Another Tool in Our Toolbox

Transcription

1 BIOLOGICAL FILTRATION Another Tool in Our Toolbox Presented by: Grant L. Meyer, PE Surface Water Treatment Workshop May 2, 2018

2 BIOLOGICAL FILTRATION What is Biological Filtration? Why Consider Biological Filtration? How does Biological Filtration Impact Design and Operation? Comparative Performance of Alternative Filtration Systems 2

3 WHAT IS BIOFILTRATION? Biological treatment (filtration) utilizes natural microbial activity to oxidize or reduce contaminants. River Bank Filtration / Horizontal Collector Wells Rapid Sand Filtration (without Chlorine) Anoxic/Anaerobic Treatment (common in wastewater applications) 3

4 WHAT IS BIOFILTRATION? At its simplest 1. Rapid biological filtration (Dual media) 2. Ozone-enhanced biological filtration 3. Biological GAC Incidental vs. Purposeful and Managed 4

5 WHAT IS BIOFILTRATION? Hieroglyphics 1870 Started using Ozone + GAC AWWA Sponsored 1st Biological Drinking Water Treatment Symposium (Denver, CO) 2008 Almost 1,500 BC First Slow Sand Filtration Plant In The US AWWA Est. the Biological Drinking Water Treatment Committee 5

6 WHY CONSIDER BIOLOGICAL FILTRATION TOOLS FOR: DBP S Taste & Odor Contaminants Organics Biogrowth Toxins

7 WHY CONSIDER BIOLOGICAL FILTRATION 1. Improved bdoc Removal 2. Reduced DBP Formation 3. Improved Taste & Odor Removal 4. Reduced Biogrowth in Distribution System 5. New/Evolving Regulations 6. Trends Toward Increasing Sustainability 7

8 BIOFILTRATION SYSTEM DESIGN Successful Biofiltration Steps RAW WATER Supplemental Food Source? FILTER DESIGN Disinfection Process? Pre Oxidation Process? Media Type? Media Depth? Backwash Protocol? TO DISTRIBUTION 8

9 BIOFILTRATION SYSTEM DESIGN Food Source: Substrate (food), nutrients and biomass Every water source is unique Supplemental Nutrients? Carbon:Nitrogen:Phosporus (100:10:1) Temperature warmer is better Use of BAC helps in colder waters 9

10 BIOFILTRATION SYSTEM DESIGN Pre Oxidation Process: In any? Ozone Peroxone Ozone + Peroxide Peroxide at High ph 10

11 BIOFILTRATION SYSTEM DESIGN Filter Design Considerations: Habitat for Biological Growth Media Selection Surface Area/Contact Media Depth Residence Time Filter Flow Capacity Retrofit vs. New Filter? 11

12 MEDIA SELECTION Media Selection In addition to the old standards: effective size, uniformity, density, porosity Specific Surface Area (SSA, m 2 /g) Conventional Media Filtration with Biological Activities Ivan X. Zhu and Brian J. Bates, 2013

13 MEDIA SELECTION Anthracite Media Sand Media Sand and Anthracite media can support biofiltration, but to a lesser extent: 13

14 MEDIA SELECTION GAC (BAC) is preferred Adsorbs more organics More habitable, and more protected space for bacteria Biofiltration can be implemented without as much head loss Biofiltration can be implemented on lower food/nutrient and/or colder waters 14

15 Biofiltration Media Selection GAC, Anthracite, Sand GAC (BAC) is clearly best: Adsorbs more organics More habitable and protected space for bacteria Biofiltration can be implemented without as much head loss Biofiltration can be implemented on lower food/nutrient and/or colder waters 15

16 Typical Media Design for Biofiltration 4 to 6 feet of GAC (or what your existing filter will bear ) 1 to 1.5 ft of Sand 16

17 DISINFECTION PLANNING Disinfection Process Primary Disifection Chlorine / Chloramine Ultraviolet Light (UV) Residual Disinfection CT Calculation & Point Dosage Level Adjustment Regulatory Consultation 17

18 OPERATIONAL CONSIDERATIONS Biofiltration will Impact the Operations Filter Performance Changes Headloss Effluent Quality Monitoring Requirements Customized Backwash Protocol 18

19 OPERATIONAL CONSIDERATIONS Increased Filter Head Loss, Shorter Run-Times 20 to 30% loss in bed porosity is possible Increased backwash frequency Potential for Reduced Particle Removal. Coagulation-flocculation performance will become more critical Changes to Backwash Regime Preserve biology 19

20 OPERATIONAL CONSIDERATIONS Increase in Filter Head Loss Extracellular Polymeric Substances (EPS) EPS is the organic material (slime/glue/gum) that bacteria excrete for adhesion, protection EPS is primary cause of filter clogging/head loss buildup Microbial production of EPS increases with stress e.g., low food, low nutrient availability, cold environments 20

21 SCWTP PILOT STUDY FINDINGS Biomass Measurement Measurement Methods Biological monitoring: 1. ATP 2. Hydrolase enzyme activity 3. DO 4. HPC 5. EPS 6. 21

22 Biofiltration Verification Biofiltration Pilot Study ATP measurement to assess biological activity in pilot study: LOG Scale!!! AOP-BAC AOP-CM Ozone-BAC Ozone-CM No Ox - CM 22

23 TOC Removal Biofiltration Pilot Study 23

24 Taste and Odor Removal Biofiltration Pilot Study 24

25 BIOLOGICAL FILTRATION What is Biological Filtration? Why Consider Biological Filtration? How does Biological Filtration Impact Design and Operation? Comparative Performance of Alternative Filtration Systems 25

26 QUESTIONS? Grant Meyer, AE2S AWWA Surface Water Treatment Workshop May 2, 2018

27 WHAT IS BIOFILTRATION? More often refers to Ozone/BAC Process: Biofiltration is a treatment technique where the biomass on a granular media filter removes organic carbon that was made more biodegradable through preozonation. (U.S. EPA, 2017) 27