In the week of the AMTA/AWWA Membrane Technology Conference 2018, in Florida, US, Brent Alspach, president of AMTA and director of applied research at Arcadis, outlines the water challenges and how current and in-development membrane-based treatments are addressing them.
Q. What are the biggest challenges for membrane specialists right now?
A. The two most significant challenges for membrane practitioners continue to be cost and, for desalination, concentrate management. In most cases, membrane processes produce the best quality water, but the cost-benefit analysis can be unfavourable.
Membrane filtration — microfiltration (MF) and ultrafiltration (UF) — consistently yield filtrate with turbidity levels near 0.02 NTU, independent of feed water quality; and, barring an integrity breach, MF and UF serve as a near-absolute barrier for bacteria and regulated protozoa, including giardia and cryptosporidium. UF provides high rejection of viruses.
Additionally, MF and UF can achieve more than 4-log, or 99.99 per cent, reduction of important unregulated pathogens such as legionella, naegleria fowleri, the so-called brain-eating amoeba, vibrio cholerae, which causes cholera, and leptospira, the bacteria behind the spread of leptospirosis through Puerto Rico in the aftermath of Hurricane Irma in 2017.
These substantial water quality benefits are largely unmatched among filtration technologies, however MF and UF are often compared to conventional processes such as dual media filtration. Dual media filtration uses less expensive equipment (the considerable cost of concrete basins, where applicable, notwithstanding), and operates by gravity flow, resulting in operational cost savings compared to the expense of the pumping required by membrane filtration (see feature, page 20).
Membrane desalination processes — nanofiltration (NF) and reverse osmosis (RO) — in addition to removing salts, reject a wide range of emerging contaminants, including pathogens, pharmaceuticals/personal care products (PPCPs), perfluorinated compounds (PFCs), hexavalent chromium, manganese, radionuclides, and arsenic. In many cases, NF/RO also removes disinfection by-product (DBP) precursor compounds — both the regulated and the burgeoning number of unregulated DBPs, many of which are considered more toxic.
However, NF/RO has higher specific energy consumption (that is, energy required per unit volume of water treated), than most other treatment processes, and viable methods for concentrate management may sometimes be prohibitively expensive, and difficult to permit. As a result, in some cases, NF/RO is avoided, even in applications where the water quality benefit would be substantial.
Q. Where’s the innovation in membrane technology?
A. The main drivers of advancements in desalination concentrate management are maximising the yield of potable water, and limiting residuals streams. Many innovations in concentrate management are not merely on the horizon, but are already in limited, full-scale deployment, or undergoing pilot testing, with the promise of making desalination more feasible, efficient, and/or economical.
These advancements largely manifest in two categories: brine concentration; and resource recovery. Activity in brine concentration is robust, with at least five or six very promising technologies primed for market penetration. Each has unique advantages and optimum conditions for use, and all are likely to be adopted among the myriad of diverse desalination applications. The technology for resource recovery (for example mineral extraction), from RO concentrate, has long been available, and now innovators are developing better economic models to transcend what has historically been a financial non-starter.
In the long-term, this expanding array of concentrate management options, for RO brine concentration and resource recovery, will facilitate many more desalination projects than would otherwise have been viable.
“Membranes can transform the poorest-quality water into the best, and government-funded
research provides substantial return-on-investment.”
Brent Alspach and director of applied research at Arcadis
Q. How do membrane technologies fit into the wider trends in water?
A. The most significant industry-wide trend is the increasing use of poorer-quality, alternative water supplies, ultimately for potable use, including brackish groundwater, recycled wastewater, stormwater, grey water, and seawater. In Florida and California, which both have large populations and long-term water resource challenges, it is easy to imagine all five sources being used as potable supplies at varying scales of implementation, from households to municipal service areas. Treatment of any such sources may require use of membranes in a comprehensive treatment strategy, and all cases could benefit from membrane processes. The need for membrane treatment has never been more acute, and addressing the current challenges that confront the technology has the potential to benefit a vast number of people in the US, and around the world.
Q. What activities form the core of AMTA’s work?
A. The American Membrane Technology Association (AMTA) works actively to counter the challenges outlined above. We partner with the American Water Work Association (AWWA) to organise the world’s premier membrane treatment event, the annual Membrane Technology Conference in the US, and this year, we have extended this partnership to include Water Environment Federation and WateReuse Association.
AMTA runs five technology transfer workshops each year across the US, to broaden understanding of membrane treatment and to discuss the latest advancements. Among other things, these workshops aim to communicate that even in applications for which membranes are not the cheapest option, the technology brings many additional advantages that should be factored into a cost-benefit analysis.
We engage with elected officials and government agencies to provide education about the benefits of membrane technology. In an era of unprecedented water demand, drought, and a changing climate, water systems around the US are by necessity using lower quality supplies to expand and diversify their resource portfolios. Membranes can transform the poorest quality water into the best, and government-funded research, aimed at reducing energy consumption and developing innovative concentrate management strategies, provides a substantial return-on-investment that is of benefit to every region and segment of the economy.
AMTA is proud to help sponsor graduate research, which addresses these same challenges, and cultivates the next generation of membrane technologists and industry leaders. Over the past decade, AMTA has partnered with the National Water Research Institute (NWRI), the Affordable Desalination Collaboration (ADC), and the United States Bureau of Reclamation (USBR) to award nearly 40 students a total of $350,000 in scholarships to support membrane research.
Brent Alspach is president of AMTA and director of applied research at Arcadis