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Re: water treatment


On Thu, 17 Feb 2000, James Purchase wrote:

> Roger, I don't know what is in New Mexican water that is so bad, but unless
> you can find a productive use for the reject water, it could be an expensive
> proposition ecologically speaking.

I agree with that completely, James.  The question as to why I need to do
the treatment came up a couple times off list, so I thought I'd give some
details.

The problem is certainly not universal to "New Mexican water"; the City's
water system is rather thoroughly compartmentalized, so the problem isn't
even common to all parts of Albuquerque.  It really only effects 30,000
people or so in the neighborhood where I live.  The water at my office is
very different from the water at home, so one option I considered and
rejected early on was to haul water from the office (or from my mother
in-law's house) to supply my tanks.  I nixed that idea.

The water contains about 600 mg/l of dissolved solids - about 4 times
normal for water supplies in the US.  Also, the water contains 60-70 mg/l
of silica (this makes bad mineral deposits); for comparison, the normal US
water supply usually contains around 10 mg/l of silica, and groundwater
supplied from deep sandstone aquifers usually carries a little less than
20 mg/l.  Finally and worst of all is that there is a fairly extreme
imbalance between between the concentrations of sodium, potassium, calcium
and magnesium - the same sort of imbalance that can come from using an ion
exchange water softener.  Calcium and magnesium together provide less than
2 dGH; there's 1 ppm of potassium and 110 ppm sodium (for comparison, the
US average water supply contains something like 130 ppm of *total*
dissolved salts).  As a result of the imbalance, fast-growing plants often
show deficiencies of calcium, magnesium and/or potassium.

I add epson salt to bring all of my change water up to 4 dGH, I add
potassium chloride to bring the potassium content to an estimated 30 ppm,
and I push calcium carbonate tablets into the substrate around some
plants.  Despite all that, I still see deficiency symptoms in some plants
and even where I don't see pathologic results I suspect that these
shortages hurt many plants.  I don't want to further increase the dose of
potassium, magnesium and calcium because the combined effects of dosing
and evaporation already have the electrical conductivity of water in my
tanks pushing 1000 uS/cm.  Typical livebearers don't mind that, but lots
of other fish do.

The imbalance is so bad that I don't even want to mix any of the untreated
tap water back into the treated water to reduce the volume of treated
water that I need.

To make things even worse, the water supply contains a fairly substantial
arsenic content.  Arsenic causes no observable aesthetic, environmental or
health problems and the water is within the existing drinking water
standards for arsenic.  EPA will soon be releasing a new and lower
drinking water standard for arsenic that will force Albuquerque to
institute the most extensive and expensive arsenic removal system in the
world.  The firm I work for wrote the Environmental Assessment for the
City's pilot treatment project and I know from that experience that the
treated water will have even higher sodium and dissolved solid levels than
the untreated water does now.  Things *don't* get better.

> I have a 50 gal/day TFC unit from Kent
> Marine and, at least under the conditions I am forced to operate mine, I'm
> lucky to see a 1:5 ratio of "good" to "reject" water. Living on the shores
> of one of the largest reservoirs of fresh water on the planet (the Great
> Lakes), I'm not too worried about wasting water, as the water which goes
> down my drain is headed back into Lake Ontario anyway, but you live in a
> desert, and water is a precious thing there.

I can't speak for the state as a whole, but I think we might be able to
arrange a trade.  We can send you all the dust and tumble weeds you ever
needed and you can send us some of that water.

Thanks for the ideas, James.  My wife already complains about having a 40
gallon Rubbermaid container sitting around the kitchen for half a day
while I mix in the epson salt and KCl and treat for chlorine.  Whatever I
do for storage I have to arrange around her.  It's amazing how untrusting
a wife can get after you spill 50 gallons or so of water onto the kitchen
floor and dining room carpet.


Roger Miller