I’m probably not the only one wondering about this. Gomi is also written in hiragana (ごみ) of course, but I usually see it in katakana, in such words as trashcan (ゴミ箱). It’s a bit odd since it is not a foreign word.
So why is this?
This short column from Environmental News provides an explanation. (I can’t find the original so I’m linking to Archive.org.)
Is it ごみ or ゴミ?
Gomi is written in both hiragana and katakana. There may not be a right or wrong way to write it, but some people at one time or another may have had trouble deciding which one to use.
A waste specialist have pointed out that gomi is not a foreign word, so it should be written in hiragana. Hiragana is also common when gomi is added to the name of a local government department, such as Garbage Control Division (ごみ対策課). So why is the katakana spelling ゴミ used? This is often because ごみ does not stand out in a text that is mostly hiragana, and the katakana spelling ゴミ gives an emphasized impression.
Garbage still has a strong negative image, such as “unnecessary things” or “dirty.” Furthermore, garbage disposal companies that handle garbage have not had a very good image. Although not all of them are written as ゴミ, there are probably quite a few cases where it is written as such with this meaning in mind.
Nowadays, garbage is also considered a “resource” and the image of garbage has gradually changed. Personally, I have been using the hiragana spelling without much thought, but from now on I would like to be a little more conscious when writing “gomi.”
It’s entirely possible of course that maybe I see more ゴミ than ごみ simply because the katakana version stands out more.
The rule seams to be: use ごみ as neutral language; use ゴミ for emphasis and easier reading.
So if I’m going to write Animal Trashcan (the product above) in Japanese, writing it as アニマルゴミ箱 looks bad for reading because it’s all katakana. Using アニマルごみ箱 would probably more be more logical.