[djrogers]

Very few cities don't 'just dump the water back' - that's actually the way it works outside of a very very small handful of places. The reason for these treatment plants is so that the water that gets dumped into the environment is clean. Well, pretty clean - there are still things that aren't removed today with even the most advanced treatments, such as hormones/contraceptives...

[s_q_b]

My family owns a civil engineering company that deals with wastewater management.

A lot of it is treated with bacterial vats, chemicals, and UV, and then run back into local tributaries, because while it's safe for the environment, it isn't quite safe for human consumption.

A glass or two won't hurt you, but I wouldn't want to drink it regularly, mostly due to the cocktail of pharmaceuticals that can't be filtered.

A lot of that water is also used to irrigate large tracks of land not used for food. Many golf courses use this method, and sometime big pipes just run through forests spraying treated water onto drought-prone areas.

Once you get past the "ick" factor, waste water management is actually pretty cool.

[JBReefer]

Don't you risk building up pharmaceuticals in the soil around the forest pipes?

What a weird world.

[s_q_b]

The concentrations of most of the medications (anti-depressants, contraceptives, antibiotics, etc.) are large in relation to drinking water, but small in relation to the ecosystem into which they're discharged.

Any animal that eats them can usually break them down given their low concentration and half-life, using liver enzymes, and since the majority of the chemicals are human-targeted, they often have much affect on local flora or fauna.

We have bigger problems biggest waster water management anyway. When it rains, your town probably dumps raw sewage into the nearest river through a CSO (Combined Sewer Overflow), which is... less than ideal.

The previously mentioned mechanisms are actually considered eco-friendly approaches in comparison.

So yes, it is a very weird world.

[ethbro]

I'd imagine (guessing) most pharmaceuticals are fairly short-lived vs biological processes? Otherwise, you'd either only need one pill or it would build up in your body.

I suppose it's possible that they're only broken down by human biological processes, but that seems unlikely given the diversity of microbial life in the environment (and inside us!).

[logfromblammo]

Some drugs are not metabolized to a great extent before they exit the body.

For instance, an arctic shaman would eat poisonous mushrooms, taking the hit for the dangerous toxins in the fungus, then other people would drink the shaman's urine, which still contained the active hallucinogenic chemical, and go on a much safer trip. The hallucinogen would persist in this fashion through multiple kidneys before it was no longer worth drinking someone else's piss.

Now imagine that instead of pissing into a cup, you're pissing into a creek, and someone downstream will be taking a lower dose of something that was prescribed to you. That's one of the current problems with just running the wastewater output to the water treatment input. The treatment systems can sterilize and flocculate, but that makes it biologically sterile, not chemically sterile.

It's similar to the difference between distilled water, deionized water, and pure water. There will be some things that your specific purification process does not remove. If you have no outflows, your water system will become like a salt lake, where soluble chemicals enter via the tributaries and are left behind when the water evaporates, thus making the lake saltier and saltier the longer it exists, until it is so salty that otherwise soluble salts precipitate out in certain weather conditions.

Essentially, you would need a desalinator plant between your wastewater plant and the water treatment plant, and those are somewhat more expensive than just diluting your more problematic waste into the whole ocean.

[ethbro]

I understand the principle (though upvote for the example!), but my question was after leaving a human body whether or not natural processes (e.g. UV) + microbes in the environment would break those chemicals down in a reasonable timescale or if they persist? From s_q_b, it sounds like they do get broken down, albeit with an effect on the flora and fauna.

[logfromblammo]

It depends on the chemical.

Protein-based drugs, such as oxytocin or insulin, are likely to be consumed and recycled into component amino acids.

Most molecules left out in the environment will eventually be oxidized, have an important bond cleaved by UV light with enough energy, or undergo thermal decomposition.

As sunlight, dissolved oxygen concentration, and temperature can vary wildly just by moving a few meters away, and the chemicals themselves have different stability, it is very difficult to predict how long a pill that was flushed down the toilet will persist in the environment.

Generally speaking, certain drugs are only useful because they take longer to degrade inside the body. It wouldn't do you much good to get an injection of a drug if your body's proteases chop it up to uselessness in the first ten minutes, or if it zooms right to the liver and gets methylated, or whatever it is the body does to clear foreign chemicals. In those cases, microbes will also have a hard time turning them into something else.

[rsync]

"My family owns a civil engineering company that deals with wastewater management."

Did you win the Putnam ?

[s_q_b]

If everyone had to win the Putnam to understand the basics of wastewater treatment, we'd be in deep... well, shit.

[cromulent]

I think it's a reference to this from some years ago.

https://news.ycombinator.com/item?id=35015

  "Did you win the Putnam?"
  Yes, I did.

[s_q_b]

Ha, even the flame wars here are brilliant.