Optimizing Coagulation with the Streaming Current Meter Chuck Veal Micrometrix Corp
Charged Particles Repel
Neutral Particles Flocculate
Coagulant Particles Al 3+ Monomeric hydrolysis products e.g. Al(OH) 2+ Various polymeric species Colloidal hydroxide precipitate Precipitated Al(OH) 3 Stable Destabilized Coagulated Restabilized Flocculated Sweep Flocculation
Floc Particle Growth 1 min 5 min 10 min 20 min 30 min
Double Layer Model Positive Counter-Ion Negative Co-Ion Highly Negative Colloid Stern Layer Diffuse Layer Ions in Equilbrium with Solution
SCM Charge Measurement ( + ) Positive ( 0 ) Neutral Ionic and Colloidal ( - ) Negative
Stabilized Colloids Repulsive Energy Attractive Energy Electric Repulsion Energy Barrier Net Interaction Energy Distance Between Colloids Attraction Van der Waals
Destabilized System Repulsive Energy Electric Repulsion Net Interaction Energy Energy Barrier Attractive Energy Distance Between Colloids Attraction Van der Waals
Common Techniques For Dose Control SCM Streaming Current Monitor PCA Particle Charge Analyzer Zeter Potential Meter Jar Tester
Zeta vs. Streaming Current Zeta Potential Induce electric field, measure particle motion Only discrete (visible) particles are measured. Off-line or batch mode only Single particles are selected visually from a charge distribution. Streaming Current Induce particle motion, measure electric field. Particles, colloids, molecular/ soluble (ionic) are measured. Real Time measurement Online or Offline modes Charge distributions are averaged and displayed electronically.
SCD AND ZETA POTENTIAL READING WITH COAGULANT DOSAGE 20 15 10 5 0-50.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8-10 -15-20 RATIO OF COAGULANT DOSAGE(OPTIMUM=1) ZETA METER(mv) SCD
Jar Tests vs. Streaming Current Jar Test Time consuming technique (30min to 1 hour) Predicts plant settling for discrete Coagulant Doses Off-line or batch mode only No Alarm Functions or Process Feedback Streaming Current Continuous Real time SCM Quick Results ie. PCA (2min) Measures actual Charge Neutralization Process. Real Time measurement Online or Offline modes Early Warning system to avoid Process Upsets
Particle Charge Analyzer
Coagulant Demand by Titration
Piston Sample Cell + Sample Electrodes PCA Measurement Cell
PCA Technique Prepare a stock solution of chemical and mimic the current plant dosage into 100ml of Raw water to determine a target endpoint This endpoint is used during changing plant conditions to quickly determine dosage
Optimum Endpoint The theoretical optimum endpoint is zero mv, but most plants run slightly above or below zero because of the unique process dynamics for a given plant.
Streaming Current Meter
Remote Sensor
SC Sensor Motor Stainless Steel Electrodes Replaceable Sleeve Teflon and Delrin Material Spare Sleeve / Piston Inlet Piston Sample Outlet Electrodes Probe Housing Sleeve
Stationary + + + + Liquid / Piston Stationary + + + + + + + + + + + + + + +
Piston Upstroke + + + + + Liquid / Piston + + + + + + + + + + + +
Te flon Piston To p Ele c tro d e Thum b sc re w Pro be Housing Elec tro de Lead Wire Te flo n Sle e v e O- Ring Bottom Elec trode/ Plug Assembly
Probe Service
Remove Boot
Remove Bottom Electrode
Remove O-Ring
Remove & Replace Teflon Sleeve
Probe Signal
SCM with Self Cleaning
Plant Diagram Coagulation Flocculation Sedimentation Filtration Pump SCM Controller Feedback Control Sample Point * Well Mixed * Quick Response Set Point * Emperical * Based on Process Performance Storage
Sample point Sample near the center of a pipe or channel Avoid sample locations prone to collecting silt, sand or grit. Shorten sample lines when possible to minimize clogging and reduce response time.
Determination of Proper Set Point First optimize plant process - flocculation, particle and TOC removal Minimize filter effluent turbidity/particle count Minimize coagulant dose and maintain water quality Maximizing plant / process efficiency Zero streaming current reading
Floc Particles Optimum Floc Vs. Light Fragile
SCM vs. NTU SCM NTU Streaming Current Response SCM@Overfeed SCM@Optimum Chemical Dosage mg/l Chemical Savings
Streaming Current Controller
SCM Control Feedback signal produced by the SCM Controller changes the output to the pump proportionally. Process controller has programmable tuning constants that allow the operator to compensate for lag times Built-in alarm functions that alert the operator immediately if an overfeed or underfeed of chemicals is encountered
Flow & SCM Control Flow meter Mixing Unit Flocculator Pump SCM Flow Proportional * No Lag * Feedforward SCC Controller SCM Control * Feedback Control * Reverse Acting
Recommendations for Successful Operation Replace piston and probe components as preventative maintenance Periodically check optimization of the process and verify the SC setpoint
Contact info Chuck Veal email: cveal@micrometrix.com Ph 770-271-1330 www.micrometrix.com