A local Southern California water agency currently uses 42 million gallons per d
ID: 1732590 • Letter: A
Question
A local Southern California water agency currently uses 42 million gallons per day (MGD) of imported water (State Project Water) to recharge a groundwater basin via surface spreading. The energy consumption associated with this water supply includes (1) pumping, to import the water from Northern California; (2) treatment, including coagulation, flocculation, sedimentation, filtration, and disinfection; (3) pumping, to transport the water from the treatment plant to the recharge site (Table 1). Due to the rising costs of imported water as well as periodic restrictions on delivery because of cyclical drought conditions, the agency is considering replacing 50% of the imported water supply with locally produced and highly treated reclaimed water. The reclaimed water would be tertiary treated wastewater that has undergone additional advanced treatment including microfiltration (MF), reverse osmosis (RO), and advanced oxidation (AO). The energy consumption associated with this water supply is also shown in Table 1.
TABLE 1: SUMMARY OF ENERGY CONSUMPTION FOR WATER SUPPLY OPTIONS
Option 1
Energy (kWh/AF)
Option 2
Energy (kWh/AF)
Imported Water Pumping
3,236
Tertiary Treatment
450
Surface Water Treatment
21
Advanced Treatment
MF/RO/AOP
1,300
Pumping to Recharge Site
221
Pumping to Recharge Site
168
TOTAL
3,478
TOTAL
1,918
Find:
Compare the two water supply options with respect to their energy costs and related carbon footprints. Assume $0.15/kWh for power costs. Both the water treatment facility and the advanced water reclamation facility are within the Southern California Edison service area.
Option 1
Energy (kWh/AF)
Option 2
Energy (kWh/AF)
Imported Water Pumping
3,236
Tertiary Treatment
450
Surface Water Treatment
21
Advanced Treatment
MF/RO/AOP
1,300
Pumping to Recharge Site
221
Pumping to Recharge Site
168
TOTAL
3,478
TOTAL
1,918
Explanation / Answer
Conversion Units : 1 Acre-Foot = 325851 Gallons = 0.326 Gallons
Water Supply Option 1 (Current ) : 42 million gallons per day (MGD) of Imported water
Energy Consumption :
1. Imported Water Pumping : Energy Consumption for 42 Million Gallons/ Day : 3236 * ((42 * 10^6)/325851) = 3236*128.8933 = 417098.6126 kWh
2. Surface Water Treatment : 21 * ((42 * 10^6)/325851) = 21*128.8933 = 2706.7593 kWh
3. Pumping to Recharge Site : 221 * ((42 * 10^6)/325851) = 221 * 128.8933 = 28485.4120 kWh
Total Energy Consumption : 417098.6126 + 2706.7593 + 28485.4120 = 448290.7839 kWh
Power Costs : 448290.7839 * 0.15 = 67243.617585 $ / Day ____________(I)
Water Supply Option 2 ( Propsed ) : 21 million gallons per day (MGD) of Imported water + 21 million gallons per day (MGD) of locally treated water.
1. Imported Water Pumping : Energy Consumption for 21 Million Gallons/ Day : 3236 * ((21 * 10^6)/325851) = 3236* 64.4466 = 208549.3063 kWh
2. Surface Water Treatment :Energy Consumption for 21 Million Gallons/ Day : 21* 64.4466 = 1353.3790 kWh
3. Pumping to Recharge Site : Energy Consumption for 21 Million Gallons/ Day = 221 * 64.4466 = 14242.7060 kWh
Total Energy Consumption From Old System of Usage : 208549.3063+1353.3790+14242.7060 = 224145.3913 kWh............(A)
Energy Consumption from Propsed System :
1. Tertiary Treatment : Energy Consumption for 21 Million Gallons/ Day = 450 * 64.4466 = 29000.9851 kWh
2. Advanced Treatment MF/RO/AOP : Energy Consumption for 21 Million Gallons/ Day = 1300*64.4466 = 83780.6236 kWh
3. Pumping to Recharge Site : Energy Consumption for 21 Million Gallons/ Day = 168*64.4466 = 10827.0344 kWh
Total Energy Consumption From New System of Usage:29000.9851+83780.6236+10827.0344 =123608.6431 kWh..............(B)
Total Consumption for Water Supply Propsed Plan = (A) + (B) = 224145.3913 + 123608.6431 = 347754.0344 kWh
Power Costs : 347754.0344 * 0.15 = 52163.10516 $. / Day _____________(II)
Therfore the Saving in Implementing the propsed Plan in Monetary Terms Will Be = 67243.617585 - 52163.10516 = 15080.512425 $ of Daily Savings
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