Trihalomethane (THM) Removal Design Parameters, Testing, & Performance Evaluation
GridBee® SN Series Spray Aeration Systems For Potable Water Storage Tanks
Practical real-world experiences combined with on-going innovation are the cornerstones for all Medora Corporation THM (trihalomethane) and other VOC (volatile organic compound) spray aeration removal systems. We have hundreds of successful SN Series Systems currently in use and are continuously conducting internal THM removal tests to provide the best product and result for our Customers.
The THM removal efficiency curve is dependent on a number of factors. Proper consideration and evaluation of these factors ensures the system is designed to provide the THM removal rates desired.
THM Removal Efficiency
THM removal efficiency is impacted by the following:
- Starting THM levels
- Water temperature
- THM formation potential
- Flow through the system
It is very important a THM removal system be judged according to agreed upon design parameters. When these parameters deviate one way or the other, the THM removal efficiency can also be impacted. For instance…
THM removal efficiency can be increased by:
- Lower flow
- Higher starting THM levels
- Higher temperatures
- Lower formation potential
THM removal efficiency can decrease with:
- Higher flows
- Lower starting THM levels
- Lower temperatures
- Higher formation potential
It is not always easy to predict how all these factors will work in concert with each other. This is why we purposefully designed scalability into SN Series THM removal systems for those special cases where more treatment may be needed based upon new information and/or revised design parameters.
THM Formation Potential
In its simplest terms, THM formation potential is the maximum THM level possible given existing conditions for disinfectant to react with natural organic matter (NOM).
THM formation potential can diverge significantly based upon differing rates of interaction throughout the distribution system. Interaction takes place at a relatively slower rate as the water flows through pipes from the water treatment plant to the end of the distribution system; whereas, water being actively and vigorously mixed inside a storage tank may cause THM formation to accelerate.
In order to fully understand the benefit of a THM removal system, THM formation potential must also be understood and accounted for.
THM is 30 µg/l at the inlet of the reservoir where the removal system is located. Mixing within the tank accelerates formation potential causing a very brief, momentary rise to 80 µg/l. Spray aeration subsequently reduces total THM to 40 µg/l at the tank outlet.
The THM removal system is working properly in this example.
THM (after formation potential consideration) was actually reduced by 40 µg/l. As formation potential is achieved in the tank, any additional formation potential down the line is lessened. In this particular case, post-treatment THM levels would not be expected to rise much above 45 µg/l (even at the end of the distribution line) and the City would be well in compliance. If testing at the reservoir inlet and outlet were performed without formation potential consideration, it would be easy (and incorrect) to conclude a 10 µg/l increase rather than a 40 µg/l decrease.
Performance Testing and Evaluation
For accurate results, cover all the bases.
We recommend performance evaluations occur during periods when the distribution system has historically shown total THM (TTHM) concentrations very near, at, or exceeding TTHM compliance limits.
In addition to THM testing at the inlet & outlet of the treated tank, we also recommend additional testing occur at sample points downstream. It is preferable these downstream tests are toward end of the distribution line and where historical data are available.
Samples properly taken at downstream locations can show how the system is affecting downstream distribution system where compliance issues are most probable. Using reasonable means of hydraulic characteristics, be sure samples collected downstream can be correlated with the on / off periods of the THM removal system.
When designing THM removal systems, Medora Corporation takes all these factors into account to provide our Customers with the best possible result. Please feel free to give us a buzz at 866-437-8076 or contact us through our website!
Posted By The GridBee® SolarBee® Team
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