Wastewater Recycling and Biofuel Production with Algal Raceways

Transcription

1 Wastewater Recycling and Biofuel Production with Algal Raceways Tryg Lundquist, Ph.D., P.E. California Polytechnic State University San Luis Obispo, California MicroBio Engineering Inc. San Luis Obispo, California ABO-WEF Workshop October 23, 2016 Glendale

2 The US wastewater treatment industry deals with 33,000 million gallons per day of sewage (publicly-owned only). Each dot is a publicly-owed treatment works (POTW). 2

3 The wastewater treatment industry focuses on these problems: Pathogens, which might reach drinking water supplies Nutrients causing excess algae growth Organic matter causing low dissolved oxygen 3

4 Solving the problems affordably means recognizing the value of wastewater: Recycle water Recover nutrients Produce biofuels 4

5 Treatment is performed using three major technologies Technology Activated Sludge Number Total Energy of Flow Intensity Facilities MGD* MWh/MG 6,800 25, Biofilm Systems 2,500 6, Traditional Ponds 5,100 2, * MGD = million gallons per day (~10,000 persons) 5

6 Typical activated sludge treatment plant

7 Providing oxygen to bacteria is expensive and energy intensive. Activated Sludge Process per 10,000 population MWh per day $5 - $12 million capital cost and higher

8 Wastewater treatment costs: high & rising Machinery and complexity require more personnel, which is the highest cost factor. $1750 per MG O&M 45% personnel 10% power 2008 NACWA Financial Survey Summary 8

9 WWT facility replacement & rehab need is huge. 5-year need is $3-5 billion* Am. Society of Civil Engineers rates US infrastructure: * National Association of Clean Water Agencies, 2011

10 Green algae typically found in wastewater pond polycultures. Micractinium Scenedesmus Actinastrum Chlorella 10

11 Still-water ponds grow enough algae to oxygenate wastewater. Can be attractive and support wildlife. 11

12 W.J. Oswald studied still-water ponds & determined the role of algae and methanogens beginning He developed high rate pond raceways to accelerate pond treatment and grow algae. Simulates a river. William Oswald, Univ. of California, Berkeley An early raceway WW treatment plant by Oswald, 1960s Concord, California. Golueke and Oswald conceived of biofuels from wastewater algae in

13 Sun CO 2 After Oswald, 1953 Reclaimed CO 2 N Algae Water Waste Water P O 2 Algal-Bacterial Symbiosis CO 2 N P Biomass Organics Bacteria

14 Algae produce oxygen and assimilate nutrients. Also uptake CO H 106 CO 2 O + 16 NH 4+ + HPO 4 + light + algae C 106 H 181 O 45 N 16 P O H 2 O + 14 H g 3776 g g/mole oxygen / 2428 g/mole algae = 1.56 g oxygen per g algae 14

15 Add CO 2 to balance C:N:P ratio and achieve completed nutrient assimilation. CO 2 Enhanced 600 mg/l Algae <1 mg/l NH 4+ -N <0.3 mg/l PO P Control CO 2 Air Sparged 130 mg/l Algae 25 mg/l NH 4+ -N 3 mg/l PO 3-4 -P 15

16 Recycle Nutrients Energy Water RNEW Technology CO 2 addition for complete nutrient removal Low energy intensity vs. conventional treatment Biofuel via digestion or hydrothermal liquefaction Harvesting by bioflocculation Low cost for treatment; biofuel still pricey Biofuel options: Methane, biocrude,?alchohol 16

17 Existing full-scale raceway systems are retrofit candidates: add CO 2 for nutrient removal & biofuels. 7 1

18 The two 3.5-acre raceways treat the WW of 10,000people. Flow is driven by two 20-ft long paddle wheels that turnslowly. 18

19 CO 2 addition to integrate wastewater treatment & biofuels at San Luis Obispo, Calif.

20 Pilot Plant Process Diagram Algae Water Tube Settler Supernatant Effluent Grow 2-6 days Supernatant Algae Slurry To crops 1-4% VS Algae Digest 40 days Thicken hours 20

21 cbod removal is good all year (in San Luis Obispo). 21

22 In secondary treatment mode (2 day retention time), NH 3 removed in summer. High biomass. Total Ammonia Nitrogen Concentration

23 In nutrient removal mode (6-d HRT), TAN removal nearly complete 8 mo per year. Nitrification- denitrification polish needed in winter. Total Ammonia Nitrogen Concentration Aeration needed in winter.

24 Bioflocculation and settling are low cost harvesting. Chemical coagulants for backup only. Influent Pond Settler Typical Pond Cont rol Experimental 24

25 Bioflocculation and settling process is similar to activated sludge. Algae floc, 100x Algae floc, 1000x 25

26 At full-scale 1 st -generation facility, algae are coagulated, settled, and solar dried. ~100,000 gallons of 3% solids algae in decanted settling basin Solar dried algae Concrete drying pad

27 Algae wastewater treatment is low cost and energy efficient. But algae nutrient removal is seasonal. Save 50% total cost. Save 67% electricity (w/out biogas) $/yr-mgd treated Cost kgco 2 /ML treated GHG $1,000,000 $900,000 $800,000 $700,000 $600,000 $500,000 $400,000 $300,000 $200,000 $100,000 $0 Sludge Electrical cost Maintanance Labor Capital Charge Electricity produced Sludge hauling Electricity consumption Electricity production Net Emissions -$100,000 A2/O Nutrient Activated Removal Sludge Secondary Algae Seasonal N Removal -200 A2/O Nutrient Removal Activated Sludge Secondary Algae Seasonal N Removal 27

28 Algae wastewater treatment plants could produce liquid algae biofuels. Or Blowdown 28

29 Pressure cooking (hydrothermal liquefaction) converts algae to biocrude oil. Pacific Northwest National Lab & Cal Poly Algae In Solids Oil & Water Out 29

30 Initial hydrothermal liquefaction (HTL) results 2 nd try: 0.35 g oil /g algae and 55% carbon into oil. 9% char+gas 36% water 55% oil Filtered solids, mostly minerals, including P Biocrude from WW algae Courtesy of Doug Elliott, PNNL 30

31 400-ha algae wastewater treatment and biofuel facility TEA (Lundquist et al., 2010) 31

32 Wastewater treatment credits (revenue) offsets most oil production costs, but the wastewater resource is limited nationally. Emphasis Break-even without WWT credit Break-even with WWT credit Treatment (100 ha) $417 /bbl $28 /bbl Oil (100 ha) $405 /bbl $332 /bbl Oil (400 ha) $300 /bbl $240 /bbl Cases 1. Wastewater Treatment Emphasis 2. Oil Production Emphasis <$200/bbl hoped for with great R&D success for 32 the non-treatment cases

33 Lifecycle Assessment

34 In US, 5 billion gallons per year (BGY) of algae biofuel is feasible with wastewater use, but 21 BGY may outstrip supply of municipal and animal wastewaters. [Preliminary, 2014 Venteris et al.] 21 BGY is US aviation kerosene use. 5 BGY in 2900 farms 21 BGY in 14,000 farms 2014 Venteris, Skaggs, Wigmosta, Coleman 37

35 Algae + wastewater + biofuel: Why do it? WW-supported biofuel is small compared to need but 5-20 billion gallons biofuel potential is substantial and we need to make use of every feedstock. WWT is needed regardless. WWT is expensive, but algae cut the cost. Algae WWT saves electricity. Algae WWT captures nutrients for reuse. Treat WW, get your feedstock for free. High fuel:co-product ratio with reclaimed water. Build algae production expertise and capacity.

36 Acknowledgments US DOE & Calif. Energy Commission grants to Cal Poly in partnership with MicroBio Engineering,Inc. Other Partners: Arizona State University ATP 3 Project Pacific Northwest NationalLab (M. Huesemann, D. Elliott) Sandia National Laboratory(Lane) LiveFuels and Phitech Ruth Spierling, Matt Hutton, Ian Woertz,John Benemann, Braden Crowe, Shelley Blackwell, and many more. Thank you! 39

37 Thank you for your attention 40