The TTHM Tango - Enhanced Coagulation vs. Disinfection Byproducts

The Setup: Your plant has been running smooth as silk. Turbidity is low, customers are happy, and your quarterly TTHM results have been well within limits. You're feeling pretty good about life. Then your latest sample results come back from the lab, and your TTHMs at the entry point to the distribution system (EDPS) are dancing dangerously close to the 80 ppb limit. Your supervisor mentions something about "enhanced coagulation" and suddenly everyone's looking at you like you should know what that means.

The Car-Crash Moment: The state inspector shows up for a surprise visit just as you're trying to figure out why increasing your coagulant dose to remove more organics (which should lower TTHMs) is actually making your chlorine demand go up. Your finished water chlorine residual is dropping faster than your confidence, and you're having to feed more chlorine to maintain residual in the distribution system. But more chlorine means more TTHMs. It's like trying to solve a Rubik's cube while riding a unicycle - every move you make seems to mess up something else.

The Reality Check: Welcome to the wonderful world of competing treatment objectives. You're caught between a rock and a hard place - or more accurately, between turbidity removal and disinfection byproduct control. The organic matter that creates TTHMs when it meets chlorine is the same stuff that can cause taste and odor problems if you don't remove it. But removing it requires coagulation, which can interfere with your disinfection process.

The Learning Moment: This is when you discover that water treatment is more art than science sometimes. You can't just follow a recipe - you need to understand the chemistry behind what's happening. Enhanced coagulation isn't just about adding more coagulant; it's about optimizing your entire treatment process to remove the specific organic compounds that form TTHMs. And sometimes, the answer isn't more of anything - it's doing things differently.