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Feasibility Study of Decentralized Blackwater Treatment: Culmination of the Methanogenesis Chronicles. Kris Bruun Email: Kris.Bruun@Colostate.edu Thesis Defense March 31 st , 2009 Colorado State University Civil and Environmental Engineering Department. Research Intent.
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Feasibility Study of Decentralized Blackwater Treatment: Culmination of the Methanogenesis Chronicles Kris Bruun Email: Kris.Bruun@Colostate.edu Thesis Defense March 31st, 2009 Colorado State University Civil and Environmental Engineering Department
Research Intent • Determine whether implementation of a decentralized blackwater treatment system in conjunction with individual home graywater recycling systems is economically feasible as compared to current municipally operated centralized wastewater treatment layout.
Decentralized Wastewater Treatment (discuss w/ Neal) • Define • Differentiate between BW and Graywater • Benefits of decentralized treatment
Anaerobic Digestion • Process in which volatile organic material is broken down by bacteria in an oxygen-free environment to yield off gases, primarily consisting of Methane and Carbon Dioxide. • Three Stages: • Hydrolysis and Fermentation • Liquefaction of cellulose, protein, and lipid compounds • Acid Stage • Organic acids are converted by acetogens to acetic acid • Methanogensis • Methane-generating micro-organisms generate CH4 (60-80%) and CO2
Digestion & Methane Production • Optimization Techniques: • Temperature • Thermophilic (130-150oF) vs Mesophilic (93-98oF) • Higher Temps = Busier Bugs • pH • Optimum range~ 6.8-7.2 • Solids Retention Time • Longer retention = more extraction from the reaction
Digester Operation • Blackwater (BW) Characteristics: • COD = 4,000 mg/l • VSS = 3,000 mg/l • TSS = 3,000 mg/l • Complete Mix Digester Operation: • Temperature = 95 oF (35 oC) • SRT = HRT = 20 days • OLR = 3 kg VSS/m3-d
Estimating Flow Rates • G-WATER Model • Water usage is based on a Fort Collins Utilities study conducted in January 2001 • 10% consumed • BW = (Toilets + Dish Washing)*90% = 61 gal/house/day • Indoor Water Usage (model inputs):
Scenarios Overview • Energy Generation • On-site reciprocating engine/micro-turbine • Thermal energy recovery (heat exchanger) • Natural Gas Supplementation • Supply biogas to individual homes • Hot water heater operation • Digester Heating • Reduce natural gas consumption • Maintain optimal digester temperature
Evaluated Scenario #1 • Electricity Generation • On-site generator, voltage regulators, transfer switch, biogas storage, and gas purification
Evaluated Scenario #2 • Natural Gas Supplementation • Biogas storage and gas purification
Evaluated Scenario #3 • Strictly Digester Heating • Gas purification
Evaluated Scenario #4 • Aerobic Treatment • Aeration equipment and sludge dewatering
Equivalent Monthly Costs • Assumptions: • Loan interest rate of 7% • System Design Life of 20 years • Household sewer connection fee of $1,500
Centralized WWTP Rate Schedule • Treated Volume = 400 gal/house/day = 12,200 gal/house/month
Centralized WWTP Cost Comparison • Total Monthly Fee = $41.29 (per house) • Equivalent Number of Houses for Decentralized Treatment Layouts: • Energy Production~ 493 houses • Natural Gas Supplementation~ 426 • Digester Heating~ 396
Future Work • Future development vs current infrastructure • Lifecycle costs • Environmental impacts • Reduced greenhouse gas emissions • Etc. • Water reuse
Acknowledgements and Questions • Sybil Sharvelle Assistant Professor, Research Advisor Civil and Environmental Engineering Department, CSU • Larry Roesner Professor Civil and Environmental Engineering Department, CSU • Scott Glick Professor Department of Construction Management, CSU • Dan Zimmerle Power Systems R&D Manager, Professor of Mechanical Engineering Engines and Energy Conversion Laboratory, CSU