Characterisation and control of the biosolids storage environment: Implications for E. coli dynamics

Area of Science:

• Environmental Science
• Microbiology
• Wastewater Treatment

Background:

• Escherichia coli (E. coli) survival in biosolids storage poses risks to product quality and agricultural safety compliance.
• Biosolids storage environments are typically uncontrolled, lacking profiling of factors influencing microbial survival.
• Current practices do not actively manage storage conditions for enhanced microbial compliance.

Purpose of the Study:

• To identify environmental factors controlling bacterial concentrations in biosolids during storage.
• To assess the impact of storage conditions on E. coli dynamics.
• To evaluate strategies for mitigating E. coli in biosolids.

Main Methods:

• A two-phased study involving long-term controlled monitoring and field-scale trials.
• Monitoring of E. coli concentrations, stockpile dry solids, temperature, redox, and weather data in operational-scale stockpiles.
• Analysis using ANCOVA to determine statistical significance of environmental factors on E. coli reduction.

Main Results:

• Statistically significant E. coli reductions observed across storage periods, with greater die-off during summer months.
• Stockpile temperature demonstrated a significant effect on E. coli survival, with a 4.5 Log reduction at 31°C.
• Covered stockpiles maintaining >25°C achieved a 3.7 Log E. coli reduction, while winter conditions showed limited suppression.

Conclusions:

• Physical environmental factors, particularly stockpile temperature, play a significant role in controlling E. coli dynamics in biosolids.
• Temperature management presents an opportunity for controlling E. coli and improving biosolids quality for agricultural applications.
• Optimizing storage conditions can enhance microbial compliance and ensure safer biosolids products.