Kibera, a dense, 2.5 square km shantytown outside Nairobi, is the largest slum in Kenya. It's estimated that possibly a million people live its maze of houses and outdoor markets. Now a group there has figured out a fast, efficient way to convert piles of trash into compost — and to convert areas that were once trash heaps into instant organic farms using just recycled PVC piping and other easily-accessible materials. One farm, which now ...