DETERMINATION OF THE PHOSPHATE
        IN SOLID WASTE USING
   THE VANADOMOLYBDOPHOSPHORIC
            ACID METHOD
U.S. ENVIRONMENTAL PROTECTION AGENCY

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DETERMINATION OF THE PHOSPHATE IN SOLID WASTE

USING THE VANADOMOLYBDOPHOSPHORIC ACID METHOD
           A Solid Waste Research
       Open-File Report (RS-03-68-17)
                 written by
         WILLIAM H. KAYLOR, Chemist
    U.S. ENVIRONMENTAL PROTECTION AGENCY
      Office of Research and Monitoring
            Solid Waste Research
                    1971

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TABLE OF CONTENTS




Reagents
P roc edure ———•-•—————•—••—••"••



Page
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              DETERMINATION OF THE PHOSPHATE  IN  SOLID WASTE

              USING THE VANADOMOLYBDOPHOSPHORIC  ACID METHOD

                           William H. Kaylor*

                              INTRODUCTION


     The reclamation of useful products from solid waste is one method

of reducing the disposal problem of solid wastes.  There are many re-

search projects concerned with recycling solid wastes into fertilizers

and food products.  In the production of fertilizers and food products

from solid waste, the phosphorous concentration is of importance because

phosphorus is a nutrient.  It is also important to know the phosphate

concentration in solid waste leachates, since these leachates may even-

tually drain into natural water supplies and cause pollution if standard

concentration limits are exceeded.  This report describes and evaluates

one method for measuring phosphorus in the form of phosphates that are

present in solid wastes.

     The vanadomolybdophosphoric acid method* was selected to be in-

vestigated as a method for solid waste analyses because of its high

range, simplicity, and freedom from interferences.  The chemistry which

makes this method useful for determining phosphates is believed to in-

volve the substitution of oxyvanadium and oxymolybdenum radicals for the

0 of PO, to give a heteropoly compound that is chromogenic.
* Chemical and Radiological Activities Section,  Engineering and Science
  Branch, Office of Air and Water Programs, Environmental Protecti&n Agency,
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     The intensity of yellow color produced is proportional to the con-




centration of phosphates present; thus the phosphates can be determined




colormetrically by measuring the intensity of the yellow color produced




when PO^ comes in contact with vanadate and molybdate in an acid solution.






                              EXPERIMENTAL






          Vanadomolydophosphoric Acid Method for Phosphates




1.  Equipment.




    a.  Erlenmeyer flasks - 125 ml




    b.  Kjeldahl flasks - 800 ml




    c.  Volumetric pipettes - 5, 10 and 20 ml




    d.  Filtering funnels



    e.  Filter paper - only specification is phosphate free




    f•  Color comparison tubes or volumetric flasks - 50 ml



    g.  Spectrophotometer - wave length setting 400 mu




2.  Reagents




    a.  Ammonium vanadate ~ molvbdate solution:  Dissolve 2.35 g ammon—




    ium metavanadate in 300 ml of boiling distilled water; cool, then




    add 400 ml concentrated HNO^ and cool.  Dissolve 40 g ammonium




    molybdate in 400 ml hot distilled water and cool.  The molybdate




    solution is then added to the vanadate solution and*diluted to




    2 liters with distilled water.






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    b.  Sulfurlc acid solution;  Add 310 ml concentrated H2SO^ cautiously



        to 500 ml distilled water and dilute to 1.0 liter.



    c.  §9diupi hydroxide:  Dissolve 450 g NaOH in distilled water; cool,




        and dilute to 1.0 liter.



    d.  Phosphate standard:  Dissolve 1.4330 NaH2PO^ (dried at 105 C) in




        distilled water and dilute to 1.0 liter (1.0 ml = l.o mg PO^).




    e.  Working Standard:  Pipet 50.0 ml of the phosphate standard into




        a 1.0 liter volumetric flask and dilute volume with distilled



        water (1.0 ml = 0.05 mg PO^).




    f.  Chemicals




        (1)  Concentrated acids - hydvobk&etic, nitric and sulfuric



        (2)  Potassium persulfate




        (3)  Sodium nitrate



3.  Procedure




    The solid sample may be prepared for analysis either by acid digestion




(a)  or by dry ashing (b).  Liquids are prepared by method (c).  The com-




pletion of the analysts is substantially the same for all three procedures.




    a.  Acid digestion of soljfd. «fynples:  Weigh accurately 1-2 g of homo-




    geneously ground sample (predried at 105 C) and place in a kjeldahl



    flask.  Add 5 ml concentrated HMO- and 25 ml concentrated H^SO^ and



    heat until the solution boils.  Then add 1 g NaN03 to the solution






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and digest for two hours.  After the sample is digested and cooled,


add 150 ml distilled water and boil the solution for five minutes.


Cool the sample and transfer to a 200 ml volumetric flask; fill to


volume with distilled water and filter.


Pipet 25 ml or an aliquot of the sample (1-25 ml depending on the


phosphate concentration in the sample) into a calibrated 50 ml con-


tainer.  Add sodium hydroxide (450 g/1), 1 ml per 5 ml of sample,


to adjust the pH and dilute the sample to approximately 40 ml with


distilled water.  Then mix the sample, add 5 ml of vanadate-molybdate


reagent, adjust the sample to the 50 ml mark with distilled water,


and mix again.  Allow solution to stand 15 minutes for maximum


color development and read the absorbance on a spectrophotometer at


4OO mu.


    Calculations:  Plot a standard curve from 1-25 mg/1 PO, vs


    absorbance.  The sample results are read directly from the


    standard curve taking into account the proper aliquot used


    for each sample.


    mg/1 P0/r=mg/l P04x 50      Percent P04= m8/l P04 x 10°

             Aliquot used      wt. of sample x 5


b.  Ashing of solid ?flnpl?ff;  Weigh accurately 1-2 of homogeneously


ground sample (predried at 105 C) and ash in a muffle furnace at
                                                  •#

6OO C for 2 hours.  Cool the ash, add 40 ml HC1 (1:3) and 3 drop


concentrated HNOq, and bring the solution to a boil.  Cool the solu-


tion, transfer it to a 200 ml volumetric flask, dilute to volume




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    with distilled water and filter.



    Fipet 25.0 ml or an aliquot of sample (depending on phosphate concen-




    tration in samples) into a calibrated 50 ml container and dilute to



    about 40 ml with distilled water.  Continue the procedure as described




    in procedure (a), except the pH does not need adjusting in this pro-




    cedure.



    c.  Digestion of liquid samples:  Place 50 ml of the sample (or an




    aliquot diluted to 50 ml) into an erlenmeyer flask.  Add one ml of




    H2SO^ (31Q ml/1) and 0.5 g potassium persulfate, and digest the sam-




    ple for 30 minutes on a hot plate.  Then dilute the sample to about




    20-25 ml with distilled water, filter it into a calibrated 50 ml con-




    tainer and dilute to approximately 40 ml with distilled, washing



    thru the filter paper in the process.  Add 0.5 ml of NaOH (450 g/1),




    mix well, and continue the procedure as described in procedure (a)



    with the addition of the vanadate reagent.






                               DISCUSSION






    The vanadomolybdophosphoric acid method can be used to determine




phosphates in many types of solid waste.  Results obtained from the




methods were compared to results from two other common-phosphate.



methods 2» 3» using standards and solid wastes samples (Table 1).   The




analyses indicate that the vanadomolybdophosphoric acid method compared






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favorably to the other methods.  This method is often more suited for




solid waste samples.  The concentrations of phosphates in solid waste




are much higher than can be measured by the other methods without




large dilution factors.  The vanadomolybdophophoric acid method has




a much higher range than the other methods; therefore little, if any,




dilution is needed.




    This method was evaluated with standards and standard addition to




solid waste samples (Table 2).  The results showed that at least 95




percent of the total phosphates present were recovered from all samples




and standards.
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                     TABLE 1 	 METHOD COMPARISON
Sample

Sodium Glycerophosphate
(Ashed) Mg/1 P04in
#1 151
#2 151
#3 151
Johnson City Compost
and sludge (Ashed)
#1
#2
Johnson City Compost (70
(Ashed)
#1
#2
#3
#4
#5
Johnson City Compost (70
(Digested)
n
#2
#3
Incin. Res. N.Y. #203
(Ashed)
#1
#2
#3
Incin. Res. N.Y. #203
(Digested)
#1
#2
#3
Food Wastes N.Y. #208
(Ashed)
#1
#2
#3
#4
#5
#6
V— ^^^^•^•^•WMHM^^B^^MVMMMVi
Molybdate Blue
Method
Dil. Factor

Std.
50
50
50


10
10
day)

25
25
25
25
25
day)

50
50
50


250
250
250


250
250
250


100
100
100
100
100
100
Me/1


148
146
146


13.8
21.9


43.0
38.0
35.3
39.4
43.8


52.5
48.0
47.5


228
226
226


122
121
120


136
156
130
135
143
134
Ascorbic
Method
Dil. Factor


50
50
50






25
25
25
25
25


50
50
50


250
250
250


250
250
250


100
100
100
100
100
100
Mp/1


160
150
155






48.8
43.3
40.3
43.3
49.8


46.0
43.5
44.0


217
230
225


117
111
115


144
173
151
161
153
160
Vanadate Yellow
Method
Dil. Fact or


10
10
10


5
5


5
5
5
5
5


5
5
5


10
10
10


5
5
5


10
10
10
10
10
10
Me/1


153
153
154


18.2
28.9


52.5
46.0
42.0
46.0
47.5


48.5
44.0
46.3


220
222
222


114
112
110


143
174
155
165
162
160
Quench Water
  Wash., D.C.
2.40
2.44
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                      TABLE 2
PRECISION AND ACCURACY OF THE VANADOMOLYBDOPHOSPHORIC
                     ACID METHOD
P04
Sample mg/1
J. C. * compost
and sludge (Ashed)
#1 18.3
" 18.5
" 18.0
J. C. compost
and sludge (Ashed)
#2 29.0
" 28.8
" 28.8
J. C. compost (70-day)
(Ashed)
#1 52.5
#2 46.0
#3 42.0
#4 46.0
#5 47.5

J. C. compost (70-day)
(Digested)
#1 48.5
#2 44.0
#3 46.3
•


Quench Water
Wash. ,D.C. (1967) 2.43
» 2.44
" 2.44
7«P04
0.36
0.37
0.35
0.41
0.40
0.40
0.47
0.46
0.43
0.46
0.47

0.47
0.44
0.46





Standard Addition
P04 Std. Added P04
mg/l
5.0
10.0
15.0
5.0
10.0
15.0
«•>„_,_ 1 „ JIO Il<-rir1.,w;— -
oampie V£. useo—
5.0
5.0
5.0
10.0
10.0
10.0
Sample #2 Used- —
10.0
10.0
10.0
20.0
20.0
20.0
10.0
10.0
10.0

Std . Recovered
mg/1
4.5
10.2
15.0
4.9
9.7
15.1

4.8
4.8
4.8
9.6
9.7
9.6
9.7
9.7
9.7
19.9
19.5
19.4
9.44
9.36
9.50
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          PRECISION AND ACCURACY OF VANADOMOLYBDOPHOSPHORIC ACID
                              METHOD (Con'd)
Standard Addition
Sample
PO^
mg/1
P04 Std. Added PO^Std. Recovered
XPO^ mg/1 mg/1
N.Y. #203 Incinerator
(Ashed) Residue






N.Y.
#1
#2
#3



#203 (Digested)
222
222
222




2.22
2.21
2.21




Incinerator Ash






N.Y.
Food






#1
#2
#3



#208 (Ashed)
Refuse
#1
#2
#3



114
112
110





165
161
161



2.1
2.20
2.19





1.65
1.61
1.62



Sample #1 Only 	
10.0
10.0
10.0
20.0
20.0
20.0

N.Y. #203 (#3 Used)
10.0
10.0
10.0
20.0
20.0
20.0

N.Y. #208 (#1 Used)
10.0
10.0
10.0
20.0
20.0
20.0


9.4
9.4
9.7
19.6
19.6
19.2

208 	
9.6
9.9
9.7
19.3
19.3
19.5

203— —
9.9
9.8
9.7
19.2
19.7
19.7
*Johnson City
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                                REFERENCES
1.  Jackson, M. L.  Soil chemical analysis.  Prentice-Hall, Inc., 1960.
    p. 151-154.

2.  Gales, M. E. Jr., Julian, E. C., Kroner, R. C., "A Method for the
    Quantitative Determination of Total Phosphorus in Filtered and Un-
    filtered Samples" JAWWA Vol. 58 #10 Oct., 1966.

3.  "FWPCA Methods for Chemical Analysis of Water and Wastes" FWPCA
    Division of Water Quality Research, Analytical Quality Control Labo-
    ratory, Nov. 1969.
                              ACKNOWLEDGEMENT

    The assistance of Donna L. Barnett is gratefully acknowledged.
                                                               ?2-l-0035s
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