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[GreenYes] Re: Whither/WhettherToronto's Sludge?


See response to Matt Cotton's post, and availability of numerous studies re
your concerns; clearly all of those issues have been thoroughly studied; NYC
DEP's comprehensive study ('97) largely used the term "de minimus" when
evaluating the impact of most of the parameters assessed before determining
that the public benefits of fully legalizing residential disposers
outweighed the potential (but manageable) impacts, with projected
penetration of 30% of NYC households over 30-year period (lacking any
economic incentive to do so, since HH waste collection is "free" to any NYC

....essentially the same conclusion reached by other municipalities in the
U.S., given that disposers are something of a discretionary appliance. [to
be clear, the NYC decision was about allowing disposers in older areas of
city served by combined storm and sanitary sewers, and included
consideration of CSO impacts]

As to the metals issue, a biosolids industry expert once told me that a)
biosolids benefit from the addtl organics (which was a premise of my initial
post re Toronto's dilemma), and b) that NYC has among the "cleanest"/best
biosolids of anywhere -- granted, of course, that we don't have much
industry left (but also an effective pre-treatment system)....

Energy recovery also is addressed in many of the studies, essentially
determining that methane recovery at WWTP is much more efficient and likely
than from landfills....

But is a better source for exploring that issue -- that
is, the efficacy of biosolids vs. SSO compost products, and any meaningful
distinctions between them.


-----Original Message-----
From: Alan Muller [mailto:amuller@no.address]
Sent: Sunday, July 09, 2006 1:53 PM
To: Kendall Christiansen; GreenYes@no.address
Subject: Re: [GreenYes] Whither/WhettherToronto's Sludge?

At 09:12 AM 7/9/2006 -0400, Kendall Christiansen wrote:
>While I know full well that food waste disposers are considered a
>"third-rail" issue for some, in the U.S. they are a fact of life -- the
>majority of U.S. homes have them (for decades), and installed in probably
>more than 80% of new homes...with growing acceptance internationally, as
>nations/states/cities struggle with how best to manage food waste and
>address GHG issues.

This is interesting. A couple of concerns/questions:

Adding food waste to the sewer system mixes it with the metals and
other toxins in the system, limiting downstream uses--as of the sludge.

To the extent that the stuff is fully oxidized to CO2 in the sewer
plant--presumably the plant is trying to do this to minimize oxygen
demand of the effluent--I would think that the organics are largely
being wasted, while contributing to climate change.

To the extent that the stuff is feeding the bugs and getting
incorporated into the bacterial biomass in the sludge, it would seem
that the "problem" is just being moved around (with the contamination
issues added).

On the other hand, if the food waste is collected separately, and
composted, or digested anerobically, the outcomes would seem more
positive--we are getting a useful soil amendment and maybe some
useful fuel gas. (Much of the carbon will still end up in the
atmosphere, but maybe while doing more good along the way....).

But I am only thinking about this qualitatively...would be
interesting to see a real analysis of alternatives.


Alan Muller, Executive Director
Green Delaware
Box 69
Port Penn, DE 19731 USA
fax (302)836-3005

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