It was hard before but the EPA Stage 2 disinfection byproducts rule with locational maximums for THM / TTHM (80 ug/l) and HAA (60 ug/l) have made it even harder.
You have THM compliance options...
It's just a matter of which path you take.
1. Front End of the Treatment Plant
- Switch to an alternative disinfectant for achieving the CT (concentration X time) requirement.
- Add a purification process at the front of the plant to remove the natural organic material (NOM, the cause of THM formation).
- Add a granulated activated carbon (GAC) process to remove the THM
In many cases these solutions are cost prohibitive based on initial capital costs and ongoing costs.
2. In the Treatment Plant: Create a vertical plug flow through the CT tank to increase your baffle factor. After a tracer test proves a higher baffle factor and longer “T”, then “C” can be reduced, resulting in less THMs being formed.
3.Put mixers in the distribution tanks: Sometimes, perhaps 10% of the time, mixing of the storage tanks will keep the residual chlorine higher throughout the entire distribution system, allowing less chlorine to be used at the plant and less boost chlorine to be used in the system, resulting in less TTHM throughout the system. Also, mixing a tank will increase the natural volatilization of THM in the tank, resulting in lower system THM.
4. Clearwell At The Back End Of The Treatment Plant: Strip THM from the clearwell with spray nozzles or air diffusers. In many systems this is the best option, particularly if there is no guarantee the water will ever enter a distribution tank where it can be stripped of THM (since often the water goes from the clearwell directly to a consumer's faucet).
5.Install a THM Removal System in one or more distribution tanks: If there are distribution tanks on the system where it is known that most of the water for a particular neighborhood or region does go into the tank, then a THM removal system can be effectively placed in that tank to solve the problems for that region.
6. Install an In-Line THM Removal System: There may be parts of town where there is no guarantee that the water will ever go through a tank after it leaves the clearwell at the plant. For those parts, add an SN In Line Skid THM removal system.
Note: THM removal equipment and associated mixing does not commonly reduce chlorine levels; however, it can be very effective for stripping dissolved gases such as H2S and methane.
Medora Corporation THM Removal Systems are high-performance systems that are easy to install and have the lowest cost in the market.
Steps some customers have taken to achieve HAA compliance:
1. Sometimes various pH adjustments can be made at the treatment plant that will minimize formation of HAA.
2. Sometimes mixing in a distribution tank can achieve HAA compliance. On the one hand, mixing a tank circulates the chlorine better which kills the beneficial bacteria which are needed to break down the HAA, which is a negative. But on the other hand, having a mixer that pulls water directly off the bottom of the tank, as fast as it enters the tank, and mixing it into the older water, which has less HAA, can give a "solution by dilution". Each case must be evaluated separately. Medora's rental program is advantageous in these situations.