Taking the Waste out of WAS: Sludge Pretreatment for Beneficial Uses

Transcription

1 Taking the Waste out of WAS: Sludge Pretreatment for Beneficial Uses December 5, 2013 Matt Van Horne, P.E. 1 1

2 Agenda Why Sludge Pretreatment? What is OpenCel? Case Study #1: Philadelphia Water Department Case Study #2: Henrico County, VA Conclusions 2

3 Project Partners 3

4 Why Sludge Pretreatment? 4

5 Just Ask Wally 5

6 But That Isn t The Whole Story 6

7 Organic Carbon Has Numerous Uses 7

8 Motivation for Considering WAS Pretreatment Lower nitrogen limits longer sludge ages decreasing degradability of WAS Increasing solids disposal costs Increasing stabilization requirements (i.e. Class A Biosolids) Minimize solids production / enhance digestion delay costly expansion (i.e. aerobic or anaerobic digester volume) Increase digester gas production Supplemental carbon source 8

9 Goals of Sludge Pretreatment Floc disintegration Cell lysis Conversion of particulate organics Increase bioavailability Increase hydrolysis rate 9

10 Where Can Sludge Pretreatment Provide Benefits? 10

11 Digester Gas Production Is Directly Related to Volatile Solids Destruction Volatile Solids Reduction (VSR) 11 Volatile Solids Soluble Organics Gases

12 Volatile Solids Reduction (%) Volatile Solids Reduction is a Function of Digester Solids Residence Time 100% 90% Ref: WEF MOP-8 (1992), Figure 18.9, Volume II, page % 70% 60% 50% WAS Pretreatment 40% 30% 20% 10% 100% WAS 100% PS 0% Solids Retention Time (days)

13 Extent of Hydrolysis (%) Volatile Solids Reduction (%) WAS Pretreatment Mechanisms Increase rate and/or extent of degradation Low intensity processes increase degradation rate High intensity processes increase degradation rate and extent How to increase degradation rate? Increase rate limiting step (hydrolysis) Floc/particulate destruction S S hyd 0 hyd 1 e k hyd t 100% 100% k hyd 75% 50% 25% % 50% 25% 75% 60% 45% 30% 0% Solids Residence Time (days) % Solids Residence Time (days) 13

14 Sludge Pretreatment Impacts Increased ultimate degradability or rate of degradation of WAS Increased volatile solids reduction More digester gas produced Increased energy availability Increased dewaterability of sludge Reduced polymer consumption in dewatering step Reduced water mass to downstream processes Reduces energy inputs to thermal process to evaporate water from the sludge 14

15 Available Technologies Thermal Thermal Hydrolysis Mechanical / Physical Ultrasonication High Pressure / Homogenizer Maceration / Mechanical Shearing Electric Pulse Chemical Ozonation Hydrogen Peroxide Alkali Treatment 15

16 What Is OpenCel? 16

17 OpenCel System Images: OpenCel 17

18 OpenCel Theory Focused electrical pulse treatment Cyclic exposure to positive and negative charges weakens the cell wall Eventually the cyclic forces cause cell rupture and release of internal contents Grinder / Macerator Focused Electrical Pulse Floc Disintegration + Cell Lysis 18

19 OpenCel Impacts Images: OpenCel 19

20 Case Study #1: Philadelphia Water Department Southwest WPCP 20

21 Southwest WPCP 21

22 Southwest WPCP Current Operations Sludge processed from Southeast WPCP also Primary sludge thickened in-tank WAS thickened by DAF Blended in tanks prior to digestion Intermittent feed (~10 minutes) cycling through digesters at ~650 gpm 12 digesters Digested sludge sent to 3 rd party dewatering/drying facility 22

23 Pilot Testing Goals Determine impact of OpenCel on digester gas production Determine impacts of OpenCel on dewaterability and polymer consumption Perform economic assessment of full scale implementation of OpenCel 23

24 Pilot Testing Configuration 24

25 Pilot Testing Configuration 25

26 Pilot Testing Container 26

27 OpenCel Unit Inside Container 27

28 So Let s Get to the Performance Startup has been completed and data is beginning to be generated Some lessons learned: Sludge conductivity is critical Constant TWAS availability is critical Need tie-in upstream of feed pumps to provide safety shutdown if TWAS not available 28

29 Soluble COD Results Average TS to scod yield = 2.3% 29

30 Volatile Solids Reduction 30

31 Digester Gas Production Average OpenCel Digester Production =21% 31

32 The Future is Bright The pilot test is well configured to provide meaningful results: Good control v. experimental setup Extent of monitoring is excellent to provide proper data Good communication between parties Dedication by all involved to make this a success 32

33 Case Study #2: Henrico County, VA Water Reclamation Facility 33

34 Henrico County WRF 34

35 Carbon s Role in Nitrogen Removal Typical nitrification-denitrification process requires external (supplemental) carbon source to complete nitrogen transformation Oxygen Nitrate Carbon Oxygen Nitrite Ammonia Nitrogen Gas 35

36 Pilot Testing Approach GBT-thickened WAS pretreated using OpenCel Lysed sludge added to initial anoxic zone to replace/augment glycerin use Considerations: Dirty carbon source Additional ammonia loads Careful coordination during pilot to meet strict effluent TN limits 36

37 Experimental Configuration Test Basin Treated TWAS Indicates profile sampling point Indicates composite sampling point PE Glycerin TBC1 RAS TBC2 TB1 TB2 TB3 TB4 TB5 TB6 TB7 Glycerin storage Glycerin storage Control Basin Glycerin CBC1 CB1 CB2 CB3 CB4 CB5 CB6 Glycerin storage 37

38 Implications for Pilot Testing Assume yield is 0.09 mg sscod/mg TS OpenCel Flow (gpm) Percent of existing first anoxic COD demand that can be replaced by OpenCel 20 39% Assume yield is 0.01 mg sscod/mg TS OpenCel Flow (gpm) Percent of existing first anoxic COD demand that can be replaced by OpenCel 20 4% 38

39 Conclusions 39

40 Conclusions and Observations Pilot testing is always critical Unforeseen issues are standard with pilot testing Bench scale and full scale operations can often vary Strong experimental setups are critical to determining true benefits Cooperation between all parties greatly improves the potential for success 40

41 Special Thanks to All Contributors Co-Authors Ya-Chi Tsao, PWD James Grandstaff, Henrico County Mark Bottin, H&S Jared Alder, OpenCel Other project staff PWD OpenCel Henrico County HRSD Hazen and Sawyer 41

42 Questions? Matt Van Horne, P.E. Hazen and Sawyer Fairfax, VA (703)

43 Additional Case Study - BioCrack 43

44 Case Study BioCrack TM Electrokinetic Disintegration Process mgd design flow 10.5 mgd annual average flow 2 Step WAS thickening Gravity thickener Gravity belt thickener Primary sludge fed directly to digesters 4 mesophilic anaerobic digesters ~60% VS from WAS (by mass) 2 primary (parallel) 30 day SRT 2 secondary (series) 50 day SRT Belt filter press dewatering

45 Process Flow Schematic 45

46 Pilot Testing Parameters Parameter Value Feed Rate 150 gpm Number of Electrodes 4 Energy Input per Electrode 35 kw Grinder Power Input 5 hp Pipe Diameter 6 Residence time (per Electrode) ~2.9 seconds Average TWAS TSS 68,820 Net Energy Input (per mass dry solids) 220 kj/kg TSS Net Energy Input (per total volume) 1.0 kwh/m 3 46

47 Gas Production (scf/day) Gas Production (scf/day) Gas Production (scf/lb VS) Results Were Inconclusive 170, , , , , , , , ,000 Total Average Daily Gas Production Begin End Pilot Pilot Gas Production per lb VS Added Begin Pilot End Pilot 115, , , ,000 95,000 90,000 Primary Digester Average Daily Gas Production Begin Pilot End Pilot 67% 66% 65% 64% 63% Percent of Gas Production Occurring in Primary Digesters Begin Pilot End Pilot 85,000 62% 80,000 61% 47

48 COD Solubilization (%) Results Were Inconclusive Parameter Untreated-TWAS Treated-TWAS TSS (mg/l) 68,820 (± 9,570) 59,430 (± 10,450) VSS (mg/l) 43,120 (± 11,890) 38,220 (± 13,850) Total COD (mg COD/L) 35,720 (± 15,880) 39,200 (± 7,350) Soluble COD (mg COD/L) 515 (± 65) 620 (± 148) TSS Disintegration 13.6% VSS Disintegration 11.4% COD Solubilisation 0.30% Net Energy Input 220 kj/kg TSS 80% 70% 60% 50% BioCrack 40% 30% 20% Upper Bound Average Lower Bound 48 10% 0% 100 1,000 10, ,000 Es (kj/kgts) Adapted from Foladori et al., 2010

49 BioCrack TM Pilot Conclusions Biogas production data inconclusive Long digester SRT may have muted BioCrack TM effect on gas production Uncontrollable variables in full scale pilot Slight increase in soluble COD Decrease in TSS and VSS Floc / Particulate destruction Lower intensity process Possibly increasing degradation rate, but not extent More suitable at facilities with low digester SRT 49