Reversing the RO flow in California

Aug. 16, 2022
The largest U.S. municipal scale development incorporating ROTEC’s Flow Reversal Reverse Osmosis innovation, the City of Santa Monica will increase water production without increasing the plant’s footprint.

Boasting some of California’s most stunning stretches of shoreline and world-famous pier, Santa Monica has embarked on an ambitious journey of water self-sufficiency.

Forget 2050 ambitions set for decades into the future. Instead, the city plans to become water resilient and self-sufficient by 2023. For the record, that's in several months’ time.

Using a “one water” approach, Santa Monica is reducing its reliance on imported water supplies.

The water ambitions include restoring the Olympic Well Field and upgrading the Arcadia water treatment plant – the beating heart of the city’s water supply. And the innovations to take the facility into the future are reminiscent of innovations from the past. A case of history repeating itself?

A brackish water desalination facility providing half of the city’s water, Arcadia will be the first major municipal installation in the U.S. to use Flow Reversal Reverse Osmosis (FR-RO) technology. Rewind to the 1960s when it was initially built, and Arcadia was similarly breaking new ground – playing host to one of the region's first ion exchange softener facilities.

Part of the plant’s innovative nature has been out of necessity. The facility has gone “above and beyond” typical processes due to a previous well contamination challenge, according to Sunny Wang, water resources manager at the City of Santa Monica.

“Arcadia is the heart of the city's water infrastructure, which has always had a multi-barrier treatment process,” he says.

Currently providing 50 percent of the city's water supply, this will increase to 60-65 percent. As a result, the 2023 goal is to combine this with imported water (1 percent), alternative water supply (19 percent), and conservation (20 percent).

Building a water self-sufficiency strategy

The $200 million investment program to achieve water self-sufficiency is part of a "one water" approach. The one water phrasing is part of the strategy to help Californians see water recycling and recharging groundwater supplies as commonplace and part of the normal water supply.

“There is no new water,” adds Wang. “We're leveraging whatever water we can, but it's a one water natural cycle. I explain to our residents that we're doing the same thing as the hydrological cycle, except we're using technology to accelerate mother nature and improve water quality.”

This "supercharging" of the hydrological cycle includes infrastructure improvements, efficiency programs, demand reduction, and local supplies.

It was in 2011 that the journey to water self-sufficiency started. Following an earthquake in the 1990s, the request came from the region’s imported water supplier, the Metropolitan Water District of Southern California, for the city to meet its water demand for a week solely on local groundwater as repairs were made on the Metropolitan Water District’s conveyance systems.

"That's really what started our city councilor thinking about the importance of being water self-sufficient and reducing our reliance on imported water supplies," adds Wang.

A combined threat of natural disasters and climate change urged the city and utility to see the critical need to reduce its reliance on external water supplies. The Department of Public Works Water Resources Division went on to develop a water self-sufficiency plan. The first draft was created in 2014 and further updated in 2018.

Avoiding scaling hazards

Engineering consultancy Brown & Caldwell and Walsh Construction are delivering the collaboration with ROTEC in a progressive design-build approach. Furthermore, a $10 million grant from the United States Bureau of Reclamation (USBR) has been used to trial and implement the process innovation.

It was a two-way race between closed-circuit reverse osmosis (CCRO) and the FR-RO system to improve the facility’s recovery rates. ROTEC’s FR-RO was selected, with the funding agency "really excited" that the city could maximize existing assets to reach ultra-high recovery.

“By implementing the flow reversal technology, we're hoping to increase our recovery to 90 percent or greater,” says Wang.

The city’s current RO system operates at a recovery of 82 percent. The inclusion of FR-RO, via retrofitting the existing four trains currently in operation, will increase the recovery rate to 90-91 percent, which allows for increased potable water production beyond that obtained from the inclusion of the Olympic Wells.

Simply put: for every 10 gallons of water treated, nine gallons of drinking water will be produced. Previously this was eight gallons. According to Wang, this is "critical because groundwater is also a limited resource”.

“The fact that we can produce more drinking water with the same amount of groundwater pumping is a plus, as part of our plan to be water self-sufficient and resilient,” he adds.

Arcadia is the first municipal scale development of its size in the U.S. to use the FR-RO technology. This follows a successful pilot with the City of Santa Monica that was operated for several months, leading to ROTEC’s selection for the project. What makes the development unique is the ability to increase water production without increasing the plant’s footprint.

Adam Zacheis, senior project manager at Brown and Caldwell, believes Arcadia could be a showcase project to demonstrate innovations.

“FR-RO incorporation does not require additional footprint, which is critical for this very tight and space-constrained plant,” he says. “The city is leading the way in implementing this promising new technology and can serve as an example to other agencies in the United States.”

Dr. Noam Perlmuter, CEO of ROTEC, the company behind the Flow Reversal technology, says the goal is to take traditional membrane systems "out of their stagnation" and dramatically increase the performance of RO systems.

“Working at high-recovery rates is no picnic, as it exposes the membranes in a system to the hazards of scaling,” he says. “The principle of FR-RO technology mitigates this by periodically changing the flow direction of the saline stream in traditional RO pressure vessels, preventing scale from forming on the membranes’ surface while simultaneously performing at ultra-high recovery rates.”

In order to use this technology in industrial-scale systems comprised of multi-stage tapered flow arrangements, ROTEC developed its unique and patented block repositioning methodology which isolates a group of pressure vessels into a block using pipes and valves.

Each block can then operate as either the first or last stage of the system, allowing the pressure vessels to spend the majority of their time as the first stage and only a small part of their time as the last stage. This ensures the block finishing its role as the last stage can recuperate and be cleaned from the scaling it may have endured, enabling the system to operate at ultra-high recovery rates.

By increasing recovery rates, it allows users to generate more clean water, utilize less raw water, and dramatically reduce brine volumes. Flow Reversal also minimizes OPEX, chemical use and clean-in-place (CIP) events, leading to a substantially more sustainable and eco-friendly water treatment approach.

 “The problem with RO systems today is that, due to the hazards of scaling, plants are reluctant to operate at high recovery rates, as this will subject their systems to membrane clogging. This substantially increases a plant’s energy consumption, and ultimately forces a plant shutdown to execute a clean-in-place (CIP). These CIPs expose the membranes to aggressive chemicals which can shorten their lifespan,” says Perlmuter.

“So we are approaching the challenge with a technology that allows you to operate at high recovery without being exposed to the hazards of scaling.

“Maintaining sustainable flux through RO membranes by inhibiting mineral scaling and limiting bio-fouling potential is the key to reducing energy consumption and maximizing water recovery for municipal plants,” adds the CEO.

Flow Reversal flows east

Elsewhere, the Singapore water agency PUB has pioneered the deployment of FR-RO and is even taking it one step further. Together with engineering consultancy Jacobs, ROTEC has been selected to include its technology in a third NEWater factory at the Changi Water Reclamation Plant.

Known as CNF3, the development will be one of the first reclamation plants globally to use Membrane Bioreactor filtration to feed RO membranes. Design of CNF3 is underway, with construction expected to begin in late 2024.

This follows the success of earlier collaborations with PUB in 2017 on the Kranji NEWater development and the TUAS water reclamation plant.

Dr. Perlmuter believes Santa Monica is a case of demonstrating innovation, not just talking about it. The water self-sufficiency plans, including Arcadia, put the utility in the ranks of the more progressive water utilities.

"It's one thing to say that innovation is important, and it's completely different to embrace it and take the alleged risk,” he says.

“Many water utilities talk about new technologies. Yet, there are several lighthouses in this industry that are adopting them. Some examples that come to mind include Mekorot in Israel, PUB in Singapore, Vitens in the Netherlands and American Water. They're beacons of innovation. They have the mentality to embrace new technologies and see them as important to save money and improve operations.”

Intense anticipation from the industry 

Independent expert Dr. Graeme Pearce has over 40 years of experience in membranes and is the principal at Membrane Consultancy Associates.

Acknowledging that “Flow Reversal" has long been recognized as effective for both RO and ultrafiltration (UF) membranes, he believes that the challenge has been to achieve scale.

"The trick is how to achieve Flow Reversal efficiently in large-scale RO systems,” he says. “There is no doubt that it offers a significant prize in improving the efficiency of RO by periodically re-creating optimized conditions of early-stage operation before polarization and fouling conditions have gradually become established.”

Pearce says that Flow Reversal potentially enables "RO to continually return to the initial high-performance part of its operation cycle”.

Commenting on the Arcadia installation, he says: "In the case study in Santa Monica, very high recoveries were achieved, which would be completely impractical and uneconomic for a standard design. This bodes well for this concept since the flow scale is large, so clearly, practical limitations have been overcome, and the cost addition has been paid for by the gain in efficiency.

"There are many RO applications that would benefit greatly from an energy efficient high recovery design, and I imagine this technology could become widely applied. The industry will watch the outcome of Santa Monica's decision with intense anticipation.”

Watch this space

Santa Monica is taking the proverbial bull by the horns and engineering its future water destiny. Knowing it could face further water challenges from earthquakes or climate change impacts, it’s proactively driving water self-sufficiency. Not for 30 years’ time, but now.

Similarly to the 1960s, when the city led the way with ion exchange softening, it continues to do so with the Arcadia development and FR-RO innovation. Increasing water production at existing RO facilities without increasing the plant footprint could generate much-needed water across the parched U.S.

"With every gallon that we save, another gallon is available for another agency that's more heavily dependent on that imported potable water supply,” says Wang.

There are other notable water project developments that the global water community watches with interest. Orange County Water District's groundwater replenishment project is one. And Singapore's NEWater, water recycling, is another. Arcadia joins that list - watch this space.

More information on ROTEC’s Flow Reversal Reverse Osmosis innovation can be found here.

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