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16-01-2006, 20:41

HMMMM? I think I'll stick with the old swipe pump and swish

It is surprising how complex a waste system can get. While designing the system on my tri, I shopped for quality rather than price, unlike my other installations. While it seems a minor point, a good functioning head that does not clog, or loose suction when drawing in water is a big comfort when everything else is going wrong on the boat. I am also considering adding a MSD to my system at some point, but I want to add it in line with the holding tank with a valve, so I can comply with the zero discharge if needed, but can discharge treated waste when appropriate. Has anyone set up this design before? is it problematic? My main concerns are the run cycle for the MSD, and the ability of the MSD to draw waste in from the tank. So far, the local chandlery and West Marine have not been able to answer these questions.

gosstyla · 17-01-2006, 18:50

Kai Nui,
ever consider a compost head?

17-01-2006, 19:06

YES! I have used them, and researched them extensively. Two problems have prevented me from going this route. One, is the size of the unit. i have not found one that would fit the space I want to use, and the other is the power draw. It is not much, and if it was the only concern, I think a solar vent could be installed to handle it, but the size of the units is the big issue. Also, it is one more thing to deal with disposing of the compost. It is a bit different on land where you can just throw it in a compost pile, but on a boat, you are throwing solids over board, and in a harbor, you need to find other means of disposal. The free pump out is easier. I still think they are a good way to go, and would not turn away from the idea if a unit was designed that fit my boat.

gosstyla · 18-01-2006, 07:47

I had the same problem - couldn't find one small enough to fit.

18-01-2006, 18:50

I considered trying to build a system into the holding tank, but it requires too much water to clear the bowl. I would also question if a composting system would work with salt water. It realy is a shame, because this is an excelent system. for a cabin it works very well, especially in an area that does not perk well. This system with a gray water system will work full time, but, on a boat, it is just too problematic.

Jim H · 18-01-2006, 19:09

A boat we're considering has a Type II Mansfield TDX that appears to work fine and does a direct discharge.

I've been reading about similar Type II MSDs at http://www.boatus.org/onlinecourse/R...ect/info4c.htm

Two things that surprise me-- it's in a relatively small boat with only two batteries. Second, the online information suggests a typical install is $4,000. Geez... Not having to do pump-outs is attactive, however.

18-01-2006, 19:21

A typical install? I guess that is subjective. The cost of the unit is about $1000 to $1500. To add it to my system would require an additional y-valve, the unit, some hose, an additional breaker, and some wire. If you combine the total cost of all the components I have listed, you would be close to that $4000 mark, especially if you are paying someone else to do it. FWIW, I have seen the MSD's on EBay for around $250 used and working. What I am not sure about, is, as I asked earlier, if the MSD can be installed in series with the holding tank, or if it needs to be in parralell. If it can be installed in series, it would be an even cheaper install.

NoTies · 18-01-2006, 22:32

OK, got to confess to knowing nothing about composting toilets but I've had some experience with both activated sludge & fixed bed aeration sytems using salt water. Both systems use bacteria as the secondary treatment (maceration is primary treatment). These systems work fine in salt water and will often work better than with fresh water if the fresh water is chlorinated. The only problem is changing from fresh to salt & back as the bacteria involved for each system takes some time adjust. An important thing to bear in mind is that secondary treatment systems do not generally remove faecal choliforms from the waste but treat the effluent to such a stage that UV sterilisation or chlorination will kill the bugs. I.E. the effluent will be clear but will still contain pathogens.
They used to call me the "sceptic avenger" down here.

18-01-2006, 22:51

Chemistry and micro biology are not my strong points, but i know septic systems (long story). I know you are correct that certain bacteria can thrive in salt water, however, the composting toilets rely more less on bacteria, and more on evaporation, so i do not think it would be a major issue. I do think evaporation rates of salt water might be a problem. And the remaining brine mey effect the composting process.
So how do you dig a latrene in perma-frost?