jmax wrote:
Peggie,
Question have you ever heard of or used forced mechanical aeration of marine
holding tanks?

Yep...in fact, Groco makes a holding tank aeration system...they call it
the Sweetank System. See it at http://www.groco.net

Two options come to mind...

You seem to be describing two different systems...a fan in a vent line
doesn't aerate, it only ventilates the airspace above the surface. And
in tanks smaller than about 30 gallons, that aren't more than about 18",
ventilation along with with an organic (bio-active or nitrate) tank
treatment should be enough to create the aerobic environment needed to
prevent odor. It does require two vents, and the fan should be be an
exhaust fan that pulls air through, not one that pushes air into the tank.

An aerator oxygenates the contents, and properly designed and installed
for the size of the tank, completely eliminates odor without the use of
any tank products. But the key is a pump big enough for the tank size,
and a system inside the tank that distributes the air throughout the
whole tank...a too-small pump and/or just a single column of air would
only push noxious gasses out the vent. It's also important to remember
that while fish tanks only contain water, waste is full of animals fats
that routinely clog up gauge senders...and can clog up the aerator too
if the design doesn't prevent it.

By the time you go through all that's needed to design and retrofit a
DIY aerator that won't create more problems than it solves, it might be
cheaper just to buy one. The Groco Sweetank has a list price of around
$250...WM quite often has it on sale for around $150. Even that sounds
like a lot till you compare it to the total amount spent on holding tank
products over a couple of years.

Both aerators and vent fans have to run 24/7/365 (except during winter
layup of course) to keep the tank aerobic. A tank that's turned septic
can be recovered, but it takes several hours, and the odor forced out
the vent is horrific for at least the first hour...then gradually
diminishes over the next 3-6 hours depending on the size of the tank.
That COULD make your battery powered pump a bit problematic if the
batteries aren't changed regularly...and batteries run up the cost too.

IMO, a far better solution than any of the above is a Type I MSD (CG
certified device that treats waste and discharges overboard legally in
all waters except those specifically designated "no discharge," which
are few and far between in coastal waters. Why have to deal with the
problems of storing waste aboard if you don't have to?

--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://69.20.93.241/store/customer/p...40&cat=&page=1