Or is it something you can just ignore, because at the end of the day everything goes to a wastewater treatment plant, and your volume/concentration is too low to be considered hazardous, and actually not more harmful than the wastewater of commercial chemical cleaners, and well within the wastewater processing capabilities for small volumes?
Can anyone give an authoritative answer to this question?
> The solution must not be put down the drain because of residual copper ions left in it. To make it safe for disposal, you can add sodium carbonate (washing soda) or sodium hydroxide to it to neutralize it, until the pH value goes up to between 7.0 and 8.0, testing it with indicator paper. Copper will be deposited as a sludge. Allow the sludge to settle, pour off the liquid, further dilute it with water and then it can be poured down the drain. Collect the sludge in plastic bags and dispose of it as required by your local waste authority.
Cu though is an aquatic herbicide (used to rid decorative ponds of all plant life including algae) and can mess up things.
> at the end of the day everything goes to a wastewater treatment plant
Some of these things, especially the photosensitive chemicals in particular ammonium dichromate will annihilate the wastewater treatment plant. Experienced this problem in an industrial context once, resulting in tens of millions of dollars in damages to taxpayers and a giant fiasco. As a result our privileges to use the municipal sewage system were withdrawn and we had to spend tens of millions in evaporation towers since no water could leave our facility ever again.
I think the biggest problems for chip fabrication waste (not circuit board etching) are HF and nonpolar organic solvents. I'd think neutralizing HF with chalk would yield fluorspar, which is resistant to weathering even over geological timescales. But again I don't know what the official answer is. Maybe dumping fluorspar in your yard will get you arrested.
From what I understand the last thing you want to experience is an explosion of hydrofluoric acid.
The internet seems to suggest lime (->fluorspar) or soda lye (->NaF, used for fluoridating water) to neutralize HF, but that's two other substances you wouldn't want raining on your head... be careful out there.
Don't mix this stuff in dilution in an enclosed space either as the H2 gas can create another explosion hazard.
As for hydrogen, neutralizing acids with bases doesn't generally produce it, but ventilation is still a good idea.
I suggested fluorspar rather than NaF because a backyard full of fluorspar is a pretty rock garden, while a backyard full of NaF is a toxic waste dump.