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.)

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

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

Kipevu WWTP Plant capacity: Electricity consumption Overall cost 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 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 5 15 360 131.400 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 5.606.400

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

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

Biogas production from Kipevu WWTP 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!

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 Substrate Food waste Biogas storage Flare CHP unit Digester #1 Digester #2 Biogas Biogas Biogas cleaning

Biogas production from Kipevu WWTP 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!

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

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!

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) 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

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