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Lavatory Waste Storage  
User currently offlinecal65 From Hong Kong, joined May 2013, 2 posts, RR: 0
Posted (10 months 3 weeks 5 days 12 hours ago) and read 4104 times:

Hello everyone,

I have a question that people I've asked in the aviation industry haven't been able to answer. I know that vacuum toilets on commercial airlines will suck the waste into a storage tank, either centrally located in the plane or one serving that section of toilets. I'm interested in knowing how well insulated these tanks are, and what kind of temperatures we can expect the liquid inside to reach, both in high altitude and upon landing. I've read up on a patent for airplane lavatory waste storage and it spends a lot of time discussing thermal heating, so I'm positive this is an issue engineers have looked into. Obviously the design will want to prevent waste from freezing, so I know that the temperature is somewhere between 0 and cabin temperature (unless this sewage has a lower freezing temperature than water).

I'm interested in this "cold turd" situation because I'm wondering if somewhere in the discharge process at the airport, maybe we could capture some of the cold energy from the tank and use it.

On a related note, I've learned that a 747 typically carries 4 tanks totalling 1000 L for waste storage. They overdesign for the storage because if the tank fills up, no one would be able to flush again and everybody loses. Does anyone know how much waste is typically produced on a 747 flight?

I realize these are super random and literally crappy questions, but I'd really appreciate it if anyone had any insight here.

Cheers,
Cal

P.S. UNRELATED question: What type of water is required to wash airplane engines? De-ionized water? Can lower quality water (reclaimed water perhaps) be used for other aircraft washing needs?

11 replies: All unread, jump to last
 
User currently offlineLH707330 From United States of America, joined Jun 2012, 594 posts, RR: 0
Reply 1, posted (10 months 3 weeks 4 days 12 hours ago) and read 3916 times:

I'd assume the tanks are just under half full on a typical 10-hour flight. Figuring 400 passengers*300ml*3 trips to the head gets you 360 liters, and with that number of passengers you will see pretty reliable (small) fluctuations over time.

User currently offline26point2 From United States of America, joined Mar 2010, 786 posts, RR: 0
Reply 2, posted (10 months 3 weeks 4 days 5 hours ago) and read 3825 times:

Does Air India order a larger waste tank? The curry usually makes me have to go...sometimes twice.

User currently offlineTod From Denmark, joined Aug 2004, 1721 posts, RR: 3
Reply 3, posted (10 months 3 weeks 4 days ago) and read 3765 times:

The 747-400 has two 85 gallon tanks and two 65 gallon tanks for a total capacity of 1135 liters.
The tanks are not thermally protected.


User currently offlinefuelfool From United States of America, joined Feb 2011, 138 posts, RR: 0
Reply 4, posted (10 months 3 weeks 3 days 20 hours ago) and read 3685 times:

Quoting cal65 (Thread starter):
unless this sewage has a lower freezing temperature than wate

The toilet water isn't just 'water'. It is like the stuff that goes in a RV. The potable water system is separate.



I love the smell of jet fuel in the morning...Smells like victory!
User currently offlineTod From Denmark, joined Aug 2004, 1721 posts, RR: 3
Reply 5, posted (10 months 3 weeks 3 days 2 hours ago) and read 3539 times:

Quoting fuelfool (Reply 4):
The toilet water isn't just 'water'. It is like the stuff that goes in a RV. The potable water system is separate

In a vacuum waste system water from the potable water system is used for the toilet flush function.


User currently offlineTristarsteve From Sweden, joined Nov 2005, 3930 posts, RR: 34
Reply 6, posted (10 months 3 weeks 3 days ago) and read 3512 times:

Quoting Tod (Reply 3):
The tanks are not thermally protected.

They don't need to be.
The toilet waste tanks, and the potable water tanks are behind the sidewall and backwall of the bulk cargo hold. Air from the passenger cabin passes them on its way to the aft outflow valve. This keeps these tanks around 20 degC.


User currently offlineTod From Denmark, joined Aug 2004, 1721 posts, RR: 3
Reply 7, posted (10 months 3 weeks 2 days 21 hours ago) and read 3478 times:

Quoting Tristarsteve (Reply 6):
They don't need to be.

Agreed.

Quoting Tristarsteve (Reply 6):
The toilet waste tanks, and the potable water tanks are behind the sidewall and backwall of the bulk cargo hold. Air from the passenger cabin passes them on its way to the aft outflow valve. This keeps these tanks around 20 degC.

Potable tank locations can vary.
747 have them aft of the forward cargo hold, up against the wing box.
A330 have either one or two outboard of the aft cargo hold, on the right side, forward of the cargo door in addition to one that is installed aft of the bulk cargo compartment on some versions.
Although neither has heated tanks, both models have heated distribution lines directly attached to them.

Last I heard, Monogram was installing a heated potable water tank on the new MRJ-90.


User currently offlinelarshjort From Denmark, joined Dec 2007, 1351 posts, RR: 0
Reply 8, posted (10 months 2 weeks 5 days 10 hours ago) and read 3105 times:

The potable water tanks on the CRJ-200 are heated, the forward one is placed in the avionics bay right below the galley. The aft is placed behind the cargo lining in aft cargo.

/Lars



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User currently offlineAA737-823 From United States of America, joined Mar 2000, 5639 posts, RR: 11
Reply 9, posted (10 months 2 weeks 2 days 23 hours ago) and read 2804 times:

Quoting Tod (Reply 5):
In a vacuum waste system water from the potable water system is used for the toilet flush function.

But the tank is pre-charged with blue juice, just like in the old days. Otherwise, you'd have an epic bacteria issue.
On the 737, the pre-charge is six gallons.

Quoting cal65 (Thread starter):
I'm interested in knowing how well insulated these tanks are, and what kind of temperatures we can expect the liquid inside to reach, both in high altitude and upon landing.

Well, residing in the aft cargo pit, the waste stays at the same temperature as the baggage. While this does get a bit chilly, it doesn't typically freeze. Even when the plane sits on the ground during turns in northern Alaska winters... no issues.

So I don't think that we'd find the use of such material as a thermal sink (recapturing the cold energy from turds, as you suggest) very useful.


User currently offlinecal65 From Hong Kong, joined May 2013, 2 posts, RR: 0
Reply 10, posted (10 months 1 week 6 days 17 hours ago) and read 2558 times:

Thanks a lot for the information everyone! I guess this is not a feasible idea.

User currently offlineHAWK21M From India, joined Jan 2001, 31573 posts, RR: 57
Reply 11, posted (10 months 1 week 4 days 8 hours ago) and read 2380 times:

Quoting 26point2 (Reply 2):

Does Air India order a larger waste tank? The curry usually makes me have to go...sometimes twice.

Thats probably because you dont have the Chaas along with it.....  

On the Topic.....Mainly Two types of Lavatories.....Vacuum type & recirculating type.



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