CCRO, FRRO, PFRO – How Long will the Membranes Last?

I've previously shared my view that the recovery gains offered by proprietary RO systems - CCRO, FRRO, and PFRO - are, in most cases, only marginal when compared to conventional multistage systems. However, today I want to focus on a different but equally critical concern: membrane longevity. Specifically, how long will the membranes last in these proprietary systems?

Conventional multistage RO processes operate at steady state with a constant flow in one direction and it is well documents that membranes can last for over 10 years on well-run brackish systems and maybe as low as 5 years for highly fouling systems that need frequent cleaning. Proprietary RO processes such as Closed Circuit RO (CCRO), Flow Reversal RO (FRRO) and Pulse Flow RO (PFRO) do not operate in steady state and have either widely fluctuating pressures and/or flow directions, which RO and NF elements were never designed for. This raises the question: what impact will the fluctuating pressures and changing flow directions have on membrane life? I have had a few membrane element manufacturers tell me, off the record, that they are concerned about the mechanical damage these processes could cause (even though it is good for membrane sales).

These proprietary processes have a lot less operating data, having only been installed for several years, at least for municipal systems, so we don’t have any published information yet on how long the membranes last. Industrial processes adopted some of these processes earlier, particularly CCRO, but information on these installations is harder to obtain. I was on a tour of the West Morgan-East Lawrence Water & Sewer Authority CCRO facility during an AMTA Workshop in Decatur AL last year and it was mentioned that they were starting to replace membranes in some of the trains only 3 years after startup. That set off some alarm bells for me since this is a relatively low scaling feed water source from the Tennessee River with pretreatment using a Pall MF system. I believe they said CIPs are conducted on the CCRO system around every 3 months, which is fairly frequent but not unlike a reuse system where membranes should last at least 5 years. The recovery was 85% which is not pushing the CCRO too hard. It raises the question, has mechanical damage shortened the life of these membranes? The application here is PFAS removal, so perhaps removal of this contaminant is more sensitive to mechanical damage than other targeted ions where the goal is to achieve non-detect levels on PFAS in the permeate.

I recently heard of a PFRO system treating MBR effluent at a municipal wastewater plant that is running at 92% recovery and doing daily acid and alkali cleans. The plant manager told me they were told the membrane would last 10 years, but he said they now think they will need to replace these after 2 years! Is it due to the frequent cleaning or mechanical damage? Probably both.

I also know of a CCRO system treating cooling tower blowdown and running at 94% recovery and they are doing CIPs once a week and replacing membranes yearly. There are several issues here, where the pretreatment is only multi-media filters which is inadequate for RO pretreatment on this type of feed water and the recovery rate is probably too high. However, the customer faces significant costs associated with offsite concentrate disposal, creating a tradeoff between minimizing hauling expenses and the increased cost of CCRO membrane replacement and chemical usage. It is worth noting though that the customer was told, when selecting CCRO, that the recovery would be even higher…

What about the valve and pump life?

Another difference between proprietary and multi-stage RO processes is that all the proprietary processes have frequently actuating valves, at least every 30 minutes for many of these compared to a few times per day for multi-stage. The FRRO process also needs many more actuated valves to be able to change flow directions in the housings and alternate stages. The more times a valve actuates, the lower the life of the valve and actuator and higher the maintenance cost. Alternatively, you could use a more expensive valve/actuator, similar to what is used on a MF/UF system to extend the life. It's also important not to overlook the toll that fluctuating pressures and frequent start-stop cycles can take on pump longevity.

Therefore, when considering the proprietary ‘high recovery’ RO processes, you should consider more than the benefits of getting a few more percent recovery. Will O&M costs for these processes be significantly higher than multi-stage processes due to more frequent membrane replacement, higher cleaning costs and added maintenance for the valves and pumps? As these systems accumulate more full-scale operational experience, I’m eager to see published data that sheds light on their actual long-term O&M costs.

The comments and opinions in this post are my own and not those of my employer.

North Dakota – The Porcelain State!

 

Two More Ceramic Membrane Projects Awarded in ND

With ceramic membrane systems recently selected for two more drinking water projects in North Dakota, we may soon be calling it the Porcelain State! By my count, that’s now at least four ceramic systems in ND, three are using Nanostone and one is with Metawater membranes. I think that currently has North Dakota with more ceramic membrane installations for drinking water treatment than any other US state. There are also a few drinking water systems retrofitted with ceramic membranes nearby in South Dakota.

What is driving the love of ceramic membranes in the Dakotas? Cold water is the reason for a few of the retrofits where existing polymeric systems had capacity challenges in winter. Cold water reduces the flux of polymeric membranes a lot more than ceramic membranes, so if a ceramic module can produce more water than a polymeric module then the capacity is increased – note, ceramic modules have a lot less surface area than polymeric modules, so just because you can get a higher flux with ceramic does not mean you will get a higher output per module – the math needs to be done to confirm this (see my previous post What the Flux!).

Most of the projects that bid in North Dakota allowed either polymeric or ceramic modules and ceramic membrane systems were selected based on an evaluation matrix, including a lifecycle cost comparison and other qualitative evaluation factors.

For two of the projects, despite the selection criteria, ceramic membranes were quite competitive based on capital cost alone. The major factor that allowed competitive capital costs for these bids was the allowed design flux for each type of membrane. On a surface water with coagulation and plate settler pre-treatment, the maximum flux allowed at 2 deg C for polymeric systems was 15 gfd and for ceramic systems was 90 gfd. Ceramic membranes were piloted to determine the design flux. As far as I am aware, there was no parallel pilot of polymeric membranes conducted and the design flux was based on a conservative design for an existing plant installed over 12 years ago. Notably, there are other polymeric membrane systems on the same water source (Missouri River) that have design fluxes over 40 gfd. 

With this spec, not surprisingly, some of the polymeric system OEMs decided not to bid because they had to bid with six times the membrane surface area. With the capital costs very close between polymeric and ceramic systems, based on the evaluation matrix, ceramic won by virtue of having a longer warranty period in both cases, which raises another concern about how these bids are evaluated – if you have a lifecycle cost comparison with the membrane replacement frequency based on the warranty period, why is there a separate evaluation scoring criteria for the warranty length? In that case you are penalizing polymeric membranes twice for a shorter warranty duration – there should not be a separate score for warranty period if there is a lifecycle cost comparison based on warranty length! Unless of course you want to make sure ceramic membranes are selected…

The most recent ceramic membrane project awarded in ND also had an evaluation matrix and while downstream reverse osmosis was also part of the evaluation, most of the evaluation criteria weighting was based on the MF/UF system. In this case, ceramic capital costs were significantly higher than polymeric, but lifecycle costs and non-cost evaluation factors resulted in the selection of ceramic membranes versus polymeric.

A water system owner is free to select a ceramic system if they want it and are happy to pay a premium for capital cost (and also operating cost if you do 21-year lifecycle – see post), just like someone can buy a Mercedes car ahead of a Lexus if that is their preference. If that is the case, flat spec ceramic membranes rather that have a flawed evaluation criteria against polymeric membranes just to get extra bids.

The comments and opinions in this post are my own and not those of my employer.

PFAS, PFOS, PFOA, PVDF?

Debunking Misleading Connections Between PFAS and PVDF Membranes

There is confusion in parts of the U.S. water industry, possibly fueled by non-PVDF membrane suppliers, around the connection of PVDF membranes and new regulations for PFAS compounds in drinking water. PVDF (Polyvinylidene fluoride) is the most widely used material in the manufacture of MF and UF membranes.

The confusion stems from proposed regulations in Europe that would broadly define PFAS as any substance that contains at least one fully fluorinated methyl (CF3) or methylene (CF2) carbon atom (without any H/Cl/Br/I attached to it). This definition would cover a wide variety of chemical structures, including PVDF. In contrast, the current USEPA definitions of PFAS exclude PVDF including the most recent update of the structural definition of PFAS.

The American Membrane Technology Association (AMTA) has stated that PVDF is considered to be part of a class of high molecular weight fluoropolymers that are distinct from non-polymeric PFAS and have distinctly different physiochemical, toxicological and environmental characteristics. AMTA also states that suppliers of PVDF used for water treatment membranes have certified that there is no use of PFAS as processing aids. See the full AMTA Fact Sheet here.

So, with all of this regulatory discussion there is an ‘opportunity’ to confuse those that are not conversant in polymer chemistry and the correct definitions. I have heard concerns from some end users and engineers that PVDF membranes may release PFAS compounds and may therefore be banned in the future. Coincidentally, these rumors are strongest where ceramic membranes are being considered… Ironically, when offered PES membranes as a non-PVDF polymeric membrane alternative, one engineer said they did not want to consider ‘unproven’ membranes, implying that ceramic membranes were considered more proven... I’d say there are orders of magnitude more PES membrane capacity installed than ceramic membranes, also with a lot longer operating history.

If an engineer and owner want to install ceramic membranes, that is their decision to make. I just want to make sure PVDF membranes are not misrepresented and decisions and made based on facts. Firstly, the European regulations are not being proposed due to any concern that PVDF membranes are releasing PFAS into drinking water. They are just a broad regulation to ban production of products using PFAS materials (like Teflon). Secondly, there is no evidence that PFAS compounds are released into drinking water from PVDF membranes after use for over 20 years. As part of the development of regulations for PFAS in drinking water, the USEPA has required extensive testing of drinking water supplies and no connection with systems using PVDF membranes has been made. Thirdly, the USEPA has indicated it has no intention of banning PVDF or classifying it is a PFAS compound, irrespective of what happens in Europe.

I know some water systems will still lean towards using ceramic membranes due to concerns about future regulations against PVDF even though this is highly unlikely. If they are prepared to pay a high premium for membranes as insurance against this low probability, sobeit. Maybe less expensive insurance would be to install an open platform/universal polymeric membrane system now, that can be converted to ceramic if needed in the future.

The comments and opinions in this post are my own and not those of my employer.

What the Flux! – Part 2

Polymeric vs Ceramic Membranes – Lifecycle Cost Comparison Myths

 

In my last post I discussed that just because ceramic membranes can operate at much higher fluxes than polymeric membranes, a ceramic system will not necessarily have a smaller footprint since ceramic modules or stacks have a lot less surface area than polymeric modules – often less than a quarter the surface area in the same footprint. Therefore, higher flux does not necessarily translate into a lower capital cost.

In this post I will focus on the operational cost comparisons and dispel some myths that ceramic membrane systems have lower lifecycle costs due to longer membrane longevity. Let’s start with the longevity. In polymeric versus ceramic membrane lifecycle cost comparisons, membrane replacement frequencies are typically based on warranty lengths which are often 10 years for polymeric and 20 years for ceramic membranes. A 10-year life for polymeric membranes is OK, but there are plenty of examples of Pall (Aria Filtra) and Toray installations still operating with the original modules after 13-15 years. To my knowledge, only Metawater has ceramic membrane installations over 20 years’ old and therefore can guarantee this lifespan. They say the strength of a chain is based on the weakest link and while I don’t doubt the ceramic membranes used in Nanostone, Ovivo and Cerafiltec systems are very durable and would probably last 20 years, what about the plastic components, polymers and glues used to construct and house these membranes? Will these parts last 20 years? I don’t know if any of these systems have been operating more than 3-5 years so far, so it is taking a great leap of faith in believing these systems will last 20 or more years. The housings on the Metawater modules on the other hand are made of stainless steel, so as long as you don’t drop a module (where it would be like dropping a ceramic pot) there isn’t a weak link to fail before the membranes fail.

 The lifecycle calculations I have seen in bid documents are typically over 20 years, and assume a polymeric replacement after 10 years, and no ceramic replacement over that period, so that is where ceramic systems have an advantage. What if we run the lifecycle cost over 20 years and one day, so we include 2 polymeric replacements and 1 ceramic replacement in the lifecycle cost? That’s fair isn’t it?

 From what I have seen, the cost of a ceramic module is at least twice that of a polymeric module while having around a fourth of the surface area. For a replacement cost comparison, let’s assume the following:

• A ceramic module has 1/4 the surface area of a Toray or Dupont polymeric module (see previous post).
• A ceramic module can get 3 times the flux of a polymeric module.
• A ceramic module costs twice as much as a Toray or Dupont module. Say the polymeric module replacement cost is $2600, Ceramic is $5200.
• Let’s say the base case is a 2 x 2 MGD train polymeric system, design flux of 50 gfd, 45 modules per train. Equivalent capacity ceramic skids will have 60 modules (3 x flux but 1/4 surface area per module).
• Cost to replace all polymeric modules is $234,000.
• Cost to replace all ceramic modules is $624,000.

 Based on the above assumptions, for a 10-year polymeric replacement period and 20-year ceramic replacement period, over 20 years and one day, the replacement cost for polymeric membranes is $156,000 less (two replacements of polymeric versus one ceramic replacement). Maybe ceramics can get a little higher flux and maybe the cost assumptions are a little off, but there is no way you are saving much if anything on membrane replacement costs with ceramics. If ceramic membranes can get four times the flux, the replacement cost is just breakeven using my pricing assumptions.

Known Fact: we know there are Pall and Toray polymeric membrane systems that have had their membranes last 13-15 years. Can we be certain the new ceramic membranes on the block will last 26-30 years to break even with the polymeric membrane replacement cost?

Every water is different, and the flux difference may vary one way or the other to shift the economics, but you can’t say there will be a significant savings in membrane replacement costs using ceramics unless you are looking at the polymeric membranes of yesteryear. Kind of like comparing the fuel efficiency of a car from the 70s with today’s modern cars.

I was going to include a comparison of lifecycle costs with coagulant included, where ceramic membranes often need a coagulant dose to achieve high fluxes, while polymeric membranes do not. This can make the lifecycle cost of a polymeric system significantly lower than a ceramic, but I have rambled on for too long already so will leave that to Part 3.

The comments and opinions in this post are my own and not those of my employer.

What the Flux!

Polymeric vs Ceramic Membranes

My sales rep in the Southeast came to me recently concerned that ceramic membrane companies are promoting fluxes to engineers and water utilities in the region in excess of 200 gfd, asking me how polymeric membranes can compete? My response was WTF! Flux is just a number and just because the flux may seem a lot higher than polymeric membranes it does not mean a ceramic system has a smaller footprint or lower cost. I’ve seen a lot of presentations from ceramic membrane companies trumpeting all the reasons ceramic is better than polymeric but I haven’t yet seen a counter argument from a polymeric membrane company or system supplier. So maybe this is the first counter to some of the ceramic membrane company’s claims. I know I’ll get a push back from the ceramic membrane companies because they are all trying to get established in the market, but I can’t just sit back and let the latest polymeric membranes be unjustly grouped with systems of the past. Note that I am not criticizing the integrity or performance of ceramic membranes at all, and there are situations where these are a great fit, but rather I am just trying to provide a balanced and up to date comparison with polymeric membranes.

WTF!*

Let’s start with the high flux claims. I have seen papers on ceramic pilot studies where fluxes up to 200 gfd have been tested but I don’t yet know of a full-scale system in the US that has been put in service with a design flux this high. The largest ceramic membrane system in the US at Butte MT has a design flux of 69 gfd. A ceramic system that was awarded at Mandaree ND a few years ago had a design flux of 120 gfd for summer. These are pressure ceramic systems where there are feed pumps supplying pressurized modules. 

Figure 1: Membrane System Configurations

The other ceramic configuration is submerged flat sheet operating in the vacuum configuration where a pump draws through the membranes (see Fig 1). Companies such as Cerafiltec and Ovivo are providing this submerged technology and are particularly active in the Southeast. I don’t think a flat sheet submerged ceramic system is installed in the US on a full-scale drinking water system yet, but I have seen several pilot study papers. What strikes me about these recent pilot studies is they are not that impressive. I won’t call out any specific studies, but go search the proceedings from recent AMTA/AWWA Membrane Technology Conferences and you will find them (there may be better pilot studies but I can't find any published). They all spend a lot of time optimizing coagulation ahead of the membranes to reduce rapid TMP buildup and then ramp up the flux in steps over 1 to 2 week periods to get to 200 gfd.  I haven’t seen more than a few weeks operation at anything near 200 gfd in the published papers. Whenever I’ve been involved in a pilot study with polymeric membranes it has been necessary to run at stable operating conditions for at least 30 days. Why is the bar lowered when ceramic membranes get evaluated? Note the Mandaree ND ceramic pilot study did have stable operating periods of at least 30 days at 120 gfd.

 Another criteria for setting design conditions for polymeric membranes is to be a little conservative on the design flux compared to what the manufacturers or pilot studies claim is possible, so if a pilot study shows a flux of 60 gfd is possible based on the feed water quality, the engineer will allow 50 gfd for the full-scale system. While the ceramic membrane companies may claim 200 gfd is possible, when it comes to the design, I haven’t seen more than 120 gfd allowed. Even so, polymeric membranes can be disadvantaged from years of full-scale experience and require a more conservative design flux while ceramic membranes can claim aggressive fluxes without past full-scale experience to suggest otherwise.

 Does Ceramic have a Smaller Footprint?

The claim is often made or implied that due to higher fluxes, ceramic membrane systems have a lot smaller footprint. I will prove to you that is absolute baloney! Let’s look at the comparative footprints of polymeric and ceramic systems. For polymeric, I’m going to use Toray’s HFUG-2020AN module which has 969 sq.ft. of surface area and is probably the most popular polymeric membrane on the market currently. Compare this with a Nanostone ceramic module at 258 sq.ft. per module. A Nanostone module has around the same diameter as a Toray module and is around 9 inches shorter, so the footprint of a membrane rack is the same for both modules (ie. a rack with 40 Toray modules is the same size as a rack with 40 Nanostone modules). Therefore, a Nanostone module needs to have 3.8 times the flux of a Toray module just to have the same footprint based on surface area per module. So, if the polymeric module is designed for a 50 gfd flux, the flux through the Nanostone module needs to be 190 gfd to match the Toray module footprint. If the design flux for ceramic is 150gfd, the Toray system at 50 gfd will have a smaller footprint.

 Now let’s look at a Cerafiltec flat sheet submerged system. These membranes are supplied as 64.6 sq.ft. modules that have a footprint of 28” x 22.7”. Based on Cerafiltec’s website, these modules can be stacked in towers 16 high, so that would add up to a surface area of 1034 sq.ft. From the photos I have seen on the website, the tallest I saw was 8 high, but I will be conservative and compare the footprint of a 16 high tower versus Toray modules in the same footprint. The Toray modules are 8.5” diameter, so within the footprint of the ceramic flat sheet tower, you could conservatively fit 4.5 Toray modules allowing for spacing between the modules (see Fig 2). Therefore a Cerafiltec tower at maximum height needs to have 4.2 times the flux of a Toray module to have the same footprint, i.e. if the Toray module flux is 50 gfd, the submerged ceramic system needs to flux of 210 gfd to match the footprint.

Figure 2: Polymeric versus Ceramic Footprint Comparison

So, I hope I have made it clear that flux is just a number and a high flux does not mean that a membrane system will have a smaller footprint. You also need to consider the amount of membrane surface area that will fit within a given footprint and that ceramic modules have a lot lower surface area than polymeric modules. The price of a ceramic membranes compared to polymeric modules on a membrane surface area basis is also a lot higher, so you can’t assume a higher flux also means a lower cost.

 Of course, there are other important considerations when comparing polymeric to ceramic membranes such membrane longevity and lifecycle cost. I have mentioned in a previous post that the longevity of the newer polymeric membranes is much improved over earlier polymeric membranes which has narrowed the lifecycle benefits of ceramic over polymeric. I’ve also calculated that when you consider the requirement of a coagulant dose ahead of ceramic membranes, the lifecycle cost of polymeric membranes can be lower than ceramic. I will elaborate on that in a future post.

*Shoutout to Stuart Leak from Avista who first used this acronym in his presentation What the Foulant.

The comments and opinions in this post are my own and not those of my employer.

PFAS Discharges into Sand Creek from Suncor’s Denver Refinery Must Stop

Suncor Refinery alongside Sand Creek - Photo by Hyoung Chang, Denver Post

I have been stewing over whether to do a post on an article I saw in the Denver Post on July 27, 2023, regarding discharges of PFAS from Suncor’s refinery in the Denver area into Sand Creek which eventually makes its way to the South Platte.  For years I have been hearing local news stories of concerns from nearby communities about air emissions from the refinery and allegations of exceeding EPA and Colorado Department of Health and Environment (CDPHE) permit levels. I have wondered if Suncor has been given some slack due to its position as a major fuel supplier in the region. Whenever the refinery is offline due to maintenance, etc., fuel prices spike which impacts the wider community’s hip pocket (does anyone keep their wallet in their hip pocket anymore?). Is that allowing Suncor some leverage over CDPHE’s permitting process? According to the Denver Post article, Suncor had been operating on an air quality permit from 2006 that is supposed to be updated every 5 years. The permits for water and stormwater discharges were last updated in 2012.  Of course, having a permit does not mean Suncor adheres to it and there have been reported incidences of benzene spills into Sand Creek over the years as well as air permit exceedances.

South Platte’s PFAS Problem

Being in the water industry and seeing the great expense many water utilities and communities are facing to meet upcoming PFAS regulations, when I read about how such high levels are being discharged from Suncor into a drinking water source used by so many Coloradans it really hit a raw nerve for me. Pretty much any water treatment system taking water from the South Platte in the Denver Metro Area and East, including nearby wells, will have to implement some sort of treatment for PFAS removal. The cost for treatment is in the millions to tens of millions of dollars each, depending on system size. While the drinking water PFAS regulations are still being finalized, many water systems are already making plans to install treatment, since it can take years to get the funds and construct the required treatment equipment (typical solutions are GAC, Ion Exchange or Reverse Osmosis).

Suncor’s source of PFAS is likely firefighting foams used onsite, although I’m not familiar with refining to know if any raw materials contain PFAS also. This contaminates groundwater under the refinery and according to the Denver Post, Suncor treats this groundwater before releasing to Sand Creek, although obviously it not treated for PFAS removal yet. Admittedly, PFAS has only been identified as a concern in drinking water relatively recently (since 2016) and drinking water regulations are still being finalized. But Suncor was issued a draft permit by CDPHE in 2020 to release no more than 70 parts per trillion into Sand Creek. Note in June 2023 Suncor reported to the CDPHE a discharge level of 2,675 ppt…this is after Suncor apparently installed in interim treatment system to reduce PFAS to 70 ppt in early 2022.

The Denver Post article reported that Suncor estimated it would take 3 years and millions of dollars to build a permanent system to remove PFAS from wastewater before discharge into Sand Creek. Suncor also said PFAS removal is extremely difficult and treatment technologies are still in development. These statements really raise my hackles. First of all, established treatment technologies for PFAS are available now – Reverse Osmosis, Granular Activated Carbon (GAC) and Ion Exchange are well proven and already in use for PFAS removal by water utilities. Secondly, if the stormwater is already being collected for treatment, a lot of the hard work is already done and it would not be difficult to add GAC or ion exchange to the treatment train. Much larger treatment systems have already been installed on contaminated Californian ground water supplies in a quick response to the detection of PFAS and the interim regulations. So don’t try to say the technologies are not yet developed! Locally, there are also treatment systems installed at water utilities south of Colorado Springs where they detected PFAS in the ground water supply originating from a local military base.

While Suncor continues to discharge PFAS into Sand Creek, communities downstream are paying the price with their health and their money where the local water treatment plants must pay for treatment.

The article in the Post was written in late July, so Suncor may very well have accelerated installing treatment for PFAS removal since then, since the media is quick to report a violation but often slow to report on a resolution. If so, then I retract some of my vitriol for Suncor not taking action.

The comments and opinions in this post are my own and not those of my employer.

“So your saying there’s a chance” - Dumb Bid Evaluation Processes

 I saw a bid evaluation process recently for membrane equipment that I hadn’t seen in about 10 years. I thought this type of evaluation had seen its last days with the demise of the bids that only allowed the ‘big-three’ proprietary system suppliers (Pall, Memcor, Zenon). I guess there are some engineers/owners still living in the past who don’t realize that bidding processes of the old days are not relevant for evaluating between todays’ membrane system suppliers (MSSs).

This particular bid process required bidders to provide in one envelope (#1) a technical proposal, including qualification and experience criteria, and in the other envelope (#2) the pricing and other commercial information. The owner and/or owner’s engineer would review the technical proposal and select the best qualified submission and only open the pricing proposal for that bidder. If the price met budget they would start negotiations to award to that bidder without looking at pricing for any other bidders. Out of the four MSSs invited to bid, one of these was one of the big-three and would clearly have the most references and be chosen as having the best score out of the technical proposals. So why would the other three bother bidding? Maybe some would hope the favorite in the race did not turn up for some reason?

In the old days, the big-three would bid nearly everything to try get market share in a fast growing and evolving market. Well hello, the MF/UF market is now quite mature, MSSs are often bidding with the same membranes supplied by independent vendors and decisions on whether to bid or not are based on whether the project can be profitable rather than buying market share. So, if you don’t have an open and fair bidding process, there may be only one bidder, which does not look good for the writer of the specifications.

This bidding situation had the look of the engineer/owner really wanting to select one manufacturer while keeping that manufacturer’s price honest. As long as the price is within budget, that manufacturer’s price could be higher than all others and the owner would never know. These days for MF/UF system procurement it is common to see a prequalification stage where a short list is made of manufacturers based on experience, company financial stability, references, local service, etc and then these bidders have a competitive bid based on price. That way the owner and engineer are happy with the quality of the bidders and the owner gets the best price from these bidders.

Another bidding process that is a combination of the above has a scoring matrix where price (or NPV) is say 40-60 points out of 100, with the rest of the points spread across reference installations, local service capabilities and other factors. This evaluated bid process can still allow the engineer/owner to pick the MSS they prefer using the subjective scoring factors, as long as the pricing of the preferred vendor is not too high. But at least all bidders will get their prices considered and therefore more MSS’s will likely bid, even those scoring lower on the non-price factors. As Lloyd said in Dumb and Dumber “So your saying there’s a chance”. I still think this bid process is not ideal, but if it is an open bid with no favorite, I’ll take this this type of evaluated bid over the two-envelope lucky draw...

Of course, if I am in the shoes of the preferred manufacturer with the best experience, I’ll take the ol’ two envelope bid process but sooner or later when this process yields only one bidder, somebody will end up looking dumb…

The comments and opinions in this post are my own and not those of my employer.

Gasson Spices up Membrane Technology Conference Opening Session

(Not one of the keynote speakers)

This year’s Membrane Technology Conference (MTC) in Knoxville TN, February 20-23, saw a spike in attendance, almost back to pre-covid levels, with a definite buzz around the presentations and exhibit hall where attendees were excited to be back networking with colleagues and technology suppliers.

Christopher Gasson, Publisher of Global Water Intelligence, was a keynote speaker for the Opening General Session, along with Harry Seah, CTO of PUB. Christopher’s ‘State of the Global Membrane Industry’ presentation certainly provided a spicey opening to the conference with his description of ‘What’s Hot and What’s Not’. Some exhibitors in the audience that were on Christopher’s ‘Not Hot’ list may have begged to differ. These included manufacturers and developers of ‘Fancy Membranes’ which I assume referred to new chlorine resistant membranes and fouling resistant membranes among others. From a global market share perspective, he is probably correct, but companies such as ZwitterCo are likely not trying to take the place of traditional RO membranes and are content targeting niche markets.

Other technologies or technological trends on the ‘Not Hot’ list included higher recovery for seawater, higher flux RO membranes and lower pressure desal membranes.

On the ‘Question Mark’ list included ceramic membranes and Universal/Open Platform low pressure systems.

During questions, Hary Seah agreed to disagree on the potential for ceramic membranes where PUB is a big advocate of ceramic membranes at its plants in Singapore. I’ve given my thoughts on the ceramic market previously and copped some flak for saying it is a niche technology, but I would agree with Christopher on his position.

I also agree that the Universal/Open Platform low pressure market may have cooled a little now that there are many direct replacement modules available for Asahi (Pall), Memcor, Toray and Dupont modules, which gives some flexibility for future membrane replacements without needing a membrane rack to accommodate modules of different configurations. Also, the proliferation of non-proprietary MF/UF systems using modules from Toray, Dupont and others has taken some steam out of the need for Universal racks. I will flesh this out further in a separate post.

 On the ‘Hot’ list were higher recovery RO in industrial applications (not seawater) which I assume is technologies such as CCRO, Pulse RO and FRRO, polymeric NF (NX Filtration), RO/NF membrane spacers, brine mining and digital monitoring (AI). Christopher pointed out that NX Filtration is capitalized at over €500M with revenues of €8M last year, having investment characteristics of a start-up tech company and a lot of pressure to perform.

I must admit I haven’t been to many opening sessions at MTC, but this one was very well attended, possibly in anticipation of the speakers’ topics. The audience was not disappointed, and Christopher’s thought-provoking statements provided a great catalyst for discussion afterwards and set the stage for a very lively conference.

The comments and opinions in this post are my own and not those of my employer.

Good Projects Spoiled by Bad Contractor Selection

 

Something that really perplexes me is how engineers and owners can put so much effort into the design of a plant, ensuring equipment vendors and components are well qualified and tightly specified, then the project is put out to bid and awarded to the contractor with the lowest price. Then it is a crapshoot if the contractor has the experience or capability to complete the project….

The contractor is the most important part of the project. They are responsible for taking the process equipment specified and all the surrounding infrastructure and turning it into a functioning water treatment plant. So why are there so many instances where unqualified, low-bid contractors win these projects?

When an incompetent contractor runs into trouble with schedule or budget when he/she missed something in the specifications, he is going to do what he can to deflect the blame to try keep the project profitable and avoid LDs. That often ends up in conflict with process equipment vendors to improve schedule to make up for poor project management, and drawn-out payments to vendors because the contractor can’t get approval for achieving project milestones. So many times I have heard the excuse from contractors that they can’t pay for start-up because they haven’t been paid for the practical completion milestone. That is compete BS when the equipment has been delivered and started up months ago and the contractor can’t get his s - it together to finish the landscaping or install the toilets… Just as frustrating is when start-up is delayed for months because the contractor is behind with installation, meanwhile the component vendors for the process equipment must be paid, so we go back to the old story of the process equipment vendor also acting as a bank for the project… (see previous post). All of this leads to conflict between the owner, engineer, contractor and OEMs and nobody feels good about the project.

Don’t get me wrong, I’m not out to bash all contractors. I have worked with a lot of very competent water treatment system contractors. And process equipment vendors are not always without blame for delays and missing items in the specifications. I have also seen specs where it wasn’t clear who was supposed to provide some items, so nobody had them, which is on the engineer who wrote the specs. My gripe is really with the process of not prequalifying contractors and ending up with a rudderless ship of a project. Similarly, process equipment vendors should be pre-qualified and most of the time they are, but when they are not it opens up the possibility of any garage integrator throwing in a price. Which takes me back to my original point – why spend so much time designing and specifying a plant and then leaving the execution in the hands of a random low bidding contractor?

Don't Blame the Pandemic

Admittedly, these days in some cases it has been hard to find contractors to bid projects. So, standards may be lowered to get competitive bids. Before a job goes out to bid, there has to be an awareness of what else is bidding locally that will cause contractors to pick and choose what to bid. I have seen bids delayed so as not to overlap with a larger project bidding in the region, which is smart. I have also seen cases where a bid is due just before a board meeting to approve the winning bidder, so there is no room to delay the bid for scope clarifications or to allow contactors more time to prepare, so bidders drop out. This happens so many times. An engineer spends a year or more pulling the spec together then allows 4-5 weeks for contractors to get a bid together and there is no flex in the bidding schedule to give contractors a few more weeks. Not smart!

 While recent years have made this situation worse with supply chain delays and a shortage of contractors to bid projects, unqualified contractors winning water treatment projects has been going on for years and is not a symptom of the pandemic. Engineers and owners need to put more thought into  the bidding process to ensure they get a competent contractor which will ensure a much more successful and harmonious project for all involved!

IDA 2022 World Congress a Global Meeting of Desal Minds

After changes of venue and multiple delays due to the Covid pandemic, the 2022 International Desalination Association (IDA) World Congress was finally held in Sydney Australia, October 9-13. It is the first time I have been to this conference, or any truly international water conference for that matter, and it was exciting and inspirational to see the global networking and established relationships across continents and the open sharing of technical knowledge and experiences. Everyone was drawn together by a common interest in water treatment, mostly by desalination, and protecting the earth’s most natural resource, no matter the country, language or culture. I may sound a bit cliché, but I was truly moved by the spirit and sense of common cause of the conference.

What’s New is the World of Desal? Brine Mining!

The main focus of the technical program was seawater desalination but there were some interesting topics and new developments being discussed in the desal world. Most notable to me was how to handle waste concentrate and a lot of interest in brine mining. Highly concentrated brine is being seen as a potential resource for rare earth metals, including lithium. First there needs to be processes to concentrate brine higher than conventional seawater membranes and companies such as Gradient and Toyobo presented on osmotically assisted RO (OARO) processes that can concentrate brine from a seawater process up to 130,000 mg/L TDS without needing significantly higher pressures. Osmotic assistance is provided by applying a saline stream on the permeate side, which lowers the osmotic pressure difference across the membrane, allowing permeate production at feed pressures less than the osmotic pressure of the feed. There is also interest in ultra-high pressure membranes and housings for achieving higher seawater recoveries and therefore higher brine concentrations, but I think if the counterflow processes are feasible, they are a safer and probably lower energy option.

 Once you have the highly concentrated brine, you have to extract the valuable constituents and from one presentation I saw from Dr. Monsalvo from Aqualia, that involves a lot of treatment steps… So it looks to me the recovered metals would need to be very valuable to offset the high cost of extraction. With world shortages in these elements, I’m sure with continued research the extraction costs will go down making these processes more feasible. There is no shortage of research in this area! There were also many presentations looking at minimizing the environmental impact of brines, indicating the industry realizes this needs to be addressed to ensure desalination is a viable water supply solution into the future.

Wastewater reuse also had a prominent share of the program, recognizing the role of desalination in reuse applications, with several dedicated sessions and two panel discussions, one of which I was very pleased to participate on.

The IDA Water Reuse Panel I was excited to be part of

I was also very impressed with how the technical sessions and panels were all conducted in the exhibit hall in walled-off areas, so it was easy to jump from session to session or to a panel discussion without leaving the hall. Meals were also served in the same area keeping attendees together all day. This is a great model for other conferences if it is logistically possible.

I can’t say I have anything negative to say about the show. Very professional production, great technical content, great networking, awesome venue! As long as you were able to get to Sydney… 

The comments and opinions in this post are my own and not those of my employer.

Manganese Removal Ain’t Manganese Removal!

 

I was looking at specifications for a project earlier this year that had very tight targets for iron and manganese (combined target of >0.06 mg/L) but there was no pilot data to back up that these targets were achievable. Bidders were required to guarantee these limits would be met by the specified pressure filter system with Greensand Plus media. When there was pushback in guaranteeing the performance of the system (that the engineer had designed) without any prior testing to show this was achievable, the response from the engineer was that there were other Greensand Plus filters in the State that were achieving these levels so there should be no issues making the performance guarantee…

This was essentially saying that the performance of a treatment process on one water source should be expected on a totally different source water without considering the water quality of the two sources. Anyone who knows anything about water treatment knows while iron is relatively easy to remove, manganese is a totally different animal. While manganese may be easy to remove on one water source, it could be very difficult to remove on another.

 In Chapter 3 of the AWWA ‘Iron and Manganese Removal Handbook, Second Edition’ the following statements are made:

• Oxidation of Fe and Mn: Manganese Dioxide (manganese in the oxidized form) forms a far finer floc (than ferric hydroxide), so fine at times that a granular media filter will not remove it.
• Organic Complexing of Fe and Mn: Operators experiencing difficulty in removing Fe and Mn (especially Mn) have uncovered some common factors:

o   A level of organic carbon (TOC) over 2 mg/L

o   Some level of ammonia or hydrogen sulfide in the feed water

• Adsorption Removal Methods (my summary): Manganese is best removed by adsorption on a manganese dioxide media like Greensand Plus or Pyrolusite. Iron is best removed by precipitation/filtration because iron adsorption blinds the media. Therefore, when both are present, the best process used is a combination of iron oxidation/filtration and manganese adsorption.

Further to the last point, oxidation of manganese takes a much longer time than iron where you are looking at from seconds to a minute for iron (Chapter 5, Chlorination) and up to up to 30 minutes or longer for manganese. Therefore in a filter system where an oxidant is dosed in the feed piping to the filters you can have adequate time in the piping and space in the filters above the media for iron oxidation (a few minutes) while allowing adsorption removal of the manganese.

There was also a very good article in AWWA’s Opflow in December 2021 titled “Evaluate and Optimize Manganese Treatment”. This article explains that the form and levels of manganese can vary considerably between wells. All manganese removal methods described in this article are based on sorption to the filter media. Therefore conditions must be optimized for the sorption mechanism on manganese oxide coated media including ensuring there is a free oxidant residual to provide a continuously regenerated adsorptive surface. The pH also impacts the Mn reaction kinetics with pHs above 7.0 more favorable.

As mentioned above, TOC, ammonia and H2S create a chlorine demand which impacts the chlorine available to oxidize the Fe and regenerate the filter media for Mn adsorption. Because the iron oxidation reaction is a lot faster compared to TOC, you typically get iron oxidation in the presence of TOC, as long as the iron is not organically bound to the TOC. When ammonia and H2S are present you may need a higher chlorine dose to overcome the demand from these compounds and provide sufficient iron oxidation. While you are not trying to remove manganese by oxidation/filtration, you still need a free oxidant residual to keep the manganese dioxide media regenerated so that is adsorbs the manganese. Therefore, a water with a high chlorine demand can impact the ability of the media to adsorb manganese. If ammonia is present, potassium permanganate may be a good option rather than chlorine as the oxidant because it does not react with the ammonia.

If iron and/or manganese is complexed with organics, the oxidation process can be significantly impacted. At a minimum, a higher oxidation dose and longer oxidation time will be required and if this works you could still create another problem with the formation of disinfection byproducts. Coagulation may be a better option to remove organically bound manganese and possibly iron also.

So clearly, iron and particularly manganese removal chemistry is not simple, and you can’t assume if the Fe and Mn levels on one water source are similar to another water source that a particular treatment technology will work equally on both. Other constituents in the water source impact removal performance and must be taken into consideration and ideally bench and/or pilot testing should be conducted to confirm the effectiveness of a proposed treatment process. To steal a saying from an old Mobile oil commercial, Manganese Removal Ain’t Manganese Removal!

The comments and opinions in this post are my own and not those of my employer.

Has Ceramic Membranes Missed its Window of Opportunity?

 

Some ceramic membrane advocates may not like what I am saying here, but I believe the window of opportunity in the U.S. for ceramic membranes is closed… Ten to fifteen years ago when many of the polymeric membranes on the market had significant integrity issues, there was a lot of interest in ceramic membranes offering warranties of 20 years or more and virtually no breakages over this period. At that time the leading manufacturer of ceramic membranes for large municipal systems was Metawater (know as NGK up to 2008) with a large installed base in Japan. Originally Metawater had an exclusive arrangement in the US to sell through Kruger and a contract for a 5 MGD system was secured with Parker CO around 2009. At this time, Memcor and Zenon, two of the largest membrane system suppliers at the time, had experienced a lot of membrane integrity issues at many installations helping to create a lot of interest in ceramic membranes. Despite this interest, high costs of ceramic membranes and the systems prevented adoption for drinking water applications at any other large-scale installations (see my 2011 post). Around 2015, when Metawater had started selling their ceramic system directly rather than through Kruger, a 7 MGD system was installed at Butte MT. I wonder if selling through Kruger was not the best strategy, where Kruger was not well known as a membrane system supplier and had a large suit of established water treatment technologies (such as Actiflo) that would have diluted the sales and marketing effort towards its ceramic membrane systems. I think the opportunity was missed to sell a lot more ceramic membrane systems 15 years ago.

Membrane Integrity Advantage over Polymeric has diminished the Past 10 years

At the time that Memcor and Zenon were having their membrane integrity issues, Pall with the Asahi membrane was quickly establishing a reputation of having a very robust membrane with minimal fiber breakages and was quickly gaining market share. Riding on the back of Pall’s success, around 2010, companies such as Toray and Dow (now Dupont) brought membranes to market that had similar fiber thicknesses, same material (PVDF) and were outside-in pressurized modules as were Asahi’s. As OEMs such as Wigen Water Technologies and H2O Innovation installed systems with these membranes it was found that these membranes did have significantly improved integrity compared to the earlier Memcor and Zenon submerged membranes. I do have to mention that as the early pioneers of large-scale MF and UF membranes, Memcor and Zenon were learning on the run about membrane materials, module construction and cleaning regimes. The later entrants to the market have capitalized on these developments to produce very good membrane modules the past ten years.

With much improved polymeric membranes available now, plus the ability to have Open Platform/Universal MF/UF racks, I do believe the opportunity for wide adoption of ceramic membranes for standard municipal applications has passed. I discussed this with some ceramic membrane veterans (ex Metawater, PWNT and Nanostone) at AWWA's ACE in San Antonio last month and they said there are still good opportunities in Europe for replacing some of the older, poor performing UF membranes (I assume these are inside-out PES membranes), none of which really gained traction in the U.S., with the exception of the Inge/Dupont multibore membrane which is a lot stronger than its predecessors. But I have to say it looks like ceramic membranes will remain to a niche product in the U.S. in the foreseeable future as I predicted in my post back in 2011.

The comments and opinions in this post are my own and not those of my employer.

Equipment Supply Contracts Should be Thrown Out and Started Again

 It is time for OEMs and Contractors to make a stand!

Ever since I have been involved in the capital supply business in North America, equipment procurement contracts in the water treatment industry have treated suppliers as banks for contractors and owners, with ridiculously long price validation periods, crippling liquidated damages for delays and uncapped liabilities. Well maybe the times are finally a-changin’!

In times of low inflation, stable government, no pandemics, reliable supply chains, no conflicts in regions with critical raw materials and a competitive contractor bidding market, perhaps the contracts of the past presented less risk to OEMs. How long ago has it been since we were in that situation??

Contracts that require the OEM to hold a bid price for 90 days before award and then when awarded, hold the price for 1-year before delivery (and I have seen up to 3 years) can’t be accepted anymore. That is being a bank for the contractor and owner where the OEM is financing the project, having to pay material suppliers well in advance of shipping the equipment (where delivery is often the major payment milestone) and absorb any price increases from the original quote from a vendor (which could be provided weeks before the bid) through submittal preparation and approval and notice to commence manufacturing which is often at least 6 months and longer for major process equipment. And that was a concern before the current supply chain issues! Not to mention preselection or direct bids as is often used for membrane systems, where following submittal approval the owner then goes to bid to contractors to install the equipment – the lead time from original quotes to actually getting the notice to commence manufacturing is often a year or longer. Engineers and owners are in for a rude awakening to OEM responses to contract terms for preselection or direct bids in the future…

Here are a few examples of how current market conditions have brought OEMs to the tipping point of outright rejection of traditional contract terms:

Following the concern with nickel supply because of the Ukrainian war, suppliers of stainless steel are only holding quoted prices for 24 hours. How can you bid a project with stainless vessels and piping without significant risk of margin erosion or even losing money? After the pandemonium in the nickel market a well-known manufacturer of stainless steel cartridge filter housings voided all quotes given before March 4. So what about the bids you used their pricing for prior to that date? Is that a case of Force Majeure?

Allen Bradley components, the predominantly specified controls for water treatment systems, already had stretched lead times from 8 weeks to 24 weeks earlier this year. Then there was a Corona Virus outbreak in Shenzen, China’s silicone valley, where some AB components are made – now AB is not committing to any delivery schedule… How then can you sign a contract with LDs when you don’t know when you can get a critical component required to operate the system? And what about contracts you signed in 2020/21 before there were these delays – that is certainly Force Majeure! I feel that controls components have become the toilet paper of the water industry with end users and equipment manufacturers hoarding them where they can, increasing leads times further...

Some may say that OEMs should just build in contingency to prices when it is known how long the price is to be held for. So when we bid a project in January where the price is to be held for 90 days before award, how do we know there is to be a war between Ukraine and Russia that starts in late February resulting in nickel prices skyrocketing in early March and stainless steel prices doubling in days? And that is only 40 days after the bid? And then ten vendors are listed on the bid, some you have never heard of, and you have to hope all ten will have same concerns as you and object to the same contract terms or put in the same contingency…

Some may say why not order materials as soon as submittals are approved to reduce the risk of price increases. This is the bank situation again. Then the OEM must pay for these materials often well before they are delivered, creating a cash flow problem, and what if the project is delayed? Will the owner accept and store the equipment when built and pay for it? Most likely not, but that is an option that should be seriously considered. Contractors on the other hand keep time sheets for work conducted and are paid for labor and materials received on site on a monthly basis. OEMs are not paid a penny for factory labor used in building the equipment each month and rarely paid for materials received in the factory.

Contractors and sometimes engineers often respond to OEM exceptions to LDs and unreasonable liability limits saying they are passing down what they have in their prime contract with the owner. Well, contractors and engineers need to show some guts and take exception to the contracts being passed to them by owners. In these times, nobody can guarantee meeting a schedule. Owners have to face reality and think of a different way to ensure contractors make their best effort to meet schedule and budget.

Currently, OEMs and contractors have a unique opportunity to change the draconian contract terms they have begrudgingly accepted for decades to terms that are fairer for all parties involved. If contractors and OEMs unite and show some gumption in objecting to these traditional one-sided contracts, OEMs may not need to be financing projects anymore and with better cash flows on projects, prices may actually come down, where lower margins are more feasible. That would be a win-win-win for OEMs, contractors and owners!

The comments and opinions in this post are my own and not those of my employer.

Why Membrane Module Manufacturers should not use Independent Sales Reps

 

In recent years a few of the membrane module manufacturers have been using independent sales representatives which I believe is a bad idea and a case of biting the hand that feeds you. Typically, module manufacturers’ internal salespeople, and I am referring to MF/UF modules here, have directly sold to OEMs/System Integrators as well as marketing to end users and consulting engineers so that their products get specified. I am perfectly OK with that. What I am not OK with is the module manufacturers signing up independent sales reps to sell their products which opens up a can of conflicts. Let me clarify that I am talking about new MF/UF systems and not replacement modules at existing systems. I get that some new module suppliers on the market want to find opportunities ASAP and see independent reps as a way to get directly to engineers and end users rather than have to go through OEMs, but this is going to do more harm than good for the following reasons:

The module manufacturers don’t build the MF/UF systems and won’t be bidding the projects, so they still need OEMs to bid with their modules. The rep may also represent one of the OEMs bidding a project who may or may not want (or be able) to bid a system using that module and that likely will prevent competitor OEMs from bidding with that module. So now there is possible conflict created between the rep, his OEM and the module manufacturer as well as conflict between the module manufacturer and other OEMs. At best you may get the rep’s membrane system OEM bidding with the module, assuming that OEM isn’t a proprietary system supplier (Pall, Suez, Memcor/Dupont) and is willing to bid with the module. You also have to understand the dynamics between reps – the module rep will expect a commission for a sale whether his OEM or a competitor’s OEM wins the job as long as the module is selected. Competing reps that win the job don’t want to see commissions going to their competitor for the membranes and will therefore encourage another membrane to be used. This is a very messy arrangement (and difficult to explain) and is going to steer many reps and OEMs away from using the module.

I understand that the objective of using a rep who may be close to the specifying engineers, is to get the membrane listed in the specs and ideally flat spec’d so all OEMs have to use it. It is a very rare situation where you will get a module flat spec’d so in the case where it is listed with other modules, at best only the module manufacturer rep’s OEM will bid the job with that module. I had a project a few years ago where one such module was listed for a project and our sales rep represented that module as well as another OEM who was also listed for the project (not an ideal situation for an OEM but with all the mergers, etc in the industry you can end up with a rep having two competing OEMs). I called the module manufacturer for a quote and was told “sorry we are teaming with the other OEM on this one, but would love to work with you on another project”….. That is the last time we seriously considered that module and it wasn’t long before we also found a new rep in that region.

Before I get some module manufacturers too angry, I’m not talking about membrane replacements on existing systems where there is no role for the OEM. In that case it can make sense to have a rep involved to get the new replacement module qualified and help with the bidding process. But the reps should not be provided any incentive to push this module on new systems and risk opening the can of conflicts.

So how does a new module manufacturer get to market? Obviously, you have to sell to OEMs with the objective of having as many as possible bid a project to increase the chances of the module being selected by the winning bidder. In parallel you have to go direct to the engineers and end users to get a comfort level with the module and have it put in the specification. This latter point is very important. As an OEM, you have a lot of options (this applies to RO membranes also) and OEMs often don’t have time to market a new product to get it spec’d. There are exceptions when the OEM sees an advantage in bidding the new product, but in this crazy busy world right now, very few have time to pause and find the right opportunity do this up-front missionary work. So that is why some module manufacturers are using reps, right? I get it, and it may help on a specific project if all the stars align but in the long run to maximize sales opportunities it is better for module manufacturers to not use reps. Don’t bite the OEM hand that feeds you!

The comments and opinions in this post are my own and not those of my employer.

’21 Membrane Technology Conference Exceeds Expectations – The Wrap

With almost 600 attendees, around 200 more than expected, the 2021 Membrane Technology Conference (MTC) at West Palm Beach, July 19-23, was a resounding success! While this show normally has 900-1200 attendees, getting 60% of this number was a fantastic result for the first National water industry conference since the Covid cancellations (this show was cancelled the week before it was due to be held in early March 2020).

So why was MTC such a success?

For me, it was seeing the beaming faces of colleagues reuniting face to face after 18 months or more of working at home. The networking opportunities that can’t be replaced by Zoom calls. The large parties of conferences past were not held but the outdoor bar at Copper Blues became a popular hangout after dinners each night.

While the technical program had a few less sessions, the quality of the presentations I went to was excellent. One thing I noticed that was a lot different from other years was a lot livelier discussion after presentations – maybe people were bursting to be heard after being locked up for so long. Whatever the reason, it was great to hear these discussions.

There were less exhibitors this year, maybe 70% of other years, but the turnout was still strong and provided a great opportunity for delegates to catch up with manufacturers. Representatives from some manufacturers who didn’t exhibit were still present. Of course, there have been a lot of acquisitions since the last MTC in March 2019, so for instance, Dupont, Inge and Memcor shared a large booth for the first time.

 I think the timing also helped with a late surge of registrations. In late June/early July the country was very optimistic about vaccines slowing Covid and the Delta variant was in its early stages.

 What was new?

The hottest technology trend that I saw was a large number of presentations on novel high recovery RO processes that are now being adopted full-scale. We have heard of CCRO applications at past shows and also this one, but we are now hearing of Pulse Flow RO and Reverse Flow RO starting to be scaled up, so the folks at Dupont/Desalitech may have some competition in the near future. I still think these are niche technologies that are a fit in certain situations and not yet mainstream technologies, but I’m open to changing my mind as more data from different applications at full scale installations becomes available.

Congratulations to AMTA/AWWA for taking the risk with the first national in-person water conference since the Covid shut-downs and pulling off a great show! With this years MTC delayed 4 months due to Covid, it wont be long until MTC22 in Las Vegas, February 21-15. I can’t wait!

Increasing RO recovery is not just a case of adding stages!

I had an engineer recently tell me he was working on a project where they needed to minimize RO brine volume and he wanted at least 90% recovery, so please quote a 3-stage system… Antiscalant projections on the raw water quality showed 78% recovery at best, even with acid dosing. The chemistry won’t allow any higher recovery on this water on matter how many stages the RO system has, and don’t get me started on whether CCRO can do better (I’ll discuss this later).

That is the fourth inquiry like this I have had in the past 6 months and the second from this engineer who is finding it hard to understand the limitations on recovery… so I thought I would put the explanation in print here.

Before you start to think of how many stages you need to design the RO system for, you first need to look at the water chemistry to see what recovery is possible. All the antiscalant manufacturers have projection programs where the raw water quality data is entered, an antiscalant is selected and from the empirical data the program calculates the maximum recovery that can be achieved and what are the limiting salts. You can adjust the feed pH to see the impact of pH correction and you can also change some feed parameters so see how pretreatment will impact recovery. At this point, stages do not even come into the equation. For a customer that wants to get as high a recovery as possible, I also often ask the antiscalant suppliers to do a projection for me, because sometimes they have a product I may not be aware of or that is not part of the projection software version I have.

PLEASE NOTE - INCREASING THE NUMBER OF STAGES DOES NOT ALLOW A HIGHER RECOVERY THAN WHAT THE ANTISCALANT PROJECTIONS PREDICT!!! ALSO, INCREASING THE NUMBER OF STAGES DOES NOT ALLOW A HIGHER RECOVERY THAN WHAT THE ANTISCALANT PROJECTIONS PREDICT!!! Got the message??

Some antiscalant projection programs incorporate calculations on RO unit arrays, but I prefer to first optimize recovery then use the membrane manufacturer’s projection programs to design the best array – I just feel more confident with the RO/NF system design when I use the membrane vendor programs.

Now that I know the maximum recovery that is possible determined by the water chemistry, not the number of RO unit stages, I then go about working out how many stages are needed to achieve this recovery. When designing an array for an RO system there are several important design conditions that need to be accounted for, including crossflow velocity and flux across the membrane elements. The projection programs have built in warnings when these are too high or low. Operating outside the safe ranges will result in membrane fouling.

A 2-stage RO system is limited to up to 80-85% recovery because somewhere in this range you will violate the minimum crossflow requirements for the membranes. When the crossflow is too low you can get concentration polarization at the membrane surface resulting in scaling. By adding a third stage you can reduce the number of housings required in the first 2 stages to increase the crossflow velocity to within the desired range and add back those housings via the third stage to maintain the desired flux rate. For instance, rather than try achieving 85% recovery using a 4:2, 7M array at an average flux of 15 gfd at a permeate flow of 175 gpm which sends some low crossflow warnings for the first stage, you could change this array to a 3:2:1, 7M 3-stage system which has the same flux but the crossflows are better balanced across the membranes.

When attempting really high recoveries, where the water chemistry allows, you may even need to add a fourth stage. Another option to adding stages, is to recycle some Stage 2 concentrate back to the Stage 1 feed to increase cross flow velocity and allow higher recoveries but this increases the concentration of feed water constituents and subsequently the permeate quality is worse.

 And CCRO is not the silver bullet either!

Now a short discussion on ClosedCircuit RO (CCRO). The recovery rate of a CCRO system, like conventional RO, is limited by the chemistry and how much the feed water salts can be concentrated with antiscalant addition. In most cases, the recovery of CCRO is predicted by the antiscalant projections exactly the same as for conventional RO. Because CCRO purges the recycled concentrate every 15-45 minutes, if silica is the constituent limiting the recovery, due to the saturated silica concentration being reached towards the end of this cycle and the slower induction time for silica to precipitate once it reaches saturation (say 10 minutes), CCRO can push past the maximum recovery predicted by antiscalant projections. For that scenario, CCRO will achieve a higher recovery than a conventional RO system.

But for more common scalants such as calcium carbonate and calcium sulfate, the induction time is just seconds and the CCRO process offers no advantage over conventional RO if these are the limiting salts. I would be happy for someone to give me a good technical explanation how CCRO can achieve a higher recovery when CaCO3 and CaSO4 are the limiting salts because from my investigations I have not found one. Don't get me wrong, I'm all for new technologies that can improve on the recovery of conventional RO systems, but I also want to see good science on how this is achieved.

The main message I want you to get from this post though is the following:

INCREASING THE NUMBER OF STAGES DOES NOT ALLOW A HIGHER RECOVERY THAN WHAT THE ANTISCALANT PROJECTIONS PREDICT!!!

The comments and opinions in this post are my own and not those of my employer.