Water. desalination + reuse

RESEARCH | 40 | Desalination & Water Reuse | November-December 2014 For their research in membrane fouling, doctoral students – Ariel Atkinson of the University of North Carolina at Chapel Hill and Erin Partlan of Clemson University – have received the 2014 Fellowship for Membrane Technology award from the American Membrane Technology Association (AMTA) and the National Water Research Institute (NWRI). This two-year, joint US$ 10,000-a-year fellowship supports research that meets NWRI's objectives in water quality, public health and the environment and AMTA's aims to promote membrane technology. Third-year doctoral student Atkinson is looking into a novel anti-biofouling membrane that could improve water quality and cut treatment costs. Her graduate advisor is assistant professor Orlando Coronell. Partlan is a fi rst-year student researching the use of dissolved carbon dioxide in preventing and removing foulants from reverse osmosis membranes. The technology could reduce treatment plant costs because carbon dioxide could be more readily recovered from water than conventional chemical cleaners. Her graduate advisor is assistant professor David Ladner. Scientists in Singapore and Saudi Arabia have reported a novel method for extracting toxic and valuable heavy metals from wastewater using forward osmosis (FO). The researchers demonstrated the removal of chromium, arsenic, lead, cadmium, copper, and mercury. The process exploits a recently established type of draw solute formed from a complex of citric acid and cobalt. This is a large complex ion so reverse fl ux across the forward osmosis membrane is minimal. At a fl ux of about 11l/m²/h heavy metals were harvested with rejections of 99.5% according to the researchers' paper in the Journal of Membrane Science. "The impressive heavy metal rejections and satisfactory water fl ux under various conditions suggest great potential for the newly developed FO system in the treatment of heavy metals wastewater," the researchers said in their report. Study shows novel heavy metal-from- wastewater method Students pick up prize for fouling studies Researchers have uncovered "an additional reverse osmosis (RO) membrane fouling mechanism," linked to organic matter found in ultrafi ltration (UF) permeate in wastewater treatment. The work, by researchers from Israel and Germany, found that organic fi lms that are deposited from UF permeate onto RO membranes in a membrane bioreactor irreversibly reduced fl ux in the RO membrane. But fl ux reduction by large molecules secreted by microorganisms – extracellular polymeric substances (EPS) – could be reversed. They proposed that the permanent damage infl icted by substances in UF permeate arose from their arrest of the swelling in the membrane polyamide as measured by the researchers. The swelling effect was crucial to water transport through the membrane, the researchers said. The scientists ran parallel fouling experiments with UF permeate and EPS in an RO plate-and-frame unit. They saw reversible changes in the RO permeate fl ux as pH values were altered from 6 to 8 and back to 6 using pristine and fouled membranes with EPS. On putting UF permeate-fouled membranes throughout he same pH variation the scientists found "irreversible fl ux decline" in the RO. The pH change, they said, promoted interaction between the UF permeate organic matter and the membrane to reduce further membrane permeability. They concluded that organic acids originating from decayed organic matter were binding irreversibly with the membrane surface: "More studies need to be carried out to analyze the effects of humic acids, abundant in the UF permeate fouling layer, that irreversibly interact with the polyamide surface," the researchers said. They found that the fi lm deposited from UF permeate enhanced the attachment of bacteria, but had no effect on EPS adsorption. The swelling changes and fi lm build-up were measured using quartz crystal microbalance with dissipation – a technique that uses shifts in a crystal's resonant frequency caused by changes in the mass of the membrane. The work was published in the Journal of Membrane Science. Study uncovers "new biofouling mechanism" Scientists to probe brine risks Scientists have been asked to investigate whether brine waste from two proposed 150 Ml/d seawater reverse osmosis desalination plants could damage or alter the marine environment along the KwaZulu-Natal coastline in South Africa. The studies, to be co-ordinated by south Africa's Council for Scientifi c and Industrial Research (CSIR), will be part of a proposal by utility, Umgeni Water, to build one or two desalination plants to boost Durban's dwindling fresh water supplies. One of the studies will examine the environmental impacts of pumping daily about 180 Ml of concentrated brine back into the sea near Tongaat, north of Durban and at Illovu, south of the city. The brine was expected to be about 1.7 times more saline than seawater. Umgeni said that a diffuser on the outlet pipes would ensure that the brine effl uent was diluted to about 3% above normal salinity levels within 10 m of the diffuser points. The brine would be pumped to sea through outlet pipes extending 350-500 m offshore. It anticipated that potential environmental impacts were likely to be restricted to a small area close to the dispersal pipeline. In a recent draft report CSIR said brine disposal caused "signifi cant detrimental effects" on coastal environments in parts of the Middle East and other coastlines with shallow water and low wave and tidal energy. CSIR said that unless currents dispersed the brine rapidly, it could sink and smother the seabed. It cited studies undertaken in the early 1990s that concluded that brine discharges reduced populations of fi sh, plankton, and coral in the Red Sea. It pointed also to Spanish researchers who in 2007 documented signifi cant changes in sea life populations close to a desalination plant near Alicante. The CSIR has recommended further studies into the effect of different water temperatures on marine life, since the brine water discharges were likely to be about 1.5ºC above normal sea temperature.

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