This document outlines a procedure to determine the total phosphate content of a water sample. Phosphorus plays an important role in biochemical processes and eutrophication of surface water. The main sources of phosphorus in wastewater are human excreta, household detergents, and some industrial effluents. The procedure involves preparing a calibration curve using standard phosphate solutions, then measuring the absorbance of the water sample reacted with ammonium molybdate and stannous chloride reagents to determine its phosphate concentration based on the calibration curve. The total phosphate content is calculated based on the volume of the water sample. The results will help assess eutrophication levels in surface waters affected by wastewater discharges.

1. Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon – 423601
(An Autonomous Institute, Affiliated to SPPU, Pune)
ISO 9001:2015 Certified, Approved by AICTE, Accredited by NBA and NAAC (A Grade)
Department of Civil Engineering
Course Title: Environmental Engineering – II (401001)
Determination of Phosphates in Wastewater
Instructor
Mr. Chaudhari V. S (Assistant Professor)
Contact id: chaudharivishalcivil@sanjivani.org.in
Environmental Engineering– II: Phosphate

2. Environmental Engineering– II: Phosphate
Introduction:-
 Phosphorus is the eleventh most abundant element on the surface of the earth and is
most commonly found as phosphate
 It plays an important role in biochemical processes and is a key factor in the eutrophication
of surface water
 The main sources of phosphorus in waste water are the human excreta, phosphorus
containing household detergents and some industrial and trade effluents.
 Precipitation runoff only little contributes to P-loads in waste water if combined sewer
systems are applied.
 P-discharges to waste water can origin from food and textile industry and from rendering
plants
Importance of solids determination:-
 Phosphorus in the form of phosphate (PO4
-3 ) is an essential plant nutrient and is a
major component of most fertilizers.
 Eutrophication, the depletion of oxygen from excessive aquatic growth.
 Animal die-off, toxins and foul water can also result.

3. Environmental Engineering– II: Phosphate
Eutrophication
 Eutrophication is an enrichment of water by nutrient salts that causes structural
changes to the ecosystem such as: increased production of algae and aquatic
plants, depletion of fish species, general deterioration of water quality

4. Environmental Engineering– II: Phosphate
Aim:- To determine the total phosphate content of given water sample.
Apparatus:- Spectrophotometer, Volumetric flask, Beakers etc.
Reagent:-
Phenolphthalein indicator aqueous solution
Strong acid solution (6N H2SO4)
Ammonium Molybdate reagent (NH4) 2MoO4
Stannous Chloride reagent SnCl2.H2O
Standard Phosphate solution: 1.0 ml = 50 g PO4
-

5. Environmental Engineering– II: Phosphate
Procedure:-
A) Preparation of Calibration Curve: -
1). 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4 ml of standard solution are pipetted into 100ml volumetric flask
and
diluted to 100 ml with distilled water.
2). Add 2 ml Ammonium molybdate reagent and 0.5 ml stannous chloride reagent to each
flask & mix thoroughly.
3) Contents of each flask is allowed to stand for 10 Min. for color development.
4) Measure the intensity (Absorbance) of blue colored solution of each flask at 690 nm
wavelengths.
5) A calibration curve is constructed for absorbance against concentration of phosphate in
100 ml of solution.
1 2 3 4 5 6 7 8 Sample

6. Environmental Engineering– II: Phosphate
B) Determination of Phosphate content of unknown sample: -
1) Take 100 ml of sample in a beaker, whose Phosphate content is to
be determined.
2). Add 2 ml Ammonium molybdate reagent and 0.5 ml stannous
chloride reagent to the beaker & mix thoroughly.
3) Contents of beaker is allowed to stand for 10 Min. for color
development.
4) Measure the intensity (Absorbance) of blue colored solution of
beaker at 690 nm wavelength and corresponding micrograms of
phosphate of sample for 100 ml volume is read from calibration
curve.
5) Then calculate phosphate content of sample in mg/lit using the
formula.

7. Environmental Engineering– II: Phosphate

8. Environmental Engineering– II: Phosphate
Observation Table:-
Sr. No. Standard solution in ml Total phosphate (mg/lit.) %Absorbance
1 0.5 0.25
2 1 0.5
3 1.5 0.75
4 2.0 1.0
5 2.5 1.25
6 3.0 1.5
7 3.5 1.75
8 4.0 2.0
9 Sample Sample
Calculation:-
Total phosphate (mg/lit.) = micrograms of phosphate in sample
ml of sample taken
Standard Phosphate solution: 1.0 ml = 50 g PO4
-
E.G. For First beaker (0.5 ml), Total Phosphate (mg/lit) = 25 x 10-3 /(100) x 10-3 = 0.25 mg/lit
For Second beaker (1ml), Total Phosphate (mg/lit) = 50 x 10-3 /(100) x 10-3 = 0.5 mg/lit

9. Environmental Engineering– II: Phosphate