The availability of clean water has emerged as one of the most serious problems facing global society in the 21st century. Nanotechnology has great potential for providing efficient, cost effective and environmentally acceptable solutions for improving water quality and for increasing quantities of fresh water. Nanomaterials have a number of key physicochemical properties that make them particularly attractive as separation media for water purification. On a mass basis, they have much larger surface areas than bulk particles. Thus, they are ideal building blocks for developing high capacity sorbents with the ability to be functionalized to enhance their affinity and selectivity. Nanomaterials can serve as high capacity and recyclable ligands for cations, anions, radionuclides, and organic compounds. They provide unprecedented opportunities for developing more efficient water-purification catalysts and redox active media due their large surface areas and their size and shape-dependent optical and electronic properties. Nanomaterials can also be used to develop chlorine-free biocides through functionalization with chemical groups that selectively target key biochemical constituents of water borne bacteria and viruses. The research and commercial examples described in the preceding chapters of this book offer but a small glimpse into the potential benefits of nanotechnology-based solutions for water purification. As discussed in this book, the first generation of “passive” nanomaterials such as metal oxide nanosorbents are being incorporated into point-of-use (POU) and point-of-entry (POE) water purification systems. However, the use of these passive nanomaterials alone will not lead to the revolutionary advances needed to tackle the global water purification challenges facing the world. For example, the development of nanoporous membranes with biofilm-resistant surfaces and embedded sensors/actuators that can automatically adjust membrane rejection, permeability and selectivity could provide a low pressure/energy desalination technology. We anticipate that active nanomaterials and nanosystems [e.g., bioactive nanostructures and 2-D arrays of multifunctional and adaptive nanomaterials] will be key components of such membranes.

Increasingly, water scientists and engineers are questioning the viability of building and operating large and centralized water treatment plants to meet the water demands of users with different water quality requirements. The convergence of nanotechnology and information technology has the potential to accelerate the development of small scale and customized water treatment systems that can either treat a local water source or provide water of a specified quality to meet a local need. For example, “smart” nano-info sensing devices—with the ability to perform a specified action upon detection of a compound—are being developed. Such devices could be placed in surface water systems or subsurface environments to track contaminant migration and and implement preventive measures to keep critical compounds from contaminating local water sources. Reduced size coupled with an accompanying increase in computational power will make these sensors particularly effective. This combined capability allows for ubiquitous placement in areas of need—water, air and soil—thereby effectively increasing spatial coverage. Current disinfectants such as chlorine and ozone have the potential to generate toxic byproducts (e.g. trihalomethanes and bromide) and have limited activeness against emerging microbes and viruses. Thus, we anticipate convergence between nanotechnology and biotechnology to accelerate the development of novel biocides able to selectively deactivate key cellular signaling and metabolic pathways of water-borne microbes without generating disinfection by-products. Ultimately, the convergence of nanotechnology with other existing and emerging technologies may lead to the development of personalized water treatments that could be mass-produced cheaply and distributed throughout the world.

Funding of innovative research will be critical to the development of the next generation of nanotechnology-based solutions for water purification. A major concern is that the current trend of decreasing research budgets will result in a significant decrease in innovative research. Note that many funding agencies are mission-oriented, i.e., they carry out and/or fund research directed toward specific goals. Consequently, when research budgets shrink, available resources become primarily devoted to the agency core mission activities at the expense of funding for exploratory and innovative research. Industry and venture capital firms often prefer to invest in technologies that are far beyond the “idea” or proof-of-concept stage. When resources are unavailable or limited for the development of these ideas into potential commercial products, society bears the burden of not being able to capitalize on the benefits of using nanotechnology to solve the water quality and supply challenges facing the world.

The characterization of the fate, transport and impacts of nanomaterials on humans and ecosystems will determine to a large extent regulatory and public acceptance of nanotechnology-based solutions for water purification. These impacts may be an impairment of human health or ecosystem viability, or they may be of a philosophical, ethical or legal nature. Whatever the possible adverse effects, these must be systematically explored. This requires research into both human and environmental health as well as in to the ethical, legal and social impacts of this technology. Finally, we would like to point out that communication of research results and public engagement will be key factors in the successful development and implementation of nanotechnology solutions to our global water needs. This communication must extend beyond scientific and technical publications. An effort should be made to condense and compile research results into more easily accessible formats for all stakeholders worldwide. Ultimately, this global communication will stimulate the development and deployment of more effective and affordable technologies for solving the water quality and supply challenges facing the world.