Assessing the usefulness of clostridia spores for evaluating sewage sludge hygienization

Bioresour Technol. 2017 Feb:225:286-292. doi: 10.1016/j.biortech.2016.11.075. Epub 2016 Nov 22.


The capability of clostridia spores to act as pathogen indicators in sewage sludge treatment was investigated. Sulfite-reducing clostridia and E. coli levels were monitored during waste activated sludge pre-treatments (alkali and ultrasound) and its subsequent mesophilic anaerobic digestion. E. coli was maintained or reduced depending on treatment type and intensity. However, alkali pre-treatment (35.3gNaOH/kgTS) by itself and alkali (157gNaOH/kgTS) and ultrasound (27,000kJ/kgTS) pre-treatments followed by anaerobic digestion provoked reproducible clostridia increases. Specifically, up to 2.7log10 after 35.3gNaOH/kgTS pre-treatment and up to 1.9 and 1.1log10 after digesting the 157gNaOH/kg TS and 27,000kJ/kgTS pre-treated sludge, respectively. Having rejected the hypotheses of sporulation and floc dissipation, the most plausible explanation for these clostridia increases is re-growth. These results question the suitability of clostridia spores as indicators of sludge treatment and other biological treatments where clostridia may have a role.

Keywords: Anaerobic digestion; Clostridium spores; Hygienization treatment; Indicator; Sewage sludge.

MeSH terms

  • Alkalies
  • Bacterial Load
  • Clostridium / isolation & purification*
  • Escherichia coli / isolation & purification*
  • Sewage / microbiology*
  • Spores, Bacterial / isolation & purification*
  • Ultrasonics


  • Alkalies
  • Sewage