T&T: The ideal waste treatment system

[Gary Bell]

Dave speculated:

I believe all heads should be routed to one of the Raritan systems (Purasan, Electro scan or Electra san) then discharged into a holding tank. From the tank it can be pumped overboard in the proper locations or pumped out. 


Great idea, but you have the sequence of things wrong...


As Kevin pointed out -- the treated blackwater from a Type I MSD must be 
directly discharged overboard.  It's the law, and it's good science.  
First, introducing the discharge into previously contaminated 
containers/plumbing will recontaminate the discharge, making the 
treatment a big waste (sorry, I couldn't help myself) of expensive 
equipment and considerable DC power.  And second, the treated discharge 
should not be held aboard either, as the remaining bacteria will happily 
repopulate in the nutrient rich solution -- typically doubling every 
twenty minutes or so, depending on temperature.  When the treated water 
is directly discharged the available nutrients are immediately diluted 
to the extent that the bacteria cannot flourish and their population is 
likewise diluted to natural levels. 

What to do?  Choice one is to put a Y valve in the blackwater input line 
so the wastewater can be directed into the holding tank or into the Type 
I MSD.  The MSD discharge cannot share any of the holding tank plumbing 
in this case, and the contents of the holding tank would have to be 
pumped out.  This is the most common installation. 

Choice two (finished installing this on my boat yesterday) is to get the 
Raritan "Hold and Treat" system which routes all the blackwater into the 
holding tank, and when the level there reaches 80% full, begins cycling 
the Electro Scan until the level reaches 20% full.  The H&T package 
comprises a small control box, a macerator pump, a foil type level 
detector, a small display panel and a key switch.  So I now have a 
completely automatic system that can be switched to hold and pumpout 
mode for No Discharge Zones, be forced to treat whatever is in the tank, 
turned off to conserve DC power when at anchor, or set to process 
automatically whenever it needs to.  My thirty eight gallon holding tank 
will allow for considerable periods between treatments or pumpouts.  So, 
I will leave the system on automatic when dockside power is available 
and force it to empty the holding tank before heading out.  I can turn 
it off for short cruises and back to automatic when I return.  I can 
force it to empty the tank before laying over in a No Discharge Zone, 
and lock it out for the duration in the zone, with pumpout or processing 
afterwards.   I think that covers all  the possibilities. 

I no longer have the plumbing to directly pump untreated wastewater 
overboard.  While that is legal at greater than 12 miles offshore, I 
didn't want to invest in an additional throughhull. 

By the way, I was surprised to learn that my Electro Scan outfit needs a 
fifty amp breaker and four gauge wire.  Next project is to finish 
upgrading my lame 200 amp hour battery bank to 820 amp hours (two Rolls 
6V batteries in series, at three hundred pounds EACH), managed by the 
new Victron Phoenix MultiPlus inverter/charger that is laying on the 
settee today. 

Gotta go,

Gary Bell,  aka that old drone Mister Science