Real-time Microbial Performance Monitoring in Biogas Production

Introduction
Anaerobic digestion is a process through which complex bacterial communities break down organic matter in the absence of oxygen in a sealed vessel called a reactor. This process produces biogas, a methane-rich gas that can be used as a fuel, and digestate, a source of nutrients that can be used as a fertiliser.

The CNETE (National Centre of Electrochemistry and Environmental Technologies) testing facility in Quebec, Canada, was interested in testing the effectiveness of biogas production of a pre-treatment stage on the anaerobic digesters processing waste activated sludge.

This project trialled a new innovative type of sensor, SENTRY, to help monitor the differences between the two identical systems, one with pre-treatment and one without, in real-time.

Approach
Most sensors measure physicochemical properties (e.g. pH, ORP, VFAs) to act as a chemical proxy for understanding biology. SENTRY directly measures the microbial metabolic activity of exoelectrogenic bacteria involved in wastewater treatment, the Microbial Electron Transfer (MET) rate.

  • Online real time microbial performance monitoring
  • One reading every minute to a professional dashboard
  • Zero maintenance, no calibration, easy installation

This means that by using SENTRY, water companies can directly and in real-time get a quantification of their biology to better understand what is happening in their wastewater and at their sites.

Analysis
The microbial activity levels recorded by SENTRY were found to trend well with biogas production, with the probes detecting distinct batch run cycles for each system. The devices identified a period of the day (typically between noon and 7pm) where additional loading could be added to the reactors, as there were lower levels of microbial activity.

It was found that the reactor with the pre-treatment stage (Reactor B) consistently had higher levels of microbial activity, as can be seen by Figure 3. This suggests a more biologically active feed material.

As well as Reactor B having the highest microbial activity, it was found that the addition of a pre-treatment stage increased biogas production by 22.9% (Figure 4).

 

SENTRY

Figure 1 3D drawing of the custom mount and the SENTRY sensor

SENTRY sensor

Figure 2 SENTRY sensor system installed

Comparison in MET between Reactor A (blue, control reactor) and Reactor B (red, pre-treated reactor)

Figure 3 Comparison in MET between Reactor A (blue, control reactor) and Reactor B (red, pre-treated reactor)

Achievements

  • Monitored anaerobic digestion for the effectivity of biogas production
  • Validated differences between different test conditions
  • Identified periods where loading could be increased based on daily biological activity trends

The SENTRY sensors demonstrated that the addition of a pre-treatment stage to the anaerobic digestion reactor increased biological activity and biogas production.

Overall, the probes were demonstrated to be a key tool in understanding both the impact of pre-treatment on the suitability of the waste organics for anaerobic digestion processing and for optimising feeding cycles to maximise utilisation of bio-available organics.

For continuing anaerobic digestion activities the sensor could be applied to:

  • Characterising the impact of pre-treatment on influent wastewater streams
  • Providing correlations to real-time biogas production
  • Optimising feed cycle times to ensure removal of bio-available carbon

5/7/2023

Biogas production and MET

Figure 4 Biogas production and MET