Applied research into the disinfection of human excreta in emergency settings using highly concentrated chlorine solutions (ARDHEES)

When infectious diseases, such as cholera or Ebola, occur in low-resource settings, the construction and operation of emergency healthcare facilities can significantly reduce mortality. However, such facilities also generate considerable quantities of human excreta that can result in the spread of the disease. On-site disinfection of excreta may prevent this.

The study described here compared the efficacy of three chlorine-based (NADCC) disinfectant concentrations (0.5%, 1% and 2%) and hydrated lime (Ca(OH)₂ at 30% concentration), using human excreta matrices containing varying amounts of organic matter.

The experiments were designed to follow MSF guidelines for disinfecting human excreta in cholera treatment centres (CTC). Excreta matrices containing raw municipal wastewater only and raw municipal wastewater with 10% and 20% (w/v) added faecal sludge, were disinfected in 14 litre high-density polyethylene (HDPE) buckets containing 4.5 litres of excreta matrix and 125 millilitres of disinfectant. The disinfection efficacy was investigated at contact times of 10, 30 and 60 minutes.

Bacterial (faecal coliforms (FC) and intestinal enterococci (IE)) and viral (somatic coliphages (SOMPH)) indicators were used to determine disinfection efficacy so as to gauge the impact of the disinfectants on both bacteria and viruses of enteric origin.

The project was funded by Médecins Sans Frontières.

The study demonstrated that 30% hydrated lime (w/v) provided the greatest overall disinfection efficacy (log reduction) for FC (M= 3.93) and for IE (M= 3.50) while 2% chlorine demonstrated the greatest overall disinfection efficacy for SOMPH (M = 2.38).

Disinfection efficacy (measured as log removal) improved as chlorine concentrations increased. Overall disinfection efficacies for 0.5% chlorine were as follows: FC (M=1.66), IE (M = 1.41); SOMPH (M = 1.28); for 1% chlorine they were: FC (M= 1.98), IE (M= 1.82); SOMPH (M = 1.79); and for 2% chlorine they were: FC (M= 2.88), IE (M = 2.60); SOMPH (M = 2.38) Furthermore, there were statistical differences in disinfection efficacy between the 2% and 0.5% chlorine solutions for FC and SOMPH. The 0.5% chlorine solution demonstrated the lowest disinfection capacity of all disinfectant doses. No statistical differences were observed between the three contact times for any of the treatments.

These findings provide valuable evidence to inform more effective health protection in future emergencies. They suggest that disinfection with 2% chlorine solution can achieve adequate disinfection of the forms of human excreta commonly encountered in emergency settings though its efficacy is much reduced in comparison with its use for wastewaters.

However, hydrated lime generally demonstrated greater disinfections efficacy of these high strength excreta mixes. This study did not investigate the potential human health impact of the chlorinated hydrocarbons and chloramines that are produced when excreta are mixed with chlorine compounds.

In conclusion, the evidence of this study suggests that the use of hydrated lime to disinfect human excreta in emergency settings as a simple public health protection measure may be preferable to the use of 2% chlorine solutions.