Closing the Gap Reaching for Energy Independence in Water Reclamation

Transcription

1 Closing the Gap Reaching for Independence in Water Reclamation Graham Juby, P.E. July 27, 2012

2 Power use in POTWs is growing steadily... more than 25 billion kwh in 2015* * Electrical Power Research Institute (2002) 2

3 Wastewater contains energy and many plants take advantage of this 3

4 For a typical POTW, the recoverable energy is about 30% of the plant s needs 140% 120% 100% 80% 60% Gap 40% 20% 0% POTW Consumption Recovered from Wastewater 4

5 New regulatory requirements typically increase the energy gap 140% 120% 100% 80% 60% 40% 20% New Requirements Gap 0% POTW Consumption Recovered from Wastewater 5

6 Switching to low-energy treatment processes reduces the energy gap 140% 120% 100% 80% 60% More Efficient Processes 40% 20% 0% POTW Consumption Recovered from Wastewater 6

7 Advanced digestion technologies increase energy extraction from sludge 140% 120% 100% 80% 60% 40% 20% 0% POTW Consumption Recovered from Wastewater Improved Conversion Efficiency 7

8 Importing energy sources such as FOG reduces the energy gap 140% 120% 100% 80% 60% 40% Import eg. FOG 20% 0% POTW Consumption Recovered from Wastewater 8

9 140% 120% 100% 80% 60% 40% 20% New Requirements Gap 0% POTW Consumption Recovered from Wastewater 9

10 Many agencies are considering as a way to augment the water supply Los Angeles 10

11 A higher level of treatment for reuse increases the plant s energy demand Wastewater From Headworks and Grit Removal High Use High Use 11

12 140% 120% 100% 80% 60% More Efficient Processes 40% 20% 0% POTW Consumption Recovered from Wastewater 12

13 An alternative treatment approach* for reuse reduces the energy footprint Eliminates the energy-intensive aerobic biological process Replaces it with microfiltration, reverse osmosis, and anaerobic digestion Wastewater From Headworks and Grit Removal High Use No Aeration Basins * Integrated Membrane Anaerobic Stabilization (IMANS ) 13

14 This alternative treatment train has been validated at pilot scale at Orange County 18-month Pilot Study MF and RO met performance goals 66% methane from UASB 14

15 OCSD pilot study was followed by demonstration testing at larger scale 0.3 mgd submerged MF process operated for 2 years 15

16 A comparison of energy consumption was made for a 5-mgd facility Process Consumption (kwh/mgd) Headworks/Grit 230 Odor Control 250 Primary 10 Activated Sludge + RAS/WAS 1,250 Anaerobic Digestion 390 Belt Press Dewatering 40 Disinfection (chlorination) 4 Plant Buildings 80 Total 2,250 All numbers were developed for a 5-mgd facility and are reported as unit values per MGD 16

17 kwh/mgd The increase in energy use to treat to reuse quality depends on the process used 5,000 4,000 3,000 2,000 1,000 0 Conventional POTW Conventional Alternative (MF/RO/UV) (IMANS ) 17

18 Power generation potential is greater for the alternative approach Conventional Alternative Electrical Power Required (kwh/mgd) 4,160 3,090 Biogas Generation (cf/day/mgd) 18,000 24,000 Conversion Efficiency (Gas engines) 35% 35% Electrical Power Production (kwh/mgd) 1,020 1,360 Electrical Power Demand Satisfied (%) 24% 44% 18

19 Power generation potential is greater for the alternative approach Conventional Alternative Electrical Power Required (kwh/mgd) 4,160 3,090 Biogas Generation (cf/day/mgd) 18,000 24,000 Conversion Efficiency (Fuel Cells) 47% 47% Electrical Power Production (kwh/mgd) 1,370 1,830 Electrical Power Demand Satisfied (%) 33% 59% 19

20 kwh/mgd The alternative approach satisfies a greater percentage of the power demand 5,000 4,000 3,000 2,000 1,000 59% 33% 44% 24% Gap Additional Power using Fuel Cells Power Generated with Gas Engines 0 Conventional Alternative 20

21 Power costs for the alternative approach are significantly lower Conventional Alternative Electrical Power Required (kwh/mgd) 4,160 3,090 Conversion Efficiency (Gas engines) 35% 35% Electrical Power Production (kwh/mgd) 1,020 1,360 Additional Purchased Power (kwh/mgd) 3,140 1,730 Annual Power Cost/MGD $0.10/kWh) $115,000 $63,000 Annual Cost Saving/MGD $52,000 Annual Cost Saving 45% 21

22 Power costs for the alternative approach are significantly lower Conventional Alternative Electrical Power Required (kwh/mgd) 4,160 3,090 Conversion Efficiency (Fuel Cells) 47% 47% Electrical Power Production (kwh/mgd) 1,370 1,830 Additional Purchased Power (kwh/mgd) 2,790 1,260 Annual Power Cost/MGD $0.10/kWh) $102,000 $46,000 Annual Cost Saving/MGD $56,000 Annual Cost Saving 55% 22

23 Another benefit of the alternative approach is less biosolids production $63,700/MGD Biosolids Production (wet tons/mgd) 4 2 $31,800/MGD Based on $40/ton Conventional Alternative 23

24 Annual cost savings for the alternative approach for power and solids is significant Annual Costs for Power and Biosolids Disposal ($000/MGD) $200 $100 $166,000 $102,000 $78,000 Total Savings > $88,000/MGD $64,000 Conventional Alternative $46,000 $32,000 24

25 Final Thoughts Eliminating aerobic processes and focusing on anaerobic processes closes the energy gap Reduces plant power needs Produces 35% more biogas Generates as much as 60% of the power needs Produce 50% less biosolids Produces a high quality effluent for reuse Also allows for nutrient recovery (both N and P) 25

26 Closing the Gap Reaching for Independence in Water Reclamation Graham Juby, P.E. July 27, 2012