Lye bath solution disposal

[Thomas Gebbia]

noobie here. what are some ways of lye bath solution disposal? is it safe to pour it down a drain that has pvc pipes?

[Russell Ware]

The 100% lye I use is sold as drain cleaner. It goes down the pvc drains with no problem, and it still keeps them clean.
Just watch the bottom of your bath. If you have a lot of sludge there, I would dump that stuff in an inconspicuous place in the backyard. Some people say the spent lye kills plants, but I haven't had that happen. I got real tough weeds here.

[Greg Stahl]

Very safe for pvc pipes. I just put a pound of pure lye down my parents drain to try to fix an issue.

[Valerie Johnson]

The only problem I see with pouring it down your drain is if you have older plumbing which might have have a cast iron pipe with a lead packing, Yes you may see PVC where you are pouring it but look at the actual main pipe that leads to your outside sewerage pipe.
 And be aware that pouring a lot of lye down your septic system may kill off the beneficial bacteria that eats the sludge in your septic system.
Also keep in mind that what ever you are pouring down your drains will eventually find it's way into your source of your water supply if you have a septic system and a private well.

[Jim Glatthaar]

I am on both septic and well water so I will have to neutralize the lye water before disposing of it.

[Jeff Friend]

Wastewater treatment engineering is what I have been doing for a living since 1988, so I know a thing or two about sewage and chemistry.  The short answer is this: I would not hesitate to put 25 gallons of lye bath water down the drain regardless if the drain went to a septic tank or to a municipal sewer.  If you are interested, my thoughts on the subject are below.  I have had a 35 gallon lye bath for over 15 years and I have only started over one time.  It was a pain in the a$$ to carry all of those buckets to the drain I used.  An option is to take some percentage of the bath out every year and replace it with fresh water and another pound or two of lye. 

1.  The municipal collection and treatment system will never be affected by any amount of lye bath water you could possibly put down the drain in a 24 hour period. 

2.  If the pH is greater than 12.5 it will make the lye bath water a hazardous waste.  This was discussed on the forum once before.  See https://www.epa.gov/hw/defining-hazardous-waste-listed-characteristic-and-mixed-radiological-wastes#corrosivity.  However, Congress granted an exemption for households, so you are permitted to dispose of waste via the sewer.  See 40 CFR 261.4 or https://www.epa.gov/hw/household-hazardous-waste-hhw#:~:text=Specifically%2C%20wastes%20covered%20by%20the,by%20consumers%20in%20their%20homes.

3.  If you are on a septic tank, keep in mind that the typical septic tank holds 1,500 gallons.  That is 12,500 pounds of water to dilute however many pounds of lye you used setting up your lye bath. 

4.  Since it is spent lye bath water, a lot of the sodium hydroxide will have reacted with the grease on your utensils.  That will mitigate the a lot of the alkalinity and high pH.  The fact that the lye solution is no longer effectively cleaning the the crud off of your pans should tell you that most of the lye is gone.

5.  The biological activity in a septic tank will buffer the wastewater within, so the pH is not likely to get to the point of killing the bacteria.

6.  Yes, concentrated caustic soda will react with lead and a few other metals.  But we are talking about lye bath water, which is really quite dilute.  If you are worried, flush your toilet or pour a few buckets of water down the drain as a "chaser." 

7.  Trying to neutralize the lye bath water is probably a waste of time.  What acid are you going to use?  You would have to use gallons of vinegar, but how many gallons?  Unless you have a pH meter or pH test strips, how will you know when you have neutralized the waste?

8.  Yes, the sodium ions from the lye will get into the water supply eventually.  But there is already lot of sodium as well as other harmless ions present in the water.  There are persistent organic chemicals in our rivers and groundwater that are much more of a concern than sodium, the effects of which are only now being understood.  If you live in New Jersey or along the Ohio River, you probably know what I am referring to.

9.  Russell makes a good point about the sludge.  Unless you can keep it suspended it in a lot of water, it may settle out and clog your drain.  You would be better off scraping the sludge out of the bottom of the container and solidifying it with kitty litter of some type.  Then just put it in the trash.  Again, the household waste exemption applies.

[Neal Birkett]

In my industry (biotech, retired), I have had to write environmental impact reports on the manufacturing process, which included high-strength washes with sodium hydroxide, ie, lye bath equivalent.  These could be many pounds of lye for specific process steps, as well cleaning.  I learned that that the sewage plants welcome the addition of sodium hydroxide in the inflow, as it reduces the amount of lye they have to add to neutralize acid (pH routinely needs to be increased to near neutral, rather than lowered).  They specifically dislike a net increase of acid in a process.

On that basis, I have never had any concern about going directly to the sewer with a lye bath.  It is the same stuff as drain cleaner anyway.  However, I have always been careful about putting lye into the septic tank.  That's a better safe than sorry for me.

[Neal Birkett]

PS It is not really that the lye is "gone."  For me, both components of lye are still present, and the more accurate descriptor is "neutralized." 

For the lay readers:
Lye is sodium hydroxide, Na-OH.  Water is dihydrogen oxide or hydrogen hydroxide (H-OH).  Acids are H-acid moiety (acetate, chloride, etc).  The relative balance is indicated by pH, a term representing the availability of active H in the water solution.  The pH number corresponds to an exponent that represents to the availability of H.  pH 7 is neutral.  Very low pH means high availability of active H and is highly acidic.  Very high pH (up to 14) means high availability of OH and is highly basic.  The active ingredient that cleans iron is OH, and the higher the pH is the greater the effect.  Importantly, high pH does not react with the iron.  Acid (think vinegar bath) will also clean iron, but can also react and dissolve iron. (Note:  both very low and very high pH solutions are dangerous chemical solutions, and should be handed with care and appropriate protection).

Base (lye) and acids each have "half" of the moieties of water.  A mixture of a equal amount of an acid and base is basically just water and some form of a salt (can be others besides just sodium chloride table salt, ie, organic salts).  So an old ineffective lye bath still has all the lye, it is has just been mostly neutralized by acid (H) being released from the gunk (ie, decreased ph, lye + acid becomes salt + water, but the reaction dissolves gunk), resulting in a decrease in pH towards neutral.

There are whole chapters if not whole chemistry texts written on this subject.  I hope this very brief summary is useful.  PS.  I deliberately left out the charge (+, -) from this discussion for simplicity.

[Jim Glatthaar]

Thanks, Jeff & Neal for your very thorough thoughts on the lye bath/septic & well water issue.  My lye baths are all 2023 creatures so they have plenty of life left in them.  When I recently pulled a no-notch, raised number on handle Lodge from the bath and wiped everything off with a few shop towels, I know I won't have to face this issue for a while.  But it is nice to know there are safe options.