Yeah, that solar method is too long for backpacking, but the lime and sun isn't.

I'd think if the GSE is highly acidic then it should work. According to the article I linked to, using lime alone is also practiced in "many cultures". I haven't looked for how long that takes yet, but I am curious to know.

I've never tried it, but I suspect you could filter the lime flavor out with a britta charcoal filter. So if you do a half hour of sun/lime and then filter, you should be pretty good.

There were caveats in that study, "noroviruses were not dramatically reduced using this technique".