# Simulation of anaerobic biodegradation process in a tubular bioreactor with a biofilm layer: Steady-state and unsteady-state conditions

## TL;DR

The paper simulates anaerobic biodegradation in a tubular bioreactor with a biofilm layer under steady and unsteady conditions, analyzing how reactor parameters affect performance.

## Contribution

The study introduces a simulation framework for anaerobic biodegradation in tubular bioreactors with biofilm under varying operational conditions.

## Key findings

- Reducing bioreactor diameter increases substrate conversion in liquid and lowers biofilm substrate concentration.
- Increased liquid residence time slightly reduces biofilm substrate concentration while boosting conversion.
- A proportional-integral controller with parameters KP=−0.131 and KI=0.02 regulates substrate conversion effectively within 120 seconds.

## Abstract

In this paper, anaerobic biodegradation process in a tubular bioreactor with an inner biofilm layer for steady-state and unsteady-state conditions are simulated. The effects of various parameters including bioreactor diameter, fraction of active biomass transferred to liquid phase, and residence time of the liquid on bioreactor performance are examined. Simulations indicate that decreasing diameter of bioreactor leads to increasing degree of conversion of the substrate in liquid phase and decreasing dimensionless concentration of the substrate in biofilm. With an increase in the fraction of active biomass transferred to liquid, substrate concentrations in liquid and biofilm slightly vary. Increased residence time of the liquid phase results in the degree of conversion of substrate goes up, but substrate concentration in biofilm lowers a little. In addition, it is found that biomass concentration of liquid phase is boosted with decreased bioreactor diameter and increased residence time of liquid. A proportional-integral controller is designed and the tuned parameters of KP=−0.131 and KI=0.02 are obtained using genetic algorithm. It is observed that controller regulate well the degree of conversion of the substrate within 120 s for both servo and regulatory modes.

Image 1

•Tubular bioreactor with biofilm is simulated for steady state and unsteady state.•Parameters of proportional-integral controller are tuned using genetic algorithm.•As Bioreactor diameter lowers, degree of conversion of substrate in liquid rises.•Rising residence time leads to a small drop in substrate concentration in biofilm.•Biomass concentration in liquid is boosted with decreased bioreactor diameter.

Tubular bioreactor with biofilm is simulated for steady state and unsteady state.

Parameters of proportional-integral controller are tuned using genetic algorithm.

As Bioreactor diameter lowers, degree of conversion of substrate in liquid rises.

Rising residence time leads to a small drop in substrate concentration in biofilm.

Biomass concentration in liquid is boosted with decreased bioreactor diameter.