Marc Heran

Ultrafiltration enhanced by coagulation in an immersed membrane system

Abstract The aim of this study is to determinate optimum conditions, membrane configuration, air flow, coagulation rate, permeate flux, for the ultrafiltration of surface water. Results show how coagulation is a necessary pre-treatment to remove micro-particles in aqueous suspension (i) before a conventional sedimentation, (ii) before a membrane filtration. When membranes are immersed in a contactor, configuration allow to maintain the permeate flow rate at high value (200 L/h/m2/bar) mainly because coagulation induces large floc size. However, when the particle concentration of the suspension is very high (2 to 5 g/L), it is important to increase the shear stresses close to the immersed membrane to minimise a deposit set up on the surface. When no high cohesion forces exist between particles, the aeration, even under weak flow rate, allows to avoid this deposit making.

Three-dimensional excitation and emission matrix fluorescence (3DEEM) for quick and pseudo-quantitative determination of protein- and humic-like substances in full-scale membrane bioreactor (MBR)

The goal of this study is to help filling the research gaps linked to the on-line application of fluorescence spectroscopy in wastewater treatment and data processing tools suitable for rapid correction and extraction of data contained in three-dimensional fluorescence excitation-emission matrix (3DEEM) for real-time studies. 3DEEM was evaluated for direct quantification of Effluent Organic Matter (EfOM) fractions in full-scale MBR bulk supernatant and permeate samples. Principal Component Analysis (PCA) was used to investigate possible correlations between conventional Lowry and Dubois methods, Liquid Chromatography coupled to Organic Carbon and Organic Nitrogen Detection (LC-OCD-OND) and 3DEEM. 3DEEM data were analyzed using the volume of fluorescence (Φ) parameter from the Fluorescence Regional Integration (FRI) method. Two mathematical correlations were established between LC-OCD-OND and 3DEEM data to quantify protein-like and humic-like substances. These correlations were validated with supplementary data from the initial full-scale MBR, and were checked with samples from other systems (a second full-scale MBR, a full-scale conventional activated sludge (CAS) and a laboratory-scale MBR). While humic-like correlation showed satisfactory prediction for a second full-scale MBR and a CAS system, further studies are required for protein-like estimation in other systems. This new approach offers interesting perspectives for the on-line application of 3DEEM for EfOM quantification (protein-like and humic-like substances), fouling prediction and MBR process control.

Biomass characterization by dielectric monitoring of viability and oxygen uptake rate measurements in a novel membrane bioreactor

The application of permittivity and oxygen uptake rate (OUR) as biological process control parameters in a wastewater treatment system was evaluated. Experiments were carried out in a novel airlift oxidation ditch membrane bioreactor under different organic loading rates (OLR). Permittivity as representative of activated sludge viability was measured by a capacitive on-line sensor. OUR was also measured as a representative for respirometric activity. Results showed that the biomass concentration increases with OLR and all biomass related measurements and simulators such as MLSS, permittivity, OUR, ASM1 and ASM3 almost follow the same increasing trends. The viability of biomass decreased when the OLR was reduced from 5 to 4 kg COD m(-3)d(-1). During decreasing of OLR, biomass related parameters generally decreased but not in a similar manner. Also, protein concentration in the system during OLR decreasing changed inversely with the activated sludge viability.

Recent developments in nanostructured inorganic materials for sorption of cesium and strontium: Synthesis and shaping, sorption capacity, mechanisms, and selectivity-A review

Liquid wastes containing non-ferrous heavy metal ions and some radionuclides, 137Cs and 90Sr in particular, represent one of the most dangerous sources of environmental contamination. The remediation of wastewater containing such pollutants continue to be among the biggest challenges of Sustainable Development and Environmental Safety. Sorption-based technologies have proven their efficiency also in reducing the radionuclide content in aqueous streams to low-level residual activity, with the concomitant decrease in the amount of ultimate solid waste generated. Although sorption of cesium and strontium by resins, clays, and zeolites has been investigated intensively and even used in real applications, there is still considerable scope for improvement in terms of retention capacity and selectivity. Recent progress in design and preparation of nanostructured inorganic materials has attracted growing interest based on the potential for improving the retention performance when coupling such functionalities as ion exchange capacity, structural flexibility that may result in steric retention effects, as well as the propensity to interact specifically with the target metal cations. Titanate, vanadate, and tungsten based materials, manganese oxides, hexacyanoferrates, metal sulfides, ammonium molybdophosphates, or hydroxyapatite, characterized by various structures and morphologies, are reviewed with the emphasis being put on synthesis and shaping of such materials, their structure in relationship with the capacity and selectivity of trapping cesium and strontium from either single or multi-component aqueous solutions, as well as the possible retention mechanism. The potential candidates for remediation uses are selected with regard to their sorption capacity and distribution coefficient towards target cations, and also the pH window for an optimum cation capture.

A modelling approach to study the fouling of an anaerobic membrane bioreactor for industrial wastewater treatment

An Anaerobic Membrane BioReactors (AnMBR) model is presented in this paper based on the combination of a simple fouling model and the Anaerobic Model 2b (AM2b) to describe biological and membrane dynamic responses in an AnMBR. In order to enhance the model calibration and validation, Trans-Membrane Pressure (TMP), Total Suspended Solid (TSS), COD, Volatile Fatty Acid (VFA) and methane production were measured. The model shows a satisfactory description of the experimental data with R2≈0.9 for TMP data and R2≈0.99 for biological parameters. This new model is also proposed as a numerical tool to predict the deposit mass composition of suspended solid and Soluble Microbial Products (SMP) on the membrane surface. The effect of SMP deposit on the TMP jump phenomenon is highlighted. This new approach offers interesting perspectives for fouling prediction and the on-line control of an AnMBR process.

Optimization of Flow Shear Stress Through a Network of Capillary Fibers With the Use of CFD

As hydrodynamics conditions govern membrane fouling, simulations with a Computational Fluid Dynamics software were run to establish optimal design of membrane network. First, simulation through one cylinder was used to calibrate model by comparing the separation angle of experiments executed by Sucker & Brauer (1975) and the separation angle of simulations. Moreover, streamlines profile were compared for different Reynolds numbers. Intermediate or turbulent flow (Red = 600) imposed the choice of turbulence models. It is proved that the standard model, k-epsilon, is not well adapted to simulate the flow around a curved body. The SST-k-omega model resulted in better simulations. Geometry and boundary conditions were taken as common used (Newman and Dirichlet). Once the model was calibrated, simulations were run with a bundle of capillary fibers (membrane network). Velocity, velocity gradient, and friction coefficient were used to define optimal design according to experimental results.

Dielectric monitoring and respirometric activity of a high cell density activated sludge

A novel method was developed to assess the viability of activated sludge present in a biological wastewater treatment process and signify its distinction from respirometric activity. The respirometric activity and viability of activated sludge at high cell density, such as typically encountered in membrane bioreactors, were investigated in batch and fed-batch systems. The method for measuring the viability of activated sludge was based on the sludge permittivity monitored online by a capacitive sensor. Results from permittivity measurement were compared with usual biological activity measurement through oxygen uptake rate determination. The similar downward trend was observed for both measurements. The respirometric activity and permittivity, respectively, reduced to 50% and 68% of initial value in the fed-batch system and 18% and 27% of initial value for the batch system which was due to quantitative and qualitative changes in the microbial culture in the activated sludge. The novel method allows to made distinction between viable versus dead and inactive versus active microbial cells in the activated sludge system and can be used for better and more efficient control of the biological processes.

Optimization of the operations conditions in membrane bioreactors through the use of ASM3 model simulations

The aim of this work was the application of the ASM3 models simulations to obtain most favorable operations conditions in membrane bioreactors for efficient organic matter removal, sludge production reduction and oxygen transfer costs. Simulations were realized used the ASM3 model (Activated Sludge Model)(Henze et al., 2000) for three theoretical influents. The organic load rate (OLR) and the hydraulic retention time (HRT) were fixed at 1 kg COD m -3 d -1 and 0.4 d -1 respectively and the sludge retention time (SRT) was varied from 2.5 d to 67 d. The steady state values of the active biomass concentration (X BH ), the total biomass concentration (X SS ) (active biomass + inert suspended solid), and the oxygen uptake rate (OUR) were obtained for each condition. Thus the observed conversion yield was evaluated (Y OBS ). The results show that, if the SRT increases, the X BH increases until a maximal value. In the other hand, a constant increase evolution of the X SS is observed, without reach a saturation value. Therefore, the suspended solids accumulation after this maximal value are due to a dilution of the active biomass by inert compounds coming from endogenous respiration and also, inert influent. If the OLR restricted the amount of active biomass, on the contrary, high SRT induced high X SS concentration, thus generating rheological sludge properties that penalize the phenomena of mixing, oxygenation and membrane separation.

Diversity of DNA viruses in effluents of membrane bioreactors in Traverse City, MI (USA) and La Grande Motte (France)

This study assesses diversity of DNA viruses in the effluents of two membrane bioreactor (MBR) wastewater treatment plants (WWTPs): an MBR in the United States and an MBR in France. Viral diversity of these effluents is compared to that of a conventional activated sludge WWTP in the U.S. Diversity analysis indicates Herpesvirales to be the most abundant order of potentially pathogenic human DNA viruses in wastewater treated effluent in all utilities. Other potentially pathogenic human viruses detected include Adenoviridae, Parvoviridae, and Polyomaviridae. Bacteriophage order Caudovirales comprises the majority of DNA virus sequences in the effluent of all utilities. The choice of treatment process (MBR versus activated sludge reactor) utilized had no impact on effluent DNA viral diversity. In contrast, the type of disinfection applied had an impact on the viral diversity present in the effluent.

New urban wastewater treatment with autotrophic membrane bioreactor at low chemical oxygen demand/N substrate ratio

The potential for total nitrogen removal from municipal wastewater has been evaluated in an autotrophic membrane bioreactor running with a low chemical oxygen demand (COD)/N ratio to simulate its combination with an upstream physicochemical process that retains a large proportion of organic matter. The tests were conducted in a laboratory scale submerged membrane bioreactor loaded with a synthetic influent. Nitrogen loading rate was 0.16 kgN-NH4+.m(-3).d(-1) and sodium acetate was added as a carbon source. Results have shown that nitrogen elimination can reach 85% for a COD/N ratio of 5, with COD removal exceeding 97%. However, a COD/N ratio of 3.5 was found to be the limiting factor for successfully reaching the overall target value of 10 mgN.L(-1) in the effluent. Nevertheless, low COD/N ratios make it possible to work with low total suspended solid concentrations in the bioreactor, which greatly facilitates membrane fouling control by a simple aeration and backwashing strategy.