Question

What's the waste product of electrons and pyruvate combining in fermentation? ​

Answer 1

That would be lactate(lactic acid). See attached pic:)

Answer 2

Answer:

Lactate

Explanation:

Under the conditions of oxygen scarcity, pyruvate does not enter the Kreb's cycle in the form of acetyl CoA. Rather pyruvate is reduced into lactate by accepting the electrons from NADH. Reduction of pyruvate and oxidation of NADH form lactate and NAD+. The process is called lactic acid fermentation.  

Here, the NAD+ enter the glycolysis to continue the energy production while lactate is a waste product.