Perfume chemists have devised a tool aimed at stopping foul smells from undermining the struggle to improve sanitation in developing countries.
A team from Swiss firm Firmenich—better known for applying aroma expertise to perfumes and food—has developed a system to quantify six major faecal aroma chemicals at the same time in toilet air. The technique is described in a paper published in Environmental Science & Technology last month.
“This is to help make a perfume to cover the malodour,” Christian Starkenmann, a chemist at Firmenich and one of the study’s authors, said. Such perfumes would improve conditions in public toilets that charge for use, supporting a business model for building and maintaining sanitation where it is lacking, he added.
Clara Rudholm, a programme officer at the Global Sanitation Fund in Geneva, said the study was useful, while stressing the importance of supporting behaviour change in local communities, too.
The Firmenich scientists analysed sludge from latrines in India, Kenya, Uganda and South Africa. They were unable to collect a fully representative toilet smell using the first method they tried: Holding a polymer-coated needle above the sludge to absorb odorant chemicals. Specifically, this technique could not capture sulphur-containing gases.
“What you smell in the toilet is the air, not the sludge,” Starkenmann said. “To analyse the air is much more difficult.”
Instead the team designed a system that pumps air from above the latrine through a water-based solution that traps sulphur-containing gases. Other odorant compounds also dissolve in the water.
The scientists ran the water through two extraction steps that collected all the odorants. They then got 40 Firmenich experts to smell and describe odour intensities, with descriptions including “vomit” and “barnyard,” against odorant concentration. “Nobody quantitatively linked intensity and concentration measured before,” Starkenmann says.
This combination of chemical and sensory analysis is the study’s most innovative aspect, according to George Preti, a researcher at the University of Pennsylvania and the Monell Chemical Senses Centre in the US. “This greatly increases the probability of understanding the chemical composition of the malodour bouquet,” he said.
The team found that Indian toilets had a lot of sulphur gas. “There’s more anaerobic fermentation that causes a lot of this eggy, sewage odour,” Starkenmann explained. The improved ventilation in the African pit latrines reduced this problem.
The study results are helpful because improving the smell of toilets means more people will use them, said Clara Rudholm, a programme officer for the Global Sanitation Fund at the Water Supply and Sanitation Collaborative Council in Switzerland.
But beyond the business-led toilet model Firmenich envisions, Rudholm said community-led models could also be effective. “People enabled to build and use well-ventilated toilets are likely to keep them clean, well-maintained and odour-free,” she added.