Our hypothesis is: If we try to purify dirty water with different coagulants, then an iron-based coagulant will purify the water better than any other coagulants.

One of the most crucial steps in the treatment of water is coagulation. The majority of the particles in contaminated water have a negative surface charge. They have more electrons than protons. Additionally, this keeps them active and prevents them from coming together. Coagulants function by having positively charged molecules, such as organic polymers or cationic metal ions. To eliminate any remaining charge, these mix with the negatively charged particles and neutralize their charge.  Ferric Chloride, also known as Iron(III) chloride is an industrial scale commodity chemical compound. Its chemical formula is FeCl3 and its CAS is 7705-08-0. When dissolved in water, the compound undergoes hydrolysis resulting in a brown highly corrosive, acidic solution that is used as a flocculant in sewage treatment and drinking water production. Anhydrous iron(III) chloride is a strong Lewis acid that is used as a catalyst in organic synthesis. Aluminum sulfate is one of the most used coagulants that is not organic. It is mainly used to purify drinking water and wastewater. Aluminum sulfate breaks down in water and forms aluminum ions (Al³⁺). These combine with really small particles and form flocs that settle easily. Aluminum sulfate has a good coagulation effect, but it is less effective in low temperature water. The use of aluminum sulfate might cause an amount of ions to stay in the water. This could have effects on our health, because some of the ions stay in the water.

When Aluminum Sulfate is added to water, it dissolves and immediately following coagulation, the water enters a basin for a period of gentle, slow mixing. During this stage, the neutralized microparticles begin to collide and aggregate. Simultaneously, the aluminum ions react with the water's Alkalinity to form a gelatinous, sticky precipitate of aluminum hydroxide (Al(OH)₃). This precipitate is the "floc." The slow mixing encourages the microparticles to collide with and become entrapped in the growing, web-like floc particles, forming larger, heavier, and more visible clumps. When Aluminum Sulfate is added to water, it dissolves and dissociates, releasing highly positive trivalent aluminum ions (Al³⁺). During a period of intense, rapid mixing (the "flash mix"), these positive ions neutralize the negative charge of the colloidal particles. With their repulsive forces eliminated, the tiny particles are no longer stable and can begin to stick together. Immediately following coagulation, the water enters a basin for a period of gentle, slow mixing. During this stage, the neutralized microparticles begin to collide and aggregate. Simultaneously, the aluminum ions react with the water's alkalinity to form a gelatinous, sticky precipitate of aluminum hydroxide (Al(OH)₃). This precipitate is the "floc." The slow mixing encourages the microparticles to collide with and become entrapped in the growing, web-like floc particles, forming larger, heavier, and more visible clumps. Poly Aluminium Chloride is an acidic solution made of the elements aluminium, chlorine, hydrogen and oxygen. Clear to slightly yellow in colour it is also referred to as PAC, PAX, or Poly Aluminium Hydroxide Chloride Sulphate Solution.It is a highly efficient water treatment chemical where it works as a coagulant to extract and clump together contaminants, colloidal and suspended matter. This results in the formation of floc (flocculation) for removal via filters. 

Chitosan is a partially deacetylated product of chitin, achieved through an alkaline deacetylation reaction. Chitosan has many diverse physico-chemical and biological properties and this diversity has allowed it to find applications in various sectors such as cosmetics, biomedical engineering, pharmacy, ophthalmology, biotechnology, agriculture, textiles, oenology, food industry, and nutrition. This amino-biopolymer has been of great interest over the last years for its use in water treatment processes for particulate and soluble matter removal. Of particular interest is the recent development of new materials based on this biopolymer exploited as coagulant and flocculant agents. These new applications are of great interest in the water and wastewater treatment sector. These new materials can operate as coagulant and flocculant agents for removal of particulate matters, either inorganic or organic, and soluble organic matter too. 

Purifying Water         By: Manuela Ribeiro and Shriya Savekar Have you ever wondered how the water that comes out of our faucets is so safe to drink? Well, we have! We decided to do an experiment on this topic. Our scientific question is, “Which coagulant will clean water the most effectively?” (A coagulant is a chemical that is added to water to purify and neutralize the particles’ charges.) We have four different coagulants: Aluminum chloride, polyaluminum chloride, ferric chloride, and chitosan. We also did three trials for the most accuracy and determined the average. But first, let’s take a look at how we actually observe how clean the water really is.

We check how clean the water is with its NTU, or its Nephelometric Turbidity Unit. A higher NTU means that the water is more cloudy and dirty. The lower the NTU is, the cleaner the water is and has the least amount of particles in it. You can measure this with a turbidimeter, which shines a light beam into the water sample, detecting how much light is reflected or absorbed by particles that make the water unclean. The fewer particles, the cleaner the water!

Here is a guide to show how to see how purified water is: < 0.3 NTU (Very Clean): High-quality, usually filtered water, like the level of cleanliness in a purification plant 0.3 – 1.0 NTU (Clearish):This water is clean enough to drink, like tap water. 1 – 5 NTU (Slightly Cloudy): Noticeable cloudiness, which means a little dust or grime is in the water, and it is not safe enough to drink without precaution. > 5 NTU (Unclean): The water is visibly cloudy and should be treated (eg: boiled or purified) before use\, because higher levels mean potential microorganisms. > 100 NTU (Extremely Dirty): Very thick\, muddy\, or murky water. Definitely not safe to drink!  Our manipulated variable (the one aspect of our experiment that we are changing) is the type of coagulant. We have four coagulants: Aluminum sulphate, polyaluminum chloride, ferric chloride, and finally, chitosan.  First, let’s take a look at aluminum sulphate. It is one of the most used coagulants that is not organic. It is mainly used to purify drinking water and wastewater. Aluminum sulfate breaks down in water and forms aluminum ions (Al³⁺). These combine with really small particles and form flocs that settle easily. Aluminum sulfate has a good coagulation effect, but it is less effective in low temperature water. This could have effects on our health, because  the use of aluminum sulfate might cause an amount of ions to stay in the water. Our second coagulant was polyaluminum chloride. It is inorganic, and is made of aluminum, chlorine, hydrogen, and oxygen. In addition, it is water-soluble and highly efficient. It can be clear or slightly yellowish, and is also referred to as PAC or PAX for short. Its precise and full name is Poly Aluminium Hydroxide Chloride Sulphate Solution. Ferric Chloride, also known as  Iron (III) chloride, or FeCI3, is a chemical compound. When dissolved into water, the substance undergoes hydrolysis, or breaking down into smaller separate molecules. This results in a very acidic and corrosive solution that is brown in colour, which is most commonly used as a flocculant in sewage treatment and drinking water.  Finally, there’s chitosan. This polymer  actually isn’t soluble in water, unlike chitin. Chitosan is a product of chitin, and is used in many products such as: biomedical engineering, pharmaceuticals, ophthalmology, nutrition/health, and yes, even cosmetics! It is an amino-biopolymer, meaning it is a polymer made of amino acids. The amino acids are linked together by peptide bonds, resembling a natural protein structure. Now that we’ve covered our coagulants, let’s discuss the actual process of coagulation. When a coagulant of any type is added, it neutralizes the negative charge of the particles in the water. Now that the particles’ charges are neutralized, they are no longer repelled by each other, allowing them to form “flocs” and “stick” together. This happens when the polymer is added as well. The flocs then settle and, as a result, the water then becomes less cloudy/dirty.  To sum up everything that has been stated so far, aluminum sulfate, polyaluminum chloride, ferric chloride and chitosan are all highly effective, inorganic coagulants except for chitosan; It is organic. The process of coagulation neutralizes the negative charges of particles and when the polymer is added, it becomes easier for the particles to floc and settle. Well, that’s coagulants in a nutshell. Thanks for listening!

Manipulated Variable: The type of coagulant.

Controlled Variables: - The amount of the coagulant added to dirty water - The amount of dirty water - Time of day - How much time we are letting the water sit with coagulants - Where water is placed

Responding Variable: Cleanliness level of water

Experimental Design: Procedure

1. First, make sure you have gloves and safety goggles on properly before proceeding with anything. 
2. Next, gather the materials you’ll need for this experiment and set them on a clean surface, preferably a table.
3. Mix the dirty water so that the dirt and water are not separated. 
4. Pour an equal amount of water into four beakers of the same size.
5. Measure the original turbidity of each of the samples/ beakers with a turbidimeter and note the results.
6. Measure initial pH with a pH meter.
7. Put the four beakers into the slots of the mixing machine.
8. After mixing rapidly for exactly 30 secs, add in coagulants to all four of the beakers. (Beaker 1-aluminum sulphate, 2-polyaluminum chloride, 3-ferric chloride, 4-chitosan)

9) After the coagulants are added, let the water mix        rapidly for another 30 seconds. 10) Add 0.75 micrometers of the Polyacrylamide  polymer while mixing 

11) Let the water mix for another 30 seconds rapidly.

12) Mix slowly (30 rpm) for 2 mins.

13) Stop mixing completely and let it settle for 10      minutes.

14) Measure the turbidity and pH of all 4 beakers and note the results.

15) Filter the samples (0.45 micrometer disc filters)

16) Measure the final turbidity of the samples and note the results.

17) Clean out the beakers as well as the containers used for sample testing

18) Repeat steps 1-16 two more times.

19) Clean everything up.

• chitosan was orange in colour and smelled pungent
• ferric chloride didn't seem to be working so well, so we increased the dosage of coagulant
• aluminum sulphate smelled like acitone
• after a few minutes the dirt in our large sample went to the bottom
• all coagulants had a different and peculiar smell
• most of the coagulants smells were pungent

Data Analysis:

| 0.59 NTU | 1.03 NTU | 1.16 NTU | 0.927 NTU |

Results/Conclusion   Based on our background research, we hypothesized that if we treat dirty water with different coagulants, an iron-based coagulant will purify the water more effectively than any other coagulant. We thought this because iron-based coagulants were one of the most used coagulants, so if it’s one of the most used, it must be a good coagulant. It also works effectively in a wide range of pH levels. In addition, it is able to form heavy flocs that settle quickly. These factors made us hypothesize what we did. However, our hypothesis was incorrect, and the coagulant that worked best was an aluminum hydroxide base (aluminum sulfate).

Our experiment showed that Aluminum Sulfate worked the most effectively in purifying the water. Following Aluminum Sulphate, there was Chitosan, Ferric chloride, and finally, Polyaluminum chloride.  From the data, Ferric Chloride was originally in the lead until after filtration. There were no patterns, but instead, changes in the results of each trial and coagulant. We were surprised by this because we had expected each sample’s NTU to be around the same amount each time.

We think that Aluminum Sulfate works the most effectively because it neutralizes charges well, and when the flocs start to form, even the fine particles do get caught. The city of Calgary uses Aluminum Sulphate as a step in its water treatment, and it is widely used as well, so it must be a good coagulant. We also think that Ferric Chloride worked well until after filtration because it is better at making flocs with certain organics. However, Aluminum Sulphate often achieves a cleaner final result.

To sum up everything that has been stated so far, the best-working coagulant was Aluminum Sulfate! This experiment shows how different coagulants work and why. We added coagulants after mixing the dirty water and polymers as well. Finally, we found the results and put them into graphs and a chart. This experiment was fun for us because we got to see how coagulants work, and before this experiment, we didn’t even know what coagulants were! Thank you so much for taking the time to listen to our presentation, and hopefully you learned something new, too!

Applications to the Real World

• Can be used to purify water in real life, like sewage or when camping!
• In countries where water purification is not possible on a large scale, small amounts of the best-working coagulant can be provided instead.
• Purification using coagulants is also used in the food industry to remove pollutants from wastewater made in food processing plants.
• Can be used to separate paint from water in industrial paint booths.
• Shows the world what cleans their water and how coagulants work
• Helps people to know which coagulants work really well and which ones don't work to well
• Encourages people to try this experiment or other versions of this experiment themselves

Questions?  

• What makes a  coagulant effective in water treatment? 
• When were coagulants created?
• How much does each coagulant cost? 

Errors/Improvements

• We could have collected different water samples with different turbidites to check if  the coagulation performance would be the same
• We could have double checked the turbidity level
• We could have made more observations about how the coagulants smelled looked like and measured the temperature of the water 

Questions?  

• What makes a  coagulant effective in water treatment? 
• When were coagulants created?
• How much does each coagulant cost? 

Errors/Improvements

• We could have collected different water samples with different turbidites to check if  the coagulation performance would be the same
• We could have double checked the turbidity level
• We could have made more observations about how the coagulants smelled looked like and measured the temperature of the water 

Bibliography Here are the links to where we got our information from:

1. Eastern technologies Inc-ETI water treatment specialists https://go2eti.com/blog/coagulants/
2. Guangzhou Chunke Environmental Technology https://www.chunkerowaterplant.com/news/what-is-the-best-coagulant-for-water-treatment
3. Science Direct .com 
   1. https://www.sciencedirect.com/science/article/abs/pii/S0014305708007222
4. Alliance chemical https://alliancechemical.com/blogs/articles/
5. Google Search Results on PAC (PolyAluminium Chloride)
   1. https://www.google.com/search?q=what+is+pac+in+water+treatment
   2. https://www.google.com/search?q=what+is+polyaluminum+chloride+made+of
   3. https://www.google.com/search?q=what+is+polyalumium+chloride

Acknowledgements

A heartfelt thank you to everyone who contributed to this experiment. We extend our gratitude to Mr. Baillie, our science teacher, and Webber Academy for providing a place for us to work and research. We would also like to thank Mr. Ribeiro for letting us use his lab and helping us perform the experiment.  Our moms, Mrs. Swami and Mrs. Ribeiro, for helping us with the design and aesthetics.