Of all plastics that have even been produced worldwide, less than 10 percent have been recycled. One of the biggest environmental dilemmas is that plastic does not decompose, but only breaks down into smaller pieces that can contaminate soil and water. Small plastic particles between one micrometer and five millimeters long are called microplastics; those smaller than one micrometer are called nanoplasts.
So far, microplastics have been found in water sources such as lake water, groundwater and tap water, and probably contain even smaller nanoplastics. In fact, studies have identified nanoplastics in tap water in China, lake water in Switzerland and even ice samples in the northern and southern polar regions. However, the full extent of small plastic contaminants in drinking water sources is not yet known, as they are difficult to detect, which can make it difficult to deal with the problem.
The potential health effects of small plastic particles
Microplastics have recently been discovered for the first time in human blood and living lung tissue, but their effects on human health have not yet been fully elucidated. Ingestion of microplastic particles can cause an imbalance in the human intestinal microbiome, which may play a role in the development of gastrointestinal disorders such as irritable bowel syndrome and inflammatory bowel disease. However, the direct connection has not yet been established.
Regardless of the risk considerations, releasing huge amounts of non-biodegradable synthetic material into the environment, leading to micro- and nanoplastic particles, is unreasonable, said Ralph Kagi, head of the particle laboratory at the Swiss Federal Institute of Aquatic Science and Technology.
“Nanoplastic particles can have side effects on ecosystems and human health,” he added. “The smaller the particles, the more likely they are to be absorbed by any organism and distributed, for example, in the gastrointestinal tract.
The number of nanoplasts in water sources is expected to increase in the future as plastics continue to degrade, which is why drinking water treatment processes need to be equipped to remove them.
Various filtration processes can help provide plastic-free drinking water
Some studies show that drinking water treatment plants can filter nanoplasts well enough. According to a study published in Science of the complete environment, a conventional drinking water treatment plant that uses sand and granular activated carbon (GAC) filters – a type of filter that uses many water pitcher filters – can remove nanoplastics by about 88.1 percent. The removal efficiency can be increased to 99.4 percent if a coagulation process is also used.
Meanwhile, another study published in Magazine for hazardous materials found that a treatment process called slow sand filtration was just as effective at trapping nanoplastic particles from water sources, if not more. In this method, the water is treated with a thick, biologically active layer called schmutzdecke, which lies on quartz sand. Untreated water passes first through the biological layer and then through the layers of sand beneath it.
The biologically active layer, which consists of organisms such as algae, bacteria and protozoa, is particularly effective at trapping the vast majority of dust particles, including micro- and nanoplastic particles, said Kyagi, one of the study’s authors. .
Pilot filtration experiments were conducted at the Zurich water plant to compare different water purification processes and to simulate nanoplast removal in a full-scale drinking water treatment plant.
In the slow sand filtration pilot unit, about 70 percent of the nanoplastics were retained in the first 0.1 meters of the sand layer, and the retention reached 99.5 percent at 0.9 meters. Other processes were not as effective. For example, ozonation or ozone infusion into water does not affect the retention of nanoplastics during water treatment. Meanwhile, activated carbon filtration retained only 10 percent in the first 0.9 meters of the filter.
As exciting as this news is, slow sand filtration is actually a fairly old technology. It was first used in the United States in 1875. Although it gradually fell out of favor in the late 1800s due to its slow flow and inadequacy to treat murky spring waters, it was still a promising filtering method for rural communities. .
Slow sand filters are also being phased out in newly built water installations due to their high space requirements. They are then replaced by ultrafiltration, a type of membrane filtration system that uses synthetic polymer membranes to physically separate or strain substances from water, such as sand or algae. They are generally more expensive, but the efficiency is comparable to slow sand filters and does not take up as much space, says Kagi.
There is very limited research on the subject, but the removal of micro- and nanoplastic particles using membrane filtration technologies seems to be more effective than other techniques. A 2021 study published in Water science and technology found that the membrane filtration method showed 100 percent efficiency in removing microplastics from wastewater, as shown in both laboratory and real filtration results.
“Membrane filtration systems are expected to even surpass slow sand filtration systems in terms of micro- and nanoplastic particle retention,” says Kyagi. Although it is very promising that some water purification processes can be effective in removing plastic particles from contaminated water sources, the root of the problem still needs to be addressed. Minimizing the use of plastics as far as possible remains paramount in providing plastic-free drinking water.