Porntip Sridang

Effect of solids retention time on membrane fouling intensity in two-stage submerged anaerobic membrane bioreactors treating palm oil mill effluent

Submerged anaerobic membrane bioreactors (SAnMBRs) treating palm oil mill effluent were analysed in terms of membrane fouling dynamics when working at three different sludge retention times (SRTs of 15, 30 and 60 d). The average permeate flux was fixed at 2.4 L·m−2·h−1. During operation, the membrane was regenerated by using two steps: membrane wiping during each experiment as soon as trans-membrane pressure reached 125–130 mbars, and complete membrane cleaning including backwash and chemical cleaning at the end of each experiment when analysing the membrane surface and foulant material. Whatever the SRT, the cake formation was the dominant effect on membrane fouling dynamics. The concentration of suspended solids in the SAnMBRs, depending on the SRT, was then a determining criterion. Scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy indicated that fouled membrane surfaces were covered with a cake layer containing organic and inorganic elements whose concentrations were higher when working at a higher SRT; the higher concentrations of such elements gave to the cake layer a denser and more compact structure. In these experiments, the soluble fractions played a secondary role because of the dominant effect of cake layer structuring.

Influence of relaxation frequency on membrane fouling control in submerged anaerobic membrane bioreactor (SAnMBR)

AbstractThe effect of different intermittent filtration modes on membrane fouling was investigated in a submerged anaerobic membrane bioreactor treating palm oil mill effluent. The filtration was operated at the range of supra critical conditions (permeate flux equal to 20 L m−2 h−1), and the submersed membranes were continuously cleaned by gas injection and intermittent periods of relaxation. Four conditions of relaxation (S1: 240 s filtration/30 s relaxation, S2: 480 s filtration/30 s relaxation, S3: 720 s filtration/30 s relaxation, and S4: 960 s filtration/30 s relaxation) were analyzed by comparing the trans-membrane pressure evolution rates, the main fouling origins, and the content of membrane cleaning solutions in terms of proteins and carbohydrates. Results showed (i) the dominant effect of the cake deposit (50% of the total hydraulic resistance) whatever the relaxation frequency, (ii) the equivalent importance of pore blocking and adsorption, and (iii) the clear interest of working with the high...

Stability of skim latex suspension and rubber content recovery by microfiltration process: operating conditions and fouling characteristics

Abstract To minimize the environmental impact of the latex industry and recover a large part of rejected skim latex, this research focused on the stabilization and concentration of skim latex suspension by chemical conditioning and microfiltration. The experiments were carried out in microfiltration stirred cell and cross-flow microfiltration unit to evaluate (1) suspension filterability and (2) critical permeate flux according to suspension conditioning. Critical permeate flux is defined as follows: when filtering feed suspension in cross-flow conditions during short time experiments, the trans-membrane pressure (TMP) increase induces firstly a linear evolution of permeate flux (J) before observing a progressive stabilization of J, even if there is a greater increase in TMP. The critical flux corresponds to the highest value of permeate flux obtained when the linear evolution J versus TMP is observed. Obtained results allowed the identification of critical filtering conditions, optimum chemical condition...

Concentration of field and skim latex by microfiltration – membrane fouling and biochemical methane potential of serum

Cross-flow microfiltration was used to concentrate field and skim latex suspensions and recover the smallest compounds (proteins, sugars, etc.) in permeate (serum solutions). The experiments were performed in a lab-scale microfiltration unit equipped with ceramic membranes. In continuous mode, the operations were performed at constant trans-membrane pressure (0.5 bars), constant cross-flow velocity (3 m/s) and constant temperature (28 ± 2°C). In retentate, the volumetric concentration factor was only close to 2 (about 54% of total solid content, TSC) when concentrating the field latex suspensions, and it reached 10 (close to 40% TSC) when concentrating skim latex suspensions. The quality of retentate suspensions let envisage a significant potential of industrial valorization. The membrane fouling rates appeared as an increasing function of dry rubber content suspension, and the main fouling origin (94%) was linked to a reversible accumulation of suspended compounds on the membrane surface. Permeate appeared as a clear yellow solution containing the smallest soluble organic fractions that show a high degree of biodegradability when using biochemical methane potential tests. The chemical oxygen demand (COD) removal was then higher than 92% and the methane production yield was close to 0.29 NLCH4/gCODremoved. The association of a membrane separation step and anaerobic digestion appeared, then, as a relevant solution to recover rubber content from skim latex suspensions and energy from the anaerobic digestion of serum.

Influence of water compositions on fouling of plane organic membrane in frontal filtration: application to water and wastewater clarification

The aim of this study was to evaluate and quantify the filterability of suspended/soluble organic and suspended inorganic matter in a condition without and with chemical conditioning on membrane fouling using cake filtration model. The experiments were conducted with different feed water concentrations under a given TMP (0.2 to 0.5 bar). The fouling potential was examined and described in terms of resistance coefficient (alpha x W) and specific resistance (alpha). The results showed an increase of alpha x W and alpha within the concentration of wastewater samples tested. The soluble fractions in wastewater induced fouling and its mechanism was due both to the interaction of soluble organic components and also some of the particular colloids in MLSS, causing irreversible fouling, followed by thin film formation on membrane surfaces with low porosity, dense structure and also internal fouling. This phenomenon promoted the values of alpha x W and alpha from final treated wastewater 5-20 times higher than in bentonite suspension and on reservoir surface water. Higher pressure than 0.2 bar induced greater hydraulic resistance values than lower applied pressure. The pore size of the porous membrane did not show any difference in the values of alpha x W and alpha obtained, but they mostly depended on the water composition tested. The hydraulic resistance values appeared largely to minimise when using chemical conditioning because of cake forming as a dynamic membrane that reduced the irreversible fouling phenomena giving a constant filtration rate.

Influence of Water Compositions and Conditioning on Flux Enhancement in an Immersed Membrane System

Abstract The objective was to quantify the importance of operational conditions, aeration, and physico‐chemical conditioning on membrane fouling intensity. The suspension filterability was also analysed by using frontal filtration and a cake filtration model. Results pointed out the moderated role of aeration to reduce compound accumulation on the membrane surface. It did not appear as a determining criterion to prevent membrane fouling. In contrast, the physico‐chemical conditioning appeared as a determining criterion to increase critical flux. According to the experimental conditions 200 l/m2/h/bar membrane permeability could be maintained transmembrane pressure (TMP) when filtering stored rainwater. This permeability value was 2–3 times higher than the values obtained without conditioning. Moreover, according to the low turbidity of such stored rainwater and because of the high selectivity of the membrane, the coagulation step, a very low amount of 10 mg/l FeCl3, was sufficient to intensify the filtration step. This conditioning interest appeared less significant when filtering salted water in immersed membrane systems, but a 20 mg/l FeCl3 addition appeared sufficient to double the value of critical flux. Nevertheless filtration in frontal mode pointed out the significant impact of physico‐chemical conditioning in reducing the cake deposit hydraulic resistance.