6.1 Nanotechnology

Nanotechnology has great potential in water treatment applications. Nanomaterials are superior filters and adsorbents because they have extremely small pore sizes (1-100 nm) and large surface areas. Also, some nanomaterials exhibit oxidative/reductive properties that can be used in the degradation of chemical pollutants. Nanomaterials that have high antibacterial properties include chitosan, metallic nanoparticles (e.g., silver ion), photocatalytic TiO₂, nanofilters (NF), aqueous fullerene nanoparticles, and carbon nanotubes (Ngwenya et al., 2013). These superior physical, chemical, and antibacterial properties, combined into one process, have the potential to provide low cost and effective full-scale water treatment (Brame et al., 2011) as well as water treatment for emergency applications. Nanotechnology water treatment could be implemented in developing countries where infrastructure is limited and water is scarce. While the benefits of using nanoparticles may seem enticing, negative environmental effects are being investigated. For example, using metal-based nanoparticles could create antibiotic-resistant bacteria strains (Brame et al., 2011). Few studies about the environmental effects of using nanomaterials exist; thus, more studies are needed before nanomaterials can be widely implemented.

Carbon nanotubes are an emerging form of nanosorbent that can be used for emergency water treatment applications. Carbon atoms can be stacked in a hexagonal pattern and then rolled up into a tube to form a nanotube. These tubes have great potential for use in water purification because they can remove contaminants such as bacteria and viruses through adsorption and size exclusion as carbon nanotubes are 10,000 × thinner than a human hair (U.S. Army Public Health Command, 2010). Carbon nanotubes are ideal for emergency situations because they have a very low propensity for fouling so they work efficiently in a wide variety of source waters and require little maintenance. Very little energy is required to pressurize flow through the nanotubes, enabling the use of gravity-driven flow (Brady-Estevez et al., 2010; Rahaman et al., 2011). Carbon nanotubes can be incorporated into membranes as a nanomesh or used in conjunction with membranes to enhance water treatment. An example of a technology that uses a carbon nanomesh filter is the Seldon WaterBox, as discussed in Section 5.3.3 (Jones, 2011; Seldon, 2012). To increase the microbiological effectiveness of a carbon nanotube (CNT), silver particles can be impregnated into the CNT to increase its disinfecting capabilities (Lukhele et al., 2010). As research and development of nanotechnologies increase, the use of carbon nanotubes will probably also increase. However, current production techniques require more development before carbon nanotubes can be used for emergency water treatment (U.S. Army Public Health Command, 2010).

6.2 Renewable Energy

Renewable energy is a highly useful power source during an emergency. During chaotic times when traditional power sources such as electricity and diesel fuel may be unavailable, energy from the sun and wind can be harnessed. Solar and wind energies are two of the main renewable energies that are used to provide drinking water. These renewable energies can be used in emergencies to provide water by pumping clean groundwater or through various other water purification processes. While renewable energy benefits the environment because it is a clean energy, and it can be used when traditional forms of power cannot, renewable energy devices require a large initial investment for the photovoltaic (PV) cells and connecting technology. Currently, the only way renewable energy can be cost effective is if it’s used in a region that has a large solar capacity and high costs for diesel fuel (Abraham and Luthra, 2011; Bilton et al., 2011).

Many case studies have examined the use of renewable energies to provide drinking water in developing countries, and a growing number of studies (currently very few) analyze the use of renewable energy technologies during the initial, acute phase of emergencies. Because renewable technology devices may be larger, more difficult to transport, and require a specific set up as well as long-term maintenance, they may be more useful for a long-term, sustainable response to an emergency. Many photovoltaic cells and wind turbines have a lifespan of 20-25 years and can provide water for a community long after an emergency is over. Both pumping systems and treatment systems can be scaled up for larger capacity or scaled down for a smaller capacity, depending on the application. Providing energy for a larger system merely requires the addition of more PV cells. Renewable energy has been employed in both rural, off-grid applications for small communities as well as in large-scale water treatment systems. Power requirements for water treatment include pumping, UV disinfection, membrane filtration, and desalination/reverse osmosis (RO) units.

Various scales of photovoltaic-powered membrane filtration water purification systems exist. RO is a popular technology for areas with brackish water and has been examined for use in both community-scale and relatively large plants. Membrane desalination is another form of purification that can be used to treat brackish water. The main disadvantage of using RO or other desalination processes is the amount of energy that’s required to run these systems. PV cells can provide enough energy for desalination if the treatment unit is small, but as the capacity of the plant grows, the process becomes more expensive. The more energy needed for the plant, the larger the area needed for PV cells. Small, personal-size RO units powered by manual pumps or PV cells can be stored on life rafts for emergency situations (Katadyn, 2013).

Wind energy is another popularly used form of renewable energy. Wind energy technology is fairly well developed and relatively cheap (Miranda and Infield, 2002). Like solar technology, wind energy is most cost effective when used in off-grid applications where traditional forms of energy are not available. Many studies have examined using wind technology for applications such as pumping water for rural irrigation (Heijman et al., 2009; Salomonsson and Thoresson, 2010) and treating brackish water or seawater to make potable water (Gauto, 2012; Liu, 2009; Park et al., 2010). The difficulty with using wind as a power source is that wind is random and variable. RO systems require a certain amount of power that may not always be achieved because of the randomness of the wind. Park et al. (2010) found that RO systems could treat low-salinity source water using wind energy at high wind speeds, but intermittent operation still needs to be studied. The lack of consistency in wind power requires either short- or long-term storage of either electricity or water to provide a constant flow of drinkable water. Batteries for electrical storage can greatly increase the initial investment costs, so research has been conducted to find power-saving alternatives, such as energy-recovery pumps (Heijman et al., 2009).

Occasionally, wind and solar energies have been combined to provide extra energy and redundancy for water treatment systems. Vick and Neall (2012) found that using hybrid wind and solar power provided enough energy to pump water during low water times, but the combination provided too much energy during wet seasons, resulting in excess pumping. These authors suggested that this excess energy could be used for other applications, such as heating a tank of water or, if the water needs to be purified, UV disinfection. Vitello et al. (2011) tested a mobile UV disinfection system that used a combination of solar and wind power supply. Like Vick and Neall (2012), these researchers found that the wind turbine provided a redundancy that was unnecessary for most situations, and removing the wind turbine drastically reduced the cost of the system. Both Vitello et al. (2011) and Vick and Neall (2012) tested off-grid systems that had capacities ranging from 9 to 40 L/min, enough for a small community water supply. Another example of hybrid solar and wind energies is the Solar Cube, a product by Spectra Watermakers (2013), which combines solar and wind energies to power a large, portable RO unit that uses a special pump to reduce the draw of power from the renewable energy source. This unit has a capacity of 3500 L/h, but it requires a relatively large investment.

6.3 Iodinated Resins

Iodine has been used for disinfection of water since World War I. Incorrect doses of iodine result in high toxicity and irritation; thus, iodine is used less frequently than chlorine to treat water. However, iodine does not produce a bad taste as chlorine does, and iodine is an effective microbial disinfectant, so its use continues to be explored (Mazumdar et al., 2010; Ngwenya et al., 2013). Different ways to “tame” iodine have been investigated in various studies (Mazumdar et al., 2010). NASA uses an iodine resin in their water treatment system to reduce microorganisms (NASA Spinoff, 1995). A product called the Survival Bag employs this process, using a filter with iodine resin to inactivate microorganisms and then an iodine scavenger to remove any iodine species and reduce toxicity related to iodine (World Wide Water, 2013). Iodine disinfection continues to be researched as it has the potential to produce harmful byproducts that are similar to chlorination byproducts. Research has found that, while an iodine solution produces a large amount of byproducts, products that used resins were not as likely to produce harmful byproducts (Mazumdar et al., 2010).