Under the hot summer sun of California’s Central Valley, Mi Nguyen, an environmental engineering doctoral student at UC Berkeley, slips on her high rubber boots and eases into the murky water of the wetland. The water comes up to her mid-calf and her boots sink two inches into the greenish slime at the bottom. This muck, known as the periphyton layer, is what keeps Nguyen coming back to this small wastewater treatment wetland in Discovery Bay.

Nguyen’s goal is to find ways to engineer low-cost, effective wastewater treatment systems, and this quest has brought her from her native Vietnam to graduate school in California and this wetland. Here, Nguyen and her colleagues are investigating the mechanisms by which sunlight can kill or inactivate bacteria in water, including the pathogens that can make us sick. They took all the help from alpharettawaterdamageremoval.com to gain an insight of what they were working on. They have found that the greenish, gunky periphyton layer has an important role to play in the process.

Armed with this knowledge, Nguyen expects to return to her native country of Vietnam and use what she has learned to improve environmental conditions for the friends, neighbors and people of her country that she hasn’t forgotten.

Raw sewage and trash pollute the waterways in Ho Chi Minh City. Credit: Cesar Harada

For dirty water in Vietnam, a need for new approaches

If you had asked Nguyen ten years ago what her future held, she would never have predicted that she’d be in California. After high school, Nguyen attended the Ho Chi Minh City University of Technology, the premier science and engineering college in Vietnam. Though she wasn’t sure what career she wanted, she enrolled in the environmental engineering program on the advice of her older brother, who described environmental engineering as a “hot new field.”

As she studied, Nguyen realized that her brother was absolutely right. “Everyone was trying to do environmental projects,” Nguyen said. “The cities were so polluted at the time.” In her time as a student in Ho Chi Minh City, she was especially struck by the foul water quality in the canal that surrounded the city. “It was completely dark with sewage,” Nguyen explained.

This situation isn’t unique to Ho Chi Minh City: in many cities in Vietnam and other developing countries, raw sewage is frequently dumped into rivers, lakes, and canals. The Vietnamese government estimates that, of the country’s domestic and industrial wastewater, 90 percent by volume is currently discharged untreated into waterways (follow this link for more information). A 2001 study of water quality in Ho Chi Minh City canals found fecal contamination in the water to be one hundred times above the country’s permissible levels.

Vietnam’s dirty waterways were having detrimental effects on Nguyen’s father’s business. He had recently lost his job as an accountant and had taken up shrimp farming in an attempt to make ends meet for his family. Shrimp farming is a risky business: the Food and Agriculture Organization reports that 39,000 hectares of shrimp farms in the Mekong Delta have been hit by disease. The Global Aquaculture Alliance estimates that if farmed shrimp larvae are exposed to infected waters, up to 70 percent of them will die before they reach a harvestable size. This fact discourages many farmers from attempting the business despite the high price of shrimp if the shrimp manage to reach adulthood. “People have ponds to grow the seafood, and whenever they need to change the water they just pump it out to the canal, and pump water from the canal directly back in to the shrimp pond,” Nguyen explained. With the growth of the seafood industry in the early 1990s in Vietnam, the canals became even more polluted, and this exchange of contaminated water served to spread the bacteria that cause diseases that kill shrimp. Because shrimp can take up to a year to grow large enough to sell, families who invest in the shrimping business often lose a significant amount of money if their shrimp die.

In the end, Nguyen’s father was one of many shrimp farmers in Vietnam whose investments—totaling more than three times the average annual salary in Vietnam—failed. “He never, never had success,” she said. “Before he actually harvested the shrimp, they all died of disease.” She continued, “It was really hard work. He would come home all tan, really dark because he was outside all day. He never could bring any money home. It was a disaster.”

Even though some people in Ho Chi Minh City were trying to address the country’s water quality problems, Nguyen noticed that the vast majority of them were not Vietnamese. Instead, engineering companies contracted out to professionals from more developed areas like Korea, Japan, or Europe. “Our country didn’t have many professionally trained environmental engineers,” Nguyen said. She was determined to get the training necessary to improve the water quality in her country.

Nguyen’s first job out of college was as an engineer for an environmental consulting company. She was getting paid more than she had ever made before and she was hopeful that her work would have a tangible impact on water quality in Vietnam. The consulting company designed and built wastewater treatment systems for the flurry of new food processing and shampoo-making factories being built in Vietnam in the late 1990s.

Soon, however, Nguyen found that the work wasn’t what she had expected. As a female engineer, she wasn’t allowed out in the field to direct construction on the new wastewater treatment systems. “Only the guys would go [to the field],” Nguyen explained, “because the engineers need to work with construction workers in the field to do the actual work [of building the wastewater treatment system]. And it’s not easy for a young female engineer to go into the field and ask construction workers to do something.” She shrugged. “So to make it easier, the company just asked the male engineers to do those things.”

The female engineers employed by the consulting company spent all day in the office, writing environmental impact assessments of new projects. Nguyen took her first assignment seriously, writing about the environmental impacts of a new factory that processed coconut and seafood for export to Thailand. She thought she had done a good job. But when she met with her boss, a distinguished-looking man twice her age, he informed her that the next step in the process was to bribe the official who would sign off on the assessment. If she didn’t do it, the new project would not be approved.

Nguyen didn’t want to bribe anyone, but she didn’t want to lose her job. “At the time, I had just graduated. I was so scared,” Nguyen said. When she tried to refuse to bribe the official, her boss replied, “If you want to work, you need to learn.” Nguyen knew that he meant it kindly, that he was teaching her how to work and fit into the system. Her mind raced. She had no idea how bribing someone actually worked. Would she just pass the cash to the official? Or put it in an envelope first? To her chagrin, she had to learn the art of bribery from her boss. He informed her that she should slip an envelope stuffed with cash between the pages of a notebook, then hand the notebook to the official with a code word to let him know what she was doing. When the moment came, Nguyen did it. “I’m not proud about that,” she said. “It’s just how our system works, and it’s crazy.”

She realized that the environmental impact assessments that her company did were a sham. Some of the other employees didn’t put much effort into writing them, since the bribes assured the assessments would pass muster regardless of their content. Even worse, she learned that the wastewater treatment systems her company designed lay idle after they were built, because the factories didn’t want to pay for the electricity to run them. Since there was very little oversight, the food processing factories often continued to release their raw wastewater, bypassing the newly-installed treatment machinery. For Nguyen, a job in which she was part bureaucratic paper-pusher and part briber was not what she had hoped or trained for.

“I wasn’t satisfied,” Nguyen said. “It wasn’t what I wanted to do.” Instead of continuing in her consulting job, she decided to pursue a PhD in environmental engineering. She thought graduate school would give her more job opportunities, and also provide her with a chance to see more of the world. “I knew that higher education was a way to get to go abroad, to get to know more, to open my eyes,” she said. Nguyen began applying to schools all over the world.

The opportunity to go abroad soon presented itself, when Nguyen won a prestigious fellowship through the Vietnam Education Foundation to fund her graduate studies in the United States. She immediately contacted Dr. Kara Nelson, a professor at UC Berkeley. Dr. Nelson’s research was interesting to Nguyen because she worked on water disinfection processes, something Nguyen had enjoyed studying in college. In addition, Dr. Nelson was interested in environmental engineering to improve conditions in developing countries. When Nguyen saw that, she thought, “This professor is great. I want to work with her.” Likewise, Dr. Nelson was impressed with Nguyen’s strong academic record and her resolve to study wastewater treatment systems that could be applied in Vietnam.

The next fall, Nguyen came to the United States and began her program at the University of California, Berkeley.

In the lab, a (free) radical solution

Her face lit by the eerie blue glow of a solar simulator, Nguyen carefully measures samples of contaminated water. Housed in a windowless room on the third floor of an austere concrete building, the solar simulator is the heart of Nguyen’s lab experiments. Its light bulb, as big as a human head, hangs over a tub of water in which six beakers sit under the glare. Two clear plastic filters over the bulb mimic the gasses in the earth’s atmosphere, effectively screening the amount of ultraviolet light to the levels that hit the earth’s surface.

Mi Nguyen uses the solar simulator to study the effect of sunlight on bacteria levels in different water samples. Credit: Jannis Wenk

Nguyen uses this machine to test how sunlight can kill or disable bacteria and viruses in wastewater. The beakers under the solar simulator contain three different mixtures. Some contain clean water that she has spiked with specific concentrations of a harmless strain of E. coli, which she uses to simulate fecal contamination. Others contain wastewater from the entrance to the treatment wetland in Discovery Bay. The third type contains wastewater from the outflow point of the same wetland.

Here in the lab, Nguyen can control the variables that might contribute to killing or inactivating the bacteria in her experiment, like the temperature of the water, the intensity of the light, and the saltiness and acidity of her samples. Her current experiment entails sampling the water from different parts of the wetland that have different types of periphyton present, to see whether the composition of the periphyton affects the rates of inactivation of bacteria. By measuring how many E. coli colonies reproduce in each water sample after treatment under the solar simulator, she can determine the different factors that contribute to their demise.

Nguyen wears a timer clipped to the front pocket of her jeans. On the hour, she meticulously collects samples from each of the beakers to bring back to her lab bench down the hall. Fluorescent lights illuminate the room with a harsh white light, and Nguyen, with her infectious laugh and brightly colored teal shirt seems incongruously alive in such a stark environment.

Working quickly, Nguyen brings her samples next to a tower of petri dishes at her bench, which she has stacked and pre-labeled. Each of the petri dishes contains a special gel that will only support the growth of E. coli, so that no other organisms, like bacterial intruders picked up from the air in the lab or E. coli-eating organisms, will be able to proliferate.

She first dilutes the samples 100 times, so that there will be few enough bacterial colonies in her petri dishes for an accurate count. Then she “plates” the samples by spreading them in a thin film in each petri dish. For these steps, time is of the essence. If Nguyen waits too long, the bacteria will die and confound her results. She’s already had to repeat this experiment multiple times because of contamination from other bacteria present in her lab, and the work is extremely time consuming. Her hands fly with speed and precision as she describes her research.

Content: Kara Nelson. Design: Helene Moorman. Click to enlarge.

Though Nguyen’s windowless lab may feel insular, her work could have ramifications for wastewater treatment around the world. Her experiments indicate that sunlight is actually most effective at killing bacteria in the cloudy water taken from the outlet of the treatment wetland. Bacteria spiked into clear water, or in the wastewater before it enters the wetland, are killed much more slowly.

Why might this be? The mechanisms are not fully understood, according to Nguyen. In general, scientists know that sunlight can kill or inactivate bacteria in at least two ways. Bacterial cells absorb lower-wavelength ultraviolet rays (UV-B) in sunlight, which wreaks havoc on the cell’s genetic material and prevents the bacterial DNA from doing its essential functions. This “direct inactivation” of bacteria by UV-B in sunlight is well recognized, and some water treatment plants in the United States use UV light bulbs to deliver a more powerful dose of radiation (UV-C) to directly disinfect their drinking water before it is piped out to customers. Though water sterilization by UV-C light bulbs is effective, it requires a constant supply of electricity that is not available in many developing countries. In small towns in the developing world that have plenty of sunlight but lack municipal drinking water systems, sunlight can be used to cheaply disinfect drinking water through a process called SODIS (solar disinfection): water is set out in clear plastic bottles in the hot sun for several days and then it’s safe to drink. These types of direct inactivation work best in clear water, without any plant material or extra particles that can interfere with the action of the UV rays.

But in Nguyen’s experiments, the sunlight is actually working best to disinfect the murky water from the outlet of a wetland—water that is laden with periphyton, algae, and other natural organic matter. This shows that the bacteria in the samples are dying from a mechanism other than direct inactivation by UV-B.

Through a process sometimes referred to as “indirect inactivation”, the natural organic matter in the water (the decomposing algae that makes it look cloudy) absorbs the sunlight, and transfers the energy from the sunlight to the oxygen molecules in the surrounding water. This blast of energy causes the formation of reactive oxygen species, which can react with and disable any bacteria in the water. Sunlight hitting the organic matter can also form oxygen free radicals, which have an extra, unpaired electron. The unpaired electron is dangerous for any molecules around it—it will essentially steal an electron from them, damaging their structure, and causing them to turn, zombie-like, into free radicals themselves that will go on to snatch an electron from another molecule. If this free radical cascade hits a bacterial cell, it will damage its molecular structure by tearing holes in the cell wall and ultimately ruining its ability to reproduce.

Household bleach works in a similar way, Nguyen explains. Chlorine bleach can make cloth whiter by breaking apart the chemical bonds that form color, or it can be added to swimming pools to react with and inactivate the bacteria and viruses in the water. In fact, chlorine is commonly used to disinfect wastewater as it leaves treatment plants in the United States.

But though chlorine is extremely effective at killing or inactivating the bacteria that make us sick, it also reacts with the natural organic material in the wastewater to make “disinfection byproducts,” chemicals that are known to cause cancer, liver disease, and nervous system disorders in humans. Adding an engineered wetland or pond to existing wastewater treatment plants could maximize the potential of sunlight to be used for disinfection—thus reducing the need for chlorine and its associated carcinogenic compounds.

Optimistic about cleaner water in Vietnam

Nguyen’s project intersects the work of two research communities at UC Berkeley: those working to prevent water-borne disease in the developing world and those working to re-think water infrastructure in the United States. In her lab, she works alongside scientists and engineers studying inactivation of pathogens and dedicated to improving water quality, sanitation, and hygiene in the developing world. At Nguyen’s wetland field site in Discovery Bay, she works with engineers who are committed to re-inventing urban water systems and are investigating ways to improve wastewater treatment in the United States, as part of a National Science Foundation engineering research center called ReNUWIt (Re-Inventing the Nation’s Urban Water Infrastructure).

Both of these communities see great potential in Nguyen’s research on wastewater treatment wetlands. In the developing world, wetlands could provide a low-cost, low-energy way to disinfect wastewater in places where no infrastructure currently exists. In the United States, wetlands could provide additional treatment for existing wastewater facilities, using vegetation to remove excess nutrients, and sunlight to help decompose pharmaceuticals and other chemicals in the water.

Mi Nguyen gets ready to take water samples from the wetland in Discovery Bay. Credit: Kara Nelson

Nguyen’s experiments will inform the design of future wastewater treatment wetlands, both in the United States and in the developing world. “Through Mi’s research, we are gaining a better understanding of how to optimize these natural treatment systems so they can be more effective,” says Dr. Nelson. This may mean designing wetlands that are shallow enough for sunlight to penetrate to the depths and slow-moving enough for a thick periphyton layer to develop.

While Nguyen’s work in the lab and in the field has become routine for her, life in the United States is decidedly different from her experiences growing up in Vietnam. Even the most basic infrastructure is different. Nguyen recalls her surprise when she figured out that she could drink the water straight out of the tap here. She was in Dr. Nelson’s class on water-borne pathogens, and she remembers staring at the professor’s water bottle. It had a sticker on it that said ‘I love tap water.’ Nguyen remembers thinking, ‘Really? I can drink tap water?’ “It was about four or five months after I got here,” she says, with a short laugh. “I was boiling water to drink, and letting it cool down. No one told me.”

Nguyen is motivated by thinking about what her research could do for people in her native country of Vietnam. Wetlands could provide a low-cost, low-energy method of providing basic sewage treatment. This would mean cleaner water in the canals, making them more enjoyable for recreation and also much safer to use. In a country where only 60% of the population has access to clean water, building new wastewater treatment systems is critical for improving people’s health.

She also hasn’t forgotten her father’s failed business: she is determined to use her research to improve the livelihoods of shrimp fishermen. “I can do something really simple,” she says. “Just have a pond before feeding the water from the canal to a shrimp farm, and let it sit in the sunlight for one or two days.” Even this type of system, with the right periphyton layer to produce natural organic matter in the water, could be enough to disinfect the water so that the shrimp would survive to harvest. Dr. Nelson is very supportive of Nguyen’s goals, “I’m delighted she intends to return to Vietnam after finishing her PhD and apply her many talents to tackling the challenging water pollution issues there.” Nguyen gives her signature smile, and says, “I’ll give it a try.”

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