Treatment of seawater sewers ?

[Externet]

Good day.

If coastal cities/islands implemented parallel water supplies using seawater for mostly toilet supply merging flow to same current sewer systems; what would happen to typical sewage treatment plants ?  Can they deal with seawater or needs to be a different treatment ?

 

If this has to be in some chemistry forum, please move.

[mistermack]

Seawater has a lot of living things in it, it would need some pretty good filtering before you could use it for plumbing. It's also more corrosive than fresh water, so your plumbing would have to be of resistant materials. And if the water or sewage system sprang a leak, then the salt water would contaminate the ground water. For that reason too, your treatment plant would need to discharge directly into the sea, you couldn't use a river. It would probably be impractical. 

Some ships have used seawater in the past, for toilets and fire extinguishing. It needs a lot of flushing to get rid of microscopic shelled creatures, that die if they come into contact with fresh water. Most cruise ships and ferries, I believe, use fresh water, and store up the waste and discharge it to land treatement plants. Don't quote me on that, but it's what I've heard. 

[studiot]

12 minutes ago, mistermack said:

Some ships have used seawater in the past, for toilets and fire extinguishing. It needs a lot of flushing to get rid of microscopic shelled creatures, that die if they come into contact with fresh water. Most cruise ships and ferries, I believe, use fresh water, and store up the waste and discharge it to land treatement plants. Don't quote me on that, but it's what I've heard. 

I have worked on oil rigs and barges that do this.
Many small pleasure vessels also still do this.

[Externet]

Thanks.

Discharge of black waters to sea is restricted to beyond 3 miles offshores for 'untreated' raw sewage if I remember well, but do not know limits for 'treated'

If treated means with dead/no living organisms in it, can be achieved fast and easy.  If 'treated' means also without certain chemicals, heavy metals, toxins, am unsure how that 'treatment' is done.

The seawater contaminating groundwater as mentioned; cannot be worse than septic sewers contaminating groundwater wells in the same neighborhood.  I believe maaaany properties have both in the same or adjacent land tracts.  How is that prevented ?

Curiosity... Groundwater wells near locations with inland ClNa salt mines yield salty water ?

[mistermack]

51 minutes ago, Externet said:

The seawater contaminating groundwater as mentioned; cannot be worse than septic sewers contaminating groundwater wells in the same neighborhood.  I believe maaaany properties have both in the same or adjacent land tracts.  How is that prevented ?

Curiosity... Groundwater wells near locations with inland ClNa salt mines yield salty water ?

Septic tanks are usually placed away from wells, but if contamination occurs, that's faulty siting. But the ground can filter out that kind of thing in the right circumstances, whereas it can't filter out salt. 

Where salt deposits are undisturbed, it might be that it doesn't dissolve quick enough to noticeably affect ground water. Salt dissolves quick in powder form, but it might be slow in rock form.