This article originally appeared in WQP November issue as "On the Rise"
Every year, more chemicals and compounds are detected in water supplies. Known as contaminants of emerging concern—or emerging contaminants—these substances denote a wide variety of chemicals and byproducts that can include pharmaceuticals and personal care products (PPCPs), medicines, cleaning products, pesticides, per-and polyfluoroalkyl substances (PFAS) and microplastics. According to the Water Quality Association (WQA), emerging contaminants are of importance because the risk they pose to human health and the environment is not yet fully understood.
The rising prevalence of emerging contaminants are a product of growth in chemical manufacturing—more than 80,000 chemicals are used in the U.S. and more than 2,000 new chemicals are introduced each year. However, contaminants are also being progressively found due to significant advancements in the analytical techniques used to detect microconstituents. Many of the contaminants that are discovered in waters may not be new but instead were previously not measurable.
As metrology has advanced, providing the ability to analyze micropollutants with more accuracy and greater precision, scientists have questioned whether the existence of certain contaminants in water systems presents a threat to aquatic life and humans, and if so, what can be done to mitigate it. For example, the U.S. EPA has expressed concern that emerging contaminants and PPCPs may have an impact on aquatic life and is making efforts to quantify these risks. EPA has stated that many emerging contaminants act as endocrine disruptors (EDCs), which alter the normal functions of hormones, resulting in a variety of health effects.
Currently, a regulatory framework is evolving in parts around the world in terms of how to manage and treat different types of emerging contaminants. Many of these micropollutants cannot be adequately treated with conventional technologies and require more robust solutions to remove them from waters. The following takes a closer look at three subsets of emerging contaminants—pharmaceuticals, PFAS and microplastics—and covers different treatment technologies that are available to address them.
Pharmaceutical products and medicines are increasingly detected at low levels in water resources. This category of emerging contaminants mostly makes its way into water sources by first being released into sewer systems through human excretion and improper disposal. According to the World Health Organization (WHO), the ubiquitous use of pharmaceuticals (both prescribed and over the counter) has resulted in a relatively continuous discharge of pharmaceuticals and their metabolites into wastewater.
Generally, pharmaceuticals are high molecular weight and composed of complex organic compounds, making them less biodegradable than simpler organic compounds. Conventional wastewater treatment plants are not designed to attenuate these types of micropollutants, and because of their recalcitrance to conventional treatment processes, they can pass into the environment. Once there, some pharmaceuticals tend to bioaccumulate since they do not readily biodegrade.
To address pharmaceutical concentrations in wastewater, treatment plants can employ biological treatment that is specifically designed to enhance the biodegradability of those substances. Additionally, operators can pretreat wastewater or use post-treatment polishing employing advanced oxidation technologies such as ozone to remove organics or peroxide to break up these long, complex organic molecules into smaller organic molecules that are less harmful in the environment and can more easily biodegrade. By adapting biological treatment in combination with pretreatment or post-treatment, operators will have more flexibility in terms of what their systems can handle.
Although no regulations currently exist that pertain to treating pharmaceuticals, the industry is becoming more aware of the need to understand and seek knowledge regarding what can be done with the technologies that are available.
PFAS are a group of chemicals that include perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), and others that are used to make a wide range of stain-resistant coatings and nonstick products. Manufactured since the 1940’s, PFAS can be found in clothing, food packaging, cookware, cleaning products and firefighting foams.
The concern with certain PFAS chemicals, most notably PFOA and PFOS, is that they generally do not biodegrade and therefore are inclined to build up in the environment, including in fish, animals and humans. Since they resist breaking down, they are known as “forever chemicals.” PFAS have been detected in surface waters, groundwater and in drinking water supplies. According to EPA, evidence exists that exposure to PFAS can lead to adverse human health effects.
Due to these concerns, the EPA is taking steps with proposing regulatory determinations for PFOA and PFOS in drinking water. Several states have already either proposed or adopted limits. Currently, there are no existing or imminent PFAS regulations for wastewater. However, regulatory momentum on the drinking water side is beginning to prompt wastewater operators to start planning.
Treatment technologies that are effective for removing PFAS from drinking water or wastewater include granular active carbon (GAC), ion exchange (IX), and high-pressure membranes such as nanofiltration (NF) and reverse osmosis (RO). In designing the most effective treatment strategy, operators should first understand the specific PFAS contaminants that are present—such as smaller-chain or larger-chain PFAS types—which will ultimately determine the most appropriate mix of technologies to use. With addressing PFAS in wastewater, special precautions should be given to co-contaminants such as organics and salts that can interfere with activated carbon and IX processes and foul membranes.
Even in small concentrations, PFAS present a serious risk. For this reason, one of the biggest challenges relates to end-of-life disposal. Using RO will concentrate PFAS contaminants in a dilute reject stream and consideration must then be given to treating that waste with GAC or IX to sequester the contaminants. The spent GAC or IX media materials must then be either incinerated and destroyed or sent to a landfill permitted to accept PFAS waste.
Managing PFAS materials for ultimate disposal is a complex issue and the EPA is currently evaluating multiple disposal techniques, including how landfilling, incineration and recycling might contribute to PFAS in the environment.
Microplastics consist of tiny plastic fragments smaller than five millimeters in size. Some microplastics were made intentionally small for use as minuscule scouring agents in toothpastes, body washes or home cleaning products. Other microplastics derive from larger pieces of plastics in the environment that have degraded and broken down over time. Scientific studies have concluded that microplastics are widespread in freshwaters and oceans around the world and are also found in various food supplies including seafood. However, what is still unknown is whether microplastics are harmful to ecological and human health.
Different scientific organizations are working to minimize these uncertainties and better understand the potential risks of microplastics. An EPA microplastics expert workshop identified the need to conduct research on the sources, transport, fate, degradation, and distribution of microplastics in the environment and to create methods to characterize human exposure to microplastics in drinking water (including source water) to assess potential human health risks.
In 2015, the U.S. established the Microbead-Free Waters Act of 2015 which prohibits the addition of plastic microbeads in the manufacturing of certain personal care products, such as toothpaste. However, at present time, it is largely unknown whether water quality regulations will be enacted to address microplastics in drinking water or wastewater. Still, treatment technologies that are adopted to address other micropollutants—such as membrane bioreactors (MBRs)—can bring the additional benefit of removing microplastics.
Issues surrounding emerging contaminants are complex, multi-dimensional and continually evolving. With some of these micropollutants, such as PFAS, the regulatory environment is actively being defined and is subject to change. As water quality professionals, it is our responsibility to keep customers updated and informed—not only with the known pollutants that they are already familiar with and may have been planning for, but also in terms of the more recently identified contaminants they should be aware of. It is also our duty to advocate to customers the importance of understanding the risks of these pollutants to aquatic life and humans and how they can play role in minimizing them.