Project Overview

Figure 1 - Water
Source: http://www.osawaterworks.com/

PROBLEM OVERVIEW

Water is an essential molecule for life here on earth. Its abundance is overwhelming on the planet, with approximately 70% of the planet covered by ocean.  The human body is speculated to contain up to 65 percent water, and in some organisms it makes up to 90 percent of their body weight. With the abundance of this resource, it is hard to believe that the shortage of clean water causes so many problems worldwide. The problem lies in the filtration of water in order to make it safe for human consumption. Although there are thousands of trillions of gallons of freshwater on earth (approx. 3% of the total water on earth), much of this water is locked up in permanent ice caps and glaciers [1]. 

Human security and wellness means to be protected from unpredictable events that disrupt human life. There is no resource on the planet that has a more critical bearing on human security than water. Studies have shown that not only is the amount of freshwater on the planet decreasing as aquifers are drying up, but the availability of clean water in many developing countries is becoming a health problem. Approximately 884 million people worldwide lack access to clean drinking water. Children and women in developing countries are especially at risk. A child dies every 20 seconds from a water-related illness, and women collectively across the globe spend 200 million hours collecting water everyday [2].

Water contamination is a main source of disease for human beings. The water of the world has been polluted by contaminants that are often the direct result of human interaction with the environment. Examples of contaminants include pathogens such as bacteria and viruses, as well as chemicals, pharmaceuticals, detergents and fertilizers. All of these pollutants pose an immediate threat to individual organisms' health, as well as the overall biosphere. The problem at hand is a large problem, as one of the most important molecules to human safety is at constant threat. New, cheaper and easier methods of water filtration must be found in order to maintain the normal balance of society and the well-being of millions of people worldwide.

PRE-EXISTING SOLUTIONS

There are currently several methods of filtration available from the local to national level. For example, Philadelphia water is treated in accordance with the U.S. Environmental Protection Agency standards [3]. The Philadelphia Water Department first adds chloramine (combination of chlorine and ammonia) to dissinfect the water from bacteria and other harmful microorganisms. The chlorine levels can vary from .2ppm (parts-per-million) to 2ppm. Lime and other natural minerals are then added to adjust the acidity, in order to keep the pH at a neutral level. Fluoride is also added at 1mg/L to help prevent tooth decay. Finally, a corrosion inhibitor (generally a phosphate) is added to prevent lead and/or copper from getting into the water from the plumbing [3]. There are also many ways to filter water in addition to large scale purification methods, such as the use of Brita and Pur water filters.

Both Brita and Pur water filters use a very similar four step filtration system. There is first a basic pre-filtration step that removes larger particles suspended in the liquid. An ion exchange resin is then used to reduce the levels of carbonate hardness. This process takes unwanted ions and replaces them. The main method of filtration is the activated carbon which eliminates substances that alter the taste and smell, such as chlorine. Finally, a fine mesh is used to retain the unwanted filtrate. In this overall process, common impurities such as copper, mercury, lead, lindane (a common pesticide), atrazine (a common herbicide), as well as 96.6% of pharmaceuticals including Acetaminophen, Carbamazepine, Estradiol, Naproxen, and Progesterone are removed from the water [4]. Figure 2 below shows a typical Pur water filtration system that is connected to an average household sink faucet.

 

Figure 2 - Pur sink water filtration system
Source: http://waterfiltersystem-s.com/pur-water-filter/

INTRODUCTION TO ELECTROSPINNING

Electrospinning is a process by which a charged polymer line is accumulated by a grounded assembler. Some assemblers rapidly rotate, creating aligned nano-fibers, while stationary assemblers create randomly aligned fiber mats. Electrospinning manipulates electric charges in order to create these fibers from a liquid droplet. Electrospinning does not need high temperatures to create solid threads, which makes it ideal for the production of fibers through large and complex molecules.

The charged polymer line is formed through electrostatic charges overcoming the surface tension of the solution. Therefore, when a high voltage passes through a liquid droplet, it causes the liquid to be charged, causing an electrostatic repulsion that offsets the surface tension. This results in the droplet being stretched, and at a certain vital point, a jet of liquid emerges from the surface. If the molecular bond of the liquid is adequately strong enough, the jet will not break up, creating a charged liquid jet. When the flow of liquid dries while it is being shot out, the current flow switches from ohmic to convective, since the charge moves to the surface [5]. Figure 3 below is a basic electrospinning setup diagram.

Figure 3 - An overview of the electrospinning device
Source: http://www.centropede.com/UKSB2006/ePoster/background.html

A video introduction to the electrospinning procedure can be found here: http://www.jove.com/video/2494/electrospinning-fundamentals-optimizing-solution-and-apparatus-parameters

PROJECT GOAL

The goal of this research is to explore electrospinning techniques that will optimize the filtration properties of nanofiber polymer mats. The design process will address critical variables in electrospinning such as humidity, polymer/solvent ratios, spinning distance and voltage. By understanding the impact of each of these components, the spinning conditions can be optimized for mats with filtration properties. The goal is to use the polymer polyethylene oxide in a water solvent to electrospin the mats. Physical components of the mat like average fiber diameter and average pore size will be evaluated to study filtration efficiency. The group will also explore alternative polymer compositions and arrangements that could increase the filtration efficiency. The team will use experimental data as well as pre-existing research to propose possible applications for this filtration technology.

Figure 4 - Polyethylene oxide
Source:http://www.oe-chemicals.com/news.html

The polymer that will be spun is polyethylene oxide (PEO). This polymer has been chosen because it is relatively easy to spin and water can be used as the solvent. Figure 4 shows a PEO monomer unit. The polyethylene oxide will be spun into a nano-fibrous mat. The optimal fiber density and diameter will be determined with testing. A scanning electron microscope (SEM) will be used to take photographs of the nano-fibers.

Figure 5 - Electron microscope images of nano-fibers

Source: http://static.ideaconnection.com/docs/5391/WO+2009011944.jpg

The optimal lab conditions need to be perfected in order to produce polymer membranes that are capable of filtering water. Figure 5 above shows electrospun nano-fibers analyzed using scanning electron microscope technology. There are many different substances that must be filtered out of fresh water in order to deem it safe for human consumption. The goal of using nano-fiber mats is to filter out contaminants such as bacteria, viruses, chemical pollutants and other microorganisms. The goal is to create polymer membranes that have a small enough pore size to filter out E. coli and similar sized microorganisms. As research moves forward, these mats could be produced in an efficient and cost effective manner in the hope that they will have a positive impact on people across the globe.

Escherichia coli (Figure 6) is a rod-shaped bacterium that is common to the intestine of many animals and humans. Some strains of E. coli can be deadly to humans and cause severe food poisoning. E. coli is one of the most important indicators of water sanitation. In many areas of the world, the water and food can become contaminated in many ways. Some of the major problems come from factory farming and sewer systems. The EPA water quality standard for E. coli bacteria is 394 colony forming units per 100 mL (water.epa.gov). Bacteria such as E. coli are normally removed from drinking water using filtration and chemical treatment with chloride, ammonia, or a combination in a form called chloramine.

Figure 6 - Escherichia coli SEM image
http://commtechlab.msu.edu/sites/dlc-me/zoo/zah0700.html

E. coli cells are typically rod-shaped and are approximately 2.0μm in legnth with a diameter of about 0.5μm and a cell volume of 0.6-0.7(μm)³ [6]. The size parameters of this bacterium drives a goal for the design. Pore size of the membrane must be small enough in order to be effective in the filtration of these microorganisms. Pore size can be controlled based on many different variables. The goal is to increase the fiber diameter in order to minimize the area of the pores. In addition, pore density in a multilayer mat plays an important role.

PROJECT DELIVERABLES

• Define parameters of lab setup that will be most successful with PEO
• Select and present a polymer and solvent combination that meets the physical and chemical demands of filtration
• Scanning Electron Microscope images of the fiber mats
• Data and graphs comparing the variables that effect the electrospinning process
• Testing results
• Discussion of future implications of the design and the design's societal relevance

DESIGN CONSTRAINTS

• PEO polymer assigned
• Availability of lab hours
• Time (10 weeks)
• Weather conditions such as humidity and temperature can affect the spinning
• Accuracy of lab equipment
• Available funding

PROJECT SCHEDULE

 Week 4

a.      Determine which polymers we will use for the filter mats, as well as physical
 specifications of the mat designs (area, fiber arrangement/density..)

b.      Arrange lab time for week 4-5 to spin

Week 5

a.       Research alternative filtration methods and additional examples of PEO spinning conditions

b.      Schedule appointment for SEM of first image

Week 6

a.   Acquire SEM images of first sample

b.      Analyze average fiber diameter and porosity with images

c.      Optimize spinning parameters for next experiment based on results

Week 7

a.      Perform second mat spinning

b.      Prepare SEM appointment for second mat and alternative control filter

Week 8

a.      Acquire second set of SEM images (no later than week 8)
b.      Analyze physical components (porosity & fiber diameter) of sample two and the control

c.   Compile and compare data from all samples

Week 9

a.     Finalize evaluation of filter efficiency
b.   Identify factors that limited the design process; provide theoretical improvements

c.     Project realistic plans for filter applications

PROJECTED BUDGET

Materials:

• Brita water filter: $7.99
• Poly(ethylene-oxide): $143.00
• Use of Scanning Electron Microscope (1 month): $250.00
•  Electrospinning Setup: $5,000.00

 Approximate total project cost: $5,400.99

For this project, laboratories and equipment from The College of Materials Engineering will be utilized. Most materials needed for testing and execution will be provided by Drexel University. Additional costs will be determined at a later time.