The rain ran serpentine paths down the windows of the rusty, blue Ford as Herbert Henry Oxidane, P.I., CWT, sat waiting for Johnny Chelant to open the side powerhouse door at Pork Bellies Processing. When the lanky man’s shaggy head popped out, the water detective made a run for it, dodging raindrops the best he could.

“Get in here, Detective H₂O, before you melt!” called Johnny.

“I’m running between the drops,” replied Detective H₂O. “Let’s see this reverse osmosis system of yours.”

“Right this way,” said Johnny as he snaked the way through the building. “Like I said on the horn, this RO system goes south real fast. We’ll clean it…clean it good…and a week later, maybe two, it’s moping along begging to be taken to the cleaners again!”

“How do you determine when it needs to be cleaned?” asked Detective H₂O.

“Well, we’re using the normalization program provided by the membrane manufacturer. When the normalized permeate flows drop by 10-15% and the pressure drops increase by 15%, we clean! We’re barely keeping up with permeate demand!”

“Hmmm, can you tell me about the water you are processing through the RO system?”

“Oh, yeah,” said Johnny. “We’re the largest pork-belly-processing plant this side of the Mississippi, you see. That requires a LOT of water. We get our water directly from the Grace Noelle River. After filtration, clarification, and disinfection, some of the water comes to this RO system to make high purity water for us. Our Silt Density Index is run daily. It is always spot on, showing good quality water for RO membranes. Our free chlorine tests before the RO is also always spot on too, you see. Yet despite my crew babying this system, the membranes have to be cleaned far more frequently than we ever imagined! That can’t be good on ‘em.”

“Have you sent any of the membranes out for an autopsy to determine what is fouling them?” asked Detective H₂O.

“Yes, three times. It is always biological fouling!” replied Johnny.

“Biological fouling…interesting,” said Detective H₂O scowling. “Let’s take a look. I’d like to walk down the length of the system, see the chemical feed points, review your data, take a look at the autopsy reports, and run a few tests myself. Let’s start with the walk through.”

For the next several hours, the water detective got the scoop on the Pork Bellies Processing water treatment system. Everything appeared to be ship shape. This was a well-run plant, and as far as he could tell, well designed. The crew’s care and dedication were obvious.

“Figured out the culprit yet, Detective?” asked Johnny.

“Not quite yet, but I have a hunch. Let’s go collect some water right before the chlorine disinfectant is added. We’ll need a clean bucket,” said Detective H2O.

After collecting the water sample, Detective H₂O lined up several beakers with 100 mLs of the water sample in each, prepared a diluted bleach solution, and carefully injected different amounts of the solution into each water sample. After thoroughly stirring, he started the timer. In the meantime, he also tested for ammonia. Earlier, the water detective had calculated the residence time of the chlorine disinfectant in the system from the point of injection to the point of dechlorination just before the RO system. It was twenty-five minutes. After this time had elapsed, he tested each 100-mL water sample for free chlorine. Then he fired up his computer (barely more than an abacus) and graphed out the data. Lastly, he smiled…or at least he defined it as a smile.

Johnny, noticing the change in the water detective’s face, said, “I don’t know whether to be scared or encouraged by that…uh…smile you’ve got going on there. Are you on to the culprit?”

“Definitely encouraged. I may have cracked this case wide open. Take a look at this. I added different levels of diluted bleach to each of the water samples you saw me pour out. The chlorine concentration added increased from left to right as I had them sitting on the lab counter. I gave them time for the free chlorine to react with what was in the water…the same time it would have in the system out there. After this time, I measured the remaining free chlorine. Finally, I graphed it out here. See this curve,” pointed out Detective H₂O.

“Yes,” replied Johnny. “There’s a hump in the middle. Is that normal?"

“Well, yes and no, but it’s what I suspected I would see in your case. When chlorine is introduced to a system, it reacts with several things. Our desire is for it to react with the microbes in the water first so the water is properly disinfected. That way your membranes won’t foul. Unfortunately, there are other components in the water that can react with the chlorine even faster. The typical culprit is ammonia. Ammonia can get into surface waters from farm runoff and so forth. When ammonia reacts with chlorine, it forms chloramines such as monochloramine, a form of combined chlorine. Now, chloramines are a disinfectant, but some research shows that monochloramine may be 25 times less effective than free chlorine at killing microbes!” explained Detective H₂O. “To get to the killing power of free chlorine, you must first react with all the ammonia. After the ammonia is gone and the chloramine reactions are at completion, the remaining chlorine disinfectant you add will form free chlorine. This is called Breakpoint Chlorination, and that’s where the upward sloping line starts after the hump on the graph.”

“Okay, I get what you’re saying there, Detective H₂O, but I still don’t get what it has to do with us. We test our water for free chlorine every shift. Not monochloramine, but for free chlorine. It is within the control range EVERY TIME! That should be good enough, shouldn’t it? What gives?” asked Johnny.

“You make an excellent point, which brings me to the second part of my story. What you see isn’t always what you get. Monochloramine can be a POSITIVE interference to the DPD free chlorine test you use. That means even though the sample turns pink and you think you have a true free chlorine residual in your water, it is actually monochloramine interfering with the test,” replied Detective H₂O. “You don’t have the killing power you think you have in your water, which could certainly explain the biological fouling on your RO membranes.”

“And you’re sure this is happening to us?” asked Johnny.

“I tested the water prior to disinfection for ammonia and found it. Look at this level. To reach breakpoint chlorination, you need to feed a weight ratio of 8 to 1 or higher of chlorine to ammonia. Based upon your records and data, you’re only feeding enough chlorine to get halfway up the hump! There’s no true free chlorine at all to do the disinfection you want.”

“Wow!” said Johnny. “What do we do?”

“You have a few options. First, you can feed more chlorine to the system to reach breakpoint chlorination and beyond to your true free-chlorine control range. Second, you could supplement the chlorine biocide with another biocide which is RO-membrane compatible. Third, you could look at replacing the chlorine biocide with another one that may be more effective considering your current water conditions. There are other options we may be able to consider as well. There are pluses and minuses that come with each option. We can do a thorough feasibility analysis on each of these options, but let’s prove my theory first by feeding more chlorine.”

“That sounds like a good plan, Detective H₂O. Thanks for your time!”

* * *

Detective H₂O’s suspicions were proven to be true over the coming year as the RO membrane cleaning intervals increased from weekly to quarterly. After initially increasing the chlorine feed, a disinfection feasibility study was conducted, systems were piloted, and changes were made that increased the cleanings to every six months. Detective H2O had truly saved the day once again.

* * *

In the underbelly and penthouses of the metropolis of Waterville, where the boilers percolate and cooling towers fog, there is one man who works tirelessly to end corrosion, stop scale, fight lowlife microbes, and conserve water. That man is Detective H2O. Best water treater this side of the Ohio. Solving water problems drop by drop.