membranes for desalination, water reuse, and disinfection in the future (Savage and Diallo 2005; Wiesner and Bottero 2007). Various nanostructured catalytic membranes could be used to selectively kill pathogens in drinking water, remove ultratrace contaminants from wastewater for water reuse, or provide bio-active degradation of pharmaceuticals or hormonally active substances from drinking water.
A very basic problem in the near future is how to replace existing, aging infrastructure in the face of a growing population and declining resources. Much of US water and wastewater infrastructure is nearly 100 years old and in dire need of modernization and replacement. The American Society of Civil Engineers grades the US water and wastewater infrastructure as “D-”. It estimates the 5-year investment needed for America’s infrastructure is over $2.2 trillion dollars (ASCE 2009). In some cases, the best designs for replacing current infrastructure may be radically different from the past (decentralized vs. centralized; large built structures vs. small green infrastructure; and low impact development, water reuse, or desalinization). Science and engineering research, coupled with systems-thinking approaches that take account of the numerous implications of water infrastructure, will determine the most cost-effective processes and infrastructure.
Nitrogen and phosphorus are essential nutrients that control the growth of plants and animals. However, problems occur when excess inputs cause large increases in aquatic plant and algal growth and in turn changes in plant and algal species (Bushaw-Newton and Sellner 1999). Decaying algal blooms consume dissolved oxygen, and this leads to hypoxic conditions that are harmful or deadly for many aquatic organisms. Nutrient pollution can cause important economic losses through damage to commercial and recreational fisheries, restrictions on contact-based water recreation, and disamenities (EPA 2012d). Nitrates also pose a human health risk when present at high concentrations in drinking water.
Water-quality conditions reported by states under the Clean Water Act indicate that at least 100,000 miles of rivers and streams; nearly 2.5 million acres of lakes, reservoirs, and ponds; and over 800 square miles of bays and estuaries across the United States are listed as impaired and not meeting state water-quality goals as a result of nitrogen and phosphorus enrichment (EPA 2012a). Only a small fraction of the nation’s total water resources are currently assessed, so those values are underestimates of the spatial extent of nutrient-impaired waters (EPA 2006, 2010a). Diaz and Rosenberg (2008) found that dead zones in the coastal oceans of the world have increased exponentially since the 1960s, and many of them are located along the US Atlantic and Gulf of Mexico coasts. Harmful algal blooms have been reported in virtually all US coastal waters (Bushaw-Newton and Sellner 1999), and symptoms of eutrophication have been found in 78% of the assessed continental US coastal area (Selman et al. 2008).