Module 4.10
Ecosan versus conventional
sanitation
How can dry UD ecosan system be
compared with a conventional
systems (open defecation, latrine pit,
water-borne)?
4 Swedish systems
with nutrient recovery compared
1.
2.
3.
4.
Reference. Conventional system. N & P removal in
WWTP. Effluent: 8 mg N & 0.24 mg P/l. Sludge
incinerated, ash landfilled.
Urine. 80% of urine diverted & recycled as fertiliser. Rest
= reference
Blackwater. Vacuum toilets. Collected blackwater
anaerobically digested, sanitised & recycled as fertiliser.
Rest = reference
Sludge. Sludge recycled as fertiliser. Rest = reference
Recycled plant available NPKS (% of tot)
Recycled plant available NPKS
80
N
P
K
70
60
50
40
30
20
10
0
Reference
Urine
Blackwater
Sludge
PhoStrip
KREPRO
BioCon
S
Energy use
1000
Pumping
Treatment
Transports
P-recovery
Spreading
Chemical fertiliser
Energy use (MJ/pers, yr)
900
800
700
600
500
400
300
200
100
0
Reference
Urine
Blackwater
Sludge
PhoStrip
KREPRO
BioCon
Non-renewable resource use (10e-16/person, yr)
Total use non-renewable
600
P,K,S
Oil, gas
Electricity
500
400
300
200
100
0
Reference
Urine
Blackwater
Sludge
Other studies of sorting systems
• Many systems analysis have found same
results:
• Urine diversion
– decreases water emissions
– gives lots of useful fertiliser
– saves chemical fertiliser
– saves energy
Recycled NPK vs degree of diversion
Recycled NPK [kg/p,yr]
3,0
2,5
Urine
Sludge
2,0
1,5
1,0
0,5
0,0
N
N
N
P
P
P
K
K.
K
Conv 40% 100% Conv 40% 100% Conv 40% 100%
Water emissions vs degree of diversion
Wateremissions [kg/p,year]
0,8
0,7
Sew plant
Field
Landfill
Chemicals
0,6
0,5
0,4
0,3
0,2
0,1
0,0
N Conv N 40%
N 65% N 100% P Conv P 40%
P 65% P 100%
Energy usage vs degree of diversion
Energy usage [MJ/p,year]
350
Fertiliser
Oil
Electric
300
250
200
150
100
50
0
Conv
40% Urine
65% Urine
100% Urine
http://www.stockholmvatten.se/pdf_arkiv/english/Urinsep_eng.pdf
Energy usage [MJ/p,yr]
Energy usage vs transport distance
400
350
300
250
200
150
100
50
0
Fertiliser
Oil
Electricity
Conv.
1 km 33 km 100 km 200 km 1 km 33 km 100 km 200 km
Urine Urine Urine Urine Urine Urine Urine Urine
truck truck truck truck
t+t
t+t
t+t
t+t
System boarders
• What to include and what to exclude?
• UDD
– Solid organic waste
– Energy production
– Fertiliser production
• Food production
– Delivered sanitational function
• Greywater
• Drinking water
• Other waste
Productive Sanitation
Excreta
Food
N=2.8kg
P=0.4kg
K=0.5 kg
Nutrient flow per person and year
N=2.8kg
P=0.4kg
K=0.5 kg
Fertiliser
Value of fertiliser - urine
•
•
•
•
2.8kg N = 6kg Urea 0.5€/kg = 3€
0.4 kg P = 2kg TPS ~0.4€/kg = 0.8€
0.5 kg K = 1kg KCl ~0.4€/kg = 0.4€
Total value 4.2€ per person and
year = 0.012€ per person day
• Value per jerry can 20L ~ 0.23€
• Can at least pay for transport and
spreading
• Non-subsidised
Cost for ecosan
•
•
Pour flush toilet 1900 INR (35€)
EcoSan toilet 4200 INR (77€)
Fertiliser per family
Fertiliser Amount, kg Difference
Nutrients
kg
160
4 persons NPK 10-5-20
2,2
16,0
10,0%
18,2
N
-1,2
3,6
2,2%
2,32
P
 NPK 10-5-20
Indian, price 5.5 INR/kg (0.1€)
 Value 880 INR/year (16€)
 Present value years 2-10:
5070 INR! (93€)
Conclusion
• Pour flush toilet cost: 1900 R
• EcoSan toilet cost: 4200 R
– Income from fertiliser: 5080 R
• Fertiliser can pay for toilet in 10 years, not just
additional cost!
Additionally
• Less hazard to ground & surface water
– Saves on drinking water
– Protects health
Cost sharing
• Having no toilet has lowest investment &
direct running costs!
• Only type of toilet where the investment can
directly pay off
• The cost of Ecosan is compatitive compared
with any other ecological solution
• The cost is largely paid by household when
building – no risk for corruption at municipal
level – higher cost acceptance
• More private enterprise – more competition –
saves taxes