A range of treatment options are available to remove contaminants of all types
Both traditional and emerging treatment technologies can be effective at reducing or removing contaminants.
There are four primary types of treatment modalities. Aesthetic, particulate and turbidity removal are achieved through sand, multimedia, bag, cartridge or packaged filtration in a housing or vessel. Filtration cartridge products are manufactured from a variety of materials, and usually are available in multiple configurations. Biological contaminant removal is achieved through membrane filtration, ultraviolet (UV) treatment, ozonation, chlorination or chloramination. Chemical contaminant removal is achieved through granular or block carbon absorption and adsorption, membrane filtration or UV/oxidation. Dissolved solids and heavy metals removal is achieved through ion exchange water softening for hardness and arsenic removal, reverse osmosis (RO), aeration, electroadhesion, electrodialysis, reduction-oxidation, absorption or adsorption.
Treatment Technologies Spotlight
Biosand filtration. The biosand filter is an adaptation of the traditional slow sand filter, which has been used for community water treatment for almost 200 years. Biosand filters have been shown to reduce waterborne pathogens and produce high-quality water in many rural areas of the world. According to the Centre for Affordable Water and Sanitation Technology, it is estimated that since 2009 more than 200,000 biosand filters have been put to use in more than 70 countries.
Biosand filters are smaller than the slow sand filters used for entire communities, and have been adapted for intermittent use, making them suitable for individual households. The filter container can be made of concrete or plastic and is filled with layers of specially selected and prepared sand and gravel.
Electroadsorptive media. A treatment modality originally developed for NASA by Argonide Corp. and now manufactured by Ahlstrom Corp. utilizes electroadsorptive technology for filtration and purification, and can be used as an alternative to membranes in many residential and commercial applications. By accomplishing sub-micron “filtration” with a charge field rather than with mechanical pores, Disruptor media have a lower pressure drop and higher flow rate than ultrafiltration membranes with similar efficiency.
Applications for electroadsorptive technology include point-of-entry (POE) and point-of use (POU) devices such as whole-house filters; countertop, tap and undercounter filters; ice machines; and food and beverage preparation. An example of this technology is United Filters Intl.’s ULTRA-D submicron filter series, which uses the Ahlstrom media in a pleated filter format for many types of water treatment. These filters have been third party tested using NSF/ANSI protocols and have been shown to remove more than 99.9% of cysts, bacteria and viruses, and more than 95% of lead, and to reduce other heavy metals, residual pharmaceuticals, volatile organic compounds (VOCs), polychlorinated biphenyls, bisphenol A and biofouling precursors.
UV/oxidation. Since the 2008 Prairie Waters Project in Aurora, Colo., was proven successful, with multiple purification processes featuring a Trojan UV UV/oxidation disinfection system, other utilities are looking at UV/oxidation as a viable option to tackle water quality issues. This technology acts as a powerful barrier to both pathogens and chemical compounds.
One municipality that recently adopted this technology is Orange County, Calif., which takes filtered secondary effluent from an Orange County Sanitation District treatment plant and treats it to higher than drinking water quality standards. The 70-million-gal-per-day system consists of microfiltration (MF), RO and a TrojanUVPhox UV/oxidation system.
While MF and RO provide treatment for a variety of organic compounds, there are a number of contaminants that, due to their small molecular size, can pass through even advanced membranes. Common in wastewater, a compound known as N-nitrosodimethylamine (NDMA) is present in Orange County’s Groundwater Replenishment System (GWRS) as a byproduct formed during upstream wastewater treatment processes. The NDMA molecule is considered to be carcinogenic at low concentrations and, although it passes through MF and RO membranes, it can be destroyed with UV light. In addition, using a low concentration (3 ppm) of hydrogen peroxide, the system initiates an oxidation reaction that destroys other contaminants such as pharmaceuticals or industrial contaminants that have been shown to be present in secondary effluent. Together with the other treatment processes in the GWRS, the TrojanUVPhox creates high-quality water from wastewater that otherwise would be lost to the ocean.
Contaminants of Concern
Fluoride. Fluoride, an inorganic chemical, has been added to drinking water supplies in the U.S. for more than 60 years due to its role in preventing tooth decay. There have been some reports recently, however, linking fluoride exposure to learning disorders, thyroid disorders and other chronic ailments. Fluoride is banned in several countries. Most developed nations, including 97% of Western Europe, do not fluoridate their drinking water. In fact, there are more people drinking fluoridated water in the U.S. than the rest of the world combined. Many people, including doctors, dentists, scientists and environmental professionals, have spoken out against fluoridation of drinking water through groups such as the Fluoride Action Network due to its purported health effects.
Fluoride is a difficult chemical to remove from water, but RO is traditionally the top treatment option. Other filtration options include using activated alumina or bone char. Natural, high-calcium bone char is made of charred animal bone. Bovine bones are taken from cold storage, thoroughly cleaned and put in the sun for at least 90 days to completely dry them out. The bones then are carbonized at 1,472°F in controlled conditions. The result is Kosher-certified, NSF/ ANSI Standard 61-certified, 100% organic bone char made of 80% phosphate of calcium, 10% carbon and 10% calcium carbonate. It is long-lasting and non-toxic, and leaves behind beneficial minerals. It has no effect on pH, and also can reduce chlorine, heavy metals, radioactive elements, pesticides and herbicides, in addition to fluoride. Bone char is considered more effective at fluoride removal than coconut carbon, because it is hundreds of times more porous and contains calcium, which attracts fluoride.
Fluoride removal requires greater contact time with the media, as it is considered a dissolved solid. The calcium content in the bone reduces the fluoride. Calcium attracts fluoride whether it is calcium- or sodium-based.
Chloramines. Since many utilities switched from chlorine to chloramine for disinfection of drinking water, reports have surfaced regarding damage to fish, pipe and appliances.
Chloramine is toxic to fish, and cannot be removed by boiling. It reacts with certain types of rubber hose and gaskets, such as those used on washing machines and hot water heaters, as well as with lead and lead solder in plumbing, potentially causing toxic levels of lead to be released into drinking water. Chloramine also is potentially lethal to kidney dialysis patients.
Unfortunately, chloramine is more difficult to remove from water than its predecessor, chlorine. It does not dissipate. Special catalytic carbon media can be used as an effective absorption technology for the removal of chloramine, because contact time is key in the removal process. Catalytic carbon is available in filter cartridges, both in granular and block forms for POE and POU systems.
Arsenic. Arsenic is a natural component of the Earth’s crust and is widely distributed throughout the environment in the air, water and land. It occurs in inorganic and organic forms. Inorganic arsenic compounds, such as those found in water, are highly toxic, while organic arsenic compounds, such as those found in seafood, are less harmful to health.
People can be exposed to elevated levels of inorganic arsenic by drinking contaminated water; using contaminated water in food preparation and irrigation of food crops; industrial processes; eating contaminated food; and smoking tobacco. The U.S. Environmental Protection Agency’s maximum contaminant level for arsenic is 10 ppb, but some health professionals disagree with that number, arguing that no amount of arsenic should be considered safe in drinking water.
Long-term exposure to inorganic arsenic, mainly through drinking contaminated water, eating food prepared with contaminated water or eating food irrigated with arsenic-rich water, can lead to chronic arsenic poisoning. Skin lesions and skin cancer are the most characteristic effects.
The greatest threat to public health from arsenic originates from contaminated groundwater. Inorganic arsenic is naturally present at high levels in the groundwater of many countries, including Argentina, Bangladesh, Chile, China, India, Mexico and the U.S. It can be difficult to remove from freshwater. Some of the treatment technologies for reducing arsenic include lime precipitation, oxidation, coagulation/filtration, adsorptive media, ion exchange and RO.
Some emerging technologies also are promising for removal of this contaminant. Several innovative arsenic removal technologies, or variations of existing technologies, have been developed over the past decade. Most aim to provide simple, low-cost arsenic removal to developing countries such as Bangladesh and India. It is estimated that more than 60 million people in those two countries drink groundwater contaminated with high levels of naturally occurring arsenic.
One of these new technologies, electrochemical arsenic remediation (ECAR), uses a low electrical current to create rust from iron plates in contaminated water. The rust binds to arsenic, which then can be removed through settling and/or filtration. It is targeted to communities or countries that do not have the resources for standard coagulation/filtration plants. The technology was developed at Lawrence Berkeley National Laboratory and is currently being pilot tested by a company called SimpleWater. The ECAR process is reportedly less expensive than conventional technologies.
Regenerating adsorptive media (AM) is another recent development. Several types of AM have been used for arsenic removal for decades. Although alumina-, titanium- and zirconium-based media cannot yet be regenerated, iron-based media can. Backwashing and regenerating iron-based media, rather than replacing it, is a development being evaluated at the Twentynine Palms Water District in California. A caustic soda solution with a pH of 13 is used to strip arsenic off the media.
Treatment Technologies on the Horizon
Fracking water treatment. As oil and gas fracturing operations increase, the industry continues to find ways to decrease water use and prevent release of toxic chemicals into the groundwater. Boston-based Gradiant has commissioned two commercial treatment facilities in the West Texas Permian Basin that combine high water recovery rates with automation and require less energy and chemical use. The first facility was built in 2013 and uses Gradiant’s carrier gas extraction (CGE) technology in combination with other technologies to treat and convert 100% of fracking flowback and produced water into reusable water resources. The CGE process incorporates a continuous, atmospheric pressure, ambient temperature desalination technique that uses a carrier gas to extract freshwater from high-salinity brine.
The second facility, completed in late 2014, is based on Gradiant’s selective chemical extraction (SCE) technology, which also is deployed with complementary technologies to treat 100% of fracking flowback and produced water to generate clean, reusable brine. SGE is a multi-step treatment process that can be customized to meet any effluent quality and is capable of oil and grease removal, hydrogen sulfide stripping, VOC and semi-volatile removal, ion-specific removal and lamella clarification.
UV-C LED. According to BlueTech Research, an O2 Environmental company, UV disinfection technologies are one of the top five fastest growing water treatment technologies. The current mercury-based UV lamps used in water disinfection and oxidation have been around for more than 100 years and serve a $700 million drinking water and wastewater UV disinfection market dominated by cost-competitive, low- and medium-pressure mercury discharge UV lamps. However, new UV-C LEDs are starting to impact the market.
Solid-state UV-C LEDs use a fundamentally different method of generating UV-C light and are anticipated to become highly disruptive to the UV disinfection market in the next five to 10 years. While UV-C LEDs cannot currently compete in terms of price and performance, they are mercury free, able to instantly reach 100% intensity when turned on, and have lifetimes that are not dependent on the number of on/off cycles. It can be expected that the technology will see improvements and cost reductions (based on predecessor technologies like blue LEDs) within the next few years.
Graphene. An atomically thin membrane with microscopically small holes may prove to be the basis for future hydrogen fuel cells and water filtration and desalination membranes, according to a group of 15 theorists and experimentalists, including three theoretical researchers from Pennsylvania State University.
Graphene is a one-atom-thick layer of carbon atoms arranged in a honeycomb lattice. This special atomic arrangement gives it unique properties. For example, electrical currents in graphene move faster than in any other known material. Graphene is the first two-dimensional material to be discovered. It is an excellent thermal and electric conductor that is harder than diamond and approximately 300 times stronger than steel, and can stretch up to 20% of its original length.
Recent developments in graphene technology may lead to applications in water treatment. Sheets of graphene can be aligned so that water—and nothing else—is transmitted. Research currently is underway at Penn State, the Massachusetts Institute of Technology and the University of South Carolina to develop various water treatment options using graphene oxide, including using it for water desalination.
There are many exciting possibilities for water treatment technology companies to deliver more cost-effective treatments. It is up to all of us to do our part in treating water with the respect it deserves before it disappears.