What do chlorella feed on?

They rely on sunlight, CO2, and water, but also a small amount of minerals to reproduce.

To kill bacteria from our body especially from stomach

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.