Pierre Le-clech

Relaxation and/or backwashing have been incorporated in most membrane bioreactor (MBR) designs as standard operating strategies to limit fouling. However, to maintain a certain net permeate production, higher instantaneous fluxes have to be applied to compensate for the loss of permeate caused by those modes of operation. To assess the effects of the different operational parameters on fouling for the

This study focuses on the performance of a submerged membrane photocatalytic reactor for the removal of 17beta-oestradiol (E2) in the presence of humic acid (HA). In addition to the impact of operating parameters, such as membrane pore size, ultraviolet (UV) intensity and hydraulic retention time (HRT), the influence of long-term operation was also assessed by advanced characterization of the fouling layer formed on the membrane. The tighter (0.04 microm) hollow fibre polyvinylydene fluoride (PVDF) membrane was found to exhibit not only higher HA removal than the (0.2 microm) module (85% and 75%, respectively), but also greater transmembrane pressure (TMP) values and higher irreversible fouling. Long-term operation conditions have been simulated by conducting an ageing catalyst process and demonstrated a decrease in performance obtained with time. The artificially aged TiO2 resulted in higher TMP values and lower HA removals (about 10-20% decrease) compared with the non-aged catalyst. For E2 removal in the presence of HA, the passive adsorption of the oestrogen onto the organic matter was found to be significant (40% of the E2 adsorbed after I h), demonstrating the importance of the nature of the water matrix for this type of treatment process. An increase in the UV light intensity was observed to favour the E2 elimination, leading to more than 90% removal when using 64 W combined with PVDF membrane and an HRT of 3 h.

ABSTRACT Microbial fuel cells (MFCs) have a great potential for cost-effective wastewater treatment; however, the effluent quality from MFC is not always satisfied. In this study, an anaerobic membrane bioelectrochemical reactor (AnMBER) with an anaerobic membrane bioreactor (AnMBR) equipped with hollow-fiber microfiltration (MF) membranes directly serving as the cathodic chamber of a dual-chamber MFC was developed. Over an operational period of more than 600 h, the AnMBER system (with 100 Omega resistor) was able to generate continuous bio-electricity (0.132 V), with a maximum power density of 116 W m(-3) net cathodic chamber (NCC), and achieved high removal efficiencies of chemical oxygen demand (COD) (91.6%) and nitrate (94.8%). Furthermore, compared with a control AnMBR (with open circuit), membrane fouling was mitigated significantly in the AnMBER system, which was mainly attributed the lower particle zeta potential and lower amount of soluble microbial products (SMP) in the cathodic mixed liquor. These results demonstrate that integrating the anaerobic MF filtration sequentially to MFCs is a feasible approach to accomplish simultaneous efficient wastewater treatment and energy recovery and also raises the possibility of using MFCs as a means to minimize fouling in combined systems by improving the mixed liquor properties.

Extracellular polymeric substances (EPS) are a major fouling component in membrane bioreactor (MBR) systems. For a better understanding of the fouling mechanisms of EPS, the evolution of fouling of sodium alginate, a microbial polysaccharide was studied during crossflow ultrafiltration and microfiltration. Incremental flux-stepping experiments and long-term subcritical flux filtration were carried out. A two-stage of transmembrane pressure (TMP) profile reported

The biological removal of 38 trace organics (pharmaceuticals, endocrine disruptors, personal care products and pesticides) was studied in an anaerobic membrane bioreactor (AnMBR). This work presents complete information on the different removal mechanisms involved in the removal of trace organics in this process. In particular, it is focused on advanced characterization of the relative amount of TO accumulated within the fouling layers formed on the membranes. The results show that only 9 out of 38 compounds were removed by more than 90% while 23 compounds were removed by less than 50%. These compounds are therefore removed in an AnMBR biologically and partially adsorbed and retained by flocs and the deposition developed on the membranes, respectively. A total amount of 288 mg of trace organics was retained per m(2) of membrane, which were distributed along the different fouling layers. Among the trace organics analyzed, 17α-ethynylestradiol, estrone, octylphenol and bisphenol A wer...

ABSTRACT With continuing growth in the reverse osmosis water treatment industry and the finite lifespan of the membranes, the number of membrane modules requiring disposal is expected to drastically increase over time. This study aimed to provide a quantitative assessment of the environmental impact from membrane manufacturing and its impact on the desalination process, using the tool of life cycle assessment. The results showed no significant difference between the manufacturing of 16″ and 8″ elements, and that module fabrication contributed to less than 1% of the CO2-e emissions for the production of potable water from seawater. The study also looked at the environmental impact of a number of proposed end-of-life disposal options for membranes within the context of the Australian desalination industry. The results of the study show that membrane reuse over one year is more environmentally favourable to landfill disposal, regardless of the transportation distance required. However, in terms of direct reduction of waste to landfill, incineration provided the greatest benefit, at the expense of increased greenhouse gas emissions. Overall, this study provides detailed quantitative information for membrane users and manufacturers to enhance their decision making process when it comes to end-of-life membrane options.

ABSTRACT Three different types of ultrafiltration (UF) membranes were investigated to treat the effluents of secondary sedimentation tank of spandex wastewater. The main parameters studied consist of the UF membrane pore size, the backwash frequency and duration time, filtration mode and the stability of the UF system. The results showed that (1) the cross-flow filtration was better in restoring K decline than the dead-end filtration; (2) the optimized backwash frequency and duration were 30 min and 2 min, respectively; (3) the modified polysulfone (PSf) UF membrane (100 kDa) was determined to be the appropriate membrane; (4) the continuous operation experiment showed that this UF system was stable.

ABSTRACT The long-term decrease of hydraulic performances observed in membrane systems is generally explained by the gradual accumulation of irreversible foulants. Although the use of chemicals is primarily aimed to remove most of the foulants, few studies have reported their potential degradation impact on the membrane, consequently leading to the decrease in hydraulic performances. However, the impact of chemical ageing on the intrinsic membrane characteristics has not been studied in details, and the understanding of its relative role in the long-term filtration behaviour is, so far, limited. In this study, a polyvinylidene fluoride (PVDF) micro-porous membrane was aged through long-term fouling/cleaning cyclical experiments using model organic and 20,000 ppm sodium hypochlorite (NaOCl) solutions. The membranes were then thoroughly characterised, both physically and chemically, by various analytical techniques. The apparent pore size of the aged membrane was observed to enhance due to the combined effect of increased wetting and hydrophilicity of the membrane. Furthermore, NaOCl exposure led to early degradation of the PVDF membrane through cross linking and thus, slight loss of its mechanical properties. The impact of NaOCl on PVDF tensile properties was found to be less pronounced on fouled membranes, revealing the relative role of fouling during membrane ageing.

ABSTRACT Dynamic membrane systems provide highly turbulent flow regimes close to the membrane surface. In this work, flux enhancement of submerged hollow fibre membrane system was achieved by imposing rotationally oscillating fluid or transverse oscillating membrane motion. The transverse vibration in the system generates the shear as well as secondary flows, contributing to fouling limitation even at low displacements (<5 mm) and frequencies (<21 Hz). Transverse vibration limits cake formation by focusing shear forces more directly on the membrane surface rather than recirculating the bulk fluid. The substantial benefits of transverse vibration on fouling limitation were observed in terms of critical flux improvement for macromolecular (alginate), particulate (yeast, bentonite) and anaerobic bioreactor solutions for 0.04 mu m polyvinylidene fluoride membrane. However, lower fouling limitation was observed for alginate with the more permeable 0.2 mu m polypropylene membranes, for which the alginate rejection was low and internal pore blocking was likely to occur. Even for a solution with high concentration (200 g/L yeast) and high viscosity, low transmembrane pressures were maintained at modest fluxes with the aid of transverse vibration. During the filtration of supernatant from an anaerobic bioreactor, filtration with transverse vibration showed better fouling control compared with traditional fouling limitation methods such as periodical backwash or relaxation. Correlations for inertial and drag force for single oscillating cylinder were used to provide preliminary estimates of the energy requirements to generate the transverse vibrations in defined frequencies and displacements. (C) 2012 Elsevier B.V. All rights reserved.