Given that plant biomass has some carbohydrates that yeast cannot easily metabolize, it might be good to have a step to enzymatically break them down into simpler sugars. So you will want to heat sterilize your algal biomass before treating with cellulase and amylase or performing an acid hydrolysis step. Else use a yeast strain engineered to handle cellulostic biomass.

Sure I will do this pre treatment to the biomass, but after that adding the yeast should be direct or incubated??

Incubation at the optimal temperature would be better.

Saccharomyces cerevisiae amount 1% or 10% w/wbiomass ???