POTENTIAL FOR
GENERATION OF ADDITIONAL REVENUE
FROM PRODUCTS OF
WASTEWATER TREATMENT
Dr. Damjan Nemec
(B.Sc.Chem.Eng.)
Wastewater treatment in general

Process of removing contaminants from collected sewage



Nature of contaminants:




Household sewage
Industrial sewage
physical (TSS)
chemical (COD)
biological (BOD)
Objective is to produce an environmentally-safe effluent
Wastewater treatment in general


Basic process steps
Preliminary
(physical)
Primary
(physical, chem.)
Secondary
(biological)
Tertiary
(advanced)
• Screening
• Grit removal
• Grease removal
• Sedimentation
• Aeration
• Sedimentation
• Nutrient removal
• Filtration
• Adsorption
• Disinfection
• Efficiency:
- TSS = -10%
- COD = - 5%
- BOD = - 5%
• Efficiency:
- TSS = -50%
- COD = -20%
- BOD = -20%
• Efficiency:
- TSS = -95%
- COD = -90%
- BOD = -95%
• Efficiency:
- TSS > -99%
- COD > -99%
- BOD > -99%
Usually regarded as the black sheep of utility services

High operating costs and rarely appreciated by the public
Wastewater treatment in Mombasa
Wastewater treatment in Mombasa
Kipevu
WWTP
Kizingo
WWTP
Kipevu WWTP
screens
& grit
removal
settling
tanks
sludge drying beds
influent
Kipevu WWTP
sludge
thickeners
aeration tanks
effluent
sludge
Kipevu WWTP

Plant capacity:


196.000 P.E.
9.580 kg/d BOD
Electricity consumption
Equipment
Aerators
Settlers
Return sludge pumps
Excess sludge pumps
Sludge thickeners
Screw pumps
Washout pump
General
Total

17.100 m3/d
No. of units
16
4
4
2
2
2
1
1
kW per unit
45
1,5
5
5
2,5
15
4
10
kW total
720
6
15
5
5
15
4
10
780
h/d
20
24
24
12
24
4
24
12
daily (kWh)
14.400
144
360
60
120
60
96
120
15.348
Overall cost

5.606.400 kWh/a × 20 KSh/kWh = 112.128.000 KSh/a
annual (kWh)
5.256.000
52.560
131.400
21.900
43.800
21.900
35.040
43.800
5.606.400
screens
& grit
removal
settling
tanks
sludge drying beds
influent
Kipevu WWTP
sludge
thickeners
aeration tanks
effluent
sludge
Biogas production from sludge
Sludge
Biogas storage
Thickened sludge
Biogas
Biogas
Flare
Digester #1
Digester #2
CHP unit
Biogas cleaning
Biogas production from Kipevu WWTP sludge

Nett production of electricity



Overall investment


7.635 - 1.455 = 6.180 kWh/d
2.255.700 kWh/a × 20 KSh/kWh = 45.114.000 KSh/d (40%)
1.826.000 € (~ 5,3 years of payback)
41% less sludge to dispose!
Kipevu WWTP
Expanding services


Biogas plant has space for additional substrate
Food waste from hotels can be collected as extra service


~100 hotels, ~6.500 tourists
~0,5 kg of food waste per tourist => 3,5 t/d of energy rich waste
Biogas production from sludge
Sludge
Food waste
Biogas storage
Substrate
Biogas
Biogas
Flare
Digester #1
Digester #2
CHP unit
Biogas cleaning
Biogas production from Kipevu WWTP sludge

Nett production of electricity



Overall investment


8.670 - 1.510 = 7.160 kWh/d
2.613.400 kWh/a × 20 KSh/kWh = 52.268.000 KSh/d (47%)
1.923.000 € (~ 4,8 years of payback)
37% less sludge to dispose!
screens
& grit
removal
settling
tanks
sludge drying beds
influent
Kipevu WWTP
sludge
thickeners
aeration tanks
effluent
sludge
Reuse of treated water from WWTP

Can be treated further with advanced methods and reused:

Urban reuse:
•
•
•

Industrial reuse:
•
•
•


Irrigation of public parks, landscapes and golf courses
Vehicle washing and decorative water features
Connecting to fire hydrants for fire protection
Cooling water
Boiler make-up water
Industrial process water
Agricultural reuse
Can even be purified to potable water standards!
Reuse of treated water from Kizingo WWTP

For irrigation of the golf course and local parks



Only filtration and disinfection required
Nutrient removal not required, their presence is beneficial!
Limited extra investment

Plant is located beneath the golf course!
Reuse of treated water from Kipevu WWTP

After treatment the water is discharged into the sea


17.100 m3/d
Focus on cooling water requirements of the local industry



Usually the largest use of reclaimed water
High quantities and moderate quality required
Numerous petroleum refineries in the US that practice this
Kipevu WWTP
Reuse of treated water from Kipevu WWTP

Potential treatment required for cooling water standard

Corrosion concerns (filtration)
•

Biological concerns (disinfection)
•
•

Removal of dissolved solids
Removal of microbiological organisms (may deposit on surface)
Removal of nutrients (may contribute to microorganism growth)
Scaling concerns (chemical treatment)
•
Removal of Calcium, Magnesium, Phosphate and Sulphate
Current conclusions

Wastewater treatment…




…is required to protect the environment (for today and tomorrow)
…can be very expensive, especially if plants are under capacity
…plants should be maintained regularly with skilled staff
The cost pressure can be reduced…

…by “exploiting” the potential of wastewater treatment products
•
•
•

Sludge for energy (biogas)
Expanding the services to collecting other energy rich waste (tipping fees)
Reuse of treated water will be gaining in importance in the coming years
Concrete results on the assessment will be made available
Thank you for your attention!
damjan.nemec@gmail.com