That's just a bloomberg article, not a full cost benefit analysis. If some of the pig waste goes to the shrimps, less of it will go elsewhere. I'd call that recycling - a positive externality here.

Pig manure is causing problems in this world. For example, some serious effort is made to find the best storage temperature to reduce methane emissions - see www.engr.usask.ca/societies/csae/protectedpapers/c0209.pdf for exemple.

So anything that will reduce or convert the amount produced is a good thing.