Cleaning water with wetlands

I think a lot of people have trouble imagining a  technological society that doesn’t decimate the environment. That’s pretty understandable, given that it’s not something we’ve seen, thus far. One trick I find helpful, is to think about how we might deal with problems that will still exist, even if we end all fossil fuel use. One of those is the presence of sundry chemical pollutants in the planet’s water. The first thing to note is that a lot of this problem will be solved by ending our societal dependence on endless growth, and endless consumerism. Leaving aside the obvious examples of industrial pollution, it’s pretty widely known by now that there are elevated levels of estrogen in the water supply. What’s less well-known is that that’s mostly from livestock, not pills. So, given that shifting to a more plant-based diet in general is a good idea for the environment, there will be less estrogen in the water even before we reach the point of trying to remove it.

Even so, it seems like it would be a good idea to have the ability to remove such things from the water supply, even if there weren’t a whole raft of other chemicals in play. There are a lot of ways one could go about this sort of thing. The “engineering solution” would probably be forms of filtration and distillation. For some chemicals, that is absolutely the best way to do things, because the less of them there is in the environment, the better. For others, however, we can turn to my favorite category of solutions: ecosystem services!

Near the end of its 96-mile course, the Santa Ana comes to a seeming standstill in the Prado Wetlands. Covering 425 acres, the wetlands site — designed by engineers — consists of a series of rectangular ponds, through which the river’s gentle flow is controlled by dam-like weir boxes. It takes about a week for water to traverse the wetlands, during which time cattails and other vegetation help remove nitrogen, phosphorous, and other contaminants.

Today, the Prado Wetlands, which are operated by the Orange County Water District, are part of a new project to remove a different kind of pollution: the residues of medical drugs and synthetic organic compounds, such as herbicides, that are found in small concentrations in rivers but that may affect endocrine activity, metabolism, and development in humans. A year-old pilot project at the Prado Wetlands channels river water through three ponds, each about the length of five Olympic swimming pools. Sunlight and bacteria degrade residues of antibiotics, anti-inflammatories, sex hormones, and other drugs and man-made chemicals before the Santa Ana reaches Anaheim, 20 miles downstream. There the river provides the drinking water for 2.5 million people in northern Orange County.


One of the early indications that constructed wetlands could help treat pharmaceuticals and other synthetic contaminants came from a study of nonylphenol, which is widely present in laundry detergents. Nonylphenol is an endocrine disruptor and has been shown to have potent toxicity in fish. When a research team led by the USGS was testing the ability of a small-scale wetlands system outside of Phoenix, Arizona, to diminish nitrogen levels in the wastewater treatment effluent, they noticed that nonylphenol and its breakdown products were also reduced, some by 90 percent.

Since those tests, the team has built a full-scale, 380-acre constructed wetlands at the site, called the Tres Rios Wetlands. It is one of the largest in the U.S. and provides water for irrigation and wildlife habitat. It also has three main ponds that remove chlorine, heavy metals, herbicides, nitrogen, and nonylphenol.

Numerous studies have shown the effectiveness of constructed wetlands in removing such contaminants. A 2004 study of the Prado Wetlands found that the site helped reduce levels of ibuprofen and organic chemicals found in pesticides and flame retardants. Scientists in Spain have reported that natural systems efficiently removed a number of anti-inflammatory drugs and pesticides.

Still, many compounds, including some estradiols and antibacterials, are more resistant to treatment in constructed wetlands, with their levels dropping by only about half. “In my mind you definitely want more than 50 percent removal, or why bother?” says David Sedlak, a professor of environmental science and engineering at the University of California, Berkeley.

Sedlak and his collaborators are behind the pilot project at the Prado Wetlands. Inspired by experiments showing that drugs are degraded by sunlight as they move down a river, they worked on developing a new type of constructed wetland design specifically to remove these compounds.

In typical constructed wetland designs, weedy aquatic plants are the focal point, because of the myriad ways they break down contaminants. But they also overshadow, literally, the contribution of sunlight. So about a year ago, Sedlak’s team started testing what they call open-water units at the Prado Wetlands. Now, before wastewater enters the series of cattail-filled ponds, it drifts through one of three large ponds over the course of a day or two. To prevent plant growth, engineers used a simple approach: They put down a tarp along the bottom of the ponds.

Although the researchers are still in the first phase of data collection, the new ponds at the Prado Wetlands seem to work as well as a similar pilot-scale system in Discovery Bay near San Francisco that has been operating for about seven years. Early data suggest that open-water units at Discovery Bay remove 90 percent of sulfamethoxazole, an antibiotic often resistant to removal in waste treatment plants. An unexpected benefit is that a layer of algae and bacteria that grows on the tarp-covered pond bottoms appears to bind and degrade compounds.

Ponds similar to open-water units will also be incorporated into the Brazos River Demonstration Wetland, a 12-acre site that engineers started building in January in Waco, Texas. Construction should finish later this year. The project marks the first constructed wetlands designed to optimize the breakdown of drugs while also removing traditional contaminants found in wastewater treatment plant discharge. Brazos will not rely solely on photodegradation to remove compounds. Water will travel through weedy ponds to remove nitrogen and then through subsurface wetlands with very low oxygen levels to help strip out chemicals.

There are always going to be downsides to a system like this. Spreading out a river could increase evaporation enough that it would cause problems downstream. Large wetlands are also great breeding grounds for mosquitoes, which in turn increases the risk of mosquito-born disease. I think these are valid concerns, but they’re also problems we can get around, especially in our hypothetical future society that values life.

Not to get all utopian, but I also know that indoor versions of this sort of thing are certainly possible, and if done well could make a building quite pleasant to live in. For example, say a public housing building had its own sewage treatment setup. A lot of the mass is converted into biogas, and the separated water is treated, filtered, and then fed into an indoor wetland system that runs through the common areas of the buildings – areas with natural or artificial light that act like indoor “parks”, and that can clean the water for re-use without becoming a breeding ground for mosquitoes!

Beyond that, as the water is cleaned, it could also be used for things like communal gardens, raising fish for food, or other stuff, depending on the stage of cleaning. It could also be a great learning tool for the people who live there, and a chance for communities to experiment with how to use such a resource. I think that could end up being especially important with the rise in killer heatwaves. As always, the way we do things now is not how we have to do things.

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  1. says

    In CZ, there are a few small “gravel-reed-bed” sewage cleaning facilities, sometimes serving whole villages or small towns. I have one very small one in my own garden (sized for about 5 people).

    I have no idea how it works on estradiols or medications etc, but t works very well on all the pollutants that need to be measured. In fact, it exceeds the limits noticeably, except for water-dissolved ammonia. However, since it does remove phosphorus very efficaciously, so when there is an algal bloom in the end pond, it tends to be non-toxic green algae, not the toxic blue-green algae. I tried to have fish in the end pond, but they got killed in winter by the anaerobic decomposition of tree leaves. I have noticed that during the current drought, very little water comes through the reed bed to the pond at the end, a lot of water is evaporated by the reed. I have also noticed that it is most effective in the summer, less so in the winter (obv.).

    The biomass this does produce is indeed used as a fuel (the willows that grow around the end pond) and as biomass to improve soil quality (the reeds are crushed and mixed in with the soil in the vegetable patch in the spring).
    I imagine the whole thing could be under a transparent roof of some sort, but it would be difficult. Firstly it would reduce the mosquitoes, but it would impede all the other wildlife that inhabits the cleaning facility – all the happy frogs, bugs, dragonflies, etc. Secondly, it would reduce the UV radiation that reaches the water, which I would imagine does help to decompose all the harmful chemicals in the water. Thirdly it would reduce the contamination of the cleaning bed with organic material from the outside (tree leaves), which would be a plus.

    I think some combination of an engineering solution (filtration, UV irradiation) and biological (like a combination of roofed-over growing beds and free growing beds, with different plants in each) would be optimal. And it could kill two birds with one stone – a cleaning facility that during summer produces biofuel for the winter.

    Except for plastic, nature has a solution to virtualy any organic waste that we can produce. We only need to implement that solution.

  2. says

    It could also be that artificial UV ends up being a worthwhile solution. Also, I’m a big fan of the idea of allowing wildlife to live in our indoor common areas. We owe them shelter from the hell-world we’re creating, and ideally we’ll have time to do stuff like clean up after them as needed.

    As to plastic, there’s good news on that! I’ll do a post about it soon, but there are numerous bacteria that can eat plastic now, as well as at least one kind of mealworm, if memory serves, that can digest plastic with the assistance of (surprise surprise) gut bacteria. That’s not to say we shouldn’t take real action on plastic pollution, just that the truism that there’s no way for nature to break it down is no longer true.

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