Wednesday, December 28, 2022
Natural wastewater treatment plants are systems that use artificial wetlands, constructed from plants from marshy areas that are therefore accustomed to living in waterlogged environments to naturally clean urban water.
With this system, urban wastewater is circulated through a bed (of sand or gravel) on which plants are placed, which "take nutrients for their growth and promote the biological processes of pollutant elimination," explained Miguel Martín Monerris, Professor of the Department of Hydraulic and Environmental Engineering at the University Institute of Water and Environmental Engineering of the Polytechnic University of Valencia.
Although bacteria decompose organic matter and transform inorganic compounds, plants help considerably in this process by providing oxygen, creating habitat for these bacteria and purifying the water.
A system for small towns
Miguel Martín explains that these natural wastewater treatment plants are suitable for small population centers because they require a large surface area where these beds and plants can be placed. "But they are technologically very simple systems that can be maintained very well with the agricultural practices that usually exist in rural municipalities."
Other possible recipients of these water treatment plants are hotels or campsites that do not have a nearby sewage system, that are somewhat isolated and that can operate autonomously with this type of treatment.
His department, however, is studying replacing this traditional bed with sludge from larger-scale water treatment plants in cities. "They are inert, inorganic sludges and are not toxic sludges, they have a pollutant retention capacity that can be very interesting to study," he explained.
His team is taking this sludge and, after a treatment that converts it into gravel, places it in the natural treatment plants so that, in addition to filtering, it eliminates certain pollutants.
“It is very important to free the water of nutrients and this is not always easy" stated the researcher, who alluded to the presence in the water of elements such as phosphorus, pesticides, and medicines.
"These are emerging polluting compounds that were not very well known before and that, now, we see are quite important, such as caffeine and ibuprofen. They are very present in the water, and these gravels from the water treatment plant sludge are capable of retaining them," he stated.
In other words, these new natural purifiers can go a step further and eliminate these emerging pollutants, including microplastics.
The study is being carried out in two areas: Carricola, a small village of 100 inhabitants, and a development also in Valencia of about 1,000 residents.
Sludge with four years of activity
In the first, two 20-square-meter units are being built, while the second will work with a 60-square-meter extension. This second space will have a shorter useful life.
In this regard, the researcher explained that these gravels from sewage sludge have a useful life that, when exhausted, are no longer capable of retaining these components. This material must therefore be replaced when it is exhausted.
In the first of the facilities, it is estimated to last about four to five years. "The more surface area you can put in for these natural scrubbers, the longer the gravel is going to last you. That's the key," he said.
At the end of its useful life, these gravels must be shoveled out and replaced with new gravel. In the second phase of the research, the focus is what to do with this discarded gravel and whether it can also be put to new uses.
This researcher assured that this system can be extrapolated to any other area in Spain, modifying the design to give it varying sizes and depths, depending on the water to be treated and its composition. "The characteristics of the water, especially what we call the hardness with its amount of magnesium carbonates, can indeed affect the structure of the material," he admitted, adding that the tests are being carried out with water from Valencia, quite hard waters. "The material maintains its physical integrity quite well, it doesn't deteriorate," he described.
In addition to studying this elimination of other components in the water, the researchers are also analyzing the impact on the habitat of the installation of a natural treatment plant of these characteristics.
"Wetlands are bodies of water where water that has been treated is brought in, which encourages the development of phytoplankton, zooplankton, vertebrates, frogs, water snakes, and more," Miguel Martín explained.
This is why his team's researchers are going to monitor the discharge from these ponds into the ravines and rivers to see to what extent this water improves the environmental quality of the natural areas where it is discharged. "Our objective is not only to demonstrate that these water treatment plant sludges can be given a second chance, but also that we can obtain water of excellent quality not only for irrigation, but also for environmental uses that are not yet very well defined but that we believe should be further enhanced to improve the biodiversity of aquatic ecosystems," he said.
In fact, he believes that it would be very beneficial if all the water from the treatment plants, before reaching the rivers, were to pass through these natural treatment plants to "improve the biological environmental quality of the water."
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