lab

University of North Dakota

CE 423L: Environmental Engineering Laboratory

Nutrients

Submission Date

Month/Day/Year

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Table of Contents 1. Objectives................................................................................................................................................. 1

3. Experimental Design ............................................................................................................................... 2

4. Relevant Equations ................................................................................................................................. 2

5. Materials and Equipment ....................................................................................................................... 2

6. Procedures ............................................................................................................................................... 3

7. Results ...................................................................................................................................................... 3

8. Discussions and Conclusions .................................................................................................................. 5

References .................................................................................................................................................... 7

List of Tables

Table 1: Alum Dosage of Each Jar …………………………………….…………………………4

Table 2: Phosphate, pH, and Removal Rate for Each Jar..………………..………………………6

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1. Objectives

The objective of this lab is to illustrate the basic principles of water treatment that

involves measuring the nutrient levels. This includes evaluating the removal of phosphate

(PO43-) from water by coagulation using the Hach photometric method. Additionally repeat for

the PO43-concentration in tap water and raw Red River water.

2. Theory

Nutrients are an important part of water with an optimum amount, if the level exceeds the

optimum amount, it can cause problems. “Phosphorus is a common constituent of agricultural

fertilizers, manure, and organic wastes in sewage and industrial effluent. It is an essential

element for plant life, but when there is too much of it in water, it can speed up eutrophication (a

reduction in dissolved oxygen in water bodies caused by an increase of mineral and organic

nutrients) of rivers and lakes.” (USGS). With phosphate often reaching unacceptable values it is

important to remove it during coagulation of water treatment process of surface water. Phosphate

can enter the surface water as it will attach to soil particles from farm application and during rain

runoff will flow into surface water. If phosphate levels are too high within a water, it can cause

eutrophication in the surface water which causes algae to form on the surface of the water.

Water that has excess nutrients and having algae formed due to the excess nutrients can

result in more problems. “Eutrophication sets off a chain reaction in the ecosystem, starting with

an overabundance of algae and plants. The excess algae and plant matter eventually decompose,

producing large amounts of carbon dioxide.” (NOAA). Once the reaction has formed carbon

dioxide in the water the carbon dioxide will shift the alkalinity of the water, lowering the pH and

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making the water more acidic. The change in pH can cause harm on aquatic life killing poisoning

the fish that can be passed on to consumers.

3. Experimental Design

The independent variable in this experiment is the water source. The three sources used

include the Red River, Tap water, and Distilled water. The dependent variables include the

phosphate in the water. For more details on the variable dependency see Section 4 Relevant

Equations.

4. Relevant Equations

The following equations were used for this lab:

% removed = (Ci-Cf1)*100/Ci

Where Ci equals initial phosphate concentration and Cfl equals the phosphate

concentration after the first round of removal by precipitation.

5. Materials and Equipment

Throughout this experiment, different materials and equipment were used to achieve the

objective of the lab. This section of the lab lists the materials and equipment used.

Materials Used:

1. Tap Water

2. Red River Water

3. De-Ionized Water

4. Alum

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Equipment Used:

1. Jar Test Flocculation Apparatus

2. Graduated Cylinder

6. Procedures

The following processes were used in this lab for coagulation and settling:

1) Collect 1 L tap water in each of the six jars.

2) Add coagulant (alum) at the following dosages (see Table 1), and measure and record the

initial phosphate concentration in the jar.

3) Start the coagulation (rapid mixing, 150 rpm for 1 min) and flocculation (slow mixing, 40

rpm for 15 min) processes at different alum doses

4) At the end of the slow stirring period, stop the stirrer.

5) After 20 minutes of settling, during which time the jars should not be disturbed, pipette

out sufficient supernatant and test it for phosphate.

7. Results

Table 1 shows the alum dosages in mg/l for the different volumes of alum stock solutions

and their respective jar numbers. The alum dosages were in linear relationship to the volume of

alum stock solution.

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Table 1: Alum Dosage of Each Jar

Table 2 shows the first trial run coagulation data that was collected. It contains the

phosphate, pH, and removal rate for each of the six jars. The pH of Grand Forks tap water was

higher than the raw Red River value. The initial phosphate level in the raw Red River water was

higher than the tap water by .4 mg/L. After the jar test, the raw Red River water phosphate

stayed the exact same and none was removed. Jar test 6, with an alum dosage of 80 mg/L, had a

phosphate removal rate of 94.41%.

Table 2: Phosphate, pH, and Removal Rate for Each Jar

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8. Discussions and Conclusions

Phosphate removal is conducted using coagulation to precipitate soluble nutrients. This

can be done with the addition of multivalent salts such as Ca (II), Al(III), Fe(III). This lab was

conducted using alum. The precipitation reaction is shown below.

𝐴𝐴𝐴𝐴3+ + 𝐻𝐻𝑛𝑛𝑃𝑃𝑃𝑃43−𝑛𝑛 → 𝐴𝐴𝐴𝐴𝑃𝑃𝑃𝑃4 + 𝑛𝑛𝐻𝐻+

Excess nutrients in water can cause many issues, due to excess nutrients there is the

potential for development of eutrophication, which is a reduction in the dissolved oxygen in the

body of water. An oligotrophic lake is a body of water with low nutrient content. This type of

lake has low algal growth, good light dispersion and high DO. An increase in nutrients could

begin the process of eutrophication which could be damaging to existing fish populations and

aesthetics. Once eutrophication occurs plant and algae growth will increase causing a blanket

over the water. The plants and algae will die forming carbon dioxide, which will shift alkalinity

of the water by lowering the pH and increasing acidity.

Phosphate nutrients are useful in suppressing corrosion in pipes, keeping drinking water

cleaner. It also suppresses dissolutions of lead in our drinking water. Having too much nitrogen

in drinking water can cause methaemoglobinaemia in babies, formation of carcinogenic

nitrosamines in the human stomach, and hypertension. Therefore, there is a limit of 3 mg/L per

WHO guidelines.

Phosphorous gets into water gets into water when there is no oxygen in the sediments at

the bottom of lakes or rivers. When there is oxygen, the phosphorous binds and sticks with the

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ground sediments, when there is no oxygen, the phosphorous becomes soluble and gets into the

water. Phosphate most commonly gets into tap water due to runoff. Poor agriculture practices

result in fertilizer infected water draining and infecting tap water. Phosphate is removed in two

ways. The first way is with calcium, Ca(OH)2 is added and pH is exceeding 10. The calcium will

react with the phosphate and precipitate hydroxylapatite which contains phosphate. The other

way is with aluminum and iron, aluminum reacts with phosphate to precipitate AlPO4 and iron

reacts to form FePO4.

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References

NOAA (February 2, 2021). What is eutrophication? National Ocean Service website, Accessed

May 5, 2022, from https://oceanservice.noaa.gov/facts/eutrophication.html

Water School Science (June 5, 2018). Phosphorus and Water, USGS, Accessed May 5, 2022,

from https://www.usgs.gov/special-topics/water-science-school/science/phosphorus-and-

water