1. GENERATION OF ADDITIONAL REVENUE FROM PRODUCTS OF
POTENTIAL FOR
GENERATION OF ADDITIONAL REVENUE FROM PRODUCTS OF
WASTEWATER TREATMENT
Dr. Damjan Nemec (B.Sc.Chem.Eng.)

2. Wastewater treatment in general
Process of removing contaminants from collected sewage
Household sewage
Industrial sewage
Nature of contaminants:
physical (TSS)
chemical (COD)
biological (BOD)
Objective is to produce an environmentally-safe effluent

3. Wastewater treatment in general
Basic process steps
Usually regarded as the black sheep of utility services
High operating costs and rarely appreciated by the public
Preliminary
(physical)
Screening
Grit removal
Grease removal
Efficiency:
- TSS = %
- COD = %
- BOD = - 5%
Primary
(physical, chem.)
Sedimentation
Efficiency:
- TSS = %
- COD = -20%
- BOD = -20%
Secondary
(biological)
Aeration
Sedimentation
Efficiency:
- TSS = %
- COD = -90%
- BOD = -95%
Tertiary
(advanced)
Nutrient removal
Filtration
Adsorption
Disinfection
Efficiency:
- TSS > %
- COD > -99%
- BOD > -99%

4. Wastewater treatment in Mombasa

5. Wastewater treatment in Mombasa
Kipevu
WWTP
Kizingo
WWTP

6. Kipevu WWTP

7. Kipevu WWTP influent screens & grit removal settling tanks
sludge
thickeners
sludge drying beds
sludge
aeration tanks
settling
tanks
effluent

8. Kipevu WWTP Plant capacity: Electricity consumption Overall cost
P.E m3/d kg/d BOD
Electricity consumption
Overall cost
kWh/a × 20 KSh/kWh = KSh/a
Equipment
No. of units
kW per unit
kW total
h/d
daily (kWh)
annual (kWh)
Aerators 16 45
720 20
14.400
Settlers 4
1,5 6 24
144
52.560
Return sludge pumps 5 15
360
Excess sludge pumps 2 12 60
21.900
Sludge thickeners
2,5
120
43.800
Screw pumps
Washout pump 1 96
35.040
General 10
Total
780
15.348

9. Kipevu WWTP influent screens & grit removal settling tanks
sludge
thickeners
sludge drying beds
sludge
aeration tanks
settling
tanks
effluent

10. Biogas production from sludge
Thickened sludge
Biogas storage
Flare
CHP unit
Digester #1
Digester #2
Biogas
Biogas
Biogas cleaning

11. Biogas production from Kipevu WWTP sludge
Nett production of electricity
= kWh/d
kWh/a × 20 KSh/kWh = KSh/d (40%)
Overall investment
€ (~ 5,3 years of payback)
41% less sludge to dispose!

12. Kipevu WWTP

13. 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

14. Biogas production from sludge
Substrate
Food waste
Biogas storage
Flare
CHP unit
Digester #1
Digester #2
Biogas
Biogas
Biogas cleaning

15. Biogas production from Kipevu WWTP sludge
Nett production of electricity
= kWh/d
kWh/a × 20 KSh/kWh = KSh/d (47%)
Overall investment
€ (~ 4,8 years of payback)
37% less sludge to dispose!

16. Kipevu WWTP influent screens & grit removal settling tanks
sludge
thickeners
sludge drying beds
sludge
aeration tanks
settling
tanks
effluent

17. Reuse of treated water from WWTP
Can be treated further with advanced methods and reused:
Urban reuse:
Irrigation of public parks, landscapes and golf courses
Vehicle washing and decorative water features
Connecting to fire hydrants for fire protection
Industrial reuse:
Cooling water
Boiler make-up water
Industrial process water
Agricultural reuse
Can even be purified to potable water standards!

18. 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!

19. Reuse of treated water from Kipevu WWTP
After treatment the water is discharged into the sea
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

20. Kipevu WWTP

21. Reuse of treated water from Kipevu WWTP
Potential treatment required for cooling water standard
Corrosion concerns (filtration)
Removal of dissolved solids
Biological concerns (disinfection)
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

22. 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

23. Thank you for your attention!