Introduction: (Initial Observation)
Humans may live for a month or more without food, but only a few days without water; only oxygen is more important. Each day, the body loses up to three quarts of water. A loss of only 10-20% of the body’s water content could be fatal.
When we take untreated water from a river or reservoir, the water often contains natural wastes and pollutants, such as bacteria, solids ( like mud, sand, and debris), inorganic minerals, and decayed organic compounds, as well as trace amounts of certain other contaminants. Such water is not good for human consumption.
Water suppliers transfer this water to a treatment plant where water will be filtered and chemically treated to be ready for human use.
People who have a water well at home, do a similar process in smaller scale and filter their own water.
There are also companies who offer varieties of filtration systems for home.
There are many government organizations who research, control and offer information about water and water treatment. Food and drug administration (FDA) and Department of environmental protection (DEP) are among the best sources for information. Also many universities continuously research and offer courses about water filtration and treatment.
Following links are recommended for additional information.
What are the impurities in water?
Water impurities are:
- Solids (Like mud, sand, debris, pollen, mold, fungal spores, dust mites, algae, cockroach dust, ..).
- Inorganic Minerals dissolved in water such as Calcium and Magnesium Salts.
- Decayed organic compounds from dead plants and animals and animal waste. These are the impurities that give a bad taste and odor to the water.
What are the sources of impurities?
- Wildlife that inhabits the water and the surrounding lands are a main cause of water contamination. Small animals such as fish, frog and insects excrete waste material from their bodies to the water.
- Mines and exposed acid producing minerals.
How each impurity is removed?
- Paper or fabric filters separate solid impurities such as mud, sand and dust.
- Ceramic or sand filters separate much of organic impurities from plants and animals. In municipal water treatment plants this separation is done by settling the organic material using Alum or Aluminum Sulfate.
- Carbon block filter removes oils, benzene, herbicides, pesticides and other volatile organic hydrocarbons.
- Granular activated carbon removes chemicals that cause bad taste and odors.
What is water treatment?
Water treatment is disinfection of water by killing disease causing virus, bacteria and parasites.
Water treatment is done by adding chlorine, ozone or using Ultra Violet light.
- Chlorine gas kills bacteria with adequate contact time.
- Ozone units super-oxygenate water which kills bacteria with adequate contact time.
- Ultraviolet light systems make use of the ability of this portion of the light spectrum to kill bacteria. Such systems are only effective on bacteria, viruses and some algae.
Using sand, ceramics and charcoal to filter water is a slow process and is not economical for large amount of water, that is why all water suppliers are using methods other than filtration.
What do water treatment facilities do?
Water treatment facilities purify large amount of water in large tanks using the following three steps.
First material floated on the water will be separated (Using steel mesh)
Then other impurities will be settled slowly and by adding chemicals
Finally Chlorine will be added for disinfection.
The purpose of this project is to learn about filtration, what it does and how it works. This project will also help us to know the difference between filtration and treatment.
Some of the specific questions that can be studies for this project are:
- How does the height of charcoal layer in a filter affect the rate in which organic impurities will be absorbed?
- How does the size of charcoal pieces in a filter affect the rate in which organic impurities will be absorbed?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
If you are doing this project as a display project, you can skip this section. However, if you are doing this as an experimental project, then you will need to come up with questions, write your hypothesis, identify variables and do experiments to test your hypothesis.
For the above two questions that we have proposed, this is how you define variables.
- The height of charcoal layer is an independent variable (manipulated variable). The rate in which organic substances are absorbed is the dependent variable. Controlled variables are: Size of filter, concentration and type of pollutants, order and amount of filter material.
- The size of charcoal pieces is an independent variable (manipulated variable). The rate in which organic substances are absorbed is the dependent variable. Controlled variables are: Size of filter, concentration and type of pollutants, order and amount of filter material.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following are two sample hypothesis for two questions suggested above.
- By increase in the height of charcoal layer, the rate of filtration of organic material will increase.
- Smaller size charcoal can result a higher rate of filtration. Large piece of charcoals may have no filtering affects at all.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1: Experiment with filters
- 2-liter soda bottle, cut and dispose 2 inches from the bottom (by an adult)
- napkins or paper towels
- gravel, sand and cotton balls for your filter
- Charcoal (Cheapest one that don’t have liquid fuel added and have no odors)
- dirty water, (If you cant find any, make it yourself)
- Put the the soda bottle upside-down (like a funnel) and secure it so it will remain that way. You may do it by making a stand for that or hang it from some place.
- Layer the filter materials inside the soda bottle. Think about what each material might remove from the dirty water and in what order you should layer the materials. For an added challenge, use one additional materials to build your filter.
- Pour the dirty water through the filter. What does the filtered water look like?
- Take the filter apart and look at the different layers. Can you tell what each material removed from the water?
- Wipe the bottle clean and try again. Try putting materials in different layers or using different amounts of materials.
Exact measurements of the layers are optional; however, they affect the quality and the price of your filter. For example you may use a lot of activated carbon in your filter. In this case your filter will be very good, but it will also become expensive. On the other hand if you use a lot of sand with no or little activated carbon, then your filter will not be good and it will be cheap.
Now it’s time to experiment. Think of a question you want answered. Like, are there better materials for cleaning water? Be sure to predict what you think is going to happen. Then, test it out using different materials and record the results for your report.
Following are sample images of water filtration experiment. Material used for filtration in these images are Fish tank charcoal, Sand, Gravel and Coffee Filter
Test the effect of charcoal layer on filtration of organic compounds.
- Mix some food coloring with water to simulate water polluted with organic material.
- Make 3 identical filters with different heights of charcoal layer.
- Filter two cups of the colored water that you have made with each of your three filters.
- Compare the color of three filtered waters and record the results. Visually determine the rate of filtration (or the rate of color loss) and write that in your results table.
Your results table may look like this:
Height of charcoal layer Rate of filtration
|Height of charcoal layer||Rate of filtration|
You may also use the above results table to draw a bar graph.
Experiment 3: (Permittivity)
Compare the filtration time of different filter materials
In a multi-layer water filter, it takes certain amount of time for water to travel each layer. The total filtration time is the sum of the individual travel times for different layers. Travel time of water in each layer depends on how pores the materials are and the attraction forces between the molecules of water and the molecules of filter materials. In this experiment we compare some of the filtration materials for their speed of filtration also known as permittivity.
- Get 5 identical bottles. Fill each bottle with 100ml water and mark the water level.
- Get 5 identical funnels and place them on the bottles. Write the name of filter materials on the funnels or bottles.
- At the bottom of each funnel place a piece of plastic mesh or steel mesh (like those used in making sieves). This is used to hold the filter materials in place.
- Fill each funnel to half with different filtration materials. (Filtration materials may include sand, clay, activated carbon, or any other substance that may be used in filtration).
- To each funnel add some water to saturate the filtration materials. Wait about 5 minutes. Empty any water that are entered in bottles.
- Add 200ml water to each funnel.
- Record the time it takes for the first 100ml of water that leave the funnel and enter the bottle. Your data table may look like this:
|Filter materials||Filtration time|
Materials and Equipment:
Multi-layer filters are normally a cylindrical container with layers of filter material. Top layers usually separate large solids and debris from the water. Middle layers separate much finer impurities to create a clear water. Lower levels are usually activated carbon to separate hydrocarbons, gasoline, insecticides and impurities that cause bad taste and bad odor.
A typical filter may start with a layer of gravel at the bottom, and then large sand, fine sand, clay, activated carbon, fine sand again, and large sand on the top.
These filters can not separate all viruses, bacteria and other micro organisms. Micro organisms later must be destroyed using chlorine or other disinfectant material.
Since filter absorbs some micro organisms such as bacteria and viruses, these micro organisms will reproduce inside the filter and exit the filter in later uses. That’s why filter material must be renewed so often.
Some filters are made only from different types of sand.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
If you do any calculations for your project, make sure to write your calculations in this section of your report.
Summery of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
How does a water softener work?
We call water “hard” if it contains a lot of calcium or magnesium impurities dissolved in it. Hard water causes two problems: It can cause “scale” to form on the inside of pipes, water heaters, tea kettles and so on. The calcium and magnesium precipitate out of the water and stick to things. The scale doesn’t conduct heat well and it also reduces the flow through pipes. Eventually pipes can become completely clogged. It reacts with soap to form a sticky scum, and also reduces the soap’s ability to lather. Since most of us like to wash with soap, hard water makes bath-time or shower-time less enjoyable. The solution to hard water is either to filter the water by distillation or reverse osmosis to remove the calcium and magnesium, or to use a water softener. Filtration would be extremely expensive to use for all the water in a house, so a water softener is usually a less costly solution. The idea behind a water softener is simple. The calcium and magnesium ions in the water are replaced with sodium ions. Since sodium does not precipitate out in pipes or react badly with soap, both of the problems of hard water are eliminated. To do the ion replacement, the water in the house runs through a bed of small plastic beads or a chemical matrix called zeolite. The beads or zeolite are covered with sodium ions. As the water flows past the sodium ions, they swap places with the calcium and magnesium ions. Eventually the beads or zeolite contain nothing but calcium and magnesium and no sodium, and at this point they stop softening the water. It is now time to regenerate the beads or zeolite.Regeneration involves soaking the beads or zeolite in a stream of sodium ions. Salt is Sodium Chloride, so the water softener mixes up a very strong brine solution and flushes it through the zeolite or beads (this is why you load up a water softener with salt). The strong brine displaces all of the calcium and magnesium that has built up in the zeolite and replaces it again with sodium. The remaining brine plus all of the calcium and magnesium is flushed out through a drain pipe. Regeneration can create a lot of salty water.
What is “activated charcoal” and why is it used in filters?
Charcoal is carbon. Activated charcoal is charcoal that has millions of tiny pores between the carbon atoms. According to Encyclopedia Britannica, “The use of special manufacturing techniques results in highly porous charcoals that have surface areas of 300-2,000 square meters per gram. These so-called active, or activated, charcoals are widely used to adsorb odorous or colored substances from gases or liquids.”
The word adsorb is important here. When a material adsorbs something, it means that it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface they attach to the surface and are trapped.
Activated charcoal is good at trapping other carbon-based impurities (“organic” chemicals), as well as things like chlorine. Many other chemicals are not attracted to carbon at all – sodium, nitrates, etc. – so they pass right through. This means that an activated charcoal filter will remove certain impurities while ignoring others. It also means that, once all of the bonding sites are filled, an activated charcoal filter stops working. At that point you must replace the filter.
Activated charcoal is most effective at removing organic compounds such as volatile organic compounds, pesticides and benzene. It can also remove some metals, chlorine and radon. As with any treatment system, it cannot remove all possible drinking water contaminants.
Because activated charcoal systems are limited in the types of compounds they can effectively remove, it is essential that the homeowner determine which water contaminants are present before purchasing such a system. Anyone who suspects they have a water quality problem should first have their water analyzed by their local health department or a reputable laboratory. These analyses are costly, but worth the expense since they are necessary to determine the appropriate home treatment system and how best to operate such a system. A state or local health official can interpret water analysis results. Some laboratories may also provide this service.
Note that home water treatment is considered only a temporary solution. The best solutions to a contaminated drinking water problem are to either end the practices causing the contamination or change water sources. Activated charcoal is a black solid substance resembling granular or powdered charcoal. It is extremely porous with a very large surface area. Certain contaminants accumulate on the surface of the activated charcoal in a process called adsorption. The two main reasons that chemicals adsorb onto activated charcoal are a “dislike” of the water, and attraction to the activated charcoal. Many organic compounds, such as chlorinated and non- chlorinated solvents, gasoline, pesticides and tri-halo-methane can be adsorbed by activated charcoal. Activated charcoal is effective in removing chlorine and moderately effective in removing some heavy metals. Activated charcoal will also remove metals that are bound to organic molecules. It is important to note that charcoal is not necessarily the same as activated charcoal. Activated charcoal removes vastly more contaminants from water than does ordinary charcoal.
Home activated charcoal treatment systems are quite simple. The activated charcoal is normally packaged in filter cartridges that are inserted into the purification device. Water needing treatment passes through the cartridge, contacting the activated charcoal on its way to the faucet. Activated charcoal filters eventually become fouled with contaminants and lose their ability to adsorb pollutants. At this time, they need to be replaced. Activated charcoal treatment systems are typically point of use installed where they typically treat water used for drinking and cooking only. Activated charcoal filters can be placed on the end of the faucet, on the countertop, or under the sink. Point of use systems often have a bypass so that water for purposes other than drinking and cooking can also be dispensed at the tap without being treated. This increases the life of the activated charcoal, reducing the time between filter replacements.
A point of entry system is more appropriate if a contaminant is present that poses a health threat from general use as well as from consumption. Volatile organic compounds and radon are examples of this type of contaminant. These contaminants may get into the indoor air when water is used for showering and washing. In this case, it is more economical to have a large pint of entry system that treats water as it enters the home than to have point of use systems at each tap.
Activated charcoal filters used for home water treatment contain either granular activated charcoal or powdered block charcoal. The amount of activated charcoal in a filter is one of the most important characteristics affecting the amount and rate of pollutant removal. More charcoal in a cartridge means more capacity for chemical removal, resulting in longer cartridge lifetime. This means fewer cartridge changes and less chance of drinking contaminated water. Particle size will also affect the rate of removal; smaller activated charcoal particles generally show higher adsorption rates. Rust, scale, sand or other sediments can clog any activated charcoal filter. A solution to this problem is to place foam or cotton filters (often called sediment or fiber filters) between the cartridge and incoming water. When sediment filters become clogged, they need to be replaced or they will cause water pressure to drop.
An activated charcoal filter must be deep enough so that the pollutants will adsorb to the activated charcoal in the time it takes the water to move through the filter. The appropriate filter depth depends on the flow rate of water through the filter. The slower the flow rate, the better the removal. The poor performance of some end of faucet devices is probably due to improper filter depth.
Physical and chemical characteristics of the water will also affect performance. The acidity and temperature can be important. Greater acidity and lower water temperatures tend to improve the performance of activated charcoal filters. Activated charcoal filters have a limited lifetime. Eventually, the surface of the activated charcoal will be saturated with adsorbed pollutants and no further purification will occur. This is called breakthrough; the pollutants have broken through the filter to emerge in the treated water. When this occurs, it is possible that the contaminant concentrations in the treated water will be even higher than those in the untreated water. At this time, the cartridge needs to be replaced. Knowing when breakthrough will occur and thus when to replace the cartridge is a major problem with activated charcoal treatment.
Some cartridges are sold with predictions about their longevity. These are generally only crude estimates since they do not take into consideration factors that are characteristic to a specific water source, such as pollutant concentration. The retailer you purchase the treatment device from can make better estimates of the filter’s useful lifetime based on water usage (flow rate) and pollutant concentrations shown in the chemical analysis. Hence, to get the most accurate estimates, you should learn what these amounts are before purchasing the system. Note that if pollutant concentrations increase over time and testing is not performed to reveal this change, such estimates may turn out to be not very practical or useful.
Unfortunately, activated charcoal filters can be excellent places for bacteria to grow. Conditions for bacterial growth are best when the filter is saturated with organic contaminants, which supply the food source for the bacteria, and when the filter has not been used for a long period of time. It is still unclear whether the bacteria growing on the charcoal poses a health threat. Some manufacturers have placed silver in the activated charcoal in order to prevent the growth of bacteria. The effectiveness of this procedure has not been independently verified. In addition, silver may contaminate the drinking water.
The above considerations have led public health officials to consider activated charcoal home treatment a temporary solution to be used only until the source of contamination can be eliminated and the water supply is safe. Even with proper installation, maintenance and operation, malfunction of home water treatment systems can occur.
Activated Charcoal Filter Guidelines
Make sure the filter contains activated charcoal.
Know the quantity of activated charcoal in the filter since this will determine the amount and rate of pollutant removal.
Use pre-filter to add life to activated charcoal filters.
Replace pre-filters and activated charcoal filters regularly.
Determine appropriate intervals for replacement of activated charcoal filters based on contaminant concentration, water characteristics, water flow rate, depth of filter, type and amount of activated charcoal and prefilter. Retailers can help in this analysis.