Applications of Variable Environmental Conditions on Biological Sludge Production in Wastewater Treatment

Transcription

1 Bruce R. Johnson P.E. BCEE and Glen T. Daigger, PhD, NAE, P.E. BCEE Advances in Solids Reduction Processes at Wastewater Treatment Facilities: NBP Webcast, April 28 th, 2010 Applications of Variable Environmental Conditions on Biological Sludge Production in Wastewater Treatment B U I L D I N G S U S T A I N A B L E S O L U T I O N S 1 Outline Introduction Sludge Reduction Overview Mechanisms of Biological Sludge Reduction Modeling of Biological Sludge Reduction Conclusions B U I L D I N G S U S T A I N A B L E S O L U T I O N S 2 1

2 Why is Sludge Production Important? Limited disposal paths and more constraints Agriculture 51% restrictive regulations lower public acceptance competition with manure restricted available land Incineration 11% Landfill 38% restrictive regulations lower public acceptance restricted access for organic wastes restrictive regulation (air emission) lower public acceptance US Biosolids production is approximately 7 million dry tons per year Favorable drivers for sludge reduction technologies B U I L D I N G S U S T A I N A B L E S O L U T I O N S 3 Introduction Reduction of solids disposal costs and quantities is of great interest to Utilities around the world WERF Project CTS-05-3: Evaluation of Processes to Reduce Activated Sludge Solids Generation and Disposal There are a wide range of sludge reduction technologies offered None of these technologies are well understood d Theoretical Basis Design Basis Modeling Approaches B U I L D I N G S U S T A I N A B L E S O L U T I O N S 4 2

3 Introduction The technologies fall into three major categories according to the methods they use to improve degradability Mechanical The physical breaking up of cells and agglomerations Chemical Changing the chemical makeup of the constituents Biological Creating conditions that improve biodegradability Combinations of the three methods B U I L D I N G S U S T A I N A B L E S O L U T I O N S 5 Introduction This presentation is focused on the principals behind improving i biological i l degradabilityd Mechanisms Modeling Examples B U I L D I N G S U S T A I N A B L E S O L U T I O N S 6 3

4 Where Can We do Solids Reduction? Plant Influent Headworks Primary Treatment Plant Effluent PS to Secondary Treatment WAS to Dewatering/ Disposal Pretreatment Extended Aeration Cannibal Ozonation Others? Homogenization Thermophilic hili Sonication Thermal Phased Hydrolysis Acid/Enzymatic Electrical Fields Hydrolysis Others? B U I L D I N G S U S T A I N A B L E S O L U T I O N S 7 Where Can We do Biological Solids Reduction? Plant Influent Headworks Primary Treatment Plant Effluent PS to Secondary Treatment WAS to Dewatering/ Disposal Pretreatment Extended Aeration Cannibal Ozonation Others? Homogenization Thermophilic hili Sonication Thermal Phased Hydrolysis Acid/Enzymatic Electrical Fields Hydrolysis Others? B U I L D I N G S U S T A I N A B L E S O L U T I O N S 8 4

5 So What are Waste Solids???? Waste Solids Biodegradable Non-Biodegradable Fast Slow Very Slow Organic Inorganic The Essence of Solids Reduction B U I L D I N G S U S T A I N A B L E S O L U T I O N S 9 Biological Sludge Reduction Occurs in Secondary Treatment Long sludge age Reduced yields with non-aerated zones Cannibal Solids Reduction Process Improved Anaerobic is achieved with Advanced digestion techniques ph changes temperature changes What do these processes have in Common? B U I L D I N G S U S T A I N A B L E S O L U T I O N S 10 5

6 Cannibal Solids Reduction Process Siemens (formerly US Filter) Cannibal process uses both biological i l and physical methods Versions in operation since 1998 B U I L D I N G S U S T A I N A B L E S O L U T I O N S 11 Cannibal Step 1 Physical: Solids Separation Module Screenings and Grit (inert material) 0.2 to 0.3 lb/lb BOD applied dewaters to 30-40% TS is 90% volatile disposed in landfill B U I L D I N G S U S T A I N A B L E S O L U T I O N S 12 6

7 Cannibal Step 2 Biological: Interchange Reactor WAS (<1% TS) sent to reactor Interchange reactor SRT d Intermittent aeration (SBR) controlled by ORP Portion returned to aeration basins every day B U I L D I N G S U S T A I N A B L E S O L U T I O N S 13 Cannibal Interchange Reactor Environmental Conditions Long periods of anaerobic/anoxic conditions are common Relies on cycling of environmental conditions Interchange Cycle, hours Fill Aerate Quiesent (Anoxic/Anaerobic) Decant Mix / Decant B U I L D I N G S U S T A I N A B L E S O L U T I O N S 14 7

8 Advanced Anaerobic Acid/Gas First Stage is low ph (5 to 6) fermentation ti step Second Stage is normally conventional Mesophillic (ph=7) Waste Solids To Dewatering Acid Phase Methanogenic B U I L D I N G S U S T A I N A B L E S O L U T I O N S 15 Advanced Anaerobic Temperature Phased Various combinations of mesophillic (35 C) and thermophillic (55 C) staged digesters Waste Solids To Dewatering Thermophillic Mesophillic B U I L D I N G S U S T A I N A B L E S O L U T I O N S 16 8

9 Advanced Concepts A recent innovation is the concept of Post Aerobic PhD research (Kumar) DCWASA experimental work with Dr. John Novak Full Scale operation in Austria (Parravicinni et. al) Waste Solids To Dewatering Mesophillic Aerobic B U I L D I N G S U S T A I N A B L E S O L U T I O N S 17 Biological Sludge Reduction Commonalities Conventional digestion/treatment is limited by the amount of non-biodegradable d bl solids (organic and inorganic) in the sludge All methods use varying environmental conditions to improve removals It is hypothesized that the non-biodegradable organics created in one environmental condition are not totally non-biodegradable in another B U I L D I N G S U S T A I N A B L E S O L U T I O N S 18 9

10 What do Variable Environmental conditions do? Waste Solids Biodegradable Non-Biodegradable Fast Slow Very Slow Organic Inorganic B U I L D I N G S U S T A I N A B L E S O L U T I O N S 19 Modeling of Sludge Reduction Johnson (2008) proposed a method of modeling the Cannibal solids reduction process where Aerobic/Anoxic Decay products are converted biodegradable material under anaerobic conditions This concept was applied to Anaerobic/Aerobic digestion Anaerobic decay products are degradable under aerobic conditions B U I L D I N G S U S T A I N A B L E S O L U T I O N S 20 10

11 Modeling of Anaerobic/Aerobic Model Results Kumar (2006) Parravicini (2008) Anaerobic SRT, days Anaerobic VSR 55% 50% Unknown Aerobic SRT, days Aerobic VSR 15% 23% 16% Total VSR 62% 60% Unknown B U I L D I N G S U S T A I N A B L E S O L U T I O N S 21 Summary and Conclusions Biological Sludge Reduction Technologies Work through the cycling of decay products through variable environmental conditions Can be modeled by the separate tracking of decay products and their conversion to particulate degradable matter under different metabolic conditions B U I L D I N G S U S T A I N A B L E S O L U T I O N S 22 11

12 Summary and Conclusions Primary Hypothesis Conventional approach includes the production of nonbiodegradable VSS. This VSS is non-biodegradable under conditions present in WWTPs This material may be the microbial pieces grown to protect the microbe in the environment it is grown In other environments it is possible that this material is at least partially degradable Modeling, Advanced, and the Cannibal process appears to support this hypothesis Principal is generally applicable throughout a WWTP B U I L D I N G S U S T A I N A B L E S O L U T I O N S 23 Bruce R. Johnson P.E. BCEE and Glen T. Daigger, PhD, NAE, P.E. BCEE Advances in Solids Reduction Processes at Wastewater Treatment Facilities: NBP Webcast, April 28 th, 2010 Questions? Applications of Variable Environmental Conditions on Biological Sludge Production in Wastewater Treatment B U I L D I N G S U S T A I N A B L E S O L U T I O N S 24 12