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Effective Decentralized Sewage Sanitation with Low CO 2 Footprint

Effective Decentralized Sewage Sanitation with Low CO 2 Footprint. Aaron A. Forbis-Stokes , Joan Colón, Lilya S. Ouksel, Marc A. Deshusses Department of Civil and Environmental Engineering Duke University, Durham, North Carolina, USA. Anaerobic Digestion Pasteurization Latrine.

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Effective Decentralized Sewage Sanitation with Low CO 2 Footprint

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  1. Effective Decentralized Sewage Sanitation with Low CO2 Footprint Aaron A. Forbis-Stokes, Joan Colón, Lilya S. Ouksel, Marc A. Deshusses Department of Civil and Environmental Engineering Duke University, Durham, North Carolina, USA

  2. Anaerobic Digestion Pasteurization Latrine Anaerobic digestion of concentrated waste Field efficacy Pit latrine/ Human wastes (Extra biogas/ cooking/lighting) Biogas Digester Heat exchanger 30°C 45°C Additional organic wastes (optional) Biogas powered heater 75°C 60°C Efficient and simple construction and operation Self-sustaining pasteurization system with sufficient pathogen inactivation Treated and sanitized effluent

  3. Proof of Concept

  4. Anaerobic Digester Biogas • 10 person system • Lab scaled 1:33 • Feed stock: • 120 g Feces/d & 300 mL Urine/d • 17 L volume, 40 day HRT • OLR = 1.8 g COD/(Lreactd) 0.13 g N/(Lreact d) • T = 30 °C • No Mixing Overflow Feed

  5. Anaerobic Digester

  6. Effect of Acclimation on Biogas ProductionBiogas potential test with different N concentrations Non-acclimated inoculum Acclimated inoculum 5 g TAN/L 5 g TAN/L 8 g TAN/L 8 g TAN/L

  7. Start-up and Biogas Production No dilution Start-up High N 1:1 u:w S4 S2 S1 S3 10 person household =400 L biogas/day Average biogas yield at steady state conditions of 0.37 NLbiogas/gCOD Methane content 62 ± 3 %

  8. COD Removal Efficiency

  9. VFA Accumulation

  10. Total Ammonia Nitrogen and Total Free Ammonia S2 S4 S1 S3

  11. Heat Sterilization System Effluent coming from the digester 30°C -Designed to treat intermittent loads (1 load of 0.6 L each hour, 14 L/d) -Optimized for heat efficiency -No moving parts, simple materials

  12. Thermal Efficiency of the Heater Methane calorific value: 33.9 KJ/L Temperature range: 55-75 °C Thermal efficiency: 55-70 %

  13. Heat Sterilization Tests Approach: -Test with E. coli (intermittent flow, 14 L/d in 0.6 L loads once per hour) -Calibrate and validate flow, heat and heat deactivation model -Simulate performance for helminth and virus* *kill rate constants from Popat et al. Wat. Res. 2010, 44, 5965-5972.

  14. Heat Sterilization Tests 230-280 Lbiogas/d for 65≤T≤75 °C Inlet Before heater After heater Effluent Cumulative

  15. Pilot Study

  16. Implementation • Sogomo Estate, Eldoret, Kenya • 1/8 acre, ~20 residents, municipal water tap, borehole well, shared pit latrines • Near University of Eldoret

  17. Community Entry • Questionnaires • Shallow wells often used for drinking water (boil) • Squat-style toilet, wipers • Pits used for solid waste disposal • System resources initially unappealing • Owner interest • Protective of current systems

  18. Toilet & Digester • Prefabricated plastic latrine labs • 2 sites with standard slabs • 1 site with urine diversion • SimGas Gesi2000 floating dome digester • <1L pour flush

  19. Heating system • Fabricated in local labor market • 16 gage galvanized steel and welded seams • Heating tank – Left • 7.7 L • Heat exchanger – Right • 9.4 L

  20. Complete System • Acclimated seed sludge and gradual loading • In use – plots with 17, 24, and 35 residents • Fully enclosed treatment system, 3x3 meter footprint • User advantages – Less odor & flies, well-lit, resources • Disadvantages – Height inconvenience, solid waste, pour flush

  21. System Cost †With a conservative estimate of 5 year lifespan and average of 25 users per system, system cost = $0.03/p/d *Gesi2000 Biodigester was donated by SimGas.

  22. Conclusions • Anaerobic digestion of undiluted human waste self-sustains effective pasteurization system • A yield ≈ 0.3-0.4 NLbiogas/g COD can be expected • 100% of E.coli inactivation was achieved at a working T ≥ 65 °C • 10 p system - produce 400 Lbiogas/d and require 230-280 Lbiogas/d to operate 65 ≤ T ≤ 75 °C • Systems were built in Eldoret, Kenya, using all local materials and are currently in operation • 3 systems, serving 15-35 people each • System outputs (nutrient-rich treated effluent & excess biogas) desirable to community members • System is simple with no moving parts, operates by gravity flow, and requires little maintenance & operation

  23. Future Work • Monitoring and evaluation of system in Eldoret, Kenya • Assess needs for design improvements • Cost assessment and scale-up • Resource evaluation of effluent for fertilization and excess biogas for multiple purposes (cooking, lighting, biogas generator) • Mass reproducible components and installation • Tertiary effluent filter for reuse purposes • Turbidity and odor removal • Different contexts and measures • Rural vsperi-urban vs urban; single family vs shared • Use, diarrheal disease, other?

  24. Thank you! Contact: aaron.forbis-stokes@duke.edu or marc.deshusses@duke.edu http://deshusses.pratt.duke.edu/ Special thanks to: Bill & Melinda Gates Foundation SimGas University of Eldoret WataalamuRepair & Mechanics

  25. Extra Slides

  26. Anaerobic Digestion 101 Source: Syed Hashsham, PhD, lecture notes, Michigan State University

  27. Faecal Sludge Simulant Properties Metals? Example: Simulant excreta: 7.2 g N p-1 d-1 Real excreta: 5.2 -8.2 g N p-1 d-1 (Uganda, Haiti, India, South Africa)

  28. Energy in Faecal Sludge… a Few Relevant Numbers 1 person: 400 gwet feces and 1 L urine per day • Heat 1 kg = 1 L water by 1 °C 4180 J • Vaporize 1 kg water 2,260,000 J • Burn 10 L = 6.4 g methane 358,000 J • Burn 10 g wood ~200,000 J • Burn 80 g dry feces (~400 g wet) ~1,600,00 J • Dry 400 g wet feces, burn solid ~880,000 J • Dry 400 g wet feces + 1 L urine, burn solid requires 1,400,000 J • Waste of 1 person digested anaerobically 860,000 J or about 10-15 Watts continuous (or 240-360 Wh per day)

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