Determining Bulk Reaction Rates for Water Quality Analysis

Product(s): WaterGEMS, WaterCAD
Version(s): V8i, Connect Edition
Area: Layout and Data Input

Problem

What is procedure for determining the bulk reaction rate to undertake a water quality (constituent) analysis?

Solution

To start with we should understand that there is no such thing as a typical bulk or wall reaction rate. Those values vary widely from system to system at different conditions. What can be done is perform a sensitivity analysis varying the reaction rates for multiple scenarios and plotting all the results on a single graph for multiple junctions.

As far as bulk decay, the first step in any chlorine study should be a bottle test.  You should do a field study and collect chlorine residuals, run the model assuming zero wall demand and compare modeled vs. measured chlorine. Based in that adjust wall demands somewhat guided by the fact that wall demand is higher in unlined cast iron pipes and smaller pipes.  The science and body of knowledge on this has not really expanded in the past two decades though."

Steps for running a bulk reaction test

  1. Take a sample of treated water leaving water treatment plant.
  2. Place water in a series of clean bottles.
  3. Seal full bottles tightly and place in the dark in a constant temperature location similar to the typical temperature of the water.
  4. At designated time steps, take one bottle and conduct a chlorine test. Initially plan on 1, 2, 6, 12, 18, 24 hours until you see a trend. You need to increase or decrease the frequency accordingly.
  5. Continue until you reach the max water age across the system or chlorine goes to near zero.
  6. Plot and analyze the data on a graph.

 Note: It’s important to use very clean bottles. Any impurity can change the expected results.

See Also

Forum Discussion - Water Quality (Constituent) Analysis for a proposed water distribution network 

Getting data and setting up for a Constituent Analysis in WaterGEMS and WaterCAD 

  • Created by Bentley Colleague
  • When: Wed, Dec 9 2020 8:45 AM
  • Revisions: 1
  • Comments: 0
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