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Sodium Hydroxide, when exposed to Carbon Dioxide (already in the air), combines to become Sodium Carbinate.
NaOH + CO2 → Na2CO3 + H2O
Sodium Carbinate then reacts with water and more Carbon Dioxide to become Sodium Bicarbinate, which is baking soda.
Na2CO3 + CO2 + H2O → 2 NaHCO3
Not only does a Sodium Oxyde fuel cell produce electricity, it takes CO2 out of the atmosphere.
From a physics and chemistry point of view, it’s pretty cool. I’m curious how well it scales though.
My guess, and it is just a guess… it’s a storm water control system being used as a basement drain, possibly flowing into the sewer line.
I’ve seen older houses where someone cut into the basmeny floor directly into a sewer line to put in a basement drain.
Based on you saying water was in there when it was raining, someone might have cut into the storm water mitigation line for a basement drain. Then someone tiled the floor and put a vent over the hole because that’s what they found that fits.
With older houses, a lot of times, the storm water system was tied directly into the main sewer. If that’s what this is, I’d be concerned about sewer gasses coming up from it.
Again, with only seeing one picture, it’s just a guess.
Edit: It could also just be a cleanout for the storm water drain too.