cal65
Topic Author
Posts: 2
Joined: Wed May 15, 2013 2:19 am

Lavatory Waste Storage

Wed May 29, 2013 6:31 am

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?
 
LH707330
Posts: 1498
Joined: Fri Jun 15, 2012 11:27 pm

RE: Lavatory Waste Storage

Thu May 30, 2013 6:05 am

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.
 
26point2
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Joined: Wed Mar 03, 2010 6:01 am

RE: Lavatory Waste Storage

Thu May 30, 2013 1:38 pm

Does Air India order a larger waste tank? The curry usually makes me have to go...sometimes twice.
 
Tod
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Joined: Sat Aug 28, 2004 6:51 am

RE: Lavatory Waste Storage

Thu May 30, 2013 5:51 pm

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.
 
fuelfool
Posts: 87
Joined: Wed Feb 16, 2011 4:41 am

RE: Lavatory Waste Storage

Thu May 30, 2013 9:56 pm

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!
 
Tod
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Joined: Sat Aug 28, 2004 6:51 am

RE: Lavatory Waste Storage

Fri May 31, 2013 3:51 pm

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.
 
Tristarsteve
Posts: 3364
Joined: Tue Nov 22, 2005 11:04 pm

RE: Lavatory Waste Storage

Fri May 31, 2013 6:30 pm

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.
 
Tod
Posts: 1709
Joined: Sat Aug 28, 2004 6:51 am

RE: Lavatory Waste Storage

Fri May 31, 2013 9:38 pm

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.
 
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larshjort
Posts: 1427
Joined: Wed Dec 19, 2007 6:54 pm

RE: Lavatory Waste Storage

Wed Jun 05, 2013 7:46 am

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
139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
 
AA737-823
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RE: Lavatory Waste Storage

Fri Jun 07, 2013 7:28 pm

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.
 
cal65
Topic Author
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Joined: Wed May 15, 2013 2:19 am

RE: Lavatory Waste Storage

Tue Jun 11, 2013 12:54 am

Thanks a lot for the information everyone! I guess this is not a feasible idea.
 
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HAWK21M
Posts: 29867
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RE: Lavatory Waste Storage

Thu Jun 13, 2013 10:28 am

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.
I may not win often, but I damn well never lose!!! ;)

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