A FRESH LOOK AT ZERO LIQUID DISCHARGE TECHNOLOGY ILLUSTRATES THE POTENTIAL FOR AFFORDABLE USE AT DESALINATION PLANTS ACROSS THE COUNTRY IN THE FORTHCOMING AWWA MANUAL OF PRACTICE M69.
Fouled nanofiltration membranes from lead and lag positions of a 2-stage pilot-scale direct potable reuse plant treating secondary municipal wastewater effluent in El Paso, Texas were thoroughly characterized after 9 months of operation to elucidate the role of silicon moieties on fouling. X-ray photoelectron (XPS), energy dispersive X-ray (EDS), and Fourier transform infrared (FTIR) spectroscopies identified silicon oxides/ silica as dominant foulants, especially on the lag element. Gas chromatography/mass spectroscopy also identified organosilicon moieties such as linear-and cyclosiloxanes on the lead element. Extensive siliceous fouling was accompanied by calcium, aluminum, and magnesium scaling as well as deposition of bioorganic materials thereby modifying membrane surfaces that resulted in irreversible productivity loss. None of the three selected cleaning agents (sodium dodecyl sulfate and NaOH, EDTA and NaOH, and HCl), either singly or in combination satisfactorily restored water permeability of the membrane. EDTA performed better in the lead element (where bioorganic fouling prevailed), and HCl was more effective in the lag element (where mineral scaling accompanied silicon oxides). This suggests the express need for novel antiscalants to reduce organosilicon/silicon oxide deposition and the necessity of harsher cleaning agents/ regimens specifically targeting silicon (e.g., hydrofluoric acid or ammonium bifluoride).
A lthough reverse osmosis (RO) is hardly commonplace relative to the vast number of water treatment facilities around the world, the technology's critical role in the contemporary development of many alternative sources of supply confer it outsized prominence in the industry discourse. For this same reason, interest in RO has never been greater, and thus it is important for all water professionals, even those with minimal membrane experience, to be aware of some of the key trends driving the modern RO renaissance. This column profiles three of the most significant trends-new applications, integrity testing, and enhanced recovery-as adapted from the forthcoming third edition of AWWA Manual of Water Supply Practices M46, Reverse Osmosis and Nanofiltration.
Innovations in salinity management currently being cultivated by the unconventional oil and gas industry may ultimately be a significant benefit to municipal water treatment.
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