Meshes and Microns: The Measurements of Water Treatment

by Gene Franks

So much attention is given to the materials of water filter media (coconut shell vs. standard bituminous filter carbon, for example) that the size measurements of filter media are often ignored. Size, however, is very important in water filters.

Filter media are usually manufactured substances that are ground to a specific size. The “grind,” usually expressed as a mesh size, greatly affects the performance of the filter.

In large tank-style filters, the general rule is that the smaller the granules of filter media, the more effective the filter will be at reducing contaminants, but the greater the restriction it will offer to the flow of water. Performance must be weighed against flow rate. A filter is of no value if water won’t go through it, nor is it of value if it’s so porous that it won’t remove the targeted contaminant.

The size of the particles in granular filter media is usually expressed as mesh size. Mesh refers to the number of holes or openings per inch in a testing sieve. A 12 mesh screen has 12 holes per inch. A 40 mesh screen has 40 much smaller openings per inch.

Filter media is usually described with a two number designation. Twelve by 40 mesh filter carbon is a common size. If filter carbon is said to be 12 X 40 mesh, it means that the granules of carbon will fall through a screen with 12 holes per inch but be caught by a screen with 40 holes per inch. (Since nothing is perfect, some allowance is made for a small percentage of granules to be outside the size range. The undersized particles that wash out of the filter when water first goes through it are called “fines.” Over-sized chunks are called “overs.”) Eight by 30 mesh carbon is a courser blend than 12 X 40 carbon. It will fall through an 8-mesh screen but be retained by a 30-mesh screen. Water goes through 8 X 30 carbon faster, but for many jobs it is less effective.

In general, the larger the mesh number, the smaller the granules.

The familiar term “granular activated carbon,” or GAC, is used to describe most granular carbon. The technical definition of GAC is carbon of which 90% is retained by an 80 mesh screen. Finer-ground carbon, often compressed into carbon block filters, is called powdered activated carbon. Powdered activated carbon is in the 80 X 325 mesh neighborhood. Powdered carbon is more effective than GAC, but it is much more restrictive.

Microns

As things get tinier, filter makers usually switch to another measurement, the micron.

Here’s the Wikipedia definition: A micrometer or micron , the symbol for which is µm, is one millionth of a meter. It can be written in scientific notation as 1×10−6 m, meaning 1⁄1000000 m. In other words, a micron is a measurement of length, like an inch or a mile.

To put this in context, an inch is 25,400 microns long, or a micron is 0.000039 inches long.

Here are measurements of some common items:

Red blood cell — 8 microns.

White blood cell–25 microns.

An average human hair (cross section) –70 microns.

Cryptosporidium Cyst — 3 microns.

Bacteria — 2 microns.

Tobacco smoke–0.5 microns.

The naked human eye can normally see objects down to about 40 microns in size.

In water treatment, the relative “tightness” of filters is usually expressed in microns. A five-micron sediment filter is a common choice for prefiltration for a reverse osmosis unit or an ultraviolet lamp. A 5-micron filter is one that prevents the passage of most of the particles of five microns or larger. A one-micron filter is much tighter than a five-micron.

Two qualifying words are used to describe the effectiveness of the filter: absolute and nominal. An absolute filter catches virtually all the particles of the specified size, while a nominal filter catches a good portion of them. There is, unfortunately, within the industry a lot of wiggle room in defining what exactly constitutes a nominal or absolute filter rating.

The nominal pore size rating describes the ability of the filter media to retain the majority of particles at the rated pore size. Depending on the standard used, a “nominal” filter can be anywhere from 60% or 98% efficient.

Absolute is a higher standard, but again the term is slippery and its meaning depends on whose definition you accept. The standard water treatment industry’s trade associations, to accommodate marketers, in some cases lower its definition of “absolute” to as little as 85% efficiency. Other standards exist, such as industrial/commercial filtration (98%-99%), US EPA “purifier grade” (99.9%), and very high purity industry standards, e. g. pharmaceutical, (99.99%).

To clarify: a “0.5 micron absolute” carbon block filter sold by an aggressive commercial marketer isn’t necessarily as tight a filter as a 0.9 micron absolute ceramic filter that is designed to purify water by removing bacteria. Marketing standards allow some leeway because the carbon block filter isn’t being sold as a purifier (i.e., bacteria remover).

Here is some common size information regarding water filtration that may be helpful.

Granular tank-style filters are generally assumed to have about a 20 micron particle rating. Some are tighter. A multi-media filter (containing filter sand, anthracite, garnet, etc.) is considered to be about a 10 micron filter. Some of the newer natural zeolite media (ChemSorb, Micro Z, for example) are considered 5 micron filters.
Good carbon block drinking water filters, which are manufactured by binding very small carbon particles together, are frequently in the 0.5 and smaller range.  Doulton ceramic filters, which are very effective bacteria reducers, are in the 0.9 micron absolute area.  As you would guess, flow rates are slow and pressure drop is significant.  Newer technologies known as ultrafiltration operate in the 0.1 micron range, and nano filtration (often called “loose reverse osmosis”) goes down to the 0.01 micron range.  Reverse osmosis membranes have a micron rating of around 0.0005 to 0.001 microns–so tight that they reduce the “dissolved solids” (minerals) in water which pass easily through carbon and ceramic filters.

Comparing and converting mesh sizes to microns is most easily done by visiting one of the many web sites that offer conversion charts. Some common equivalents, to give you the idea:

10 mesh equals about 2,000 microns.

100 mesh equals about 149 microns.

400 mesh equals 37 microns.

If you’d like to figure it out for yourself,  an engineer has worked it all down to this neat formula: microns = 14,992 X mesh(-1.0046). This can be rounded off to mesh = 15,000/microns. That’s certainly a lot easier than looking it up on a chart.

Coca Cola Donates Syrup Barrels to Celebrate Earth Day

In a press release, Coca Cola announced that to celebrate Earth Day it has donated 1000 syrup barrels to be used as rain barrels. Read the full story of Coke’s largesse. 

 Also read  Jim Hightower’s thoughts on Coke  in “Drink More Coke”  and Joshua Frank’s “Death by Coke” from our website.

Water Filter Delays Flights for 90 Minutes at Minneapolis Airport

The Humphrey terminal at Minneapolis-St. Paul International Airport was evacuated for more than 90 minutes after a suspicious bag set off an alarm.

The suspicion centered on the bag’s two capped PVC pipes containing a benign granular substance and wires that were not connected to the pipes. The Bloomington bomb squad removed the bag and determined that the “sandlike substance was not an explosive.”

The bag’s owner said the items were for a water filtration device and that had caused a similar disruption in 2009 at the airport in Long Beach, Calif. The water filter owner was placed on a later flight.

Read all the gruesome details here.

Ultraviolet 101

by Gene Franks

Although ultraviolet light has several water treatment applications, such as reducing chlorine and chloramine, its main use by far is for microbe control.

Getting rid of microbial water contaminants can be done with chemicals, like chlorine or chloramines, by very tight filtration, as with ceramic filters, or by disabling the microbes with ultraviolet light.

Ultraviolet, UV, is not new. As early as 1877, the germicidal properties of sunlight were known.

Landmark events in the development of modern UV treatment include the use of mercury lamps as an artificial germicidal light source (1901), the development of quartz as a UV transmitting medium (1906), and finally the development of the first genuine drinking water application of ultraviolet as a disinfectant in France in 1910.

The technology is, therefore, a century old, and it is used world wide. Nevertheless, it is still unknown to many US state and local regulating agencies, who continue to accept chlorination as the only acceptable way to purify water.

UV treatment works not by “killing” bacteria, protozoa, and viruses, but by altering their DNA so that they cannot reproduce or infect. If chlorination is like chemical warfare directed at microbes, UV is more like a spaying and neutering program.

UV Light

UV light in the 200 to 300 nanometer (nm) range is the most effective at treating bacteria and viruses. (Visible light falls in the 400-700 nm area.) For most practical UV applications in water treatment today, the light is generated by a mercury vapor lamp, or in a gas mixture that contains mercury. Mercury is the gas of choice because the light it puts out is in the germicidal wavelength range.

Lamp output depends on concentration of mercury within the lamp, and the concentration depends on pressure. Low pressure lamps (called LP), the most common, produce UV light primarily at 253.7 nm, an ideal treatment wavelength. Some newer lamps are called “low pressure/high output” (LPHO) and some applications now use mixed vapor lamps called “amalgam” lamps. These require more electrical input and generate more UV output. LPHO lamps are roughly twice as powerful as LP, and amalgams may be about four times as powerful as LP.

The Delivery System

The standard way to treat unsafe water with UV is to send it though an elongated chamber where it is exposed to the intense light from the mercury lamp. UV bulbs are long and narrow to allow prolonged exposure as the water passes the length of the lamp.

The lamp itself is inside a “quartz sleeve,” which protects it from contact with the water, and on the other side of the sleeve there is normally a metal reflective chamber. The water enters one end of the chamber, flows past the lamp to exit at the other end, and is in the process exposed for some time and at close proximity to the UV dosage put out by the lamp.

UV Lamp, on left, and a quartz sleeve (for a smaller unit).

UV dosage is typically measured in units called “Joules,” and it is most frequently expressed in terms of “mega Joules per square centimeter,” or mJ/cm². (Microwatts per second per square centimeter, expressed as µWs/cm2, and mJ/cm2 represent the same dosage and the two systems are used interchangeably.) The higher the number, the higher the dosage.

UV Dosage

The UV dosage received by the water increases as the flow rate of the water decreases, so a UV unit that puts out a dosage of 16 mJ/cm² while treating water at a flow rate of eleven gallons per minute (gpm) will be rated as 40 mJ/cm² if the flow rate is decreased to 4.5 gpm.

Put another way, a UV system rated by its manufacturer to treat water at 40 mJ/cm² at 4.5 gpm will be delivering a dosage of 16 mJ/cm² even if the user exceeds the recommended limit and runs the water at eleven gpm.

The tendency now in UV dosage is to follow the “more is better” view we’ve all been indoctrinated in. If ten nuclear bombs will destroy the world, to be safe we need ten thousand. The most common concerns, E. coli, Giardia, and Cryptosporidium, are effectively eliminated at less than seven mJ/cm². The minimum dosage now recommended by NSF, however, is 40 mJ/cm².

Factors That Affect UV Effectiveness

First, there is the age of the lamp. UV lamps lose strength with time, and almost all manufacturers assume a once-a-year replacement when they design their units. It is a mistake to believe that if the lamp is still burning all is well. UV lamps should be replaced once a year, and when replaced they should still be burning strong.

Then there is flow rate. The unit should be sized to provide adequate protection at the highest possible flow rates, but practicality should tell you that in most residential situations, most water is used at a couple of gallons per minute and a great deal of the time—most of the time, in fact—no water at all is being used.

Also a factor is general absorption of the UV light for unintended purposes. UV makers usually require that water have less than seven grains per gallon of hardness, less that 0.3 ppm iron, less than 0.05 ppm manganese, and that it be generally clear and free of particulate and tannins. All of these can create situations where the light is absorbed and, therefore, its anti-microbial activity is diminished. Hardness, for example, can form scale on the outside of the quartz sleeve which blocks the passage of light and greatly diminishes dosage.

A related factor is called shadowing. It is primarily caused by particles in the water which can allow microbes to “hide” from the light and not receive adequate UV dosage. The commonly accepted practice in UV treatment is to put a sediment filter of 5 microns or less in front of the treatment chamber to screen out any particles that could allow shadowing. Even if the water looks perfectly clear to the eye, putting a five-micron filter in front of the UV unit is a good idea.

UV as a Germicidal Treatment. Pros and Cons

The good thing about UV is that in addition to being a very effective treatment for microbes, it is relatively simple and inexpensive to buy and to maintain. It adds no chemicals to the water and leaves no “by-products.” It is very safe, if you follow a couple of simple rules (like don’t stare at a burning UV lamp because it can damage your eyes, and remember that treatment chambers can be hot to the touch). Compared to ozone, chlorine, or even hydrogen peroxide, UV is a very safe home treatment. Also compared with other treatments, UV requires little maintenance.

The main disadvantage of UV as germicidal treatment is that it has no residual effect. Bacteria are treated when they pass the lamp, but contamination that occurs downstream of the lamp is not treated. Chlorine, by contrast, stays in the water from the point of treatment to the final point of use and prevents reinfection. The need for a constant supply of electricity can be seen as an additional disadvantage. If the power goes out, you should not use the water.

Above, a very basic UV system. The quartz sleeve, lamp inside, inserts into the stainless treatment chamber. The simple control system provides both visual and audible warning of UV lamp failure. The system comes in 2, 6, 8, and 12 gpm versions. The lamps provide strong UV dosage (30 mJ/cm2 at the end of the lamp’s life). Very easy to install, the unit wall mounts with two simple clips.

Number of dogs believed to be living in the United States–78.000,000.

Estimated percentage of these dogs that are in the country illegally– 23.9%.

Daily excrement output of these dogs, in tons–30.000.

Yearly excrement output of these dogs, in tons–10,000,000.

Number of 18-wheel tractor trailer trucks that would be required to haul away 10,000,000 tons of dog manure–267,500.

Length in miles of the caravan made by these 267,500 manure wagons if they were lined up bumper to bumper–3800.

Rank of the roundworm as the most common dog excrement parasite — #1

Percentage of Americans who tested positive for roundworms in a CDC study – 14%.

Number of canines required to generate enough bacteria in three days to close 20-miles of beach –100.

Approximate percentage of Americans who don’t pick up their dogs’ feces–40%

Percentage of US households that have at least one dog–60%.

Numerical rank of dog waste among the largest contributors of bacterial pollution in urban watersheds– 3 or 4.

According to a Seattle study, the percentage of watershed pollution that can be attributed to dog wastes–20.

Average daily output in pounds of feces per day per dog–3 to 4.

Pounds of excrement produced by 1000 dogs in a week — 750.

Percentage of the total residential waste stream that was found to be dog waste in a San Francisco study — 4%

Sharper’s Index

Gazette columnist B. Bea Sharper Ferrets Out the Facts that Harper’s Misses

B. Bee’s Second Series of Random Number Wisdom

Average time it takes blood to complete a complete circulatory cycle among vertebrates: 10 to 30 seconds.

Average time for a complete circulatory cycle among many insects: 30 minutes.

111,111,111 x 111,111,111 = 12,345,678,987,654,321

The longest recorded flight of a chicken : 13 seconds.

Distance that the cruise liner Queen Elizabeth II moves for each gallon of diesel that it burns: 6 inches.

Number of persons in two billion who will live to be 116 or older: 1.

Number of cows required to make enough leather for a year’s supply of NFL footballs: 3,000.

Percentage of people who use personals ads for dating that are already married: 35.

Percentage of total weight of the world’s humans as compared with the total weight of the world’s termites: 10%

Average speed of catsup leaving the bottle: 25 miles per year.

Percentage of Russian government income that comes from vodka sales: 10.

Number of muscles in a cat’s ear: 32.

Average number of people who choke to death each year on ballpoint pens: 100.

Gallons of water required to produce a pound of wheat: 25.

Gallons of water required to produce a pound of meat: 2,500.

Percentage of typing done by the average person’s left hand: 56%

Percentage of harmful organic waste water pollution attributable to humans: 10.

Percentage of harmful organic waste water pollution attributable to livestock: 90.

Average pounds of paper consumed per person each year in the United States: 560.

Average pounds of paper consumed per person each year in Nigeria: 7.

Number of possible ways to make change for a dollar: 293.

Estimated percentage of the generic diversity of the world’s 20 key food crops that has been lost in just the past 50 years: 75%.

Gallons of water required to produce a ton of paper from virgin wood pulp: 24,000.

Number of dimples on a regulation golf ball: 336.

Amount contributed to members of Congress in the period 1987-96 by the National Cattlemen’s Beef Association: $1,422,434.

Amount received during the same period from meat industry lobbyists by Senator Phil Gramm of Texas: $611, 484.

Percentage of American grain that is fed to livestock: 70%.

Number of people in the U.S. killed each year by assault rifles: 250.

Number of people in the U.S. who die each year from cancer related to pesticides: 10,400.

Percentage of all pesticides used in the world that are used on cotton: 25%.

Average number of American soldiers who died per year during the 12 years of the Viet Nam War: 4,800.

Number of medical schools in the United States: 127.

Number of these schools that don’t offer even one course in basic nutrition: 102.

According to a Life magazine report, percentage of babies born to Gulf War veterans who have been born deformed: 67%.

Number of Americans who die prematurely each year because of alcohol abuse: 125,000.

Percentage of Britons opposed to Monsanto’s efforts to introduce genetically altered foods before the company staged an advertising blitz in 1998 to gain public support: 44%.

Percentage of Britons opposed to Monsanto’s efforts to introduce genetically altered foods after the 1998 advertising campaign: 51%.

Percentage of the American population that is made up by three out of four Americans: 75%.

Number of Americans who miss work each day because of digestive health problems: 200,000.

Approximate number of people on earth who have the same birthday as you: 9,000,000.

Number of bombs the United States has dropped on Iraq since 1990: Thousands.

Approximate cost of a single “smart bomb” dropped on Iraq: $1,100,000.

Number of year-long jobs paying $10 per hour that could be paid for by the price of a single bomb dropped on Iraq: 60.

Number of $10 meals that could have been purchased for the price of a single bomb dropped on Iraq: 1,000,000.

Number of four-year scholarships to a top private American university that could have been paid for by the cost of a single bomb dropped on Iraq: 10.

Number of computers that could have been bought for American schools for the cost of a single bomb dropped on Iraq: 1,000.

According to an audit commissioned by the EPA, percentage of violations to federal safe drinking water rules that are not reported: 88.

Percentage of Americans who believe that the sun revolves around the earth: 18%.

Percentage increase in American children aged two to four taking psychiatric drugs like Prozac and Ritalin between 1991 and 1995:  50%.

Percentage of these children who were 2-year-olds: 10%. 

Read BB Sharper regularly in the Pure Water Occasional.

Sharper’s Index

Gazette columnist B. Bea Sharper Ferrets Out the Facts that Harper’s Misses

B. Bee’s Third Series of Miscellaneous Number Wisdom

Amount that Americans spend annually on lawn equipment: $40, 000, 000, 000.

Number of chemicals estimated to be in use in the United States: 75.000.

Number of chemicals currently monitored under U.S. drinking water standards: 75.

Rank of cancer among the killers of children in the United States: #2.

Rank of automobile accidents among the killers of children in the United States: #1.

Estimated number of leaking underground gasoline storage tanks in Texas: 21,000.

Percentage of the 2,700 most widely used chemicals for which human health effects data exists: 7%.

Estimated percentage of violations of the Safe Drinking Water Act that are not reported: 90%.

Number of plastic bottles sold daily by the Coca Cola Company,  sponsor of national America Recycles Day: 20,000,000.

Number of these bottles that are made from recycled plastic: 0.

Year in which the United States Congress granted citizenship to Native North American Indians: 1924.

Number of the top ten U.S. counties for per capita marijuana arrests that are in Texas: 5.

Your chances of being arrested for a marijuana offense if you live in Hudspeth, Texas (population 3,079): 1 in 15.

Number of people killed worldwide each day by waterborne diseases: 25,000.

Amount of money pharmaceuticals companies have contributed to Sen. Orrin Hatch (R-UT) between 1993 and 2000: $26, 400,000.

Percentage of Americans over 12 who have Herpes: 21%.

Fraction of America’s prisoners at the turn of the century who were incarcerated for non-violent drug offenses: 1/4.

Approximate annual cost of incarcerating these non-violent drug prisoners: $9,400,000.000.

Number of words in Archimedes’ Principle: 6

Number of words in the Pythagorean theorem: 24.

Number of words in the Lord’s Prayer: 66.

Number of words in the Ten Commandments: 179.

Number of words in the Gettysburg Address: 286.

Number of words in the Declaration of Independence: 1,300.

Number of words in the U. S Government’s regulations on the sale of cabbage: 26,911.

Amount spent in 1999 by the National Institutes of Health on clinical research: $18.000.000.000.

Amount spent on clinical research during the same period by the top ten pharmaceuticals companies: $23.000.000.000.

Amount that Colin Powell was paid to give a mediocre address to the 1999 American Librarian Association Convention about “volunteerism:”: $70,000.

Annual earnings of General Motors for pay-per-view sex films aired through its DirectTV subsidiary: $200,000,000.

Percentage of Black men in the United States who are not allowed to vote because they are in jail or have a felony conviction: 13%.

Fraction of the world’s prisoner’s that are now behind bars in “the land of the free”: 1/4.

Day in January which should be made a national holiday because on that day in 2001 “Drug Czar” Barry McCaffrey’s resignation became effective: 6.

Total number of  U.S. marijuana arrests in 1999: 704,812.

Percentage of these arrests that were for simple possession: 88%.

Total number of marijuana arrests (a record for any U. S. presidency) made during the Clinton Administration: 4,175,357.

Number of families who, together, own 95% of the wealth of Mexico: 14.

Number of the poorest people in the world who now own almost as much wealth as the richest 350: 350,000,000.

Number of children made homeless by wars during the last 10 years: 30,000,000.

Number of people estimated to be slaves in the year 2,000: 27,000,000.

Year by which Time magazine predicted,  in 1966,  that production by  machines would in effect make everyone in the United States independently wealthy: 2000.

The hottest year ever recorded: 1998.

Second hottest year ever recorded: 2001.

Gazette Columnist Bee Bea Sharper Describes an Imaginary World Village of 100 People in Exact Proportion to the Current Earth Population

• Precise number of people in the proportional imaginary world village described in the following items: 100.
• Number of these 100 people who would be Asians: 57.
• Number of Europeans: 21
• Number of Americans (North and South): 14.
• Number of Africans: 8.
• Number of females: 51.
• Number of males: 49.
• Number of Christians: 30
• Number of Non-Christians: 70
• Number of people who would own 59% of the world’s total wealth: 6.
• Number of these six very wealthy people who would be U. S. citizens: 6.
• Number of people who would live in sub-standard housing: 80.
• Number of people who would be able to read: 30.
• Number who would be suffering from malnutrition: 50.
• Number who would be near death: 1.
• Number who would be near birth: 1.
• Number who would have a college education: 1.
• Number who would be heterosexual: 89.
• Number who would be homosexual: 11.
• Number who would own a computer: 0.
• Number of reasons we have for being tolerant and understanding of each other: many.

Sharper’s Index

Special Animal Manure Issue

Pure Water Gazette columnist B. Bee Sharper Ferrets out the facts that Harper’s misses.

Introduction

by Gene Franks

The Agriculture Committee of the U. S. Senate, directed by chairman Tom Harkin (D-Iowa), performed an extensive study of the state of our nation’s manure.  Although the findings of Harkin’s committee were called “staggering” by the Associated Press, the story was essentially ignored except for a few page 22 newspaper stories.  Our numbers columnist, Bee Bee Sharper, intrigued by the big numbers that figure into animal manure statistics, decided to turn the committee’s findings into a column.  B. Bea’s numerical facts are taken from an excellent article on the Harkin findings, Pamela Rice’s  “Everything You Never Wanted To Know About Manure,” which appeared in the Fall 1999 issue of Vegetarian Voice. Here are B. Bea’s findings.

• Pounds of waste produced each year by farm animals in the United States: 2.74 trillion.

• If this waste were loaded on the boxcars of a single train (Heaven forbid!), the number of times this train’s length would reach around the earth: 12.5.

• Human population of a city that would create the same amount of excrement as the dairies in California’s Central Valley: 21,000,000.

• Estimated number of manure-generating animal-feeding operations in the United States: 450,000.

• Percentage of rivers that have been identified by the EPA as “impaired” in which agricultural runoff from animal waste is the largest problem: 60%.

• Number of Olympic-size swimming pools that would fit into one of the innumerable large “lagoons” (temporary excrement storage facilities) spread throughout the United States: 200.

• Percentage of the older lagoons in North Carolina that are leaking enough to contaminate groundwater: 50%.

• Number of separate noxious gasses that contribute to the foul odor which emanates from hog barns: 150.

• Number of dead birds that are composted or incinerated by the poultry industry each year: 160,000,000.

• Factor by which U.S. animal excrement exceeds human: 130 times.