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By Aurora Ginzburg, Education Specialist, ACS Green Chemistry Institute
The U.N. reports that 2.2 billion people still lack safely managed drinking water and 1 in 4 health care facilities lacks basic water services. It’s been estimated that in 2015 alone 1.8 million deaths were caused by water pollution. The U.N. has designated targets within Sustainable Development Goal (SDG) 6, Clean Water and Sanitation, that aim to address these issues. These challenging, expansive issues resulting from a lack of or aging infrastructure, legacy chemical pollution, drought, and water rights issues will require different solutions depending on the region. There are issues of both water purity and access, and chemists are best equipped to address the challenge of purity. In particular, Targets 6.3 and 6.A necessitate chemistry technologies:
6.3 By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally
6.A By 2030, expand international cooperation and capacity-building support to developing countries in water- and sanitation-related activities and programmes, including water harvesting, desalination, water efficiency, wastewater treatment, recycling and reuse technologies
Technologies and strategies for (I) treating and (II) preventing water pollution must be carried out in a greener, more sustainable fashion if these targets are to be met. Common water contaminants include pathogens, persistent small molecules, microplastics, radioactive elements, and toxic metals. Some groundwater contaminants, such as arsenic, are a natural part of some aquifers found across the globe from which communities draw their water. Adding to naturally occurring hazards, cities and industrialized areas are experiencing emerging issues with synthetic chemical mixtures, such as those containing polyfluoroalkyl substances (PFAS), personal care products, pharmaceuticals and pesticides that enter the environment and can end up in food chains. In developing communities, pathogen-contaminated water continues to claim the lives of over 500,000 children year. So what can chemists do?
I. Water Treatment
Adsorption, ion-exchange, and membranes have all been developed to remove harmful metals, like arsenic, from water. Each has its advantages and drawbacks and it is important for chemists to consider not only their efficacy, but also their ability to be manufactured in a more sustainable fashion. Adsorbents can often be made affordably but vary widely in their performance. Low-cost point-of-use water treatment technologies via physical separation (e.g., flocculation and filtration) or chemical degradation (i.e., disinfection) remains the go-to option for pathogen removal. While removing pathogens from water is critical for short-term health, removing metals such as lead, chromium, arsenic, and mercury is essential for long-term health and this remains an unmet need.
Advancements in membrane filtration offer the capacity to not only remove pollutants, but also desalinate water, at an efficiency that is increasingly approaching the thermodynamic limit. Polymeric membranes can be quite sophisticated, with surface modifications designed for specific applications. However, this rational design is not the current industry standard. As described by Werber et al., membrane synthesis is more often an art than a science. Ongoing materials chemistry research that further develops the chemical functionality of membranes can provide new routes for water usage going forward
Mauter and Fiske recently outlined how advancements in water desalination will help advance society towards a circular water economy. To meet the global demand for clean water there will need to be paradigm shifts in water system design with increased reuse of nontraditional water sources, such as those from municipal wastewater, seawater or industrial discharge. Using these waters requires desalination though, and desalination is not currently efficient or cost-effective for waters with complex chemistries, particularly at small scales. The largest desalination operation in North America, the Claude Lewis Carlsbad Plant just north of San Diego, provides about 10% of local freshwater needs but at double the cost of other water sources.
II. Pollution Prevention Strategies
Despite advances in separation technologies, treating effluent has limits. Treatment is often incomplete and consumes energy and chemicals. The diversity and volume of chemicals used in society is ever-increasing, thereby requiring treatment technologies of increasing sophistication. For these reasons, it is desirable to have a proactive approach to water purification that focuses on pollution reduction at the source.
A mantra within the green chemistry community is that it is better to prevent waste than to clean it up. Although this is not always possible, the goal is to make any necessary waste chemically simple so that treatment can be targeted and effective. This idea is particularly true for water systems, where trace contaminants can migrate throughout the ecosystem for many years.
Increasing consumer awareness to change the way they interact with chemicals is important. Common household activities such as laundering, cleaning, showering, and gardening send chemical waste into municipal waters. This waste is chemically complex, creating the potential for synergistic effects and posing challenges for separation. Designing consumer products to be less chemically complex, and even increasing product performance so smaller volumes can be used or the products can be used in different ways, is increasingly important. Chemists can communicate with the broader community to encourage consumers to seek out products with simple and transparent formulations. While consumers may not have the background to identify hazardous chemicals, they can signal to companies their desire for environmentally benign products. This is especially true for the personal care cosmetics sector which has seen growth in the popularity of “clean” formulations, though still suffers from other sustainability blind spots, such as the use of shark-derived squalene when there are alternative, more sustainable sources of squalene.
A broad array of materials and technologies are needed for achieving SDG 6. These innovations should consider the community in which they will be used and the specific goals of the water treatment. The benefit to society will be maximized when accompanied with paradigm shifts that include changes to water systems and moving away from diverse chemical compositions in products. There is no shortage of work for chemists in helping to ensure access to water and sanitation for all.