Grade: 11 | State: Pennsylvania
Grade: 11 | State: Pennsylvania
Because heavy metals enter water through many sources, scientists are motivated to develop purification and extraction methods. Some of these techniques have been successful, but at great cost or with detrimental effects to the environment. The purpose of this experiment was to determine if the agricultural by-product Curcurbita (pumpkin) could be used to remove metal ions from an aqueous solution. Previous research has demonstrated that other agricultural wastes have been successful at metal adsorption due to the presence of carboxylic groups and lignocellulosic materials (Harmon 2007). Because these compounds are also prevalent in pumpkin, it should be successful at metal adsorption. Two different dosages of dehydrated pumpkin were applied to two different concentrations of chromium and lead ions, and then analyzed using ICP, Inductively Coupled Plasma Spectrometry. This experiment clearly showed a novel material for removing heavy metal ions from wastewater. At every concentration of metal, pH environment, and dosage of pumpkin, the level of heavy metal ions declined significantly following the pumpkin treatment. The toxic metals can be recovered from the agricultural products, making them reusable, low-cost alternatives to current purification methods.
Our environment is continually exposed to pollution by organic and inorganic compounds such as pesticides and metals. Heavy metals enter the water through a variety of sources, such as atmospheric deposition, mining, industry and agriculture. Because of the world’s growing population and resource demands, the rate at which these compounds enter our environment has been on an upward trend. These metals can bioaccumulate, so scientists are motivated to develop purification and extraction methods using a variety of techniques (Igwe 2003). Some of these techniques have been successful but are expensive or have detrimental effects on the environment. This justifies the need to investigate additional methods.
I recently read an interesting journal article that discussed the ability of banana peels to remove copper and lead from polluted river water. The success of this research was attributed to the presence of carboxylic groups in the banana peel (Castro 2011). Shortly after I read this article, my neighborhood and much of the East Coast experienced historic flooding. As I walked past our garden, I noticed pumpkins growing and anticipated creating jack-o’-lanterns. I wondered if the waste from pumpkins might also be successful at removing heavy metal ions. Considering the size of the pumpkins, they would produce more waste than banana peels.
The purpose of this experiment was to determine whether prepared pumpkin waste could be used to remove heavy metal ions from solution. Two different pumpkin masses were examined: 0.05 grams and 0.5 grams. The metal ions investigated were chromium and lead in solution, and were prepared in two different concentrations: 1.0 part per million and 5.0 parts per million. Fifteen additional control samples were examined. All samples were analyzed using ICP.
This experiment aimed to determine if pumpkin waste is a possible resource for heavy metal removal, if metal uptake is dependent on the strength of the pumpkin dosage, and if variation exists in the efficiency of heavy metal uptake depending on the specific element and its concentration. Banana peels and other natural waste products have been successful for adsorption of heavy metals, in part due to the presence of carboxylic groups, but also because of the presence of cellulose, hemicellulose, and lignin (Harmon 2007). Because these components are present in pumpkin waste, my hypothesis was that pumpkin waste would be successful in removing the toxic metal ions chromium and lead from an aqueous solution.
Clean drinking water is often taken for granted, especially in the United States. Despite the fact that approximately 70% of the Earth is covered in water, about 98% of it is in oceans and is therefore unsuitable for most human needs due to its salt content. Out of the 2% that is fresh water, the majority of it is locked up in glaciers and ice caps, leaving less than 1% usable by humans (Schwarzenbach 2010). Because humanity relies so heavily on fresh water, there is a need to reduce and remove pollutants from water sources locally, nationally and worldwide.
Water pollution is a serious issue, but many people assume these concerns are limited to developing countries. For example, nearly 25% of Chinese citizens lack access to clean drinking water, and more than 70% of Chinese lakes and rivers are polluted. In Shanxi Province, in the Yellow River watershed, rice contains excessive levels of chromium and lead, and cabbage is tainted with cadmium due to polluted water (Brown 1998). Unfortunately, water pollution is not limited to developing countries; it is a worldwide concern that exists even in my backyard. The Susquehanna River is a 444-mile-long lifeline and is the second-largest watershed in the eastern United States, covering portions of Pennsylvania, Maryland and New York. According to the Environmental Protection Agency’s Chesapeake Bay Management Study from 2010, 12,531 pounds of toxic metals flow through the Susquehanna each day. These figures are difficult to believe and even harder to accept.
Heavy metals are elements that have a relatively high density, and they are toxic or poisonous even at low concentrations (Lenntech 2004). Even though some heavy metals, such as chromium, are biologically important and needed in trace quantities, lead is toxic even in small dosages. Another negative characteristic of heavy metals is the tendency for them to bioaccumulate.
Many methods for treatment are available, including chemical and surface-chemistry processes such as precipitation, adsorption, membrane processes, and ionic exchange. However, these techniques have inherent limitations, such as poor efficiency, sensitive operating conditions, and the production of a secondary sludge requiring further costly disposal (Abbas 2010). These disadvantages, together with the need for more economical and effective methods for recovering the metals, have resulted in the development of alternative separation technologies. One such alternative is biosorption, in which certain types of biomass are able to bind and concentrate metals from even very dilute aqueous solutions. The biosorption process offers a number of advantages when compared to the conventional methods currently used. One advantage is that the heavy metals can be recovered from the biomass (Harmon 2007).
For this reason, the use of low-cost materials as adsorbent for metal-ion removal from wastewater has been investigated. Using agricultural waste products for metal removal not only has the same advantages as other adsorption materials, but it also uses what was once a waste product. A number of biological adsorption materials have been investigated for their potential to remove toxic metals, including apple waste (Maranon 1992); corn cobs (Igwe 2003); cereal crops (Abbas 2010); woody materials such as bark, leaves and sawdust (Harmon 2007); and, most recently, banana peels (Castro 2011). These materials were successful in removing heavy metals to varying degrees.
The success of heavy metal uptake by agricultural products is believed to be dependent on a number of factors, one of which is chemical composition (Harmon 2007). One compositional characteristic of successful heavy-metal adsorption products is the presence of lignocellulosic biomass. Lignocellulosic biomass refers to plant biomass that contains cellulose, hemicellulose, and lignin.
Another characteristic of successful agricultural products is the presence of acidic groups such as carboxylic and phenolic groups (Castro 2011). Carboxylic acids are the most common type of organic acids and are characterized by the presence of at least one carboxyl group.
Pumpkin waste was selected because of its high cellulose content and the presence of carboxylic acids. Although other agricultural products have been investigated, this is the first study to investigate metal adsorption in pumpkins. Additionally, pumpkins are a common crop in my geographical region and are grown on every continent except for Antarctica.
This procedure was divided into three stages: preparation of the pumpkin, preparation of the contaminated water, and the experiment. Four pumpkins were obtained from a local farm, washed and rinsed thoroughly, and labeled A, B, C and D. After removing the stems, seeds and inner membranes, I cut the pumpkins into sections and sliced them into thin strips approximately 1 by 3 by 0.125 inches. The strips were placed on a cooking sheet and placed in a 200°F oven for four hours. The cooled pumpkin strips were then pulverized into a fine powder in a blender and transferred to sterilized glass jars. The pumpkin powder was sieved using a 75 µm sieve and the 12-gram homogeneous pumpkin mixture ABCD was prepared.
Stage 2 of the experiment consisted of preparing the water samples. The dilutions of 1 ppm were prepared by pouring 4 ml of each metal (from a stock solution of 1,000 parts per million) into a 250 ml volumetric flask and adding deionized water to prepare a solution with a total of volume of 250 ml. The dilutions of 5 ppm were prepared by pouring 20 ml of each metal (from a stock solution of 1,000 parts per million) into a 250 ml volumetric flask and adding deionized water to prepare a solution with a total volume of 250 ml. This procedure resulted in four solutions: 250 ml lead at 1 ppm, 250 ml lead at 5 ppm, 250 ml chromium at 1 ppm, and 250 ml chromium at 5 ppm. Unbuffered portions of the solutions were reserved before adjusting pH. The buffered solutions were titrated with sodium hydroxide while the electronic probe monitored pH. The titration was completed when the pH stabilized at about 5.5.
Stage 3 consisted of combining the pumpkin with the prepared samples: 15 ml of the 1 ppm lead solution was poured into six labeled centrifuge tubes; 15 ml of the 5 ppm leaf solution was poured into six labeled centrifuge tubes. This was then done for the two chromium concentrations of 1 ppm and 5 ppm. Next I measured the amounts of pumpkin. When preparing the 0.05 g of pumpkin, a piece of weighing paper was creased, placed onto the digital scale and 0.05 g of the prepared pumpkin powder was measured out and placed into each of the 12 corresponding centrifuge tubes. When preparing the 0.50 g of pumpkin powder, a 25 ml beaker was used to hold the pumpkin powder on the scale. The scale was zeroed between each massing for both methods.
Fifteen additional control samples were also prepared, and were used as a comparison for the experimental samples to take into account any outside sources of heavy metals. Four controls were used to compare experimental results; these were 1 ppm and 5 ppm buffered lead, and 1 ppm and 5 ppm buffered chromium. Eight unbuffered controls were run in order to determine how adjusting the pH impacted metal uptake: lead at 5 ppm, lead at 5 ppm with 0.05 g of pumpkin, chromium at 5 ppm, chromium at 5 ppm with 0.05 g pumpkin, lead at 1 ppm, lead with 0.05 g of pumpkin, chromium at 1 ppm, and chromium at 1 ppm with 0.05 g pumpkin. Three additional samples investigated the lead and chromium levels in the pumpkins; these samples were deionized water with 0.50 g of pumpkin, deionized water with 0.05 g of pumpkin, and filtered deionized water. All samples were centrifuged, filtered to remove excess solids, transferred into numbered ICP vials, and run through ICP.
Data and Results
Using the mass measured from each pumpkin and calculating the mean, an 8- to 12-pound pumpkin yielded approximately 203 g of biomass. The volume of stock solution needed was calculated using the dilution equation m1V1=m2V2 . The unknown volumes for the 1 ppm and 5 ppm concentrations were determined to be 0.25 ml and 1.25 ml. The pH was adjusted after the dilutions were prepared in order to simulate wastewater environments; this data is summarized below.
Data Table 1: pH Adjustment
|INITIAL pH||ADJUSTED pH||DIFFERENCE|
|LEAD 1 ppm||3.31||5.75||2.44|
|LEAD 5 ppm||2.63||5.31||2.68|
|CHROMIUM 1 ppm||3.48||5.37||1.89|
|CHROMIUM 5 ppm||2.78||5.20||2.42|
Data Table 2: Metal Concentrations for 0.05 g Biomass
|CHROMIUM (ppm)||LEAD (ppm)|
|1.0 ppm 1||0.619||0.177|
|1.0 ppm 1||0.603||0.149|
|1.0 ppm 3||0.612||0.199|
|1.0 ppm MEAN||0.611||0.163|
|5.0 ppm 1||2.93||0.955|
|5.0 ppm 2||2.85||0.955|
|5.0 ppm 3||2.88||1.08|
|5.0 ppm MEAN||2.88||0.996|
Data Table 3: Metal Concentrations for 0.5 g Biomass
|CHROMIUM (ppm)||LEAD (ppm)|
|1.0 ppm 1||0.667||0.326|
|1.0 ppm 2||0.689||0.398|
|1.0 ppm 3||0.726||0.309|
|1.0 ppm MEAN||0.694||0.344|
|5.0 ppm 1||3.44||0.984|
|5.0 ppm 2||3.38||1.04|
|5.0 ppm 3||3.47||1.16|
|5.0 ppm MEAN||3.43||1.06|
Data Table 4: Chromium Control Data
|SAMPLE DESCRIPTION||Cr ppm|
|Cr 5 ppm unbuffered||4.92|
|Cr 5 ppm unbuffered w/ 0.05 g||2.87|
|Cr 1 ppm unbuffered||1.02|
|Cr 1 ppm unbuffered w/ 0.05 g||0.668|
|Deionized water w/ 0.5 g||0.00450|
|Deionized water w/ 0.05 g||0.00126|
|Filtered deionized water||0.00188|
|Cr 1 ppm buffered||0.991|
|Cr 5 ppm buffered||4.81|
Data Table 5: Lead Control Data
|SAMPLE DESCRIPTION||Pb ppm|
|Pb 5 ppm unbuffered||4.65|
|Pb 5 ppm unbuffered w/ 0.05 g||1.03|
|Pb 1 ppm unbuffered||1.04|
|Pb 1 ppm unbuffered w/ 0.05 g||0.168|
|Deionized water w/ 0.5 g||0.198|
|Deionized water w/ 0.05 g||0.0719|
|Filtered deionized water||0.0778|
|Pb 1 ppm buffered||1.06|
|Pb 5 ppm buffered||4.72|
Because the research examined different metal concentrations and biomass amounts, the percentage of metals removed is used for comparison. This was calculated using the following equation:
where ce is the calculated mean experimental metal concentration (what was determined through ICP after pumpkin treatment), ck is the known metal concentration without pumpkin added to the solution (the value determined in the metal control samples), and x is the percentage of metal removed. Because all experimental samples had an adjusted pH, all calculations use the buffered figures.
Data Table 6: Percentage of Metal Removed for 0.05 g Biomass
|Experimental 1 ppm||% Metal Removed||Experimental 5 ppm||% Metal Removed|
Data Table 7: Percentage of Metal Removed for 0.5 g Biomass
|Experimental 1 ppm||% Metal Removed||Experimental 5 ppm||% Metal Removed|
Data Table 8: Percentage of Metals Removed in Unbuffered Solutions
|Unbuffered 1 ppm||Unbuffered 1 ppm with Treatment||% of Metal Removed||Unbuffered 5 ppm||Unbuffered 5 ppm Treatment||% of Metal Removed|
Data Table 8 illustrates the percentage of metal removed when the pH was not adjusted with a dosage of 0.05 g; in this case, the unbuffered metal solution with pumpkin treatment was being compared to the unbuffered metal solution without pumpkin treatment. The second dosage of 0.50 g was not examined due to time and because lower dosages appeared to be more successful. Higher dosages tended to form clumps and were not able to mix as well. Consequently, the middle of the clumps was not consistently in contact with the metal solution. Also, the pumpkin powder seemed to collect in the bottom of the centrifuge tube.
Graph 1 shows the actual amount of metal remaining and the percentage remaining. The data is shown in orange for lead and in green for chromium.
Graph 2 shows the actual amount of metal remaining and the percentage remaining. The data is shown in orange for lead and in green for chromium.
The results proved to be incredibly exciting because they clearly showed a novel material for removing heavy metal ions from wastewater. At every concentration of metal ions, pH environment, and dosage with pumpkin, the level of toxic heavy metal ions declined significantly after treatment with pumpkin biomass. Using the strongest data, 85% of lead and 40% of chromium was removed following the pumpkin treatment. Because toxic metals can be recovered and recycled from agricultural products, pumpkin waste is indeed a reusable, low-cost alternative to current methods.
Although it was not the focus of this study, a number of unbuffered samples were run. After an unbuffered 1 ppm solution was treated with 0.05 g of pumpkin, 34.5% of the chromium and 83.8% of the lead were removed. When compared to the removal percentages of 38.3% for chromium and 84.6% for lead in the buffered solutions, there is only a slight increase in heavy metal removal after pH adjustment. An unbuffered 5 ppm solution after treatment with pumpkin saw 41.7% of the chromium and 77.8% of the lead removed. When compared to removal percentages of 40.1% for chromium and 78.9% for lead in buffered solutions, the lower pH was actually favorable for chromium, and there was very little difference between the two for lead.
This project has enormous applications in two areas: wastewater treatment and contaminated fresh water. Although further research is needed, pumpkin waste shows promise for being able to adsorb heavy metals. Using the estimated average biomass (200 grams from each pumpkin) obtained in this research, five pumpkins would generate 1 kg of biomass and would cost $0.19 to dehydrate. Other substances are significantly greater in cost. The NaOH precipitate in EMD Chemical Pellets ACS costs $106/kg; ion exchange resin (50wx 8-100) from Dowex was found on eBay for $389.66/kg, and activated charcoal from EMD costs $164/kg. Even taking into account the cost of labor in obtaining the pumpkins and preparing them for dehydration, pumpkin is promising.
Although this study is the first to investigate using Curcurbita as a material for removing heavy metals from water, further studies are needed to investigate other toxic metals, ease of heavy metal recovery, and reuse of the pumpkin product. Research has shown that by pre-treating or activating biomass products, their adsorption capability can increase. Because the goal of this study was to investigate inexpensive methods, this process was not implemented. Further research could investigate different pre-treatment processes, keeping ease of procedure and cost efficiency in mind.
Many studies evaluate the efficiency of biomass materials through use of isotherms and adsorption capacity; this would be a logical next step for comparing pumpkin to other products, and for helping to understand the chemical processes at work. My hope is to investigate further the possibility of utilizing agricultural products to remove pharmaceuticals, specifically antibiotics, from wastewater.
I would like to thank Dr. Todd Walter, associate professor at Cornell University, for his guidance and advice, and for creating the opportunity for me to work in his lab. I would also like to thank Mr. and Mrs. Markey for generously donating the pumpkins used for my research. Finally, I would like to thank Mr. Mark Ilyes, the Dallastown Area High School department chair, for his suggestions and guidance.
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This winning entry in the museum's Young Naturalist Awards 2012 is from a Pennsylvania eleventh grader. Lauren investigated whether a filter made of pumpkin could be used to remove heavy metal ions from an aqueous solution. Her essay discusses:
Supplement a study of ecology with an activity drawn from this winning student essay.