The hygienisation process

The hygienisation process
Urea
Pathogens
Faeces
Urine


In studies performed on urine at different dilutions and on urea-amended faeces* microbial inactivation rates have shown a positive linear correlation to concentrations of NH3 (aq), especially at concentrations above 50 mM. However, inactivation rate increases with temperature and a higher inactivation can be achieved at 34ºC than 24ºC at the same NH3 (aq) concentration. In the single use toilet, the excreta are not diluted and high pathogen concentrations must be assumed. Approximating bacterial and viral concentrations to 9 log10 cfu g-1 faeces and ascaris eggs to 4 log10 g-1 faeces when an infected person uses the toilet bag **, a respective decrease in pathogen concentration of 0.64 and 0.29 log10 per day is needed to sanitize the bag within two weeks, for four weeks the needed inactivation rates are 0.32 and 0.14 log10 per day, respectively.
With 4 grams of urea per Peepoo, the resulting ammonia concentration (NH3/4) is dependent on faecal load and dry matter content of the faeces. With pH 9 at 24 and 34ºC, 35 and 51% of the ammonia will be in the form of NH3 respectively. Assuming weight per defecation in the range 100-300 grams and water content in the range 75-99%, ammonia concentration in faeces was approximated at 0.711 mole g-1 DM. The NH3 target concentration for inactivation could be met at 34ºC with maximum 250 g faeces and DM<15%. At the lower temperature of 24ºC to totally inactivate ascaris suum eggs the maximal accepted load was 100 g.
The positive data on reduction of pathogens by ammonia in combination with the distribution of ammonia within the faecal matter *** indicates that faecal matter collected in a Peepoo will be sanitized within four weeks of storage and at high temperatures the sanitation time will be even faster. During this time, the bags will not degrade to such an extent that there will be a risk of diseases spreading to the environment.

* Nordin et al, submitted; Vinnerås et al.,2008; Nordin, 2007
** Westrell, 2004
*** Vinnerås et al., 2008