Bryan D. Coday

Effects of Transmembrane Hydraulic Pressure on Performance of Forward Osmosis Membranes

Forward osmosis (FO) is an emerging membrane separation process that continues to be tested and implemented in various industrial water and wastewater treatment applications. The growing interests in the technology have prompted laboratories and manufacturers to adopt standard testing methods to ensure accurate comparison of membrane performance under laboratory-controlled conditions; however, standardized methods might not capture specific operating conditions unique to industrial applications. Experiments with cellulose triacetate (CTA) and polyamide thin-film composite (TFC) FO membranes demonstrated that hydraulic transmembrane pressure (TMP), common in industrial operation of FO membrane elements, could affect membrane performance. Experiments were conducted with three FO membranes and with increasing TMP up to a maximum of 50 psi (3.45 bar). The feed solution was a mixture of salts and the draw solution was either a NaCl solution or concentrated seawater at similar osmotic pressure. Results revealed that TMP minimally affected water flux, reverse salt flux (RSF), and solute rejection of the CTA membrane. However, water flux through TFC membranes might slightly increase with increasing TMP, and RSF substantially declines with increasing TMP. It was observed that rejection of feed constituents was influenced by TMP and RSF.

Rejection of Trace Organic Compounds by Forward Osmosis Membranes: A Literature Review

To meet surging water demands, water reuse is being sought as an alternative to traditional water resources. However, contamination of water resources by trace organic compounds (TOrCs), including pharmaceuticals, personal care products, disinfection byproducts, and industrial chemicals is of increasing concern. These compounds are not readily removed by conventional water treatment processes and require new treatment technologies to enable potable water reuse. Forward osmosis (FO) has been recognized in recent years as a robust process suitable for the treatment of highly impaired streams and a good barrier to TOrCs. To date, at least 14 studies have been published that investigated the rejection of various TOrCs by FO membranes under a variety of experimental conditions. In this paper, TOrC rejection by FO has been critically reviewed, evaluating the effects of membrane characteristics and orientation, experimental scale and duration, membrane fouling, feed solution chemistry, draw solution composition and concentration, and transmembrane temperature on process performance. Although it is important to continue to investigate the removal of diverse TOrCs by FO, and especially with new FO membranes, it is critically important to adhere to standard testing conditions to enable comparison of results between studies. Likewise, feed concentration of TOrCs during FO testing must be environmentally relevant (most commonly 10-100 ng/L range for most wastewaters) and not excessively high, and in addition to testing TOrC rejection in clean feedwater, the effects of real water matrix and membrane fouling on TOrC rejection must be evaluated.

Solid-phase extraction followed by gas chromatography-mass spectrometry for the quantitative analysis of semi-volatile hydrocarbons in hydraulic fracturing wastewaters

A versatile method was developed for the quantitative analysis of semi-volatile linear aliphatic hydrocarbons in the n-C10 to n-C32 range and 16 polycyclic aromatic hydrocarbons (PAH) in hydraulic fracturing wastewaters using solid-phase extraction (SPE) on disposable octadecyl-bonded silica (C18) cartridges followed by gas chromatography-mass spectrometry. Matrix spikes revealed SPE recovery rates in the range of 38–120% for linear aliphatic hydrocarbons (n-C10 to n-C32) and 84–116% for PAH. Limits of detection were in the lower ng L−1 range for both compound groups. To prove the practicability of the developed method in real applications, the treatment performance of a hybrid forward osmosis–reverse osmosis pilot system treating produced water from the Denver-Julesburg basin in Colorado was assessed over a period of eight weeks. The removal efficiency of the overall system after reverse osmosis treatment for n-alkanes was constantly better than 99.4%. The lower molecular weight PAH naphthalene, fluorene, and phenanthrene were the most abundant PAH detected in the produced water feed, filtrate and concentrate streams during treatment. Their concentrations in the produced water feed reached up to 359.3 μg L−1, 40.7 μg L−1, and 68.3 μg L−1, respectively. However, naphthalene (0.5 ± 0.2 μg L−1) was the only analyzed PAH in the final treated water that exceeded the general US Environmental Protection Agency maximum contaminant level for PAH in drinking water of 0.2 μg L−1.