Inactivation of ESBL-/AmpC-producing Escherichia coli during mesophilic and thermophilic anaerobic digestion of chicken manure

•Bacteria reduction during anaerobic digestion of chicken manure was investigated.•Anaerobic digestion effectively reduced antibiotic-resistant E. coli in chicken manure.•Temperature and retention time were the main inactivation factors.•Calculated D-values help adjust retention times for a safe inactivation. The high prevalence of extended-spectrum-ß-lactamase (ESBL)-/AmpC-producing Escherichia (E.) coli in European broiler farms leads to the possible dissemination of antibiotic-resistant strains into the environment using contaminated feces as organic fertilizer. The aim of the present study was to determine the influence of temperature on the reduction kinetics of two artificially added ESBL-/AmpC-producing E. coli strains during lab-scale mesophilic (37 °C, 42 °C) and thermophilic (55 °C) anaerobic digestion of chicken manure. The decimal reduction times (D-value) were approximately 3–6 days at 37 °C, 1.5 days at 42 °C and 48 min at 55 °C. Starting with initial E. coli counts of 7 log10 colony forming units (CFU) per milliliter, both E. coli strains were below the detection limit after 35 days at all temperatures; however, at 37 °C and 42 °C, ESBL-producing E. coli were still partially detectable by enrichment. Temperature and retention time were the main inactivation factors. No direct correlation could be found between pH, volatile fatty acids (VFA) or ammonia (NH3) and E. coli reduction. D-values were predicted for several temperatures between 37 °C and 55 °C and may help define time-temperature guidelines. Thermophilic digestion is an adequate method to rapidly inactivate ESBL-producing E. coli in chicken manure. At mesophilic temperatures, however, strict compliance of retention times and the prevention of short-circuiting become essential to gain an ESBL-producing E. coli free digestate.