Biofuel Bioreactor: Enzymatic Hydrolysis & SSF

Process Controls

Cellulase enzyme loading 15 FPU/g

Process temperature 38 °C

Feedstock loading 10% w/v

Yeast pitch rate 2.0 g/L

Batch Status

Simultaneous saccharification & fermentation (SSF) starting…

Glucose

0.0 g/L

Ethanol

0.0 g/L

Cellulose converted

0.0%

Batch time

0.0 h

How it works

This models SSF (simultaneous saccharification and fermentation) — the industrial route from lignocellulosic biomass to ethanol. Two coupled processes run in the same tank: cellulase enzymes hydrolyse solid cellulose into glucose, while yeast ferments that glucose into ethanol as fast as it appears.

Enzymatic hydrolysis (Michaelis–Menten):
  dS/dt = −k_cat·f_E(T)·E·S / (K_S + S)
  glucose released: r_hyd = 1.11 × (−dS/dt)

Yeast growth (Monod, product-inhibited):
  μ = μ_max·f_Y(T)·[G/(K_G+G)]·(1 − P/P_max)
  dX/dt = μ·X
  glucose used:   r_ferm = (μ·X) / Y_x/g

Mass balances:
  dG/dt = r_hyd − r_ferm
  dP/dt = Y_p/g · r_ferm   (ethanol, ~0.48 g/g glucose)

S = solid cellulose (g/L), E = enzyme dose, G = glucose, X = yeast biomass, P = ethanol.
f_E(T) peaks near 50 °C (cellulase's thermal optimum); f_Y(T) peaks near 32 °C and collapses above ~42 °C (yeast heat death) — the two enzymes want different temperatures, which is why real SSF plants compromise around 35–40 °C.
Ethanol itself throttles yeast growth once P approaches P_max (~90 g/L) — product inhibition, the same effect that caps alcohol content in any fermentation.
The tank view shows fiber particles (cellulose) shrinking as they're hydrolysed, yeast cell particles multiplying as glucose becomes available, and CO₂ bubbles rising at a rate tied to the live fermentation rate.

Cellulose fiber Yeast cells CO₂ bubbles

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Biofuel Production Simulation: Enzymatic Hydrolysis & SSF