Modelling PAHs removal in activated sludge process: effect of disintegration.

The removal of polycyclic aromatic hydrocarbons (PAHs) in activated sludge was evaluated using two laboratory-scale bioreactors, coupled or not with a disintegration system (sonication). Mass balances performed on each system underlined that PAHs removal was significantly improved after sludge disintegration, especially for the higher molecular weight PAHs studied, which tended to adsorb to suspended matter. A model was developed in order to study the effect of sludge disintegration on the content of dissolved and colloidal matter (DCM), and to predict the potential impacts on PAHs availability and degradation. Results showed that this new model was efficient for capturing apparent degradation improvement trends and for discriminating between the involved mechanisms. This study showed that DCM content increased after sludge disintegration, and proved to be the main driver for improving PAHs apparent degradation.

Modelling PAH partitioning during sludge disintegration: The key role of dissolved and colloidal matter.

The partitioning between solids and the aqueous phase largely controls the fate of PAH compounds in biological treatment. The prediction of PAH sorption behaviour into activated sludge was investigated here. The suitability of a three-compartment model to describe partitioning in such a complex matrix was first evaluated by adding increasing quantities of dissolved and colloidal matter (DCM) (from 0 to 34.9% of the total matter). In a range of DCM concentrations varying from 0 to 1.4 g L-1, the PAH aqueous fraction, including both freely dissolved and sorbed to DCM molecules, increased from 9.9% to 33% for naphthalene (the most soluble PAH) and from 0.29% to 13.3% for indeno(1,2,3,c,d)pyrene (the least soluble PAH tested). The sorption of PAHs on dissolved and colloidal matter (DCM) was assessed by determining two partitioning constants (KPART and KDCM) for the 16 PAHs listed by the US EPA. New experiments were carried out for model validation and show that the model properly predicts the PAH partitioning following sludge disintegration by sonication.

[Digestive surgical complications during pregnancy following bariatric surgery: Experience of a center for perinatology and obesity]. / Complications digestives chirurgicales après chirurgie bariatrique pendant la grossesse : expérience d'un centre de périnatalité et de chirurgie bariatrique.

OBJECTIVE: To describe severe complications during pregnancy requiring surgery in patients with a history of obesity surgery. MATERIEL AND METHODS: A retrospective study in a hospital with tertiary care perinatology and an obesity reference center, on all pregnancies following bariatric surgery over a 10-year period, analyzing all cases of surgical complications. RESULTS: There were 8 major complications related to the procedure in 141 pregnancies with bariatric surgery. The 2 complications in women with gastric banding were band slippage resulting in severe dysphagia, one of which leading to intractable vomiting and serious hydrolectric disorders. Among the 6 complications after bypass surgery, 4 were occlusions: 3 on internal hernias of which 2 with volvulus and 1 associated with intestinal invagination, as well as one with intestinal invagination only. One patient had a laparotomy for a suspected invagination which was not confirmed. The other surgical complications after gastric bypass were a hernia and an exploratory laparotomy for suspected intussusception which was overturned. There was no case of maternal or perinatal death. CONCLUSION: Pregnancies in patients with a history of bariatric surgery are at high risk, in particular for complications related to the surgery and thus require careful interdisciplinary surveillance, and determination of predictive factors.

Maternal mortality among women with sickle-cell disease in France, 1996-2009.

OBJECTIVE: To describe maternal mortality among women with sickle-cell disease in France. STUDY DESIGN: Data from the national confidential enquiry into maternal deaths and from reference centres for sickle-cell disease were examined to identify women with this disease who died in France during 1996-2009. The maternal mortality ratio among women with sickle-cell disease was estimated and compared with the ratio in the general population. Characteristics of these women and their pregnancies and circumstances of their deaths were examined in detail. RESULTS: Fifteen maternal deaths occurred among an estimated 3300 live births to women with sickle-cell disease, for a maternal mortality ratio of 454 per 100000 live births (95% CI [254; 750]), versus 9.4/100000 in the general population. Ten women were homozygous (SS) for sickle-cell disease, and five were composite heterozygotes. The episode leading to death appeared in the antepartum period for seven women (47%). Two women died of septic shock during pregnancy, one at 6 weeks, the other at 24 weeks. The other 13 women (87%) died postpartum. Thirteen deaths were directly attributable to sickle-cell disease. The other two maternal deaths, both considered direct obstetric causes, were due to amniotic fluid embolism and septic shock after post-amniocentesis chorioamnionitis. The expert committee on maternal mortality judged seven of these 15 deaths (47%) to be avoidable. CONCLUSION: Sickle-cell disease is responsible for a major excess risk of maternal death in France, due mainly to direct complications of the disease.

Fate of hazardous aromatic substances in membrane bioreactors.

In this work, the removal of hazardous aromatic compounds was investigated in two types of membrane bioreactors (MBRs), based on cross-flow and semi dead-end filtration systems. BTEX and PAH were efficiently eliminated from wastewater during treatment via a membrane bioreactor (90-99.9%) but non-biotic processes, i.e. volatilisation and sorption, contributed significantly. The semi dead-end MBR showed slightly better removal efficiencies than the cross-flow MBR. However, non-biotic processes were more significant in the first process and, finally, degradation rates were higher in the cross-flow MBR. Higher degradation rates were explained by a higher bio-availability of pollutants. Differences in shear stress imposed in cross-flow and semi dead-end filtration systems radically modify the sludge morphology. High shear stress (cross-flow filtration) generates dispersed bacteria and larger quantities of dissolved and colloidal matter. Sorption of hydrophobic compounds (PAHs) on suspended solid was less marked in disaggregated sludge. The results suggest new strategies for improving micro-pollutant degradation in MBRs.

Side-stream membrane bioreactors: Influence of stress generated by hydrodynamics on floc structure, supernatant quality and fouling propensity.

This work aims to characterise the impact of hydrodynamics on sludge properties and consequently on fouling mechanisms in side-stream membrane bioreactors (MBRs). Two side-stream processes which generate very different shear stresses are compared, without filtration. This operating mode permits specific quantification of the impact of the external loop (and of induced shear stress) on floc structure/morphology, supernatant quality and fouling propensity. The study shows that low constraints (7 x 10(-3) Pa) generated on submerged side-stream hollow fibre modules have no significant impact on sludge properties. In contrast, high shear stresses (72 Pa) associated with a crossflow configuration induce very significant modifications of the mixed liquor which increases its fouling propensity (measured in a standard filtration cell). A theoretical explanation of the role of turbulence on the floc size distribution is given. Based on a Kolmogorov microscale calculation, it seems possible to predict the mean floc size reached in both filtration systems, for a given shear stress intensity. Disaggregation is characterised by a two-step kinetic: first a short-term breakage attributed to fragmentation and loss of weak strength bonds, and secondly a longer-term breakage probably due to erosion phenomena and removal of high strength bonds. Only the second step induces a significant release and an accumulation of soluble protein-like substances. Soluble organic matter strongly enhances the fouling propensity of the mixed liquor. This seems to be amplified by the concentration of protein-like substances. The importance of considering the protein and carbohydrate content as well as floc size is also pointed out in the paper.

Performances of a hybrid adsorption/submerged membrane biological process for toxic waste removal.

This study focuses on a hybrid process, which combines adsorption on powdered activated carbon (PAC), membrane separation using immersed hollow fibers and biological activity. The first part shows that PAC addition in a complex system (containing dissolved molecules and biological particles) can reduce membrane fouling. In that system, DMP removal is function of the activated carbon concentration. Then, respirometric experiments allowed comparison of toxic sensitivity and biological degradation of different bioreactors (membrane bioreactor (MBR), adsorptive membrane bioreactor (PAC-MBR) and classical activated sludge bioreactor (AS)). Results point out that MBR sludge is less sensitive to the toxic than the AS. For high toxic concentration, PAC addition in the MBR decreases rapidly the toxic concentration under the EC50 in the bioreactor, which allows a better biodegradation of the toxic compound. DMP assimilation is completed more rapidly with the PAC-MBR than the MBR.