“Water, water everywhere, nor any drop to drink”
-Samuel Taylor Coleridge, “The Rime of the Ancient Mariner”
To this day, the Ancient Mariner’s utterance remains ominously relevant. Water covers almost three-quarters of the Earth’s surface, yet approximately half of the world’s 6.78 billion people do not have access to safe drinking water. Growing populations around the world are draining water resources and causing local shortages, while communities with ample water supplies are often facing new challenges in maintaining their water quality.
The wide-ranging human health, political, and environmental implications of water scarcity have necessitated the development of techniques and technology to make drinkable water from low-quality sources. Environmental engineers at Yale’s School of Engineering and Applied Science are at the cutting edge in the development of sustainable and inexpensive water treatment technologies for use in both developed and developing countries.
To Drink Or Not To Drink
Water is essential to all living things. Depending upon body weight, the average person is anywhere from 55% to 78% water. To avoid dehydration, the body needs to take in between one and seven liters of water a day; the exact amount depends upon climatic conditions, level of activity, and various other factors.
Drinking water, also known as potable water, is defined as water that is of high enough quality to be consumed without immediate or long-term harm. Water may not be potable because of the presence of unhealthy bacteria, chemicals, excessive sediment, or other impurities. It can be made potable by filtration, distillation, or chemical or heat treatment.
So Close, Yet So Far
Access to improved drinking water has improved dramatically in the last two decades. According to the United Nations’ 2008 Millennium Developmental Goals Report, 1.6 billion people have gained access to safe drinking water since 1990. At this rate, the world is expected to meet the drinking water target set by the United Nations (UN), which requires that 89% of the population in developing regions use improved sources of drinking water by 2015.
Despite this promising progress, the use of unsafe drinking water sources continues to be the norm in the developing world. Nearly a billion people still lack safe sources of drinking water, and 2.4 billion people lack access to adequate sanitation services.
The availability and quality of drinking water and sanitation services is directly linked to human health. Over 2 million deaths in the world a year are attributed to unsafe water. The majority of these deaths are due to waterborne diarrheal diseases, with the vast majority of victims children in developing countries.
Problems related to water scarcity loom in the future of the developed world as well. Half of the population growth during the coming century in the US is expected to occur in California, Texas, and Florida – states that already experience frequent water shortages.
Where is All the Water?
Water covers more than two-thirds of the earth’s surface. Overall, there are about 1.360 billion cubic kilometers of water on the planet. Of this collective amount of water, the overwhelming majority, 97.2%, is found in the oceans. 1.8% is permanently frozen in glaciers, ice caps, and ice sheets, 0.9% is groundwater in the form of aquifers (underground layers of permeable rock, like gravel or silt, containing water), and 0.02% is freshwater found in lakes, inland seas, and rivers. 0.001% is atmospheric water vapor at any given time. With all this water, how can there be shortages?
Though the Earth has immense stores of water, it is not equally distributed across geographical regions. Nor is all water safely drinkable. Seawater, for instance, is too salty for people to consume regularly. Drinking seawater in large quantities actually dehydrates the body in the long run because of the high salt content.
Only groundwater and freshwater are suitable for drinking. But the Antarctic ice sheet holds 90% of all freshwater on Earth, and a number of other freshwater sources are too contaminated for use as drinking water. In the developing world, the majority of rivers and streams are contaminated from wastewater runoff.
Adding to these problems, seventeen countries currently use more water per year than annually falls in the form of rain and snow. This causes rivers, lakes and underground aquifers to run dry over long periods.
Thus, even though the earth is covered with water, finding ample amounts to drink is a major social and economic concern.
Material Science to the Rescue
The world’s thirst far exceeds its limited supply of drinking water. In order to sustain the current human population, wastewater must be recycled and purified through a combination of chemical treatment and solid-waste management processes.
Professor Menachem Elimelech, Chair of the Department of Chemical Engineering, Roberto Goizueta Professor of Environmental and Chemical Engineering and the Director of the Environmental Engineering Program at Yale, aims to improve filtration and purification of water by studying physical and chemical systems which act on a microscopic level.
Novel materials and minute nanostructures might prove tremendously useful in purifying water. Elimelech is currently investigating if nanomaterials like fullerenes and carbon nanotubes might bind to impurities and aid in the filtration of dirty water. Simultaneously, he is studying the biotoxicity of these nanomaterials, looking at their interactions with model organisms and trying to figure out if they would be safe for human consumption.
Such structures might prove very useful in removing chemical contaminants from wastewater. Much of the US drinking water is laced with pharmacueticals like articificial hormones, and it is crucial that a system is developed to remove these impurities.
Elimelech is also doing a large amount of research on membranes. Many water filtration systems rely on membrane-based processes such as reverse osmosis (RO). By studying the mechanisms by which membranes used in water treatment are clogged by organic matter, small particles, and biological growth, Elimelech hopes to improve the efficiency of existing processes. He is searching for strategies to minimize this fouling and to chemically clean dirty membranes. In addition, Elimelech is looking to develop a forward osmosis (FO) desalination process that would allow people worldwide to remove the salt from seawater and make it safe to drink.
Modeling the Future
Assistant Professor Julie Zimmerman, jointly of the Department of Chemical Engineering, Environmental Engineering Program, and the School of Forestry and Environment, also works on water sustainability-related projects. Her lab has received a $2 million grant from the National Science Foundation to model and study the Great Lakes Basin.
“We chose the Great Lakes Basin as our area of study because its international boundary complicates our research,” notes Professor Zimmerman, half-jokingly. Because the Great Lakes Basin is an important shipping venue, it is protected under the Great Lakes-St. Lawrence River Basin Sustainable Water Resources Agreement. The terms of the agreement make the region optimal for the modeling of the human water cycle alongside the natural water cycle.
Professor Zimmerman’s research hails back to the severe drought in the city of Atlanta, Georgia, which began in 2007 and has only recently abated. “Atlanta city officials restricted activities like car washing in the residential sector but neglected to impose significant limitations upon the industrial sector,” remarks Zimmerman. The objective of her modeling program is to see whether measures such as those taken by Atlanta city officials were indeed effective in addressing their water shortage crisis.
“The system doesn’t care if the input is manmade or regional,” explains Professor Zimmerman. All of the water input is factored into the simulation, which can then be used to predict behavioral changes in response to policy and market mechanisms. This subsequently affects the allocation of water between industrial, residential, agricultural, recreational, and ecosystem sectors and allows scientists to explore pertinent questions about water management.
Beyond the Developed World
Water treatment processes utilized in the developed world are often neither practical nor sustainable in developing regions. In developing regions, small-scale water treatment technologies, are much more effective and culturally appropriate.
Cost is often the problem. It is difficult to buy a million-dollar filtration system if you are living on only a few dollars a day. By developing a cheap way of removing the toxic chemical arsenic from wastewater, Zimmerman has pushed the world one step closer to providing safe drinking water for all.
Her method involves running water through a column of chitosan (acetylated chitin) and titanium dioxide. Chitin is the main component of the exoskeletons of arthropods and of the cell walls of fungi. Titanium dioxide forms a complex with arsenic, removing it from free water. Alone, titanium dioxide, which comes in a fine powder form, leaches into the water it is purifying. Combining the titanium dioxide with chitosan beads prevents the titanium dioxide from entering the water. This process allows arsenic to be almost completely removed from contaminated water.
“We take what is normally a biodegradable waste product [chitin] and reuse it,” said Zimmerman, highlighting the sustainability of her lab’s system. The cyclical nature of the system is indeed quite impressive: the complexed arsenic can be removed from the chitinase beads and concentrated into pure arsenic, and the chitinase beads can then be reused to purify more water.
“My hope is that a major company like Intel can use the arsenic recovered through this method instead of mining arsenic and fund water treatment for arsenic in return,” said Zimmerman.
Engineers Without Borders
Yale students, as part of the international Engineers Without Borders (EWB) organization, are also heading the initiative to bring sustainable water resource engineering solutions to developing countries. The Yale chapter of EWB has been working on constructing a water distribution system to bring clean water to the town of Kikoo, in Cameroon, since 2007.
EWB co-president Liz Marshman, TD ’10, explains, “Kikoo is a small village of about 1000 people with plentiful streams running through it, but almost all of them are contaminated by bacteria from agricultural runoff, human feces, and residue of laundry and other washing done upstream. Without a clean water source nearby, the residents use this dirty water for cooking and drinking, and thus put themselves, and particularly their children, at risk for gastrointestinal illness and death.”
Members of Yale EWB will next be making their third trip to Kikoo to examine village politics and the technical possibility of extending the project into the neighboring village of Robitante.
The Dirty Side of Clean Water
Every process has its problems. Professor Jordan Peccia, Associate Professor of the Environmental Engineering Program, presented an alternative perspective of effective water treatment in a recent interview. “We treat our wastewater to a pretty high standard in the United States,” he said, “but, by virtue of our attempts to make the cleanest water, we also get the most byproducts—8 million dry tons of sludge.”
The resultant sludge is applied in aerosol form to agricultural lands in 40 states as fertilizer. Reuse of the sludge as fertilizer is generally preferable to putting them in landfills or burning them in hazardous waste incinerators.
However, such practices have been implicated as a threat to the health of people living near fields treated with these fertilizers. Peccia’s investigation of wastewater byproducts has confirmed the presence of many viral and bacterial pathogens in the sludge recovered from wastewater treatment.
Peccia’s research highlights the complexity and magnitude of the obstacles that water resource engineers face around the world. The quest to bring everyone clean, safe, and sustainable drinking water is likely to continue for many decades. Fresh, clean water is only going to become scarcer as time goes on. But each step forward is important. Water resource engineering is a necessary investment toward forestalling global thirst.
About the Author
JOYCE CHENG is a sophomore in Berkeley College majoring in Molecular Biophysics and Biochemistry. She is by no means subliminally promoting dehydration in this article.
Acknowledgements
The author would like to thank Professors Zimmerman, Peccia, and Elimelech, and Elizabeth Marshman, TD ’10, for their gracious contributions to this article.