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Reducing the Amount of Waste Activated Sludge

Reducing the Amount of Waste Activated Sludge. Sara Schmidt CE 479 December 6, 2006. Overview of Presentation:. Background information Concerns regarding waste activated sludge What is MicroSludge® ? Design comparisons of two digester systems. Background Information.

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Reducing the Amount of Waste Activated Sludge

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  1. Reducing the Amount of Waste Activated Sludge Sara Schmidt CE 479 December 6, 2006

  2. Overview of Presentation: • Background information • Concerns regarding waste activated sludge • What is MicroSludge®? • Design comparisons of two digester systems

  3. Background Information • Primary sludge – produced from the primary settling of untreated wastewater • Waste activated sludge (WAS) – excess sludge produced from activated sludge process • CMAD – Conventional Mesophilic Anaerobic Digester • Mesophilic – operating temperature of 25 - 40°C

  4. Background Information • Thermophilic – operating temperature of 50-60°C • MicroSludge –Sludge pre-treatment that greatly enhances the performance of digesters

  5. Concerns Regarding WAS: • Risks to public health from sludge residuals • High capital and operating costs • Contribute to the public’s growing concerns regarding odors • Negative environmental impacts

  6. How much waste do people really produce? • A typical secondary wastewater treatment plant that serves 1 million people generates 25 football fields (about three feet deep) of biosolids each year.

  7. What is MicroSludge®? • MicroSludge works by destroying microbial cell membranes and enabling anaerobic digesters to achieve significantly greater conversion of WAS to biogas. www.microsludge.com

  8. MicroSludge and Microbes • The image to the left shows intact microbes (magnified 20,000 times) • The image to the right shows the same microbes after the MicroSludge process

  9. Benefits of MicroSludge • Major reduction in WAS residual biosolids (VSr) • Lowers retention time => additional digester capacity • Increased amount of biogas production • Reduces operating, disposal, & mixing costs

  10. MicroSludge Location in a Wastewater Treatment Plant

  11. Design Parameters (Design 1) • Q = 2Mgal/d = 7440 m3/d • Dry volatile solids = 0.16 kg/m3 • Biodegradable COD removed = 0.17 kg/m3 • HRT (hydraulic retention time) = 15 days • Efficiency of waste utilization, E = overall VSr = Mass fractionPS x VSrPS + Mass fractionTWAS x VSrTWAS = (0.65 x 0.68) + (0.35 x 0.45) = 0.60 = E

  12. Design Parameters • Y = 0.08kg VSS/kg bCOD utilized • Kd = 0.03d-1 • Digester gas is 65% methane • Sludge contains 94% moisture, 6% solids = 0.06 = Ps • Sludge has a specific gravity, Ssl = 1.02

  13. Calculations • Sludge volume = [Ms] ÷ [(Ssl)(ρw)(Ps)] = [(0.16 kg/m3)(7440 m3/d)] ÷ [1.02(103 kg/m3)(0.06)] = 19.45 m3/d

  14. Calculations • bCOD loading = (0.17 kg/m3)(7440 m3/d) = 1265 kg/d • HRT = V/Q => V = Q * HRT = (19.45 m3/d)(15 d) V1 = 292 m3

  15. Calculations • bCOD in inffluent, So So = 1265 kg/d • bCOD in effluent, S S = 1265(1 - E) = 1265(1 – 0.60) = 506 kg/d

  16. Calculations • Quantity of volatile solids produced per day, Px Px= [Y(So – S)] ÷ [1 + (kd)(HRT)] = [0.08kg VSS/kg bCOD(759)] ÷ [1 + (0.03d-1)(15 d)] Px(1) = 41.88 kg/d

  17. Calculations • Volume of methane produced per day @ 35°C, VCH4 VCH4 = (0.40)[(So – S) – 1.42Px] = (0.40m3/kg)[759 kg/d – 1.42*(41.88 kg/d)] VCH4 = 280 m3/d • Estimate total gas production = 280/0.65 = 430 m3/d

  18. Design Parameters (Design 2) • Q = 2Mgal/d = 7440 m3/d • Dry volatile solids = 0.16 kg/m3 • Biodegradable COD removed = 0.17 kg/m3 • HRT (hydraulic retention time) = 15 days • Efficiency of waste utilization, E = overall VSr = Mass fractionPS x VSrPS + Mass fractionTWAS x VSrTWAS = (0.65 x 0.68) + (0.35 x 0.97) = 0.78 = E

  19. Design Parameters • Y = 0.08kg VSS/kg bCOD utilized • Kd = 0.03d-1 • Digester gas is 65% methane • Sludge contains 94% moisture, 6% solids = 0.06 = Ps • Sludge has a specific gravity, Ssl = 1.02

  20. Calculations • Sludge volume = [Ms] ÷ [(Ssl)(ρw)(Ps)] = [(0.16 kg/m3)(7440 m3/d)] ÷ [1.02(103 kg/m3)(0.06)] = 19.45 m3/d

  21. Calculations • bCOD loading = (0.17 kg/m3)(7440 m3/d) = 1265 kg/d • HRT = V/Q => V = Q * HRT = (19.45 m3/d)(13 d) V2 = 253 m3

  22. Calculations • bCOD in inffluent, So So = 1265 kg/d • bCOD in effluent, S S = 1265(1 - E) = 1265(1 – 0.78) = 278 kg/d

  23. Calculations • Quantity of volatile solids produced per day, Px Px= [Y(So – S)] ÷ [1 + (kd)(HRT)] = [0.08kg VSS/kg bCOD(987)] ÷ [1 + (0.03d-1)(13 d)] Px(2) = 56.79 kg/d

  24. Calculations • Volume of methane produced per day @ 35°C, VCH4 VCH4 = (0.40)[(So – S) – 1.42Px] = (0.40m3/kg)[987 kg/d – 1.42*(56.79 kg/d)] VCH4 = 362 m3/d • Estimate total gas production = 362/0.65 = 557 m3/d

  25. Comparison of two designs • Without using MicroSludge (Design 1): • V(1) = 292 m3 • Px(1) = 41.88 kg/d • VCH4 = 280 m3/d • With using MicroSludge (Design 2): • V(2) = 253 m3 • Px(2) = 56.79 kg/d • VCH4 = 362 m3/d

  26. Cost Comparison • The major difference between these two designs are the volume needed for the digesters, volatile solids production, and methane gas production . • These differences are a major cost reductions for a wastewater treatment plant.

  27. Questions???

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