Forward osmosis (FO) has proven to be a robust, low-pressure membrane separation process capable of rejecting a broad range of contaminants; thus, providing a high quality diluted brine suitable for ...further desalination by reverse osmosis (RO). In this study, a pilot-scale FO-RO system treated >10,000 L of raw produced water from the Denver-Julesburg basin (Colorado) over a four-week period using commercially available FO and RO membranes. Overall, the FO-RO pilot system maintained >99% rejection of nearly all measured ions and >95% rejection of hydrocarbons such as semi-volatile linear aliphatic hydrocarbons and polycyclic aromatic hydrocarbons. Although the FO-RO system was able to treat raw produced water, high concentrations of organic compounds severely fouled the FO membrane and substantially reduced water flux by 68% within 21 days. Membrane degradation due to interaction between organic constituents such as aliphatic and aromatic hydrocarbons and the membrane polymer may have compromised the FO membranes, resulting in substantial increase (×15) in reverse salt flux within 21 days. Further investigations of membrane cleaning and pretreatment will be required in order to better understand the overall economic feasibility of treating raw produced water using FO.
•FO-RO pilot system treated 10,000 L of produced water for >600 h.•High removal efficiency of inorganic and organic constituents was observed.•The hybrid FO-RO system generated permeate with a TDS < 500 mg/L.•Migration of membrane polymer additives into the draw solution was detected.•FO membranes were potentially damaged during long-term exposure to harsh conditions.
•Combination of NF and UV-sulfite more cost effective PFAS degradation method.•NF effective technology to concentrate (> 10x) and reject PFASs (∼95%).•Faster UV-sulfite degradation in alkaline pH ...11.2.•UV-sulfite degradation of all PFCAs < 2 h and PFOS < 4 h in NF reject.•Treatment train EE/O ≤ 13.1 kWh/m3 for all PFCAs and 14.1 kWh/m3 for PFOS.
Previous laboratory scale studies indicate nanofiltration (NF) and UV-sulfite photochemical treatments as promising technologies for the removal and destruction, respectively, of per- and polyfluoroalkyl substances (PFASs) from contaminated water. This study reports on a field demonstration of a pilot-scale hybrid NF and UV-sulfite treatment train for the remediation of 12 PFASs detected in groundwater impacted by aqueous film-forming foam (AFFF) at a U.S. Department of Defense installation. For most of the detected PFASs, NF rejection was consistently ≥ 95% over a 30-day field trial when operating at 90% total permeate recovery. Rejection of short-chain perfluorosulfonic acids (PFSAs) by NF decreased when recoveries increased from 90 to 97%; tests with a reverse osmosis (RO) membrane showed ≥ 99% rejection of all PFASs regardless of increasing recovery. UV treatment of the NF reject following 90% permeate recovery resulted in variable destruction of individual PFASs, with rates also being dependent on pH and the identity and concentration of UV photosensitizer. Rates of perfluorocarboxylic acid (PFCA) degradation were greater than those measured for PFSAs and perfluoroalkyl acid (PFAA) precursors and were independent of perfluoroalkyl chain length. In contrast, rates of PFSA degradation increased with increasing chain length. Consistent levels of PFAS degradation by UV-sulfite were observed during a 30-day demonstration experiment in NF reject water amended with 10 mM sulfite and adjusted to pH 11.2. Collectively, > 75% of the detected PFAS mass in the NF reject was destroyed after 4 h of UV treatment, increasing to > 90% after 8 h of treatment. An analysis of electrical energy inputs for the hybrid NF/UV-sulfite treatment train showed energy per order magnitude (EE/O) requirements ranging from ≤ 13.1 kWh/m3 for PFCAs and 14.1 kWh/m3 for PFOS to values > 100 kWh/m3 for more recalcitrant short-chain PFSA analogues. The UV reactor and water-cooling system were the major contributors to overall energy requirements and represent the greatest opportunities for improving efficiency of the technology.
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Wave-driven desalination systems are proposed water treatment systems that involve reverse osmosis of seawater powered directly by wave motion. Such a configuration would result in drastic feed ...pressure fluctuations. For a technology conventionally operated with a constant feed condition, the effect of these variable pressures on membrane integrity and performance is unknown. Experiments were conducted with spiral wound membranes coupled to a system capable of producing feed pressure fluctuations of more than 400 psi. Feed composition included 5, 20, and 35 g/L NaCl, and a synthetic seawater at normal and 1.5× concentration. The variable feed conditions included sine-like pressure waves swings of 200–500 and 500–900 psi with frequencies of 1.25, 7.5, and 12 waves/min, and a model-generated random waveform. Between each wave experiment we performed membrane integrity tests at 650 psi and 25 g/L NaCl feed, which showed a 7.4% drop in the membrane's water permeability coefficient, an 18.4% flux decline, and more than 99% salt rejection over 1770 h of cumulative experimental time. Analysis of permeate samples showed high salt rejection. In general, variable feed pressure had no significant deleterious effect on membrane integrity or performance.
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•Impact of large feed pressure variations on membrane integrity was investigated.•Permeability showed no substantial decline over 1800 h of dynamic feed pressure.•Permeate water quality did not deviate from expectations under dynamic operation.
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