Superior removal of organic pollutants from water by cyclodextrin polymers

As a consequence of population growth, continued industrialization, and climate change, water utilities in the United States are increasingly faced with the challenge of dwindling water supplies and are turning to drinking water resources that have been impacted by agricultural runoff or wastewater discharges. There are two main challenges associated with utilizing these impaired water sources for drinking water production. First, impacted water resources contain a variety of trace organic chemicals including pesticides, pharmaceuticals, and personal care products.1,2 Another troublesome class of emerging contaminants include environmentally persistent perfluorinated compounds (PFCs) arising from industrial fluoropolymer production and firefighting foams. PFC contamination led to the state of emergency declarations in three communities in 2016, which ushered in expensive emergency remediation efforts and bottled water distribution.3 Toxicological data for these chemicals are limited, but significant developmental, reproductive, endocrine disrupting, and other chronic health effects have been reported.4–6 Further, existing technologies for removing these so-called emerging contaminants are energy intensive and not always effective.7 Second, drinking water utilities in the United States have historically struggled with meeting disinfectant byproduct (DBP) regulations for trihalomethanes (THMs) and haloacetic acids (HAAs).8 This burden is expected to increase as utilities exploit source waters impaired by algal blooms and wastewater discharges, which contain elevated concentrations of organic DBP precursors.9 These challenges are not confined to water production in the United States and the developed world; many developing countries face similar or exacerbated conditions resulting from intense pesticide usage in agriculture and poor sanitation.10,11 Adsorption processes are widely employed to remove specific contaminants or contaminant classes from water. The ideal purification adsorbent would feature rapid contaminant extraction, high total contaminant uptake, and facile regeneration and reuse procedures. Activated carbons (ACs) are the most widespread sorbents used to remove organic pollutants, and their efficacy derives primarily from their high surface areas, nanostructured pores, and hydrophobicity.12 However, no single AC removes all contaminants well. Their poorly defined structures and adsorption selectivities require empirical screening at new installations and preclude the rational optimization of their performance. Furthermore, regenerating used AC is energy intensive (heating to 500-900 °C) and degrades its performance relative to new AC.13 AC has a slow uptake rate, achieving its uptake equilibrium in hours to days, and more rapid contaminant removal requires large excesses of the sorbent. Finally, AC performs poorly for many emerging contaminants, particularly those that are relatively hydrophilic.14 New sorbents that address the deficiencies of AC will contribute to sustainability by providing more effective water purification with reduced energy inputs.