Microplastics in wastewater: Towards solutions

The world demands and produces more and more plastic every year, much of which eventually finds its way into rivers, lakes and the ocean. Analysis of water and sediment worldwide indicates that microplastics are ubiquitous in freshwater, marine ecosystems and soils.

Many plastic products are essential, but industries and consumers need to consider the trade-offs which include microplastic pollution and global heating. Over time, plastic products tend to shed smaller particles through natural weathering processes, creating microplastics, defined as less than 5mm in size.

Other microplastics are directly released into the environment in the form of small particulates. Toiletries and cosmetics may contain microplastics. The abrasion of large plastic objects such as the erosion of tyres when driving, or the abrasion of synthetic textiles during washing, are other sources of microplastics.

Microplastics enter water bodies through different pathways, including atmospheric deposition, run-off from contaminated land or through municipal wastewater. Microplastics come in a large variety of sizes, colours and chemical compositions, and include fibres, fragments, pellets, flakes, sheets or foams.

Microfibres, which have been reported as the most abundant type of microplastics in wastewater and freshwaters, are of particular concern. They have been identified in the intestinal tract of zooplankton, river-bed organisms, and mussels. They can result in gut blockage and starvation.

“Water pollution by microplastics is complex and multidimensional, and managing it effectively requires a range of responses,” said Birguy Lamizana, a wastewater expert with the United Nations Environment Programme (UNEP) and co-author of a study on microplastics in wastewater due to be launched either at the Stockholm World Water Week in August 2020 or at the United Nations Environment Assembly slated for February 2021.

The ongoing study, provisionally titled Assessing available technologies and providing a toolkit of options of technologies to remove plastic, microplastic and microfibres from wastewater and sludge, is a collaboration between UNEP and the International Water Management Institute.

The Tunasan river in the Philippines is one of 21 main tributaries to the country’s largest lake, Laguna da Bay

Different approaches to tackling microplastic pollution
Bans on single-use plastics and microplastics in personal care and cosmetic products have already been introduced in some countries. Behaviour change “nudges” and campaigns can reduce the use of such products. While certain textile designs can reduce microfibre generation during washing, such products may be expensive.

“Around 35% of microplastics in the oceans are believed to originate from the washing of synthetic textiles,” said Javier Mateo-Sagasta, the water quality coordinator with the International Water Management Institute and a co-author of the study. “One possible solution is to develop household-based systems to prevent microplastics from being released into sewer lines or the environment. Technologies exist, for instance, which are able to remove 97% of microfibres.”

“We need effective legislation for microplastics management beyond microbeads in cosmetics. So far, microfibres have been completely left out of the policy realm. We need to explore enforcement of levies on fabrics or products that result in high microfibre releases to help finance increased treatment costs.

“We must also improve the management of runoff to treat microplastics in water since land sources contribute up to 80% of microplastics entering water bodies,” said Javier Mateo-Sagasta.

Protecting water bodies and the landscape from microplastics is a major issue. “We need to design and adopt solutions able to limit the export of microplastics from cities and the landscape, protect water bodies from pollution loads, restore affected water ecosystems and minimize exposure to populations at risk,” said Josiane Nikiema, the research group leader with the International Water Management Institute on the circular economy and water pollution and a co-author of the study.

“The treatment of wastewater and run-off and the safe management of sewage sludge are key milestones on the path towards achieving these outcomes. The adoption and implementation of these solutions must be supported by legislation, sound technologies, economic instruments, education and awareness that drive real change on the ground,” she added.

In Europe and North America, hundreds of thousands of tonnes of microplastics are added to soils annually through sewage sludge.

“Incineration of sewage sludge to avoid soil contamination by microplastics is a possibility but it’s costly and deprives soils of organic matter which is also highly essential to its health,” said Nikiema.