Well a couple of things u can do. 1.adsense 2.sell ad space 3. sell blog can u tell me the niche of blogs and are they auto or manual and the alexa ranking +traffic per week might help me evalute your options
I have 10 blogs and I don't earn any money with them. If you have 30 active blogs that rank well in Google and get traffic then write articles and link to affiliate schemes or use adsense or link to your own related products/sales website.
Erm ... If you say, you have 30 blogs, do you mean, you have 30 entries in one blog or really 30 blogs on different topics? In either case you loose. The only way to make money as a blogger is to sell your content to advertisers, so they can get in contact with your users. Your userbase is your asset, in case you don't have one, you will not make money either. As harsh as it sounds: As long as you write about trivialities, you will not attract one. There is an article on my site, that may help you understand your problem (see my profile for a link).