some of it has to do with what happens after we flush our toilets.
As I understand, about 80% of Minneapolis's septic sewage goes for processing
to the Pig's Eye sewage treatment plant in St Paul. Surfing around on the
internet, I determined that there is all sorts of settling and sludge removal
that takes place. Part of the process involves burning the sludge in a big
incinerator, which eventually produces both heat and electricity (apparently
the Met Council makes over a million dollars a year on this electricity).
So I cannot find any reference at all to methane gas, which is used as a
substitute for natural gas and can be used in mixtures with diesel fuel or to
produce electricity. I came across a news article (which I cannot now find)
that indicated that San Diego has installed an anaerobic digester for their
sewage. The project cost $1.6 million (as I remember), but it produced an
additional $320,000 every year of operation. Which is a VERY fast payback for
any sustainable energy project.
I have already read enough about this issue that I know that methane digesters
cannot eliminate the odors associated with sewage. And I realize that the
methane digesters do nothing to eliminate the toxic metals that end up in
sewage sludge and that can cause air pollution problems during incineration or
when the sludge is used as a fertilizer. But these problems are current
problems as well, with or without a methane digester.
One article I read indicated that Germany used captured methane gas during
World War II and that several other post-war European companies did as well,
until petroleum became cheap and available again.
To my simple way of thinking, methane makes a very complimentary energy source
when we think about obtaining our electricity with wind. Wind, of course,
comes and goes. Thus many argue that big coal-fired plants are necessary to
maintain a baseline. Gas-powered plants can be brought on-line very quickly,
but natural gas is getting hugely expensive since we are apparently a couple of
years beyond peak natural gas.
But what if we hooked up digesters to all our sewage systems? What if we
hooked digesters up to feed lots and even city compost piles? We lose none of
the fertilizing nutrients, but we could capture and store and use the methane
gas to run electric turbines much as we now use natural gas.
So now I have to admit that I am a kindergarten teacher, not an engineer or a
scientist or even citizen who has spent much of my life exploring these issues.
I am very eager to have others provide information and criticism on these
suggestions.
Here's one way of saying the question simply: Would it be possible for
Minneapolis to become completely sustainable in its electricity use by
contracting wind farms for most of our electricity needs and supplementing with
our own methane-fueled plants when the wind dies down?
Comments? Flaws in my thinking? Stories you heard about from other cities? I
am quite eager to get some feedback on this subject.