Optimizing the Operation of Gravity Media Filters

Transcription

1 Optimizing the Operation of Gravity Media Filters Thomas M. Getting, P.E., BCEE Principal Engineer-Filtration Leopold, a xylem brand Tom.Getting@xyleminc.com Website:

2 Presentation Outline Pretreatment Optimization Minimizing the Initial Turbidity Spike Controlling the Filter Flow Rate Optimizing Backwash Periodic Maintenance

3 What is optimization? Optimization is producing high quality water on a continuous basis regardless of changes in raw water quality, flow rate or treatment operations.

4 Paths to Producing High Quality Water Provide Multiple Barriers Pre-Treatment Filtration Disinfection Set Goals Settled Water should be 2-3 NTU or less Filtered water <0.1

5 Filtration Goals Provide filtered water <0.1 NTU After a backwash: the initial turbidity spike should be <0.3 NTU After 15 minutes the turbidity should be <0.1 NTU If filter to waste is available, return the filters online when the turbidity is <0.1 NTU

6 Road to Filtration Goals Optimize Pretreatment Good chemical pretreatment Efficient flocculation and sedimentation Excellent Filtration State of the industry monitoring Comprehensive maintenance program

7 2014 Safety Awards-5 th Place

8 Starting the filter Operating the Filter Ending the filter run Backwashing the filter Four Stages of Filtration

9 1. Lag Phase 2. Media disturbance and intramedia remnant stage 3. Upper filter remnant stage 4. Influent mixing and particle stabilization stage 5. Filter media conditioning and dispersed remnant particles stage Amburgey, James E., New Techniques for Controlling the Passage of Particles and Cryptosporidium Oocysts During the Filter Ripening Period, AWWA WQTC, 2003

10 Filter Start-Up Stage 1 (Minimizing ripening and the initial turbidity spike) Filter to Waste Delayed Start Slow Start Chemical addition to the backwash water Chemical addition to the settled water Stepped ramp down of the backwash (Extended Terminal Sub-fluidized Wash)

11 Filter Operation - Stage 2 Control filtration rate to avoid rapid rate changes through the filter: Make gradual flow changes Provide finished water storage Bring extra filters online Use the pre-treatment basins to store excess flow during a backwash

12 Ending the Filter Run Stage 3 Decrease in demand Maximum headloss achieved Maximum run time achieved Increase in effluent turbidity

13 2014 Safety Awards- 4 th Place

14 Backwashing Stage 4 Cleans the media, removes the dirt from the filter and prepares the filter for the next run Five types of backwash: Water only Water only with surface wash Air/water-sequential or air followed by water (high rate/ low rate) Air/water-concurrent or air and low rate water followed by high rate backwash Air/water-sustained or air and water that crests the backwash weir followed by high rate water

15 Backwash Optimization Consider the effect of each step During high rate: Too high backwash rate may cause media loss Not enough backwash rate will not expand and allow dirt to exit the filter The backwash stream can effect plant treatment-should be <5% of forward flow

16 Backwash Water Turbidity vs Time

17 Filter Monitoring Each filter should have a turbidimeter Only one on the clearwell can mask a poorly performing filter Particle counters provide different, more subtle information than turbidity Work best at <0.5 NTU Still not recognized by regulators Headloss is used to indicate filter clogging Flow meters monitor rate and indicate high flows that can cause particle breakthrough

18 Filter Historical Records Purpose is to establish long term trends for troubleshooting problems Weekly operational data Clean bed headloss Run time Average influent turbidity Average effluent turbidity Visual inspection results - good, action required, uncontrolled air, hydraulic shock, failures, media Monthly maintenance activity Valves, controls, piping, pumps, structures, etc

19 2014 Safety Awards-3rd Place

20 Simple tools, readily available Assemble a team

21 Simple Tools Additional Tools

22 General Guidelines Specific Steps

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26 2014 Safety Awards-2 nd Place

27 Filter Maintenance and Operations Guidance Manual AWWARF-Published in 2002, Publication #90908 Logsdon, Hess, Chipps, Rachwal Black & Veatch and Thames Water Go to Can download a pdf for FREE!!!

28 Table of Contents Introduction to Manual How to Use this Manual for Routine or Periodic Operations and Troubleshooting The Regulatory Environment Filter Operation and Optimization Filter Performance Monitoring Backwash Management and Optimization Filter Ripening and Controlling the Initial Turbidity Spike Pretreatment:Chemical Dosage, Selection, and Mixing Pretreatment:Flocculation and Clarification

29 Table of Contents Filter Inspection and Maintenance Filter Media Characteristics, Selection, and Replacement Quality Control and Instrumentation Issues Case Studies Equations, Example Problems, and Jar Test Procedures Research Needs Identified in this Project

30 Additional Resources AWWA Video-Filter Evaluation AWWA Video-Optimizing Filtration Operations

31 2014 Safety Awards-1 st Place Tie

32 Questions??