature of 600°C, CaO reacts with FeP04, forminghydroxyapatite. Increasing the caJcining temperature leads to transformations thatresult in Ca-Fe (POJ7 and hematite formation. In the case of experiment 3, where amolar ratio of CalFe of 8.97 mol/mol was used, the hematite phase does not appear. Theinfluence of the Ca/PO~- molar ratio on the phase constitution of the modelcompositions after the caJcining process was observed. The most beneficial value ofthis parameter is l.29 in experiment 2 (Table m, where, after the caJcination process,

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Model counterparts Model compositionsCa/PO~- CalFe Cao FeP04 . 2H20 Ca/PO~- CalFe

Experirnent Compound (mol/mol) (mol/mol) (g) (g) (mol/mol) (mol/mol)

l Ca3(P04)z 1.5 3.1034 6.9017 1.50 1.50Table I. 2 CagFe(p04h 1.29 9 2.7817 7.2235 1.29 1.29Chemical constitution ot 3 7.2913 2.7132 8.97 8.97model compositions 4 Ash P950sr 1.08 0.87 2.4518 7.5532 1.08 1.08analysed 5 2.0604 7.9414 0.866 0.87

Sample:FePOc2H20Size: 15.4654mgCommen\:Odczynnik

100~k-------------------------------------------------~

~f'r5'C--\ .

95

90~EC>

Gl::85

80

75O

Exo Up

6661.8Z·C 21.07%

(3.259mg)

713.34'C----

Ci 0.0

~ 4

Gl "2uc: ]~ -0.1:5. ~i:5 Ee 2C>

~'0;::

" .~~ -0.2 <>{!? c

o-0.3

TGA-DTAFile:C:...\SDnK.Gorazda.010Operator.ZWRun Date:22-May-Q314:36

Influence ofcalcining

parameters

631

200 400 600+---------,---------,---------,---------,---------4-2

1,000

Temperature('C)

(a) FeP042H20

Sample:CaOSize: 11.6981mgCommen!: Prazony- po 6 dinach

101

800

UniversalV2.3CTA Instrumenls

TGA-DTAFile:C:...\SDT'.K.Gorazda.009Operator:ZWRun Date:22-May-Q311:42

0.6

1.043%

100(0.1220mg)

~E 99C>

Gl::

98

97+---~-__,--~---.---~--,__--~-__,--~--4 -0.2O 200 400 600 800 1,000

Exo Up UniversalV2.3CTA InstrumentsTemperature('C)

(b) CaO

0.03

Ci 0.4

t O.OZ"2

l'! ]c:e ~~ 0.01 0.2 Ei:5 Ol

e ~.3~ ,,;Gl

0.00.~c,CE

{!?0.0

-O.Ot

(continued)

Figurę 2.Results of thennal

analysis

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Sample:F - Ca/Fe 1.50Size:10.9948mgComment:Powtorzeniew powietrzu

100~~--------~r----------------------------------.4

TGA-DTAFile:C:...\SDT\K.GorazdaO.008Operator:MRunDale:22-May-0308:31

13c:e~Cie::>'§

0.3611% ~o.7478%

Ic:====:::::r~(~0~.OS39~7~1m>g<)~=========§~~(0~.0~8222~m~g~)o...Q.3

607.75·C

...Q. 1

4632 95

zz 90!?~

85

411.64·C Ci 0.0Ee.

14.26%(1.568mg)

...Q.2

Figure 2.

80+---------~--~----r--------,--------_.----~--_+-2o 200 400 600 800 1,000

ExoUp Temperatune(OC) UniversalV2.3CTAInstnuments

(c) model compostion at molar ratio Ca/P043- 1.50 mol/mol, experiment l

Model compositions Identified crystalline phasesModel Ca/PO~- CalFe After caJcining at After caJcining at

Experiment counterparts (mol/mol) (mol/mol) 600°C 950°C

Ca3(P04h 1.50 1.50 FeP04 CagFe(POJ7Hydroxylapatite HematiteCao

2 CagFe(P04h 1.29 1.29 Cao CaoHydroxylapatite HematiteFeP04 Ca(PO:V2

3 8.97 8.97 FeP04 CaoHydroxylapatite HydroxylapatiteCao Ca2Fe20S

4 Ash P950sr 1.08 1.08 FeP04 CagFe(P04hTable II. Hydroxylapatite Ca(PO:V2The constitution ot model Cao Hematitecompositions after 5 0.866 0.866 FeP04 CagFe(P04hcaJcining at 600°C and Hydroxylapatite Hematite950°C Cao FeP04

only two crystalline products were formed - CagFe (POJ7 and hematite. The goal offurther experiments was the observation of changes during the calcining of modelcompositions of CaO and FeP04' 2HzO in the range 0.5-5.0 CaO/FeP04 . 2HzO molarratio and analysis of its influence on the solubility of the phosphorus compoundsformed. A scheme of the experiments conducted is shown in Table III.

Compositions after the calcining process were analysed with thermal ana1yses andcompared with the results of preliminary investigations, and then sintered in achamber kiln to 950°C and calcined at that temperature for a further 3 h withoutmechanical mixing. Cooled compositions were submitted to X-ray analyses (Figure 4)and chemical analysis.

The X-ray analysis indicates that the molar ratio of CaO to FeP042H20 has asignificant influence on the type of crystalline phases formed in model compositions.

W%or24~Lt'lic Common:l.:.c"..=S,:=,n,-' _

ł ~~~A Q~ ~ll l--.--e~l j2 nwta/- (Sc:anAXIr 2 I ~ )

r.. r

(a) After calcining at 600°C

(b) After caIcining at 950°C

Experiment oo (g)Model compositions

FeP04 ·2H20 (g) CaOIFeP04 ·2H20 (mol/mol)

67891011

1.30322.30593.74774.73445.45215.9976

8.69687.694162523526254.54794.0024

0.51.02.03.04.05.0

Influence ofcalcining

parameters

633

rr

Figure 3.X-ray anaJysis ot model

composition at molar ratioot Ca/PO:-, 1.29 mol/mol

from experiment 2

Table nr,Constitution ot model

compositions

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634

Figurę 4.X-ray analysis of modelcomposition with molarratio of CaO/FeP04 . 2H20

WZ0r267. tlICCornmon:l {1 8'*'11

.5-311 l:.a..,II'WI~.k fCdhfP'04rn

1 I I' I' ,II ,II I ! I50-17" łroII Atu,.. tłytłrW JFa Pl 07!2: ta O}

I I . I II H II I r , III! l· 111"11111· HI 1111 li !I!I ił! iii II· 4 I

I i 3- H4 H:ca..tfte. 2" ]Fe2 011 !

_ 4l--CH Iron Pb • .,...tełłtdfo)6dc [c4IP0>4)3(OHp!

l! . II 'I II IIII II II!· li, niI 1I '~~.i

L(a) 0.5 - experiment 6

W'::cr26B.rvc Conwncn 1 (I seen

. ~ "'.. ~.

(b) 1.0 - experiment 7

W'::or27TJVC Common 1 (1 ~n)

.A

" "2TMta;,· (~FlhI. Z,~)

DlJ ITI

(c) 2.0 - experiment 8

(continued)

...•Wl0t278.rec COtnmorr1 (1 Stan)

Influence ofcalcining

parameters

!,d Jl 635

..•

FI'l-"" Hema*.5Y! reZO!

3N.a7 liIIK.!y!I re- OJI ! I I I

I I I III I I III II III I II III, I II I

I I I I iI I I I I I i~ II i I II I II II I I III I III ~I I, - .1U ~2; fCallPo.m

I I . j: II, 1:;111 II Pll II 1111 '11111.1' II 1111I111illll II(d) 3.0 - experirnent 9

WZOr21ł1.'1C CGnYnon.l (1 5c:an)

l t-1 ~~ .!! j • I•..__ ~~JJL1~.b~.~'U~'~~~~~'~'~"~~M_.~~~~..~J~\J~"~'-~~~t~~,~N~l~'~_~h~~.

'21'heta,'" (St-anĄl(".2.1~.)

(e) 4.0 - experiment 10

1I'4Of280Jlit;Con)lJll()n.'.o.:.:" S=~:::..n) _

". H". I~ l.'t J ..l

(1) 5.0 - experiment 11Figure 4.

The excess of CaO breaks the hematite phase formation (experiment 10 and ll). Themost favourable condition for hematite phase formation is a molar ratio of Caf) toFeP042H20 of close to 2.0. Chemical analysis was performed to examine whether thephosphorus compound was soluble in 0.4 percent HCI, 2 percent citric acid and aquaregia (total phosphorus). In products from experiments 6-11 the tota! pho pbo andphosphorus soluble in citric acid were analysed according to Wzorek et al. (2003) andPN-88/C-870l5 (n.d.) and the phosphorus soluble in HCI in accordance with Po ish

-------- norms (pN-97/R-64803, n.d.). The results are compared in Table IV. The sa ubi iryresults are also compared in Figure 5 where 100 percent of the total phosphate eontent(phosphate soluble in aqua regia) was assumed.

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636

ConclusionsThis research has allowed the determination of the influence of additions of calciumcompounds on phase transitions during thermal processing of sewage sludge anddefining the changes under different molar ratios of Ca to FeP04. In the case ofcalcining at 600°C, CaO reacts with FeP04, forming hydroxylapatite. The hematitephase, which is insoluble in mineral acids, crystallizes above 600°C. Further increasingthe calcining temperature leads to transformations resulting in Ca9Fe(p04h andhematite formation. The molar ratio of CaO to FeP04· 2H20 has a significant influenceon the crystalline phases forming in compositions after the calcining process. Molarratios of 1.0 and 2.0 lead to hematite phase formation and increase the availability ofphosphorus compounds (characterized by phosphate solubility in 0.4 percent HCI and 2

Phosphate eontentTotal Phosphate soluble

CaOIFeP04 Identified phosphate Phosphate soluble in 2 percent citric'2HzO crystalline (percentage in 0.4 percent Hel acid (percentage

Experiments . (mol/mol) phases PO~-) (percentage P~-) PO~-)

6 0.5 CaP206 37.9 2.21 1.87CagFe(P04hHernatite

7 1.0 CagFe(P04h 30.96 15.88 11.57HematiteCaP206

8 2.0 Hematite 38.33 19.78 21.55HydroxylapatiteCaPOJ2

9 3.0 Hernatite 18.86 1.01 12.92CaoHydroxylapatite

10 4.0 Cao 24.38 BMDa 8.18HydroxylapatiteCa2Fe20S

Table IV.11 5.0 Cao 20.98 BMDa 5.10

HydroxylapatitePhosphate eontent in Ca2Fe20Smodel composition aftercalcining at 950°C Note: "Below method delectability

10

I_ soluble at aqua-regia _ soluble at 0.4% Hel

soluble at 2% citric acid

10/

0/,,",

0""""- .<J_ I0""""- - I

~'0/- - ,- Lv

0/ ":r: .r: ~ ••••...J- ....)-

8

2

0.5 1 2 3 4molar ratio of CaO/FeP042H20

5

percent citric aciel) in composirions after calcining. When molar rarios of 4.0 and 5.0were used the sampIes revealed minimal solubility in HCl and reduced solubility incitric acid, because excess Cao hampers hematite phase formation.

The addition of CaO to sewage sludge before the combustion process should bebeneficial from the point of view of the extraction of further phosphorus compoundsfrom the ash obtained. Suitable Caf) addition favours iron binding into the hematitephase and raises the solubility of phosphorus compounds in the ash formed.

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Commission, DG-Environment B/2, SEDEs", CEEP Scope Newsletter, No. 50, pp. 2-3.Bernacka, ]., Kurbiel, ]. and Pawłowska, L. (1995), Usuwanie zwiąsków biogennych ze ścieków

miejskich, Wydawnictwo Instytutu Ochrony Środowiska, Warszawa.Brett, S., Guy, ]., Morse, GK and Lester, ].N. (1997), Phosphorus Remoual and Recouery

Technologies, Selper Publications, London.Chmiel, A (1998), Biotechnologia, Podstawy mikrobiologiczne i biochemiczne, Wydawnictwo

Naukowe PWN, Warszawa.Dulley, B. (2001), "Recycling phosphorus by recovery from sewage", Rhodia Consumer

Specialities UK Ud for Centre Europeen d'Etudes des Polyphosphates, SecondInternational Conference on the Recovery of Phosphorus from Sewage and AnimaIWastes, oordwijkerhout, March 12-13.

Dyrektywa Wspólnot Europejskich (1991), "Dyrektywa Wspólnot Europejskich z dnia21.05.1991, Nr 91/271 EEC, dotyczęca oczyszczania ścieków", Official [ournal of theEuropeon Communities, Vol. L 135, p. 40.

Gorazda, K. (2004), "Badania nad odzyskiem fosforu z osadów powstałych w wynikusymultanicznego oczyszczania ścieków komunalnych z uzyciem siarczanutvt) zelazaun),jako czynnika stręcajęcego zwięzki fosforu", praca doktorska, Politechnika Krakowska,Kraków.

Kijkowska, R,Kowalski, Z., Pawłowska-Kozińska, D., jodko, M. and Wzorek, Z. (1999), "Odzyskfosforu ze ścieków", praca niepublikowana C1I131/OS./99, Politechnika Krakowska,Kraków.

Influence ofcalcining

parameters

637

Figure 5.Comparison of phosphate

solubility at modelcompositions aftercalcining at 950°C

638

Klimuk, E. and Łebkowska, M. (2003), Biotechnologia w ochronie środowiska, Wydawnictwoaukowe PWN, Warszawa.

Kurbiel, ]. and Bartoszewski, K. (2002), "Oczyszczanie ścieków komunalnych, inżynieriaśrodowiska, stan obecny i perspektywy rozwoju", Monografie Komitetu OchronyŚrodowiska PAN, Vol. 10, Komitetu Ochrony Środowiska PAN, Lublin, pp. 85-1l4.

Kurbiel, ]. and Rybicki, SM. (1997), "Technologie wysokoefektywnego biologicznego waniaazotu i fosforu wdrazane w Polsce", Materiały konferencji Naukowo technicznej"Usuwanie zwięzków biogennych ze ścieków", Kraków.

Miksch, K. and Czerska, B. (1997), "Efektywność biologicznych i chemicznych metod u uwaniafosforanów ze ścieków", Materiały konferencji Naukowo technicznej "U uwanie zwięzkówbiogennych ze ścieków", Kraków.

Phosphorus & Potassium (1998), "Phosphate recovery and removal from was ewater",Phosphorus & Potassium, No. 213, pp. 30·9.

PN-88/C-87015 (n.d.), PN-88/C-87015 - Nawozy sztuczne, Metody badań zawartości fosforanów.PN-97/R-64803 (n.d.), Pasze, Fosforany paszowe, PN-97/R-64803.Rozporzędzenie Ministra Ochrony Środowiska (2002), Rozporzędzenie Mini tra Ochrony

Środowiska, nr 1799/2002 z dn. 29.11.2002, Dz.U. nr 212.Rzepecki, T. (2003), "Badania nad utylizację odpadów z procesów z oczyszczania ścieków

komunalnych i odzyskiem z nich zwięzków fosforu", praca doktorska, PolitechnikaKrakowska,Kraków.

Takahashi, M., Kato, S., Shima, H., Sarai, E., !chioka, T., Hatykawa, S. and Miyajiri, H. (2001),"Technology for recovering phosphorus from incinerated wastewater treatment sludge",Chemosphere, Vol. 44, pp. 23-9.

Wzorek, Z., Kowalski, Z., [odko, M. and Gorazda, K. (2003), "Właściwości osadów z oczyszczaniaścieków komunalnych i popiołów z ich obróbki termicznej", Przemysł Chemiczny, Vol. 82

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