Fuel cells and waste

If a robot used a microbial fuel cell to “digest” food and biomass, would it produce waste the way the human digestive system has waste left behind after digestion? Is there any possible way to do something with this waste or not create it at all so that there is nothing to dispose of?

EDIT: Would the answer be any different if the fuel cell used artificial materials and methods to replicate the bacteria’s process of creating energy?

submitted by /u/teenytoons2
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