Produced water treatment by membranes: A review from a colloidal perspective.

While the world faces an increased scarcity in fresh water supply, it is of great importance that water from industry and waste streams can be treated for re-use. One of the largest waste streams in the oil and gas industry is produced water. After the phase separation of oil and gas, the produced water is left. This mixture contains dissolved and dispersed hydrocarbons, surfactants, clay particles and salts. Before this water can be used for re-injection, irrigation or as industrial water, it has to be treated. Conventional filtration techniques such as multi media filters and cartridge filters, are able to remove the majority of the contaminants, but the smallest, stabilized oil droplets (<10µm) remain present in the treated water. In recent years, research has focused on membranes to remove these small oil droplets, because this technology requires no frequent replacement of filters and the water quality after treatment is better. Membranes however suffer from fouling by the contaminants in produced water, leading to a lower clean water flux and increased energy costs. Current research on produced water treatment by membranes is mainly focused on improving existing processes and developing fouling-resistant membranes. Multiple investigations have determined the importance of different factors (such as emulsion properties and operating conditions) on the fouling process, but understanding the background of fouling is largely absent. In this review, we describe the interaction between the membrane and a produced water emulsion from a colloidal perspective, with the aim to create a clear framework that can lead to much more detailed understanding of membrane fouling in produced water treatment. Better understanding of the complex interactions at the produced water/membrane interface is essential to achieve more efficient applications.

Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth.

The effect of ultrasonic irradiation (42,150 Hz, 17 W dm(-3)/7.1 W cm(-2)) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface.

Visualization of acoustic cavitation effects on suspended calcite crystals.

The acoustic cavitation (42,080 Hz, 7.1 W cm(-2) or 17 W) effects on suspended calcite crystals, sized between 5 and 50 µm, have been visualized for the first time using high speed photography. High speed recordings with a duration of 1 s containing up to 300,000 frames per second, revealed the effect of cluster and streamer cavitation on several calcite crystals. Cavitation clusters, evolved from cavitation inception and collapse, caused attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation was observed to cause deagglomeration only. Cavitation on the surface gave the crystals momentum. However, it is shown that breakage of accelerated crystals by interparticle collisions is unrealistic because of their small sizes and low velocities. Crystals that were accelerated by bubble expansion, subsequently experienced a deceleration much stronger than expected from drag forces, upon bubble collapse. Experiments with pre-dried crystals seemed to support the current theory on bubble nucleation through the presence of pre-existing gas pockets. However, experiments with fully wetted crystals also showed the nucleation of bubbles on the crystal surface. Although microjet impingement on the crystal surface could not be directly visualized with high speed photography, scanning electron microscopy (SEM) analysis of irradiated calcite seeds showed deep circular indentations. It was suggested that these indentations might be caused by shockwave induced jet impingement. Furthermore, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures.

Adsorptive removal of nitrilotris(methylenephosphonic acid) antiscalant from membrane concentrates by iron-coated waste filtration sand.

Iron-coated waste filtration sand was investigated as a low-cost adsorbent for the removal of nitrilotris(methylenephosphonic acid) (NTMP) from membrane concentrates. The adsorption of this phosphonate-based antiscalant on this material was measured and compared with two commercially available anion exchange resins and activated carbon. Comprehensive adsorption experiments were conducted in several synthetic concentrate solutions and in a concentrate collected from a full scale nano-filtration brackish water desalination plant. The effect of pH, ionic strength and the presence of competitive anions on the equilibrium adsorption were investigated. The results showed that, in contrast to the anion exchange resins, the adsorption on coated filtration sand is not suppressed at increasing ionic strength and is much less affected by the competitive anions carbonate and sulphate. The adsorption decreased slightly when the pH was raised from 7.0 to 8.0. The adsorption isotherms in the real nano-filtration concentrate, measured in the concentration interval of 5-50 mg dm(-1) NTMP, showed that the maximum adsorption capacity of coated filtration sand was 4.06 mg g(-1). The adsorption capacity per unit mass of the adsorbents at low NTMP concentration (12.5 mg dm(-3)) followed the decreasing order Amberlite IRA-410>coated filtration sand>Amberlite IRA-900>Norit SAE Super. This demonstrates that the use of iron-coated waste filtration sand offers a promising means for the removal of NTMP from membrane concentrates.

Thin-layer liquid-based cervical cytology and PCR for detecting and typing human papillomavirus DNA in Flemish women.

The objective of this study was to document the occurrence and to correlate the prevalence of different human papillomavirus (HPV) types with the cytological results on simultaneously performed thin-layer preparations in a large population of Flemish women. During 1 year, 69 290 thin-layer preparations were interpreted using the Bethesda classification system. Using an algorithm for HPV testing based on consensus primers and type-specific PCRs in combination with liquid-based cytology, we determined the occurrence and distribution of 14 different oncogenic HPV types (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66 and 68). Reflex HPV testing was performed on cytologically abnormal samples and on an age matched randomly selected control group with normal cervical cytology (n=1351). Correlation between cytology, age and prevalence for the 14 different high-risk HPV types is given. There is a significant increase in predominance of high-risk HPV types, with increasing abnormal cytology. Coinfection with multiple HPV types also increased with cytological abnormalities, and was highest in HSIL (16.7%). In Flanders, HSIL was most often associated with HPV types 16, 33, 35, 31, 18 and 51. Using thin-layer liquid-based cytology and PCR to detect HPV, it is feasible to screen large numbers of women.

Sperm morphology assessment: diagnostic potential and comparative analysis of strict or WHO criteria in a fertile and a subfertile population.

This prospective study compared the diagnostic and predictive potential of sperm morphology assessments in a fertile vs. a subfertile population, evaluated in three different laboratories. The fertile population included 144 men who had recently fertilized their partners. As subfertile controls, 136 men with a history of subfertility for more than 12 months were used. All semen samples (280) were evaluated in three different centres in a blind fashion, without any patient information. The evaluation of sperm morphology was performed according to the criteria normally used in the different laboratories: WHO (1992) criteria for laboratory A, and Tygerberg strict criteria for laboratories B and C. Using ROC analysis, the predictive power of sperm morphology turned out to be different in the three laboratories (area under ROC curve: 69% for lab A, 72% for lab B and 78% for lab C). Using percentile 10 of the fertile population as the cut-off value for normality, we obtained the following results: 2, 1 and 5% for laboratories A, B and C, respectively. Using ROC analysis cut-off values with optimal specificity and sensitivity were 6, 1 and 10%, respectively. Although our data highlight a reasonable predictive power of sperm morphology in centres using different or the same criteria, cut-off values for normality were different, even when the same criteria were applied. These results stress the importance of standardization in sperm morphology evaluation and the need for examining a reference population in estimating the real threshold value in different laboratories.