In this episode of the Chemical Processing Distilled Podcast, Brad Buecker of SAMCO Technologies joins editor-in-chief Traci Purdum to dig deeper into reverse osmosis for boiler makeup water. Buecker contrasts RO with sodium softening, explaining how RO removes up to 99% of dissolved ions, cutting corrosion, scaling and blowdown compared to softening alone. He stresses that raw water quality and pretreatment reliability — not snapshot testing — determine RO success, and warns against microbiological fouling, chlorine damage and cutting corners on monitoring. Buecker also covers normalization programs, cleaning triggers and design considerations for plants weighing a switch from softening to RO.

Transcript (Edited for clarity)

Welcome to the Chemical Processing Distilled Podcast. This podcast and its transcript can be found at chemicalprocessing.com. You can also download this podcast on your favorite player. I'm Traci Purdum, editor-in-chief of CP, and joining me once again is Brad Buecker, a frequent contributor and podcast guest, talking about all things water and wastewater — and then some.

Brad currently serves as senior technical consultant with SAMCO Technologies and has many years of experience supporting the power industry, much of it in steam generation chemistry, water treatment and air quality control. He has a degree in chemistry from Iowa State University, with additional coursework in fluid mechanics, energy and materials balances, and advanced inorganic chemistry. One of his last articles for us explored reverse osmosis, so today we're going to delve a little deeper. Thanks for joining me again, Brad. It's a solemn day for us, since we're recording this on Sept. 11, and I know you have some thoughts on that.

Brad: Yeah, Traci, just very briefly, I'd like to join the chorus around the country remembering the victims, the victims' families and all the responders — both the ones on-site and everyone around the country who came to help during that awful time. It really showed what the human spirit is in this country.

Traci: Indeed. And always remembering the past and what happened is a way to help the future move forward. So thank you for those words.

As promised, let's talk about reverse osmosis. Can you explain what real difference RO makes for boiler makeup water, and how plant personnel can evaluate whether RO would be better than softening?

When is RO better than Softening?

Brad: I certainly can, Traci. We've discussed this a little in the past, but I'll review a few things. Sodium softening, often with downstream decarbonation, was — and still is — used at a lot of industrial plants. It can do a good job. It removes some of the primary bad actors that cause scaling in boilers, like hardness and bicarbonate alkalinity, that form calcium carbonate. But other ions, like chlorides and sulfates, still make it to the boiler.

There are many good boiler guidelines out there — I follow the ASME industrial boiler guidelines a lot. But these impurities can still cause corrosion. And if the concentration gets too high, they can carry over with the steam, which is a problem particularly in plants where steam drives turbines or specialty processes. That often requires heavy blowdown to keep impurities under control and keep the boilers and steam systems safe. I ran through a set of calculations a few days ago as a reminder, and it showed just how extensive that blowdown can be when you're trying to control this chemistry.

One approach — which really developed in the power industry, at least from my experience back in the '80s — was to use RO to eliminate most impurities, then add a final polishing step for high-pressure applications: mixed-bed ion exchange, electrodeionization, or something similar. But for industrial plants with low- and moderate-pressure boilers, a basic reverse osmosis system can remove 99% of dissolved ions. That means you can send really good water to these boilers, greatly reduce blowdown requirements, and save energy.

Given my experience with RO in the power industry, I've started looking at its potential industrial applications — and I'm not alone. A lot of people are looking at it, and there seem to be some very good benefits to the process.

Coming up in this industry, I've seen two philosophies that run counter to each other, and you have to weigh them case by case. One is the old saying, "If it ain't broke, don't fix it." The other is, "That's what we've always done" — which can lead to its own problems.

Here's where I want to take this: At plants where sodium softeners and decarbonators have worked well and the boilers have operated reliably, I wouldn't come in waving my arms, insisting you replace the softener with an RO. If you've had good results, maybe you don't want to make a change.

But so often — and this is something I've experienced directly, and heard from many colleagues in the water treatment industry — a consultant gets called into a plant because of boiler tube failures. Management says a process is offline all the time because of them. Then, when you look at the softener log books and other data, you find the unit wasn't operated properly or had a lot of malfunctions. That's often the root cause. With RO — and good oversight, which I'll come back to — you can potentially eliminate a lot of those issues. Instead of being reactive, it becomes a proactive approach.

So the question is always: Were these boiler tube failures, or other problems in the steam system, properly evaluated? I read an article the other day — slightly off subject — about a combustion turbine power plant using water to cool the turbine inlet. They were having problems in the combustion turbine, rather than the steam turbine of the heat recovery boiler, and found calcium sulfate deposits on the turbine blades. That was due to poor water quality in the evaporator ahead of the compressor. All kinds of things can happen, so you really need to pay attention to water quality.

That brings up an important issue when considering a change from softening to RO, or building RO directly into a new plant's design: What is the raw water source, and what is the raw water quality? I know I harp on that — people hear me say it all the time — but it's so important, and it's a lesson I learned the hard way.

Years ago, I was asked to look at a plant that wanted to install an RO system. They had a clarifier and sand filter upstream to remove particulates, so I ran a silt density index test on the effluent, and it came back well. Good-quality water was coming into the proposed RO, so they installed it. Then they ran into fouling problems.

My mistake was relying on a snapshot analysis instead of collecting data over time — either myself or through plant personnel — because the clarifier and sand filter weren't always steady. Sometimes they had particulate carryover that went straight to the RO, even with cartridge filters ahead of it, and that caused problems. Ongoing analyses are really important.

For existing plants, that leads to the question of what pretreatment is in place — is it reliable, or should you consider something new? At one of my former power plants, we replaced two aging clarifiers and sand filters with microfiltration units — a membrane process — and it proved extremely effective, dramatically improving the water quality going to the ROs. That's become standard practice at a lot of plants. But even with new membrane systems, if you're pulling from a highly variable source, like river water, a big rainstorm can wash in debris and spike turbidity, which can cause problems for the RO pretreatment system. So understanding your water source and water quality is essential.

Then you need to look at energy, labor and maintenance costs for a new system, and where it will be placed. Is space available? Obviously, water treatment equipment needs to be indoors and protected from freezing. Those are some of the major considerations in switching from softeners to RO, or using RO as primary pretreatment for a new plant.

As for cutting corners: RO units can be very reliable, but they need attention and some TLC. I've already mentioned upstream particulate removal — it may be worth looking beyond old clarifiers and filters. As water passes through an RO, it produces purified water and a waste stream, in what's known as a cross-flow filtration process. I won't get into the weeds, but the dissolved ion concentration in that waste stream, in a standard RO, increases roughly fourfold. So water that isn't scale-forming at the inlet elements might be by the time it reaches the trailing elements, creating scaling potential from a number of compounds. That's why anti-scalant treatment needs to be evaluated. In a few cases I've seen, people have actually put a sodium softener ahead of an RO just to remove hardness and minimize scaling that way.

Water coming into a plant is typically treated with an oxidizing biocide to kill microorganisms, and chlorine in particular will quickly damage RO membranes — so it needs to be consistently removed with a good chemical feed system and good monitoring before it reaches the RO. But I've also seen, more than once, microbes survive oxidizing biocide treatment. They go into hibernation, essentially becoming spores, and then flourish again once the oxidizer is removed, causing fouling downstream. RO membranes, with their very tight spacing, make a great environment for microbiological fouling. That needs to be considered.

So, on cutting corners: I've seen plant managers or operators assume all they need to do is get the system set up, turn it on, and let it run — that it'll just do the job. But you have to pay attention, follow the data and track system performance, because it can get out of hand if you don't.

Know When RO Drifts Out of Spec

Traci: That's a good point — you have to follow the data. Hindsight is 20/20, but looking at the data after the fact, you can see the issues. How can operators tell when an RO system is starting to drift out of spec before it becomes a real problem, and what should they watch day to day?

Brad: The standard setup now: An RO unit is normally equipped with pressure gauges, flow meters, conductivity meters, maybe a chlorine analyzer or ORP analyzer, and various other instruments to track performance. A reputable RO manufacturer, or a water treatment chemical firm, will typically supply what's known as a normalization program — I actually have an Excel version of one myself.

The key factor in normalization is that, depending on water temperature, the channels in an RO membrane will shrink or enlarge as temperature rises or falls. That influences flow rates through the membrane, and somewhat affects salt passage. So it's common to design an RO based on the coldest water temperature it will see, to ensure proper flow, then back it off as the water warms. Most ROs also have a permeate tank — a storage tank at the end of the system — so you can store water and shut down periodically while still having plenty on hand.

That said, in monitoring RO performance, you have to watch for temperature changes, because they can mask problems like particulate buildup, scale formation or microbiological fouling. Normalization programs take instrument data — pressures, temperatures and so on — and compute a normalized flow or pressure reading; there are several normalized readings you can get from an RO. So operators need to not only check instruments periodically, but understand these normalization programs.

Even well-treated RO systems accumulate solids over time. You have fairly high-pressure water — 100 to 200 psi — pushing through these membranes, and things collect on the membrane surface. Typically, once output has decreased by about 10%, it's time to take the RO offline for a clean-in-place process. There are variations, but often you'd clean first with a caustic or higher-pH solution to remove organics and microbes, rinse, then clean with an acid solution to remove iron particulates or similar deposits. Again, without going into the weeds, the normalization program is the tool for determining how the RO is running and when to clean it.

There are also times when a mechanical failure will show up very quickly. RO membranes have what are known as brine seals, which separate the elements and keep water from flowing where it shouldn't. If one of those fails, or there's a failure elsewhere in an element or pressure vessel, you can get a sudden spike in conductivity. In one RO design I worked with, each pressure vessel had a manual valve and sample tap on its permeate outlet. If the overall conductivity reading suddenly spiked, an operator or chemist could sample each pressure vessel individually to pinpoint the problem. Those are some of the tools operators and technical personnel can use to track RO performance.

Traci: And to help distinguish between a routine fix and something more serious with the membranes.

Brad: Yes, absolutely.

Avoid These Mistakes with RO

Traci: What's the biggest mistake you see companies make when planning a new RO system? And what would you tell someone designing one from scratch — where should they start?

Brad: Again, very briefly: comprehensive water analysis. If I were at a plant now considering RO, I'd be inclined to design for the flow needed at the coldest water conditions, then trim back as the water warmed. I've actually seen plants that didn't design for the coldest conditions and ended up needing to install a preheater for the RO inlet to reach the required flow — sometimes using bleed steam. A lot of industrial plants have building heat systems that take bleed steam, run it through a heat exchanger, and send warmed water to heaters throughout the plant. That became an option for RO preheating, too — something worth keeping in mind.

And here's another point I'll make, at the risk of repeating myself: Have trained, conscientious operators. I've seen this in the combined-cycle power industry — as coal plants have retired and combined-cycle plants have come online, plant owners have adopted a "lean and mean" mindset: minimal staff, keep costs low. In practice, that often means no experienced technical personnel beyond the operators.

One area where that can be especially problematic is water treatment and steam generation chemistry in heat recovery steam generators. You can save money by not having someone educated on hand to monitor these systems, but one failure can cost far more than that salary would have — a boiler failure, or heaven forbid, a turbine failure. Coming from a power and industrial plant chemistry background, I'll admit my bias, but the larger point stands: Be proactive, not reactive.

Traci: Absolutely. Saving money, safety and conscientious operations do more to bolster the bottom line than almost anything else. Well, Brad, thank you for always making sure we ask the question: What's in the water? I appreciate the time you put into every podcast we do together.

If you want to stay on top of best practices in the chemical industry, subscribe to this free podcast on your favorite platform. You can also visit us at chemicalprocessing.com for more tools and resources aimed at helping you succeed. On behalf of Brad, I'm Traci, and this is the Chemical Processing Distilled Podcast. Thanks for listening. Thanks again, Brad.

Brad: Thank you, Traci.