Transcript 4.5a Treatment of excreta for safe reuse

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?
Incineration
Chimney
Removable top, through which faeces
are fed into the incinerator
• 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
Access door through which the stove is
passed and locked inside after firing
Incineration - function
• To avoid odour,
moisture should not be
above 10%
• Large amounts of nonorganic material calls
for additional fuel
• Very efficient pathogen
reduction
• Mass of faeces reduced
by more than 90%
Chimney
Removable top, through which faeces
are fed into the incinerator
Access door through which the stove is
passed and locked inside after firing
Incineration - nutrient transformations
• N: All is lost – most as
N2, but some as NOx
• P: Partly fixed –
availability probably 3070% 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
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
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)
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
Ammonia distribution as %NH3
• The distribution
depends on
• Temperature
• pH
Ammonia treatment
• Closed vessel required
• Temp. >20°C
• Temp. <20°C
8
7
Concentration(log)
– High effect on all
pathogens esp with NH3
>50mM
9
– Low effect on Ascaris and
viruses
– High effect on bacteria
• No effect on spore formers
6
Phage
E. coli
Clostridia
Enterococci
5
4
3
2
1
0
0
10
20
30
Time (days)
40
50
60
Ammonia treatment - in praxis
• Lower dosage  longer time
needed for treatment
– 0.6% N-NH4 Drsalmonella=6d
• Temperature
– Higher temperature  faster
die-off
– Main effect on enzymatic
activity
• In large scale ammonia
cheaper than urea and more
efficient
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
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
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
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)
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.
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!!
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
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
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
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)
Albumin
watercont aprox cog T
50
56
25
76
15
96
5
149
0
165
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
Anaerobic digestion
• 1-3 log10 reduction
• Longer HRT and MRT
higher reduction
• Sedimentation in nonmixed systems
(parasites)
• Additional treatment
required
– Heat
– Ammonia