Emerging Technologies in Sludge Minimization

Transcription

1 Emerging Technologies in Sludge Minimization Overview for Municipal Wastewater Treatment Michigan Water Environment Association 84 th Annual Conference June 2009 Art K. Umble, Ph.D., P.E., BCEE

2 Outline The increasing challenges with biosolids disposal Opportunities for Sludge Reduction across the Wastewater Treatment System Overview of Minimization Techniques Chemical Mechanical Electrical Biological Thermal 2 mwea 2009

3 What to do with Biosolids? Conventional Alternatives Deposit on Land (agriculture or landfills) Deposit in the ocean No Longer Permitted Deposit in the air (incineration) Ash considered hazardous waste Europe Difficult to obtain permit USA Extremely expensive everywhere 3 mwea 2009

4 What to do with Biosolids? Currently, US produces about 7 million tons/yr; projected at 8.2 million tons by 2010 Land application costs are escalating Landfill availability is in decline Regulatory controls are increasing More research needed on beneficial reuse Public scrutiny over biosolids disposal is increasing (NIMBY) 4 mwea 2009

5 What to do with Biosolids? Conventional Activated Sludge Conventional Anaerobic Digestion CH 4 + CO 2 200,000 Population Equivalents 8,000 DT/yr Primary Sludge Waste Activated Sludge 60% 30% How can this volume be reduced? How can we optimize its beneficial resource? ~5,000 DT/yr for Disposal (3x if wet tons) 5 mwea 2009

6 Opportunities for Sludge Reduction Minimize Sludge Production Chemical Biological Primary Secondary RAS WAS Mechanical Electrical Anaerobic Digestion Thermal Maximize Sludge Destruction 6 mwea 2009

7 Concept: Sludge Minimization Reduce Biomass Produced Within Biological Process [MLSS] Baseline Y t Y obs = Y t 1 + k d θ Accumulation of inert material zero discharge of excess solids Excess Sludge Practical limit for Sludge Minimization t Bioreactor RAS Biomass trtmt WAS To solids Processing 7 mwea 2009

8 Chemical: Anabolic Inhibition Attack the Energy Transfer 2,4 Dinitrophenol (DNP) CELL 40% Anabolic Pathways New Cell Production ATP Substrate Decouple Intracellular Maintenance Other Chemicals: Chlorpomazine Rotenone Vancomycin 60% Catabolic Pathways Indicator of pathway disruption is oxygen uptake rate: OUR increases with time. Yield decreases from 0.42 to 0.3 g MLSS/g COD removed with addition of 2,4 DNP at 4 mg/l. Adapted from Meyhew, et al. (1997) 8 mwea 2009

9 Chemical: Ozonation Cellular & Dissolved Organics Basic Mechanism: Solubilization Mineralization O 3 OH Cellular & Dissolved Organics Decomposition of O 3 via OH Bioreactor RAS 2/3 OH Consumed by carbonates and other minerals Ozonation Reactor WAS 1/3 9 mwea 2009

10 Disintegration Mechanism STEP 1: Floc Dispersion Backbone Filaments Exocellular Polymeric Substance 10 mwea 2009

11 Disintegration Mechanism STEP 2: Cell Wall Disruption Nucleoid Release Soluble Organics Cytoplasm Solubilize Particulates Cell Wall Disruption Cell Membrane 11 mwea 2009

12 Resulting Biomass Reduction [MLSS] Y t Y obs Baseline Disintegrated Fraction Cryptic Growth Substrate Growth Inert Solids Excess Sludge t 12 mwea 2009

13 Cellular Disintegration BEFORE DISRUPTION AFTER DISRUPTION 13 mwea 2009

14 Disintegration Techniques D = disintegration process D Bioreactor D RAS D WAS To Solids Processing 14 mwea 2009

15 Mechanical: Sonication Bioreactor RAS Sonication Reactor WAS NaOH To Digestion Biomass Disintegrated and Solubilized Overall about a 30% Reduction in Solids Reasonably Achievable 15 mwea 2009

16 Mechanical: Sonication Sonicator Sonic Wave Disintegration Mechanisms: 1. Oxidation of organics via hydroxyl radical species 2. Collapse of cavitation bubble (pressure / temperature) 3. Hydrodynamic shear from bubble collapse Bulk Fluid HO khz Rarefaction Compression Up to 80% cellular disintegration HO 2 H 2 O 2 O HO 16 mwea 2009

17 Mechanical: Hydrodynamic Microsludge Hydrodynamic Cavitation PSI WAS 17 mwea 2009

18 Electrical: Pulsating Electrical Field OpenCEL Electric Pulse + Voltage Adapted from: OpenCEL Time 18 mwea 2009

19 Biological: Microbial Predation Aeration Basin Cannibal Influent Clarifier Purge RAS Trash, grit, inerts Solids Separation Module Effluent Controls Interchange Bioreactor Interchange Mixed Liquor 19 mwea 2009

20 Microbial Predation Effluent Screened Influent Coarse Bubble Fine Bubble Fixed Film Media in all stages AQUARIUS Technologies Coccacae; Pseudomonodacae Zooglea; Spaeroillus Flagellaeta; Amobea Increasing Protozoa Predation Multi-Staged Activated Sludge Biological Process (MSABP) Monosov, et al. (2007) Copoda; Vorticella Bacterial Community Transition by Stage 20 mwea 2009

21 Pre-Treatment Processes to Anaerobic Digestion High Heat High Pressure Improved Digestability Improved Biogas Production Improved Dewatering Reduced Reactor Volumes WAS CF TH Anaerobic Digestion CF PS PS + WAS Operating Temperature: 150 o C 180 o C Operating Pressure: 8 10 bars Pulp Reactor Thermal Reactor (steam injection) Flash Reactor (pressure reduction) WAS WAS (Ind) Kepp, et al. (2000) Yield of COD from Hydrolysis, % CAMBI 21 mwea 2009

22 Thermal Hydrolysis with Multi- Phase Anaerobic Digestion Hydrolysate to BNR Boiler Heat Recovery Biogas CF Dewater (15%-20%) TH Reactor 10%- 12% Anaerobic Digestion (Acid Phase) HX Anaerobic Digestion (gas phase) CF Dewater (30%-40%) Steam Turbine Electrical Generator Enhanced CHP Benefits 22 mwea 2009

23 Summary Conventional Options for Biosolids Disposal are Diminishing Achieving Zero Discharge in Sludge Production Remains Elusive Most of the Emerging Technologies Rely on Cellular Disintegration Mechanisms Most Biological Techniques Remain Difficult to Control and Model Processes Based on Heat and Pressure Mechanisms for Hydrolysis are Promising Thermal Hydrolysis and Multi-phase Anaerobic Digestion are Likely First Wave 23