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 m 3 /d Dry volatile solids = 0.16 kg/m 3 Biodegradable COD removed = 0.17 kg/m 3 HRT (hydraulic retention time) = 15 days Efficiency of waste utilization, E = overall VSr = Mass fraction PS x VSr PS + Mass fraction TWAS x VSr TWAS = (0.65 x 0.68) + (0.35 x 0.45) = 0.60 = E

12. Design Parameters Y = 0.08kg VSS/kg bCOD utilized K d = 0.03d -1 Digester gas is 65% methane Sludge contains 94% moisture, 6% solids = 0.06 = P s Sludge has a specific gravity, S sl = 1.02

13. Calculations Sludge volume = [M s ] ÷ [(S sl) (ρ w )(P s )] = [(0.16 kg/m 3 )(7440 m 3 /d)] ÷ [1.02(10 3 kg/m 3 )(0.06)] = 19.45 m 3 /d

14. Calculations bCOD loading = (0.17 kg/m 3 )(7440 m 3 /d) = 1265 kg/d HRT = V/Q => V = Q * HRT = (19.45 m 3 /d)(15 d) V 1 = 292 m 3

15. Calculations bCOD in inffluent, S o S o = 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, P x P x = [Y(S o – S)] ÷ [1 + (k d )(HRT)] = [0.08kg VSS/kg bCOD(759)] ÷ [1 + (0.03d -1 )(15 d)] P x(1) = 41.88 kg/d

17. Calculations Volume of methane produced per day @ 35°C, V CH 4 V CH 4 = (0.40)[(S o – S) – 1.42P x ] = (0.40m 3 /kg)[759 kg/d – 1.42*(41.88 kg/d)] V CH 4 = 280 m 3 /d Estimate total gas production = 280/0.65 = 430 m 3 /d

18. Design Parameters (Design 2) Q = 2Mgal/d = 7440 m 3 /d Dry volatile solids = 0.16 kg/m 3 Biodegradable COD removed = 0.17 kg/m 3 HRT (hydraulic retention time) = 15 days Efficiency of waste utilization, E = overall VSr = Mass fraction PS x VSr PS + Mass fraction TWAS x VSr TWAS = (0.65 x 0.68) + (0.35 x 0.97) = 0.78 = E

19. Design Parameters Y = 0.08kg VSS/kg bCOD utilized K d = 0.03d -1 Digester gas is 65% methane Sludge contains 94% moisture, 6% solids = 0.06 = P s Sludge has a specific gravity, S sl = 1.02

20. Calculations Sludge volume = [M s ] ÷ [(S sl) (ρ w )(P s )] = [(0.16 kg/m 3 )(7440 m 3 /d)] ÷ [1.02(10 3 kg/m 3 )(0.06)] = 19.45 m 3 /d

21. Calculations bCOD loading = (0.17 kg/m 3 )(7440 m 3 /d) = 1265 kg/d HRT = V/Q => V = Q * HRT = (19.45 m 3 /d)(13 d) V 2 = 253 m 3

22. Calculations bCOD in inffluent, S o S o = 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, P x P x = [Y(S o – S)] ÷ [1 + (k d )(HRT)] = [0.08kg VSS/kg bCOD(987)] ÷ [1 + (0.03d -1 )(13 d)] P x(2) = 56.79 kg/d

24. Calculations Volume of methane produced per day @ 35°C, V CH 4 V CH 4 = (0.40)[(S o – S) – 1.42P x ] = (0.40m 3 /kg)[987 kg/d – 1.42*(56.79 kg/d)] V CH 4 = 362 m 3 /d Estimate total gas production = 362/0.65 = 557 m 3 /d

25. Comparison of two designs Without using MicroSludge (Design 1): – V (1) = 292 m 3 – P x(1) = 41.88 kg/d – V CH 4 = 280 m 3 /d With using MicroSludge (Design 2): – V (2) = 253 m 3 – P x(2) = 56.79 kg/d – V CH 4 = 362 m 3 /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???