The use of some kind of chemistry is an important and unavoidable part of most industrial cleaning processes. Chemistries can remain effective for as little as a few hours or as long as a year or more depending on the chemistry and how it is used. In the end, however, cleaning chemistry must be disposed of and it isn’t as simple as opening the drain valve! Don’t you love how most of the MSDS’s you read say “dispose of in accordance with local regulations” at the bottom? What does that mean anyway?
Most industrial cleaning chemistries are either acidic or caustic in nature (the vast majority of them are caustic). It is more than likely that “local regulations” won’t be met if you put a liquid that is significantly acidic or basic down the drain. This means that the chemistry needs to first be neutralized before you can get rid of it. The usual measure used to express either the acidic or caustic nature of a liquid is pH. The pH scale runs from 1 to approximately 13 with 1 being strongly acid and 13 being strongly caustic or “basic.” A neutral liquid has a pH of 7 which is what most “local regulations” demand, give or take a pH or so. So, one of the first things you need to do is measure the pH of the chemistry you wish to get rid of. This can be done using either a pH meter or pH indicator paper strips which change color to indicate the pH when they are immersed in the liquid.
Once you know the pH of the liquid, you next have to determine how best to bring it to the required pH of 7. Usually, it’s just a matter of mixing in another liquid or (in some cases) powder of a contrasting pH until the mixture reaches a pH of 7. This sounds simple but can be a little tricky – especially if you skipped chemistry class a few too many times like I did! The problem is that if you have a solution with a pH of 12, it isn’t just a matter of mixing in an equal volume of some liquid with a pH of 2 to make the “average” pH be 7 or “neutral.” The pH of an acid or caustic may not vary significantly as its concentration is changed. Also, two acids that measure the same pH may have differing abilities to neutralize a given caustic. This means that, depending on the neutralizing agent used, it may take a whole lot more or a whole lot less than you may expect to produce a mixture with a neutral pH. I remember, for example, one instance in which neutralizing a few gallons of a caustic solution required several 55 gallon drums of the selected neutralizing acid. Unless you are a chemist, it’s a good idea to try your neutralization on a small scale first to determine the ratio required to affect neutralization. Once you know the approximate ratio required you can scale up to whatever volume is required. However, make sure you test as you approach the expected end point of your neutralization because the transition from base to acid or vice versa can be pretty rapid in some cases.
Neutralization of chemistry prior to disposal is only one of the many considerations required by most “local regulations.” A few of the other concerns are concentrations of certain metals, hydrocarbons (oil), solids, radioactivity, and the list goes on. The whole disposal thing is further complicated by the fact that the chemistry you put into the cleaning tank to start out with is NOT the same once it’s been used for as long as a year in the cleaning process. Proper disposal is, undoubtedly, one of the largest ongoing concerns and expenses for most industrial cleaning operations. In subsequent blogs I will try to touch on many of these concerns and also offer possible disposal alternatives for your consideration.