Well, progress has been made. Holding tank is almost installed, and I'm going to subscribe to the aerobic bacteria theory of eliminating odour. I have two 1" vent lines - one on either side of the boat to ensure the best possible cross ventilation. Because of the run lengths, I will probably add a fan to force air (draw it actually) through the tank, but for now I will try it unassisted. The downside to this is I won't be able to run one of those chemical "bullet" intake line deodorizer/critter killers (one of my heads will still be raw water). Apparently, they kill off the bacteria in the tank as well. One question though: how long does it take for these critters to effectively "neutralize" raw material. In all these discussions, I have assumed holding tank odour to be that old pongy smell associated with waste that has been around for a while, but fresh solid waste can be quite aromatic as well. My situation is a liveaboard one, where the waste will be pumped every few days as the tank fills. So will the aerobic bacteria get a chance to do it's thing? If not, then it seems that won't be a viable solution, and I'll have to resort to chemical deodorants. Thanks....Randy
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Peggie Hall/Head Mistress
"Relief" is immediate...
Oxygen PREVENTS odor from forming...it doesn't kill off odors or mask them as chemicals do. So if the system is working aerobically, there should never be any odor. It may surprise you to know that fresh solid waste actually only stinks for a short while after it leaves the anaerobic environment of the lower intestine...the longer it's exposed to air, the less odor it generates. A dog pile that's been in the yard a while only stinks if you step in it because a "crust" has hardened on the outside of it, sealing it. If it were in deposited in water where it could dissolve, it would cease to stink fairly quickly. In fact, if a tank is sufficiently aerated, it could be odorless without adding anything to it...adding bacteria only accelerates breakdown to liquid and gives the naturally occurring aerobic bacteria a "boost." None of this applies ONLY to waste...the same principles apply to waste that apply to all organic material. It's the reason stagnant swamps (including wet bilges) stink, but running streams don't...why compost piles have to tossed and aerated...why there are fountains and waterfalls in decorative ponds...etc. All organic matter breaks down according to the same principles: when oxygenated it doesn't stink--it converts to CO2, which is odorless...without oxygen it can only produce sulphurous gasses that stink. Btw...any fan in the system should exhaust--pull air through--not push air in.
Oxygen PREVENTS odor from forming...it doesn't kill off odors or mask them as chemicals do. So if the system is working aerobically, there should never be any odor. It may surprise you to know that fresh solid waste actually only stinks for a short while after it leaves the anaerobic environment of the lower intestine...the longer it's exposed to air, the less odor it generates. A dog pile that's been in the yard a while only stinks if you step in it because a "crust" has hardened on the outside of it, sealing it. If it were in deposited in water where it could dissolve, it would cease to stink fairly quickly. In fact, if a tank is sufficiently aerated, it could be odorless without adding anything to it...adding bacteria only accelerates breakdown to liquid and gives the naturally occurring aerobic bacteria a "boost." None of this applies ONLY to waste...the same principles apply to waste that apply to all organic material. It's the reason stagnant swamps (including wet bilges) stink, but running streams don't...why compost piles have to tossed and aerated...why there are fountains and waterfalls in decorative ponds...etc. All organic matter breaks down according to the same principles: when oxygenated it doesn't stink--it converts to CO2, which is odorless...without oxygen it can only produce sulphurous gasses that stink. Btw...any fan in the system should exhaust--pull air through--not push air in.
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Randy S.
Thanks Peggy
We will be putting this theory to *THE* test; and you are hereby invited to continue your research onboard our vessel the day after Mexican food night - hooah! And yes, the fan will be a "sucker", not a "blower". Thx again.....Randy
We will be putting this theory to *THE* test; and you are hereby invited to continue your research onboard our vessel the day after Mexican food night - hooah! And yes, the fan will be a "sucker", not a "blower". Thx again.....Randy
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Ernst
why should fans only exhaust (not push air in)?
Peggie, subject says it all: I don't understand your last sentence saying fans should only exhaust (not push air in)? What difference does it make? I am thinking about running a small battery-powered aquarium pump (maybe solar powered) to aerate my holding tank (to be constructed...) since I am not too eager to drill _two_ 1-inch holes in my hull. I realize I will need at least one exhaust but one is better than two... --Ernst
Peggie, subject says it all: I don't understand your last sentence saying fans should only exhaust (not push air in)? What difference does it make? I am thinking about running a small battery-powered aquarium pump (maybe solar powered) to aerate my holding tank (to be constructed...) since I am not too eager to drill _two_ 1-inch holes in my hull. I realize I will need at least one exhaust but one is better than two... --Ernst
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Randy S.
Exhaust
Fans should exhaust because you never want to positively pressurize an area that contains badness - like bad odour, toxic gas, fumes, etc. By doing so you run the risk of even the slight pressure causing the substance to leak out any opening or fissure or other crack that may develop. By drawing air instead, you create a negative pressure (never understood that term - to me it is a vacuum) and any potential leak will be from the outside into the foul space. You can then control the dispersion by filtering, redirecting etc. Regards....Randy
Fans should exhaust because you never want to positively pressurize an area that contains badness - like bad odour, toxic gas, fumes, etc. By doing so you run the risk of even the slight pressure causing the substance to leak out any opening or fissure or other crack that may develop. By drawing air instead, you create a negative pressure (never understood that term - to me it is a vacuum) and any potential leak will be from the outside into the foul space. You can then control the dispersion by filtering, redirecting etc. Regards....Randy
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Ernst
negative pressure good, positive pressure bad
Randy, thank you for your explanation. Yes, it makes sense not to pressurize a volume with 'bad stuff' in it. It would sure be unpleasant to blow the contents of your holding tank into the boat if the exhaust got clogged. However: The plan I had (actually, based on a suggestion on some other forum) was to continuously blow air at very low pressure thru the tank, using e.g. a low-voltage aquarium air pump. The exhaust could go thru a stanchion (well above where I would ever want green water to be, well ventilated, invisible...). This would replace the two huge holes in the hull (1" each, at least) that Peggie Hall suggests for ventilation. The simplest installation would be an aquarium pump drawing air from inside the boat. I suppose one could draw the air out the stanchion thru the pump (and have some small air inlet into the tank) but this would create another problem: the other function of the ventilation is to allow air in during pump-out and this would not work so well through the pump... --Ernst
Randy, thank you for your explanation. Yes, it makes sense not to pressurize a volume with 'bad stuff' in it. It would sure be unpleasant to blow the contents of your holding tank into the boat if the exhaust got clogged. However: The plan I had (actually, based on a suggestion on some other forum) was to continuously blow air at very low pressure thru the tank, using e.g. a low-voltage aquarium air pump. The exhaust could go thru a stanchion (well above where I would ever want green water to be, well ventilated, invisible...). This would replace the two huge holes in the hull (1" each, at least) that Peggie Hall suggests for ventilation. The simplest installation would be an aquarium pump drawing air from inside the boat. I suppose one could draw the air out the stanchion thru the pump (and have some small air inlet into the tank) but this would create another problem: the other function of the ventilation is to allow air in during pump-out and this would not work so well through the pump... --Ernst
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