ACTIVITY

Introduction:

We depend on access to clean water for drinking, preparing food and bathing, as well as for agriculture, industry and recreation. The presence of contaminants can severely impede its use and lead to serious health problems. Even the most pristine water contains some salts and natural organic compounds. But where does “natural organic matter” come from? What are factors that could influence how easily this material enters water? How can it be removed?

In this activity we will use leaf material as a source of organic matter, but in the environment organic matter could originate from many different plant, animal, fungal, or microbial sources. We will use a digital camera to measure the leaching of natural organic matter into water as well as the effects of various treatment methods.

What to do:

Part 1: Organic matter leaves the leaves…

Which kind of leaf material do you think would leach the most organic matter into water… older, dry leaves, or young green ones? Evergreens or deciduous? Oak or maple? Tree or grass? Trees living in the sun or the shade? Large leaves vs small ones…? Another really interesting factor that is not listed here yet…?

What is your hypothesis? Fill in the following with your group’s idea:

______leaves will leach more organic matter than ______leaves

because ______.

Each group will gather two different leaf types to compare. You will need a 2.50 gram sample of each type of leaf material if you are using the smaller containers, 6.25 g if you are using the aquaria or terrariums. Be careful in your sampling to choose leaves that are different only in the trait you have identified in your hypothesis, but are the same otherwise.

Describe leaf sample and site #1:

Describe leaf sample and site #2:

Setting up your experiment:

a. Cut your leaf samples into strips of equal width.

b. Measure 2.50 g or 6.25 g of each kind of leaf strip (depending on your container as described above). Set aside for step e.

c. Fill each container with 2 L of water (5 L for the glass aquaria or terrariums).

d. Position your experimental containers on either side of the control container. Adjust your digital camera to take an image of the three together so that they all fit and fill up the image with an even white background. Focus on the control container. This is the method and position that you will use for all of your data collection during the leaching phase. This image is designated as "Time 0".

e. Add your measured leaf material to their respective "experimental" containers. Use a stirring rod to swirl the water gently so all of the leaf material can be submerged.

f. Record digital images of the control and experimental containers every 3-6 hours for the next two days to record the progress of the leaching.

Data Analysis:

1. Import your photos into your computer. Name each file according to leaf type and time.

2. Create a spreadsheet in excel or similar program to keep track of the red, green and blue values for each leaf type, and the control over time.

3. Open the Analyzing Digital Images program. Open your Time 0 image. Use the rectangle tool to highlight a section in the center of your control container of 100,000 pixels. Record the red, green, and blue values for Time 0. Repeat for the Time 0 leaf (experimental) containers.

4. Record the red, green, and blue values for each container in each image in the time series as done for Time 0.

5. Make a graph of red, green, and blue intensities vs time for each leaf type.

Questions:

What does your graph tell you about the leaching for each leaf type over time?

Which color was most affected? Was this true of other groups?

What difference is made by using different containers? What challenges in data collection and normalization are introduced? What containers do you have available for use with your classes?

How might you tailor this activity to work with your students, curriculum, and classroom setting?

Experimental Extensions… a start… there are many possibilities!

How do other factors such as pH, salinity, temperature, particle size, amount of sunlight, water motion….affect the progress of leaching?

How are the properties of the leaves changed by the process of leaching?

Part 2: Cleaning up the water

Now that we have leached some organic matter into the water, how can we take it out? In this part, two methods of water purification (alum coagulation and activated carbon adsorption) will be compared. The digital camera will be used to assess the removal of organic matter from water by these two methods.

Each group will have seven 250-mL tissue culture bottles (3 for each leaf type, and 1 for pure water) in which to perform treatments and image collection.

Samples need to be filtered prior to treatment to minimize the effects of light scattering.

Set up your funnel stand so you can be filtering several samples (into their respective tissue culture bottles) simultaneously. Use Whatman #1 filter paper to filter your samples.

What to do: For each Leaf type, prepare three tissue culture bottles:

Bottle 1: Activated carbon treatment (adsorption):

a. Add 2.0 of activated carbon to the filter paper.

b. Treat the sample by passing it through the filter with the activated carbon.

Bottle 2: Alum treatment (coagulation)

a. Filter the sample.

b. Measure the pH using pH paper. Add 7% NaHCO3 solution 5 drops at a time (add, stir, check…) until the pH is 7.

c. Add alum solution (1% Al2(SO4)318H2O) 5 drops at a time (add, stir, check…) until flocculation (solids) can be seen throughout the sample.

Alternatively, use the following formula to calculate the alum dose, and test it using the above titration

Alum (mg/L) = (170/PL)*(log (Intensityblank/Intensitysample))

where PL = pathlength (length of container in cm)

d. Allow the floc to settle.

Bottle 3: Filtered, but untreated

a. Filter the sample. This will serve as the untreated control.

Bottle 4: Water control

To collect images:

Position the treated bottles on either side of the water control dish in front of a white background.

Filtered, Water Filtered,

Untreated Untreated

Leaf 1 Leaf 2

Adjust your digital camera to take an image of the three together so that they fit and fill up the image. Focus on the control dish. Replace the filtered, untreated bottles with the alum treated. Repeat image collection.

Repeat with the activated carbon treated samples.

Data Analysis:

1. Import your photos onto your computer. Name each file according to leaf type and treatment method.

2. Create a spreadsheet as before to keep track of the red, green and blue values for each treatment method and the control.

3. Open the Analyzing Digital Images program. Open your activated carbon/ filtered control image. Use the rectangle tool to highlight a section in the center of your control bottle of 100,000 pixels. Record the red, green, and blue values. Repeat for the treatment bottle. Repeat for activated carbon/ water image.

4. Record the red, green, and blue values for each treatment method and leaf type

Question:

Which treatment method removed the most organic matter? Is the treated water clean enough to drink?

Experimental Extensions… again, just a start…

Compare other treatment methods (bleach, Britta filter, water purification tablets (e.g., iodine), sand filter, ion exchange resin…)

How does pH affect the ability of alum to form a floc? Will other bases (NaOH, CaCO3…) work as well? Will other forms of alum (potassium alum, ammonium alum…) work as well?

How do treatment methods compare with respect to total dissolved solids?

Other extensions, questions, inquiries, interesting excursions…? Please ponder and share!

TEACHER’S GUIDE

Background information:

What is natural organic matter (NOM)?

Natural organic matter is complex mixture of organic substances present in all natural surface and ground waters. It can include substances that are:

  • leached from soil
  • decomposition products of plants, animals, fungi, microbes…
  • excretion products of plants, animals, fungi, microbes…

A body of water can become a sink for NOM as dissolved organics are washed into it from various sources. The composition and amount of NOM depends on the properties of the surrounding soil such as the pH, temperature, particle size and type, mineral content. Other factors such as rainfall, leaf litter depth and composition, and rate of decay are also important considerations. For example, water leaching through soil with a high clay content tends to have a lower NOM than water moving through sandy soil, and NOM values tend to peak in summer months when rates of decay and photosynthesis are highest.

By knowing what specific substance are making up the NOM in water, scientists can track the movement of material through the environment, and water treatment plant operators can evaluate the effectiveness of the treatment process. Because of the complexity of the mixture of organic substances comprising NOM, characterization of NOM begins with filtration (to remove particulates for analysis) followed by fractionation (dividing it into parts). The water is fractionated by passage through a column containing specific resins to which organic substances will adsorb depending on their surface charges or through membranes which can separate substances based on their molecular weights.

What problems are associated with NOM?

The presence of NOM in drinking water is linked to:

  • Esthetic issues: they can impart color, odor and taste.
  • Greater need/ cost of water treatment measures
  • Interferes with the removal of other contaminants.
  • Interaction with chlorine to form disinfection by products.
  • Increased bacteria and biofilm production as NOM can be a carbon or energy source for bacteria biofilm growth.
  • Lowered performance of water treatment processes such as membrane filtration and activated carbon filtration due to fouling.
  • Decreased oxygen levels in aquatic ecosystems.

BUT, NOM can also be helpful in aquatic ecosystems because it:

  • Acts as a buffer to maintain a more constant pH.
  • Transports nutrients.
  • Binds to metals and minerals

How is the organic matter in water measured?

Analysis following fractionation depends on the question at hand. Samples may be tested for total organic carbon (TOC) content, ultraviolet (UV) absorbance, or for specific organic compounds by gas chromatography and mass spectrometry (GC/MS) or liquid chromatography and mass spectrometry (LC/MS). If the overall levels of NOM are to be determined (as done in the water quality activity for this institute), several methods can be employed.

The strategy used in the institute was to use the color values in the visible spectrum to estimate the leaching and removal of NOM in water. This method was designed as a way to collect data using digital photography with students.

Here is a summary of some of the methods used in environmental chemistry and engineering laboratories to measure NOM.

Absorbance at 254 nm is a simple measurement of the sample’s ability to absorb light of a wavelength of 254 nm (in the UV part of the spectrum). This method takes advantage of the tendency for the bonds in organic molecules (particularly aromatics and double bonds) to absorb UV light, therefore this measure is correlated with the total amount of dissolved organic matter in water samples.

Bacterial Regrowth Potential (BRP) measures the ability of a water sample to support the growth of bacteria. The more organics that are in the water, the faster bacteria will grow because there is more for them to utilize for energy and food. In this test, a filtered water sample is inoculated with bacteria from the original sample. Bacterial growth can be monitored by measuring the cloudiness (optical density) of the sample using a spectrometer.

Total Organic Carbon analyzers measure total carbon. First, the inorganic carbon is removed from the sample by treatment with an acid, and sparging with an inert gas to volatilize the carbon dioxide. The remaining carbon (only “organic carbon” at this point) is determined by oxidation (either by combusting the sample at high temperatures or using UV radiation) to carbon dioxide and then the CO2 is detected measuring it absorption of infrared light.

Urbansky, 2001

For more information about sources of NOM and methods for measuring it, see the following:

Urbansky, E.T. 2001. Total organic carbon analyzers as tools for measuring carbonaceous matter in natural waters. Journal of Environmental Monitoring. 3: 102-112.

Natural Organic Matter: Understanding and Controlling the Impact on Water Quality and Water Treatment Processes. 2005. CRC for Water Quality and Treatment.

How is NOM removed from water?

Several strategies exist for to treat NOM in water. The choice of methods depends on the amount of water to be treated, the budgetary constraints, and the desired level of purity. Three of the most common methods are described below.

Coagulation employs a substance such as aluminum sulfate or ferric salts that form flocs (solids) with NOM that then settle out of the water. These flocs form because in solution at near-neutral pH, aluminum or ferric iron combine with water to form aluminum hydroxide and ferric hydroxide, respectively (see equation below). These are highly insoluble substances that will slowly settle if the water is allowed to sit quiescently. A certain fraction of the dissolved NOM will adsorb to the surface of the flocs and thereby settle with them. In addition, complexes of positively charged Al+3 and Fe+3 ions will be attracted to the surfaces of any negatively charged organic colloids, neutralizing their charge and causing them to stick together. For aluminum sulfate, the pH needs to be above 6.3 for the flocs to be large enough to effectively settle out, as shown in the following image.

Water sample (pH 6) Water sample (pH 7)

+ Alum + Alum

When alum is added to water containing sodium bicarbonate it undergoes the reaction below. The alum reacts with water to form aluminum hydroxide, a precipitate. The bicarbonate neutralizes any acid production so that the pH remains at a favorable level.

Al2(SO4)3*18H2O + 6NaHCO3<=====> 2Al(OH)3+ 6CO2+ 3Na2SO4+ 18H2O

The solubility product constant of aluminum hydroxide, Al(OH)3is 1.26 X 10 -33 indicating that aluminum hydroxide is essentially insoluble in water. This precipitation is at the core of floc formation.

After the flocs form and settle, separation can be accomplished by drawing off the water layer or by filtering. Residual aluminum and sulfate ions will remain soluble, and the “clean water” will be made slightly more acidic due to the small amount of carbonic acid that forms from dissolved CO2.

Activated carbon is made by heating natural materials containing carbon (e.g., anthracite coal, wood, nut shells, peat…) in a controlled atmosphere (containing carbon monoxide, oxygen, or steam) in order to make it more porous. It has a very large surface area (as you can see in the following image) which enables it to adsorb (attract and stick to) charged substances in the water sample.

Activated carbon sample, unknown magnification.

Activated carbon is commonly found in water purification systems, aquaria, and filters made for consumer use (like Britta filters). The absorptive properties of activated carbon are also applied in air filters, radon detection kits, and emergency treatments for poisoning.

Because it is toxic to microorganisms, Bleach, or sodium hypochlorite is commonly used to disinfect water. It also removes or oxidizes colored substances. The use of bleach and other forms of chlorine (or other halogens like bromine and iodine) is problematic because they react with NOM to form disinfection byproducts, substances such as trihalomethanes and haloacetic acids which have been shown to be carcinogenic.

For more information about the chemistry of flocculation, the benefits and disadvantages of various treatment methods, and the health effects and regulation of disinfection byproducts see the following:

Matilainen A, Vepsalainen V, Sillanpaa M. 2010. Natural organic matter removal by coagulation during drinking water treatment: A review. Advances in Colloid and Interface Science. 159: 189-197.

Kornegay, B.H., Kornegay, K.J.,Torres, E.. 2000. Natural Organic Matter in Drinking Water: Recommendations to Water Utilities. Denver, CO: AWWA Research Foundation and American Water Works Association

“Basic Information about Disinfection Byproducts in Drinking Water: Total Trihalomethanes, Haloacetic Acids, Bromate, and Chlorite”

Sources for supplies: Carolina Biological Supply:

Item / Cat Number / Description / Price
Aquarium / 671228 / Aquarium Tank, Glass, 5.5 gal / $21.50
Whatman #1 filter paper / 712810 / Filter Paper, Quantitative, 12.5 cm, 100 circles / $12.50
Aluminum sulfate / 843490 / Aluminum Sulfate Octadecahydrate, Reagent Grade, 500 g / $15.95
pH paper / 895280 / pH 1.0 to 12.0. 100 strips per vial, 5 vials per pkg / $21.25
activated carbon / 853740 / Charcoal, Activated Carbon, Reagent Grade, 500 g / $24.95
disposable pipets / 214561 / Disposable Plastic Needle-Point Pipets. Pack of 100 / $18.50
tissue culture flasks / 727030 / Pack of 20 / $36.10

Lamotte: Tap water Tour/ Test kits:

Hach: Test kits for water quality monitoring

Other Potentially Useful Websites

North American Association for Environmental Education: Lots of great links.

US EPA: High school environmental center

American Water Works Association

The International Water Association (IWA) Network of 10,000+ water professionals.

The Urban Water Research Center at the University of California, Irvine

The National Water Research Institute (NWRI)

The Southeast Environmental Research Center at Florida International University, Miami