1 Parallel Bench-Scale Digestion Studies Richard O. Mines, Jr. Laura W. Lackey Mercer University Environmental Engineering Mitchell Murchison Brett Northernor 2007 World Environmental & Water Resources Congress

2 Acknowledgements Thank the Macon Water Authority for providing us with the ozonators. This project was performed by Mitchell Murchison and Brett Northenor as part of their senior design project at Mercer University.

3 Presentation Outline Background Objectives of Study Materials & Methods Results Summary & Conclusions

4 Background Sludge or biosolids are generated as a by-product of wastewater treatment Sludge treatment and disposal costs represents 35-40% of the total cost of treating wastewater and they continue to increase Stringent effluent limits result in higher removals and higher sludge production rates

5 Where is sludge produced? WWTP Grit Removal Bar Racks and Screens Flow Meter Aeration Basin Secondary Clarifier Chlorine Contact Basin EffluentInfluent Waste Activated Sludge Return Activated Sludge

6 Aerobic Digestion Continuation of activated sludge process. Digesters operated in the endogenous phase. Microorganisms oxidize their own protoplasm into CO 2,H 2 O, and NH 3. Subsequently, ammonia is removed through nitrification.

7 Ozonation Destruction Mechanism Scheminski et al.: O 3 attacks and destroys the cell wall releasing intracellular components. Cesbron et al. : O 3 solubilizes and converts slowly biodegradable particulate organics into low molecular weight, readily biodegradable compounds.

8 Ozonation of Digested Sludge Scheminski et al. : 60% of the digested sludge solid organic components can be transformed into soluble substances at an O 3 dose of 0.5 g O 3 per g of organic dry matter. Dissolved organic carbon (DOC) increased to 2300 mg/L.

9 Ozonation of WAS Park et al. achieved: 70% mass reduction 85% volume reduction at an ozone dose of 0.5 g O 3 consumed per g of dried solids compared to the control.

10 Ozonation of RAS Yasui et al. reported elimination of excess sludge by ozonating 4Xtimes amount of waste sludge at kg O 3 /kg SS. SVIs of ozonated sludge were ml/g compared to for AS. Sakai et al. eliminated excess sludge production by ozonating RAS at a dose of 34 mg O 3 per gram of SS.

11 Objectives of Study 1. Evaluate the reduction of Total Solids and Volatile Solids in aerobic versus ozonated digesters. 2. Evaluate the kinetics of Total Solids/Volatile Solids reduction in aerobic versus ozonated digesters.

12 Objectives of Study 3. Estimate quantity of oxygen required to destroy Total Volatile Solids. 4. Determine quantity of ozone required to destroy Total Solids.

13 Materials and Methods: Both Phases COD was measured colorimetrically by HACH method Solids analyses were conducted in accordance with Standard Methods. Ozone transfer rate measured by sparging O 3 into potassium iodide solution. Ozone was measured by titration with 0.005N sodium thiosulfate (Standard Methods).

14 Materials and Methods: O 3 Collection in Off-Gas

15 Bench-Scale Aerated and Ozonated Digester

16 Materials and Methods: Phase I Two, 2-L batch digesters were operated in parallel for 30 days. Aerobic digester supplied with 2.7 Lpm or 810 mg O 2 /min: 1.84 g O 2 /mgTS. Ozonated digester supplied with air ladened with O a rate of 6.5 Lpm or 0.88 mg O 3 /min: 2.0 mg O 3 /mgTS.

17 Materials and Methods: Phase II Two, 2-L batch digesters were operated in parallel for 32 days. Aerobic digester supplied with 4.0 Lpm or 1200 mg O 2 /min: 3.25 g O 2 /mg TS. Ozonated digester supplied with air ladened with O a rate of 3.25 Lpm or 0.44 mg O 3 /min: 1.2 mg O 3 /mg TS.

18 Results: Aerobic Digestion Increased O 2 Loading 77% Oxygen Applied per Mass of TS TS Removal VS Removal 1.84 g O 2 /mg TS 23%42% 3.25 g O 2 /mg TS 35%40%

19 Results: Ozonation Increased O 3 Loading 67% Ozone Applied per Mass of TS TS Removal VS Removal 1.20 mg O 3 /mg TS 50%57% 2.00 mg O 3 /mg TS 56%74%

20 Solids Degradation Rate: Phase I

21 Solids Degradation Rate: Phase II

22 Solids Degradation Rates K D Air0.067 d d -1 Increased O 2 77% 1.3 K D Ozone0.082 d d -1 Increased Ozone 67% 1.5 K D

23 Oxygen Consumed: Aerobic Digestion

24 Oxygen Utilized per TVS Destroyed Digester Oxygen Utilized per TVS Destroyed Aerobic: Phase I Aerobic: Phase II Average1.89 EPA Manual1.74 – 2.07 lb oxygen per lb of cell mass oxidized.

25 Ozone Consumed:

26 mg Ozone Utilized per mg TS Destroyed: Increased O 3 67% PhaseOzone Applied Ozone Utilized per TS Destroyed II1.20 mg O 3 /mg TS 0.57 mg/mg I2.00 mg O 3 /mg TS 2.6 mg/mg

27 Total COD Removals Air30%40% Increased Applied O 2 77% Ozone58%57% Increased Applied Ozone 67%

28 Total COD Concentration: Phases I and II

29 Soluble COD Concentration: Phases I and II 4.2–9.5 mg sCOD/g TS destroyed aerated 120–146 mg sCOD/g TS destroyed ozonated

30 pH: Phases I and II

31 SOUR: Phases I and II

32 Operating Cost Comparison 30 mgd WWTP 20/20 mg/L effluent limits for BOD/TSS SRT = 10 days Y = 0.6 g TSS/g BOD k d =0.05 d % VS destruction $1.46 per lb ozone;$0.10 per kWH

33 Operating Cost Ozonation 13,010 ppd TSS VS $1.46 per lb ozone;$0.10 per kWH 38% VS destroyed resulting in 3362 ppd TS destroyed

34 Operating Cost Aerobic Digestion 38% VS destroyed resulting in 3362 ppd TS destroyed 2.0 lb O 2 /lb VS destroyed;$0.10 per kWH STOR = 2.5 lb O 2 /HP-hr; 112 HP aerator

35 Settling Characteristics Aerobic Ozonated After 30 minutes of settling following 30 day testing period

36 Summary Two, 2-L batch digesters operated in parallel for 30 and 32 days, respectively One, sparged with air and one with O 3. Higher TS, VS, and TCOD removals were achieved in the ozonated digesters. Soluble COD concentrations increased during digestion for both the aerobic and ozonated digesters.

37 Major Conclusions: 1 Ozone more effective at reducing TS and VS: 50-56% for TS and 57-74% for VS ozone 23-35% for TS and 40-42% for VS aerobic Ozone degraded solids faster than air: 0.067d -1 and 0.089d -1 for aerobic digesters d -1 and 0.12d -1 for ozonated digesters.

38 Major Conclusions: 2 Average oxygen required per mg of TVS destroyed was 1.89 for the aerobic digesters. Average ozone consumption: 0.57 and 2.6 mg O 3 consumed per mg of TS destroyed.

39 Major Conclusions: 3 SOUR values were below 1.5 mg of O 2 /g of TS at the beginning of study and remained below this value. Ozonated sludge settled better than did aerated sludge; however a cloudy supernatant produced.

40 Future Work Pilot-scale studies (8-10 L) Biodegradability of supernatant N & P characterization in supernatant Total & fecal coliform reduction studies Investigate the effect of pH on degradation rates

41 Questions?

42 Pathogen Reduction: Class A Six Alternatives Monitor: Fecal coliform < 1000 MPN per gm TS Salmonella sp. < 3 MPN per 4 gm TS 1: Thermally Treated Sludge. 2: High pH-High Temperature. 3: Test for Viruses and Helminth Ova. 4: Unknown Sludge Treatment Process. 5: Use PFRP Process. 6: Use PFRP Equivalent Process

43 Pathogen Reduction: Class B Three Alternatives 1: geometric mean fecal coliform density of 7 samples < 2 million CFU or MPN per gm of TS. 2: Use PSRP Process. Aerobic Digestion Air Drying Anaerobic Digestion Composting Lime Stabilization 3:Use PSRP Equivalent Process.

44 Vector Attraction Reduction: Eleven Options 1: 38% VS reduction by aerobic or anaerobic digestion. 3: additional VS destruction < 15% after 30 days further aerobic digestion. 4: SOUR for aerobically digested sludge  1.5 mg O 2 per hr per gm TS.