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 Household sewage Industrial sewage

Nature of contaminants: physical (TSS) chemical (COD) biological (BOD)

Objective is to produce an environmentally-safe effluent

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 = -10% - COD = - 5% - BOD = - 5%

Primary(physical, chem.)

• Sedimentation

• Efficiency: - TSS = -50% - COD = -20% - BOD = -20%

Secondary(biological)

• Aeration• Sedimentation

• Efficiency: - TSS = -95% - COD = -90% - BOD = -95%

Tertiary(advanced)

• Nutrient removal• Filtration• Adsorption• Disinfection

• Efficiency: - TSS > -99% - COD > -99% - BOD > -99%

Wastewater treatment in Mombasa

Wastewater treatment in Mombasa

Kipevu WWTP

Kizingo WWTP

Kipevu WWTP

influentKipevu WWTP

effluent

aeration tanks

sludge thickeners

screens & grit

removal

sludg

e dr

ying

bed

s

sludge

settlingtanks

Plant capacity: 196.000 P.E. 17.100 m3/d 9.580 kg/d BOD

Electricity consumption

Overall cost 5.606.400 kWh/a × 20 KSh/kWh = 112.128.000 KSh/a

Kipevu WWTP

Equipment No. of units kW per unit kW total h/d daily (kWh) annual (kWh) Aerators 16 45 720 20 14.400 5.256.000 Settlers 4 1,5 6 24 144 52.560 Return sludge pumps 4 5 15 24 360 131.400 Excess sludge pumps 2 5 5 12 60 21.900 Sludge thickeners 2 2,5 5 24 120 43.800 Screw pumps 2 15 15 4 60 21.900 Washout pump 1 4 4 24 96 35.040 General 1 10 10 12 120 43.800 Total 780 15.348 5.606.400

influentKipevu WWTP

effluent

aeration tanks

sludge thickeners

screens & grit

removal

sludg

e dr

ying

bed

s

sludge

settlingtanks

Digester #1 Digester #2Biogas cleaning

Biogas storage

Flare CHP unit

Sludge

Thickened sludge

Biogas Biogas

Biogas production from sludge

Nett production of electricity 7.635 - 1.455 = 6.180 kWh/d 2.255.700 kWh/a × 20 KSh/kWh = 45.114.000 KSh/d (40%)

Overall investment 1.826.000 € (~ 5,3 years of payback)

41% less sludge to dispose!

Biogas production from Kipevu WWTP sludge

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 storage

Flare CHP unit

Food waste

Digester #1 Digester #2Biogas cleaning

Sludge

Substrate

Biogas Biogas

Biogas production from sludge

Nett production of electricity 8.670 - 1.510 = 7.160 kWh/d 2.613.400 kWh/a × 20 KSh/kWh = 52.268.000 KSh/d (47%)

Overall investment 1.923.000 € (~ 4,8 years of payback)

37% less sludge to dispose!

Biogas production from Kipevu WWTP sludge

influentKipevu WWTP

effluent

aeration tanks

sludge thickeners

screens & grit

removal

sludg

e dr

ying

bed

s

sludge

settlingtanks

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!

Reuse of treated water from WWTP

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!

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

Reuse of treated water from Kipevu WWTP

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

Reuse of treated water from Kipevu WWTP

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

Current conclusions

Thank you for your attention!

damjan.nemec@gmail.com