A Simple Method for Estimating Total Phosphate in SewageAuthor(s): John H. HowardSource: Sewage and Industrial Wastes, Vol. 28, No. 6 (Jun., 1956), pp. 785-786Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25033087 .

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A SIMPLE METHOD FOR ESTIMATING TOTAL PHOSPHATE IN SEWAGE

By John H. Howard

Eesearch Chemist, Eesearch and Development Laboratories, Cranston Print Works Company,

Cranston, E. I.

Biological methods for treating in dustrial wastes which contain high concentrations of organic matter are

attaining considerable importance. Two such methods are the activated

sludge and the trickling filter proc esses. Both depend upon microorgan isms which consume the organic mat ter. Optimum amounts of oxygen, ni

trogen and phosphorus are required for the performance of this function

with maximum efficiency. A simple method for estimating phosphorus content is therefore essential to evalu

ating the effectiveness of either proc ess.

A search of the literature failed to disclose a simple, exact method de scribed in any detail. Standard Meth ods for the Examination of Water, Sewage, and Industrial Wastes (1) gives a method for estimating ortho

phosphate in water by a colorimetric

technique. This is a modification of the Deniges colorimetric procedure as

improved by Truog and Meyer (2).

Official Methods of Analysis of the As sociation of Official Agricultural Chem ists (3) gives a method for estimating total phosphoric acid in fertilizers

gravimetrically or volumetrically. The

following method is a modification of the procedures cited.

Reagents

1. Ammonium Molybdate Stock So lution: Dissolve 25 g. of (NH4)6Mo7

024-4H20 in 150 ml. water and add to 280 ml. concentrated H2S04 diluted to 750 ml. with water ; dilute to 1 1. For

use, dilute one part of the stock so

lution with four parts of water. Make up this diluted solution fresh for

each use.

2. Stannous Chloride Stock Solu tion: Add 25 g. of SnCl2 to 11. of 1:9

HC1, filtering if necessary. For use, dilute one part of the stock solution

with four parts of water. Make up this diluted solution fresh for each

use.

3. Potassium Phosphate Standard

fiolution: Add 0.7164 g. of dry KH2P04 to 800 ml. water and dilute to one 1. Dilute 5 ml. of this solution to 500 ml. Each ml. will contain 5

fig. of P04 4. Concentrated Sulfuric Acid. 5. Concentrated Ammonium Hy

droxide. 6. Dilute Nitric Acid: Dilute con

centrated HN03 with three volumes of water.

Procedure

Duplicate determinations are made for each sample. Place 10-ml. aliquots of sample in 30-ml. microkjeldahl flasks. Add 3 ml. concentrated H2S04 and four or five glass beads. Heat on a microkjeldahl digestion rack for 2 hr. after the excess water has boiled

away. (No difficulty will be encoun tered with bumping when boiling be

gins if the flask is continuously turned from the time the heat is first applied.

After the contents of the flask begin to boil, the turning is no longer neces

sary.) Remove flasks and cool. Trans fer contents of flasks to 125-ml.

Erlenmeyer flasks, using four 4-ml.

aliquots of water in the transfer. Af

785

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786 SEWAGE AND INDUSTRIAL WASTES June, 1956

ter cooling, neutralize until just alka line to litmus paper using concentrated

NH40H (about 10 ml. will be re

quired). Then make slightly acid with dilute HN03. Cool and dilute to 50

ml.

Place 1-, 3- and 5-ml. aliquots of each unknown in 20 X 150 mm. test tubes. Adjust volumes to 10 ml. In

five other test tubes, place aliquots of the KH2P04 standard solution to cover

the range from 5 to 25 ?xg. Adjust the volumes to 10 ml. To each test tube add 2 ml. of ammonium molybdate solution and mix. Add 0.25 ml. of

SnCl2 solution and mix. Visually com

pare the unknowns against the stand ards at the end of 5 min.

Report in parts per million of P04~ (micrograms per 5 ml. of digested and

diluted sample.)

Discussion

Pyrophosphates, metaphosphates and

orthophosphates all report quanti tatively as orthophosphate. The opti

mum range for the standard phosphate solution is 5 to 25 /xg. in 5 /?g. incre

ments, giving five tubes in all. It is

possible to shorten this range to 3 to

12 fig. or 4 to 20 fig. if so desired.

Of course the number of standard

tubes is still restricted to five. Defi

nition is quite sharp in any case.

As outlined the method is rapid and

does not require photometric compari son; visual comparison suffices. The

colors have been found to be suffi

ciently stable for precise results 24

hr. after development, providing the

standards and unknowns were pre

pared at the same time.

The hydrolysis method is superior to any cited in the literature. The

need for any acid other than sulfuric

acid during digestion is eliminated.

References

1. "Standard Methods for the Examination

of Water, Sewage, and Industrial

Wastes." 10th Ed., Amer. Pub.

Health Assn., New York, N. Y. (1955). 2. Truog, E., and Meyer, A. H., "Improve

ment in the Deniges Colorimetric

Method for Phosphorous and Arsenic. ' '

Ind. Eng. Chem., 1, 136 (1929). 3. "Oficial Methods of Analysis of the As

sociation of Official Agricultural Chemists." 7th Ed., Assn. of Off.

Agr. Chemists, Washington, D. C.

(1950).

JOURNAL BACK NUMBERS

Response to previous appeals for Journal back numbers has been most

gratifying and is sincerely appreciated. The January, 1955 issue of Sewage and Industrial Wastes, however, is still in short supply and back numbers are needed. Reimbursement is at the rate of $0.50 per copy plus postage.

Back numbers of the Journal also are

available for purchase by members who

desire to complete their libraries. Al

though a complete selection of all back numbers is not available and a few cop ies are limited, most of them are avail able. Orders for scarce numbers are filled if and when copies are obtained.

Occasionally a complete Journal file becomes available through the death of a Federation member. The Federation

Secretary would be pleased at any time to help prospective Journal buyers and sellers make contact.

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