Alain Grasmick

Influence of macromolecule adsorption during filtration of a membrane bioreactor mixed liquor suspension

Abstract The aim of this study was to quantify the specific effect of adsorption on membrane fouling during filtration of a membrane bioreactor (MBR) mixed liquor suspension. Adsorption experiments were performed on well-defined protein solutions (β-lactoglobulin solutions) to provide reference results and compare them to those obtained during the filtration of MBR suspensions (raw suspension and settled suspension). Two different methods were used to quantify the role of adsorption in membrane fouling: a “static” method in which membranes were immersed in the biological suspension and a “dynamic” method supposing that the resistance due to adsorption is an irreversible phenomenon that remains after filtration and back-washing. It was shown for the two types of suspensions that (i) due to limited diffusion, the dynamic method appears to be more adapted than the static method; (ii) adsorption is a rapid fouling phenomenon that induces irreversible resistance and that, in frontal mode takes place at the beginning of the operation; (iii) the adsorption phenomenon shows specific hydraulic resistance of the same order of magnitude as the clean membrane resistance; (iv) other phenomena, i.e. progressive pore clogging, can also take place though subcritical hydrodynamic conditions.

Characterisation and modelling of fouling in membrane bioreactors

Abstract A membrane bioreactor used for denitrification of a synthetic substrate was studied in term of membrane fouling. For standard pH and temperature conditions, subcritical conditions were defined to ensure the process stability. The stepwise method was used to determine the critical flux for the deposition of colloidal particles. Under standard physicochemical conditions, only a low and constant fouling resistance was observed if the permeate flux was maintained below the critical flux. The influence of physicochemical variations was then investigated by varying pH and temperature in the biological reactor. It was observed that, when the pH value was higher than a critical one, the membrane was rapidly fouled. This maximum admissible pH value decreased when the temperature increased. On analysing the reversible nature of fouling and the variations of ionic concentrations with the pH, the role of carbonate calcium precipitation was pointed out. By using classical filtration models, it was shown that the fouling mechanism could be the deposition of CaCO3 particles formed in the bulk suspension by bulk crystallisation.

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.

Potential Foulants and Fouling Indicators in MBRs: A Critical Review

Membrane fouling is one of the major obstacles for wide applications of MBRs. Over the past decade, the behaviors of colloidal and soluble substances have attracted much attention, and intensive efforts have been dedicated to the clarification of their role in membrane fouling. However, to date, the conclusions are often different and even controversial. The review is attempted to clarify their interrelations and to eliminate some confusions by reviewing the recent literature. The similarities and differences of those potential foulants are analyzed through comparing definitions, extraction methods, fouling indicators, and fouling behaviors. The implications of future research directions are also discussed in this paper.

Denitrification of drinking water by the association of an electrodialysis process and a membrane bioreactor: feasibility and application

Abstract A hybrid process combining electrodialysis and a membrane bioreactor was investigated to treat ground waters with excessive nitrate concentrations. Electrodialysis (ED) allowed the nitrate separation producing, on one hand, partially demineralized waters whose ion concentrations were in agreement with the norm, and on the other hand, brines that were treated by a membrane bioreactor. Experiments performed at laboratory scale with synthetic solutions and pre-industrial scale to treat a ground water contaminated by nitrates showed high efficiency of the hybrid process. The nitrate concentration of the treated water remained below the acceptable value (50 mg/l−1) and even below the recommended value (25 mg/l−1) for drinking water. Moreover, the ED treatment induced a softening of the treated water. The biological denitrification allowed the almost total removal of nitrates (99%) with kinetics close to 0.3kgN NO3/kg MVS/d and a limited sludge production of 0.5 gV.S.S./gN NO3.

Use of a membrane bioreactor for denitrification of brine from an electrodialysis process

Electrodialysis (ED) is an efficient process for the treatment of drinking water with high nitrate concentration. However it achieves only a transfer of pollution by producing concentrated brines. This study demonstrated the feasibility of ED brine denitrification in a membrane bioreactor (MBR). The results showed the high efficiency of the MBR despite the drastic conditions of nitrate concentration, pH and salinity of the ED concentrates. The denitrification kinetics close to 0.01 mgNO 3 – -N mgVSS –1 h –1 were in agreement with the literature values obtained with usual conditions. Next, the efficiency and performance of the hybrid process to treat ground water contaminated by nitrate was demonstrated in situ at Rodilhan (France). After ED treatment, the nitrate concentration of the treated water remained below the acceptable value (50 mg l –1 ) and a softening of the treated water was obtained. The membrane bioreactor allowed the almost total destruction of ED concentrate nitrate (99 %) with kinetics close to 0.3 kgNO 3 – -N kgVSS –1 d –1 and a sludge production of 0.5 gVSS gNO 3 – .

Separation efficiency of a vacuum gas lift for microalgae harvesting.

Low-energy and low-cost separation of microalgae from water is important to the economics of microalgae harvesting and processing. Flotation under vacuum using a vacuum gas lift for microalgae harvesting was investigated for different airflow rates, bubble sizes, salinities and harvest volumes. Harvesting efficiency (HE) and concentration factor (CF) of the vacuum gas lift increased by around 50% when the airflow rate was reduced from 20 to 10 L min(-1). Reduced bubble size multiplied HE and CF 10 times when specific microbubble diffusers were used or when the salinity of the water was increased from 0‰ to 40‰. The reduction in harvest volume from 100 to 1L increased the CF from 10 to 130. An optimized vacuum gas lift could allow partial microalgae harvesting using less than 0.2 kWh kg(-1) DW, thus reducing energy costs 10-100 times compared to complete harvesting processes, albeit at the expense of a less concentrated biomass harvest.

Effect of imposed flux on fouling behavior in high rate membrane bioreactor

The influence of imposed flux and aeration rates on membrane fouling in a submerged membrane bioreactor was studied. The experiments were conducted at four imposed fluxes and three aeration rates. The effect of flux on the reduction of membrane fouling was much higher than that caused by aeration rate. A lower flux of 20 L/m(2) h produced 75 times more water than a higher flux of 40 L/m(2) h with an aeration rate of 2 L/min. Low flux showed slightly higher removal of NH(4)-N and 93-96% removal of dissolved organic matter and chemical oxygen demand. Imposed flux also had a significant effect on the composition of organics present in the soluble microbial product (SMP) and extracellular polymeric substances (EPS). At a higher flux, both SMP and EPS had organics of high molecular weight (MW) of around 48 kDa as well as lower MW organics below 200 Da.

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.

Respirometric needs of heterotrophic populations developed in an immersed membrane bioreactor working in sequenced aeration

The aim of this work is first to determine the respirometric needs of heterotrophic populations developed in a submerged membrane bioreactor (MBR) working in sequenced aeration (BIOSEP® process). The oxygen needs were quantified in known conditions of substrate nature and concentration. The respirometric parameters were measured in a particular system, called Respir’Eaux. Samples of the biological suspension were taken from the BIOSEP® process and introduced into the Respir’Eaux in which the oxygen supply was controlled. First experiments, carried out without any substrate addition, showed that: (i) endogenous needs remained approximately constant during the 5 months of study, showing an apparent stability of the culture; (ii) exogenous needs were very variable, supposedly because the culture was subjected to very variable biodegradable substrate material flows. With the aim of better underlining the importance of the nature and the concentration of the available substrate, experiments were performed from biomass samples subjected to the addition of specific nutrients (acetate and calibrated fractions of municipal wastewater). The results showed that: (i) oxygen needs depend directly on the nature and the quantity of added substrate; (ii) oxygen needs depend on the acclimation of the micro-organisms to the added substrate; (iii) in the experimental conditions investigated, oxygen needs demonstrate the complete oxidation of the soluble organic fraction of the wastewater by the MBR suspension, although this part may contain recalcitrant compounds for conventional biological culture.