Regarding backlinks, your comment box is by default set to make the links nofollow, so you don't lose any link juice.
However, in general you should allow only those comments with link which add value to your articles. Comments like 'thank you for this article', 'well written post' etc should not be allowed. Allow only those comments which add valid points to your articles.
Don't allow comments like this "Hey I just got through with the pages, I should say Pretty nice work done there.Thanks for sharing your ideas!!I really Keep sharing your views appreciate it!" These are spam comments used to get backlinks.
You are a teacher, why not provide good quality articles with in-depth content rather than short pieces of articles? I also have a blogspot blog, not actively managed but has good in depth engineering content along with other topics I like to cover. These articles fetch good traffic in long terms and considering that is your personal blog, you should focus on increasing its quality rather than having it just for money.
Sorry if I am wrong, but I checked 5-6 articles on your blog and they were not as in-depth as I was hoping for. So just thought I would share how I manage my own blog with Engineering content.