Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/946410
RECLAIMED WATER IS POISED TO BECOME A MORE COMMON PART OF THE DRINKING WATER PORTFOLIO IN THE SOUTHEAST On the eve of the annual AMTA/ AWWA Membrane Technology Conference 2018 in Florida, the number one US State for desalination by capacity, discussions around what are the appropriate ways to implement water reuse are shaping up. In Florida, water reuse is already well established for uses such as irrigation of public parks and golf courses, and many municipalities have purple pipe infrastructures in place. The questions now arising are about recycled water for potable use, including what could be the appropriate technologies to produce such supplies. There are soƒ challenges for water reuse in terms of public perception, and harder, technological questions. "In Florida, we are 60 per cent of the way to getting people to understand that water reuse can be done safely and appropriately. People now have a better understanding of water cycles than 10 or 15 years ago," says Christine Owen, director of water and reuse innovations, Hazen and Sawyer, and senior manager of water quality services, Tampa Bay Water, Florida. "In Florida, we are probably the leading US state in March 2018 Water.desalination+reuse On Site 17 Florida is coming around to potable reuse Desalination plants in operation and under construction CALIFORNIA 320 plants 15% FLORIDA 250 plants 12% TEXAS 179 plants 8% OTHERS 1,414 plants 65% Source: International Desalination Association (IDA)/DesalData terms of beneŒ cial reuse. We do a lot of purple pipe for irrigating public plants and golf courses, and many municipalities have it for lawn irrigation." The big discussion is around reuse for drinking purposes; because Florida already has strict discharge requirements in place, the question is, 'Why not treat the water a step further, and use it as a potable supply?' "In terms of the technology used, it depends on the source water. You may have highly treated water with high total dissolved solids (TDS). For the potable market, you then have to do TDS removal, and currently that's a mid to high-pressure reverse osmosis (RO) system," Owen explains. "If your reclaimed water has a lower TDS — in the US, TDS is a secondary maximum contaminant level — you're supposed to be below 500 milligrams per litre, and if you're above that it would trigger membrane treatment, but if you're below that, you can use something like advanced oxidation, biological Œ ltration, maybe ion exchange, or advanced oxidation through ultraviolet (UV) peroxide. There is a non-RO camp and an RO camp. It really should be driven by what your reclaimed water source looks like," she says. Many water treatment practitioners naturally turn to membrane technologies for all types of requirement, but Owen cautions that it's important to keep in mind what you want at the end. "Membranes are a phenomenal water treatment technology, but they can't treat everything, and as well as RO, you may have to do some ion exchange, or advanced oxidation like UV peroxide. Take some of the perž uorinated compounds — some people are touting that you can use carbon on those, well you can, on the mid to long-chain compounds, but the small chain ones just blow right through. And we don't have good information yet about how membranes deal with those smaller chains. Membranes are great, they absolutely are great. It's just that don't take care of everything." Alternatively, Owen argues that it's better to keep an open mind about how to conŒ gure water treatment technology. "There are always new things coming out, and the RO train is not the only option that you can do," she says. More tailoring of technology to meet speciŒ c water quality goals, including making use of a wider range of technologies, is anticipated for the future. "We are going to see more reclaimed water in the drinking water portfolio, whether direct or indirect, and I hope to see more ceramic membranes. The drinking water community is conservative, but as we understand more about our source waters and how they are impacted by human activities, we are going to see a lot more tailoring and innovative uses of technology." Membranes are absolutely great, but they don't take care of everything. Christine Owen, director of water and reuse innovations, Hazen and Sawyer California, Florida, and Texas together account for 35 per cent of all desalination plants in the US Top three US states for desalination by capacity Desalination capacity in Florida is more that twice that of California 1. FLORIDA 3.30 million m3/d 2. CALIFORNIA 1.76 million m3/d 3. TEXAS 1.18 million m3/d