We already know airplanes don’t have enough toilets.
But where does all the waste go once the vacuum has sucked the waste out of the toilet bowl?
No, it doesn’t get ejected.
But on a busy flight recently (Easyjet, many drunk tourists, lots of trips to the toilet) I started to think; how big is the waste tank? Can it ever get full?
Plane waste tank sizes
| Manufacturer | Model | Total waste capacity (L) |
|---|---|---|
| Boeing | 747-400 | 1135 |
| Boeing | 787-8 | 1628 |
| Airbus | A380 | 2096 |
Using publicly available data sheets for aircraft, I found the above specifications for each waste tank.
Waste capacity per passenger
Let’s assume the toilets are exclusively for urination to simplify the calculations.
According to Healthline:
The normal range of urine output is 800 to 2,000 milliliters per day if you have a normal fluid intake of about 2 liters per day.
Let’s take also assume this is passed during waking hours, so 16 hours (960 mins), and that people are awake on flights.
At the lower estimate (800ml) that’s 50ml per hour. At the higher estimate (2000ml) that’s 125ml per hour.
The planes for which I have collected statistics for all fly predominantly long haul routes. Let’s assume that to be 6 to 11 hours.
| Hour | Low (urinate vol ave ml) | High (urinate vol ave ml) |
|---|---|---|
| 1 | 50 | 125 |
| 2 | 100 | 250 |
| 3 | 150 | 375 |
| 4 | 200 | 500 |
| 5 | 250 | 625 |
| 6 | 300 | 750 |
| 7 | 350 | 875 |
| 8 | 400 | 1000 |
| 9 | 450 | 1125 |
| 10 | 500 | 1250 |
| 11 | 550 | 1375 |
| 12 | 600 | 1500 |
Assuming a full 11 hour flight, best case, each passenger will pass 550 ml, worst case, 1375 ml.
| Manufacturer | Model | Total waste capacity (L) | Total pax (typical) | Total wast capacity per pax (L) |
|---|---|---|---|---|
| Boeing | 747-400 | 1135 | 416 | 2.73 |
| Boeing | 787-8 | 1628 | 467 | 3.49 |
| Airbus | A380 | 2096 | 525 | 3.99 |
Even on the 747-800 which has the lowest waste tank volume per passenger, this still leaves room for 1 extra litre in the tank per passenger. On the A380, there’s over 2.5 spare litres of waste tank capacity per passenger.
It’s unlikely they’ll overflow, even on a particularly boozy flight.
Dealing with waste
When a plane lands, most of you would have noticed a fuel truck and the baggage carts arrive to empty the plane and prepare it for the next flight. You might not have seen the waste disposal truck arrive to empty the tank (generally at the back of the plane).
Let’s assume the average flight time for planes arriving at airports is 4 hours (so planes are carrying between 200ml – 500ml of urine per passenger).
| Airport | Country | Passengers Apr 2021 (mil) | Total waste low Apr 2021 (urinate vol ave l) | Total waste high Apr 2021 (urinate vol ave l) |
|---|---|---|---|---|
| Guangzhou (CAN) | China | 2.572 | 5144000 | 1286000 |
| Atlanta (ATL) | United States | 2.459 | 4918000 | 1229500 |
| Dallas (DFW) | United States | 2.364 | 4728000 | 1182000 |
| Chengdu (CTU) | China | 2.329 | 4658000 | 1164500 |
| Denver (DEN) | United States | 2.182 | 4364000 | 1091000 |
| Beijing (PEK) | China | 2.061 | 4122000 | 1030500 |
| Shenzhen (SZX) | China | 2.055 | 4110000 | 1027500 |
| Shanghai (PVG) | China | 1.994 | 3988000 | 997000 |
| Charlotte (CLT) | United States | 1.889 | 3778000 | 944500 |
| Shanghai (SHA) | China | 1.863 | 3726000 | 931500 |
| Chicago (ORD) | United States | 1.768 | 3536000 | 884000 |
| Hangzhou (HGH) | China | 1.669 | 3338000 | 834500 |
| Orlando (MCO) | United States | 1.637 | 3274000 | 818500 |
| Phoenix (PHX) | United States | 1.585 | 3170000 | 792500 |
| Los Angeles (LAX) | United States | 1.537 | 3074000 | 768500 |
Let’s assume the upper end of the estimates, the world’s busiest airport by passenger volume, Guangzhou, would have handled 5.14 million litres of pee from 2.57 million passengers in April 2021. At that rate, they’d be dealing with over 60 million litres of pee every year.
For reference, an Olympic sized swimming pool holds 2.5 million litres.
According to ICAO:
the total number of passengers carried on scheduled services rose to 4.5 billion in 2019
Assuming that low estimate (200ml per pax), that equates to 900 million litres of waste from all planes in 2019.
If we consider each passenger passed an average of 500ml, that’s 2.2 billion litres (or 880 Olympic swimming pools… which to me doesn’t sound that much!).
tl;dr
The world’s busiest airport by passenger volume, Guangzhou, could have handled 5.14 million litres of pee in April 2021. On a worldwide scale, airplane yearly toilet waste is estimated to be 900 million – 2.2 billion litres total. Despite this volume of pee, it’s unlikely the waste tank on a plane will ever reach capacity.