By Lawrence R. ‘Larry’ Zinser
In the November 2022 issue of Water Conditioning & Purification International Magazine, writer Kaitlyn Longstaff outlined the wide range of natural and man-made threats to the quality of our water in her feature article “Groundwater Contamination from Natural Disasters, Urban Development, and Global Conflict.” Since all living things require a consistent source of compatible water, these threats are of significant consequence. Even though our planet contains 333,000,000 cubic miles of water, most is either nonpotable or not immediately accessible, leaving about 26 percent of the world’s population without ready access to safe water. Many of the threats Longstaff listed have existed or have been exercised for centuries. Many others, such as industrial discharge products, have been discovered only recently. Both natural events and human activity will continue to yield nonpotable water due to contamination.
The remedy for this situation is the treatment of water sources. The treatment of water for drinking has progressed a great deal from sand filtration in the 1800s. Moreover, our science and technology have advanced our understanding of what constitutes safe drinking water—that is, water free from harmful contaminants—and continue to raise the bar on drinking-water quality. With today’s technology, however, it is possible to remove water contamination and convert contaminated water to a state of human compatibility. The issues complicating that task are cost and required water volume.
The water treatment equation will continue to rise in prominence as contamination issues arise. (FIGURE 1) The product water quality—that which will sustain human life—is well documented by both international and national agencies. The first step in providing water at this standard is to understand the specific source water available. Once the source is understood, today’s technology may be brought to bear to provide the product quality required.
Source water quality depends on the contaminants present in that water. Both the nature of the contaminants and their respective treatment technologies can best be understood with an understanding of the water molecule itself. The water molecule is polar: it has two opposite charges, plus and minus, similar to a magnet. Consequently, each pole is attracted to its opposite charge. The positive pole is attracted to negative charges, and the negative pole is attracted to positive charges. This simple characteristic has made water the fundamental component of all life on Earth and the key target in the search for life outside of Earth.
Because of the attractive nature of the water molecule, absolutely pure water is a rarity. All water sources have some amount of contamination, either visible or not. The basic issue in water quality is the acceptability of the contaminants present, and contaminant acceptability is determined by the intended use for that water. A water quality that is acceptable for irrigation, for example, may be unacceptable for drinking water, and a water quality acceptable for drinking may not be acceptable for the manufacture of pharmaceuticals or for dialysis.
The contaminants in water may come from one of two basic sources: inorganic (nonliving, mineral) or organic (living) material. In this article, I will address the treatment of water contaminants in suspended or dissolved form from both sources.
CONTAMINANT: Suspended Solids
Because of the polar nature of water, water molecules are attracted to each other. This attraction, called hydrogen bonding, produces a medium that can suspend small particles. These suspended solids are not attracted to the water molecule itself but are merely suspended within the medium. Many suspended solids are natural, such as silt, clays, and oxidized iron, and many of these, such as fine silt or clay, colloids of orange iron particles, or yellow tannins, are visible to the naked eye. Some, however, are too small to be visible to the naked eye.
Suspended solids are most frequently found in the surface water of lakes, rivers, and reservoirs. The water in the aquifers of groundwater has been filtered by its seepage through layers of soil. The suspended solids in groundwater are from the silt and clay particles drawn from the aquifer by pumps.
Suspended solids contamination is widespread in surface water, wells, and groundwater as a result of natural disasters such as floods and earthquakes. Other suspended solids, such as microplastics, which range in size from visible to invisible, are generated by human activity. The important characteristic of suspended solids is that they can be removed from the source water through physical separation, or percolation, by passing the source water through a selective barrier that captures the suspended solids by filtration.
Since the size of most suspended particles is so small, we cannot use the inch or even the millimeter scale to measure them. The scale used is microns. To appreciate the size of a micron, consider that a period on a page is 615 microns in diameter. The use of the micron scale allows us to specify the relative size of suspended solids. For example, a human hair has a diameter of about 100 microns. We can usually see a suspended solid when it has a size greater than 40 microns.
The effect of suspended solids is primarily cosmetic. Suspended solids provide color and cloudiness, or turbidity, to water, making the water less palatable and inhibiting the operation of appliances. More importantly, however, suspended solids can provide a vehicle for the transport of dangerous microbes within a water supply system. This combined threat is more significant than the mere presence of suspended solids.
Filtration is perhaps the oldest water treatment technology. It is primarily a process of capturing suspended solids as the water supply flows through a sieve. The sieve must be small enough to capture the suspended solids at whatever size they are, yet large enough to allow the free flow of the filtered water.
The source water is pushed through the sieve by either gravity or applied pressure, as from a water pump. Solids are captured by the sieve as the source water passes through. The accumulation of suspended particles on the filter surface will cause an increase in the pressure necessary to allow water to pass, so filter surfaces require periodic cleaning or replacement.
The level of filtration refers to the size of solid that is captured by the filter. These filtration levels are grouped into five categories:
1. macrofiltration (solids greater than 1 micron),
2. microfiltration (solids between 1 micron to 0.1 micron),
3. ultrafiltration (solids between 0.1 micron and 0.01 micron),
4. nanofiltration (solids between 0.01 micron and 0.001 micron), and
5. hyperfiltration, also known as reverse osmosis (solids less than 0.001 micron).
Most of the suspended solids we are familiar with are from nonliving, or inorganic, solids. There is another category of suspended solids that is considered separately in water quality and its treatment: living microbes, including bacteria, viruses, and protozoa. These are living, organic-based suspended solids—organic because they are living particles and suspended because they do not interact with water.
The health threat posed by viruses, bacteria, and protozoa is well known, documented, and appreciated. Besides the threat posed by pathogenic microbes—those affecting health—nonpathogens may pose a cosmetic concern with slime buildup and its effect on appliances. A good example of the nonpathogenic danger is the presence of iron bacteria, which causes a buildup of slime, called biofilm, in piping and beyond.
Microbial contamination may result from flooding, sanitary spills, or failures of municipal water treatment facilities or septic systems. Treatment for microbes in water involves destruction of the microbe membrane, called lysing; removal of microbes through filtration; or deactivating the microbes so they cannot form colonies in the human body. Lysing is typically accomplished by the injection of an oxidizer, such as chlorine, hydrogen peroxide, or ozone, into the water stream. Filtration is accomplished with ultrafiltration. Microbe deactivation is accomplished using ultraviolet (UV) light.
This combination of intensity and time is important in most treatments for microbes and is called contact time. There are two components to contact time: strength and exposure time. Microbe oxidizer system specifications include specific injection dosages and specific delay/exposure times. The manufacturers of UV lights design UV models for specific flow rates. By testing, they determine whether the size of the UV lamp and the dimensions of the UV chamber will allow water to pass through the chamber at a specific flow rate and any microbe passing through to receive the required dosage of UV radiation,
therefore becoming deactivated.
UV light—electromagnetic radiation of between 10 and 400 nanometers wavelength—is widely used for microbe control. For microbes, the harmful effects of UV light are quick and deadly. Specifically, the band of UV around 254 nanometers wavelength quickly damages the DNA of microbes so that they become incapable of reproducing. This makes UV light a valuable treatment tool for microbe contamination. However, the UV radiation must be applied at the required intensity and for sufficient time to have the desired effect.
The true danger of pathogenic microbes to the human body is not from one or two stray microbes; rather, the danger is from the microbe colonies that develop from ingested microbes once inside the human body. These colonies invade and adversely affect cells and organs. It is important to note that microbes that become deactivated by exposure to UV light are still viable; they just cannot reproduce. They will remain in the water flow after the UV light exposure and can then enter the human body. However, they will never reproduce within the human body. This deactivation is the basis for disinfection by UV radiation.
In part two, I will address inorganic- and organic-based dissolved contaminants.
1.“How Much Water Is There on Earth?” Water Science School, U.S. Geological Survey, November 13, 2019. https://www.usgs.gov/special-topics/water-science-school/science/how-much-water-there-earth
About the author
Following an education in chemistry (BS Degree) at Georgetown University, graduate work at Wayne State University and a 27-year career with the US Marine Corps, Lawrence R. ‘Larry’ Zinser has served an additional 27 years in design, manufacture, education and troubleshooting of residential, commercial and industrial water treatment systems. He has provided numerous technical courses throughout the country and internationally, which have been accredited by the Water Quality Association, the Pennsylvania, North Carolina, Maryland, Virginia, and Delaware Ground Water Associations, the American Nephrology Nurses Association and the Lehigh-Carbon County Community College. Zinser can be reached at [email protected] or cell phone, (215) 421-7115.