Chapter 4 module 2: Treatment of excreta for safe reuse

1. Chapter 4 module 2: Treatment of excreta for safe reuse How should urine and faeces be treated for safe handling and reuse in crop cultivation? How can organic material from households be co-treated?

2. Incineration • Quick and simple method • Faeces are applied in the stove • Require external fuel • Is quick and gives a product, the treatment of which can be verified by the eye

3. Incineration - function • To avoid odour, moisture should not be above 10% • Large amounts of non-organic material calls for additional fuel • Very efficient pathogen reduction • Mass of faeces reduced by more than 90%

4. Incineration - nutrient transformations • N: All is lost – most as N2, but some as NOx • P: Partly fixed – availability probably 30-70% of that in chemical fertiliser • K: high availability • S: lost to air as SOx • Ash is a concentrated K fertiliser containing large amounts of P • Can be reused as amendment in toilet

5. Storage of faeces • Biological degradation during storage • Final product look like soil • Risk for pathogenic survival • Current recommendation • >20°C >1 year • <20°V >2 years • Restriction in usage

6. Ammonia treatment • Uncharged ammonia is toxic to all organisms • animals, plants, bacteria, viruses and parasites • The ammonia distributes by itself through the material • The ammonia can be added as urea or as ammonia(aq)

7. Ammonia treatment • Urea is enzymatic degraded to ammonia • CO(NH2)2 + 2 H2O  2NH3 + H2CO3 • NH4++OH- NH3(aq)+ H2O • pKa=9.25 at 25°C • NH3(aq)  NH3(g) • Upon addition pH reach 9 • the higher the pH, the more NH3(g), the more toxic

8. Ammonia distribution as %NH3 • The distribution depends on • Temperature • pH

9. Ammonia treatment • Closed vessel required • Temp. >20°C • High effect on all pathogens esp with NH3>50mM • Temp. <20°C • Low effect on Ascaris and viruses • High effect on bacteria • No effect on spore formers

10. Ammonia treatment - in praxis • Lower dosage  longer time needed for treatment • 0.6% N-NH4 Dr-salmonella=6d • Temperature • Higher temperature  faster die-off • Main effect on enzymatic activity • In large scale ammonia cheaper than urea and more efficient

11. Ammonia treatment - recommendations • For human consumption • T>20°C • 2% urea • 8 weeks • T>30°C • 1.5%urea • 4 weeks • For fodder/non-food • T<20°C • 1% urea • 12 weeks • T>20°C • 1% urea • 1 week • T>30°C • 1%urea • 1 week

12. Ammonia treatment - nutrient transformations • N: left in initial form NH3 = high availability • Buffered in soil to pH~7 = no toxicity • P: Probably similar to chemical fertiliser • K: high availability • High content of organic substances • Ammonia treatment gives a fertiliser with very high fertilising value

13. Ammonia treatment • Pro • Increases fertilising value • High content of organics • No mixing necessary after initial mix • No risk for regrowth • Con • Corrosive • Smelly • Require closed container • Risk for ammonia emission at application

14. Urea treatment in use • Peepoo • Single use • Biodegradable • Self sanitising toilet • Contain 4g urea • 4 weeks T>20°C safe to use • 2 weeks T>30°C safe to use Photo: Camilla Wirsen (www.peepoople.com)

15. Storage of urine • Approx. 90% of N in fresh urine is urea • Enzymatic degradation to ammonia • pH increase from 7 to 9 • Pathogens inactivated by ammonia • Sanitation faster at high temperature and high concentration.

16. Storage of urine • Ureaammonium/ammonia • CO(NH2)2 + 3 H2O  2 NH4+ + 2 OH- + CO2 • pH 6 – 7  8.8 – 9.4 • NH3/4 pKa=9,25 at 25°C • Precipitation as metal phosphates (in pipe and tank) • NH4++OH- NH3(aq)+ H2O • NH3(aq)  NH3(g) •  Minimum ventilation!!

17. Urine storage recommended times • Faecal contamination main source of pathogens • Storage >20°C 6 month no restrictions in use • Storage <20°C 2 month not to crop consumed raw

18. Urine storage - nutrient transformations • N: Plant availability of N in urine is very high, similar to chemical ammonium fertiliser • P: Similar availability as chemical fertiliser • K: Similar availability as chemical fertiliser • Urine is a fertiliser with uniquely high availability for being a biological fertiliser

19. Hygiene and composting • Main effect from heat • Require T>50°C • WHO guidelines 1 week • Other effects • Stablilisation of material • No easy available organics • Competing microbiota • Risk for regrowth

20. Heat inactivation • Most common treatment • Only heat, removes all available organisms • Risk for re-growth of unwanted bacteria. First on site wins • Combination of heat and stabilisation from removal of available carbon is better • Moisture result in faster inactivation • Heat transport • Albumin p164 (haug)

21. Rule of thumb – hygiene treatment • Reactor turn 3 times in high temp • Pile or windrow turn 5 times in high temp • Calculation of ternings for hygiene • nt=n0[fl]N+1 • Nt= number of surviving organisms • N0=number of initial organisms • Fl= fraction in cold zone • N=number of turnings

22. Anaerobic digestion • 1-3 log10 reduction • Longer HRT and MRT higher reduction • Sedimentation in non-mixed systems (parasites) • Additional treatment required • Heat • Ammonia