I read through the OP - he's making good choices and doing it much as we did fifty years ago. I would have killed to get that maskless photolith setup, though.
For a small fab (three furnace tubes, two fume hoods), the main issue is acids from photoresist ashing, wafer cleaning, tube etch cleaning, and metal etching. These are easily neutralized with a vat of marble chips built into the plumbing under the fume hoods.
If you are doing this, avoid epitaxy, which involves arsine and phosphine. I would say never attempt those! You can buy epi wafers. Either use spin-on dopants like he did, or use oxidized boron nitride wafers and small amounts of phosphorous oxychloride like we did.
The effluent from a plating facility or a dry cleaning establishment would be far more concerning.
Our furnace and photolith operation fit in a 20 x 30 ft room. It was one of the leading operations of its kind in the world at that time.
Please develop a workable waste disposal strategy BEFORE thinking about cool disruptive home brew nanofab MEMS/circuit hacks.
The first step is easy: neutralize them with any base, such as baking soda. You don't need precision, just add a lot of it, and make sure the pH is close to 7 (or beyond, baking soda is not corrosive) at the end. After this step, the solution is no longer acidic or corrosive and much safer to handle.
Unfortunately, the next step is tricky. The solution is safe, but it still contains a lot of Cu+ ions, which is a heavy metal pollutant and poisonous.
On the other hand, if your sulfuric or hydrochloric acid is unused for etching anything (clean without those nasty ions), you are good to go, just dump them in the sink after you've neutralized them (test with pH paper) it's perfectly safe.
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.
The solvents can be broken down to things that are compatible with the sewer system.
The hard part to deal with is the material you dissolved with the solvent.
I see a lot of people say this, but I rarely see any actionable advice.
How does your average residential person find and dispose of chemicals like this? Seems like most people end up pouring them down the drain simply because they don't know how to actually find a better means of disposing them.
Ultimately if you want to use chemicals that have the potential to poison our shared environment you need to be willing to do the legwork to be confident that you are doing things responsibly.
If you're planning out your own home fab, you're researching a bunch of other things and giving serious thought to a lot of nontrivial problems. Choosing to ignore waste disposal is irresponsible, and you deserve any legal hassle you run in to.
If you have industrial quantities of chemicals (more than a gallon or so), you need to call the relevant entities.
If you are lucky enough to have a hazardous waste disposal locally, obviously use that.
If you have stuff that doesn't break down well in water (cooking grease, for example), pouring that down the drain is always a recipe for trouble. You're simply going to clog your pipes. You need to dispose of that properly. There is a reason why restaurants have grease traps. Normally, residential quantities of this stuff can be placed in normal trash.
You can try to dispose of motor oil at gas stations, service stations, etc., but a lot of places won't take oil from end consumers anymore as it may be contaminated and their recycler will charge them. I actually had a very difficult time disposing of motor oil about 15 years ago. (I don't do my own oil changes anymore for this reason). I got told by the local enforcement "At the end of the day, dishwashing liquid and pour it down the toilet and the sewage treatment plant will chew it up the rest of the way." Obviously if everybody does this, it's a problem, but if it's really a one-off, it's okay-ish.
If, however, your stuff is soluble in water and you have a relatively small amount of it and your waste goes to a sewage treatment plant, pouring it down the drain while diluting it with a lot of water is often your only choice (be careful--solvents and acids can produce fairly noxious vapors even when diluted heavily) Quite often industrial disposal sites simply will not take small quantities of waste from individuals as there are liability issues involved.
Now, you may not like what even a dilute solution does to your plumbing, but that's a different issue. If your sewage doesn't go to a sewage treatment plant, but instead goes to something like a septic system, then you probably don't want to do this.
DO NOT POUR STUFF DOWN STORM DRAINS. Those normally do NOT go to sewage treatment plants (there are exceptions--but they are rare) and, as such, are a really quick way to contaminate the environment.
How's this? If you don't know how to safely dispose of the toxic chemicals used in chip fabrication don't fabricate chips at home.
Other states probably have similar things?
Very much worth researching before you get into a hobby where you start accumulating hazmats!
How do you dispose electronics? Batteries? Oil? Tires? Cars? Furniture? construction materials? ...
You go to the webpage of your local garbage disposal authority, and read their FAQ, which typically contains where all their disposal centers are, their addresses, opening hours, etc. and what can you dispose on each one.
If what you want to dispose is not listed anywhere, you call them and ask them.
In my country if you want to buy these types of chemicals, you need to ask a company for a price, and the company will ask: who are you? what do you want them for? what's your process for the chemicals? Etc. If you fail to answer any of the questions, they are obligated to report that a "sketchy" party tried to buy some chemicals from them. That might get you a visit from the police, asking even more questions.
That's balancing your freedom to do whatever you want with chemicals with my freedom to enjoy a world that hasn't been polluted by idiots that didn't know what they were doing.