Solving fecal coliform growth/reactivation in biosolids during full-scale post-digestion processes

Area of Science:

• Environmental microbiology
• Wastewater treatment engineering

Background:

• Fecal coliform recurrence was observed during pilot-scale thermophilic anaerobic digestion at the Hyperion Treatment Plant.
• This occurred while some digesters remained at mesophilic temperatures, indicating potential process instability.

Purpose of the Study:

• To investigate the causes of fecal coliform regrowth in post-digestion biosolids.
• To identify and implement solutions for preventing fecal coliform recurrence in treated biosolids.

Main Methods:

• Conducted pilot-scale experiments using thermophilic anaerobic digesters alongside mesophilic digesters.
• Performed laboratory and full-scale experiments to identify contamination and temperature drop issues.
• Implemented full plant conversion to thermophilic anaerobic digestion and modified the post-digestion train.

Main Results:

• Identified contamination between thermophilic and mesophilic biosolids as a potential cause.
• Determined significant temperature drops between centrifuges and silos could lead to fecal coliform reactivation.
• Observed resolution of fecal coliform recurrence after full plant conversion and process modifications.

Conclusions:

• Contamination and temperature fluctuations are critical factors influencing fecal coliform regrowth in biosolids.
• Full conversion to thermophilic anaerobic digestion and optimized post-digestion design effectively resolved fecal coliform recurrence.
• The findings provide valuable insights for optimizing thermophilic anaerobic digestion processes in wastewater treatment plants.