DETERMINATION OF THE PHOSPHATE IN SOLID WASTE USING THE VANADOMOLYBDOPHOSPHORIC ACID METHOD U.S. ENVIRONMENTAL PROTECTION AGENCY ------- 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 ------- TABLE OF CONTENTS Reagents P roc edure -" Page __ ______ __ __ i """""""""""""~"""" 5 / iii ------- 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, - 1 - ------- 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. - 2 - ------- 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 - 3 - ------- 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 - 4 - ------- 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 - 5 - ------- 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. - 6 - ------- 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 - 7 - ------- 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 - 8 - ------- 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 - 9 - ------- 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 - 10 - ------- |