I see that there are many questions on whether putting/putting how many affiliation(s) on a paper. My situation does not quite fit into all the existing questions, so I am posting my question here.
First of all I am currently working as a part-time lecturer at two different colleges in the same city. I am writing my paper on my own, and neither of them has support for my research (besides having access to some database of my field and access to journal papers). I am not sure if I should put any of the colleges I am currently working at as affiliations. The reasons of my concern are
The number of courses I teach at these two colleges vary from semester to semester. I expect in some semester I would not have any course to teach at one or even both of the colleges. This means in some coming semesters I may not affiliate with these colleges (for example the summer semester).
I would prefer to put the university I obtained my PhD degree as the affiliation, and write something like "Alumni of XXX University". But I have not seen this before in any paper, and I am not sure if this is the norm.
I do not object writing myself as independent scholar, but I probably will use the email of the university I obtained my PhD degree in this case. But then I would think why don't I do 2. in above.
Sometimes I think submitting a paper to a journal by a university email address is better than personal email address in the sense that the editor will take it slightly more seriously.