Formation of Trihalomethanes in Water Distribution Systems and Their Removal

Giovanna Esteves & Erin Schatkowsky

Age: 17 | Hometown: Winnipeg, MB

Manitoba Schools Science Symposium 2018 Best Overall Group Project & Best Overall Physical Sciences Project | Freshwater Fish Marketing Corporation Special Award | Kids New Horizons Special Award | Canadian Representatives, Japan Super Science Fair 2018

Disinfection by-products, specifically Trihalomethanes (THMs), are a common problem in Manitoba which uses mainly surface water as the source of drinking water. They are formed when disinfectants, such as chlorine, used to control microbial contaminants, react with organic content, which Manitoba`s surface water is rich in. THMs include four chemicals: Chloroform (CCl3), Bromodichloromethane (CCl2Br), Dibromochloromethane (CClBr2) and Bromoform (CBr3) (Oram, n.d.). Due to their dangerous health risks, such as cancer, the concentration of THMs in the water is regulated, and the guideline in Canada is of 100 µg/L (Health Canada, 2016). However, THM levels in Manitoba, especially along the distribution system, are extremely high and exceed the limit. Water treatment plants should minimize the levels of all disinfection by-products without reducing the effectiveness of the disinfection. There are many methods to combat the proliferation of THMs, such as reducing chlorination before filtering the water and reducing the precursors (organic material that reacts with chlorine and form THMs) in general. However, they only reduce the probability of THMs’ formation at the water treatment plant and are not being used in Manitoba. Therefore, this project presents aeration as a simple and effective post-treatment process to completely or almost completely remove THMs and meet the guidelines.


Due to the presence of chlorine residual in the water, THMs along the distribution system would rapidly increase with the retention time of the water in the pipes as there will be more contact between chlorine and organic material, allowing more THMs to form.  Aeration should remove THMs effectively due to their volatility. Air would be injected at the bottom of a tank by air blowers and THMs would diffuse from water to air bubbles, and they would finally be released into headspace air with the bubbles.


DPD Chlorine Test Kit, DPD Free Chlorine and Total Chlorine Powder Pillows were used to calculate chlorine demand in order calculate required amount of chlorine to be added to different samples when simulating conditions at the distribution system.

In order to measure THMs, pentane was used as the organic solvent by liquid-liquid extraction, and all samples were quenched with sodium sulfite. Gas Chromatography vials were filled with the collected pentane (HPLC grade pentane, Fisher Scientific, New Jersey, NY, USA), (Agilent 7890A GC System, Agilent Technologies, Santa Clara, California.  Equipped with CombiPAL CTC Analytics auto sampler and electron capture detection).and the extracted THMs were then measured by Gas Chromatography equipped with an electron capture detector.

Aeration was done on 900 mL of water and required air provided by a spherical 1 inch in diameter Fisherbrand™ Gas Diffusing Stone with average pore size of 60µm. A clean air cylinder was connected to the diffuser by a VWR 0-5 LPM flow meter.


Water samples were taken from the Letellier Water treatment plant, located in Manitoba, and since the water has to have about 4mg/L of residual chlorine at all times along the distributions system, chlorine demand was calculated and the required amount of chlorine was added to each sample, so they would have 4mg/L of residual chlorine at all times like the water distribution system. Each sample represented a different retention time, therefore after waiting the specified time, the bottle was opened to measure formed THMs to see the relation between their formation and retention time. 

THMs were extracted from water to pentane as the organic solvent by liquid-liquid extraction (Standard Methods 6232B Liquid-Liquid Extraction). A total of 10 mL of Pentane was added in 3 sections and samples were vigorously shaken; 100 µL of concentrated sodium sulfite was added to quench the residual chlorine; and GC vials were filled with the collected pentane (top organic layer which is pentane containing THMs). The extracted THMs were then measured by Gas Chromatography equipped with an electron capture detector. 

A setup was created to simulate the air blowers at the plant. The set up included 900ml of water, a diffuser (a spherical 1 inch in diameter Fisherbrand™ Gas Diffusing Stone with average pore size of 60µm) which was connected to a clean air cylinder by a VWR 0-5 LPM flow meter. Air flow was fixed at 1.5 LPM and different air-to-water ratios were provided by changing the time of aeration, therefore the best ratio could be determined. 

Each 1 L bottle of water sample was just opened before the aeration and pH measured. 20 mL was taken to measure initial THMs concentration by the same method used previously. Then, required amount of chlorine was added to have about 3 mg/L of free chlorine in water to be able to measure chlorine loss during aeration. Four different air-to-water ratios were used to evaluate THMs removal including: 15.7, 23.5, 31.4, and 39.2, based on installing 2, 3, 4, and 5 blowers respectively and the annual average flow of water of the Letellier. ([Number of blowers X capacity of blowers] ÷ average annual air flow to plant = ratio) Therefore, the most efficient ratio at removing THMs could be determined. After aeration, 20 mL sample was taken and quenched to measure THMs, and the removal percentage was calculated.


By finding a relationship between the amount of total THMs and retention time in the water, the amount of THMs present at different locations of the distribution can be predicted based on different retention times. Therefore, plants can evaluate where and when they need to apply the removal method, which is aeration, as well as the aeration capacity based on the concentration of THMs. 

When measuring THMs, GC vials need to be tightly capped, since pentane is highly volatile as well.

After aeration, samples were taken to study reformation of THMs in distribution system. They were kept for 7, 24, 48, 72, and 168 hours. Since water had about 3 mg/L of chlorine after aeration, no additional chlorine was added to 7-hour sample. For the rest, required amounts of chlorine were added according to water chlorine demand for the desired retention time.

Chlorine loss was measured and samples did not lose a significant amount of chlorine after aeration process.


Results showed high predictability of THMs based on water residence time, therefore, for example, after 2 weeks THM levels triple the Canadian guidelines, which is extremely concerning (Figure 1). Regarding the aeration method, THMs were reduced by 61% to 72%, depending on the ratio. The ratio that worked best was the 39 (using 5 air blowers at the plant), which reduced THMs by 72% (Figure 3). THMs reformation study showed that aeration kept THM levels within the guidelines for about 24 hours, which is a reasonable amount of time since THMs are easily being formed and the reactions are always taking place as long as there is chlorine and organic material in the water.

Figure 1. Relationship Between the Concentration of the THMs (µg/L) and the Residence Time in Water (hr).

Figure 1. Relationship Between the Concentration of the THMs (µg/L) and the Residence Time in Water (hr).

Figure 2. Effect-of-Air to Water Ratio on THM Removal (%).

Figure 2. Effect-of-Air to Water Ratio on THM Removal (%).

Figure 3. Effect of Retention Time in Water (hr) on THM Levels (µL).

Figure 3. Effect of Retention Time in Water (hr) on THM Levels (µL).


At elevated levels, THMs have been associated with negative health effects such as cancer and adverse reproductive outcomes by oral ingestion, dermal absorption and inhalation of the water.  They are Cancer Group B carcinogens, and chloroform is associated with cardiac arrhythmias and abnormalities of the liver and kidneys including cancerous tumors.  Rats that ingested drinking water with chloroform formed liver and kidney tumors (National Toxicology Program, n.d.). Many water treatment plants in the Canadian Prairie draw water from surface water sources with high levels of dissolved organic carbon that require a higher use of chlorination, which greatly increases the levels of THMs. The levels exceed the guidelines after 10 hours, and triple the guidelines after two weeks of retention. It is crucial for the health of our population to decrease these levels. Therefore, aeration of treated water, by using the concept of volatility, has gained attention due to its simplicity, low capital and operating costs compared to other methods.


As shown in the graph of THMs and retention time, THMs  increase along the distribution system after the water treatment. Therefore, action must be taken to reduce THMs to a lower, safer, and regulated value. Aeration is a very simple and cost efficient method that can easily be applied to already existing water treatment plants. By aerating the water, the THM levels were reduced by 61% to 71%, depending on the air to water ratio used. Re-formation of THMs was investigated after aeration and residence time was measured to be about 24 hours. The success of keeping THMs under the maximum acceptable level was also attributed to removal of some volatile dissolved organic carbon by aeration besides THMs removal. There are currently no efficient methods being used to remove them and it is very important for the health of our population to decrease those dangerous levels. 


Brooke, E., & Collins, M. (2011). Posttreatment aeration to reduce THMs. American Water Works Association, 10(103), 84-96.

National Toxicology Program. (n.d.). Report on Carcinogens, Fourteenth Edition. Retrieved from

Oram, B. (n.d.). Four chemicals that are formed along with other disinfection by products when chlorine used to control microbial contaminants in drinking water. Pennsylvania Well Water Testing Private Wellowners Drinking Water Pennsylvania Ground Water Education Program. Retrieved from

Health Canada. (2016, August 8). Canadian Drinking Water Guidelines. Federal-Provincial-Territorial Committee on Drinking Water. Retrieved from

New Hampshire Department of Environmental Services. (n.d). Trihalomethanes : Health Information Summary. Retrieved from



Giovanna Esteves and Erin Montebruno Schatkowsky both currently live in Winnipeg, Manitoba and attend Shaftesbury High School.  They are hardworking students who have a passion for science and are eager to learn. They have been involved with the Formation of Trihalomethanes in Water Distribution Systems and Their Removal project since October of 2017 and have taken it to science fairs, such as the MSSS and the Sanofi Biogenius Competition. The project gained recognition and they have won a few awards. They are currently Grade 11 students who want to pursue careers in Science and are engaged in different Science classes and activities at school and outside of school.