A Pseudomonas aeruginosa culture has a maximum specific growth rate μmax = 0.8 h^-1 on glucose. In a chemostat, what dilution rate D will prevent washout?

Introduction / Context:
In a chemostat, steady state requires that the net specific growth rate equals the dilution rate (μ = D). If D exceeds the culture’s μ at the operating conditions, biomass cannot keep up with outflow and washout occurs. Choosing D relative to μmax is a basic control decision.

Given Data / Assumptions:

• μmax = 0.8 h^-1 for Pseudomonas aeruginosa on the stated medium.
• Operating substrate concentration supports μ ≤ μmax.
• No cell retention device.

Concept / Approach:
To avoid washout, set D < μ at the achieved substrate level. Since μ cannot exceed μmax, a safe guideline is D < μmax, with margin for disturbances and maintenance requirements.

Step-by-Step Solution:

Verification / Alternative check:
Chemostat theory predicts X → 0 as D approaches μmax from below if substrate is limiting and any perturbation pushes μ < D.

Why Other Options Are Wrong:

• D > 0.8: guarantees washout.
• D = 0.8: marginal; susceptible to washout.
• D = 1.6: far above μmax; immediate washout.
• D = 0: not a chemostat (becomes batch).

Common Pitfalls:
Ignoring that μ depends on substrate; operating too close to μmax reduces robustness to fluctuations.

Final Answer:
Less than 0.8 h^-1