Emerging Water Pollutants: Challenges and Solutions for a Sustainable Future

Introduction

Fresh water is one of the essential resources on our planet that humanity needs to carefully manage and maintain. Access to healthy, unpolluted water is a fundamental human right. Unfortunately, there are many water quality problems, and technological progress often creates new ones.

For example, the burgeoning pharmaceutical industry generates more and more human and veterinary health drugs that eventually end up in freshwater streams. The concentration of broad-spectrum antibiotics, hormones, nonsteroidal anti-inflammatory drugs (NSAIDs), β-blockers, and blood lipid regulators reaches dangerous levels and keeps growing. The same concern applies to personal care products: bactericides/disinfectants, insect repellents, soaps, detergents, fragrances, and sunscreen USFilter’s.

There is no immediate health risk from most of these pollutants, but their accumulation in human bodies can have as yet unknown long-term consequences. The United States Environmental Protection Agency (USEPA) and the European Union (EU) identified various chemicals present in wastewater and placed them on the list of priority pollutants. The future emerging pollutants on the list include such ubiquitous substances as ibuprofen or triclosan.

Another class of novel pollutants is related to the growing demand for electronic products and electric vehicles, hence the proliferation of Li-ion batteries. As part of the recycling process, large amounts of spent cathodes, anodes, and electrolytes will become available; an estimated total weight of spent batteries is expected to be around a million tons in 2025. Unfortunately, most of the recovery efforts are aimed at extracting and reusing valuable metals (Co, Ni, Mn). On the other hand, cathodes of ferrous lithium phosphate, LFP, are of less interest and mostly end up in groundwater through the landfill route.

Water decontamination from such pollutants is a complex process, and various technologies in sewage plants have different success rates for other pollutants. The search for better adsorbents, preferably the ones that capture and decompose offending molecules, is ongoing and represents a serious societal challenge to materials science. An examination of the list of BIOVIA scientific articles shows that many users of BIOVIA software are actively contributing to developing novel materials and technologies for water decontamination. Here are some recent examples of combined experimental and theoretical (V+R) studies that used BIOVIA Materials Studio to understand interactions between pollutants and adsorbents on a molecular level.

Collaboration

An international collaboration of scientists from Technische Universität Berlin, Maria Curie-Skłodowska University in Lublin, Tohoku University in Japan, and the National University of Uzbekistan suggested a mixture of ZnS and SnO₂ particles as photocatalysts for adsorption and degradation of many offending pharmaceutical compounds. Molecular simulation of the photocatalytic degradation required Materials Studio modules Adsorption Locator and Forcite. Adsorption affinities calculated with these tools correlate very well with the experimentally observed photocatalytic activities, so this workflow can be used to screen and optimize new catalysts (Journal of Alloys and Compounds 827 (2020) 154339, doi: 10.1016/j.jallcom.2020.154339)

Another technique for the removal of pharmaceutical pollutants, as well as organic dyes and phenols, is pioneered by a team from Tokyo, Qingdao in China, and Sheffield. They use a tightly bonded flake-like 2D/2D BiOBr/MoS₂ heterojunction to photoactivate peroxymonosulfate (PMS), an efficient material for oxidation and removal of organic contaminants. The CASTEP solver in the Materials Studio package helped explain the electronic and catalytic properties of the heterojunction. This work is now moving into a large-scale pilot project for real wastewater treatment (Journal of Colloid and Interface Science 594 (2021) 635-649; doi: 10.1016/j.jcis.2021.03.066)

A team of researchers from Shanghai, including Shanghai Julang Environmental Protection Co., investigated the potential rejuvenation of discarded LFP and its use as a catalyst for S(IV) activation and consequent decontamination of organic pollutants in groundwater. Their combined experimental and theoretical study showed how radical generation by LFPs makes them a useful catalyst and demonstrated strategies for optimizing their performance. Quantum mechanical solvers CASTEP and DMol3 in BIOVIA Materials Studio were used to quantify adsorption and explain catalytic reaction mechanisms on the surface of LFPs (Chemical Engineering Journal 446 (2022) 137123, doi: 10.1016/j.cej.2022.137123)

The next project focused on the dangerous class of contaminants – arsenic and selenium compounds from agricultural wastes and mining processes. Uncontrolled release of such materials into groundwater caused major health problems not only in the less developed countries around the world (Bangladesh, India, Pakistan) but also in the USA and China. Environmental scientists in Baoding (China) developed a novel manufacturing process for a stable Fe/Zr metal-organic framework, MOF, for exceptional decontamination of arsenic in water. Quantum mechanical solver DMol3 in BIOVIA Materials Studio helped to quantify arsenic species adsorption on this novel MOF. Arsenic species were adsorbed and immobilized by the adsorbent with a very low release rate after use (Journal of Environmental Sciences 128 ( 2023) 213-223, doi: 10.1016/j.jes.2022.08.002)

Conclusion

These are just some examples where atomistic simulations complement experiments to explain and optimize various materials and technologies for water purification. The topic does require urgent action worldwide, so at least some of the suggested recipes should promptly find their way into water treatment practices. Many of these research studies are sponsored by environmental agencies in the respective countries, giving us hope to see improvements soon.

The goal is not only to prevent future contaminations but to use advanced technologies from research labs at scale and clean up freshwater reserves back to their pristine state. Molecular modeling and simulation are important tools in the environmental research arsenal, and BIOVIA is proud to see our software used in these studies.