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02/27/2001
Drink It Down
It''s 43 degrees Fahrenheit here on Marco Island in Florida. With
a wind chill that must be in the 30s, I''ve opted to forego my pre-
sunrise walk to work on this column, stealing occasional glances
at the Gulf of Mexico. Last year at this time, I wrote about the
microorganisms causing the red tide then affecting the coastal
waters of the Gulf in Southwest Florida. Happily, I have found
no evidence of red tide this year. Especially on an island, the
quality of the marine environment is of major concern. Water is
everywhere.
When it comes to drinking water, supermarkets here do a brisk
business in the bottled variety. I''ve been assured by local
residents that the water on Marco is perfectly safe but the taste is
what spurs the choice of bottled water. Personally, I find the
water''s taste perfectly fine, at least compared to that of our water
back home in New Jersey. At home, I find a marked
improvement in the taste of our tap water when allowed to stand
for a couple of hours. I assume this allows the volatile chemicals
in the water to evaporate. Although the water would not win any
prizes, we are fortunate not to have had any incidents of the type
experienced by Milwaukee residents in 1993.
You may remember the headlines that year when Milwaukee''s
water supply was contaminated with the microorganism
Cryptosporidium (let''s call it Crypto for short).
Well, Crypto not only infected some 400,000 people with
symptoms resembling the flu, but also caused over 50 deaths,
primarily in residents whose immune systems were compromised
by other maladies. An article by Karen Paulus on water
purification in the latest issue of Chemistry tells the story of
Milwaukee''s actions to minimize the chances of any such
incidents in the future.
In earlier columns, we''ve considered the uncertain state of water
supplies in earlier times. The choice of wine or beer as a
beverage under these circumstances could prove the difference
between life and death! Indeed, right up near the top of the list
of 20th century accomplishments in engineering, as well as in
public health, was the widespread achievement of safe water
supplies. Immediately, a dramatic reduction in fatalities
associated with waterborne diseases took place.
The history of the Milwaukee Water Works (MWW) illustrates
the simplicity of early water purification and its increasing
complexity as we enter the 21st century. MWW was formed in
1871 and all it did was pump water from Lake Michigan and
pipe it around Milwaukee. This was standard procedure for
almost 40 years until it was realized that too many people were
succumbing to typhoid, associated with the water supply. In
1910, MWW took the step of adding chlorine as a disinfectant.
The chlorine was added as a calcium compound by MWW and
chlorine became the workhorse of water purification for most of
the rest of the 20th century. It wasn''t until 1935 that MWW
constructed its Linnwood plant and added a filtration step to its
water purification. You might say that MWW then had a "2-
barrier" system with the filtering and chlorine addition.
Over the years, new challenges to water safety appeared and
some disturbing factors emerged that had been there all along but
were only revealed by new, very sensitive techniques of analysis.
As a result, MWW now has a much more complicated "multiple-
barrier" system. One new challenge concerns just getting the
water into the system. Back in the 1980s, an unwelcome alien
arrived in the Great Lakes from Europe on board freighters
crossing the Atlantic. The Zebra mussel found the lakes so
inviting a habitat that they multiplied like crazy and became a
major environmental concern. For MWW, the Zebras liked to
gather at the water intake pipes, clogging them up. MWW
fought back by instituting a blast of chlorine at the entrance to
the pipes. Apparently, chlorine is not a Zebra preferred food
item and the intake pipes are clear. Barrier number 1.
The chlorine gets diluted by the inrushing water from the lake.
What about any Crypto? It turns out that chlorine is not a great
Crypto-killer and most Cryptos will survive. So, let''s turn to one
of our favorite molecules in these columns - ozone. With its 3
atoms of oxygen, ozone is a good-guy/bad-guy type, playing a
crucial role in absorbing UV light in our upper atmosphere but an
undesirable air pollutant at ground level. As far as Crypto is
concerned, ozone is deadly, close to 100 percent effective as a
Crypto-killer so, when the water arrives at Linnwood, ozone is
bubbled through it. The ozone is generated from liquid oxygen
contained in massive tanks. Barrier number 2.
OK, we''re rid of Crypto and, hopefully, other harmful microbes
but now our water is loaded with ozone. Ozone is a super
oxidizing agent with that extra oxygen atom and we all know that
we''re continually being urged to eat foods with lots of anti-
oxidants! So, we want to get rid of the ozone and add hydrogen
peroxide, another familiar chemical. Hydrogen peroxide is just
water with an extra oxygen atom and I''m assuming that that
extra oxygen combines with ozone''s extra oxygen to form plain
old oxygen that we breathe routinely. Barrier number 3.
Now, our water still has all sorts of suspended stuff in it - stuff
like silt, organic materials from animals, vegetation and the like.
Some of this stuff makes a good home for all sorts of microbes
so it''s on to the "mixing" and "settling" basins. In the mixing
basin, a compound known as alum (aluminum sulfate) is added.
The alum promotes coagulation of the particles of "stuff" and, in
the settling basin, these larger particles settle out to the bottom of
the basin. Barrier number 4.
We still have some particles that haven''t settled out and it''s on to
the filtration section. In the past, filtration just involved passing
the water through columns of sand. However, MWW has
inserted a column of anthracite (as in anthracite coal) ahead of
the sand. The combo of anthracite and sand is found to be more
effective than plain sand. Barrier number 5.
After filtering, the water goes to the "clearwell" where, for good
measure, another dose of chlorine is added. Barrier number 6.
[Also, for your dental well being, a shot of a fluorine compound
is added in the clearwell.]
It''s time to send the water through the exit tunnel to Milwaukee,
but wait! That chlorine we just added is one of the things that
makes water taste bad, like our water at home in New Jersey. So
what do we do? Of course, we add a shot of ammonia! I don''t
know about you, but ammonia seems an unlikely addition for
tasty water. However, the article indicates that the ammonia
reacts to form better tasting chloramines. You could fool me -
I''m not familiar with chloramines. At the same time, in addition
to ammonia, phosphoric acid is added. As I recall, phosperic
acid is one of the tasty components of Coca Cola. But, in our
case, the phosphoric acid helps prevent lead and copper from
leaching from the pipes into our water, certainly a laudable
objective. Barrier number 7.
Other measures are being taken to improve the quality of the
water before it enters the system. For example, MWW, in
another plant, has extended the intake pipe several thousand
additional feet into Lake Michigan to avoid taking in water from
a nearby river that empties into the lake. Today''s widespread
efforts to clean up our lakes, rivers and other waterways should
also contribute to cleaner drinking water.
One of the factors which has only come to light toward the end
of the 20th century is the discovery that chlorine itself can react
with organic compounds introduced naturally into our water.
Decaying leaves and algae are just two obvious sources. The
possible harmful effects of the compounds formed in the
reactions with chlorine are the subject of current research. I
personally take heart in the knowledge that these compounds
have been around for most, if not all of my 73 years.
Time to hoist another of the 8 recommended glasses of water for
the day!
Allen F. Bortrum
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