The Importance of Green Chemistry in Addressing Global Freshwater Shortages

By: Mimi Martinez 

As the need for freshwater intensifies, innovative solutions rooted in green chemistry are emerging to address this global challenge, particularly in the field of desalination. Currently, approximately 4 billion people experience severe freshwater shortages for at least one month a year[i]. This alarming situation is predicted to worsen, with global freshwater demand expected to increase by 19% by 2050, resulting in 75% of the world's population facing clean water shortages[ii].

Desalination offers the opportunity to address freshwater shortages by converting seawater into drinkable water. For areas with dire freshwater needs, this could be a solution to the escalating crisis of freshwater insecurity. However, traditional desalination methods are energy-intensive and costly. Recent breakthroughs in green chemistry, particularly in the development of more efficient and sustainable desalination technologies, offer promising alternatives that could revolutionize the way we address freshwater scarcity.

One such breakthrough is the advancements in interfacial solar-powered evaporation, a more energy-efficient desalination method that harnesses solar energy to evaporate seawater. A team of researchers from the University of South Australia has made significant strides in enhancing the efficiency of this process[iii]. By introducing inexpensive, common clay minerals into a floating photothermal hydrogel evaporator, they achieved seawater evaporation rates 18.8% higher than pure water. This improvement is crucial, as traditional desalination methods have seawater evaporation rates typically 8% lower than those for pure water. This is due to the salts present in seawater, which hinder the evaporation process.

The innovation lies in the ion exchange process at the photothermal interface, where light energy is converted into heat. The addition of clay minerals facilitates the removal of salts from the evaporation surface, preventing their accumulation and improving the efficiency of the solar evaporation process. Specifically, Mg2+ and Ca2+ ions are added to the photothermal hydrogel, a material that absorbs and holds large amounts of water while converting light into heat [iv].  

While this breakthrough enhances desalination efficiency and reduces costs, it is equally important to ensure the sustainability of these practices as global freshwater demand continues to rise. Applying the Principles of Green Chemistry [v] to all stages of the desalination process is an effective starting point for ensuring its long-term sustainability. A prime example is the effort to tackle environmental concerns related to brine disposal. Zero Liquid Discharge (ZLD) systems aim to eliminate liquid waste by recovering both water and valuable salts. Successful experiments have demonstrated the use of interfacial solar evaporators to treat high-salinity wastewater, achieving zero liquid discharge by concentrating brines and recovering salts, all powered by solar energy [vi]. 

Taking such measures will help ensure we step in the right direction, ensuring that we minimize negative byproducts throughout the acquisition, processing, and output stages of desalination, ultimately promoting a more sustainable and environmentally responsible approach to addressing global water scarcity.