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The role of steric hindrance and charge interactions in governing ionic transport through reduced graphene oxide (rGO) and commercial (DOW-Filmtec NF270) membranes was elucidated by a comprehensive study of experimental and established mathematical analysis based on Nernst-Planck equation. A charge-dominated salt exclusion mechanism was observed for the rGO membranes, which exhibited retention from low (7%) to moderate (70%) extent depending on the nature of ions (5 mM). Swelling of GO (1.2 nm interlayer distance) in water beyond the hydrated diameter of ions was attributed as a primary cause for lowering steric hindrance effects. The influence of parameters affecting charge interactions, such as pH and ionic strength, on the extent of salt rejection was modelled. The potential impact of the membranes charge density, GO loading and interlayer spacing on salt retention was quantified by performing sensitivity analyses. For a high TDS produced water sample, the rGO membranes partially retained divalent cations (Ca:13%) and exhibited high dissolved oil rejection. The membranes were found to be suitable for the treatment of high TDS water with the goal of selectively removing organic impurities, and thus minimizing the impact of osmotic pressure effect. Performance of the membranes was also investigated for retention of water remediation related organic anions, using perfluoro octanoic (PFOA) acid as a model compound. rGO membranes exhibited a charge-dominated exclusion mechanism for retention (90%) of PFOA (1 ppm).

Although calibration should always be included in any hydraulic analysis, it is often neglected or done haphazardly. As a result, inappropriate data may be used or data errors may be overlooked, so the resulting hydraulic model is of limited value. The novice may see calibrating a hydraulic network model as a task as daunting as climbing Mt. Everest. This article presents a seven-step method for use in calibrating a hydraulic network model. The last and most difficult step is microlevel calibration, which involves the adjustment of demand loadings and pipe roughnesses until computed and observed field pressures or flow rates are within reasonable agreement for various levels and extremes of demand, pumping, and storage. Various explicit calibration algorithms have reduced the need for trial-and-error proceduresand have improved the reliability of the resulting calibration. There remains little justification for failing to develop good calibrated network models prior to network analysis. [ABSTRACT FROM AUTHOR]