Digester Stability Phase Portrait: VFA vs Alkalinity

Biogas digesters run on a division of labor between fast-growing acid-forming bacteria and slow-growing methanogens, and the two can fall out of balance. This 2D companion to the tank simulator plots the identical Monod-kinetics stability model as a phase-plane trajectory in VFA/alkalinity space plus a scrolling multi-trace strip chart of pH, the VFA/TA ratio, methanogen population and methane rate — so the same souring feedback loop (VFA outpaces alkalinity buffering, pH falls, methanogens are inhibited, methane collapses) reads as pure state-space geometry instead of a rendered vessel. Push organic loading rate too high or fire a shock-load slug, dose alkalinity, and manage temperature to keep the trajectory inside the stable green wedge.